Advances in membrane bioreactor for landfill leachate treatment: A review of characterization, challenges, and novel configurations

Landfill leachate (LFL) is a complex wastewater that poses a serious environmental threat for the public health, owing to the toxic and recalcitrant nature of its components. Hence, an effective treatment is imperative before being discharged into the environment. To ensure an appropriate treatment, a thorough comprehension of LFL physico-chemical properties is essential. In addition to conventional contaminants such as chemical oxygen demand, biochemical oxygen demand, solids, ammonia, metals, recent studies have reported the presence of dissolved organic matter (DOM) and emerging contaminants such as bisphenols, PFAS, xenobiotics in trace concentrations. While conventional detection techniques are chemical and time consuming and reveal limited information regarding DOM, spectroscopic techniques such as UV-visible spectroscopy, Fourier-transform ion cyclotron resonance mass spectrometry, excitation emission matrix fluorescence spectroscopy are comparably more efficient, and effective. Furthermore, the conventional MBR has shown lower efficiency for treating old LFL and removal of heavy metals, phosphorus, micropollutants and recalcitrant. However, novel configurations in MBR such as high-retention MBRs (nanofiltration-MBR, osmotic MBR, and membrane distillation bioreactor), and electrochemical MBR are more effective alternatives with excellent removal efficiencies of micropollutants, and pharmaceuticals. One of the major limitations in MBR is membrane fouling which reduces the lifetime of membrane and in turn increases the operational cost of MBRs. Novel strategies such as electrically or mechanically assisted scouring, chemical cleaning, enzymatic treatment and the development of novel nanomaterialbased membranes have been proposed to mitigate membrane fouling in MBRs. Further, it is essential to decipher the microbial dynamics in MBR which facilitates contaminant removal by using genome sequencing tools and understand the economic and environmental aspects of MBR.