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Organic small molecules doping in polymer carbon nitride (PCN) skeleton can dramatically improve photocatalytic performance owing to its effective regulation effect on molecular and electronic structure. Here, a new PCN-based photocatalyst is obtained via polymerization of urea with 1-benzyl-3-phenylthiourea (BPT). The doping effect of BPT in PCN skeleton directly adjusts the hybridization states and delocalization of molecular orbitals, so that the visible light harvest ability, adsorption capacity, charge separation efficiency and transfer kinetics are improved significantly. Consequently, the photocatalytic hydrogen evolution reaction (HER) rate reaches to 125.0 μmol h−1 over the optimal PCN-BPT15 photocatalyst, which is as 13.9 times as PCN (9.0 μmol h−1). Noteworthily, a high apparent quantum efficiency (AQE) of 24.2% is achieved at 420 nm for photocatalytic HER. This work enriches the functionalized investigations of PCN-like photocatalysts by insight into regulated effect of organic small molecules in the skeleton for photocatalytic applications.

Developing biofilm carriers is of great significance for efficient wastewater treatment. In this work, ferric citrate was used to modify inorganic basalt fiber (BF) biocarrier, thus improving its surface properties and the nitrogen removal in hybrid wastewater treatment system. The results showed that the iron element on modified basalt fiber (Fe-MBF) existed in the forms of ferric citrate, Fe(OH)3, Fe2O3, and FeO. The ferric deposition increased the surface roughness, hydrophilicity and reduced the electronegativity of BF. The water contact angle of BF and Fe-MBF was 117.46° and 64.85°, respectively. The surface zeta potential of BF was -17.64 mV, but shifted positively (-8.67 mV) after deposition modification. The microorganism adhesion tests showed that the attached biomass and extracellular polymeric substances (EPS) content on Fe-MBF biocarrier significantly increased and the attached bacteria had also high viability. The Fe-MBF biocarrier showed good nitrogen removal performance in the hybrid bioreactor, with total nitrogen removal efficiency up to 95.35±0.82%, increasing by about 16% compared to that with unmodified BF biocarrier. This work also provided a green modification strategy to enhance biofilm carrier in wastewater treatment.

In this study, baffled anaerobic-aerobic reactors (AOBRs) with modified basalt fiber (MBF) carriers and felt were used to treat domestic wastewater (DWW). The influent was first treated in anaerobic compartments, with the NH

Numerous studies have shown that zinc oxide nanoparticles (nZnO) have an inhibitory effect on wastewater biotreatment, where doses exceeding ambient concentrations are used. However, the effect of ambient concentrations of ZnO (1 mg/L) on anaerobic digestion processes is not clear. Herein, this study comprehensively explored the impact of nZnO on the denitrification performance and core microbial community of activated sludge under ambient concentrations. Results showed that only 0.075 mg/L nZnO had shown a beneficial effect on nitrogen removal by activated sludge. When nZnO concentration reached 0.75 mg/L, significant enhancement of nitrate reduction and mitigation of nitrite accumulation were observed, indicating a remarkable stimulatory effect on nitrogen removal. Simultaneously, nZnO could weaken the sludge surface charge and improve the secretion of extracellular polymeric substances, thus enhancing sludge flocculation for denitrification. Microbial community analysis revealed that nZnO exposure increased the relative abundance of denitrifying bacteria, which could contribute to the reinforcement of traditional denitrification. Furthermore, exogenous addition of NH

In this report, environmental and energy issues were deal with a Z-scheme photocatalytic system toward the synthetic ammonia by N2 photofixation. Different from traditional double-charge-transfer model, a direct all-solid-state Z-scheme system of modified TiO2 (MT) loaded with ZnFe2O4 (ZFO) was obtained by solvothermal-calcination method, in which calcination temperature is crucial for the mesoporous structure and formation of Z-scheme TiO2/ZnFe2O4. At ambient temperature and pressure, the MT/ZFO photocatalyst presented the ammonia generation rate of about 1.48 μmol/L/min, which is higher than that of single MT or ZFO. The photocatalytic activity enhancement of ammonia generation was attributed to the Z-scheme charge transfer model with a more negative reduction potential in the conduction band of ZnFe2O4. Combining the commonly TiO2 and ZnFe2O4 by a special method shows a desirable Z-scheme photocatalytic system, which can be extended to the fabrication of other Z-scheme photocatalyst according to the various application need.

In this work, a novel hydrophilic reactive polyurethane (HRPU) material and HRPU-based composite materials were prepared and used as chemical anti-water erodibility materials for Pisha sandstone. The compressive strength, surface hardness, penetrability and water contact angle were investigated. The results showed that the deformation rate of Pisha sandstone sprayed with HRPU/ethylene-vinyl acetate (EVA) material was approximately 15%, significantly larger than that of other Pisha sandstone samples, while the compressive strength was significantly improved, providing a good penetrability to form a hydrophobic consolidation layer, locking the water in soil. Meanwhile, the micro-morphology of Pisha sandstone was observed by scanning electron microscopy (SEM) images and the water retaining ability of HRPU/EVA material was discussed in detail. The results showed that the water content of Pisha sandstone sprayed with HRPU/EVA material could reach more than 20%, even after 16 h, which presented an excellent water retaining ability. In addition, the anti-water erodibility of Pisha sandstone with HRPU/EVA was improved to prevent soil and water loss, and provide some feasibility for growing plants. Therefore, it could provide a new material and idea to protect the Pisha sandstone area and other erosion areas.

Bio-carrier plays important roles in the performance of biological contact oxidation reactors for wastewater treatment. Most of the conventional bio-carriers are polymeric. Developing more sustainable materials is necessary to reduce the overconsumption of petrochemicals and second pollution after disposal. This work studied the inorganic basalt fiber (BF) fabricated from nature basalt rock as a green and sustainable bio-carrier medium for wastewater treatment. To improve the bio-affinity, the silica-based BF was modified with a hydrophilic cationic polymer (hexadecyl trimethyl ammonium chloride, CTAC). The modified basalt fiber (MBF) showed a more hydrophilic and positively charged surface. The bio-affinity of BF and MBF bio-carriers were evaluated in Bacillus subtilis adhesion and activated sludge immobilization tests. The influence of CTAC coating on the initial adhesion of bacteria and subsequent biomass immobilization was investigated. The results showed that MBF bio-carriers had higher biomass attachment capacity and microorganism diversity with shorter biofilm formation time. The reported MBF provided an environmental-friendly, sustainable and economical alternative to conventional bio-carriers for wastewater treatment.

Surface properties of carrier are critical for microorganism initial adhesion and biofilm formation in wastewater treatment. Until now, there are few reports on adhesion behaviors between bacteria and inorganic fiber surface. In this study, inorganic basalt fiber (BF) was modified with cationic polyacrylamide (CPAM) to make surface more hydrophilic and positively charged. The initial adhesion behaviors of BF modified with CPAM (CMBF) were interpreted by thermodynamics and extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. According to the total interaction energy calculated by the extended DLVO theory, insurmountable energy barrier between BF and Escherichia coli (E. coli) made irreversible adhesion unachievable due to hydrophobicity and electronegativity of BF, but allowed reversible adhesion at second minimum. By contrast, the energy barrier between CMBF and E. coli could be overcome allowing irreversible bacterial adhesion and thus a huge amount of biomass because of hydrophilicity and electropositivity of CMBF. The results showed the total interaction energies were dominated by Lewis acid-base and electrostatic interactions and coating BF with CPAM could promote initial bacterial adhesion on carrier surface. Overall, the extended DLVO theory provides a comprehensive tool to interpret initial adhesion behaviors between bacteria and inorganic fibers.

The traditional biological nitrogen removal (BNR) follows the conventional scheme of sequential nitrification and denitrification. In recent years, novel processes such as anaerobic ammonia oxidation (anammox), complete oxidation of ammonia to nitrate in one organism (comammox), heterotrophic nitrification and aerobic denitrification (HN-AD), and dissimilatory nitrate reduction to ammonium (DNRA) are gaining tremendous attention after the discovery of metabolically versatile bacteria. Among them, HN-AD offers several advantages because individual bacteria could achieve one-stage nitrogen removal under aerobic conditions in the presence of organic carbon. In this review, besides classical BNR processes, we summarized the existing literature on HN-AD bacteria which have been isolated from diverse habitats. A particular focus was given on the diversity and physiology of HN-AD bacteria, influences of physiological and biochemical factors on their growth, nitrogen removal performances, as well as limitations and strategies in unraveling HN-AD metabolic pathways. We also presented case studies of HN-AD application in wastewater treatment facilities, pointed out forthcoming challenges of HN-AD in these systems, and presented modulation strategies for HN-AD application in engineering. This review may help improve the existing design of wastewater treatment plants by harnessing HN-AD bacteria for effective nitrogen removal.

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Developing biofilm carriers is of great significance for efficient wastewater treatment. In this work, ferric citrate was used to modify inorganic basalt fiber (BF) biocarrier, thus improving its surface properties and the nitrogen removal in hybrid wastewater treatment system. The results showed that the iron element on modified basalt fiber (Fe-MBF) existed in the forms of ferric citrate, Fe(OH)

The carrier medium plays a key role in improving existing remediation potential of conventional biological contact oxidation reactors. In this study, a biological contact oxidation r eactor was constructed using b asalt f iber (R-BF) as a biological carrier. The bioreactor performance was investigated in terms of reduction in chemical oxygen demand (COD), ammonium nitrogen (NH4+-N), and total nitrogen (TN) at organic loadings rate of 15.243 kg/m3·d and nitrogen loading rate of 1.068 kg/m3·d. We found that COD, NH4+-N, and TN were reduced to 99.1%, 97.9%, and 97.8%, respectively. Within the R-BF, a bio-nest was developed which had abundant pores and channels and supported successful movement of nutrients, resulting in high biological activity (55.78%). The microbial communities within the bio-nest were diverse and rich and sludge production during operation was minimal. This makes BF a promising application for wastewater treatment. This research might be useful in the construction of integrated bioreactors that can operate under high organic and nitrogen loadings rates with reduced energy consumption, i.e. 75% in this study.

Classical adsorbents such as activated carbon are inefficient to remove Cu(II)-EDTA in solution. Moreover, the heavy metals in the generated sludge can easily be dissolved back into solution. In this research, a novel strategy developed by coupling green rust adsorption and ferrite formation technology was proposed for Cu(II)-EDTA chelate removal. At the adsorption stage, green rust sulfate (GRME(SO42−)) showed a high adsorption efficiency of chelated copper, with a capacity of 126.41 mg g−1, compared to other classical adsorbents. During the ferrite formation stage, GRME(SO42−)-based precipitate with high moisture content and slow settling rate could be transformed into ferrite-based precipitate with low moisture content and rapid settling rate. The volume and moisture content of ferrite were 2.20 and 1.45 times lower than those of GRME(SO42−) and the sedimentation velocity of ferrite was also 1.23 times higher than that of GRME(SO42−), which strongly demonstrated the necessity of the ferrite formation process. Toxicity characteristic leaching procedure (TCLP) test results showed that the metallic copper of GRME(SO42−) sludge could be more easily dissolved back into solution than that of ferrite precipitate under weak-acid conditions, indicating the stability of ferrite. In addition, after the ferrite process, the generated sludge exhibited soft magnetism and could be quickly separated within few seconds using an external magnetic field. All these results showed that the combined green rust adsorption with ferrite formation method was an efficient, recyclable and eco-friendly method for the treatment of wastewater containing Cu(II)-EDTA.

Heavy metals usually coexist with a variety of chelating agents to form heavy metal complexes in industrial wastewater. The decomplexation of heavy metal complexes is the crucial step before the removal of heavy metals via alkaline precipitation process. An efficient synergistic activation of persulfate (PS) with alkali and CuO was used for the simultaneous decomplexation of Cu-ethylenediamine tetraacetic acid (Cu(II)-EDTA) (3.14 mM) and the Cu(II) precipitation. The experimental results demonstrated that nearly complete removal of Cu(II) could be achieved by synergistic activation of PS with alkali and CuO at pH 11 after 2 h of decomplexation reaction. However, sole PS could not effectively decomplex Cu(II)-EDTA (13.5%), while the alkaline activation of PS could accomplish 57.0% removal of Cu(II). Radical scavenger tests indicated that reactive oxygen species (ROS) including SO

Generally, biofilms developed for wastewater treatment readily detach from carrier medium once available thickness exceeds about 2 mm. Carrier media made of basalt fibers (BFs) could form ball-like aggregates (more than 10 cm in size, and called bio-nest). To demonstrate its feasibility for wastewater treatment, both reactors with and without BF carriers (R BF and R CO) were evaluated in terms of nutrient removal, oxygen mass transport and biological viabilities as well as biofilm adsorption characteristics. Therefore, oxygen microprofiles and confocal images for bio-nest as well as functional groups for biofilm-attached BF were performed on microsensor systems, confocal laser scanning microscopy (CLSM) and Fourier transform infrared (FTIR). Despite COD:N ratio, both reactors removed about 90% of COD, while only R BF reactor achieved high denitrification capabilities, with nitrogen removal efficiencies varying between 60.10 ± 0.45% and 82.07 ± 0.64%. Microprofile and confocal images showed that dissolved oxygen could reach the core with depth up to 50 mm, at which viable bacteria were detected. Characteristic peaks on FT-IR spectrum demonstrated that various functional groups of polysaccharide and proteins in EPS played a key role in aggregating biofilm-attached BFs into a bio-nest. Thus, BF provides a promising alternative to conventional carrier medium for wastewater treatment.

The N2 photofixation has been considered as a green and eco-friendly ammonia synthesis approach. In this work, Bi2Te3 was employed to modify BiOCl for the formation of a highly active composited micro flower-like structure photocatalyst. Efficient ammonia evolution rate reached 315.9 μmol/L·h over Bi2Te3/BiOCl under UV light irradiation. Based on the analysis of bandgap and reduction potential of two components, the electrons generated from BiOCl is attributed to the N2 photofixation, while the photogenerated charges from the excitation of Bi2Te3 suppress the recombination of photogenerated hole-electron of BiOCl effectively.

Cross-weaved basalt fiber fabric (CBFF) woven from basalt fiber (BF), as a natural inorganic product, which presented a highly research value and widely application field, due to its high chemical stability, non-toxic, non-combustible and sound mechanical property. (Super)hydrophobic surface has recently received extraordinary attention, focusing both on novel preparation-used materials and application. In this work, cross-weaved basalt fiber fabric was synergistically decorated by MnO2 nanosheets/stearic acid (SA) and the superhydrophobic inorganic/organic composite (CBFF@MnO2/SA) was obtained by hydrothermal processes. MnO2 nanosheets self-assembled on the surface of CBFF (CBFF@MnO2) presented honeycomb roughness with the micro/nanometer-sized spaces among the MnO2 nanosheets. The water contact angles of CBFF, CBFF@MnO2 and CBFF@MnO2/SA samples were 21.6, 120.0 and 155.5°, respectively. The result indicated that cross-weaved basalt fiber fabric exhibited an obvious superhydrophobic property after the modification by MnO2 nanosheets and stearic acid. The as-prepared materials were applied in the simulation of oil/water separation and anti-icing process. Oil/water separation results not only displayed the separation efficiency up 95.0% by selective absorption for light oil/water system, but also showed the separation efficiency above 97.2% by filtration of oil for heavy oil/water system. Furthermore, CBFF@MnO2/SA could be used as the filter membrane in dynamic suction filtration device for oil recovery in oil spill accidents. Anti-icing experiments demonstrated that prepared CBFF@MnO2/SA had an obviously ice-over delay with the value of 166.6%.

Inspired by the multi-enzymes cascade catalysis, a novel photon-enzyme cascade catalysis system described as hybrid HRP-CN/Cu3(PO4)2 nanoflowers was constructed successfully for the first time. It not only exhibits excellent immobilized enzyme enzymatic properties but also has better tolerance to extreme acid, alkali and high temperature compared with the free HRP. Moreover, the encapsulation yield of HRP reaches up to 36.2% and the residual activity after 5 cycles still has 83.6% over HRP-CN/Cu3(PO4)2 catalyst. Specifically, the HRP-CN/Cu3(PO4)2 showed excellent degradation performance for bisphenol A (BPA), which reached up to 72.98% far more than that of CN/Cu3(PO4)2 (41.89%) and HRP/Cu3(PO4)2 (4.71%). Those unique advantages are mainly owing to the introduction of photocatalyst (g-C3N4), which not only increases the encapsulation yield of HRP, but also realizes the complete mineralization of BPA. The photon-enzyme cascade catalysis system could replace the traditional system composed of glucose oxidase and horseradish peroxidase (GOx&HRP) for the harmless treatment of BPA, providing a new strategy for HRP in wastewater treatment.

Support carrier constitutes the technical core of biofilm processes in wastewater treatment. In this study, basalt fiber (BF) was modified by grafting an organic/inorganic composite, attached to which rich microorganisms were supposed to form biofilm for wastewater treatment. The modified BF (MBF) used as biofilm carriers were investigated in terms of hydrophilicity and surface roughness, which determined their bioaffinity. Fourier transforms infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS) were conducted to study the chemical components. Scanning electron microscopy (SEM) was carried out to observe BF surface morphology. The bioaffinity of BF and MBF was compared in terms of the rate of bacterial adhesion and the ratio of immobilization onto basalt fiber. The bioaffinity of MBF was significantly improved due to introduction of many hydrophilic groups onto BF surfaces, which were subsequently proved to facilitate biofilm formation. The results s...

Modified basalt fiber (MBF) is a sustainable material studied as novel wastewater treatment bio-carrier recently. This work studied the effects of calcium modification on the bacterial affinity of modified fiber (Ca-MBF), bacterial community, and nitrogen removal performance. Results showed that Ca-MBF with hydrophilic (62.66°) and positively-charged (7.80 mV) surface accelerated bacterial attachment. Volatile suspended solids on Ca-MBF (5.46 g VSS/g fiber) were increased by 2.61 times after modification, with high bacterial activity when bio-carriers were cultured in activated sludge. Extracellular polymeric substances on Ca-MBF was 4.35 times higher and consisted of more protein. Bio-nests with unique aerobic/anaerobic structure formed on the ultrafine carriers in bioreactor. Ca-MBF bioreactor exhibited total nitrogen removal efficiency above 72.2% and COD removal efficiency above 94.2% with more stable performance than unmodified carrier in long-term treatment using synthetic domestic wastewater.16S rRNA gene sequencing revealed enhanced abundance of nitrifying and denitrifying bacteria in Ca-MBF bio-nest.

In this study, environment-friendly inorganic basalt fiber (BF) was used as bio-carrier for wastewater treatment. To enhance the bio-affinity, raw BF was modified by grafting the diethylamino functional groups to make the surface more hydrophilic and electro-positive. Contact angle and zeta potential of modified basalt fiber (MBF) were characterized. The capacity of MBF bio-carriers was evaluated by microorganism immobilization tests. To explain the mechanism of capacity enhancement by modification, the profiles of total interaction energy barrier between raw BF (or MBF) and bacteria (Escherichia coli, E. coli) were discussed based on the extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The results showed the contact angle of fiber decreased from 89.71° to 63.08° after modification, and zeta potential increased from - 18.53 to +10.58 mV. The microorganism immobilization tests showed that the surface modification accelerated the initial bacterial adhesion on fiber. The total interaction energy barrier between MBF and E. coli disappeared as a result of electrostatic and hydrophilic attractive forces, and enhanced the irreversible adhesion. MBF bio-carrier medium provides a promising alternative to conventional bio-carrier materials for wastewater treatment. Graphical abstract.

A solid state ferricarboxylate photocatalyst, magnetite/carboxylate-rich carbon sheets (MCRCSs), was synthesized in air via a low-temperature carbonization process. In the structure of MCRCSs, both Fe3O4 nanoparticles and EDTA are homogeneously dispersed into carbon sheets forming ferricarboxylate complexes. Abundant ferricarboxylate complexes endow the MCRCSs with marked visible light absorption properties. MCRCSs exhibit excellent visible-light-driven photoreduction activities of Cr(VI). Fe(II), O2˙−, and carboxylate radicals (R-COO)n3−n* produced from the Fe(II)/Fe(III) photoredox cycle of MCRCSs are the main reductants for the reduction of Cr(VI). After the photoreduction of Cr(VI), MCRCSs can be magnetically separated from aqueous solution easily. Unlike a conventional ferricarboxylate photocatalyst (homogeneous and heterogeneous) fabricated from two components, iron species (dissolved or solid) and dissolved low-molecular-weight carboxylic acids, MCRCSs exist in the all solid state and every particle of MCRCSs is an individual unit which can release active radicals O2˙− by itself. The special nature of the all solid state will simplify the operation process of MCRCSs.

A hybrid photoelectrochemical and microbial fuel cell (HPMFC) is constructed for simultaneous utilization of solar energy and bioenergy by installing a TiO2 photoanode next to a bioanode that shares the same cathode in a microbial fuel cell (MFC). Connecting the photoelectrochemical (PEC) circuit results in enhanced cathode potentials for the MFC based on the differences in power output characteristics of MFC and PEC alone. The improved power production of the MFC is accompanied by a relatively small decline in the power density of the PEC, yielding an overall enhancement in power output for the HPMFC.

Electrochemically active bacteria (EAB) are effective for the bioreduction of nitroaromatic compounds (NACs), but the exact reduction mechanisms are unclear yet. Therefore, 3-nitrobenzenesulfonate (NBS) was used to explore the biodegradation mechanism of NACs by EAB. Results show that NBS could be anaerobically degraded by Shewanella oneidensis MR-1. The generation of aminoaromatic compounds was accompanied with the NBS reduction, indicating that NBS was biodegraded via reductive approach by S. oneidensis MR-1. The impacts of NBS concentration and cell density on the NBS reduction were evaluated. The removal of NBS depends mainly on the transmembrane electron transfer of S. oneidensis MR-1. Impairment of Mtr respiratory pathway was found to mitigate the reduction of NBS, suggesting that the anaerobic biodegradation of NBS occurred extracellularly. Knocking out cymA severely impaired the extracellular reduction ability of S. oneidensis MR-1. However, the phenotype of ΔcymA mutant could be compensated by the exogenous electron mediators, implying the trans-outer membrane diffusion of mediators into the periplasmic space. This work provides a new insight into the anaerobic reduction of aromatic contaminants by EAB.

An energy-efficient and environmentally friendly nitrogen fixation process is urgently needed for cleaner ammonia production. In this study, a Z-scheme single-layer g-C3N4/ZnFe2O4 photocatalyst was designed, characterized and used for the cleaner production of ammonia by N2 photofixation. From the N2 photofixation evaluation experiments, the ammonia generation concentration reached about 122.3 μmol/L in 120 min. In this ammonia production process, the design of a visible-light-driven photocatalyst was energy-saving and environmentally friendly without CO2 emission, which are potential advantages in the field of nitrogen fixation.

A looming global energy crisis has directly increased biomethanation processes using anaerobic digestion technology. However, much knowledge on the microbial community structure, their distribution within the digester and related functions remains extremely scanty and unavailable in some cases, yet very valuable in the improvement of the anaerobic bioprocesses. Using pyrosequencing technique based on Miseq PE 3000, microbial community population profiles were determined in an operated mesophilic expanded granular sludge bed (EGSB) reactor treating beet sugar industrial wastewater (BSIW) in the laboratory scale. Further, the distribution of the organisms in the lower, middle and upper sections within the reactor was examined. To our knowledge, this kind of analysis of the microbial community in a reactor treating BSIW is the first of its kind. A total of 44,204 non-chimeric reads with average length beyond 450 bp were yielded. Both bacterial and archaeal communities were identified with archaea predominance (60 %) observed in the middle section. Bayesian classifier yielded 164 families with only 0.73 % sequences which could not be classified to any taxa at family level. The overall phylum predominance in the reactor showed Firmicutes, Euryarchaeota, Chloroflexi, Proteobacteria and Bacteroidetes in the descending order. Our results clearly demonstrate a highly diverse microbial community population of an anaerobic reactor treating BSIW, with distinct distribution levels within the reactor.

A nitrogen-doped activated carbon (NDAC) as a cathode catalyst in microbial fuel cells (MFCs) was synthesized by a microwave-assisted method using ammonium carbonate as a nitrogen source. The prepared NDAC showed a higher BET surface area of up to 1717.8 m2 g−1 and a total pore volume of 0.79 cm3 g−1. X-ray photoelectron spectroscopic analysis demonstrated that N was successfully doped on the surface of AC in three species, corresponding to pyrrolic N, pyridinic N and pyridine-N-oxide. Compared with untreated AC, the NDAC exhibited better electrocatalytic activity for the oxygen reduction reaction in rotating disk electrode tests, with a current density of 12.4 mA cm−2 at a set potential of −0.8 V (vs. SCE) (AC, 11.3 mA cm−2) and an electron transfer number of 3.14 (AC, n = 2.83). MFCs equipped with a NDAC cathode achieved a higher maximum power density of 471 ± 11 mW m−2 when fed with domestic wastewater, which was 1.3 times higher than that of the AC cathode. It also displayed long-term operation stability when dealing with real wastewater, indicating a promising cathode catalyst for MFCs towards practical applications.

A continuous stirred microbial electrochemical reactor (CSMER) was developed by integrating anaerobic digestion (AD) and microbial electrochemical system (MES). The system was capable of treating high strength artificial wastewater and simultaneously recovering electric and methane energy. Maximum power density of 583 ± 9, 562 ± 7, 533 ± 10 and 572 ± 6 mW m−2 were obtained by each cell in a four-independent circuit mode operation at an OLR of 12 kg COD m−3 d−1. COD removal and energy recovery efficiency were 87.1% and 32.1%, which were 1.6 and 2.5 times higher than that of a continuous stirred tank reactor (CSTR). Larger amount of Deltaproteobacteria (5.3%) and hydrogenotrophic methanogens (47%) can account for the better performance of CSMER, since syntrophic associations among them provided more degradation pathways compared to the CSTR. Results demonstrate the CSMER holds great promise for efficient wastewater treatment and energy recovery.

Azide could be used as an oxidant in the cathodic reaction in BESs, and produced a peak current of 0.37 mA. An estimation based on electron balance showed that azide reduction at the abiotic cathode was an eight-electron reaction, with NH3 as the only reduction product.

Biocathode coupled photoelectrochemical cells (Bio-PEC) have the potential for electricity generation and pollutant removal, with the simultaneous utilization of both solar energy and bioenergy. However, their performance is influenced by many factors. In this work, crucial parameters, including the pollutant type, electrolyte concentration and gas atmosphere of the photoanode, were investigated to optimize the operation of the Bio-PEC in terms of electricity generation.

Azide is known to be a respiratory inhibitor, which can disrupt electron transfer in the process of aerobic respiration. It has been proposed for preventing the reduction of oxygen in the anode compartment of MFC-based biosensors, but has also been found to function as an electron acceptor in recent research. However, there are few reports about the effects of azide on the structure and composition of the microbial community in air-cathode MFCs, as well as on their corresponding performance. Therefore, the current generation, electroactivity and community structure of anodic biofilms were investigated using air-cathode MFCs acclimated with (1.5 mM) and without azide. The enrichment process was much slower in the presence of azide compared to the control. Biofilms enriched with and without azide were found to produce similar voltammograms, but the difference lay in the current intensity of the predominant peaks. Pyrosequencing indicated that the distribution of microbes at the genus level was more uniform, with Geobacter and Ignavibacterium being the dominant genera on both biofilms, although the community of the azide-enriched film was less diverse than that of the control. These results demonstrate that the microbial community enriched with azide was not significantly altered compared to the control and the difference in the maximum current or peak current of cyclic voltammograms (CVs) was thought to be related to the amount of biomass.

Bioelectrochemical systems (BESs) offer a strategy for treating source-separated urine with current generation, but the high content of ammonia is still a challenge for sustainable maintenance of BESs due to ammonia inhibition. Therefore, an integrated BES setup was developed to overcome this problem by ammonia recovery. This setup, working in closed circuit mode with nitrogen purging (CN), allowed for the produced ammonia to be continuously channeled to an absorption bottle. In addition, control reactors in closed circuit (CC) or in open circuit mode (OC) were also run for comparison. A maximum power density of 310.9 ± 1.0 mW m−2 was obtained for the CN reactor, and 127.1 ± 0.9 mW m−2 was obtained for the CC reactor. Total nitrogen (TN) removal efficiency (84.9% ± 2.2%) from urine was considerably higher in the CN reactor than it was in the CC (29.7% ± 6.7%) or OC (30.0% ± 8.2%) reactor. In the CN reactor, 52.8% ± 3.6% of the TN was recovered in the form of NH3-N, with a NH3 recovery rate of 435.7 ± 29.6 gN m−3 d−1. The improved performance of the CN reactor was attributed to the mitigation of ammonia inhibition to the anode electro-activity. 16S rDNA sequencing showed that no Anammox and nitrifiers were detected on the anodes and cathodes. Overall, nitrogen purging provides the urine-fed BESs with a useful approach for maintaining the system performance by ammonia recovery.

Exoelectrogenic bacteria (EEB) can transfer electrons to extracellular electron acceptors and have wide applications in environmental bioremediation and bioenergy generation. Thus, methods for effectively probing the exoelectrogenic ability of EEB are highly desirable. In this work, a simple but efficient photometric assay based on the extracellular reduction of high polar dyes was developed to evaluate the microbial exoelectrogenic ability. Methyl orange were proven to be used as a probe for evaluating the exoelectrogenic ability of EEB. Through monitoring the extracellular dye decolorization under anaerobic conditions, this plate-based photometric assay could rapidly measure the exoelectrogenic ability of various EEB. This approach was also able to evaluate the exoelectrogenic capacity of Shewanella oneidensis MR-1 wild-type strain and its Mtr mutants. Furthermore, the exoelectrogenic ability of mixed cultures in microbial fuel cells was correlated with the extracellular dye decolorization. Thus, this work is useful for the practical implementation of microbial exoelectrogenic ability evaluation.

The effects of azide on electron transport of exoelectrogens were investigated using air-cathode MFCs. These MFCs enriched with azide at the concentration higher than 0.5mM generated lower current and coulomb efficiency (CE) than the control reactors, but at the concentration lower than 0.2mM MFCs generated higher current and CE. Power density curves showed overshoot at higher azide concentrations, with power and current density decreasing simultaneously. Electrochemical impedance spectroscopy (EIS) showed that azide at high concentration increased the charge transfer resistance. These analyses might reflect that a part of electrons were consumed by the anode microbial population rather than transferred to the anode. Bacterial population analyses showed azide-enriched anodes were dominated by Deltaproteobacteria compared with the controls. Based on these results it is hypothesized that azide can eliminate the growth of aerobic respiratory bacteria, and at the same time is used as an electron acceptor/sink.

Certain mixed consortia colonized on aerobic biocathodes can improve the 4-electron oxygen reduction of cathodes; however, the coupling interaction of the cathodic reaction and microbial metabolism remains unclear. To better understand the abovementioned interaction evolved in the cathodic process, biocathodes were enriched using nitrifying sludge and operated at various NH4Cl and NaHCO3 concentrations in both the open and closed external circuit conditions. Based on the variation of the nitrification and cathodic oxygen reduction activities, it was shown that the oxygen reduction process, to some extent, relied on the nitrification activity of the biocathode; the external electrons from the cathode, in turn, might benefit the nitrifying bacteria selected in the MFC habitat by entering the electron transfer chains as the energy source. Nitrifiers, including Nitrosomonas sp., Nitrospira sp. and Nitrobacter sp., were detected in all the biocathodes that were cultured in different conditions, even the ones cultured without NH4Cl in the medium. These findings provided valuable insights into the possible working mechanism of biocathodes.

The main characteristic of discarded flue-cured tobacco leaves is their high nicotine content. Aerobic composting is an effective method to decrease the nicotine level in tobacco leaves and stabilize tobacco wastes. However, high levels of nicotine in discarded flue-cured tobacco leaves complicate tobacco waste composting. This work proposes a drying pretreatment process to reduce the nicotine content in discarded flue-cured tobacco leaves and thus enhance its carbon-to-nitrogen ratio to a suitable level for composting. The effect of another pretreatment method, particle size adjustment, on composting efficiency was also tested in this work. The results indicated that the air-dried (nicotine content: 1.35%) and relatively long discarded flue-cured tobacco leaves (25 mm) had a higher composting efficiency than damp (nicotine content: 1.57%) and short discarded flue-cured tobacco leaves (15 mm). When dry/25 mm discarded flue-cured tobacco leaves mixed with tobacco stems in an 8:2 ratio was composted at a temperature above 55 °C for 9 days, the nicotine content dropped from 1.29% to 0.28%. Since the discarded flue-cured tobacco leaves was successfully composted to a fertile and harmless material, the germination index values increased to 85.2%. The drying pretreatment and particle size adjustment offered ideal physical and chemical conditions to support microbial growth and bioactivity during the composting process, resulting in efficient conversion of discarded flue-cured tobacco leaves into a high quality and mature compost.

1. To identify the origin of table eggs more accurately, a method based on hyperspectral imaging technology was studied. 2. The hyperspectral data of 200 samples of intensive and extensive eggs were collected. Standard normalised variables combined with a Savitzky-Golay were used to eliminate noise, then stepwise regression (SWR) was used for feature selection. Grid search algorithm (GS), genetic search algorithm (GA), particle swarm optimisation algorithm (PSO) and cuckoo search algorithm (CS) were applied by support vector machine (SVM) methods to establish an SVM identification model with the optimal parameters. The full spectrum data and the data after feature selection were the input of the model, while egg category was the output. 3. The SWR-CS-SVM model performed better than the other models, including SWR-GS-SVM, SWR-GA-SVM, SWR-PSO-SVM and others based on full spectral data. The training and test classification accuracy of the SWR-CS-SVM model were respectively 99.3% and 96%. 4. SWR-CS-SVM proved effective for identifying egg varieties and could also be useful for the non-destructive identification of other types of egg.

Electrodes, catalysts, membranes, if present, are three main components in constructing an MFC for harvesting desired maximum power density and achieving higher coulombic efficiency (CE). Great improvements have been made, based on previous researches, in developing and diversifying materials, aside from architectures. Electrodes most familiar to us are widely used carbon materials. For anodes, carbon matrix composites (e.g., a combination of polyaniline (PANI) with TiO2 using carbon as substrate) have gained special attention, though carbon material itself can exhibit excellent performance by diversifying molecular structures such as carbon nanotubes (CNTs). In the meanwhile, the evolution of MFC architectures, heading to the direction of improving power generation, contributes to the combination of membranes and cathodes from separate modes to diverse assemblies, on which all sorts of catalysts, such as from commonly used Pt to iron phthalocyanine (Pc), metal tetramethoxyphenylporphyrin (TMPP), MnOx, or pyrolyzed iron(ll) phthalocyanine (pyr-FePc), can immobilize through synthesis of these catalysts with polymer such as Nafion 117 (Dupont Co., USA) or tetrafluoroethylene (Teflon) containing functional groups or Polypyrrole (PPy). In addition, catholytes with aqueous cathode immersed or flowing through the surface of air-cathode are favorably proposed containing transition metal redox couples or iron chelates. This paper is mainly aimed at reviewing the development of materials in recent years and making several proposals.

A continuous stirred microbial electrochemical reactor (CSMER), comprising of a complete mixing zone (CMZ) and microbial electrochemical zone (MEZ), was used for brewery wastewater treatment. The system realized 75.4 ± 5.7% of TCOD and 64.9 ± 4.9% of TSS when fed with brewery wastewater concomitantly achieving an average maximum power density of 304 ± 31 m W m−2. Cascade utilization of organic matters made the CSMER remove a wider range of substrates compared with a continuous stirred tank reactor (CSTR), in which process 79.1 ± 5.6% of soluble protein and 86.6 ± 2.2% of soluble carbohydrates were degraded by anaerobic digestion in the CMZ and short-chain volatile fatty acids were further decomposed and generated current in the MEZ. Co-existence of fermentative bacteria (Clostridium and Bacteroides, 19.7% and 5.0%), acetogenic bacteria (Syntrophobacter, 20.8%), methanogenic archaea (Methanosaeta and Methanobacterium, 40.3% and 38.4%) and exoelectrogens (Geobacter, 12.4%) as well as a clear spatial distribution and syntrophic interaction among them contributed to the cascade degradation process in CSMER. The CSMER shows great promise for practical wastewater treatment application due to high pre-hydrolysis and acidification rate, high energy recovery and low capital cost.

Energy self-sufficiency is a highly desirable goal of sustainable wastewater treatment. Herein, a combined system of a microbial fuel cell and an intermittently aerated biological filter (MFC-IABF) was designed and operated in an energy self-sufficient manner. The system was fed with synthetic wastewater (COD = 1000 mg L−1) in continuous mode for more than 3 months at room temperature (~25 °C). Voltage output was increased to 5 ± 0.4 V using a capacitor-based circuit. The MFC produced electricity to power the pumping and aeration systems in IABF, concomitantly removing COD. The IABF operating under an intermittent aeration mode (aeration rate 1000 ± 80 mL h−1) removed the residual nutrients and improved the water quality at HRT = 7.2 h. This two-stage combined system obtained 93.9% SCOD removal and 91.7% TCOD removal (effluent SCOD = 61 mg L−1, TCOD = 82.8 mg L−1). Energy analysis indicated that the MFC unit produced sufficient energy (0.27 kWh m−3) to support the pumping system (0.014 kWh m−3) and aeration system (0.22 kWh m−3). These results demonstrated that the combined MFC-IABF system could be operated in an energy self-sufficient manner, resulting to high-quality effluent.