Co-composting of sewage sludge and eggplant waste at full scale: Feasibility study to valorize eggplant waste and minimize the odoriferous impact of sewage sludge.

Sewage sludge and bulking agent with small proportions of eggplant waste (EP) (4.7 and 8.6%) were co-composted at full scale to evaluate the feasibility of their joint valorization and to reduce the odorous impact during composting. In this sense, physico-chemical, respirometric and olfactometric variables were monitored throughout the co-composting process. The physico-chemical variables studied were related to each other to evaluate their effect on the quality of the final product and the odoriferous impact. It was observed that the reduction in nitrogen concentration was not parallel to the removal of organic matter, which influenced the odor concentration emitted. Furthermore, during the hydrolytic stage of the co-composting process, the odor concentration was lower when the agricultural waste content was highest (8.6% EP: 6317 and 8192 ou/m) in comparison with the lowest concentration of EP (4.7% EP: 9214 and 14720 ou/m) or without the addition of EP (reference composting pile: 10200 and 22500 ou/m). Although sewage sludge is more biodegradable than eggplant waste, the co-composting process was carried out under suitable conditions. Approximately 90 days were required to obtain a stabilized compost. Consequently, co-composting might be a suitable alternative to valorize EP and reduce the odoriferous impact of sewage sludge, with the consequent economic, social and environmental benefits.