Enhanced disinfection and methane production from sewage sludge by microwave irradiation

The effect of inoculum acclimation on methane production from mesophilic digestion of microwave pretreated of thickened waste activated sludge (TWAS) was investigated. In a range of 50–175°C, microwave disintegrated waste activated sludge and enhanced methane production. Soluble to total chemical oxygen demand ratios increased from 9 ± 1 (control; unpretreated) to 24 ± 3, 28 ± 1 and 35 ± 1% at 120, 150 and 175°C, respectively. Biological Methane Potential tests indicated that despite mild acute inhibition in the first 9 d, acclimated inoculum digesting sludge, irradiated to 175°C produced 31 ± 6% higher biogas compared to control after 18 d of digestion. However, initial acute inhibition was more severe for non-acclimatized inoculum requiring 2 times longer recovery with only 18 ± 2% higher biogas after 20 d. Inoculum acclimation did not only accelerate production of biogas, but also increased the extent of the ultimate biodegradation of pretreated waste sludge.