Studies on influence of process parameters on simultaneous biodegradation of atrazine and nutrients in aquatic environments by a membrane photobioreactor
A Lab scale algal-bacterial membrane photobioreactor (MPBR) was designed and operated under 12-h light and 12-h dark conditions with a light intensity of 8000 lx, in order to investigate the effects of initial concentrations of atrazine, carbon concentration, and hydraulic retention time on the ability of this photobioreactor in simultaneous removal of atrazine and nutrients in the continuous mode. The removal efficiencies of atrazine (ATZ), chemical oxygen demand (COD), phosphorus (PO43--P) and nitrogen (NOx) in optimum condition was more than 95%, 99%, 98% and 97% when the maximum removal rates were 9.5 × 10−3, 99.231, 11.773 and 7.762 mg/L-day, respectively. Results showed that the quality of the effluent was reduced by the increase of atrazine concentration. The outcomes on the hydraulic and toxic shocks indicated that the system has a relatively good resistance to the shocks and can return to the stable conditions. Microalgae showed a great deal of interest and capability in cultivating and attaching to the surface of the membrane and bioreactor, and the total biomass accumulated in the system was greater than 6 g/L. The kinetic coefficients of atrazine removal were also studied using various kinetic models. The maximum atrazine removal rate was determined by the modified Stover-Kincannon model. The results approved the ability of the MPBR reactor in wastewater treatment and microalgae cultivation and growth. The decline of atrazine concentration in this system could be attributed to the algal-bacterial symbiosis and co-metabolism process. Accordingly, the MPBR reactor is a practical, simple, economical and therefore suitable process for simultaneous biodegradation of chlorinated organic compounds and nutrients removal from aquatic environments.