This work aims to control foaming in a submerged membrane bioreactor (SMBR) by optimizing the organic loading rate (OLR) and sludge retention time (SRT) values to decrease the extracellular polymeric substance (EPS) production used for the pharmaceutical wastewater treatment. Four lab-scale SMBRs were operated for a period of more than 8 months to determine the biokinetic coefficients and optimize the SMBR systems operation under the SRT of 5, 10, 15, 20, 25 days and OLRs of 0.03-0.32 gCOD/L.day. The investigation revealed that the lowest foaming quantity was at an organic loading rate of 0.32 gCOD/L.day and a sludge retention time of 15 days related to few protein concentration of EPS. The results also showed that the foaming quality at the OLR of 0.03 gCOD/L.day was higher compared to the greater OLRs in all SRTs. It was found that the yield (Y), the endogenous decay coefficient (kd), the maximum specific growth rate (μmax), and the saturation constant (Ks) of four SMBRs were in the range of 73.53-232.55 mg/mg, 1-3.156 day-1, 1.269-3.708 day-1, and 2.57-145.8 mgCOD/L, respectively. Furthermore, the most appropriate operating condition to activated sludge among the SMBRs was the OLR of 0.1 gCOD/L.day and SRT of 15 days. Under these optimum conditions, a 92.8% COD removal efficiency and 3.708 1/day μmax were achieved.
