The application of membrane sequencing batch reactors in high rate activated sludge processes: the effect of the organic loading rate on the bioflocculation and fouling phenomenon

Abstract

In the current study, for the first time a membrane sequencing batch reactor (MSBR) was assessed for use in a high rate activated sludge process (HRAS). For this purpose, the effect of the organic loading rate (OLR), an important operating parameter in a HRAS process, at four levels, in the range of 4–16 kg COD m⁻³ d⁻¹, on the chemical oxygen demand (COD) and energy recovery performance and membrane fouling characteristics of a high loaded (HL) MSBR (i.e. one operated under HRAS conditions) was investigated. With the increase in OLR from 4 to 16 kg COD m⁻³ d⁻¹, the COD recovery reached a maximum value of 84%, which was significantly better than previously reported values for non-membrane-based bioreactors. Also, a total energy recovery of 0.25 g COD CH₄ per g COD_inf was achieved for the waste activated sludge (WAS) stream produced under the HL-MSBR operating conditions. The highest OLR, however, also yielded the highest rate of membrane fouling, and the principal membrane fouling mechanism was found to be the cake layer formation at all OLRs. The soluble microbial products (especially their protein fraction) were identified as the major contributing factor to fouling in the HL-MSBR. Based on these findings, the use of membrane relaxation and the addition of FeCl₃ were proposed as the membrane fouling control strategies during the use of the HL-MSBR in HRAS processes. However, a comprehensive economic assessment of the HL-MSBR for such use necessitates the optimization of the SRT as well as the experimental investigation of the proposed fouling control strategies.