Methane production from anaerobic pre-treatment of municipal wastewater combined with olive mill wastewater: A demonstration study

The advanced anaerobic technology (AAT), developed based on an immobilized high-rate anaerobic reactor, was applied as a pretreatment of municipal wastewater (WW) at Karmiel’s treatment plant in Israel. The demonstration-scale AAT (21 m³) system was operated at a flow rate of 100 m³ day^–1 municipal WW mixed with olive mill wastewater (OMW) (0.5 m³ day^–1) to simulate the scenario of illegal discharge of agro-industrial WW. The AAT provided a stable performance. Specifically, AAT enabled treating high organic loads (9.3 kg m^–3 day^–1) resulting from OMW discharge by shaving the high peaks of organic content and protecting the subsequent activated sludge process. This system enabled the recovery of a significant part of the organic load by anaerobic biodegradation to produce biogas, shown to be highly dependent on temperature and partly on the organic loading rate. The outcomes indicate that the AAT could tolerate an addition of up to 0.5% OMW to municipal WW by removing more than 50% of the total chemical oxygen demand and 18–47% of polyphenols. This work shows that the AAT system has the potential of pretreating municipal WW, increasing the energy efficiency of the plant, and protecting small-medium WWTPs from sudden agro-industrial discharges.