A few years ago (2015), Germany published a fascinating and frightening look at the sewage sludge situation. It is a wonderful guide to the present-day production, treatment and possible uses of this sludge. Below I will present some of the more interesting and sobering findings in this German study.
The entire document can be accessed here in English Translation -
Sewage Sludge Management in Germany
"Sewage sludge can be regarded as a multisubstance mixture. Because of the inhomogeneity and tremendous differences in the concentrations of its components, it is difficult to determine or define a standard composition for sewage sludge, which is mainly composed of organic substances. Sewage sludge (i. e. stabilized primary, secondary or tertiary sludge that occurs in a mixture at the end of the treatment process) contains plant nutrients such as nitrogen and phosphorous, as well as harmful substances such as pathogens, endocrine disrupters and heavy metals"
"Sewage sludge fertilizer is a pollution sink for harmful sewage components from households, businesses and diffuse sources, concerning whose environmental impact too little is known. The extent of the possible soil, plant, groundwater, and surface-water pollution resulting from these sources is difficult to determine, even in cases where relatively small amounts of sewage sludge are used ... new breakdown products of pharmaceutical drugs are discovered in sewage sludge all the time. These breakdown products are incorporated into sewage sludge via human excretion and in other ways. It is simply not humanly possible for scientists to develop specific detection processes for and assess the environmental impact of all of these substances, whose combined impact is particularly difficult to characterize and assess. Scientists can merely estimate the theoretical hazards posed by these substances; and unfortunately, by the time the relevant hard facts become available, the pollutants in question will already have found their way into the biosphere."
"Owing to its extreme inhomogeneity, the quality of sewage sludge is difficult to characterize. Sewage sludge fertilizer contains the following elements, all of which are potential ecosystem pollutants: various organic substances that exert hormonal effects; various infectious agents; heavy metals; residues of pharmaceutical drugs."
"Sewage sludge fertilizer is also a pollution sink for harmful sewage components from households, businesses and diffuse sources, concerning whose environmental relevance too little is known. Notwithstanding tighter controls and stricter limit values for certain sewage sludge pollutants, uncontrolled pollutants such as hydrocarbons inevitably find their way into the soil. Incorporation of certain pollutants into the food chain cannot always be avoided, despite the fact that, for example, plants normally do not absorb organic pollutants. Nonetheless, new breakdown products of pharmaceutical drugs are discovered in sewage sludge all the time, and they are incorporated into sewage sludge via human excretion carried by the wastewater that is treated by sewage treatment plants."
"In keeping with the precautionary principle and in light of the pollutants and pathogens found in sewage sludge, the UBA deems the agricultural use of sewage sludge to be a serious public health and environmental hazard and advocates that this practice be phased out."