Biological purification of acidic Fenton effluent by a fungal consortium without pre-neutralization upon base addition: Microbial screening and performance

Abstract

Great progresses have been made to carry out Fenton oxidation under neutral or alkaline pH in which, nevertheless, organic acids and other acidic intermediates usually result in acidic Fenton effluent. To eliminate the classical neutralization step prior to biological treatment, acid-tolerant microbes were here screened and used for purification of acidic Fenton effluent to achieve pH increase and further COD (chemical oxygen demand) removal. The bacterial and fungal community diversity was analyzed before and after screening for acid-tolerant microbes. After screening the bacterial diversity sharply decreased while the fungal diversity at the genus level became richer, mainly including Phialemoniopsis (relative abundance 38.69%), Vanrija (20.08%), Hypocreaceae (18.44%) and Candida (14.74%). Acidic pH and residual H2O2 are the features of Fenton effluent; hence, effects of pH and H2O2 on the screened acid-tolerant microbes were investigated in the aspects of growth rate and oxygen uptake rate. The kinetic parameters, including YH–biomass yield coefficient; Kd–biomass decay coefficient; μm–specific maximum COD removal rate; Ks–half saturation constant for COD removal, of the acid-tolerant microbes using 1/5 YM (yeast extract and malt extract culture medium) as substrate at 25 °C were measured by respirometric methodology. In BAC (biological activated carbon) inoculated with acid-tolerant microbes to treat actual Fenton effluent, the average COD removal efficiency was 72% at HRT (hydraulic retention time) of 3 h and the effluent pH was above 6 after removing the dissolved CO2 by air stripping. This study will provide a basis for developing a new combined process including Fenton and biological oxidation without pH adjustment.