Sewage sludge is not only the sink for nutrients removed from wastewater but also for hazardous substances. When sewage sludge is reused in agriculture these hazardous substances can be harmful to the environment depending on their concentration. Nevertheless, the mere disposal of sewage sludge cannot be purposeful as the contained nutrients and the organic material offer a biologically valuable fertilizer. Currently, agricultural reuse of sewage sludge is discussed controversially in Germany. Changes in legal requirements for sewage sludge application are planned that will set lower limit values for hazardous substances and higher quality requirements in general. With these new restrictions, sewage sludges may not be suitable for agricultural reuse any longer. The focus is on alternative sewage sludge treatment technologies that gain the most economic and ecological benefit from the sludge's valuables. Several technologies for nutrient recovery, especially phosphorus, have been developed to recycle finite natural resources. This article will provide an overview on novel strategies for sewage sludge treatment and management especially in regard to new legal requirements.

At present, the annual loads from long-term series simulations are mostly used for the evaluation of rainwater management and treatment measures although the relevance of the temporal distribution of both pollution and quantity has a recognizable influence on the performance of the treatment. With the idea of dynamizing the simulation output values in relation to (i) single rainfall events, (ii) specific catchment characteristics, and (iii) the duration of the dry period between two rainfall events measurement devices and scenario studies were established in a joint research project in Lower Saxony. First measurement results of surface runoff qualities of an urban sub-catchment in Braunschweig/Germany are presented in a high temporal definition for several pollution parameters. A correlation analysis was performed identifying additional explanatory parameters that have an influence on the first flush effect, such as rainfall characteristics or antecedent dry period. First calculations of the possible reduction in the decentralized storm water treatment by disconnecting the first flush showed values of 42–65%, depending on the pollution parameters. The comparative evaluation of the data with different statistical methods shows that the uncertainties in the calculation of rainwater pollution, or the duration of the first flush, are still very high and do not yet allow researchers to derive a pollution forecast for, e.g., a throttle control solely from the recording of the rain and area characteristics.

Sewage sludge accumulating during biological wastewater treatment has to be treated appropriately to avoid impacts on the environment and risks to public health. Especially pathogen reduction is necessary when sludge is disposed or reused in such a way that human contact is possible. In industrialized countries various sludge treatment technologies are available, but these are often only approved under local conditions. When exporting these technologies and experiences to other countries, a number of factors have to be taken into account including climatic, sociocultural, political and financial aspects. This paper gives an overview of current knowledge regarding sewage sludge treatment in developing countries. Various sanitation projects are realized worldwide and experiences from these plants already in operation are summarized. Results of on going laboratory experiments in climatic chambers regarding aerobic and anaerobic stabilization as well as lime treatment are shown to define the best-practicable sludge treatment technology for a certain climate. Options for final reuse or disposal are presented depending on end-product quality.

Sewage sludge produced during municipal wastewater treatment has to be treated efficiently in order to reduce impacts on the environment and on public health. In Germany and many countries, large quantities of sludge are reused in agriculture in order to recycle nutrients and organic material. In order to quantify the effect of different ambient temperatures on conventional and advanced sludge treatment technologies as well as on disinfection efficiency, a comprehensive research study was performed at Braunschweig Institute of Technology. The detailed results show that ambient temperature has a strong effect on biological liquid sludge stabilization and on natural dewatering and drying technologies, although microbiological quality of treated sludge, indicated by Escherichia coli concentration, does not meet the requirements for unrestricted reuse in agriculture. Composting and lime treatment of sludge are most efficient on reducing E. coli, as high temperatures and high pH values arise in the material respectively.

No abstract