Effect of recycling flux on performance and characteristics of activated sludge hydrolytic–aerobic recycling process in degradation of 2,4-dichlorophenol

The degradation of a model molecule, 2,4-dichlorophenol (2,4-DCP), was studied using an activated sludge hydrolytic–aerobic recycling process (HARP). 2,4-DCP and chemical oxygen demand (COD) total removal efficiency in the recycling process was 98% and 96% at the recycling flux of 15 mL/min after 24 h degradation, respectively. With the recycling flux increasing, the peak values of the concentration of volatile fatty acid (VFA) declined. Polysaccharide and protein contents in EPS were dramatically increased as recycling flux increasing from 5 to 15 mL/min in the HARP. There is obviously fit to the linear correlation between the PN/PS ratios and recycling flux. The zeta potentials decreased with recycling flux increasing. As the recycling flux increasing at a certain degree, the increase in polysaccharide and protein contents of EPS could more favor the stability of the HARP.