MCPA biodegradation in an anoxic sequencing batch reactor (SBR)

This research investigated the potential for industrial-strength 2-methyl-4-chlorophenoxyacetic acid (MCPA) degradation by activated sludge microorganisms in a sequencing batch reactor (SBR) under nitrate-reducing conditions. The research was divided into four phases consisting of Phase I (a “proof-of-concept” phase); Phase II (an initial “tolerance” exploration phase); Phase III (an “effect of hydraulic retention time” phase), and Phase IV (a “limits” phase). The SBR successfully and simultaneously removed the nitrates completely and around 98 % of the MCPA up to an initial concentration of 50 mg/L MCPA in the dimethylamine salt form (DMCPA) (Phases I, II and III); however, it took approximately 28 days to observe a steady, high-level of MCPA removal. When the concentration of DMCPA was increased to 75 mg/L (Phase IV), the MCPA removal efficiency dropped to 85 %, but removal was observed only for a relatively short period of time since the biomass appeared to eventually become saturated with the herbicide, stopping conversion of DMCPA to its acid form and halting biodegradation.