Impact of (RS)-MCPP herbicide and sulphate on the treatment performance, kinetics and microbial diversity of anaerobic membrane bioreactor

The impact of mecoprop herbicide 2-(2-methyl-4-chlrophenoxy)-propionic acid [(RS)-MCPP] under different COD:SO42− ratios of 8, 2 and 1, utilizing sulphate as the terminal electron acceptor was examined in an anaerobic membrane bioreactor. Results showed the predomination of sulphate reducing bacteria (SRB) at COD:SO42− ratio of 1 with 60%-70% COD removal via sulphate reduction. Low acetate concentration as derived from the total volatile fatty acid (VFA) production indicates consumption by active populations of methane-producing bacteria (MPB) and sulphate reducing bacteria (SRB). Additionally, at COD:SO42− ratio of 8, (RS)-MCPP removal efficiency was around 11%, but increased to 28% and 34% when COD:SO42− ratio was decreased to 2 and 1, respectively. The empirical kinetic models for substrate utilization and CH4 production were used to explain the inhibition of methanogenesis in an Anaerobic Membrane Bioreactor (AnMBR). Sulphate has a negative impact on the bioreactor performance as methane production dropped to below detection level when COD:SO42− ratio was decreased to 1.