TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The drain pipe is vertically adjustable. The buffer tank has: a front portion, into which wastewater is introduced via a feed, such that the front portion is closed for producing anaerobic conditions; and a rear portion into which the wastewater is introduced from the front portion. An agent means is provided in the rear portion for monitoring and adjusting a pH and a temperature of the wastewater and for the anaerobic degradation of materials. A gas discharge line is provided in an upper region of the rear portion of the buffer tank for the removal of biogas produced by the anaerobic digestion in the rear portion. The filter tank comprises a wastewater discharge conduit for passing wastewater which has passed through the filter medium. The filter medium is disposed such that it is immersed in an operating state in wastewater in the filtration tank, and the filter tank has an inlet opening in a lower region for conducting wastewater from the bioreactor tank from below through the submerged filter medium. The filter tank is formed as an anaerobic membrane bioreactor tank, in which microorganisms in waste water are degraded under anaerobic conditions. A number of pumps are connected in parallel to the wastewater line with a variable amount of wastewater to increase lead-in pressure of wastewater into the filter tank, where the wastewater is passed to the filter tank, and pump is variably fixed. A return line is provided on a top of the filter tank and arranged to receive wastewater, which has not passed through the filter medium, where the return line is connected with a wastewater line for reintroducing the wastewater to the filter tank, which leads from the wastewater drain pipe of the bioreactor tank to the filter tank. A cleaning tank is provided for washing the filter medium with a rinsing liquid from the cleaning tank and valves are provided on a wastewater discharge line of the filter tank with which: a fluid connection is made from the wastewater discharge line to a final tank for the waste discharge from the filter tank; and a fluid connection is prepared between the tank and wastewater discharge line to rinse the filter tank, where the filter tank is located lower than the cleaning tank for conducting flushing fluid from the cleaning tank to the filter tank. A header tank is provided for receiving wastewater which is filtered through the filter medium in the filtration tank, where the header tank comprises: gas discharge line at an upper portion for discharging the biogas which is formed in the header tank, and a water discharge line at a lower portion for discharge of purified wastewater. The header tank is arranged lower than the filter tank to conduct wastewater from the filter tank to the header tank. A pump for separating gas by increasing the pressure in the wastewater is provided in the water discharge line of the header tank and pump control valves are provided downstream to control a return line or output line. A gas collecting line is provided for receiving gas from the gas discharge lines of the buffer tank, bioreactor tank, filter tank and header tank.