Free ammonia pretreatment assists potassium ferrate to enhance the production of short-chain fatty acids from waste activated sludge: Performance, mechanisms and applications

Anaerobic fermentation of waste activated sludge (WAS) is often limited by low disintegration rates of WAS and quick consumptions of short-chain fatty acids (SCFAs) by methanogens. This work proposed a novel, efficient and harmless pretreatment approach i.e., using potassium ferrate (PF) combined with free ammonia (FA), to enhance the disintegration of WAS and the accumulation of SCFAs from WAS anaerobic fermentation. It was found in this work, the best pretreating condition of WAS is 0.10 g PF/g VSS + 180 mg FA/L, under which the SCFAs consistence reached its maximum value (342.5 mg COD/g VSS), which was respectively 7.45-fold, 3.50-fold and 2.06-fold of that from the Blank, FA and PF reactor. Further in-depth mechanism study showed that the disintegration of WAS promoted and the biodegradability of fermentation broth enhanced under the PF + FA pretreatment condition. Moreover, the populations of fecal coliforms in WAS reduced significantly when PF + FA was adopted. Considering that FA could be produced in situ during the ammoniating process, the findings in this work promoted the utilization of PF-based pretreatment method in actual operations.