There are several physical, chemical and biological methods to treat petroleum pollutants. Moving bed biofilm reactor is a biological process for treatment of these pollutants. In this research, moving bed biofilm reactor has been selected owing to its eco-friendly features and because of its high efficiency in removing these pollutants. In this study, for the first time, serial moving bed biofilm reactor was introduced and used to remove petroleum pollutants from wastewater. In this biological system, two moving bed biofilm reactors were connected. Feed forward and feed backward systems were used for this connection. Also, in this research, the response surface methodology was used to model the removal efficiency of petroleum pollutants in serial moving bed biofilm reactor. The optimal operation conditions were obtained by examining three effective independent parameters: retention time (11.23-34.77 h), influent total petroleum hydrocarbon concentration (164.78-585.22 mg/L), and media filling ratio (28.18-61.82%). The results of the study showed that decreasing influent total petroleum hydrocarbon concentration and increasing retention time and media filling ratio led to a decline in the food to microorganism ratio, and thereby improved removal efficiency of pollutants. The experiments showed that retention time of 23 h, influent total petroleum hydrocarbon of 164.78 mg/L, and media filling ratio of 45% yielded the highest efficiency of 97% in removing petroleum pollutants. This high efficiency under optimal conditions makes it possible to use serial moving bed biofilm reactors for petroleum wastewater treatment.
