Phase B - Evaluation of a combined anaerobic/aerobic/anoxic sludge digestion system for Annacis Island wastewater treatment plant

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In Canada, medium-to-large scale municipal wastewater treatment plants (WWTPs) have been adapting anaerobic (AN) digestion technologies to generate energy in the form of biogas (60-75% methane) from wastewater sludge. Other benefits of AN digestion are diversion of organic waste from landfills, reduction of pathogens and odour, production of organic fertilizer, and reduction of greenhouse emissions. While AN digestion process is effective for reducing pathogens and destroying organic matter, solids reduction above 50% is often difficult to achieve. Therefore, advanced AN digestion processes with pretreatments and different digestion combinations (i.e. stage digestion) have gained interest in recent years. Furthermore, substantial ammonia and phosphate are released in AN digesters through hydrolysis of waste sludge which can degrade the final effluent quality of a WWTP. Therefore, sequential AN/ aerobic (AERO) sludge digestion process has been recommended due to many additional advantages (e.g. higher solids/pathogen destruction, ammonia removal, odour reduction and better dewaterability) over the single-stage AN digestion.