Retracted Article: Synergetic effects of ultrasound combined with Fenton pretreatment that accelerates wasted activated sludge anaerobic fermentation to produce volatile fatty acids

Abstract

Abstract Due to the problems of the hydrolysis of wasted activated sludge (WAS), fermentation stage takes a long time and volatile fatty acids (VFAs) output efficiency is low. This study investigated the effect of ultrasound combined with Fenton (US/Fenton) pretreatment on the sludge disintegration and anaerobic fermentation. The sludge was treated by three different pretreatments respectively: ultrasound alone, Fenton alone and US/Fenton. Results show that after three pretreatments, sludge floc structure was disintegrated and oxidized, the sludge particle morphology after US/Fenton pretreatment was changed the most obviously. After US/Fenton, specific surface area was the largest and the particle size reduction was remarkable from 50.24 μm to22.44 μm. The SCOD concentration after US/Fenton was 3461.72 mg COD L-1, which was raised 1.73 times, 2.68 times and13.29 times as against that after ultrasound, Fenton and the untreated. The degree of disintegration (DDCOD) of the US/Fenton pretreatment was 15.4% which was greater than ultrasound pretreatment of 9.97% and Fenton pretreatment of 3.18%. The VFAs concentration after US/Fenton pretreatment reached a maximum value of 4594 mg COD L-1 at the eighth day, it was raised 31.8% and 70.15% as separately compared with the Fenton and ultrasound pretreatments. The pretreatments changed the VFAs composition and proportion. The highest HAC concentration after US/Fenton was 2039 mg COD L-1, which was 1.72 and 1.78 times of that in Fenton and ultrasound, respectively. This study showed that the US/Fenton pretreatment had a certain synergistic promotion effect on the sludge anaerobic fermentation. The ultrasound and Fenton co-work, the ability of the VFAs production is further improved.