Triclosan biodegradation performance of adapted mixed cultures in batch and continuous operating systems at high-concentration levels

Abstract

Pollutants like triclosan (TCS) of medium to high logKow value tend to be mainly adsorbed and poorly biodegraded during waste water treatment, complicating removal after release. Complete mineralization of TCS is crucial, since transformation products may be even more toxic, but has been proven only in a few cases. In this study, the performance of different batch (cultivation flask, TCSmix100) and continuous operating systems (submerged biotrickling filter, TCSmix100; biomembrane reactor, TCSmix200) was tested with two pre-adapted mixed cultures named TCSmix100 and TCSmix200, and compared to non-adapted cultures in a biotrickling filter and a sand filter as reference systems. Mineralization rates up to 172 mg TCS/L/d were observed during batch conditions for TCSmix100 at 1.45 g TCS/L as initial concentration. Triclosan was completely mineralized by both cultures, as shown by stoichiometric release of chloride at conversion rates of 5,7–11.4 mg TCS/L/d (biotrickling filter) and 0.72–1.45 mg TCS/L/d (biomembrane reactor) at 20 and 7.5–15 mg TCS/L as influent concentrations. In TCSmix100, Achromobacter sp. was identified as the relevant strain in TCS biodegradation. Community analysis of TCSmix200 revealed Nitrosomonas europaea, Nitrospira moscoviensis, Nitrosospira multiformis , and Rhodanobacter lindaniclasticus as the predominant strains. In contrast, chloride formation and triclosan elimination in the non-adapted biotrickling filter was less than 12% of the expected chloride concentration at hydraulic retention times up to 60 d. In the reference sand filter, TCS abatement was 42.8% in average with neither formation of chloride nor increase in biofilm density, indicating mostly sorptive or precipitative effects for elimination. With mineralization levels surpassing those of comparable references by a factor of 3–11, both adapted fixed-biomass reactor systems proved highly suitable for treatment of effluents containing high concentrations of TCS as they occur in industrial discharges or concentrates of membrane-based wastewater treatment plants. • Two aerobic mixed cultures were enriched able to completely mineralize triclosan (TCS) • Mixed cultures were dominated by Achromobacter sp. or nitrifying bacteria • Turnover rates were up to two orders higher than in literature (172 mg TCS L −1 d −1 ) • Fixed biomass systems showed stable performance during 110 d and 137 d of operation • TCS was solely eliminated by sorptive effects in a sand filter as reference system