Yueping Ren

Impacts of sludge retention time on sludge characteristics and membrane fouling in a submerged osmotic membrane bioreactor.

Sludge retention time (SRT) is a feasible method to alleviate the salt accumulation in the osmotic membrane bioreactor (OMBR) by discharging the waste activated sludge. In this study, effects of SRT on sludge characteristics and membrane fouling were investigated using a submerged OMBR under two SRTs of 10 and 15d. The results showed that the lower SRT was helpful for alleviating the salt accumulation and flux decline. Besides that, the removal of NH3-N was significantly influenced by SRT. SRT also had a strong effect on soluble microbial products (SMP) and microbial activity due to the variation of salinity. Microbial diversity analysis indicated that the high salinity environment in the OMBR significantly affected the microbial communities. The flux decline in the OMBR was mainly attributed to the reduced driving force resulting from the salt accumulation, and the reversible fouling was the dominant forward osmosis (FO) membrane fouling in the OMBR.

Integration of micro-filtration into osmotic membrane bioreactors to prevent salinity build-up.

The high salinity remains as one of major obstacles of the osmotic membrane bioreactor (OMBR). In this study, a new pathway was explored to prevent the salinity build-up by integrating the micro-filtration (MF) membrane to the OMBR (MF-OMBR). The results indicated that the salinity characterized by conductivity in the MF-OMBR was effectively alleviated and controlled at a lower value of about 5 mS/cm, and the stable flux of forward osmosis (FO) membrane correspondingly increased to approximately 5.5L/(m(2)h). Besides, the addition of MF membrane in the OMBR could increase the total organic carbon (TOC) and ammonium nitrogen (NH3-N) removals due to the activated sludge by improving the microbial activity. The membrane fouling especially the reversible fouling in the MF-OMBR was severer compared to that in the conventional OMBR, which resulted in a lower water flux than the expectation due to the increase of filtration resistance and external concentration polarization.

Comparison of biofouling mechanisms between cellulose triacetate (CTA) and thin-film composite (TFC) polyamide forward osmosis membranes in osmotic membrane bioreactors

There are two types of popular forward osmosis (FO) membrane materials applied for researches on FO process, cellulose triacetate (CTA) and thin film composite (TFC) polyamide. However, performance and fouling mechanisms of commercial TFC FO membrane in osmotic membrane bioreactors (OMBRs) are still unknown. In current study, its biofouling behaviors in OMBRs were investigated and further compared to the CTA FO membrane. The results indicated that β-D-glucopyranose polysaccharides and microorganisms accounted for approximately 77% of total biovolume on the CTA FO membrane while β-D-glucopyranose polysaccharides (biovolume ratio of 81.1%) were the only dominant biofoulants on the TFC FO membrane. The analyses on the biofouling structure implied that a tighter biofouling layer with a larger biovolume was formed on the CTA FO membrane. The differences in biofouling behaviors including biofoulants composition and biofouling structure between CTA and TFC FO membranes were attributed to different membrane surface properties.

A monolithic three-dimensional macroporous graphene anode with low cost for high performance microbial fuel cells

Microbial fuel cells (MFCs), capable of simultaneously degrading substrates and producing bioelectricity, have drawn great attention. However, low power output and high cost have severely hindered their practical application. The present study prepared a monolithic three-dimensional graphene (3D-G) electrode through a self-assembly method. The as-prepared 3D-G electrode featured inflexibility, a crumpled surface, a macroporous structure (with pore spaces of dozens of microns), high specific surface area (188.32 m2 g−1), good conductivity and low cost, favoring high bacterial loading capacity and enhancing the extracellular electron transfer (EET) efficiency. Equipped with the prepared 3D-G anode in an air-cathode single chamber MFC reactor, the maximum power density (Pmax) increased to 1516 ± 87 mW m−2 in the 3D-G reactor from 877 ± 57 mW m−2 in the graphite felt (GF) control and from 584 ± 39 mW m−2 in the carbon cloth (CC) control after 2 weeks of operation. Moreover, the Pmax of the reactor with the 3D-G anode decreased only by 15% after 2 months of operation, which showed durability of the anode due to having macropores which are not easily blocked. Normalized to the cost of the anode, the Pmax in the 3D-G reactor was 93 and 133 times those in the GF and CC reactors, respectively. Dynamic analysis results (CV, Tafel and EIS) showed that the 3D-G anode improved the efficiency of EET due to having an appropriate structure and good conductivity. The 3D-G anode, with superior performance and low cost, would powerfully promote the practical and large-scale application of MFCs.

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.

Effect of Fe(III) on the performance of sediment microbial fuel cells in treating waste-activated sludge

Chemical energy stored in organic waste can be directly converted into electricity using sediment microbial fuel cell (SMFC) technology. The present study showed that adding Fe(III) enhanced the generation of electricity and degradation of waste-activated sludge (WAS) by increasing the content of c-type cytochromes (Cyt c) within the anode biofilm of SMFC reactors. With addition of 500 mg L−1 Fe(III), the cell voltage increased to 501.0 mV from 187.1 mV and VSS removal of WAS increased to 37.21% from 31.47% in the control. The content of crude Cyt c per mg biomass increased to 13.05 μg mg−1 in the SMFC-500 anode biofilm from 3.86 μg mg−1 in the control. However, the electron-transfer efficiencies of Cyt c were 2.25 mol-electron per μg in the SMFC-500 reactor and 3.64 mol-electron per μg in the control, showing that the addition of Fe(III) slightly inhibited the activity of Cyt c. Purified Cyt c possessed a molecular mass of 24 310 Da with 4.7 mol heme groups, and its secondary structure had 21% α-helix, 13.5% β-sheet, and was 31.3% unordered. Proteobacteria and iron-reducing bacteria within the SMFC anode biofilm were enriched by 500 mg L−1 Fe(III), but this same amount inhibited archaea colonization and decreased the diversity of the microbial community without an obvious difference in the dominant phylum.

Synchronous recovery of iron and electricity using a single chamber air-cathode microbial fuel cell

In recent years, microbial fuel cell (MFC) technology has become an attractive option for metal recovery/removal at the cathode combined with electricity generation, using organic substrates as electron donor at the anode. With no organic substrate supply, a single chamber air-cathode MFC was used to synchronously recover metal and electricity from a real stream containing high-strength metal, sulfate, strong acid and acidophilic chemoautotrophic bacteria (ACB). Instead, ferrous ions were used as electron donor which made the single chamber air-cathode MFC applicable for the (bio)leachate and mining/metallurgical stream sites possibly lacking organics. We showed that 71.8% iron was recovered, and 95.9% ferrous ions were removed from a real iron-laden stream. At the same time, 360.1 mV cell voltage was achieved with 88.1% of coulombic efficiency. In the presence of ACB microbes, the iron recovery and power density were increased by 8.6% and 29.2%, respectively, via promoting the anode electron transferring and preventing sulfur passivation of electrodes. Iron in the form of FeOOH (goethite) was recovered mainly at the anode via the ferrous oxidization to Fe(OH)3. At the cathode, ferrous ions directly combined with oxygen and electrons into FeO, and further into Fe2O3. It was prospective at sites lack of organics to synchronously recover metals and electricity from real metal-laden streams using single chamber air-cathode MFC technology.

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.

Nanoparticle fouling and its combination with organic fouling during forward osmosis process for silver nanoparticles removal from simulated wastewater.

The increasing and wide application of silver nanoparticles (Ag NPs) has resulted in their appearance in wastewater. In consideration of their potential toxicity and environmental impacts, it is necessary to find effective technology for their removal from wastewater. Here, forward osmosis (FO) membrane was applied for Ag NPs removal from wastewater, and single and combined fouling of nanoparticles and organic macromolecules were further investigated during the FO process. The findings demonstrated that FO membrane can effectively remove Ag NPs from wastewater due to its high rejection performance. Fouling tests indicated that water flux declined appreciably even at the beginning of the single Ag NPs fouling test, and more remarkable flux decline and larger amounts of deposited Ag NPs were observed with an increase of Ag NPs concentration. However, the addition of bovine serum albumin (BSA) could effectively alleviate the FO membrane fouling induced by Ag NPs. The interaction between Ag NPs and BSA was responsible for this phenomenon. BSA can easily form a nanoparticle-protein corona surrounded nanoparticles, which prevented nanoparticles from aggregation due to the steric stabilization mechanism. Furthermore, the interaction between BSA and Ag NPs occurred not only in wastewater but also on FO membrane surface.