Anaerobic digestion of thickened waste activated sludge after microwave enhanced advance oxidation pretreatment

A microwave-enhanced, advanced oxidation process (MW-AOP) was used to treat thickened waste-secondary sludge (TWSS), prior to anaerobic digestion (AD). A large amount of soluble chemical oxygen demand (SCOD) and volatile fatty acid (VFA) were formed in the solution, after pretreatment. Both single and two-phase systems loaded up to 18.2 g volatile solids per liter per day (gVS/L/d), while achieving high methane production, as well as overall high treatment efficiency. Both the up-flow anaerobic blanket reactor (UASB) and the continuous stirred tank reactor (CSTR) could operate at very short HRTs as low as 2 days without any evidence of souring. The results indicated that an acid reactor in the two-phase system was not required, due to very high SCOD and VFA produced in the MW-AOP pre-treated solution. As such, a single AD should be able to handle this easily biodegradable substrate following microwave pretreatment.