Fungal pretreatment of citrus waste improves the hydrolysis and acidogenesis of the organic fraction of urban solids wastes

This work shows the increase in hydrolysis and acidogenesis of the organic fraction of urban solid waste (OFUSW) by the action of fungal hydrolytic enzymes obtained by solid-state fermentation (SSF) with Aspergillus niger C25B28 on citrus wastes (CW) without sterilization or the addition of nutrients. To quantify the hydrolysis and acidogenesis of the organic fraction of urban solid waste, three treatments were studied in triplicate: OFUSW plus 10 % fresh CW (RC treatment), and OFUSW plus 10 % citrus wastes pretreated by SSF (RCA treatment). The mixtures were packed into an anaerobic hydrolytic leaching bed reactor. The results showed that SSF decreased the limonene concentration by 97 %, removing 20 % of fiber and 46 % of fat from fresh CW. Pectinases (37 U/g DM [dry matter]), cellulases (33 U/g DM), xylanases (98 U/gDM), and proteases (0.2 U/gDM) were produced. Significant differences were observed between the different treatments: the greatest reduction in total solids (24 %), the highest removal efficiency of organic matter as chemical oxygen demand (COD), and the reduction of fats (23 % and 28 %, respectively), was achieved in RCA, compared to those obtained in the reactors with OFUSW and ReC without pretreatment. The production rate of volatile fatty acids (VFA) was 1.4 gVFA/Ld for RCA, 4.5 times higher than in the reactors without pretreatment.