Methane Production and Nutrient Recovery After Applying Microwave Technology in Sewage Sludge Pretreatment

This study investigates the effect of microwave treatment on the disintegration of municipal activated sludge. Sludge samples underwent heating at a targeted temperature of 90 °C for 35 min, with a 5-min retention time. Soluble chemical oxygen demand, sugars, proteins, nitrogen, and phosphorus exhibited notable increases compared to untreated samples. Results indicate a substantial (42–45%) rise in CH₄ production during the anaerobic digestion process of the disintegrated sludge compared to the untreated counterpart CH₄ production was estimated using a transference model, which showed the best fit compared to other models. Further experimentation involved testing digested sludge with excess soluble NH₄–N and PO₄–P for the recovery of struvite at a 1.50/1/1 (Mg/N/P) ratio. The findings reveal that up to 90.1% and 90.4% of PO₄–P and NH₄–N, respectively, can be efficiently removed from the solution. Despite the increased CH₄ output, the energy recovered was insufficient to offset the electrical energy used by the microwave. There was a significant deterioration in sludge filter resistance due to the increase in fine particles and bound water after anaerobic digestion of the pretreated sludge.

Graphical abstract