Development of salt-tolerant microbial consortium during the treatment of saline bisphenol A-containing wastewater: Removal mechanisms and microbial characterization

Recalcitrant compounds and high salinity in industrial wastewaters are two major inhibitory parameter against the bacterial metabolism leading to necessity for the application of halotolerant microorganisms in biological treatment technologies. Hence, this study focused on the biological treatment of saline bisphenol A (BPA)containing wastewater at different total dissolved solids (TDS) (5, 10 and 15 g/L) with BPA concentration of 50 mg/L. Three sequencing batch reactors (SBR) were operated which applied different experimental conditions during 9 months. The pure adsorption behavior of BPA onto sludge was described via Freundlich isotherm model in batch experiments. The operation of sequencing reactors with 5 days hydraulic retention time (HRT) indicated that optimal removal rates exceeded 96.3%, 88% and 57% for BPA, COD, TOC, respectively, which was attained at high salinity. The organisms responsible for BPA removal appeared to be more sensitive to different operating conditions than changes in salinity; the BPA removal efficiency decreased from 96.3% to 69.8%, when HRT decreased from 5 days to 0.25 days. Results indicated that biodegradation was the predominant process for BPA removal. The biokinetic parameters in saline substrates were in the range of Y = 0.54-0.61 (mg VSS/mg BPA), k(d) = 0.006-0.013 (1/d), K-s = 8.94-13.6 (mg BPA/L) and mu(m) = 0.3-0.4 (1/d). Identification of mixed consortium at high salinity was included the species Pseudomonas aeruginosa, three different Serratia marcescens, Bordetella muralis, and Bacillus subtilis by using 16S rRNA-analysis.