Effect of substrate characteristics on microbial community structure, function, resistance, and resilience; application to coupled photocatalytic-biological treatment

Advanced oxidation (AO) coupled with biodegradation is an emerging treatment technology for wastewaters containing biologically recalcitrant and inhibitory organics, including those containing chlorinated aromatic compounds. The composition of the AO effluent organics can vary significantly with reaction conditions, and this composition can affect the performance of subsequent biodegradation. Three synthetic effluents were used to mimic varying degrees of AO of 2,4,5-trichlorophenol: 4-chlorocatechol to mimic light transformation, 2-chloromuconic acid to mimic moderate transformation, and acetate to mimic extensive transformation. The substrates were fed to identical chemostats and analyzed at steady state for removal of chemical oxygen demand (COD) and dissolved organic carbon (DOC), biomass concentration, and bacterial diversity. The chemostat fed acetate performed best at steady state. The 2-chloromuconic acid chemostat was next in terms of steady-state performance, and the 4-chlorocatechol reactor performed worst, correlating with degree of AO transformation. A spike of 100 μM 2,4,5-trichlorophenol was then applied to each chemostat. The chemostat fed 4-chlorocatechol exhibited the best resistance to the perturbation in terms of maintaining consistent community structure and biomass concentration, whereas the performance of the acetate-fed chemostat was severely impaired in these categories, although it quickly regained capacity to remove organics near pre-perturbation levels demonstrating good resilience. The opposing trends for steady-state versus perturbed performance highlight tradeoffs inherent in coupled chemical-biological systems.