Liu Junxin

Landfill leachate treatment by MBR: Performance and molecular weight distribution of organic contaminant

A membrane bioreactor (MBR) with an air-lift bioreactor and gravity flow is applied to treating landfill leachate. More than 99% of BOD5 (biochemical oxygen demand for five days) removal efficiency is achieved with less than 35 mg/L of BOD5 in the effluent at less than 1.71 kg BOD5/m3·d of BOD5 loading rate. When DO (dissolved oxygen) is maintained at the range of 2.3–2.8 mg/L and the loading rate of NH4+-N (ammonium nitrogen) is kept at 0.16–0.24 kg NH4+-N/m3·d, the NH4+-N in the effluent is less than 15 mg/L. However, compared with high removal rates of BOD5 and NH4+-N, the removal efficiency of soluble chemical oxygen demand (SCOD) varies between 70% and 96%. The investigation of molecular weight (MW) distribution has been carried out by the gel permeation chromatography (GPC) so as to understand the fate of organic matters in the MBR treating of landfill leachate. Results indicate that organic matters of the landfill leachate are composed of a high MW fraction (MW of the peak, MWp = 11480–13182 Da) and a low MW fraction (MWp = 158–275 Da). The high MW fraction is not biodegradable, but can be decreased with microfiltration membrane. The most of the low MW fraction is biodegradable, but the residue of the low MW fraction is able to permeate through the membrane, thus resulting in high SCOD in the effluent of the MBR.

Evaluation of virus removal in MBR using coliphages T4

A membrane bioreactor (MBR) with gravity drain was tested for domestic wastewater for 65 days. Results showed that the effluent quality was excellent, and met with the reuse water standard of China (GB/T 18920–2002). Virus removal in the membrane separation process was investigated by employing coliphages T4 as a tracer. Two microfiltration membrane modules, with pore sizes of 0.22 and 0.1 μm, were used to investigate their effects on virus rejection at the transmembrane pressure of 8.5 kPa. It was found that 0.1 μm, membrane had complete rejection of virus, and 0.22 μm, membrane had significant rejection of virus. In the longterm operation of this MBR, no significant difference was observed between both pore sizes because the virus concentrations of the effluent in both cases were in the same order. Effluent virus concentration at steady state of MBR running was less than 2 PFU/mL. The removal ratios of coliphage T4 in MF processes were more than 105.5. The membrane surface deposits played an important role in the rejection of virus. The formation of cake clay on the membrane surface was the main cause of high rejection of coliphage T4 with MF of 0.22 μm.