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Reducing the formation of filtration sludge using integrated microfiltration technology – Author: Dr. Jrg Kempf. The Fraunhofer Institute for Surfaces and Biotechnology in Stuttgart (Grenzflächen) has successfully developed a fermentation method for the sludge resulting from filtration. This new fermentation method utilizes an integrated microfiltration device to improve the filtration capacity of the sludge, while also extracting ammonium from the filtered water, which can be used as fertilizer. During the purification of wastewater, an astonishing amount of sludge is generated. Typically, the sludge filtered out from these wastewater treatments must undergo secondary detoxification through biological fermentation, which converts the organic matter in the sludge into biogas. The remaining sludge left after fermentation also must be dewatered. The water after dehydration has a high ammonium content (1–2 g/l), and ammonium removal techniques are often required for ammonia-free purification. At this point, ammonium is first nitrated to nitrate, and then denitrified to nitrogen. At the inlet of purification systems without ammonia removal, the ammonium concentration in the wastewater is generally in the milligram range. To prevent the nitrification tank and denitrification tank of ammonia-free purification equipment from becoming overloaded, wastewater that requires ammonia removal must enter the ammonia removal purification equipment at a specified flow rate. The task of the Fraunhofer Institute is to find a solution for directly obtaining ammonium from ammonia-containing wastewater. The Fraunhofer Institute for Surfaces and Biotechnology in Stuttgart has developed a wastewater sludge treatment device equipped with an integrated microfiltration unit for this purpose. By using this set of sewage sludge treatment equipment, it is possible to obtain sewage with almost no ammonia content, produce *ao acid and agricultural fertilizers, and significantly reduce the amount of sludge left after filtration. In July 2004, at the wastewater treatment plant in the city of Heldelberg, a unit of this type of equipment developed by the Fraunhofer Institute was put into operation. This device is part of the entire secondary fermentation process ； The first-stage fermentation equipment is also a high-efficiency decomposition device developed by the Fraunhofer Institute. Due to the efficient degradation at the first stage, the concentration of organic dry matter increases, reducing the amount of sludge deposited after wastewater treatment. Since 2001, since the commissioning of first-stage high-efficiency degradation equipment, the sludge resulting from wastewater treatment has been effectively converted into biogas. In this two-stage wastewater treatment system, the sludge fermentation unit equipped with an integrated microfiltration device consists of a bioreactor with a capacity of 3.5 m3. The sludge from the high-efficiency degradation reactor continues to undergo fermentation in this bioreactor. The rotary disc filter further filters the wastewater generated during the fermentation process in the bioreactor. The sludge with a higher concentration obtained after filtration is sent back into the bioreactor, thereby further increasing the organic matter concentration in the reactor and reducing the amount of sludge discharged after treatment. In this way, on the one hand, the amount of sludge that needs to be processed again is reduced, and on the other hand, the costs associated with further harmless treatment are saved. The rotary disc filter developed by the Fraunhofer Institute consists of ceramic discs stacked on top of each other, is maintenance-free, features a filtering membrane, and requires very little energy to operate. It is also highly cost-effective when used in regional small-scale wastewater treatment equipment and sludge treatment systems. The filtered wastewater, which is free of solid impurities and microorganisms, will be sent to the ammoniation reactor where ammonium is extracted from it. In the subsequent pickling tank, the pickled product can be obtained: *ao acid an. Wastewater free of ammonium compounds is introduced into the water purification tank, and the wastewater after such treatment fully meets environmental protection requirements. For many wastewater treatment systems, eliminating the nitrification and denitrification processes is very meaningful. It can reduce the equipment investment for regional sewage treatment plants. Tests have shown that this new fermentation method, equipped with an integrated microfiltration unit, can also be used in traditional sewage sludge fermentation systems that consist only of a single-stage fermentation unit.