The Membrane Wastewater Treatment Plant in Ihn Layman s report

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1 The Membrane Wastewater Treatment Plant in Ihn Layman s report 1 Entsorgungsverband Saar, Tel / , P.O.Box , D Saarbrücken,

2 The Wastewater Treatment Plant in Ihn Model project for using innovative wastewater treatment technology in rural areas The Entsorgungsverband Saar (Waste Disposal Association, Saarland) developed the membrane wastewater treatment plant in Ihn, which was completed in August 2006, in collaboration with several partners as part of a pilot project. The Institute for Environmentally Compatible Process Technology (upt) not only supervised the project at scientific level, but also designed and developed this new type of wastewater treatment plant, which is particularly suitable for rural areas. The membrane activated sludge tank was constructed by the BAMAG company located in the state of Hessen. The construction of the wastewater treatment plant was funded by the EU and local government because of its prototype character. Total investment costs amounted to 1.8 million Euro, to which the Ministry for the Environment in Saarland contributed 745,000 Euro and the European Union 370,000 Euro within the framework of the EU LIFE Programme. The operating results obtained provide benchmarks for optimum plant design and process control as well as for calculating the investment and operating costs of similar plants. The Entsorgungsverband Saar will use the results from the pilot project in the district of Wallerfangen to test the operation of the membrane process in new plants as well as its capacity to quickly upgrade and optimise existing plants. The construction of the membrane wastewater treament plant was funded by: Overall view of the wastewater treatment plant in Ihn. The membrane filtration unit is installed in the functional building beside the activated sludge tank 2

3 The wastewater treatment plant in Ihn the first municipal membrane wastewater treatment plant in Saarland The wastewater from roughly 700 residents in the districts of Leidingen and Ihn in Wallerfangen is treated in the wastewater treatment plant in Ihn which is the first municipal plant, operated by the Entsorgungsverband Saar, to use innovative membrane technology. It is also the first prototype in Germany to be fitted with an aerated lagoon and an upstream membrane biological stage. The wastewater is pre-treated in the aerated lagoon which also operates as a buffer for rainwater. The lagoon, as a buffer for the different types of wastewater, provides a natural, cost-effective operating unit which is conducive to reducing the water quantities which are routed to the upstream, highly technological stage. This plant allows operating costs to be saved in contrast to purely technical membrane wastewater treatment plants. The values in the effluent from the plant in Ihn are far below the offical limit values for the discharge of wastewater into surface water bodies. The permeate from the membrane filtration unit is so low in bacteria concentrations that it complies with the EU Directive regarding water re-use as service water. The river Ihn, which flows through a valuable meadow landscape, benefits from this since only clean water is discharged into it. The wastewater treatment plant in Ihn, Wallerfangen, district of Saarlouis 3

4 Operation of the wastewater treatment plant in Ihn The mixed wastewater (wastewater and rainwater) from the locations Ihn and Leidingen is pumped through a pressure pipe to the wastewater treatment plant. When rainfall is heavy, a certain quantity of the mixed wastewater is stored in the sewage network and routed later to the treatment plant. An overflow tank for rainwater in Leidingen and a storage channel in Ihn with a comparatively low volume of 60 m 3 respectively are used for this purpose. The greatest quantity of rainwater is treated in the lagoon of the wastewater plant. 1st stage: Aerated lagoon and fine screening Firstly, the wastewater is fed via an overflow for rainwater into the inlet area of the aerated lagoon where coarse solid matter such as sand, gravel and rubble sinks to the bottom. Lighter solids (oils, sanitary products), that float on the surface, are retained at an inverted weir situated between the inlet and the lagoon and removed later. The wastewater flows from the inlet into the areated lagoon where the sludge settles at the bottom of the tank. In addition to this mechanical treatment, partial biological treatment takes place in the pre-treatment pond using bacteria that are naturally present in mixed wastewater. These bacteria reduce organic contamination in the wastewater by feeding on oxygen which is fed into the water by a surface aerator. The partially treated wastewater is then routed via a pumping station from the pond to a fine screening unit in the functional building in order to remove the smallest solids. Following this, the wastewater flows freely into the activated sludge tank. Stage 1: Aerated lagoon 4

5 2nd treatment stage: Activated sludge tank and membrane filtration Activated sludge tank More extensive biological treatment of the wastewater is carried out in the activated sludge tank under optimised technical conditions. This tank is divided into an aerated and a non-aerated zone where different degradation processes take place. Aerobic bacteria break down the organic carbon compounds and convert ammonium into nitrate (nitrification) in the oxygen-enriched, aerated zone. Nitrate is then degraded further in the non-aerated zone by anaerobic bacteria that split the oxygen, chemically bonded in the nitrate, under anaerobic conditions. The gaseous nitrogen formed, is then released into the air. No environmental pollution is caused by this process since nitrogen is the main component in air. The wastewater is recirculated through the tank so that these two stages for nitrogen degradation, i.e. nitrification and denitrification, are in continuous, alternative operation. After biological treatment, the water still contains the biomass (flakes of bacteria), small germs and pathogenic germs which have to be filtered out in the membrane unit. Fine screening and membrane filtration are located in the building. Sludge is aerated and stored in the dual-purpose tank made of prefabricated sections (on the right.). 5

6 Membrane filtration The membrane filtration units consists of two separate tanks in which hundreds of hollow-fibre membranes are fitted. The two-level design of the plant allows continuous operation even when the membranes in one of the two chambers have to undergo intensive cleaning. Flow diagram of the membrane filtration process The water is drawn through the membrane from the outside to the inside. In this process, components larger than membrane pores, which are only some thousandth parts of a millimetre in diameter, are retained. The optimally treated wastewater is then routed from the inside of the membrane to the river Ihn via an effluent meter. Part of the water is used to clean the membrane module, a process which has to be carried out at regular intervals to ensure that permeability is maintained. Stage 2: Membrane filtration with two membrane modules 6

7 Purifying performance The plant had only been charged with waste water coming from Leidingen by the commissioning between the end of August 2006 and April 2007; both parts of the town have been connected to it since May The mechanical pre-purification in the lagoon is very good. Sieved material only accumulates in the drum sieve s area to a very slight extent. The following membranous biology system - especially the filtration - is protected very well in this way. Regarding the CSB, a purifying performance of more than 50% is achieved in the upstream lagoon - even under maximum loading - since both localities have been connected to the waste water treatment plant. The plant s discharge values are compared with the limiting values or the minimum requirements according to Appendix 1 entitled Communal waste water guidelines in the table. The Ihn waste water treatment plant does not only operate very reliably but it also has a good purifying performance. Both the minimum requirements and the tightened-up limiting values for the specific plant are significantly below the achieved discharge values. The number of germs which were established in the discharge from the Ihn waste water treatment plant - according to the independent analyses conducted by the responsible testing authority - are clearly below the standard values of the EU bathing water guidelines. Summary A new kind of concept for treating mixed water has been implemented and tested with the LAGOON MEMB concept in Ihn. The concept has proved itself against the background of positive operating results and experience. Good retention of solids in the lagoon, no clogging in the sieve, no clogging, blockage or plaiting of the membrane, good discharge values and good elimination of germs should be emphasized in this connection. The concept has proved to be economical. The entire plant s specific consumption of energy in relation to the waste water s flow rate through the membranous biological system amounts to 1.35 kwh/m 3 on average. The LAGOON MEMB concept is not only suitable to extract industrial or domestic water for reuse from the communal waste water. It also represents a good solution for sensitive catchment areas (e.g., catchment areas for drinking water, or water reserves), discharges in low-performance main outfalls, or in rural localities without suitable main outfalls. Not only regional transferability is therefore given but also a transfer whenever there are other types of problems concerning an orderly disposal of waste water. Parameter Unit Discharges values Limiting values (random samples) Average values Sept April 2007 Mai Feb according to the approval Minimum requirements CSB mg/l 9,2 8,3 < 90 < 150 BSB 5 mg/l 3,5 1,8 < 15 < 40 NH 4 -N mg/l 0,8 0,1 < 10 NO 3 -N mg/l 10,1 7,9 P ges mg/l 1,8 1,4 ph - 7,8 7,8 6,0-8,5 6,0-8,5 Table 1: Comparison between average values of the waste water treatment plant s discharge (random samples) and the limiting values. 7

8 Technical data for the wastewater treatment plant in Ihn Operator: Entsorgungsverband Saar (Waste Disposal Association, Saarland) Total costs (including planning, construction and scientific program): 1.8 million Euro Funding/Allocation of costs: Euro from the European Union Euro from the Ministry for the Environment Euro from the Entsorgungsverband Saar Euro from BAMAG Euro from the upt Completion: August 2006 Size: 700 PE - Ihn: 472 PE - Leidingen: 189 PE - Leidingen (on the French side): 30 PE - Rest: 9 PE Type of plant: aerated lagoon with upstream membrane biology Dewatering system in the collective network: mixed water sewage network Hydraulic loading: Daily dry-weather flow: 161 m³/d Max. dry-weather flow: 3.7 l/s Max. rain-water flow: 28.9 l/s Max. flow to the membrane biology stage: 4.0 l/s Pollution load in the feed: COD: 84.0 kg/d BDD5: 42.0 kg/d Total nitrogen: 7.7 kg/d NH4-N: 5.1 kg/d Total phosphorus: 1.3 kg/d Minimum requirements for discharging wastewater into surface water bodies COD: 150 mg/l BOD5: 40 mg/l NH4-N: no limit value Total nitrogen: no limit value Fish egg test: 2 ph-value: Limit values for the wastewater treatment plant in Ihn COD: 90 mg/l BOD5: 15 mg/l NH4-N: 10 mg/l Total nitrogen: 25 mg/l Fish toxicity: 2 ph-value: The values for the effluent from the wastewater treatment plant in Ihn are well below the official minimum requirements. Furthermore the wastewater treatment plant in Ihn comply with the standards laid down in the EU Directive 76/160 regarding the quality of bathing water (service water quality). 8

9 Technical specifications of the plant Rainwater treatment: Storage channel in Ihn with 60 m³ Rainwater overflow tank in Leidingen with 60 m³ Rainwater is mainly treated in the pre-treatment pond in the wastewater treatment plant in Ihn Feed: 1 pumping station in Leidingen: flow rate 9.2 l/s Pressure pipe Da 140 to the treatment plant, approx m 1 pumping station in Ihn: flow rate 19.7 l/s Pressure pipe Da 160 to the treatment plant, approx m 1st stage: Aerated lagoon Total volume: 1890 m³ of which: m³ wastewater treatment <> m³ storage volume for rainwater treatment m³ sludge lagoon 2nd stage: Membrane biology Booster pump 4 l/s Fine screening rake, gap 0.75 mm Activated sludge tank: Total volume: 100 m³ Denitrification: 0-50 m³ Nitrification: m³ Dry matter concentration : <12 kg/m³ Age of sludge: > 25 d Blowers: 2 blowers (1 as a stand-by) Oxygen supply via rotary piston blowers: 300 m³/h Membrane module: Ultrafiltration with a pore size of 0.05 m Membrane area: 2 x 350 m² Flow through the membrane: 25 l(m² x h) Flow through the membrane in backflushing mode: 45 l/(m²x h) Filtrate pumps: 1 rotary piston pump per membrane chamber Reversible flow direction Flow rate in filtration mode: 8.74 m³/h Flow rate in backflusing mode: m³/h Sludge treatment Sludge storage for membrane filtration 250 m³ of the total volume of the lagoon used for sludge settling area Automatic sampler Effluent meter (IDM) 9

10 Catchment area for the wastewater treatment plant in Ihn 10

11 Flow diagram of the membrane wastewater treatment plant in Ihn 11

12 Site plan of the membrane wastewater treatment plant in Ihn EVS Entsorgungsverband Saar Tel / P.O. Box D Saarbrücken Broschure as of: June