Energy recovery potential of thermophilic high-solids co-digestion of coffee processing wastewater and waste activated sludge by anaerobic membrane bioreactor

A large amount of wastewater is generated in the processing of coffee from fruit to cup. Thermophilic high-solids co-digestion of coffee processing wastewater (CPW) and waste activated sludge (WAS) has been succeeded by anaerobic membrane bioreactor (AnMBR). Chemical oxygen demand (COD) removal efficiencies of 92 ± 3% with an average methane yield of 0.28 LCH₄/gCOD_removed were achieved at a high solids content of 50 g/L in the AnMBR. The optimal digestion performance of 82.4% removal COD conversion to CH₄ was achieved at hydraulic retention time (HRT) 10 d. Energy balance analysis revealed AnMBR has succeeded in energy positive at all the HRTs. The net energy potential (NEP) was determined to average 2.12–2.82 kJ/gCOD, amongst which the maximum NEP was achieved at HRT 15 d. These results indicated the high-solids co-digestion by AnMBR is a promising approach to maximize the bioenergy conversion from the co-substrate of CPW and WAS.