Effects of biochar addition on vermicomposting of food industry sewage sludge

Sewage sludge (SS) is a byproduct of wastewater treatment which is commonly used as fertilizer in the world. However, due to the possible contamination with heavy metals, xenobiotics and fecal pathogens, its application on fields is not so common in Poland. A safer alternative for agricultural use is the SS produced by food industry in small "inhouse" wastewater treatment plants, as substances that are used in its production are usually less harmful. As pretreatment of industrial wastewater is required before dumping the wastewater into common stream, the SS is an abundant byproduct that needs to be managed in an environmentally friendly and cost effective manner. Because the water content in SS is usually high, the dosage and logistics are problematic and thus we propose converting the sewage sludge into solid granular fertilizer in the vermicomposting process. Not only are the weight and volume of product decreased as a result, but also the nutrients such as N, P, and K become concentrated and made more accessible for plants. The SS is also further stabilized and less prone to produce odors and becoming putrid. The aim of this study was the in-depth analysis of the SS process vermicomposting with biochar. The SS was acquired from a local soft drink factory wastewater treatment plant. The batches of SS were inoculated with 20% mature vermicompost and E. fetida worms. Instead of typical bulking agents (like woodchips or straw) powdered biochar was used in the concentrations of 5, 10 and 15% as it exhibits beneficial influence on the process and increase the value of the final product. © 2019, Journal of Ecological Engineering.Polish Ministry of Science and Higher EducationMinistry of Science and Higher Education, Poland [BS/PB -401-304/11