Combined effects of enrichment procedure and non-fermentable or fermentable co-substrate on performance and bacterial community for pentachlorophenol degradation in microbial fuel cells

Enhanced etching terminal wastewater treatment and H2 production by in-situ deposited heavy metals on carbon dots/g-C3N4 photocathode microbial electrolysis cells

Sustainable and cost-effective semiconducting photocathodes of microbial electrolysis cells (MECs) are attractively promising for efficient treatment of actual industrial wastewaters containing complex recalcitrant organics and multiple heavy metals. Herein carbon dots/graphitic carbon nitride (CDs/g-C3N4) photocathodes were employed to achieve efficient treatment of actual etching terminal wastewater (ETW) with simultaneous H2 production in MECs, allowing the effluent meeting national discharge standards (GB39731-2020). The progressively in-situ deposited heavy metals on the CDs/g-C3N4 photocathodes, formed as metal oxides/CDs/g-C3N4 after simple calcinations, further enhanced the ETW treatment (recalcitrant organics mineralization: 42.2 mg/L/h vs. 35.5 mg/L/h; heavy metal removal: Cu(II): 9.9 mg/L/h vs. 7.4 mg/L/h, Ni(II): 4.7 mg/L/h vs. 3.5 mg/L/h, Zn(II): 0.7 mg/L/h vs. 0.5 mg/L/h) and H2 production (0.1138 m3/m3/d vs. 0.0662 m3/m3/d). The importation of heavy metals, formed as metal oxides/CDs/g-C3N4 altered the proportion of reactive oxidative species and thus promoted mineralization of recalcitrant organics, besides offering additional electrochemical removal of heavy metals with simultaneous more H2 production. This study demonstrates a new feasible protocol for achieving efficient ETW treatment, and gives a comprehensive appreciation of the effect of in-situ deposited heavy metals on the CDs/g-C3N4 photocathodes, which has a profound effect on subsequent ETW treatment with simultaneous H2 production.

Effects of Increasing Concentrations of Enrofloxacin on Co-Digestion of Pig Manure and Corn Straw

Enrofloxacin (ENR) is one of the most commonly used antibiotics in pig farms. In this study, using fresh pig manure and corn straw powder as substrates, the effects of different concentrations of ENR (2.5, 10, and 20 mg/L) on anaerobic digestion in completely mixed anaerobic reactors were investigated. A relatively low concentration of ENR (2.5 mg/L) increased methane production by 47.58% compared with the control group. Among the volatile fatty acids (VFAs) in the reactors, the propionic acid content was the lowest, and the concentrations of acetic acid kinase and coenzyme F420 were highest in the first seven days during peak gas production. However, methane production in the reactors with 10 mg/L and 20 mg/L ENR decreased by 8.59% and 20.25%, respectively. Furthermore, the accelerated hydrolysis of extracellular polymeric substances causes a significant accumulation of VFA levels. The microbial community in anaerobic reactors was analyzed by 16S rRNA sequencing. Proteiniphilum was the dominant bacterial genus. In addition, ENR at 2.5 mg/L effectively increased the abundance and diversity of anaerobic microorganisms, whereas a high concentration of ENR (10 and 20 mg/L) significantly decreased these parameters. This study demonstrated that different concentrations of ENR had significantly different effects on anaerobic digestion.

Synergistic degradation for o-chlorophenol and enhancement of power generation by a coupled photocatalytic-microbial fuel cell system

A hierarchically photocatalytic microbial fuel cell system (PMFC) coupled with TiO₂ photoanode and bioanode was established to enhance the power generation based on single-chamber MFC. Compared with the conventional anaerobic mode, oxygen in the solution could be utilized by the photoanode of PMFC to improve the removal of o-chlorophenol (2-CP). The maximum power densities were increasing from 261 (MFC) to 301 mW/m² (PMFC). The removal efficiency of 2-CP (5 mg/L) in PMFC was 76.20% and higher than that in MFC (19.33%) and by photocatalysis (49.23%). The electron-hole separation efficiencies were decreasing with the increasing of dissolved oxygen, causing a low efficiency of photocatalysis, due to the reduction of the current density of the systems. The abundance of Geobacter sp., PHOS-HE36 fam., and Pseudomonas sp. was increased with illumination, contributing to improve the electricity production and 2-CP degradation. The only detective intermediate of 1,2-dichlorobenzene in PMFC indicated that the microbes could regulate the degradation pathway of 2-CP in the coupling system. These findings provided an feasible method for the effective degradation of refractory organic compounds and simultaneous energy recovery by combining photocatalysis and microbial power generation.

Response of 2,4,6-trichlorophenol-reducing biocathode to burial depth in constructed wetland sediments

Biocathode systems could be used for in-situ bioremediation of chlorophenols (CPs) in constructed wetland (CW) sediments. However, little is known regarding whether or how cathode burial depths affect the dechlorination of CPs in sediments. Here, 2,4,6-trichlorophenol (2,4,6-TCP)-dechlorinating biocathode systems were constructed under a cathode potential of - 0.7 V (vs. a saturated calomel electrode, SCE) at three different cathode burial depths (5, 10, and 15 cm). The 2,4,6-TCP removal efficiency and average transformation rate with the biocathode increased by 21.46-36.86% and 14.63-34.88% compared to those in the non-electrode groups. Deeper cathode burial depths enhanced the 2,4,6-TCP dechlorination performance. Furthermore, the oxidation-reduction potential (ORP) of the sediment decreased with sediment depth and the applied potential created a more favorable redox environment for the enrichment of functional bacteria. Deeper cathode burial depths also promoted the selective enrichment of electro-active and dechlorinating bacteria (e.g., Bacillus and Dehalobacter, respectively). The biocathode thus served as the carrier, electron source, and regulator of functional bacteria to accelerate the transformation of 2,4,6-TCP (2,4,6-TCP → 2,4-dichlorophenol → 4-chlorophenol → phenol) in sediments. These results offer insights into the effects of cathode burial depth on 2,4,6-TCP dechlorination in sediments from a redox environment and microbial community structure standpoint.

Physiological metabolism of electrochemically active bacteria directed by combined acetate and Cd(II) in single-chamber microbial electrolysis cells

It is of great interest to explore physiological metabolism of electrochemically active bacteria (EAB) for combined organics and heavy metals in single-chamber microbial electrolysis cells (MECs). Four pure culture EAB varying degrees responded to the combined acetate (1.0-5.0 g/L) and Cd(II) (20-150 mg/L) at different initial concentrations in the single-chamber MECs, shown as significant relevance of Cd(II) removal (2.57-7.35 mg/L/h) and H₂ production (0-0.0011 m³/m³/h) instead of acetate removal (73-130 mg/L/h), to these EAB species at initial Cd(II) below 120 mg/L and initial acetate below 3.0 g/L. A high initial acetate (5.0 g/L) compensated the Cd(II) inhibition and broadened the removal of Cd(II) to 150 mg/L. These EAB physiologically released variable amounts of extracellular polymeric substances with a compositional diversity in response to the changes of initial Cd(II) and circuital current whereas the activities of typical intracellular enzymes were more apparently altered by the initial Cd(II) than the circuital current. These results provide experimental validation of the presence, the metabolic plasticity and the physiological response of these EAB directed by the changes of initial Cd(II) and acetate concentrations in the single-chamber MECs, deepening our understanding of EAB physiological coping strategies in metallurgical microbial electro-ecological cycles.

"Self-degradation" of 2-chlorophenol in a sequential cathode-anode cascade mode bioelectrochemical system

A sequential cathode-anode cascade mode bioelectrochemical system (BES) was designed and developed to achieve the "self-degradation" of 2-chlorophenol (2-CP). With the cooperation of cathode and anode, the electrons supplied for the cathode 2-CP dechlorination come from its own dechlorinated product in the anode, phenol. Separate degradation experiments of cathode 2-CP and anode phenol were firstly conducted. The optimum concentration ratio of anode acetate to phenolic compound (3.66/1.56) and the phenolic compound degradation ability of BES were investigated. With the formation of the bioanode able to degrade phenol, the sequential cathode-anode cascade mode BES was further developed, where 2-CP could achieve sequential dechlorination and ring-cleavage degradation. When applied voltage was 0.6 V and cathode influent pH was 7, 1.56 mM 2-CP reached 80.15% cathode dechlorination efficiency and 58.91% total cathode-anode phenolic compounds degradation efficiency. The bioanodes played a decisive role in BES. Different operating conditions would affect the overall performance of BES by changing the electrochemical activity and microbial community structure of the bioanodes. This study demonstrated the feasibility of the sequential cathode-anode cascade mode BES to degrade 2-CP wastewater and provided perspectives for the cooperation of cathode and anode, aiming to explore more potential of BES in wastewater treatment field.

Challenges and opportunities for the biodegradation of chlorophenols: Aerobic, anaerobic and bioelectrochemical processes

Chlorophenols (CPs) are highly toxic and refractory contaminants which widely exist in various environments and cause serious harm to human and environment health and safety. This review provides comprehensive information on typical CPs biodegradation technologies, the most green and benign ones for CPs removal. The known aerobic and anaerobic degradative bacteria, functional enzymes, and metabolic pathways of CPs as well as several improving methods and critical parameters affecting the overall degradation efficiency are systematically summarized and clarified. The challenges for CPs mineralization are also discussed, mainly including the dechlorination of polychlorophenols (poly-CPs) under aerobic condition and the ring-cleavage of monochlorophenols (MCPs) under anaerobic condition. The coupling of functional materials and degraders as well as the operation of sequential anaerobic-aerobic bioreactors and bioelectrochemical system (BES) are promising strategies to overcome some current limitations. Future perspective and research gaps in this field are also proposed, including the further understanding of microbial information and the specific role of materials in CPs biodegradation, the potential application of innovative biotechnologies and new operating modes to optimize and maximize the function of the system, and the scale-up of bioreactors towards the efficient biodegradation of CPs.

Co-metabolism for enhanced phenol degradation and bioelectricity generation in microbial fuel cell

Co-metabolism is one of the effective approaches to increase the removal of refractory pollutants in microbial fuel cells (MFCs), but studies on the links between the co-substrates and biodegradation remain limited. In this study, four external carbon resources were used as co-substrates for phenol removal and power generation in MFC. The result demonstrated that acetate was the most efficient co-substrate with an initial phenol degradation of 78.8% and the voltage output of 389.0 mV. Polarization curves and cyclic voltammogram analysis indicated that acetate significantly increased the activity of extracellular electron transfer (EET) enzyme of the anodic microorganism, such as cytochrome c OmcA. GC-MS and LC-MS results suggested that phenol was biodegraded via catechol, 2-hydroxymuconic semialdehyde, and pyruvic acid, and these intermediates were reduced apparently in acetate feeding MFC. The microbial community analysis by high-throughput sequencing showed that Acidovorax, Geobacter, and Thauera were predominant species when using acetate as co-substrate. It can be concluded that the efficient removal of phenol was contributed to the positive interactions between electrochemically active bacteria and phenolic degradation bacteria. This study might provide new insight into the positive role of the co-substrate during the treatment of phenolic wastewater by MFC.

Geochemical and microbial characterizations of flowback and produced water in three shale oil and gas plays in the central and western United States

Limited understanding of wastewater streams produced from shale oil and gas wells impedes best practices of wastewater treatment and reuse. This study provides a comprehensive and comparative analysis of flowback and produced water from three major and newly developed shale plays (the Bakken shale, North Dakota; the Barnett shale, Texas; and the Denver-Julesburg (DJ) basin, Colorado) in central and western United States. Geochemical features that included more than 10 water quality parameters, dissolved organic matter, as well as microbial community structures were characterized and compared. Results showed that wastewater from Bakken and Barnett shales has extremely high salinity (∼295 g/L total dissolved solids (TDS)) and low organic concentration (80-252 mg/L dissolved organic carbon (DOC)). In contrast, DJ basin showed an opposite trend with low TDS (∼30 g/L) and high organic content (644 mg/L DOC). Excitation-emission matrix (EEM) fluorescence spectra demonstrated that more humic acid and fluvic acid-like organics with higher aromaticity existed in Bakken wastewater than that in Barnett and DJ basin. Microbial communities of Bakken samples were dominated by Fe (III)-reducing bacteria Geobacter, lactic acid bacteria Lactococcus and Enterococcus, and Bradyrhizobium, while DJ basin water showed higher abundance of Rhodococcus, Thermovirga, and sulfate reducing bacteria Thermotoga and Petrotoga. All these bacteria are capable of hydrocarbon degradation. Hydrogenotrophic methanogens dominated the archaeal communities in all samples.

Dominance of electroactive microbiomes in bioelectrochemical remediation of hydrocarbon-contaminated soils with different textures

Bioelectrochemical systems (BESs) are known to enhance the remediation of hydrocarbon-contaminated soil and sediments compared with natural attenuation, and the primary mechanism has been assumed as anaerobic degradation facilitated by electroactive bacteria (EAB) using the electrode as electron acceptor. However, known EAB were rarely found on the anodes of reported BESs, which challenged the fundamental mechanism of BESs although significant current generation was always observed during degradation of these recalcitrant substrates. This study however found the abundant EAB Geobacter (∼27.3%) in the anodic biofilms, which confirmed the role of electroactive bio-anode on the conversion of hydrocarbons into the current for the enhancement of remediation. Widespread occurrence of aerobic hydrocarbon-degrading bacteria (HDB) (e.g. ∼24.0% Parvibaculum and ∼30.6% Pseudomonas) was observed in soils with limited dissolved oxygen (∼0.4 mg/L). The higher abundance of dehydrogenase genes was found in the anode biofilms than that in soils, indicating anodic microorganisms may be mainly responsible for the removal of intermediates of aerobic hydrocarbons degradation in soils. High water saturation level and sandy soil texture showed positive impacts on bioelectrochemical remediation, while clay soil and unsaturation condition pose challenges in mass transfers in the matrix. The reactor performance was consistent with the phylogenetic molecular ecological network (pMENs) analysis, which showed that sandy soil BESs had tighter microbial network interactions than clay soil reactors.

Power generation and microbial community analysis in microbial fuel cells: A promising system to treat organic acid fermentation wastewater

To explore a sustainable and efficient treatment approach for organic acid fermentation wastewater, two microbial fuel cells (MFCs) systems inoculated with wastewater or domesticated microbial community were constructed in this study. Compared with the MFC inoculated with domesticated microbial community, the MFC inoculated with wastewater not only showed higher power density (543.75 mW m^-2) and coulomb efficiency (22.10%), but also exhibited higher removal rates of chemical oxygen demand (75.59%), total nitrogen (76.15%), and ammonia nitrogen (83.23%), meeting the demand of wastewater discharge standard of China. Sequencing analysis revealed that the MFC inoculated with wastewater were richer in microbial community, and some bacteria such as Saprospiraceae and Caldilineaceae were beneficial for its good performance. In contrast, the microbial community of the MFC inoculated with domesticated microbial community was relatively simple. These results indicated that MFCs may be a sustainable method for organic acid fermentation wastewater treatment without any preprocessing.

Bioelectrogenesis from Raw Algal Biomass Through Microbial Fuel Cells: Effect of Acetate as Co-substrate

Algae are autotrophic organisms that are widespread in water bodies. Increased pollution in water bodies leads to eutrophication. However, algae growing in lakes undergoing eutrophication could be utilized towards the generation of added-value bio-electricity using microbial fuel cells (MFCs). In the present study, two methods of electricity generation using raw algae (RA) and RA + acetate (AC) as co-substrate were analyzed in single chamber air cathode MFCs. MFCs supplemented with RA and RA + AC clearly showed higher power density, greater current generation, and improved COD (chemical oxygen demand) removal, which demonstrated the feasibility of using AC as substrate for MFC. The MFC-RA + AC (0.48 mA) generated 28% higher current relative to that generated by MFC with RA alone. Notably, the maximum power densities generated by MFC-RA and MFC-RA + AC were 230 and 410 mW/m2, respectively. MFC-RA and MFC-RA + AC exhibited TCOD (total chemical oxygen reduction) removal values of 77% and 86.6%, respectively. Despite the high influent TCOD (758 mg/l) concentration, the MFC-RA + AC exhibited an 8.5% higher COD removal relative to that of MFC-RA (525 mg/l). Our current findings demonstrated effective energy generation using algae biomass with a co-substrate.

Potential enhancement of direct interspecies electron transfer for anaerobic degradation of coal gasification wastewater using up-flow anaerobic sludge blanket (UASB) with nitrogen doped sewage sludge carbon assisted

Waste sewage sludge was converted into the novel conductive material of nitrogen doped sewage sludge carbon (N-SC) to enhance anaerobic degradation of coal gasification wastewater (CGW). The results indicated that N-SC played a significant role in enhanced efficiencies, with chemical oxygen demand (COD) removal efficiency increased by 25.4%, methane production rate improved by 68.1% and total volatile fatty acids (VFA) decreased by 37.5% than that of controlled reactor. The conductivity, activity of electron transport, and extracellular polymeric substances (EPS) of anaerobic sludge were remarkably enhanced with N-SC, which promoted sludge granulation and supplied better conductive environment for microorganisms. The microbial community analysis revealed that potential enhancement of direct interspecies electron transfer (DIET) was achieved by electrical connection between enriched Geobacter, Pseudomonas and Methanosaeta with N-SC assisted, which enhanced the anaerobic degradation of CGW. Moreover, anaerobic degradation with N-SC had higher capacity to resist acidic shocks, facilitating the process stability.

Degradation of 2,4,6-trichlorophenol and determination of bacterial community structure by micro-electrical stimulation with or without external organic carbon source

This study aimed to investigate the degradation efficiency of 2,4,6-trichlorophenol through a batch of potentiostatic experiments (0.2 V vs. Ag/AgCl). Efficiencies in the presence and absence of acetate and glucose were compared through open-circuit reference experiments. Significant differences in degradation efficiency were observed in six reactors. The highest and lowest degradation efficiencies were observed in the closed-circuit reactor fed with glucose and in the open-circuit reactor, respectively. This finding was due to the enhanced bacterial metabolism caused by the application of micro-electrical field and degradable organics as co-substrates. The different treatment efficiencies were also caused by the distinct bacterial communities. The composition of bacterial community was affected by adding different organics as co-substrates. At the phylum level, the most dominant bacteria in the reactor with the added acetate and glucose were Proteobacteria and Firmicutes, respectively.

Driving force behind electrochemical performance of microbial fuel cells fed with different substrates

The performance of miniaturized microbial fuel cells operating with five different substrates (acetate, lactate, glucose and octanoate) were studied with the aim to identify the reason for its different performance. In all cases, the COD removal rate was about 650 mg COD L^-1 d^-1. However, the bio-electrochemical performance of the MFC was very different, showing the MFC fed with acetate the best performance: 20 A m^-2 as maximum current density, 2 W m^-2 of maximum power density, 0.376 V of OCV and 12.6% of CE. In addition, the acetate showed the best bio-electrochemical performance in the polarization curves and cyclic voltammetries. These polarization curves were modelled and the key to explain the better electrical performance of acetate was its lower ohmic losses. When working with acetate, its ohmic losses were one log-unit below those attained by the other substrates. These lower ohmic losses were not associated to the electrolyte conductivity of the fuel but to the lower ohmic loses of the biofilm generated.

Energy generation through bioelectrochemical degradation of pentachlorophenol in microbial fuel cell

Bio-electrochemical degradation of pentachlorophenol was carried out in single as well as dual chambered microbial fuel cell (MFC) with simultaneous production of electricity. The maximum cell potential was recorded to be 787 and 1021 mV in single and dual chambered systems respectively. The results presented nearly 66 and 89% COD removal in single and dual chambered systems with corresponding power densities of 872.7 and 1468.85 mW m⁻² respectively. The highest coulombic efficiency for single and dual chambered counterparts was found to be 33.9% and 58.55%. GC-MS data revealed that pentachlorophenol was more effectively degraded under aerobic conditions in dual-chambered MFC. Real-time polymerase chain reaction showed the dominance of exoelectrogenic Geobacter in the two reactor systems with a slightly higher concentration in the dual-chambered system. The findings of this work suggested that the aerobic treatment of pentachlorophenol in cathodic compartment of dual chambered MFC is better than its anaerobic treatment in single chambered MFC in terms of chemical oxygen demand (COD) removal and output power density.

Bio-electrochemical degradation of pentachlorophenol was carried out in single as well as dual chambered microbial fuel cell (MFC) with simultaneous production of electricity.

Response of microbial community structure to pre-acclimation strategies in microbial fuel cells for domestic wastewater treatment

Microbial community structures and performance of air-cathode microbial fuel cells (MFCs) inoculated with activated sludge from domestic wastewater were investigated to evaluate the effects of three substrate pre-acclimation strategies: 1, serial pre-acclimation with acetate and glucose before supplying domestic wastewater; 2, one step pre-acclimation with acetate before supplying domestic wastewater; and 3, direct supply of domestic wastewater without any pre-acclimation. Strategy 1 showed much higher current generation (1.4mA) and Coulombic efficiency (33.5%) than strategies 2 (0.7mA and 9.4%) and 3 (0.9mA and 10.3%). Pyrosequencing showed that microbial communities were significantly affected by pre-acclimation strategy. Although Proteobacteria was the dominant phylum with all strategies, Actinobacteria was abundant when MFCs were pre-acclimated with glucose after acetate. Not only anode-respiring bacteria (ARB) in the genus Geobacter but also non-ARB belonging to the family Anaerolinaceae seemed to play important roles in air-cathode MFCs to produce electricity from domestic wastewater.

Cathodic bacterial community structure applying the different co-substrates for reductive decolorization of Alizarin Yellow R

Selective enrichment of cathodic bacterial community was investigated during reductive decolorization of AYR fedding with glucose or acetate as co-substrates in biocathode. A clear distinction of phylotype structures were observed between glucose-fed and acetate-fed biocathodes. In glucose-fed biocathode, Citrobacter (29.2%), Enterococcus (14.7%) and Alkaliflexus (9.2%) were predominant, and while, in acetate-fed biocathode, Acinetobacter (17.8%) and Achromobacter (6.4%) were dominant. Some electroactive or reductive decolorization genera, like Pseudomonas, Delftia and Dechloromonas were commonly enriched. Both of the higher AYR decolorization rate (k(AYR)=0.46) and p-phenylenediamine (PPD) generation rate (k(PPD)=0.38) were obtained fed with glucose than acetate (k(AYR)=0.18; k(PPD)=0.16). The electrochemical behavior analysis represented a total resistance in glucose-fed condition was about 73.2% lower than acetate-fed condition. The different co-substrate types, resulted in alteration of structure, richness and composition of bacterial communities, which significantly impacted the performances and electrochemical behaviors during reductive decolorization of azo dyes in biocathode.

Simultaneous microbial and electrochemical reductions of vanadium (V) with bioelectricity generation in microbial fuel cells

Simultaneous microbial and electrochemical reductions of vanadium (V) with bioelectricity generation were realized in microbial fuel cells (MFCs). With initial V(V) concentrations of 75 mg/l and 150 mg/l in anolyte and catholyte, respectively, stable power output of 419±11 mW/m(2) was achieved. After 12h operation, V(V) concentration in the catholyte decreased to the value similar to that of the initial one in the anolyte, meanwhile it was nearly reduced completely in the anolyte. V(IV) was the main reduction product, which subsequently precipitated, acquiring total vanadium removal efficiencies of 76.8±2.9%. Microbial community analysis revealed the emergence of the new species of Deltaproteobacteria and Bacteroidetes as well as the enhanced Spirochaetes mainly functioned in the anode. This study opens new pathways to successful remediation of vanadium contamination.

Simultaneous bioelectricity generation and decolorization of methyl orange in a two-chambered microbial fuel cell and bacterial diversity

The objectives of this study were to investigate the simultaneous bioelectricity generation and decolorization of methyl orange (MO) in the anode chamber of microbial fuel cells (MFCs) in a wide concentration range (from 50 to 800 mg L(-1)) and to reveal the microbial communities on the anode after the MFC was operated continuously for more than 6 months using MO-glucose mixtures as fuel. Interestingly, the added MO played an active role in the production of electricity. The maximum voltage outputs were 565, 658, 640, 629, 617, and 605 mV for the 1 g L(-1) glucose with 0, 50, 100, 200, 300, and 500 mg L(-1) of MO, respectively. The results of three groups of comparison experiments showed that accelerated decolorization of methyl orange (MO) was achieved in the MFC as compared to MFC in open circuit mode and MFC without extra carbon sources. The decolorization efficiency decreased with an increase of MO concentration in the studied concentration range for the dye load increased. A 454 high-throughput pyrosequencing revealed the microbial communities. Geobacter genus known to generate electricity was detected. Bacteroidia class, Desulfovibrio, and Trichococcus genus, which were most likely responsible for degrading methyl orange, were also detected.

Continuous volatile fatty acid production from waste activated sludge hydrolyzed at pH 12

This study adopted rapid alkaline treatment at pH 12 to hydrolyze 66% of total chemical oxygen demands. Then the hydrolyzed liquor was fermented in a continuous-flow stirred reactor to produce volatile fatty acids (VFAs) at 8-h hydraulic retention time and at 35 °C. The maximum VFA productivity reached 365 mg VFAs g(-1) volatile suspended solids in a 45-d operation, with most produced VFAs being acetate and propionate, principally produced by protein degradation. The Bacteroidia, ε-proteobacteria and the Clostridia were identified to be the classes correlating with the fermentation processes. The fermented liquor was applied to denitrifying phosphorus removal process as alternative carbon source after excess phosphorus and nitrogen being recycled via struvite precipitation. Fermented liquors from alkaline hydrolysis-acid fermentation on waste activated sludge are a potential renewable resource for applications that need organic carbons.

Improved dechlorination and mineralization of 4-chlorophenol in a sequential biocathode-bioanode bioelectrochemical system with mixed photosynthetic bacteria

A new approach that improved the dechlorination and mineralization of 4-chlorophenol (4-CP) was demonstrated in a sequential biocathode-bioanode bioelectrochemical system (BES) with mixed photosynthetic bacteria (PSB). The biocathode with additional PSB inoculation showed higher 4-CP dechlorination efficiency (DE) and maximum current (81.8 ± 2.9%, 0.021 ± 0.002A) than that at abiotic cathode (45.3 ± 3.7%, 0.011 ± 0.002A) (P<0.005). Light response in biocathode BES with or without PSB ascertained the important role of PSB played in the dechlorination and current generation. Dechlorination and mineralization of 4-CP was achieved in the sequential biocathode-bioanode BES, which could be further enhanced with PSB inoculation in both cathode chamber and anode chamber. 4-CP DE in the cathode chamber was improved from 55.0 ± 2.0% to 78.8 ± 4.9%, and the phenol degradation in the anode chamber was improved from 65.3 ± 2.1% to 71.3 ± 1.4%. This study directed a new way for improving dechlorination at biocathode and product degradation at bioanode with PSB inoculation in BES.