Evaluation of microbiological and chemical parameters during wastewater Sludge and Sawdust Co-composting

Environmental specialists classified sewage sludge as a hazardous waste because of high organic compounds and pathogenic microorganisms. Therefore sewage sludge should be stabilized before disposal. Composting is an effective and economical method to stabilize sewage sludge. The object of this study is determining the optimum conditions of co- composting of dewatered sewage sludge and sawdust. Pilot scale study was performed in Isfahan municipal wastewater treatment plant. To perform this study, the dewatered sewage sludge with humidity between 78-82 percent was mixed with sawdust. Turning over did once a week for aeration. Temperature was monitored at different depths daily. Other parameters such as N, C, organic matters, pH, heavy metals, total and fecal Coliform and Salmonella were determined three times a week. The results of this study showed that after about 15th days, temperature of the mixture reached up to 55 °C, and was stabled for fifteen days. Humidity, organic matter, organic carbon and C/N ratio of the mixture decreased during of the study, due to increasing the temperature. Also organic matter and humidity mainly decreased in thermophilic phase. The number of total and fecal coliforms and also Salmonella decreased to A class standards of U.S. EPA at the end of the operation. The result indicated that co-composting of sewage sludge with sawdust is a reliable and simple method to schedule, with high flexibility and low odor production. Organic compounds and pathogenic microorganisms reduced and EPA standards were met during this method.