Bio-cake formed on the membrane surface plays an important role in providing high quality permeate in membrane biofiltration process which includes self-forming dynamic membrane bioreactor (SFDMBRs) and conventional membrane bioreactors (MBRs). To date, few quantitative analysis or mathematic models in term of bio-cake formation mechanism, structure and distribution has been conducted due to complicated relationship between bio-cake properties and its influence factors influencing it. Moreover, the mechanism of bio-cake attachment and detachment are still not clear, which has led to several operational drawbacks especially in simultaneously achieving high effluent quality and low membrane fouling frequency. In this research, the mechanism of bio-cake attachment and detachment i...[ Read more ]

Bio-cake formed on the membrane surface plays an important role in providing high quality permeate in membrane biofiltration process which includes self-forming dynamic membrane bioreactor (SFDMBRs) and conventional membrane bioreactors (MBRs). To date, few quantitative analysis or mathematic models in term of bio-cake formation mechanism, structure and distribution has been conducted due to complicated relationship between bio-cake properties and its influence factors influencing it. Moreover, the mechanism of bio-cake attachment and detachment are still not clear, which has led to several operational drawbacks especially in simultaneously achieving high effluent quality and low membrane fouling frequency. In this research, the mechanism of bio-cake attachment and detachment is predicted and/or described successfully by mathematic models. Finally, a novel low-cost SFDMBR pilot plant was built for saline wastewater treatment based on the dynamic models developed in this research.

A dynamic bio-cake attachment model (DBAM) was first developed in this research, and membrane pore size effect on bio-cake formation analyzed at the start. Biomass accumulation rate and extracellular polymeric substance (EPS) production rate were calculated and then used in the DBAM while considering the backwash effect. The DBAM was validated by experimental data in a lab-scale SFDMBR system and other results published, which provided evidence proving the disclosed bio-cake attachment mechanism and backwash effect. Then, a novel dynamic bio-cake detachment model (DBDM) was developed in order to simulate bio-cake detachment in aerobic flat-sheet MBRs. Lab-scale experiments were also conducted for model calibration and validation. The results showed that the DBDM could dynamically simulate the variation and distribution of shear stress and bio-cake detachment rate on the membrane surface. All the results suggested that, the developed DBAM and DBDM can soundly simulate the bio-cake attachment and detachment process in flat-sheet MBRs, and can be used as a tool to better understand bio-cake formation mechanisms and help control fouling in MBRs.

A 7 m³/d pilot-scale SFDMBR system was built by treating real saline municipal wastewater based on the DBAM and DBDM. Optimized membrane pore size and aeration system determined from the dynamic models, were applied in this pilot plant. The SFDMBR pilot plant treating saline wastewater successfully operated in 370 days without membrane fouling. The average total suspended solids (TSS), chemical oxygen demand (COD) and total Kjeldahl nitrogen (TKN) removal efficiency were 92, 90, and 93 percent respectively, in the context of a high effective permeate flux of 4.8 m/d. Membrane fouling happened only once when aeration stopped for more than 30 h, which was caused by EPS increase in the reactor as well as the bio-cake on the membrane surface. In this study, optimized membrane pore size (55 μm) and complexity bio-cake formation mechanisms were determined and well simulated by the developed models. The models were validated by both lab- and pilot-scale experiments. Furthermore, the developed models can be used as a helpful tool in membrane fouling control, which was validated by pilot-scale long-term operation.