Xinhua Wang

Integrating microbial fuel cells with anaerobic acidification and forward osmosis membrane for enhancing bio-electricity and water recovery from low-strength wastewater

Microbial fuel cells (MFCs) and forward osmosis (FO) are two emerging technologies with great potential for energy-efficient wastewater treatment. In this study, anaerobic acidification and FO membrane were simultaneously integrated into an air-cathode MFC (AAFO-MFC) for enhancing bio-electricity and water recovery from low-strength wastewater. During a long-term operation of approximately 40 days, the AAFO-MFC system achieved a continuous and relatively stable power generation, and the maximum power density reached 4.38xa0W/m3. The higher bio-electricity production in the AAFO-MFC system was mainly due to the accumulation of ethanol resulted from anaerobic acidification process and the rejection of FO membrane. In addition, a proper salinity environment in the system controlled by the addition of MF membrane enhanced the electricity production. Furthermore, the AAFO-MFC system produced a high quality effluent, with the removal rates of organic matters and total phosphorus of more than 97%. However, the nitrogen removal was limited for the lower rejection of FO membrane. The combined biofouling and inorganic fouling were responsible for the lower water flux of FO membrane, and the Desulfuromonas sp. utilized the ethanol for bio-electricity production was observed in the anode. These results substantially improve the prospects for simultaneous wastewater treatment and energy recovery, and further studies are needed to optimize the system integration and operating parameters.

Impacts of inorganic draw solutes on the performance of thin-film composite forward osmosis membrane in a microfiltration assisted anaerobic osmotic membrane bioreactor

The influences of inorganic draw solutes on the performance of the thin-film composite forward osmosis (TFC–FO) membrane in microfiltration (MF) assisted anaerobic osmotic membrane bioreactors (AnMF–OMBRs) were investigated in this study. The results indicated that compared to sodium chloride (NaCl) at the same osmotic pressure, magnesium chloride (MgCl2) led to a higher flux decline of the TFC–FO membrane, induced by more severe membrane fouling. In addition, the NaCl and MgCl2 had no impacts on the rejection for organic matters by the TFC–FO membrane. However, the NH4+–N rejection of TFC–FO membrane was neglected in the AnMF–OMBR with NaCl as draw solute, while it was enhanced to a range of 57.5–87.6% for the draw solute MgCl2. The different NH4+–N rejection and membrane fouling of TFC–FO membrane with draw solutes NaCl and MgCl2 could be attributed to the Donnan potential. As for NaCl, more Na+ diffused into the mixed liquor resulting in NH4+–N passing through the TFC–FO membrane to the draw solution for keeping a charge balance. With regard to MgCl2, more Cl− passing through the FO membrane to the mixed liquor led to an accumulation of NH4+–N in the reactor. Moreover, Mg2+ passing from the draw solution to the mixed liquor enhanced the biofouling on the active layer of the FO membrane, and in the meanwhile more anions passing to the draw solution aggravated the inorganic fouling of the support layer.

Effect of short-term alkaline intervention on the performance of buffer-free single-chamber microbial fuel cell

Anolyte acidification is a drawback restricting the electricity generation performance of the buffer-free microbial fuel cells (MFC). In this paper, a small amount of alkali-treated anion exchange resin (AER) was placed in front of the anode in the KCl mediated single-chamber MFC to slowly release hydroxyl ions (OH-) and neutralize the H+ ions that are generated by the anodic reaction in two running cycles. This short-term alkaline intervention to the KCl anolyte has promoted the proliferation of electroactive Geobacter sp. and enhanced the self-buffering capacity of the KCl-AER-MFC. The pH of the KCl anolyte in the KCl-AER-MFC increased and became more stable in each running cycle compared with that of the KCl-MFC after the short-term alkaline intervention. The maximum power density (Pmax) of the KCl-AER-MFC increased from 307.5mW·m-2 to 542.8mW·m-2, slightly lower than that of the PBS-MFC (640.7mW·m-2). The coulombic efficiency (CE) of the KCl-AER-MFC increased from 54.1% to 61.2% which is already very close to that of the PBS-MFC (61.9%). The results in this paper indicate that short-term alkaline intervention to the anolyte is an effective strategy to further promote the performance of buffer-free MFCs.

Preparation of conductive microfiltration membrane and its performance in a coupled configuration of membrane bioreactor with microbial fuel cell

A conductive flat microfiltration membrane (G-FM) was prepared with polyvinylidene fluoride (PVDF), N-methyl-2-pyrrolidone (NMP), polyvinyl pyrrolidone (PVP) and reduced graphene oxide (RGO) on stainless steel mesh base by the method of immersion-precipitation phase transformation. The pure water flux and mean pore size of the prepared G-FM were 712 ± 62 L m−2 h−1 bar−1 and 0.09 ± 0.01 μm, respectively. Equipped with the prepared G-FM, the coupled configurations of membrane bioreactor (MBR) with microbial fuel cell (MFC) removed 96.6% ± 3.9% COD, 95.8% ± 5.7% NH3–N and 94.7% ± 5.2% total nitrogen and generated 349 ± 19 mW m−2 bioelectricity from the synthetic municipal wastewater. Moreover, the membrane fouling was reduced due to enhanced hydrophilicity and electrostatic repulsive forces. The coupled configuration with the G-FM presents a bright future in the field of wastewater treatment and greatly promotes the practical application of MBR and MFC.

Insight into the distribution of metallic elements in membrane bioreactor: Influence of operational temperature and role of extracellular polymeric substances

The distribution of metallic elements in a submerged membrane bioreactor (MBR) was revealed at different temperatures using inductively coupled plasma-optical emission spectrometry (ICP-OES), and the role of extracellular polymeric substances (EPS) was probed by integrating scanning electron microscopy (SEM) with confocal laser scanning microscopy (CLSM) over long-term operation. More metallic elements in the influent were captured by suspended sludge and built up in the fouling layer at lower temperature. The concentration of metallic elements in the effluent was 5.60mg/L at 10°C operational temperature, far lower than that in the influent (51.35mg/L). The total contents of metallic elements in suspended sludge and the membrane fouling layer increased to 40.20 and 52.19mg/g at 10°C compared to 35.14 and 32.45mg/g at 30°C, and were dominated by the organically bound fraction. The EPS contents in suspended sludge and membrane fouling layer sharply increased to 37.88 and 101.51mg/g at 10°C, compared to 16.87 and 30.03mg/g at 30°C. The increase in EPS content at lower temperature was responsible for the deposition of more metallic ions. The strong bridging between EPS and metallic elements at lower temperature enhanced the compactness of the fouling layer and further decreased membrane flux. This was helpful for understanding the mechanism of membrane fouling at different operational temperatures and the role of EPS, and also of significance for the design of cleaning strategies for fouled membranes after long-term operation.

Simultaneously recovering electricity and water from wastewater by osmotic microbial fuel cells: Performance and membrane fouling

AbstractSince the concept of the osmotic microbial fuel cell (OsMFC) was introduced in 2011, it has attracted growing interests for its potential applications in wastewater treatment and energy recovery. However, forward osmosis (FO) membrane fouling resulting in a severe water flux decline remains a main obstacle. Until now, the fouling mechanisms of FO membrane especially the development of biofouling layer in the OsMFC are not yet clear. Here, the fouling behavior of FO membrane in OsMFCs was systematically investigated. The results indicated that a thick fouling layer including biofouling and inorganic fouling was existed on the FO membrane surface. Compared to the inorganic fouling, the biofouling played a more important role in the development of the fouling layer. Further analyses by the confocal laser scanning microscopy (CLSM) implied that the growth of biofouling layer on the FO membrane surface in the OsMFC could be divided into three stages. Initially, microorganisms associated with ß-D-glucopyranose polysaccharides were deposited on the FO membrane surface. After that, the microorganisms grew into a biofilm caused a quick decrease of water flux. Subsequently, some of microorganisms were dead due to lack of nutrient source, in the meantime, polysaccharide and proteins in the biofouling layer were decomposed as nutrient source, thus leading to a slow development of the biofouling layer. Moreover, the microorganisms played a significant role in the formation and development of the biofouling layer, and further studies are needed to mitigate the deposition of microorganisms on FO membrane surfaces in OsMFCs.n

Enhanced bioelectricity generation of air-cathode buffer-free microbial fuel cells through short-term anolyte pH adjustment

Short-term initial anolyte pH adjustment can relieve the performance deterioration of the single-chamber air-cathode buffer-free microbial fuel cell (BFMFC) caused by anolyte acidification. Adjusting the initial anolyte pH to 9 in 5 running cycles is the optimum strategy. The relative abundance of the electrochemically active Geobacter in the KCl-pH9-MFC anode biofilm increased from 59.01% to 75.13% after the short-term adjustment. The maximum power density (Pmax) of the KCl-pH9-MFC was elevated from 316.4mW·m-2 to 511.6mW·m-2, which was comparable with that of the PBS-MFC. And, after the short-term adjusting, new equilibrium between the anolyte pH and the anode biofilm electrochemical activity has been established in the BFMFC, which ensured the sustainability of the improved bioelectricity generation performance.

Anolyte recycling enhanced bioelectricity generation of the buffer-free single-chamber air-cathode microbial fuel cell

Anolyte acidification is an inevitable restriction for the bioelectricity generation of buffer-free microbial fuel cells (MFCs). In this work, acidification of the buffer-free KCl anolyte has been thoroughly eliminated through anolyte recycling. The accumulated HCO3- concentration in the recycled KCl anolyte was above 50mM, which played as natural buffer and elevated the anolyte pH to above 8. The maximum power density (Pmax) increased from 322.9mWm-2 to 527.2mWm-2, which is comparable with the phosphate buffered MFC. Besides Geobacter genus, the gradually increased anolyte pH and conductivity induced the growing of electrochemically active Geoalkalibacter genus, in the anode biofilm. Anolyte recycling is a feasible strategy to strengthen the self-buffering capacity of buffer-free MFCs, thoroughly eliminate the anolyte acidification and prominently enhance the electric power.