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AGROIWATECH Résumé de rapport

Project ID: ICA2-CT-2002-10010
Financé au titre de: FP5-INCO 2
Pays: Germany

Process: Determination of treatment efficiency of bio-membrane technology employing ultrasound

Usually, wastewater from agricultural industries is treated with a biological treatment plant. Conventionally, this implies the use of a post settlement basin. Replacing this by a membrane system (MBR) will increase the concentration of dry substance and can lead to higher con-centrations of micro organisms, which will improve the cleaning capabilities of the biological system significantly. The decrease of the effectiveness of the membrane is induced by fouling and scaling. This leads to a significant amount of chemicals and operation time needed for cleaning and maintenance of the membranes. A new, practically not tested possibility of reducing the fouling and scaling is the use of ultrasound (US) to clean the membranes in-situ.

Different membranes and different US-intensities have been tested with test substances to measure the flux-rate with respect to the pressure. Tests with membrane of the type C030F and UF-PS-100H with demin. Water and without ultrasound did not confirm the technical data given by the manufacturer after two and four hours of operation. PVP K30 was rejected at 80-88 % from the membrane C030F and at 10 % for the membrane UF-PS-100. For further investigations, the membrane UF-PS-100 was chosen with the use of ultrasound at 15.5 kHz. It has been found, that the flux-rate increases by using ultrasound. Nevertheless, after approx. nine hours, the membrane’s surface has to be cleaned conventionally. The rejection of the membrane could be increased by ultrasound as well. No damage of the membrane was found during the tests. With these results a pilot scale membrane module with ultrasound has been constructed and built up. Further tests with the pilot scale module have been made.

Following the results of these tests, small modules and an MBR-system have been built additionally for investigations. It was found, that the pure water flux of the membrane increases with the ultrasound intensity but is compensated by high temperatures. Tests with dextran showed no or little rejection of the hollow-fibre membrane even at the cut-off of the membrane, which was a hint of damage to the membrane. The damage of the membrane was confirmed by the particle size distribution of a kaolin suspension in permeate and feed, because no differences between the distributions were found. Pre-tests of the new small module with approx. 0.1 m2 total membrane surface showed volumetric flow rates of 2,500 mL/h, which confirms the data given by the manufacturer. The combined treatment of wastewater with activated sludge followed by filtration through the membrane module resulted in decreases in the organic material content in total of 89-95%, and in the biodegradable organic fraction of 88-97%, with respect to HRT (1.13-2.3 days). The contribution of the activated sludge to the total organic material content was in agreement with previous investigations, and lay in the range 45-79%. The efficiency of the membrane process alone, in reducing this material, was in the range of 63-81% with respect to their content in water after activated sludge treatment, and depending on the applied organic load. Permeate show a slight fluctuation under the investigated organic load conditions, suggesting a high efficiency of the membrane process in decreasing the organic content retained in the water after activated sludge treatment. In terms of ammonia content, with the activated sludge treatment, a high removal efficiency of 93-96% was achieved, to values <1 mg NH4+/l. Further treatment of the wastewater using membrane technology decreased the ammonia content further (<0.6 mg NH4+/l).

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