Abstract:
Quaternary ammonium compounds (QACs) are cationic surfactants that are active ingredients of many commercial and industrial disinfectants. Therefore they are major micropollutants found in industrial effluents, sewage, activated sludge, treated wastewater and receiving waters. Biodegradation is considered as the ultimate process to alleviate the impacts of QACs on the environment. The main objective of this study is to determine the optimum conditions for biotransformation of benzalkonium chlorides (BACs), an extensively used QACs, in biological systems. Strain BIOMIG1, a new Pseudomonas species that belongs to none of the previously described Pseudomonas groups, was identified as the key microorganism degrading BACs in activated sludge. BIOMIG1 is an oxidase and catalase positive γ-Proteobacterium that has an optimum growth temperature at 28 oC. BIOMIG1 can degrade BACs up to 2.8 mM (1000 mg/L) with a maximum rate of 4 μM/hr (1.4 mg/L-hr). A set of kinetic assays testing the effect of various bio-physico-chemical factors on BAC degradation by BIOMIG1 was performed. At each condition, kinetic parameters such as maximum growth rate and half-saturation coefficient of BAC degradation by BIOMIG1 were calculated by curve fitting to the experimental data using Michaelis-Menten growth model. Results of kinetic assays and modeling can be summarized as follows: (1) BAC biotransformation experienced a lag-period below 108 CFU/mL cell density and the lag period increased as cell density decreases; (2) Biodegradation rate of BAC with 14 carbon chain length was the highest followed by BACs with 12 and 16 carbon chain length; (3) Optimum BAC degradation temperature was determined as 42 oC. On the other hand, BAC degradation resulted in accumulation of benzyldimethylamine at 45 oC or ceased at 50 oC. Moreover, threshold oxygen concentration for BAC biotransformation was measured as 0.83 mg O2/L.
