Organic fertilizer production through composting of sewage sludge

Abstract

Sewage sludge produced by purification plant of Bom Retiro (Londrina-PR) and husks of sugarcane were analyzed and five mixtures of these components were composted in ventilated piles. Sewage sludge with previous excessive anaerobic digestion (4 months) obstructs high levels of microbial activity. Thermophilic stage was attained by the better balanced (nitrogen and energetic components) mixture. Ventilation system leads to a short stabilization period (15 days) which will allow better use of composting area if process is performed on a full scale. The levels of heavy metals observed are low if compared with international standards. After 180 days of ripening, organic fertilizer has C/N rate between 12 and 24, easy handling and 7-10% of humus content.