The Institute of Sanitation Engineering and Waste Management of the University of Hannover made investigations on sediments in sanitary sewers. These were aimed to assess how sediments influence the sewer environment, with regard especially to water quality, gas atmosphere and corrosion progress. The sulfate reduction from sediments could be determined. It was 82 % higher than the reduction rate of biofilm. A prediction of sulfate reduction with equations from biofilm theory is possible. The biologically active sediment layer for sulfate reduction has a thickness of 5 to 7.5 cm. The sulfide formation in a large sanitary sewer in Hannover depends only on water temperature with a correlation of 91 %.
Membrane fouling is a major concern for the optimization of membrane bioreactor (MBR) technologies. Numerous studies have been led in the field of membrane fouling control in order to assess with precision the fouling mechanisms which affect membrane resistance to filtration, such as the wastewater characteristics, the mixed liquor constituents, or the operational conditions, for example. Worldwide applications of MBRs in wastewater treatment plants treating all kinds of influents require new methods to predict membrane fouling and thus optimize operating MBRs. That is why new models capable of simulating membrane fouling phenomenon were progressively developed, using mainly a mathematical or numerical approach. Faced with the limits of such models, artificial neural networks (ANNs) were progressively considered to predict membrane fouling in MBRs and showed great potential. This review summarizes fouling control methods used in MBRs and models built in order to predict membrane fouling. A critical study of the application of ANNs in the prediction of membrane fouling in MBRs was carried out with the aim of presenting the bottlenecks associated with this method and the possibilities for further investigation on the subject.
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