The application of a mesh filter for the separation of the liquid-solid phase in wastewater treatment to produce clean permeate provides a substitute for the conventional membrane bioreactor (MBR). This approach decreases the overall capital cost and achieves high flux while lowering the risk of fouling. Sludge floc contributes to the formation of a dynamic layer on the mesh during the filtration process, so the technology is named the self-formed dynamic membrane bioreactor (SFDMBR). Up to now, most SFDMBR researches have been mainly focused on the aerobic condition. However, the feasibility of an anaerobic self-forming dynamic membrane bioreactor (AnSFDMBR) incorporated with an up-flow anaerobic sludge blanket (UASB) reactor for saline wastewater treatment was barely studied....[ Read more ]

The application of a mesh filter for the separation of the liquid-solid phase in wastewater treatment to produce clean permeate provides a substitute for the conventional membrane bioreactor (MBR). This approach decreases the overall capital cost and achieves high flux while lowering the risk of fouling. Sludge floc contributes to the formation of a dynamic layer on the mesh during the filtration process, so the technology is named the self-formed dynamic membrane bioreactor (SFDMBR). Up to now, most SFDMBR researches have been mainly focused on the aerobic condition. However, the feasibility of an anaerobic self-forming dynamic membrane bioreactor (AnSFDMBR) incorporated with an up-flow anaerobic sludge blanket (UASB) reactor for saline wastewater treatment was barely studied. Therefore, the purpose of this study is to fill the research gaps in AnSFDMBR for saline wastewater treatment with an investigation of the change in dynamic layer properties during the entire operation period, covering the formation, different backwashing strategies and long-term operation.

The dynamic layer can be formed successfully within 60 to 90 minutes, producing permeates of less than 10 nephelometric turbidity units (NTU) after system optimization. Extracellular polymeric substances (EPS) play an essential role in the dynamic layer formation. Humic acid (HA) was the dominant EPS in the sludge, but it did not significantly affect the dynamic layer formation. Polysaccharides (PS) only represented 3.7% of the total EPS in the sludge and accumulated on the supporting material as a percentage of the total EPS, increasing significantly from 6.2% after 60 minutes to 10.8% after 720 minutes.

Based on the findings, time-based backwashing at different intervals and trans-membrane pressure (TMP)-based backwashing were conducted for further comparison. It was found that both operation strategies could achieve stable operation with effluent turbidity less than 5 NTU and low accumulation of TMP. However, the EPS accumulation rate in the dynamic layer and mesh was much higher in the time-based backwashing strategy, indicating that frequent backwashing might have a negative impact on the AnSFDMBR system. PS in the dynamic layer was the main reason for the compactness of the dynamic layer, which negatively correlated with the surface area and led to the TMP increase.

To widen the scope of work, batch operation and long-term operation were conducted in order to examine the chemical properties coupled with the filtration performance. The results revealed that during the batch operation, the median flux (0.75 m³/m²/day) was more pronounced for long-term operation and the system could be operated continuously for 243 days without dropping a flux during long-term operation. EPSs, including total organic sulfur (TOS) and total organic nitrogen (TON), played a critical role in the AnSFDMBR performance. PS was the least abundant among all the EPSs, but the PS dynamic layer to sludge ratio was most impressive with the highest ratio. TON in the system behaved like a protein and its concentration decreased with operation time in both systems. TOS accumulated with the polysaccharides but its deposition on the mesh during long-term operation was significantly high and led to fouling in the system. Under stable conditions, 86% organic removal efficiency and 34% sulfate reduction was achieved. 16Sr-RNA high-throughput amplicon sequencing revealed the richness and diversity of the microorganisms enriched in the reactor sludge samples and accumulated on the dynamic layer were different. Among the bacterial communities, the genus Trichococcus belonged to Bacilli class and genus Desulfovibrio (sulfate-reducing bacteria, Deltaproteobacteria class) was predominant in both the sludge and dynamic layer samples. In the archaeal community, two methanogenic genera, namely Methanobacterium and Methanolinea affiliated to the class Methanomicrobia were detected with higher abundance in the sludge than in the dynamic layer. Overall, the results of this study revealed that the AnSFDMBR has a high potential for commercial and industrial applications.