Treatment efficiency and sludge characteristics in conventional and suspended PVA gel beads activated sludge treating phenol containing wastewater

Protozoa play a significant role in activated sludge systems, since they graze on dispersed bacteria, supporting a healthy food web in the activated sludge artificial ecosystem. However, operational parameters and influent properties are the most important factors affecting the composition of activated sludge microfauna. The objective of this study was the assessment of the treatment efficiency and the protozoan populations in activated sludge systems with and without the addition of polyvinyl alcohol (PVA) gel beads while treating wastewater in the presence of phenol. Six activated sludge reactors - 3 of them supplied with PVA gel beads –were used for the treatment of synthetic wastewater influent containing phenol at concentrations up to 10 mg/L. During the treatment of synthetic wastewater, dominance of the sessile species was observed mainly in the reactors supplied with PVA beads. Physicochemical analyses of the effluent indicated good efficiency of reactors supplied with PVA beads in removing nutrients and organic load. Introduction of phenol in the influent at a concentration of 5 mg/L did not affect significantly the operation of the reactors and the composition and abundance of activated sludge microfauna, while a high phenol removal rate was observed. The increase of influent phenol concentration to 10 mg/L resulted to the formation of foam on the surface of the reactors and the presence of Zoogleasp, while an increase was observed in the abundance of crawling species in activated sludge and PVA supplied reactors respectively.