Wastewater at LFKW is treated in accordance with the latest technical standards. The aim is to achieve the highest possible removal of oxygen-consuming organic substances (measured as BOD and COD), nitrogen and phosphorus compounds (ammonium nitrogen, inorganic nitrogen and total phosphorus), as well as particulate matter (filterable solids).
Thanks to the generous design of the facilities at the time, LFKW has largely been able to meet the significantly increased requirements introduced over the years through modifications and changes to the pipework layout, without the need for extensive expansions. However, the advanced age of most plant components means that the need for refurbishment is steadily increasing.
The process flow diagram below provides an overview of the individual treatment stages at LFKW.
The following structures and treatment stages are available for wastewater treatment:
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Two underground tanks in the inlet area, each with a capacity of 570 m³, which can be used as storm overflow tanks, emergency containment tanks or wastewater storage tanks.
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Two mechanically cleaned coarse screens, designed as counter-current bar screens with a bar spacing of 30 mm, for removing coarse solids from incoming wastewater. The screenings are collected and processed in a screenings washer-compactor, where the organic fraction is washed out and the remaining material is dewatered.
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Two fine screens with integrated screenings dewatering. The screen surfaces are made of perforated plate with 5 mm openings. They prevent blockages and the formation of floating scum layers in subsequent treatment stages.
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One aerated longitudinal grit chamber and one circular grit chamber for removing mineral solids from the wastewater. The separated solids are processed in a classifier, where they are separated from organic matter and dewatered.
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Two smaller tanks, each with a capacity of 16 m³, equipped with fine-bubble pressure aeration. These tanks are now used for storage, for example, of sludge water.
- One small primary clarifier with a capacity of 51 m³ and two larger primary clarifiers, each with a capacity of 95 m³, for preliminary sludge removal and the separation of floating matter. Alternatively, they can be used as settling tanks or storage tanks.
- A cascade of rotating disc contactors, housed in a dedicated building and providing a total disc surface area of 6,000 m², for aerobic biological wastewater treatment with or without nitrification.
- One oxidation ditch with a capacity of 116 m³ and two rectangular secondary clarifiers with capacities of 30 m³ and 15 m³, respectively, for biological wastewater treatment with or without targeted nitrogen removal through intermittent denitrification. Aeration and circulation are provided by a Mammut rotor and a mixer.
- Two fish ponds, with capacities of 80 m³ and 110 m³, respectively, for further treatment of the treated wastewater, with or without the addition of stream water.
- The operations building, which houses the central control room, including the process control system used to monitor and control the wastewater treatment plant facilities, as well as offices, laboratories and a lecture room.
- A two-storey pilot plant building with adjoining workshops.
- The energy building, which houses the heating plant (operated alternately using biogas and natural gas), the transformer station and an additional workshop.
- A funnel-shaped tank (volume: 290 m³) equipped with a mixer for upstream denitrification. In this anoxic tank, the mechanically treated wastewater is mixed with nitrate-rich return sludge flows and the internal recirculation flow.
- A storage and dosing station for external carbon sources to enhance the efficiency of upstream denitrification (storage tank volume: 13 m³).
- Four aeration tanks arranged in series (volume: 110 m³ each) for nitrification using fine-bubble diffused aeration at the bottom of the tanks. The first tank is equipped with a mixer for intermittent denitrification.
- An enclosed storage and dosing station for chemical precipitants for targeted chemical phosphorus removal by simultaneous precipitation (storage capacity: 7.2 m³).
- Two rectangular secondary clarifiers (volume: 140 m³ each, surface area: 55 m² each). One clarifier is divided into two sections, with vertical and horizontal flow, respectively. The second clarifier operates with horizontal flow.
- Two microscreen drum filters housed in a building (each with a diameter and length of 2 m), fitted with microscreens with mesh openings of 15 and 20 µm, respectively. Upstream flocculation tanks are provided to enhance suspended solids removal and phosphorus removal from the secondary clarifier effluent.
- A vertically flow-through, funnel-shaped secondary clarifier (volume: 290 m³, surface area: 109 m²) for the separation of activated sludge.
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Two microscreen drum filters housed in a building (each with a diameter and length of 2 m), fitted with microscreens with mesh openings of 15 and 20 µm, respectively. Upstream flocculation tanks are provided for enhanced suspended solids removal and phosphorus removal from the secondary clarifier effluent.
The sludge generated during wastewater treatment is mechanically thickened and subsequently aerobically stabilised. The biogas produced is fully utilised for energy recovery through combustion.
Overall, the sludge treatment section comprises:
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Three tanks for intermediate sludge storage.
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One static pre-thickener.
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One mechanical sludge dewatering station using a centrifuge, including a polymer dosing system, a centrate tank and two biofilters for exhaust air treatment.
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Two heated anaerobic digesters with a gas compressor station for mixing the digester contents.
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One sludge storage tank and one sludge discharge sump.
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Two combined gravel and condensate traps and one dry desulphurisation unit for biogas treatment.
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One biogas storage tank.
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Contact
Peter Maurer
Dipl.-Ing.Technical Operations Manager of the Treatment Plant for Education and Research at the University of Stuttgart (LFKW)