KÄLLBY WASTEWATER TREATMENT PLANT 1

Welcome to

Källby Wastewater Treatment Plant A large treatment plant

Why treat wastewater?

Källby Wastewater Treatment Plant is situated a couple of km south-west of Lund, and receives 350 litres wastewater per second, which is equivalent to about 110 bathtubs per minute. The water is received from the city of Lund and its surroundings. Construction of the plant was started in 1933, and today over 100,000 residents are connected to the plant.

The average Swede uses approximately 190 litres, or about one bathtub full, of water every day. Water that is flushed from toilets or washed down the drain is directed to our treatment plants, where it is treated and then discharged back into the natural water courses.

REDUCING SOCIETY’S ENVIRONMENTAL IMPACT

the goal of the Källby plant is to ensure safe wastewater treatment for residents in the neighbourhood, as well as for the society in general. The best possible wastewater treatment methods are combined with specialist competence to achieve a sustainable process that is well adjusted to the ecological cycle, having a minimum environmental impact.

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REMOVING NITROGEN AND PHOSPHORUS

The purpose of wastewater treatment is to protect the environment, animals and people from the harmful substances in wastewater. For example, high levels of nitrogen and phosphorus can result in eutrophication (enrichment of an ecosystem with nutrients, typically compounds contain nitrogen and/or phosphorus) of our waterways, causing algal blooms and other problems. High amounts of organic substances in water result in the depletion of oxygen, as oxygen is consumed when these substances are degraded, and this can have serious effects on many aquatic organisms.

The sewerage system Most of the sewerage system in Lund (90%) is a duplicate system. This means that sewage and stormwater are collected in separate sewers. The remaining 10% is a combined system carrying all types of wastewater. Källby receives wastewater from central Lund and the villages of Stångby, Dalby, Värpinge, Valkärra, Björnstorp, Veberöd and Genarp.

Wastewater treatment plant Duplicate sewer system Combined sewer system

Future challenges How is the treatment process controlled? The main task of the Källby Plant is to handle and treat wastewater in compliance with wastewater treatment regulations. A computerized control system is used to continuously monitor and regulate the treatment process, to ensure that these requirements are met. COMPUTERIZED MONITORING

Various meters are used to continuously measure the phosphorus concentration, the water flow and other important parameters. Wastewater samples from the different stages of the process are also analysed in the plant’s laboratory. The advantage of continuous monitoring is that it is possible to detect changes in the treatment process as soon as they occur, and to adjust the process accordingly. Laboratory analyses take longer, but they are often more accurate than the meters.

The strategy for wastewater treatment in the municipality of Lund has changed in recent years. Running several small wastewater treatment plants is resource-demanding, and larger wastewater treatment plants provide better and more reliable treatment. For these reasons, it is planned to redirect wastewater currently treated at smaller plants to the Källby Plant in Lund. This will lead to increasing load on the Källby Plant, and thus further optimization of the treatment process will be necessary. More stringent restrictions can also be expected, as greater emphasis is being placed on protecting the environment in our communities. CONTINUOUS IMPROVEMENTS

At our wastewater treatment plants, we follow the general trend in society of endeavouring to make use of the available resources in the best possible way. Some of the environmentally friendly measures we have taken include advanced control to reduce the electricity demand, optimal utilization of the produced biogas, minimizing the amount of chemicals used in the treatment process, and the recycling of nutrients.

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Glossary ACTIVATED SLUDGE PROCESS: An aerated treatment stage in which microorganisms decompose organic material and convert ammonium into nitrite and nitrate AEROBIC: Containing oxygen ANAEROBIC: Being completely

devoid of oxygen

ANAEROBIC DIGESTION: Anaerobic biological decomposition of organic material resulting in the production of biogas (mainly methane) ANOXIC: Containing oxygen only

in the form of compounds such as nitrite, nitrate and/or sulphate

BOD: Biochemical Oxygen Demand or Biological Oxygen Demand, a measure of the content of biodegradable substances in the wastewater CLARIFICATION: Settling of heavy particles in the water by gravity DENSITY: Mass per unit volume, g/cm3 or kg/m3 EUTROPHICATION: A process in

which excessive amounts of nutrients, for example, phosphorus and nitrogen, are deposited in soil or water

OVERFLOW: During periods of high

water flow, the flow of wastewater sometimes exceeds the capacity of the plant, and incoming water has to be diverted past some stages of the treatment process

POST-PRECIPITATION: Chemical precipitation of residual phosphorus after the biological treatment PRE-PRECIPITATION: Chemical precipitation of phosphorous in the primary treatment SEWAGE: Wastewater from house-

holds and industrial processes

SLUDGE: The material produced

during wastewater treatment, consisting of decaying products in the wastewater

STORMWATER: Rainwater and snow

melt run-off

The treatment process 1. INLET PIPES

Wastewater is directed into the Källby Wastewater Treatment Plant through three large pipes, under the force of gravity. 2. SEPARATION OF SCREENINGS

The wastewater is passed through screens where particles larger than 3 mm, called screenings, are removed. The volume of screenings varies depending on the weather and the flow rate. Under dry weather conditions and low flow rates, the screenings accumulate in the sewers. When it starts to rain, the rate of flow increases, and the screenings follow the wastewater into the wastewater treatment plant. This places a considerable hydraulic load on the plant for a short period. The screenings are washed and then transported to an incineration facility.

6. ACTIVATED SLUDGE PROCESS

The activated sludge process is part of the biological treatment stage, where microorganisms in the sludge remove nitrogen from the wastewater and degrade the organic material to carbon dioxide and water in the presence of oxygen (aerobic conditions). Nitrogen is removed by two biological processes called nitrification and denitrification. In nitrification, ammonia is converted into nitrate, and in the denitrification process the nitrate is converted into nitrogen gas, which is discharged to the atmosphere. Nitrification is performed by microorganisms in the presence of oxygen (aerobic conditions), and the water in the basins used for this is aerated. The air flow is regulated with the aid of oxygen and ammonia meters in the basins. Denitrification is not possible in the presence of oxygen, and the denitrification basins are therefore not aerated (anoxic conditions). The activated sludge process at the Källby Plant is divided into four parallel lines.

3. GRIT REMOVAL

Grit is removed in aerated basins. Particles lighter than water follow the wastewater further downstream, while heavier particles, such as sand, sink to the bottom. The grit is then pumped to the grit treatment stage. In order to remove particles of the desired size it is important to use the appropriate water velocity. Aeration helps in obtaining the correct velocity.

7. SECONDARY CLARIFICATION

In the secondary clarifiers, the activated sludge is separated from the wastewater. Most of the sludge is transferred back to the activated sludge basins and is called return sludge. The purpose of this is to maintain an adequate sludge content in the aeration basins. The remaining sludge, called waste activated sludge, is transferred through the primary clarifiers to the sludge treatment.

4. GRIT TREATMENT

The removed grit is pumped to a grit washer where it is washed and dewatered to remove the organic material, as it is forbidden by law to deposit organic material. The grit and sand is then transported to an external site.

8. POST-PRECIPITATION

5. PRIMARY CLARIFICATION

9. FINAL CLARIFICATION

In the primary clarifiers, particles with a density greater than water sink to the bottom and form primary sludge. The sludge is scraped into hoppers from which it is pumped into the sludge treatment. The wastewater entering the clarifiers is mixed with reject water from the sludge treatment. 5

This is a chemical stage in which ferric chloride is added to the wastewater to precipitate residual phosphorus from the activated sludge process.

In the final clarification stage, the phosphorus-rich particles formed in the chemical treatment stage are allowed to sink to the bottom. This sludge is called chemical sludge, and is first transported to the primary clarifiers, and then to the sludge treatment stage.

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10. THE PONDS

Following the wastewater treatment process there are six ponds connected in series. These ponds have a polishing effect, which means that they remove some of the residual phosphorus and nitrogen. The wastewater passes through the ponds under the force of gravity. The treated water is then released to a stream called Höje å. 11. WASTEWATER OVERFLOW

Under conditions of high water flow, such as heavy rain, the influent flow to the plant is sometimes higher than the capacity of the biological treatment stage in the activated sludge basins. When this happens, the wastewater can be

directed to overflow basins for storage. From the overflow basins the wastewater is transported to the chemical stage for post-precipitation. The sludge formed in the overflow basins is returned to the plant inlet. 12. RAW SLUDGE THICKENING

The primary sludge and the chemical sludge from the primary clarifiers is transported to a gravity thickener, where the water content is reduced by allowing the solid particles to sink to the bottom. The thickened sludge is then pumped to the next thickening stage, while the water phase (the reject water) is directed back to the plant inlet.

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FeCl3 6

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Polymer

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Polymer

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13. MECHANICAL THICKENING OF PRIMARY SLUDGE

In order to further reduce the water content, the raw sludge is thickened in a drum thickener. Polymer is added to the sludge which is transported to a rotating drum. The water that passes through the screen cloth is returned to the inlet of the plant, while the sludge is transported through the drum by a screw. 14. THICKENING OF SURPLUS SLUDGE

The surplus sludge from the activated sludge process is thickened in gravity thickeners in the same way as the primary sludge.

15. MECHANICAL THICKENING OF SURPLUS SLUDGE

The surplus sludge can either be thickened separately, or be mixed with the primary sludge before mechanical thickening. 16. ANAEROBIC DIGESTION

The thickened sludge is directed to the digesters where part of the organic material is degraded (digested) under anaerobic conditions. Anaerobic digestion is a microbiologically complex process carried out by many different types of microorganisms, leading to the formation of biogas. At the Källby Plant, there are two digesters, with a total retention time of about 20 days.

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Polymer 20

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17. BIOGAS HOLDER

The biogas formed during the anaerobic digestion is collected and stored in a gasholder to equalize variations in the biogas production rate. 18. BIOGAS UPGRADING

The biogas consists of about 60-65 % methane, the remaining part is mainly carbon dioxide. It is purified (upgraded) by removing the carbon dioxide so that the gas contains over 96 % of methane. The biogas is delivered to the natural gas network, and is used mainly as vehicle fuel. 19. DIGESTED SLUDGE STORAGE

The digested sludge is tapped off from the digesters at regular intervals and pumped to a storage tank.

20. SLUDGE DEWATERING

The digested sludge is dewatered in centrifuges. A polymer is added to the sludge before it enters the centrifuges for better separation of water and sludge, resulting in a higher dry solids content. The dry solids content at the inlet of the centrifuges is approximately 5% and at the outlet, approximately 20-25%. The water phase is called reject water and is returned to the inlet of the plant. 21. SLUDGE UTILIZATION

The dewatered sludge is certified, which means that it has a sufficiently high quality to be used as an agricultural fertilizer.

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Technical data

Plant data

THE SEWERAGE SYSTEM Lund uptake area Length of wastewater sewers Length of stormwater sewers Pumping stations for wastewater Pumping stations for stormwater Overflow basins Overflow outlets Percentage of combined sewerage system Percentage of duplicate sewerage system

32 km 380 km 370 km 26 19 3 5 10% 90%

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DESIGN DATA Population equivalents Qmax biological stage Qmax chemical stage

120,000 3,960 m3/h 8,640 m3/h

INCOMING AND OUTGOING QUANTITIES DURING 2015

Incoming (kg/d)

Outgoing (kg/d)

BOD7 6,400 60%

PRIMARY TREATMENT

POST-TREATMENT

Screens 2 with 3 mm mesh

Flocculation basins Number Total volume

6 1,040 m3

Chemical clarifiers Number Total area Total volume

12 2,160 m2 4,320 m3

Screenings washing Number

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Grit removal basins Number 4 Total volume 620 m3 Primary clarifiers Number 12 Total area 1,600 m2 Total volume 3,100 m3

Biological ponds Number Total area Total volume

Overflow basins Number Total area Total volume

SLUDGE TREATMENT

3 990 m2 1,850 m3

BIOLOGICAL TREATMENT Aeration basins Number Total volume

4 21,900 m3

Secondary clarifiers Number 18 Total area 3,420 m2 Total volume 9,040 m3

Thickeners Number Total area Total volume

6 111,250 m2 122,500 m3

3 234 m2 704 m3

Mechanical thickeners Number 2 Capacity 350 kg dry solids/h + 650 kg dry solids/h Digesters Number Total volume Centrifuges Number Capacity Gas holder Number Volume

2 3,000 m3 2 2 x 20 m3/h 1 510 m3

Other wastewater treatment plants in the Municipality of Lund HÅSTAD

SÖDRA SANDBY

Lund

REVINGEBY

TORNA HÄLLESTAD

VOMBSJÖN

Källby

Revinge No. of users connected 550 Flow 100,000 m3/year Influent BOD7 20 tons/year

Torna Hällestad No. of users connected 590 Flow 47,000 m3/year Influent BOD7 9 tons/year

Håstad No. of users connected 160 Flow 100,000 m3/year Influent BOD7 1 tons/year

Södra Sandby No. of users connected 6,000 Flow 820,000 m3/year Influent BOD7 130 tons/year 11

KÄLLBY WASTEWATER TREATMENT PLANT • Issue 01 2016.09 • Photo: Linda Berglund, Marika Wennberg. llustration: Millimeter.

Everyone plays an important role Everyone can contribute to improving the environment by reducing the demand/ hydraulic load on wastewater treatment plants. You can do this by not wasting water, and by not disposing of harmful substances down the drain. If we all increase our “water awareness” the environment will benefit, and we can preserve both the flora and fauna in nature.

KEEP A WASTE BIN IN YOUR BATHROOM

RETURN OLD MEDICINES TO THE PHARMACY

Wastewater treatment, more than most other environmental areas, is directly influenced by what we do as individuals. We can all help to save our natural resources through a few simple measures.

It is very difficult, and sometimes impossible, to decompose pharmaceuticals in a wastewater treatment plant. Most pharmaceuticals simply pass through the treatment plant and end up in our water courses, where they can have a highly detrimental effect on aquatic organisms. Always return expired and surplus medicines to a pharmacy. HAZARDOUS WASTE BELONGS IN A RECYCLING CENTRE

Hazardous waste, such as paint, glue and other chemicals (such as solvents), should be taken to a recycling centre. Never pour these down the drain or throw them away in the refuse bin. You can read more about recycling centres and hazardous waste on SYSAVs website: www.sysav.se. GREASE CLOGS THE PIPES

Grease clogs pipes and promotes the growth of microorganisms that interfere with the wastewater treatment process. A good tip is to wipe your frying pan with kitchen paper and throw this in the bin before washing the pan.

We frequently have problems at treatment plants caused by “foreign objects” such as tampons, sanitary towels, condoms, cigarette ends, snuff, hair, cotton swabs and cat litter. These should be thrown in a bin instead. If you don’t already have one, place a small pedal bin in your bathroom. WHAT YOU DO MATTERS

t the toilet is Remember tha posal unit. not a waste dis

you should The only things toilet are poo, flush down the aper. wee and toilet p

VA SYD supplies fresh drinking water, treats wastewater and is responsible for waste management for over half a million people. We encourage you to drink tap water, sort your household waste, and be careful about what you dispose of 3041 0140 TRYCKSAK

Customer Service tel. 040-635 10 00

down the drain. Together we can actively contribute to sus-

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tainable urban development. For the environment, near you.

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