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.
On the basis of a cost-benefit analysis it was decided to expand the Arnsberg WWTP by a multistage biological process which allows for cost-effective integration of the existing facilities. Carbon removal will then be accomplished in a high-loaded activated sludge stage for which the existing primary clarifier is to be reconstructed. The existing trickling filters will be used for nitrification during a midterm period and will be replaced later on either by a moving bed system or by new trickling filters. Line 3 of the existing secondary clarifiers will be reconstructed and used for post denitrification in a moving bed system. The carbon needed for denitrification will be provided by means of sludge hydrolysis and the use of an external carbon source.
The Ruhrverband, acting as a water association responsible for integrated water resources management within the entire natural river basin of the Ruhr, operates a network of 83 wastewater treatment plants (WWTPs) and connected sludge disposal facilities. According to German regulations, the disposal of sewage sludge containing more than 5% of organic dry solids will be prohibited as of 1 June 2005. In Germany, the only future alternative to incineration will be the agricultural utilization of sludge. However, this way of sludge disposal is presently the subject of critical discussions in Germany because of the organic and inorganic toxic substances, which may be contained in sewage sludge, despite the fact that very stringent standards are to be met by agricultural uses. On the other hand, application of sewage sludge to agricultural land is explicitly supported by the European Sewage Sludge Directive 86/278/EEC. In the face of this controversial situation the Ruhrverband has initiated, in 2000, the development of a comprehensive and sustainable sludge and waste disposal concept for all wastewater facilities it operates in the entire Ruhr River Basin. The concept includes de-central sludge digestion and dewatering and subsequent transport to two central sludge incineration plants. It is expected that in future not more than 5% of all sludges produced in Ruhrverband's WWTPs will be used in agriculture. That means, the major part of 95% will have to be incinerated.
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