Transactions on Ecology and the Environment vol 4, © 1994 WIT Press, www.witpress.com, ISSN 1743-3541
Air pollution caused by odours - basics, measurement techniques and emission inventory at waste and
wastewater
treatment facilities F.-B. Frechen Aqua System Consult, Am
Hackenbruch ^7, 40231
Diisseldorf, Germany Abstract Annoyance caused by odours can become an important environmental impact. The necessary measurement technique is significantly different compared with standard analytical methods, as odours must be measured by using sensory methods involving a test person panel for assessment. At waste and wastewater treatment facilities, sampling techniques are important as these facilities have large areas with odour emissions, but without measurable emission flow rates. Basics, measurement and sampling techniques are explained and results of inventory measurement programs are presented. Introduction Due to people's increasing demand on life quality, annoyance caused by odours gains more attention these days. When discussing odour problems, it is not sufficient to have knowledge of engineering sciences, as the problem includes important aspects of other disciplines such as medical sciences, psychology and meteorological sciences. In Germany, inside the German Association of Engineers (VDI) and the German Institute for Standardization (DIN), the VDI/DIN-Commission on Clean Air, on behalf of the federal authorities, works on odour problems. Recently, this work also is carried out in the european community by CEN TC264/WG2. Since it is most important to understand the basic concepts of odour perception and odour measurement techniques in order to be able to judge the results of measurements, basics are explained in the text. Then, some remarks on sampling are necessary, and subsequent results of measurements at waste and wastewater facilities are presented.
Transactions on Ecology and the Environment vol 4, © 1994 WIT Press, www.witpress.com, ISSN 1743-3541
186 Pollution Control and Monitoring Basics of odour reception, measurement and sampling Odour Reception Odour is a human sensation caused by the presence of so-called "odorants" and is based upon a two-step process: rtrtr&DAMT v reception ^ interpretation _^ ODOUR UIJUKAJNI =^ (physiological)^ (psychological) ^ IMPRESSION Until today, the physiological part of the process is not known completely. In addition, psychological interpretation is an individual process that cannot be described in terms of universally valid relations or equations. The intensity of the impression reported by various test persons differs and until today it is not possible to give equations that are able to predict the impression in relation to the presence of different airborne compounds. All kinds of effects from antagonistic through additive to synergistic are reported so far. Thus, although the presence of odorants lead to the odour impression, these substances are not the main point of interest, as will be explained later. Measurement Methods Figure 1 gives a general view of the situation when waste air is present that has to be assessed and analyzed. no I odor odor measurable: nose and brain: waste air containing physiological and odor numerous compsychological pounds and odorous processing of K sensation compounds stimulus s odor strength: odorants concentration analytical methods ( \ odor strength: for identifying odor and measuring intensity kind of odor
analytical part: "substance-related"
hedonic tone j sensoric part: 'effect-related'
Figure 1: Analytical and sensory measurement possibilities. The left part of figure 1 deals with the chemical aspects of the air to be analyzed. Different methods, ranging from tube tests to gas-chromatography in connection with various detectors, are applicable and give informations about specific gas compounds. If the composition is unknown, usually massspectrography is used to detect the compounds present in the air. But as it is not possible to derive statements concerning odour from these substance-
Transactions on Ecology and the Environment vol 4, © 1994 WIT Press, www.witpress.com, ISSN 1743-3541
Pollution Control and Monitoring
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related values, this part of the Figure is headed with "no odour". The relevant problem in the case of odour is not the presence or absence of specific air compounds, which can be determined by means of analytical measurement techniques and would give compound-related measurement results. The main problem is to achieve knowledge about the effects of the airborne compounds, this means to get an effect-related measurement result. Since, in general, measurements must apply to the question that has to be answered, in the case of odour, measurement techniques are necessary that are based upon the judgement of test persons. As in the case of odour the judgement varies in a fairly wide range from person to person, the laws of statistics additionally must be obeyed to get something like "true" and "reliable" measurement results. The right part of Figure 1 deals with odour. Different questions lead to different "measurement values". In the case of odour the measurement method depends upon the question to be answered. The most important parameter is the "strength of odour - odorants concentration". The method to determine the odorants concentration is prescribed in a bilingual german/english guideline in Germany (VDI 3881 [6]). The basic concept of this measurement method is to dilute an air sample with clean, odorless air until half of the test panel does not smell anything whilst the other half of the test panel still smells something - odour perception threshold. The number of dilutions necessary to reach the odour perception threshold is called "odorants concentration o.c." and is given in the unit of "odour unit per cubic meter o.u./nf", although in fact it has no dimension. The concept behind this is that a certain amount of "odorants" is present leading to the resulting odour impression. The connection between dilution and one cubic meter of air of course is arbitrary. As the device that is necessary to prepare the mixture of sample air and odorless air is called an "olfactometer", this measurement technique is called "olfactometry". The VDI-guideline 3881 at this moment is in revision and a new issue is expected in 1994. The other parameters shown in figure 1 - odour intensity, kind of odour and hedonic tone - are of high interest, but of minor relevance at this time. They are discussed by Frechen [2]. Sampling For purposes of atmospheric dispersion calculations, it is necessary to know the mass flow emitted which is the emissions concentration mutiplied by the emissions airflow. The odorants concentration is the relevant concentration in this concern. Different types of sources have to be considered, see table 1. Usually, passive point sources are not relevant. With active point sources, sampling of gas samples as well as determining the emitted airflow is easy. When having active area sources, as for example biofilters, it is most important to apply a sampling scheme for both gas samples and airflow that gives representative values for assessment of the whole area. Until now, no
Transactions on Ecology and the Environment vol 4, © 1994 WIT Press, www.witpress.com, ISSN 1743-3541
188 Pollution Control and Monitoring Table 1: Characterization of emission source types defined airflow present
not present
size of
point
active point source
passive point source
source
area
active area source
passive area source
prescriptions exist giving hints on the number of sampling points necessary in relation to the size or type of the area to be assessed. Passive area sources, as for example clarifiers, thickeners on waste water treatment plants or landfill surface, slopes on waste facilities, turn out to be the most difficult type of source, as no airflow is measurable, but, however, emission of odorants can be recognized. Concerning this type of source, a sampling strategy is necessary which is explained in figure 2. odorless air V-n = defined Cod= 0
sample air 6 = c*d ' Vout with COQ« measured and Vt =V
odour emitting surface, e.g. sludge in thickener Fig. 2. Principle of emission measurement on surfaces without airflow A known portion of the area is covered with a box, open at the bottom. Then, a certain amount of odorless, synthetic air, about 3 through 10 nf/(nf-h),is pumped through the box. From the off-gas, the odorants concentration can be measured via olfactometry in o.u./nf, and thus, specific emission flow in o.u./(nf-h) as well as total emission flow in o.u./h, using the total size of the area, can be determined. Further work on the prescriptions regarding sampling strategy for all kinds of sources is planned to be done in conjunction with CEN TC264/WG2. Emissions at waste treatment facilities Domestic landfill sites The results of several measurement programs at domestic landfill sites as well as at hazardous landfill sites were presented by Frechen [3] earlier. Data are also available from other authors, e.g. Cernuschi and Giugliano [1]. Regarding
Transactions on Ecology and the Environment vol 4, © 1994 WIT Press, www.witpress.com, ISSN 1743-3541
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domestic waste landfills, the following values may apply as a first approach, which, however, should always be established by measurement at the respective landfill: • • #
site surface, slightly covered: slopes (depending on cleft formation): freshly tipped waste:
300 - 1,000 o.u./(nf h) 200 - 2,000 o.u./(nf h) 5,000 - 30,000 o.u./(nf-h)
In addition, different kinds of installations such as leachate pits/containers, passive degassing installations etc. have to be considered. Hazardous waste landfill sites No numbers should be given for hazardous landfill sites, as in these cases always a specialized measurement program is required. Due to the different types of waste and due to interaction between different wastes it is not possible to use "average" emission flow rates. Waste composition, operation of the landfill and many other factors strongly influence the emissions of these kind of landfills. The only possible general statement is that according to measurement programs like those presented by Frechen and Kettern [5] the emission concentrations often exceed those evaluated at domestic landfill sites by a factor of ten or more. Composting facilities Frechen [4] reported in detail about odour emissions at composting facilities. Emissions can be located at different parts of these facilities and depend on the type of waste to be composted and the operation conditions. Storage or mechanical preparation During storage or mechanical preparation of the incoming waste, the following values may serve as a first estimation, to be assured by further measurement at the specific place: • • •
green waste (garden waste): domestic waste biowaste (kitchen waste etc.)
300 - 3,000 o.u./(nf-h) 800 - 10,000 o.u./(nf h) 2,000 - 15,000 o.u./(nf-h)
Composting machine While using a composting machine, the fan attached should ensure aerobic conditions inside the reactor. The air that leaves the reactor, consequently, is loaded with all kinds of smell composting can produce, including ugly odours generated during anaerobic degradation, if the air supply or air distribution do not meet the needs of the process. Of course, the odorants concentration of the reactors off-gas depends upon a variety of factors such as composting time, raw material, aeration rate, and others. Due to this fact, universally valid values are not available; the range may be between some thousand and some hundred thousand o.u./nf. Composting by windrowing If no mechanical composting is used, as is the case usually with small composting facilities or with composting biowaste or
Transactions on Ecology and the Environment vol 4, © 1994 WIT Press, www.witpress.com, ISSN 1743-3541
190 Pollution Control and Monitoring green waste, then composting itself takes place when the material is set up in long heaps about 1 to 2 m high. As the process has to be aerobic and the oxygen demand is high in the beginning, it is necessary to turn over the heaps quite often to achieve aerobic conditions and maintain sufficient oxygen supply. Although emissions decrease quickly after the heaps are set up, every turnover of the heaps will cause odour emissions that can be compared with the values given with mechanical preparation. Maturing After the compost has passed through the stage of digestion, whether by windrowing or in a mechanical composting plant, it has to be set up in piles to continue aerobic digestion and to mature the material. 100000 _c •*
