Improving waste-to-energy process by co-digestion of exhausted coffee biowaste and WWTP sludge

The purpose of this study is to investigate the effects of using pre-treated exhausted coffee biowaste (ECB) as a co-substrate to optimize sewage sludge (SS) biogas production. The trials were conducted in semi-continuous mode at mesophilic conditions (36 +/- 1 degrees C) with a Hydraulic Retention Time of 17 days and an average organic loading rate (0.94 +/- 0.05 g VS L-reactor.day(-1)). An anaerobic co-digestion trial (T1) was assessed using a feeding mixture with a ratio of SS (80 %) and LECB (20%), v:v, and compared against a reference scenario (TO). Results showed that the addition of the co-substrate had a significant influence on specific methane production (3 times higher) and biogas quality (12% higher), which is a feasible strategy towards self-sufficient wastewater treatment plant. Furthermore, the stability along assays was ensured monitoring the digestate characteristics (pH, electrical conductivity, total alkalinity and ammonia content) and the specific energy loading rate. (C) 2017 The Authors. Published by Elsevier Ltd.