Mohan Qin

Recovery of nitrogen and water from landfill leachate by a microbial electrolysis cell–forward osmosis system

A microbial electrolysis cell (MEC)-forward osmosis (FO) system was previously reported for recovering ammonium and water from synthetic solutions, and here it has been advanced with treating landfill leachate. In the MEC, 65.7±9.1% of ammonium could be recovered in the presence of cathode aeration. Without aeration, the MEC could remove 54.1±10.9% of ammonium from the leachate, but little ammonia was recovered. With 2M NH4HCO3 as the draw solution, the FO process achieved 51% water recovery from the MEC anode effluent in 3.5-h operation, higher than that from the raw leachate. The recovered ammonia was used as a draw solute in the FO for successful water recovery from the treated leachate. Despite the challenges with treating returning solution from the FO, this MEC-FO system has demonstrated the potential for resource recovery from wastes, and provide a new solution for sustainable leachate management.

Understanding electricity generation in osmotic microbial fuel cells through integrated experimental investigation and mathematical modeling.

Osmotic microbial fuel cells (OsMFCs) are a new type of MFCs with integrating forward osmosis (FO). However, it is not well understood why electricity generation is improved in OsMFCs compared to regular MFCs. Herein, an approach integrating experimental investigation and mathematical model was adopted to address the question. Both an OsMFC and an MFC achieved similar organic removal efficiency, but the OsMFC generated higher current than the MFC with or without water flux, resulting from the lower resistance of FO membrane. Combining NaCl and glucose as a catholyte demonstrated that the catholyte conductivity affected the electricity generation in the OsMFC. A mathematical model of OsMFCs was developed and validated with the experimental data. The model predicated the variation of internal resistance with increasing water flux, and confirmed the importance of membrane resistance. Increasing water flux with higher catholyte conductivity could decrease the membrane resistance.

Understanding Ammonium Transport in Bioelectrochemical Systems towards its Recovery

We report an integrated experimental and simulation study of ammonia recovery using microbial electrolysis cells (MECs). The transport of various species during the batch-mode operation of an MEC was examined experimentally and the results were used to validate the mathematical model for such an operation. It was found that, while the generated electrical current through the system tends to acidify (or basify) the anolyte (or catholyte), their effects are buffered by a cascade of chemical groups such as the NH3/NH4+ group, leading to relatively stable pH values in both anolyte and catholyte. The transport of NH4+ ions accounts for ~90% of the total current, thus quantitatively confirming that the NH4+ ions serve as effective proton shuttles during MEC operations. Analysis further indicated that, because of the Donnan equilibrium at cation exchange membrane-anolyte/catholyte interfaces, the Na+ ion in the anolyte actually facilitates the transport of NH4+ ions during the early stage of a batch cycle and they compete with the NH4+ ions weakly at later time. These insights, along with a new and simple method for predicting the strength of ammonia diffusion from the catholyte toward the anolyte, will help effective design and operation of bioeletrochemical system-based ammonia recovery systems.

Resource recovery by osmotic bioelectrochemical systems towards sustainable wastewater treatment

Recovering valuable resources from wastewater will transform wastewater management from a treatment focused strategy to a sustainability focused strategy, creating a need for new technology development. Osmotic bioelectrochemical systems (OsBESs), an innovative treatment concept which is based on cooperation between bioelectrochemical systems (BESs) and forward osmosis (FO), have been introduced and studied in the past few years. An OsBES can accomplish the simultaneous treatment of wastewater and recovery of resources such as nutrients, energy, and water (NEW). The cooperation can be accomplished in either an internal (integrated OsBES) or external (coupled OsBES) configuration, through a strong synergy between a BES and FO. A BES can provide draw solute, perform pre-treatment, or reduce reverse salt flux to help with FO operation, while FO can achieve water recovery, enhance current generation, and supply energy sources to BES operation. Given that there has been much progress and interest in the OsBES, this paper reviews the previous studies, describes the current status, presents qualitative and quantitative analyses, and discusses the perspectives of the OsBES technology, focusing on NEW recovery from wastewater. The challenges for further research and development of OsBESs have also been identified.