Aerobic submerged membrane bioreactor for spent caustic wastewater treatment
Spent caustic (SC) is one of the petroleum industry wastewater that is toxic and hazardous to living things and environment. The aim of this study is to treat SC by aerobic submerged membrane bioreactor (ASMBR) using microfiltration (MF) hollow fibre membrane to improve the quality effluent that su...
| Summary: | Spent caustic (SC) is one of the petroleum industry wastewater that is toxic and hazardous to living things and environment. The aim of this study is to treat SC
by aerobic submerged membrane bioreactor (ASMBR) using microfiltration (MF) hollow fibre membrane to improve the quality effluent that subsequently reduces the membrane fouling. At the beginning, the new operation parameters were identified namely mixed liquor suspended solid (MLSS) and solid retention time (SRT) for this system. MLSS was designed from 5 to 9 g L-1 and SRT from 20 to 80 days. Since membrane was used, membrane fouling remains a problem for MBR. Hence, biofouling reducers (BFRs) consisting of powdered activated carbon (PAC), zeolite
(ZEO) and eggshell (ES) were added during the operation into ASMBR and eggshell is the new biofouling reducer in MBR area. Furthermore, the capability of ASMBR was continued by increasing the organic loading (OL) from 2 to 4 gCOD L-1. The effluent quality, microbial products trend, and long-term trans-membrane pressure (TMP) performance were observed in all BFR experiments in ASMBR. Meanwhile, a dominant bacteria strain has been identified in ASMBR where it was implicated in treating spent caustic by using biochemical and molecular methods. Finally, this study developed a respirometric analysis by Activated Sludge Model No. 1 (ASMl) to calibrate design parameters that describe the degradation process in ASMBR. The models require characterisation of SC wastewater using chemical oxygen demand (COD) fractionation. Thus, the model was completed by observing COD effluent model trend from validation process. As a result, a good ASMBR was found to be the one operated at MLSS 5 g L-1 at SRT 40 days with less microbial products, good quality effluent and low membrane fouling rate. The average percentage removal showed 99% sulphide removal and more than 94% of COD removal during steady state operation. By adding PAC, higher reduction of the fouling rate (92%) and enhanced the removal performance were observed with 69 .1 % efficiency as compared with other BFRs. The sequences of amplified DNA fragment show 99% similarity with 16S rRNA sequence of Bacillus thuringiesis Bt407 and Carnobacterium maltaromaticum LMA28. The COD fractionation shows inert particulate COD (Xi) (1.8 - 2.3 g L-1) dominating in SC wastewater. The
accumulation of Xi in ASMBR is correlated to hasten membrane fouling rate. From model simulation, BFR was proven to increase the growth rate of biomass with maximum specific growth rate (μmaxH) in the range of 0.177 to 0.2 d-1 as BFRs were added. |
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