Bioaugmentation Combined with Biofilim Process in the Treatment of Petrochemical Wastewater at Low Temperatures

Three sets of lab-scale reactors, which applied activated sludge process, bioaugmented activated sludge process and bioagumented biofilm process, respectively, were operated parallel to explore the optimum process for the treatment of petrochemical wastewater at low temperatures (13-15 degC ). Though being inoculated twice with enriched specialized bacteria, the bioaugmented activated sludge reactor (R2) did not show significant overall improvement on effluent quality when compared with the unbioaugmented reactor (Rl) (average removal efficiency, COD: Rl=65.02%, R2=70.39%; NH4+-N: Rl=42.07%, R2=52.49%), except for increased levels of enzyme activity as described by dehydrogenase activity (DHA) and slightly better performance at the early stage of inoculation. Microscopic observation indicated that free-living cells were scarce in R2 and the main explanation was the grazing of protozoa to the bioaugmented cells. However, the application of porous polyurethane foam as carrier in the bioaugmented biofilm reactor (R3) could retain sufficient biomass within the reactor, and the COD (75.80%) and NH₄ ⁺-N (70.13%) removal efficiencies were enhanced with more stable performances. In conclusion, massive inoculation could not always warrant successful bioaugmentation due to predation to the inoculated specialized bacteria, and biofilm process was promising when combined with bioaugmentation technology in the treatment of petrochemical wastewater at low temperatures.