Pilot-Scale Vermicomposting of Dewatered Sewage Sludge From Medium-Sized WWTP

Abstract

The transformation of dewatered sewage sludge into vermicompost provides an advantageous solution in cases where the sludge is not too contaminated with inorganic pollutants, especially heavy metals. In addition to the conversion of the sludge to a product with a higher-added value, undesirable organic pollutants and micropollutants are partially eliminated. Anaerobically stabilized dewatered sewage sludge from a medium-sized WWTP was subjected to the vermicomposting process under field conditions. Straw was used as the bedding material in the form of two mixing ratios. The almost 1 year of the monitoring of the process focused on the hazardous substances present, the concentrations of which are regulated by legislation on the use of sludge on agricultural land. In addition, the contents of macro- and micro-nutrients such as N, P, K, Mo, Ca, Mg, and the wintering of the earthworm inocula were monitored. The potential of the vermicomposting process to reduce the content of emergent pollutants from the PPCP group was described with respect to 34 detected substances, including five endocrine disruptors. The study suggested that the bio-stabilization of dewatered sewage sludge using earthworms provides an effective technology for converting noxious wastewater treatment products into nutrient-rich bio-fertilizers.