Recycling municipal wastes in the future: from organic to inorganic forms?

Abstract. This paper highlights the principal problems related to the recycling of municipal wastes to arable land and outlines future solutions. History reveals that transport of sewage with water was introduced early (2500 bc ), but only some Asian societies, which did not utilize sewage flushing, redistributed toilet wastes to arable land effectively. Nutrient flow analyses in developed countries indicate a withdrawal of 20 kg N and 3 kg P ha^?1 yr^?1 from arable land because of non-return of organic human wastes. Limited reuse of municipal organic wastes in agriculture in several European countries is often seen as a question of waste quality. However, we believe that despite acceptable quality levels only minor progress in recycling has been achieved. Higher water contents in organic wastes than in harvested crops and, consequently, high costs for drying or transportation of wastes, often in combination with non-optimal plant nutrient composition, will remain the bottleneck which restricts the recycling of nutrients in wastes. One solution is to extract nutrients out of organic wastes and thereby derive concentrated compounds similar to those in inorganic fertilizers that can be redistributed and applied to soil. The challenge for modern sewage treatment systems is to shift perspective from removal to recovery of nutrients.