Comparison and toxicity assessment of co-composting process by pistachio wastes and date-palm straw combined with municipal sewage sludge

Abstract

\n This study aimed to toxicity evaluate and compare the new co-composting process of pistachio dehulling waste combined with municipal sewage sludge (PW\u2009+\u2009SS) and date-palm straw combined with municipal sewage sludge (PS\u2009+\u2009SS). The process was evaluated over a 60-day period. During the process, physicochemical parameters (temperature, humidity, pH, electrical conductivity (EC), carbon to nitrogen ratio (C/N), ash and organic carbon (OC)), microbial indicators (parasite eggs, salmonella, E. coli), heavy metals (copper, zinc, Iron, manganese, lead, cadmium, nickel), and germination index were measured. The results showed that in the PW\u2009+\u2009SS reactor the maximum temperature reached 59°C on the 32th day and in the PS\u2009+\u2009SS reactor reached 39°C on 18th day. The pH level in PW\u2009+\u2009SS reached a minimum of 3.2 on the 14th day and then increased and finally reached a maximum of 9.5. The pH level in PS\u2009+\u2009SS had an increasing trend and finally reached 7.1. Ash percentage had an increasing trend in PW\u2009+\u2009SS and finally reached 27.5 and reached 19.1 in PS\u2009+\u2009SS (p\u2009=\u20090.038). EC, C/N and OC in both reactors had a significant decreasing trend. E. coli microbial indicator in both reactors decreased from ≥\u2009105 to zero at the end of the process. The amounts of heavy metals in both reactors had an increasing trend and were within the standard range. Toxicity assessment showed that the PS\u2009+\u2009SS compost was 100% in all concentrations and the PW\u2009+\u2009SS compost reached 100% by dilution; therefore, the product of PS\u2009+\u2009SS was less toxic than the product of PW\u2009+\u2009SS.