Energy from domestic wastewater and kitchen waste with Eureka-HD “An Energy Balance”

Acknowledgement This study (training thesis) has been performed within the master course Energy & Environmental Sciences of the University of Groningen. During this training thesis I had the opportunity to work with new technology and to gain new skills in doing scientific research. Thanks to Bareau I could focus on a more process technological aspect of an innovative concept for waste management. Therefore I would like to thank C.E. Zagt and J. Barelds (Bareau) for providing the possibilities for this thesis and their support in my activities. From the University of Groningen I’d like to thank prof. dr. H.C. Moll and dr. R.M.J. Benders for their support, their analytical view and their feedback on my results. Additionally I’d like to thank H.J. Bouwers of the Province of Friesland for financially supporting Bareau in this study. Because I had contacts with SenterNovem about the Uniforme Maatlat and the energy performance norms of buildings I also would like to thank ir. J. Rienstra and ir. L. Bosselaar from this agency. SenterNovem is part of the Dutch Ministry of Economic Affairs and acts as an information center for sustainability, innovation and international businesses. Since beginning of this year (2010) SenterNovem is merged and is active as ‘Agentschap NL’. In this report I consistently use ‘SenterNovem’ to refer to this organization in order to avoid confusion. In the last weeks of my thesis Bareau and Wageningen University published the new technology of Eureka-HD and Autogenerative High Pressure Digestion in the H2O, this is a specialist journal about water technology and water management. My share (this research) of the total development of EurekaHD was briefly discussed in this publication. I adopted this publication in the reference list of this report; see Zagt et al., 2010.

Acronyms AD

=

Anaerobic Digestion

AHPD

=

Autogenerative High Pressure Digestion

Cap

=

Capita (= inhabitant)

CHP

=

Combined Heat and Power engine

COD

=

Chemical Oxygen Demand

COP

=

Coefficient Of Performance

EPC

=

Energy Performance Coefficient

EPDB

=

Energy Performance Directive of Buildings (from the European Commission)

Eureka-HD

=

Energy From Sewage and Kitchen Waste under High Pressure

GJ

=

Giga Joules (*109 Joules)

I.e.

=

Inhabitant Equivalent (in this report equal to ‘Inhabitant’)

MJ

=

Mega Joules (*106 Joules)

OC

=

Oxygenation Capacity

UM

=

‘Uniforme Maatlat’ (model of SenterNovem)

Summary Treatment of wastewater is commonly done centralized, bringing high costs for collecting a big flow of low concentrated wastewater. A mixed input of black water, grey water, rainwater and groundwater has a low concentration of contamination making recovery and reuse of nutrients difficult and expensive. Scientists agree on the need for separation of waste streams, maintaining high concentrations and recovery of nutrients, energy and water. Source separation based sanitation positively influences the reuse potential of resources in the different streams. Bareau Duurzame Technologie is a Dutch company developing a new sanitation concept for treatment of domestic wastewater and kitchen waste that produces two forms of energy: methane and pressure. The concept is called ‘Eureka-HD’. Eureka-HD is a decentralized treatment facility that uses a vacuum system for the collection of high concentrations of waste, to be treated in an Autogenerative High Pressure Digestion (AHPD) reactor. This is an innovation on anaerobic digestion where biological produced pressure is used to perform work (driving pumps and pressure exchangers). Eureka-HD is designed to run on this biologically produced pressure completely, meaning that no external energy is needed to treat the waste streams. Additionally, the pressure results in biogas upgrading because CO2 and H2S are dissolving into the liquid phase as a function of pressure (Henry’s law). Since this gas becomes available at higher pressure, Bareau aims for direct injection into the gas grid. There is a lack of information on the actual energy performance of this system. In this report I will discuss the potential of Eureka-HD considering energy production and CO2 emission reduction in relation to a district area of EPC 0.8 dwellings (reference building). The focus of this study is on: (i) the total potential for energy production, (ii) the energy needed in the total treatment process, (iii) potential for fossil CO2 emission reduction and (iiii) the potential effect of Eureka-HD on the EPC of dwellings. All these aspects are directly related to the load of wastewater and kitchen waste (black water) that is produced by a household, which is on average 200 to 230 grams of COD per person per day. In the conventional treatment system the COD from wastewater is oxidized to mainly CO2, consuming energy. Kitchen waste is mainly composted, emitting CO2 and CH4 into the atmosphere. The energy demand for aerobic treatment of wastewater is about 5 to 15 Watt*i.e.-1 (primary energy use). When treating these waste streams anaerobically (AHPD) biogas (CH4 + CO2) can be produced. In this way each person can indirectly produce about 70 - 80 liters of CH4 per day, accounting for approximately 29 Watt*i.e.-1. Because AHPD is used, significant amounts of pressure energy are being produced, depending on the process pressure. The total treatment process of domestic wastewater and kitchen waste includes driving essential machinery for the AHPD process, treatment of grey water and nitritation/denitrification of the effluent. These processes are accounting for an energy demand of approximately 6 Watt*i.e.-1. This means that enough pressure energy has to be produced by biology to sustain this complete process. My calculations show that at least 60 atmospheres of pressure is needed to comply with the energy demand for treatment. In order to complete the energy balance and to conclude on the effects of Eureka-HD on the primary energy use (of an EPC 0.8 dwelling, reference building) and the EPC, I used a model of SenterNovem, called the ‘Uniforme Maatlat’. This is a protocol with a set of uniform calculation rules and figures for the assessment of energy measures, considering CO2 emissions, energy use and contribution to sustainable

energy production. This model is developed to provide in a prosperous transition from the current energy performance norm for buildings (EPN) to an upcoming new norm (EPG). Combining an energy balance with the figures and protocol of the Uniforme Maatlat I came to following results. From an energy consumption of 5 – 15 Watt*i.e.-1 in the current situation of wastewater treatment, treatment of domestic wastewater and kitchen waste using Eureka-HD produces 29 Watt*i.e.-1. In relation to the current system of wastewater treatment of domestic wastewater, Eureka-HD has the potential to reduce the primary fossil energy use of the reference building with 6%, resulting is a fossil CO2 emission reduction of 5%. The potential effect on the EPC of a building can be 0.07 points. Within these calculations I did not consider the potential pressure energy that is present in the effluent of AHPD. CO2 and CH4 will be dissolved in this discard at the process pressure (possibly 60 atmospheres), further research should be done on the possibilities to recover this energy. Besides, the exact gas quality from AHPD deserves specific attention since injection of gas into the grid requires strict gas specifications.

Samenvatting (NL) Behandeling van huishoudelijk afvalwater wordt hoofdzakelijk centraal gedaan. Dit resulteert in relatief hoge kosten voor de zuivering van een groot volume afvalwater met een lage concentratie vervuiling. Door de gemengde stroom van zwart-, grijs- en regenwater zijn de concentraties organische stof en nutrienten laag waardoor terugwinning bemoeilijkt wordt. Wetenschappers zijn het erover eens dat afvalscheiding mogelijkheden voor hergebruik van nutrienten, energie en water bevordert. Brongescheiden sanitatie verhoogt de potentie voor hergebruik van waardevolle componenten die aanwezig zijn in huishoudelijk afvalwater. Bareau Duurzame Technologie is een nederlands bedrijf dat een nieuw sanitatie concept ontwikkelt voor behandeling van huishoudelijk afvalwater en keukenafval. Dit concept is genaamd 'Eureka-HD' en produceert twee vormen van energie, zijnde methaan en druk. Eureka-HD is een decentraal zuiveringssysteem dat gebruik maakt van een vacuum systeem voor de inzameling van huishoudelijk afvalwater en keukenafval. De afvalstroom wordt vervolgens gezuiverd in een 'Autogenerative High Pressure Digestion' (AHPD) reactor. Dit is een innovatie op de huidige technologie voor anaerobe vergisting waarbij biologisch opgebouwde druk wordt gebruikt om werk te verrichten (aandrijving van pompen en pressure exchangers). Eureka-HD is dusdanig ontworpen dat deze biologisch opgebouwde druk wordt gebruikt om het hele zuiveringssysteem operationeel te houden. Dit betekent dat er geen externe energiebron nodig is voor de behandeling van huishoudelijk afvalwater en keukenafval. Daarnaast heeft de bio-druk effect op de samestelling van het geproduceerde biogas. Als functie van de verhoogde druk zullen CO2 en H2S oplossen in de waterfase, het gas wordt dus in de reactor opgewaardeerd. Omdat het opgewaardeerde gas vrij komt onder druk is het doel om het gas direct te injecteren op het locale gasnet. Momenteel is er weinig kennis over de energieprestatie van het systeem. Tijdens dit onderzoek is de energetische potentie van Eureka-HD onderzocht. Daarbinnen is er gericht gekeken naar de energieproductie en de CO2 emissie reductie van het systeem in een woonwijk van EPC 0.8 woningen. Het onderzoek richtte zich op: (i) de totale potentie voor energieproductie, (ii) de energiebehoefte in alle stappen van de zuivering, (iii) de potentie voor CO2 emissie reductie en (iiii) het potentiele effect op de EPC van de woningen die aangesloten zijn op een Eureka-HD systeem. Al deze aspecten zijn direct gerelateerd aan de vuilvracht van huishoudelijk afvalwater en keukenafval (zwartwater). Gemiddeld komt deze vracht neer op zo'n 200 tot 230 gram COD per persoon per dag. In het huidige afvalwatersysteem wordt er energie geconsumeerd om dit COD te oxideren naar CO2. Voor deze aerobe behandeling van huishoudelijk afvalwater wordt 5 tot 15 Watt*i.e.-1 geconsumeerd (primair energiegebruik). Keukenafval wordt over het algemeen gecomposteerd waarbij CO2 en CH4 ontstaan, deze gassen worden veelal deels afgevangen of uitgestoten naar de atmosfeer. Indien deze stromen anaeroob (AHPD) behandeld worden kan er 70 – 80 liter CH4 per persoon per dag geproduceerd worden. Uitgedrukt in een energetische waarde komt deze CH4 productie neer op ongeveer 29 Watt*i.e.-1. Afhankelijk van de procesdruk in AHPD wordt er tevens een significante hoeveelheid druk energie geproduceerd. Voor de complete zuivering van grijs- en zwartwater zal er energie gebruikt worden voor de essentiele onderdelen van het AHPD proces (pompen en filters) maar ook voor beluchting en nitritatie en denitrificatie. Deze processtappen vereisen ongeveer 6 Watt*i.e.-1. Wanneer deze energie geleverd wordt door drukenergie zal de procesdruk dus voldoende hoog moeten zijn. Hoewel Eureka-HD ontworpen is

om op maximaal 20 bar te werken, laten mijn berekeningen zien dat een procesdruk van tenminste 60 bar nodig is om in de energievraag van het totale zuiveringsproces te voorzien. Om tot een conclusie te komen wat betreft de energieprestatie, in relatie tot een EPC 0.8 woning, is in deze studie gebruik gemaakt van de 'Uniforme Maatlat', dit is een model van SenterNovem. De Uniforme Maatlat is een protocol dat bestaat uit een set van uniforme rekenregels en kengetallen voor het vaststellen van CO2-emissies, het energiegebruik en de bijdrage aan duurzame energie in de gebruiksfase van energiealternatieven. Het model is ontwikkeld om de transitie van de huidige energieprestatie norm (EPN) naar de nieuwe norm EPG te vergemakkelijken. Door een energiebalans te combineren met het protocol van de Uniforme Maatlat was het mogelijk om een conclusie te verkrijgen omtrent de energieprestatie van Eureka-HD en de effecten op de EPC van woningen. Deze is als volgt: Van een energieconsumptie van 5 – 15 Watt*i.e.-1 in de huidige situatie van waterzuivering, kan afvalwaterbehandeling (inclusief keukenafval) door middel van Eureka-HD resulteren in een energieproductie van 29 Watt*i.e.-1. Hiermee heeft het systeem het potentieel om het fossiele energiegebuik van de referentie woningen (EPC 0.8) te verlagen met 6%. Dit vertaalt zich naar een fossiele CO2 emissie reductie van 5% en een potentiele verlaging van de EPC met 0.07 punten. Tijdens deze studie heb ik geen rekening gehouden met de potentiele drukenergie die aanwezig is in het effluent van AHPD. In deze effluentstroom zijn CO2 en CH4 opgelost onder procesdruk (mogelijk 60 bar), er dient verder onderzoek gedaan te worden naar de mogelijkheden om deze energie nuttig toe te passen. Verder is er in het rapport uitgegaan van mogelijkheden om het AHPD gas direct te injecteren in het locale gasnet. Echter, de eisen voor invoeding van gas in een gasnet zijn streng en daarom adviseer ik dat er in een later stadium van de ontwikkeling van Eureka-HD aandacht besteedt wordt aan de exacte samenstelling van het AHPD gas.

Table of contents 1.

Introduction....................................................................................................................................... 13 1.1 Problem description .................................................................................................................... 13 1.2 Research objectives and main questions..................................................................................... 13 1.3 Structure of report ....................................................................................................................... 14

2.

Background & Significance.............................................................................................................. 15 2.1 Conventional wastewater treatment ............................................................................................ 15 2.1.1 Domestic wastewater .......................................................................................................... 15 2.1.2 Conventional sewage systems ............................................................................................. 16 2.1.2 Energy in the process.......................................................................................................... 16 2.2 Anaerobic Digestion (AD) .......................................................................................................... 17 2.2.1 Basic principles of AD process ........................................................................................... 17 2.2.2 Biological processes ........................................................................................................... 17 2.2.3 Autogenerative High Pressure Digestion (AHPD) ............................................................. 19 2.2.3.1 Literature ........................................................................................................................ 19 2.2.3.2 Applications .................................................................................................................... 20 2.2.4 Comparative conclusion AD & AHPD ............................................................................... 20 2.3 Energy in households .................................................................................................................. 21 2.3.1 Energy performance norms in the EU and the Netherlands ............................................... 21 2.3.1.1 Energy Label ....................................................................................................................... 21 2.3.1.2 Energy Performance Advice (EPA) ................................................................................ 22 2.3.1.3 Energy Performance for a Location (EPL)..................................................................... 22 2.3.1.4 Energy Performance Coefficient (EPC).......................................................................... 22 2.3.1.5 Energy Performance of Buildings (EPG) ....................................................................... 23 2.3.1.6 Energy Savings Measure on District level (EMG).......................................................... 23 2.3.2 Basic figures of energy use in households. ......................................................................... 24

3.

Eureka-HD: Technology .................................................................................................................. 25 3.1 Basic Principles/System description ........................................................................................... 25 3.2 Fields of interest.......................................................................................................................... 28 3.2.1 Waste and wastewater......................................................................................................... 28 3.2.2 Energy ................................................................................................................................. 28 3.2.3 Drinking water .................................................................................................................... 28

4.

Methodology ...................................................................................................................................... 29 4.1 System description ...................................................................................................................... 29 4.2 SenterNovem: ‘Uniforme Maatlat’ ............................................................................................. 29 4.3 Energy potential of decentralized Eureka-HD for treatment of domestic wastewater................ 29 4.4 Potential of a heat pump driven by biological produced pressure in Eureka-HD....................... 31 4.5 Energy requirements total treatment process .............................................................................. 31 4.5.1 Aeration of grey water ........................................................................................................ 32 4.5.2 Nitritation/Denitrification................................................................................................... 32 4.5.3 Process temperature reactor............................................................................................... 32 4.6 CO2 emission reduction potential Eureka-HD ............................................................................ 33 4.7 Effect of Eureka-HD on the energy performance coefficient ..................................................... 33 4.8 Model assumptions ..................................................................................................................... 33

5.

Results ................................................................................................................................................ 35 5.1 Eureka-HD in the built environment........................................................................................... 35 5.2 Conclusion .................................................................................................................................. 36

6.

Discussion .......................................................................................................................................... 37

References.................................................................................................................................................. 39 Web pages:.......................................................................................................................................... 43 Email reference:.................................................................................................................................. 43 Appendix I.

Uniforme Maatlat: referentiesituatie .......................................................................... 44

Appendix II.

Uniforme Maatlat: Eureka-HD ................................................................................... 45

Appendix III.

Energy balance Eureka-HD (Input for Uniforme Maatlat) ...................................... 47

Appendix IV.

Heat losses Eureka-HD (Input for energy balance) ................................................... 48

Appendix V.

Results from Dynameau simulation (Input for energy balance)............................... 49

Appendix VI.

Requirements for gas injection and transport (NMa, 2006) ..................................... 50

1.

Introduction

Current centralized wastewater treatment systems are inefficient and produce significant quantities of highly polluted secondary sludge (Zeeman & Lettinga, 1999). Although the plants do comply with given standards, the rate of recovery (energy, nutrients and water) is not very high. Treatment of wastewater is commonly done centralized, bringing high costs for collecting a big flow of low concentrated wastewater. These treatment systems cope with problems caused by a mixed input of waste streams and dilution of the total wastewater by rain- and groundwater. Because of the low efficiency caused by dilution of waste water and long transportation distances, conventional waste water treatment is a costly activity (Zeeman & Lettinga, 1999). A mixed input of black water, grey water, rainwater and groundwater has a low concentration of contamination making recovery and reuse of nutrients difficult and expensive. Scientists often propose different alternative treatment systems and although the design differs strongly, they all agree on the need for separation of waste streams (black, grey, domestic solid waste and rainwater), maintaining high input concentrations, decentralized treatment and recovery of nutrients, energy and water (Hammes, Kalogo & Verstraete, 2000). Source separation based sanitation positively influences the reuse potential of resources in the different streams. Maintaining nutritional and energetic value of black water and combining it with easy biodegradable kitchen waste optimizes treatment efficiency and can produce significant amounts of methane (Kujawa-Roeleveld & Zeeman, 2006). Even though the goal of wastewater treatment used to be to protect downstream users, there is a shift going on which is more focused on energy, climate and water conservation (Verstraete, Gaveye & Diamantis, 2009), (STOWA, 2006). Separate collection of domestic wastewater streams creates possibilities for further innovation. Because of high concentrations of organic waste in domestic wastewater, the load becomes valuable. This philosophy drove Bareau Duurzame Technologie to develop new technology for domestic wastewater treatment. Using the combination of source separation based sanitation and a new innovative approach on anaerobic digestion, the company developed Eureka-HD. The innovative concept makes use of a vacuum system for the collection of waste and uses “Autogenerative High Pressure Digestion” (AHPD) for treatment of the waste streams.

1.1

Problem description

National housing companies, energy suppliers and different bodies of surveyors of water management have shown their interest in this new sanitation concept. However, there is a lack of information on the potential of this system. Scientifically evaluating the energy performance is of key importance for the communication of Bareau, about Eureka-HD, towards potential clients (decision makers). In this report I will discuss the potential of Eureka-HD in relation to energy production, savings on fossil energy and CO2 emission reduction.

1.2

Research objectives and main questions

This research focuses on the direct and indirect fossil energy and CO2 emission reduction potential of Eureka-HD in a district area (of dwellings). The lack of information on the effects of Eureka-HD applied in a district area, with respect to the reduction of fossil energy use and CO2 emissions, leads to the following questions: 13

1. 2. 3. 4. 5.

1.3

What is the potential of decentralized Eureka-HD for treatment of domestic wastewater and kitchen waste, in terms of energy? What might be the potential of a heat pump driven by biological produced pressure in EurekaHD? How much energy is needed in the total treatment process? What can be the potential in terms of CO2 emission reduction when applied on a large scale? What is the effect of Eureka-HD on district level for the energy performance coefficient of the considered dwellings?

Structure of report

In order to understand and correctly interpret the methodology used and the results given, it is important to provide enough background information. The following section (chapter 2) gives insight in the relevant subjects and topics, starting with some basics about domestic organic waste and wastewater. General information about waste load and the conventional technology for treatment is given. Following, basic principles about anaerobic digestion will be discussed, followed by information about the innovative AHPD process. The energy performance norms and household energy use are discussed in paragraph 2.3. In chapter 3 the basics and principles of the Eureka-HD concept are discussed. The methodology that has been used to find answers to the study questions will be discussed in chapter 4. The results and a conclusion are given in chapter 5, followed by a discussion in chapter 6.

14

2.

Background & Significance

This chapter gives relevant information about domestic sewage water and kitchen waste, the process and technology of anaerobic digestion and energy use in households. This chapter describes the background for the overall report, based on mainly scientific literature. Paragraph 2.1 discusses the conventional method for the treatment of domestic sewage, including basic figures of organic load and the energy that is used for sewage treatment. Paragraph 2.2 describes both the conventional method for anaerobic digestion (AD) and an innovative technology for anaerobic digestion where in situ methane enrichment takes place, called Autogenerative High Pressure Digestion (AHPD). The last part of this chapter focuses on domestic energy use and measures to improve the energy performance of buildings. This latter is a relevant subject because Eureka-HD can affect the energy performance of buildings. Since this topic is gaining political attention it might be useful address it.

2.1

Conventional wastewater treatment

Nearly all (99.6%) dwellings in the Netherlands are connected to a sewage system, where after the waste water is treated centralized (Stichting Rioned, 2009). A small percentage of all dwellings is connected to an IBA (Individuele Behandeling Afvalwater) and/or a septic tank (0.4%), these are decentralized water treatment systems for buildings in rural, unsewered areas (Stichting Rioned, 2009).

2.1.1

Domestic wastewater

In the Netherlands, each person produces about 2.5 kg anthropogenic nutrient solutions (ANS) a day, of which the largest share is urine (Hammes, Kalago & Verstraete, 2000), (STOWA 2005a). The rate of contamination of this wastewater is often giving in grams of COD (Chemical Oxygen Demand). Discharge regulations prescribe a maximum COD content of 125 mg per liter discharged, this is according to the European Directive on Urban Wastewater Treatment, 91/271/EEC (Kujawa-Roeleveld & Zeeman, 2006). In literature different numbers for COD content in domestic wastewater can be found. Kroiss & Zessner (2007) report 110 grams of COD per capita per day in a study performed with data from Austria. Hammes, Kalago & Verstraete (2000) and Zeeman & Lettinga (1999) reported 119 g COD*cap-1*day-1 and 174 g COD*cap-1*day-1 respectively, both with data from the Netherlands. The significant differences in these values for COD in domestic wastewater can be explained by the consideration of kitchen waste. Kroiss & Zessner (2007) and Hammes, Kalago & Verstraete (2000) do not take into account the biodegradable waste fraction produced by households, where Zeeman & Lettinga (1999) do. Results from field research in Sneek (NL), where 32 dwellings were attached to a vacuum collecting system, showed that the average COD load of households was about 100 g COD*cap-1*day-1 (Zeeman & Roeleveld, 2008). This is excluding kitchen waste. According to prof. Koning (Intech K&S, 2003) the average COD load in kitchen waste is approximately 95 g COD*cap-1*day-1.

15

Figure 1: Conventional sewage treatment (centralized).

2.1.2

Conventional sewage systems

The common methodology for domestic waste water management is to discharge it into an extended sewerage (Kujawa-Roeleveld & Zeeman, 2006). From here it is transported over long distances to central treatment facilities. During this transport, the waste water stream is supplemented by rainwater (Zeeman & Lettinga, 1999). At the treatment facility the collected wastewater (black water, grey water and rainwater) is treated mainly aerobically. These conventional treatment systems are inefficient and produce significant quantities of highly polluted secondary sludge (Zeeman & Lettinga, 1999). Sludge is subsequently stabilized using anaerobic digestion and further transported to processing facilities, where the sludge is combusted. Because centralized treatment facilities treat highly diluted wastewater, the treatment efficiency is low and the rate of recovery (energy, nutrients and water) is not very high (STOWA, 2005a). This combination of diluted wastewater and tightening discharge requirements has direct effects on the use of energy and chemicals in the treatment process (Puig et al., 2008). Awareness is increasing in the Netherlands that this end-of-pipe approach may not be suitable anymore in the near future (STOWA, 2006). 2.1.2

Energy in the process

Chemical Oxygen Demand (COD) can be expressed in terms of chemical energy potential, meaning that wastewater treatment plants collect valuable matter. One kilogram of COD contains approximately 13.5 MJ, chemically bounded inside organic compounds (van Lier, 2010). In the conventional system this COD is oxidized to mainly CO2, consuming energy. The energy demand for aerobic treatment is about 9 MJprimary per kg COD removed (van Lier, 2010). One could state that the conventional (aerobic) method for wastewater treatment totally costs 9 + 13.5 = 22.5 MJ per kg COD. Oxidizing the organic material means that chemically bound energy is lost, reflected by the number 13.5 MJ in the sum. The energy consumption for the treatment process is, however, dependent on the technologies used in the process. When the site is equipped with a digester and a combined heat-and16

power (CHP) unit, some of the energy can be recovered. Depending on the exact technologies, the average external energy consumption of waste water treatment plants in the Netherlands is in the range of 5 to 15 Watt*i.e.-1 or 0.34 to 1.30 MJ*i.e.-1*day-1 (van Lier, 2010), (STOWA, 2005b), (Unie van Waterschappen, 2006).

2.2

Anaerobic Digestion (AD)

2.2.1 Basic principles of AD process This paragraph discusses the process of anaerobic digestion as usually done. This is a process operating at atmospheric pressure, producing low quality biogas. The biogas composition is generally in the range of 50% - 85% methane and 15% - 50% carbon dioxide (Verstraete, 1981). However, values above 65% CH4 are rare (Noyola et al., 2006). Also a few percent of the gas mixture are other gases: hydrogen sulfide (H2S), nitrogen (N2), hydrogen (H2), oxygen (O2), carbon monoxide (CO), ammonia (NH3) and some volatile organic compounds (VOC) (Noyola et al., 2006). The exact gas composition is highly dependent on the type and concentration of the substrate and process parameters like temperature, pH, and alkalinity (Noyola et al., 2006). For the sake of this research, the factor “pressure” is added to the process parameters. In scientific literature one will often find values for the organic compound in a certain substrate, expressed in grams of COD (Chemical Oxygen Demand). Anaerobic degradation of organic matter (COD) results in the formation of methane (CH4) and carbon dioxide (CO2). Van Haandel & Lettinga (1994), Verstraete (1981) and Kalago & Verstraete (1999) report a theoretical maximum methane production from COD of 350 L CH4*kg-1 COD (at normal conditions, being 273.15 K and 1.01325 atm). Considering an average COD load in domestic wastewater of about 130 gram*cap-1*day-1, theoretically 45 L CH4*cap-1*day-1 can be produced. Additionally people produce approximately 95 grams of COD from kitchen waste each day (Intech K&S, 2003), meaning that the potential theoretical methane production from domestic wastewater almost doubles when kitchen waste is added. However, one should consider 70% COD removal efficiency for conventional AD (Kujawa-Roeleveld & Zeeman, 2006). Anaerobic digestion of both domestic wastewater and kitchen waste can practically result in 55 L CH4*cap-1*day-1. However, Luostarinen & Rintala (2006) report a COD removal efficiency of 90% in a two-phase UASB (Upflow Anaerobic Sludge Blanket) reactor at 283 Kelvin and 293 Kelvin, where kitchen waste explicitly increased the removal efficiency in comparison with AD of only black water. This is in compliance with reported removal efficiencies in the DeSaR project in Sneek (Zeeman & Kujawa-Roeleveld, 2008). The biodegradability of kitchen waste is more than 90% (Veeken & Hamelers, 1999). The total energetic value of biogas is related to the methane content. Methane has a caloric value of 35.9 MJ*Nm-3 (Noyola et al., 2006). As a function of the methane content, the caloric value of biogas varies from 18 MJ to 30 MJ per cubic meter at normal pressure (1.01325 atm) and temperature (273.15 K) (Noyola et al., 2006).

2.2.2

Biological processes

The biological conversion from organic matter to biogas occurs in four steps in which complex compounds are degraded to simple matter and gasses. Figure 2 shows schematically what the following 17

text illustrates. One remark could be made with this figure: according to Van Haandel & Lettinga (1994) 100% of incoming COD is finally converted to gas. From an energetic point of view this is not possible because biology uses organic material for their metabolism. Assuming that this factor can be neglected, the values are valid. Figure 2: A schematic overview of the anaerobic digestion process.

In the first step, which is called hydrolysis, complex compounds such as polysaccharides, proteins, lipids

and nucleic acids are enzymatic degraded into simple compounds that will be the energy sources for the microorganisms in the next step, i.e. monosaccharides, amino acids and fatty acids. This step is carried out by anaerobic (e.g. Bactericides and Lactobacillus) and facultative (an)aerobic (tolerant to both aerobic and anaerobic environments) bacteria (Streptococci etc.). The second step is the fermentation step and is called acidogenesis, carried out by Clostridia, Ruminococcus and Escherichia. Break-down products are fermented to propionate, butyrate, alcohols, carbon dioxide and hydrogen. In the acetogenesis these (volatile) acids are converted into acetate, carbon dioxide and hydrogen. Butyribacterium, Propionibacterium, Zymosarcina and some Neisseria species are responsible for this process. Methanogenic bacteria (Methanosarcina barkeri, Methanobacterium soehngenii, Methanospirillum hungatii and Methanococcus vannielli) produce methane (CH4) from acetate and hydrogen, this last step is called methanogenesis. (Yadvika et al., 2004), (IEU, 2006), (Verstraete, 1981) These four steps happen through different microorganisms which all have other optima considering pH, temperature and retention time. Hydrolysis and acidogeneses organisms have pH optimum of 4.5 – 6.3 and 6.8 – 7.5 respectively (Kool et al 2005). Methanogenes function optimal in a pH range of 6.2 to 7.8.

18

2.2.3

Autogenerative High Pressure Digestion (AHPD)

Anaerobic digestion in a closed reactor results in increasing pressure, purifying biogas in methane. The pressure inside the reactor strongly influences the gas quality, due to Henry’s law. This law indicates that the solubility of a gas is directly proportional to pressure (Ort, 1976). Carbon dioxide is 40 to 60 times more soluble than methane (Hayes et al., 1990), resulting in a methane content that is comparable to Dutch natural gas at pressures above 15 atmospheres (Ort, 1976). This means that the caloric value of biogas increases significantly as pressure rises. Additional to the higher heating value of AHPD gas, pressure energy can be encountered. Using the International System of Units (SI) the potential energy of pressurised gas can be determined, showing that 10 atmospheres of pressure is equal to 1 MJ*Nm-3 (Kimmenaede, 1976). Since 2005 Bareau performs laboratory experiments on AHPD to fully understand all processes that occur when anaerobic digestion operates at various pressures. In April 2009 the first report with results has been published (Lindeboom et al., 2009). In batch experiments methanogenic activity was tested using several substrate (acetate) concentrations, reactor volumes, retention times and pressure regimes. Results from laboratory experiments showed the presence of the pressure tolerant Methanococcus culture in the AHPD reactor. Methanogenic activity until 90 atmospheres has been proven, without decreasing production activity (see figure 3). The degradation efficiency as a percentage of COD was 90%. This conversion rate was also reported in the patent by Ort in 1976 and in scientific literature on the anaerobic digestion of black water and kitchen waste (Zeeman & Kujawa-Roeleveld, 2008), (Luostarinen & Rintala, 2006), (Veeken & Hamelers, 1999).

Lindeboom et al., 2009 Figure: Pressure built up as a function of methanogenic activity.

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2.2.3.1 Literature In 1976 Jay E. Ort got the patent on “high quality methane gas through modified anaerobic digestion”. This patent describes the effect of increased pressure on the gas composition in the digester, resulting in internal methane purification (up to 100% methane). Besides this patent only few reports (Vavilin, Vasiliev & Rytov, 1995), (Kapp, 1992), (Hayes et al., 1990), (Rak Lee, Kee Cho & Jai Maeng, 1995) are available in scientific literature on high pressure digestion of waste(water). However, numerous studies have been done on methanogenic bacteria in deep-sea environments or effects of pressure on biology in the food industry. Lettinga Associates Foundations (LeAF) performed literature study on the biology in high-pressure environments, which mostly are deep-sea marine ecosystems. Organisms that tolerate high pressures are called barophilic or piezophilic organisms. Described methanogenic barophilics of which sensitivity has been tested all belong to the thermophilic Methanococcus: M. Igneus, M. Jannaschii and M. Thermolithotroficus. In 1987 and 1988 Miller et al. published information about growth rates and methane production rates of M. Jannaschii by several temperatures. The effects of pressure on biological processes have been described by many scientists, e.g. Bartlett (2002), Macdonald (1984, 1997), Marquis (1976), Somero (1990, 1991, 1992a & 1992b) and Yayanos et al. (2002). Hauben (1997) described effects of high pressures up to 7000 atmospheres on organisms for sterilization purposes in the food industry. He found that pressure tolerance could be created by repeatedly exposing pressure intolerant bacteria to middle-high pressures, followed by continuously inoculating surviving cells into the culture.

2.2.3.2 Applications The biological produced pressure has great value. Because biogas is purified inside the AHPD reactor, the available gas is immediately available for injection into the gas grid. Additionally, the pressure can be used to drive pumps, or to force media through membranes. Dependency on electricity for wastewater treatment or drinking water production will be decreased or even deducted. AHPD will be highly valuable for regions where sanitation is not available and where the availability of energy and drinking water is scarce. Next to application for wastewater treatment AHPD might also be interesting for digestion of agricultural waste products. On site recovery of nutrients from manure and plant material using biological produced pressure may in the future become valuable as costs for fertilizers may increase. Since the majority of conventional digesters (in agriculture) is attached to a CHP for the production of electricity and heat, lots of energy is lost through heat emission to the atmosphere. AHPD gas can directly be stored or injected into the gas grid, making CHP and additional technology for gas upgrading redundant and thereby significantly increases the chain efficiency of anaerobic digestion for energy production. Also applications at industry where biodegradable matter is present in some effluent stream are possible. Treatment of waste streams close to the production area increases recovery possibilities. Pressure energy from AHPD can be used efficiently where pressure is required in the production process. 2.2.4 Comparative conclusion AD & AHPD Autogenerative High Pressure Digestion has great potential for the treatment of domestic wastewater streams and might be an interesting technology for digestion of industrial and agricultural waste. The 20

main advantage of AHPD over conventional AD is that the produced biogas is directly purified inside the reactor, up to 97% methane. Additional costs (energetic and financial) for upgrading conventional biogas might be avoided when AHPD is applied. This directly results in an improved chain efficiency of green gas from anaerobic digestion. Besides, AHPD produces a new potential form of sustainable energy: “green pressure”. This pressure can be used to drive pumps or to force gas or liquid through membranes. Using AHPD, wastewater treatment can be done without the consumption of external energy. While producing green gas, the recovery of nutrients and water can be done energy neutral. Latter argument will be of great importance for the developed world in the near future and already is of great value for developing countries.

2.3

Energy in households

Since Eureka-HD is likely to have significant effects on the energy performance of buildings, the existing energy performance measures are discussed here. The Energy Performance Norm (EPN) and its calculation methodology (EPC) are being used in this thesis to assess the energy performance of EurekaHD and it’s thus relevant to note it here. Paragraph 2.3.2 gives a brief overview of the energy use of households. 2.3.1

Energy performance norms in the EU and the Netherlands

Both climate targets and the drive to reduce the fossil fuel dependency led to the decision of the European Commission (EC) to create a directive on the energy performance of buildings, to be implemented by all member states (Sunikka & Beerepoot, 2006). In 2002 the EC published the Energy Performance of Buildings Directive (EPBD) 2002/91/EG, obliging all member states to change their law in compliance with the requirements given in the directive no later than 4 January 2006 (www.epdb.nl). However, the Netherlands had already implemented a directive on the energy performance of buildings in 1996, the Energie Prestatie Norm (EPN). This regulation has proven to be successful in improving the energy performance and lowering carbon emissions in the residential housing and utility building sector. Such a performance based approach is expected to stimulate innovation in both installation- and construction technology (Beerepoot & Beerepoot, 2007b). Following you will find the existing and future norms and labels for indicating the energy performance of buildings in the Netherlands. Nowadays the Energy Performance Coefficient resulting from the EPN is the only measure that is legally obliged for every new building. However, from 2011 all current labels and norms will be replaced by the EPG (described below) (Bosselaar, 2009). 2.3.1.1 Energy Label Since 2008 there should be an Energy Label available when an existing building is hired or sold. The label indicates both energy performance and possible adjustments for improvement of the performance. By making use of colors the building is rated, where green is very efficient and red is very inefficient. The topics taken into account are energy use for heating, cooling, hot water, ventilation and lighting. Such a label is valid for a maximum of 10 years.

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2.3.1.2 Energy Performance Advice (EPA) To gain more information about the energy performance of a building (both residential and utility) it is possible to get an energy performance advice (EPA) on the constructional and installation-technical improvement measures. It will give information on both current state of the building and possible measures for improvement, including costs, benefits and pay-back time. The EPA is not the same as an Energy Label but can result in it. The information included in the EPA goes beyond the information needed for an Energy Label. Since the first of January 2009 there are possibilities to receive a governmental subsidy when applying for an EPA.

2.3.1.3 Energy Performance for a Location (EPL) The main goal of this value is to help municipalities, developers, housing associations, network administrators and energy companies with decision-making on initiatives for fossil energy savings on district level. An EPL calculation is not legally obliged for appliance of any license. It can be used for both new to build areas as reconstruction of an existing area. The scale for an EPL value is between 0 – 10, where ten is the ideal situation of completely using non-fossil energy in the relevant area.

2.3.1.4 Energy Performance Coefficient (EPC) Since 1996 an EPC calculation is obligatory in the appliance for construction licenses for new housing estates. The EPC indicates the primary energy use of a building and has to be within the borders of the Energy Performance Norm (EPN). The primary energy use addressed by the EPN consists of the energy use for heating, ventilation, hot water, lighting and extra energy needed for pumps and moister conditioning etc (NEN, 2009b). The EPC is described in two NEN (Dutch Normalization Institute) documents. The NEN 2916 for utility buildings, including the calculation method and attached calculation program NPR 2917. For residential houses there is the NEN 5128, including the calculation method and attached calculation program NPR 5129. Basically the calculation for the EPC value is as follows (SenterNovem, 2005), (Beerepoot, 2007a):

EPC =

1 Qtotal * (330* Ausable) + (65* Alosses) cEPC

[1]

EPC Qtotal

= Energy Performance Coefficient = Total energy use for heating, ventilation, hot water, lighting and extra energy needed for pumps etc. (MJprimary) Ausable = Surface area which is usable for the inhabitants (m2) Alosses = Surface area that results in energy losses (m2) cEPC = Correction factor to level an older version of the EPN with this later one. Value is set to 1.12. An EPC of zero indicates an energy neutral building. The following table gives an overview of the valid values in time for the domestic housing sector (NEN, 2009a).

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Table 1: Overview of EPN trend.

Year of implementation

Norm EPC

1995

1.4

1998

1.2

2000

1.0

2003

1.0

2006

0.8

2009

0.8

2011

0.6

2015

0.4

2020 (ambition)

0.0

As described in the table, the government has the ambition to lower the energy performance norm to 0.0 in 2020. This is why it is relevant to stay focused on improvement of the energy performance of buildings.

2.3.1.5 Energy Performance of Buildings (EPG) As stated above the EPDB has become active in the Netherlands since the first of January 2008. Because of this EC measure the government is developing a new normalized method for determining the energy performance of buildings, for both new and existing buildings. This method will result in a new value (EPG) that replaces all existing labels, coefficients and indexes (EPC, Energy Label, EI and EPA) for buildings. The EPG can be seen as the extension of the current EPN, enriched with the EPBD requirements. The EPG will pay attention to district measures as well. A local initiative can comply with the performance of a building when the initiative is assessed within the EMG, this method will be discussed below. The method for determining the EPG will be published by the Dutch Normalization Institute (NEN) and will result in the NEN 7120. This will be published in January 2011 and when active, this norm will be legally obliged in order to obtain a construction license (Bosselaar, 2009)

2.3.1.6 Energy Savings Measure on District level (EMG) The EMG is a new norm brought forward under the EPDB and will be part of the EPG. Within the EPG, this norm will review initiatives on district level. According to L. Bosselaar (SenterNovem) the EMG will be translatable to the new EPG in order to use uniform values. Until this norm will be introduced (publication is expected in 2011), district level initiatives can be assessed with the “Uniforme Maatlat”, which is developed by SenterNovem and Harmelink Consultancy (Bosselaar, 2009). The Uniforme Maatlat will be discussed in chapter 4. 23

2.3.2

Basic figures of energy use in households.

There are great differences in the total energy use in households. Both behavioral and building characteristics are important parameters for the total energy demand, where the latter determines about 42% of total energy use (Santin, Itard & Visscher, 2009). Approximately 57% of the domestic energy is for space heating (average building before 2000), according to Santin, Itard & Visscher (2009). In this same study the mean for energy use is given per type of dwelling, see table 2. Table 2: Mean energy use of a dwelling.

Type of dwelling

Mean energy use (GJ*year-1)

Detached

115

Double

92

Corner

83

Row (terraced)

72

Maisonette

63

Flat apartment

52

However, since the energy efficiency associated with the building characteristics is increasing over time, the relative contribution of the behavioral characteristics is increasing simultaneously (Santin, Itard & Visscher, 2009). In 1997 Ossebaard et al. reported a prognosis for energy use for space heating in 2010 and 2030, being 15 GJfinal*year-1 and 10 GJfinal*year-1 respectively (high scenarios). Also the Expertise Center of Heat (SenterNovem) published similar values for dwellings complying with the 2010 energy performance norm (EPN). Following graph (figure 4) shows the energy use of an EPC 0.8 terraced dwelling (SenterNovem, 2009).

Figure 4: Household energy use of an EPC 0.8 dwelling.

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3.

Eureka-HD: Technology

Basically Eureka-HD is a sanitation system that combines vacuum collection of concentrated wastewater with an innovative treatment technology, scientifically called “Autogenerative High Pressure Digestion” (AHPD). The process of AHPD is discussed in chapter 2.2.3 In 2005 Bareau started to research the possibilities to treat domestic wastewater streams anaerobically in a closed reactor. In cooperation with Wageningen University Bareau performs laboratory experiment to examine the effects of increasing pressure inside the reactor. Biological produced pressures of 90 atmospheres have been shown. This new sanitation concept is called Eureka-HD, which is an abbreviation for [NL] “Energie Uit Rioolwater En Keuken Afval bij Hoge Druk”. Translated to English this would mean “Energy From Sewage And Kitchen Waste under High Pressure”. Eureka-HD is patented by Bareau.

3.1

Basic Principles/System description

Eureka-HD is a system aiming for decentralized treatment of highly concentrated domestic wastewater streams or sludge, producing energy and water of quality similar to surface water. The considered scale for Eureka-HD is 200 to 1000 households. This system is developed to operate without any external energy source. High concentrations of contamination can be achieved by using a vacuum system for the separate collection of black and grey water. Such a collecting system has positive effects on the recoverability of nutrients, water and energy (STOWA, 2005a). Black water includes both toilet and kitchen waste, of which the latter is collected using a kitchen grinder attached to the vacuum system. This stream contains high concentrations of organic material. Black water is enriched by nutrients and COD from grey water and will be treated in an AHPD reactor. Microorganisms break down complex organic matter and produce methane and carbon dioxide (biogas). Preventing biogas from leaving the reactor results in a pressure built up, causing gas purification (by Henry’s law). The whole process is driven by biological produced pressure and does not require any external energy source. The pressure is used to feed new influent into the reactor, creating a vacuum for the collection of waste water, forcing gas and liquids through membranes, drive pressure exchangers for the other steps in the treatment process and feeding green gas into the gas grid. Before gas is fed into the grid (8 or 2 atm.) the surplus pressure energy can be used for several applications that normally use electrical energy to create air or gas pressure. A common example is a heat pump, in which electricity is used to drive a compressor for the compression and evaporation of a certain refrigerant. In the system of Eureka-HD a heat pump is needed to add thermal energy to the reactor. In the current situation most biogas is used in a combined heat-and-power unit, producing heat and electricity. This heat generally is partly used to keep the digester on its optimal temperature. In the system of Eureka-HD the gas is supposed to be fed into the grid, meaning that there will not be a CHP unit involved. Figure 5 describes the principles of Eureka-HD schematically. Both grey and black water are collected separately by a vacuum sewerage. In the treatment of grey water by aeration the organic fraction and the nutrients are extracted and added to the black water. The pneumatic pump forces black water into the AHPD reactor, in which the organic material is biologically degraded into biogas. By controlled deflation 25

of the gas the process pressure will be maintained in the range of 15 to 20 atmospheres. The pressurized gas is deflated through a pressure exchanger for aeration of grey water and the nitritation/denitrification step. Besides, the pressure energy is used to drive the pneumatic influent pump, for the intake of new organic material. Then, the heat pump has to be driven in order to add thermal energy to the reactor, maintaining a process temperature of 303 Kelvin. The system is designed in a way that there still is enough pressure energy left to feed gas into the gas grid (8 or 2 atm).

Figure 5: System design Eureka-HD

In order to maintain the pressure inside the reactor, the process of waste water intake, treatment, effluent discharge and gas release occurs in several working strokes. Figure 6 shows the basic principle on which the process of Eureka-HD is based on. It visually describes the process related to the working strokes mentioned above. Table 3 is a description of figure 6.

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Figure 6: Working strokes AHPD process. Table 3: Description of working strokes in the Eureka-HD process.

Traject

Process

Description

1.

Waste intake.

The pneumatic pump uses gas pressure to feed new influent into the reactor.

2.

Degradation of organic matter into biogas.

Anaerobic digestion, gas production.

3.

Effluent discard.

Part of the pressure energy in the reactor is used to force out some digested material. The effluent is discarded to the last treatment step of nitritation/denitrification.

4.

Pressure energy for work.

The excess pressure energy will be used to ensure the other steps in the treatment process. Part of this pressure energy is for treatment of the grey water and AHPD effluent and part is used in a heat pump to add thermal energy to the reactor. Depending on the process pressure, there might be energy left for work.

Figure 6 has to be considered as a model, in which the exact amount of strokes for gas release is directly related to the health of the AHPD process and the applied process parameters. Also the physical design of the reactor determines the number of strokes that can be performed. Videlicet, a small volume of the gas phase relative to the volume of the liquid phase results in more strokes.

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3.2

Fields of interest

Essentially Eureka-HD produces energy (gas and pressure) and semi clean water (surface water quality) from domestic wastewater. This has direct and indirect effects on the water and energy chain. In the next paragraphs these effects will be discussed briefly. 3.2.1

Waste and wastewater

Biological degradable domestic waste (kitchen waste) is encountered in the Eureka-HD system. In the conventional situation this waste stream is collected and treated centralised. In the majority of municipalities in the Netherlands, kitchen waste together with garden waste is collected separately from domestic solid waste. This biodegradable matter is often composted to a soil enriching product (fertilizer) or burned in power plants (after drying). Drawbacks for this process are that this waste stream (containing mainly water) is transported over significant distances and subsequently oxidised to CO2. Within EurekaHD kitchen waste will contribute significantly to the production of biogas since it will be collected together with black water using kitchen grinders. When the daily per capita load of kitchen waste is added to black water stream the methane potential almost doubles (Intech K&S, 2003). Odour nuisance can be avoided when such grinders are used since the use of a collecting bin is redundant. Paragraph 2.1.1 focuses on the load of wastewater per capita and the energy potential. A conclusion one can draw is that Eureka-HD efficiently uses the energy captured in domestic wastewater and kitchen waste. The conventional system of wastewater treatment does not only use energy for the treatment process but also demolishes potential energy (van Lier, 2010). 3.2.2 Energy Direct effects on the use of natural gas and electricity in households will occur since green gas is produced. Also savings at waste water treatment plants are expected, since the contaminated load from households will be treated decentralized without using energy for the treatment process. Eureka-HD produces energy (gas and pressure) from wastewater and results in indirect energy savings. Chapter 5 will discuss the amount of energy produced by Eureka-HD and will conclude on the impact on the energy use of households. Considering drinking water, the use of clean water diminishes, and thus the indirect energy consumption for preparation will decrease significantly. According to STOWA 2009b a diminishing demand for drinking water results in significant energy savings in the water chain. However, this effect has not been encountered in this study. 3.2.3

Drinking water

Eureka-HD has direct effects on the use of drinking water by households. By using a vacuum system to flush toilets 5 – 10 litres of drinking water can be saved, each flush. According to Hammes, Kalogo & Verstraete (2000) vacuum toilettes use only 0.8 – 2 L per flush instead of 6 – 12 L in a conventional toilet. The average demand for drinking water is 120 – 130 liter per inhabitant per day (STOWA, 2009b). In previous research Bareau and Wageningen University specifically examined the effects of a vacuum system in a district of 32 households. Results from this case study showed that the water use decreased from 130 L*cap-1*day-1 to 65 L*cap-1*day-1 (Zeeman & Kujawa-Roeleveld, 2008).

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4.

Methodology

4.1

System description

In this study it is assumed that Eureka-HD is implemented in a newly built district area where all dwellings are equipped with a vacuum collecting system for separate collection of black and grey water. This vacuum system is attached to an Autogenerative High Pressure Digestion reactor for treatment of urine, faeces and kitchen waste from black water and the biodegradable matter from grey water. The AHPD reactor produces high quality gas, which is injected into the grid, and pressure energy. See chapter 3 and figure 5 for the system description. In order to determine the energy and CO2 performance of Eureka-HD in the upper described design and to inventory the effects on EPC, I made use of the “Uniforme Maatlat”. Firstly I will explain the Uniforme Maatlat, where after I will discuss the methodology used to answer the research questions.

4.2

SenterNovem: ‘Uniforme Maatlat’

Basically the Uniforme Maatlat is a protocol with a set of uniform calculation rules and figures for the assessment of energy measures, considering CO2 emissions, energy use and contribution to sustainable energy production (SenterNovem, 2009). This method is developed by the Heat Expertise Center, a subdivision of SenterNovem. The main goal of the UM is to assess the energy and CO2 performance of a certain technology for domestic energy supply, i.e. solar boilers, heat pumps, heat & cold storage, waste heat or a combined heat and power unit. Decision makers and investors often stand for a difficult choice about which system should be implemented in a certain district. In practice the performance and sustainability of these techniques are not always transparent enough. There is an upcoming demand for a uniform approach for the assessment of energy measures. The Uniforme Maatlat (UM) is a model that gives this transparency. At this moment the UM is suitable for houses and utility buildings but in the near future the model will also be suitable for other sectors, e.g. industry. As subscribed by the European Commission Energy Performance of Buildings Directive (2002) energy measures on district level will be obligatory in a new energy performance norm for buildings, de EPG (see paragraph 2.3.1.5). The UM will be further developed to give ground to the determination methods in this new norm. This argument was the main reason for choosing the UM as a method to determine the energy performance of Eureka-HD in district areas. Appendix II shows a print screen of the UM-spreadsheet, including the exact calculation methodology given by the Heat Expertise Center (SenterNovem).

4.3

Energy potential of decentralized Eureka-HD for treatment of domestic wastewater

The potential for energy production from human excreta and kitchen waste in the Eureka-HD system can be determined by calculating the potential for methane gas and pressure energy. In this paragraph the methodology for determining the gas production is given.

29

As a basis for the values needed to perform calculations on gas production I used a reference project in Heerenveen which was performed by Bareau, based on the DeSaR project in Sneek (Zeeman & KujawaRoeleveld, 2008). These values consider a total organic load from 465 i.e. and a degradation efficiency of 90%, which are both comparable to values given in scientific literature (Hammes, Kalago & Verstraete, 2000), (Zeeman & Lettinga, 1999), (Kroiss & Zessner, 2007), (Intech K&S, 2003), (Ort, 1976). Using these values the potential energy, in liters of methane and in MJ, in domestic wastewater was determined. Table 4 indicates the values that were used to make the energy balance. Table 4: Waste load of 465 i.e. (± 180 households) and corresponding energy potential (Bareau, 2009)

Domestic sewage

Waste stream L/day

COD load g/L

COD load kg/day

COD degradable 90%

CH4 potential Nm3/day

Energy potential MJ/day

Black water (incl. KW)

2400

33

79

71

28

887

Grey water

31200

0.7

23

21

8

260

Total

33600

33

102

92

36

1147

Per capita values

72

33

0.2

0.2

0.08

2

Note: Methane potential: 393 L/kg COD; Energy potential (caloric value of methane at 303 Kelvin): 31.9 MJ/m3

The used value for methane production from organic matter is not in compliance with data found in scientific literature. Numbers given in paragraph 2.2.1 about methane formation are based on normal conditions (273.15 Kelvin and 1.01325 atm.), which is not realistic in the more extreme environment of AHPD. The following way of reasoning will clarify the value I used and thereby also the differences. To determine the potential methane production from organic matter I used following equations, also given by Van Haandel & Lettinga (1994):

The top arrow in the equation describes the oxidation (with O2) of organic matter to CO2 and H2O. This reaction requires 6 moles of oxygen per mole of organic material, weighing 0.192 kg. So in the aerobic route 0.192 kg of COD is degraded. When considering anaerobic digestion one mole of organic material breaks down in the absence of oxygen into 3 moles of CO2 and 3 moles of CH4. Since the volume of all gasses is 22.4 L*mol-1 at normal conditions, 1 kg of COD produces 350 normal liters of methane.

30

When considering AHPD the process operates at temperatures of 303 Kelvin and varying pressures, resulting in an average gas volume of 25.2 L*mole-1 (Barelds, 2010). Calculating with this value the methane potential from 1 kg of COD, given in actual liters, is 393 L*mole-1. Since gas expands at increasing temperatures, the caloric value of methane gas (in MJ*m-3) decreases when considering a certain amount of moles of methane. At normal conditions, methane has a caloric value of 35.9 MJ*m-3. However, when considering AHPD gas the caloric value of methane is 31.9 MJ per actual cubic meter produced. This number is found when calculating from the combustion enthalpy (802.7 kJ*mole-1) of methane (Bruggemans & Herzog, 2005) and the volume of AHPD gas per mole (25.2 L*mole-1).

4.4

Potential of a heat pump driven by biological produced pressure in Eureka-HD

Additional to the energy production from the organic load of households, pressure energy produced in the AHPD process is considered. This potential can be determined using SI-units (International System of Units) for the calculation of the internal energy (Joules) as a function of the pressure (Pascal = N.m2) multiplied by the volume (cubic meters = m3). By doing this one will find a pressure energy potential (MJ) of 0.1 times the prevailing pressure (atmospheres) multiplied by the gas flow (m3/unit of time). So at a process pressure of 20 atmospheres, the energy potential from pressure corresponds to 2 MJ*Nm-3 of gas. This has to be multiplied by the rate of produced AHPD gas in the gas phase of the reactor to determine the exact amount of available pressure energy. However, about 44% of the pressure energy is needed to drive essential parts to maintain the process, such as the influent pump and some filtration membranes. Remaining pressure energy can be used for work, e.g. in the other steps of the total treatment process. Depending on the process pressure there might be an excess of pressure energy. When this is used in a heat pump, this amount of energy (joules) can be multiplied by the COP (coefficient of performance) of the heat pump to determine the thermal power that can be generated. This is an efficient way to recover thermal energy from grey water. STOWA (2009b) describes the thermal energy that is daily produced per inhabitant, being 127 liter with an average temperature of 300 Kelvin. This is a thermal capacity of 1.800 Watt/i.e. Assuming that 10 degrees can effectively be recovered, the thermal capacity available is more than 60 Watt/i.e. (about 33% of energy demand for space heating in EPC 0.8 building).

4.5

Energy requirements total treatment process

In order to operate the AHPD reactor, a large part of the pressure energy produced is needed for the influent pump and discarding the effluent. This accounts for 44% of the total power capacity from the pressure energy. This means that the remaining 56% is available for work en for injection of methane on the local grid. Treatment of both black and grey water requires additional treatment processes in order to meet the discharge requirements. The remaining 56% of pressure energy after the influent pump and gas injection is available for these other treatment processes. Grey water can be treated with aeration and a sand filter to comply with surface water quality (STOWA, 2006). The effluent from the AHPD reactor consists of high concentrations of NH4+ that have to be removed before discharging. This can be done by using a nitritation/denitrification unit such as an Anammox or an Oland system. 31

Besides that the AHPD reactor looses thermal energy by radiation and input of an influent stream that has a lower temperature than the process temperature. Therefore the reactor requires additional heating. 4.5.1

Aeration of grey water

For the aeration of grey water it is assumed that a system is used that provides aeration with fine bells in a deep tank. This system delivers 0.55 kg O2/MJ of energy input (Koot, 1980). Calculating with an OC/load of 1.8 and the amount of COD that has to be removed, the energy needed for treatment can be determined (Koot, 1980). The Oxygenation Capacity (OC) describes the rapidity of oxygen transfer to a certain media (wastewater in this case) and is given in kg O2/hour (STOWA, 2009a). As shown in table 4.2 the total amount of COD in the grey water stream of 465 i.e. is 23 kg per day. Meaning that 23*1.8 = 41.5 kg O2/day is needed. Total energy demand to remove this fraction is 41.5/0.55 = 75.6 MJ/day. 4.5.2

Nitritation/Denitrification

The treatment of NH4+ can be done by several processes. Eureka-HD uses the Sharon-Anammox process to remove 80% of the total nitrogen load (NH4-N) in the effluent. The daily nitrogen load per person excreted corresponds to approximately 10-11 gram (Kroiss & Zessner, 2007), (STOWA, 2005a), (Hach Lange, 2008). Using the Sharon-Anammox process 1.9 kg O2 is needed to 1 kg of NH4-N (STOWA, 2008b). In a district of 465 i.e. about 5 kg of NH4-N is being produced. For the removal of 80% of this load 7.6 kg O2 is needed. With an OC/load of 1.8 and an aeration efficiency of 0.55 this means that 24.9 MJ/day is needed to remove the NH4-N load of 465 i.e. 4.5.3

Process temperature reactor

The AHPD reactor for treatment of domestic wastewater operates at 303 Kelvin. When the temperature difference between the reactor and the surrounding environment is known and the surface area of the reactor determined, calculations can be made on the thermal losses of the reactor. I used the law of Fourier for the calculations. Law of Fourier: Q = Thermal t = Time λ = Thermal conductivity (W/m.K) A = Surface area (m2) T = Temperature (Kelvin) χ = Thickness of material (m)

energy (Joules) (seconds)

Additional to the thermal losses through conductivity, the reactor looses thermal energy through effluent discard. The effluent leaves the reactor at 303 Kelvin and new influent is entering at 288 Kelvin. These losses can partly be decreased by using a heat exchanger for heat transfer from the effluent to the influent stream. Because these flows are equal the influent can be heated to (((303-288)/2)+288) = 295.5 Kelvin by using a heat exchanger. This means that the influent has to be heated 7.5 degrees Kelvin. To calculated the needed power to do this, I calculated with the specific heat capacity of water (4180 J*kg-1*K-1). Within the system of Eureka-HD a heat pump will be used to produce this thermal power. A pressure driven heat pump with a Coefficient Of Performance (COP) of 7.5 is used (SenterNovem, 2008).

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4.6

CO2 emission reduction potential Eureka-HD

Carbon dioxide emissions are directly related to energy use. Reducing the fossil energy use of households results in a reduction of fossil CO2 emissions, taking into account standard values for the amount of carbon dioxide emitted per unit of electricity produced or natural gas combusted, being 59 kg CO2 / GJprimary and 56 kg CO2 / GJprimary respectively. This difference can primary be explained by the fact that electricity is produced from a certain mix of energy carriers (e.g. coal, gas, biomass etc.), determining the exact CO2 emissions. Besides, the conversion technologies used have different efficiencies. The CO2 calculations are shown in Appendix II and are based on SenterNovem 2009.

4.7

Effect of Eureka-HD on the energy performance coefficient

Firstly it is important to state that the EPC methodology is an official standardized method, meaning that technologies cannot have an officially recognized effect on the EPC without being certified. Eureka-HD is not in that stadium yet. The calculations I performed on the EPC are based on equation [1], but are not official. However, it gives an indication about the effect of Eureka-HD on the energy performance of dwellings, expressed in a commonly used unit. Using the equation formulated in paragraph 2.3.1.1 and the correct values I performed this calculation. Assumptions on the valid surface areas are given in paragraph 4.3 “Model assumptions”. This data is valid for a terraced dwelling, of which all my calculations are based on.

4.8

Model assumptions

Although most of the assumptions used were explained earlier in this report, table 5 gives an overview. This table includes figures that were used for the calculations to determine the energy and CO2 potential and the EPC, as well as references used to validate them.

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Table 5: Model assumptions Subject Description

Value

Reference

Domestic situation

Occupation rate of dwellings (number of inhabitants)

2.6

Practical living surface per dwelling (terraced dwelling) Practical losses surface per dwelling (terraced dwelling) Energy use for space heating

135 m2

Energy use for hot water

8 GJfinal / year

Energy use for wastewater treatment (current situation) COD from black water (incl. kitchen waste)

0.85 GJprimary / hh / year 169 gram / cap / day

Planbureau voor de Leefomgeving / CBS: European average SenterNovem 2005 SenterNovem 2005 SenterNovem 2009 SenterNovem 2009 Van Lier 2010

COD from grey water

50 gram / cap / day

Bareau 2009

Reactor volume

43 m3

Barelds 2010

Process temperature

303 Kelvin

Bareau 2009

Degradable COD (% of total COD)

90%

Theoretical maximum methane potential from COD

393 L / Kg

Zeeman & Kujawa-Roeleveld 2008, Lindeboom et al. 2009 See paragraph 4.3

Gas volume

25.2 L / mole

Caloric value of methane at 303 Kelvin

31.9 MJ / m3

Pressure energy for process maintenance

44% of total pressure energy 7.5 (temp lift 7.5 Kelvin)

Waste load Eureka-HD AHPD process

Heat pump COP

Eureka-HD other treatment processes

CO2 emission

34

240 m2 15 GJfinal / year

Bareau 2009

Barelds 2010 (Dynameau©) See paragraph 4.3 Barelds 2010 (Dynameau©) SenterNovem 2008, paragraph 4.5.3 Koot 1980

Aeration capacity

0.55 kg O2 / MJ input

OC/load

1.8 (-)

Koot 1980

Daily nitrogen load

10-11 gram / cap / day

Oxidation of NH4-N CO2 emission electricity generation

1.9 kg O2 / kg NH4N 59 kg / GJprimary

Kroiss & Zessner 2007, STOWA 2005a, Hach Lange 2008 STOWA 2008b

CO2 emission natural gas consumption

56 kg / GJprimary

SenterNovem 2009 SenterNovem 2009

5.

Results

An important conclusion I have to make is that the original design to operate the AHPD process of Eureka-HD at 18 atmospheres on average is inadequate to completely sustain the treatment of both grey and black water with the energy from biologically produced pressure. There is a shortage of 2 Watt/i.e. for total wastewater treatment driven by pressure energy. Calculations with Dynameau© and the energy balance in the Uniforme Maatlat show that at least 60 atmospheres is needed in the AHPD process to produce enough power to drive all machinery in the total treatment process. This includes aeration of grey water, the Sharon-Anammox process, the heat pump for maintaining the process temperature and the energy needed to inject the AHPD-gas on the local gas grid (at 2 atmospheres).

5.1

Eureka-HD in the built environment

What is the bottom line potential of decentralized Eureka-HD for treatment of domestic wastewater and kitchen waste, in terms of energy? The renewable energy production potential of Eureka-HD is approximately 200 L methane per dwelling per day, excluding pressure energy. Expressed in a functional unit, this corresponds to 6.4 MJ per dwelling per day. This corresponds to 29 Watt/i.e. However, since Eureka-HD is based on AHPD a significant amount of pressure energy is available. In order to realize a grey and black water treatment system that is completely sustained by biologically produced pressure, the AHPD process pressure has to be at least 60 atmospheres. The total treatment process driven by pressure costs 6 Watt/i.e. The AHPDgas is purely benefit and accounts for approximately 16% of the energy demand for space heating. This corresponds to 5% of primary energy use of an EPC 0.8 household. Secondary energy savings occur at the centralized wastewater treatment plant, accounting for approximately 2 MJprimary per dwelling per day, this is app. 10 Watt/i.e. Please note that the energy needed to perform treatment of domestic wastewater with Eureka-HD is 6 Watt/i.e., meaning that there is a difference of 4 Watt/i.e. This difference can be explained by two things: Eureka-HD treats a concentrated stream of wastewater instead of a diluted stream. This is realized by using a vacuum system instead of a combined sewerage. The second reason is the difference in machinery efficiency (related to primary energy use). In the current situation mostly electrical machinery is used, where Eureka-HD uses pressure driven machinery. What can be the potential in terms of CO2 emissions when applied on a large scale? This study discusses the CO2 reduction potential of Eureka-HD in relation to the CO2 emissions of an EPC 0.8 dwelling. The primary energy reduction is directly related to a reduction in fossil CO2 emissions. Eureka-HD results in a fossil CO2 saving of 100 kg per dwelling per year, corresponding to a reduction of 3.5%. When including the current energy consumption for treatment of domestic wastewater the fossil CO2 savings would be 160 kg per dwelling per year, corresponding to a reduction of 5%. In a prospects document of the Dutch government about the construction of new dwellings (CPB, 2006), a prognosis is made that in the next 30 years (2010 – 2040) about 700.000 new estates will be built. If all these buildings would be equipped with Eureka-HD, the emission of 112.000 tons of fossil CO2 is avoided yearly. This is 0.5% of the total CO2 emission of the built environment in 2020, in a business as usual scenario (VROM, 2007).

35

What is the effect of Eureka-HD on district level for the Energy Performance Coefficient of the considered dwellings? When Eureka-HD is applied in a district of newly build EPC 0.8 dwellings, the EPC can be lowered by 0.05 points. However, within the current methodology for the determination of the EPC energy use for conventional wastewater treatment is not encountered. When encountering these energy costs to the reference situation, Eureka-HD lowers the total EPC by 0.07 points.

5.2

Conclusion

Eureka-HD significantly improves the energy balance of wastewater treatment. From an energy consumption of 5 – 15 Watt/i.e. in the current situation of wastewater treatment, treatment of domestic wastewater and kitchen waste using Eureka-HD produces 29 Watt/i.e. When encountering the energy for wastewater treatment of domestic wastewater in the calculations for the Energy Performance Coefficient (EPC), Eureka-HD realizes a reduction of 0.07 points. Figure 7 shows this conclusion. Figure 7: Energy balance Eureka-HD

36

6.

Discussion

The development of AHPD is in progress at this moment. From autumn 2010 Bareau will perform tests on the continuously operating process with a reactor designed for a small district area (2 m3). Results from testing the AHPD process on this scale is essential for concluding on the actual energy performance of the system. Biological efficiency When operating a biological process at higher pressures you might expect that the efficiency of the biology will decrease. In this report, with the tools I had available in this study, I calculated with a biological efficiency that was the same for different process pressures. This means that the efficiency of biological conversion at 1 atmosphere was the same as the conversion efficiency at 40 or 60 atmospheres. This assumption might seem irrational when reasoning from basic physics. However, experiments show that the pressure as a function of biological activity increases linearly up to 90 atmospheres (see figure 3). At this pressure, the physical capabilities of the reactor were being exceeded. Gas quality As a function of Henry’s law the gas is upgraded inside the AHPD reactor. However, removal of CO2 and H2S might not be sufficient to reach natural gas quality for injection on the local grid. Other components such as siloxanes or micro biological traces might be present in gas from anaerobic digestion as well. The specifications for injection of green gas on a gas grid are very strict (see Appendix VI). In my opinion this is an important aspect for Bareau to research in a later stadium of the development of Eureka-HD. Dissolving gasses In this study and in the dynamic model Dynameau© dissolving methane as a function of the process pressure is encountered. Depending on the pressure we calculated with about 20% dissolving, related to the Henry coefficient of methane. However, during my literature study I found various scientists claiming that sometimes 30% or even 50% dissolves, at ambient conditions. In latter stadium of research to Eureka-HD, the exact amount of methane dissolving in the AHPD process might need some extra attention. Besides the dissolving methane, a large part of the produced carbon dioxide is dissolving as well. Both gasses are dissolving at high pressures. In my energy balance I did not encounter this pressure energy, still available in the discarded effluent, as potential energy for work. We (Bareau) expect that maybe 20% – 30% of this pressure potential might be available for work (roughly estimated). At 60 atmospheres about 20 Nm3*day-1 of CO2 is dissolved in the liquid phase and will be discarded with the effluent. This is roughly 30 kg to 40 kg of CO2 per day (at a waste load of 465 i.e.). Energy demand for treatment with Eureka-HD The other processes in the total treatment of domestic wastewater and kitchen waste, being aeration of grey water and the Sharon-Anammox process, consume pressure energy. However, I calculated with values that are valid when performing these steps with pumps that are electrically driven. The efficiency, related to primary energy use of this electrical machinery is lower than pneumatic or hydraulic machinery (driven by pressure). Since these processes are responsible for a large share (25%) of the pressure energy

37

consumption in the total treatment process, there might be big potential for improvement here. Increasing the efficiency of these processes could significantly influence the required process pressure of AHPD. Thermal energy domestic wastewater The thermal energy potential from grey water is relatively high compared to the total energy demand for space heating (approximately 33%, see paragraph 4.4). However, the problem with thermal energy in grey water is that the supply does not always correspond to the moment of demand. This means that this energy flow has to be stored very efficiently. In an ideal situation considering energy, one can think of heat and cold storage for every household. The environmental effects of these systems, when implemented on a large scale, have to be studied in order to prevent problem shifting. Currently, the energy consumption for treatment of domestic wastewater is not encountered in the EPC calculations. Since this energy demand is always related to a household I would suggest that this has to be encountered in the calculations for EPC.

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VROM, Ministry (2008). Lente-Akkoord “Energiebesparing in de nieuwbouw”. April 2008. Yadvika, Santosh, Sreekrishnan, T.R., Kohli, S. & Rana, V. (2004). Enhancement of biogas production from solid substrates using different techniques – a review. Bioresource Technology, 95, 110. Yayanos, A.A., et al. (2002). Are cells viable at gigapascal pressures? Science, 297, 295a-295. Zagt, C.E., Barelds, J., Lier, van J.B., Lindeboom, R., Weijma, J. & Plugge, C. (2010). Energie uit rioolwater en keukenafval bij hoge druk. H2O (43), 4, 10-13. Zeeman, G. & Lettinga, G. (1999). The role of anaerobic digestion of domestic sewage in closing the water and nutrient cycle at community level. Water Science & Technology (39), 5, 187-194. Zeeman, G. & Kujawa-Roeleveld, K. (2008). Decentralised Sanitation and Reuse (DESAR), EET Project Final Report, SenterNovem. Web pages: Energy label:

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44

Appendix I.

Uniforme Maatlat: reference situation

Uitgangpunten referentiesituatie Type woning

Nieuwbouw rijtjeswoning

Aantal woningen Referentiesituatie Aardgasgebruik ruimteverwarming

1