A novel bioadsorption-flocculation fluidized bed bioreactor prior to membrane filtration for wastewater treatment and reuse
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As one of the advanced technologies, fluidized bed bioreactor (FBBR) with high treatment efficiency, low operating and capital costs has attracted more attention for wastewater treatment and reuse. The natural based flocculants (NBFs) are environmentally friendly and biodegradable, as well as present good flocculating ability. They can minimize environmental and health risks. Membrane technology has been developed as one of the reliable treatment methods. However, it has some limitation. Besides the high operation costs, membrane fouling is a major obstacle for the widespread application of this technology. The pretreatment technologies are an effective way for improving the filtration performance of the membrane and minimizing membrane fouling. This study was successfully completed with a number of developments which is relevant to all the above issues. Firstly, the granular activated carbon (GAC) fluidised bed bioreactor was designed and developed through a series of study on (i) bioadsorption capacity of granular activated carbon (GAC) in terms of dissolved organic carbon (DOC) removal from wastewaters, (ii) optimization of the operating conditions of granular activated carbon fluidized bed bioreactor (GAC-FBBRs), and (iii) evaluation of GAC-FBBR for treating synthetic wastewater. Secondly, a new sustainable bioflocculant (NSBF) was developed based on the experimental study of the effect of trace nutrients on the biodegradability of a natural starch based cationic flocculant (SBCF) and the possible use of NSBF as efficient enhancer for FBBR as well as anti-membrane fouling agent for FBBR- Microfiltration (MF) hybrid system. Thirdly, a novel integrated fluidized bed bioreactor (iFBBR) was developed with the design of incorporating an aerobic sponge bioreactor (ASB-FBBR) to an anoxic granular activated carbon FBBR (GAC--FBBR). The detailed investigation on both laboratory and pilot-scale iFBBR and iFFBR-MF with NSBF addition were also conducted. The main specific findings from this study are as follows: Biological GAC (BGAC) bioadsorption perfonned significantly better than GAC adsorption. BGAC bioadsorption could lower the GAC dose and prolong the life time of GAC. The NSBF, containing 22 mg/L of SBCF, 0.5 mg/L of FeCl3, 5 mg/L of MgS04 and 2 mg/L CaCb, was discovered in this study. The addition of NSBF to the GAC-FBBR, Jab-scale and pilot-scale iFBBR is helpful for biomass growth and enhances the performance of bioreactors in terms of organic and nutrient removals. As a pretreatment to SMF, GAC-FBBR, lab-scale and pilot-scale iFBBR are successful in increasing the critical flux and reducing the membrane fouling. The pilot-scale iFBBR-SMF hybrid system could remove more than 95% of organics from real domestic wastewater with effluent DOC and COD concentrations of 2 mg/L and 4.5 mg/L, respectively.
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