What is the potential for utilizing the resources in sludge?

Abstract

The successful strategy for water protection by biological wastewater treatment results in a sludge production of about 20 to 40 kg dry matter per population equivalent and year. In the context of regional material fluxes, sewage sludge has a low resource potential and a low pollution potential despite the fact that it can be characterised as a sink, concentrating wastewater compounds. The mass flow of nutrients (N, P) in the sewage sludge is comparatively small as compared to the losses of nutrients in agriculture. The most valuable element in the sludge is phosphorus, as the availability of phosphorus for the production of low-cost mineral fertiliser is limited. The most economical means of P-recycling is agricultural sludge application, which can also be seen as the option with the lowest loss of all valuable compounds of the sludge, and the lowest increase of entropy. The reliability of this disposal route for the treatment plant operator depends on several major pre-requisites:reliability in regard to hygienereliability in regard to long-term soil protectionpublic acceptance (politicians, media)acceptance by all parties involved in sludge application and its consequences (farmers, farmer unions, land owners, food industry, food trade, retailers, consumers, consumer associations, NGOs, etc.) Only the first two prerequisites can be based on scientific research and risk assessment. As a consequence, only for these two aspects can quality criteria and adequate procedures be developed and introduced into a legal framework and quality assurance procedures. The latter two pre-requisites must be addressed in terms of sociology, psychology and political science and have a strong educational aspect.