Toxicity evaluation and management of co-composting pistachio wastes combined with cattle manure and municipal sewage sludge.

ABSTRACT

To manage the pistachio de-hulling waste (PW), investigated the co-composting process using a mixture of PW and cattle manure (CM) (5.510 dry weight) as well as PW and municipal dewatering sewage sludge (DSS) (110 dry weight) at the laboratory scale for 60 days. Compost toxicity was evaluated using the seed germination index (GI). The maximum temperatures in co-composting processes of PW+CM (51.9 °C) and PW+DSS (49.9 °C) were reported on the seventh day. The increase of temperature was higher in PW+CM and remained in the thermophilic phase for five days. In both reactors, the pH rates decreased, increased, and finally remained neutral. The C/N ratio decreased in both reactors, but the reduction rate was faster in the PW+DSS reactor. Sodium (Na%) and potassium (K%) contents were increased, while the concentrations of Cu, Zn, Fe, and Mn were decreased during the processes. The numbers of parasite eggs in the final composts of the reactors containing PW+CM and PW+DSS were zero and 8 Number/4gDW, respectively. The amounts of Salmonella were zero in the final products of reactors containing PW+CM and PW+DSS. The results of GI showed that the final compost of PW+CM process was not toxic for the plants, whereas the PW+DDS final compost was toxic. In conclusion, the co-compost product of the PW+CM reactor had higher quality than the PW+DSS reactor. So, it is suitable for PW management.