Enhanced treatment of Fischer-Tropsch (F-T) wastewater using the up-flow anaerobic sludge blanket coupled with bioelectrochemical system: Effect of electric field

Paradigm shift in Nutrient-Energy-Water centered sustainable wastewater treatment system through synergy of bioelectrochemical system and anaerobic digestion

With advancements in research and the necessity of improving the performance of bioelectrochemical system (BES), coupling anaerobic digestion (AD) with BES is crucial for energy gain from wastewater and bioremediation. Hybridization of BES-AD concept opens new avenues for pollutant degradation, carbon capture and nutrient-resource recovery from wastewater. The strength of merging BES-AD lies in synergy, and this approach was employed to differentiate fads from strategies with the potential for full-scale implementation and making it an energy-positive system. The integration of BES and AD system increases the overall performance and complexity of combined system and the cost of operation. From a technical standpoint, the primary determinants of BES-AD feasibility for field applications are the scalability and economic viability. High potential market for such integrated system attract industrial partners for more industrial trials and investment before commercialization. However, BES-AD with high energy efficacy and negative economics demands performance boost.

Insights into current bio-processes and future perspectives of carbon-neutral treatment of industrial organic wastewater: A critical review

With the rise of the concept of carbon neutrality, the current wastewater treatment process of industrial organic wastewater is moving towards the goal of energy conservation and carbon emission reduction. The advantages of anaerobic digestion (AD) processes in industrial organic wastewater treatment for bio-energy recovery, which is in line with the concept of carbon neutrality. This study summarized the significance and advantages of the state-of-the-art AD processes were reviewed in detail. The application of expanded granular sludge bed (EGSB) reactors and anaerobic membrane bioreactor (AnMBR) were particularly introduced for the effective treatment of industrial organic wastewater treatment due to its remarkable prospect of engineering application for the high-strength wastewater. This study also looks forward to the optimization of the AD processes through the enhancement strategies of micro-aeration pretreatment, acidic-alkaline pretreatment, co-digestion, and biochar addition to improve the stability of the AD system and energy recovery from of industrial organic wastewater. The integration of anaerobic ammonia oxidation (Anammox) with the AD processes for the post-treatment of nitrogenous pollutants for the industrial organic wastewater is also introduced as a feasible carbon-neutral process. The combination of AnMBR and Anammox is highly recommended as a promising carbon-neutral process for the removal of both organic and inorganic pollutants from the industrial organic wastewater for future perspective. It is also suggested that the AD processes combined with biological hydrogen production, microalgae culture, bioelectrochemical technology and other bio-processes are suitable for the low-carbon treatment of industrial organic wastewater with the concept of carbon neutrality in future.

The variation of microorganisms and organics during methane production from lignite under an electric field

OBJECTIVES

The succession of microbial communities and intermediates during methane production was determined by pyrosequencing and GC-MS to investigate the mechanism of biomethanation enhancement from coal.

RESULTS

The maximum methane production at 1.2 V was significantly higher than that at 0 V. Bacterial flora have been changed as a result of the addition of an electric field, e.g., the abundance of Pseudomonas significantly increased to enhance the coal degradation which improved the methane yield by facilitating the electron transfer. The fungal structure was also found stabilized by the electric field when compared to the control after 7 days of cultivation. The predominance of Methanosarcina could also stimulate interspecies electron transfer. The GC-MS analysis revealed that the electric field can selectively promote the metabolism of refractory intermediates such as esters and aromatics during coal biodegradation.

CONCLUSION

The application of an electric field could enhance methane production from coal by changing the structure and succession of microbial communities, improving electron transfer, and enhancing the fermentation of intermediates during coal biodegradation.

Contribution analysis of different electron transfer pathways to methane production in anaerobic digestion coupled with bioelectrochemical system

The contribution analysis of different electron transfer pathways to CH₄ production was investigated in bioelectrochemical anaerobic digestion (BEAD). It demonstrates that the indirect interspecies electron transfer (IIET) pathway and the direct interspecies electron transfer (DIET) pathways contributed to 41.7 % and 58.3 % of the CH₄ production in the BEAD reactor, respectively. The DIET pathway was further divided into DIET via electrode (eDIET) and biological DIET (bDIET) in the bulk solution, and contributed 11.1 % and 47.2 % of CH₄ production, respectively. This indicates that the dominant electron transfer pathway for CH₄ production is from the bulk solution, rather than on the polarized electrode. The electroactive microorganisms were well enriched in the bulk solution by the electric field generated between anode and cathode. The enriched electroactive microorganisms significantly improved the CH₄ production in the bulk solution through the bDIET pathway.

Effect of applying potentials on anaerobic digestion of high salinity organic wastewater

High salinity organic wastewater (HSOW) contains both organic pollutants and high concentration of inorganic salts. If it is discharged into the environment without proper treatment, it will cause adverse consequences such as dehydration and death of aquatic organisms, and soil salinization. Bioelectrochemical systems (BESs) have been applied in various wastewater treatment processes. To assess the feasibility of using BESs to treat HSOW, the effect of applying potential on anaerobic digestion of HSOW was explored in an up-flow anaerobic sludge blanket (UASB) reactor poised at -0.6 V (vs. Ag/AgCl). When organic loading rate (OLR) was 2.16-2.88 kg chemical oxygen demand/(m³d) (kg COD/(m³d)), the applied potential had no significant effect on the UASB performance. After OLR was increased to 4.32 kg COD/(m³d), the applied potential decreased COD removal efficiency and methane production and resulted in VFAs accumulation. Mesotoga was enriched on the electrode when potential was applied, causing decrease in relative abundances of acetoclastic methanogens. The abundance of Methanothrix on the electrode in the reactor with applied potential was much lower than in the control reactor (10% vs 28.9%), which might lead to decrease in performance of the reactor due to the depressed direct interspecies electron transfer (DIET) and less formation of granular sludge. These results suggest that applying external potentials has negative effect on the anaerobic treatment of HSOW, and should be taken into consideration in real HSOW treatment projects.

A negative-carbon footprint process with mixed biomass feedstock maximizes conversion efficiency, product value and CO2 mitigation

The great variety of biomass species offers unique features for synergistic optimization of process outcomes. In this work, spent mushroom substrate and bagasse with optimize ratio were processed to produce value-added products of activated carbon and biofuel yet achieve negative CO₂ emission. By integrating experimental characterization, this work uses process simulation, techno-economic analysis and life-cycle assessment to evaluate the techno-economic viability and CO₂ footprint of processes with single or dual-/mixed-biomass feedstocks. The combination of biomass species provides unique match of the production of flue gas and primary carbon that is critical for the optimization of mass and energy flow. Such combination has been demonstrated effective to improve product yield and energy efficiency. Results show that mixed biomass feedstock offers favourable figures such as high carbon efficiency of 66.74%, short payback period of 3.16 years, considerable net present value of 80.48 million dollars, and low GWP of -2.37 kg CO₂-eq.

Pretreatment of Rubber Additives Processing Wastewater by Aluminum–Carbon Micro-Electrolysis Process: Process Optimization and Mechanism Analysis

The pretreatment of rubber additives processing wastewater was performed by Al/AC micro-electrolysis (ME). The single-factor experiments for the removal of COD and chroma were investigated. The Box-Behnken Design (BBD) was also applied to optimize the experimental conditions, and the fitted response surface model supplied highly significant quadratic models for the process. The COD removal efficiency reached 51.6% at an initial pH of 9.8, Al scrap dosage of 98.6 g L−1, Al/AC mass ratio of 0.26, and reaction time of 176 min, which was reasonably consistent with the predicated value of 51.9%. Moreover, we proposed a reaction mechanism of the process for the degradation of organic contaminants, and found that the removal of COD and chroma were mainly ascribed to the combination of active hydrogen [H] with strong chemical reactivity and flocculation of aluminum hydroxide. All these results showed that Al/AC ME is a promising pretreatment technique for this wastewater.

Integrating anaerobic digestion with bioelectrochemical system for performance enhancement: A mini review

Strategies for enhancing performance of anaerobic digestion (AD) process has been widely studied. The bioelectrochemical system (BES), including microbial fuel cell, microbial electrolysis cell (MEC), microbial desalination cell, and microbial electrosynthesis, had been proposed to integrate with AD for performance enhancement. This mini-review summarizes the current researches that integrated AD with BES to enhance the performance of the former. The working principles of BES were introduced. The integrated configurations of AD-BES as well as the associated applications were summarized. The statistics analysis for AD-MEC performances reported in literature were then performed to confirm the effects of reactor size and applied voltage on the methane productivity and enhancement. The challenges and prospects of the integrated AD-BES were delineated, and the potential scenarios of applying integrated AD-BES in field were discussed.

Bioelectrochemical system for dehalogenation: A review

Halogenated organic compounds are persistent pollutants, whose persistent contamination and rapid spread seriously threaten human health and the safety of ecosystems. It is difficult to remove them completely by traditional physicochemical techniques. In-situ remediation utilizing bioelectrochemical technology represents a promising strategy for degradation of halogenated organic compounds, which can be achieved through potential modulation. In this review, we summarize the reactor configuration of microbial electrochemical dehalogenation systems and relevant organohalide-respiring bacteria. We also highlight the mechanisms of electrode potential regulation of microbial dehalogenation and the role of extracellular electron transfer in dehalogenation process, and further discuss the application of bioelectrochemical technology in bioremediation of halogenated organic compounds. Therefore, this review summarizes the status of research on microbial electrochemical dehalogenation systems from macroscopic to microscopic levels, providing theoretical support for the development of rapid and efficient in situ bioremediation technologies for halogenated organic compounds contaminated sites, as well as insights for the removal of refractory fluorides.

Integrating anaerobic digestion with microbial electrolysis cell for performance enhancement: A review

Anaerobic digestion has been recognized as promising technology for bioenergy production, while the bottlenecks including long start up times, low methane contents, and susceptibility toward environmental change attenuate the process benefits. Integrating microbials electrolysis cell (MEC) with anaerobic digestion (AD) has been recognized as a promising strategy for alleviate the performance bottleneck. This review summarized and updated the current researches that utilize MEC-AD for enhanced methane production from biomass. The integrated AD-MEC was first elucidated, followed by illustrations on strategies for process performance enhancements, parameters effects, and the associated applications. Finally, the challenges and prospects were outlined in this work.

Electrostatic Fields Promote Methanogenesis More than Polarized Bioelectrodes in Anaerobic Reactors with Conductive Materials

Direct interspecies electron transfer (DIET) is a breakthrough that can surpass the limitations of anaerobic digestion. Conductive materials and polarized bioelectrodes are known to induce DIET for methane production but are still challenging to apply at a field scale. Herein, compared to polarized bioelectrodes, electrostatic fields that promote DIET were investigated in an anaerobic reactor with conductive materials. As a conductive material, activated carbon enriched its surface with electroactive microorganisms to induce DIET (cDIET). cDIET improved the methane yield to 254.6 mL/g COD_r, compared to the control. However, polarized bioelectrodes induced electrode-mediated DIET and biological DIET (bDIET), in addition to cDIET, improving the methane yield to 310.7 mL/g COD_r. Electrostatic fields selectively promoted bDIET and cDIET for further methane production compared to the polarized bioelectrodes. As the contribution of DIET increased, the methane yield increased, and the substrate residue decreased, resulting in a significant improvement in methane production.

Simultaneously autotrophic denitrification and organics degradation in low-strength coal gasification wastewater (LSCGW) treatment via microelectrolysis-triggered Fe(II)/Fe(III) cycle

The autotrophic iron-depended denitrification (AIDD), triggered by microelectrolysis, was established in the microelectrolysis-assistant up-flow anaerobic sludge blanket (MEA-UASB) with the purpose of low-strength coal gasification wastewater (LSCGW) treatment while control UASB operated in parallel. The results revealed that chemical oxygen demand (COD) removal efficiency and total nitrogen (TN) removal load at optimum current (2.5 A/m³) in MEA-UASB (83.2 ± 2.6% and 0.220 ± 0.010 kg N/m³·d) were 1.42-fold and 1.57-fold higher than those (58.5 ± 2.1% and 0.139 ± 0.011 kg N/m³·d) in UASB, verifying that AIDD and following dissimilatory iron reduction (DIR) process could offer the novel pathway to solve the electron donor-deficient and traditionally denitrification-infeasible problems. High-throughput 16S rRNA gene pyrosequencing shown that iron-oxidizing denitrifiers (Thiobacillus and Acidovorax species) and iron reducing bacteria (Geothrix and Ignavibacterium speices), acted as microbial iron cycle of contributors, were specially enriched at optimum operating condition. Additionally, the activities of microbial electron transfer chain, electron transporters (complex I, II, III and cytochrome c) and abundance of genes encoding important enzymes (narG, nirK/S, norB and nosZ) were remarkably promoted, suggesting that electron transport and consumption capacities were stimulated during denitrification process. This study could shed light on better understanding about microelectrolysis-triggered AIDD for treatment of refractory LSCGW and further widen its application potential in the future.

Comparative evaluation on the utilization of applied electrical potential in a conductive granule packed biotrickling filter for continuous abatement of xylene: Performance, limitation, and microbial community

This study investigates the use of electrically conductive granules as packing material in biotrickling filter (BTF) systems as to provide insights on the specific microbial abundance and functions during the treatment of xylene-containing waste gas. In addition, the effect of applied potential on attached biofilm on conductive granules during xylene degradation was briefly investigated. During stable operation period, the conductive granules packed BTF achieved reactor performance of no less than 80% with a maximum EC of 137.7 g/m³ h. Under applied potential of 1V, the BTF system showed deterioration of xylene removal by ranging from 21 to 76%, which also affected the distribution and relative abundance of the major microorganisms such as Xanthobacter, Acidovorax, Rhodococcus, Hydrogenophaga, Arthrobacter, Brevundimonas, Pseudoxanthomonas, Devosia, Shinella, Sphingobium, Dokdonella, Pseudomonas and Bosea. The acclimation of applied potential led to the enrichment of autotrophic bacteria and strains, which are correlated to improved nitrogen cycling. In general, applying electrical potential is feasible to shape the microbiological structure of biofilms to selectively adjust their biochemical functions.

Towards the practical application of bioelectrochemical anaerobic digestion (BEAD): Insights into electrode materials, reactor configurations, and process designs

Anaerobic digestion (AD) is one of the most widely adopted bioenergy recovery technologies globally. Despite the wide adoption, AD has been challenged by the unstable performances caused by imbalanced substrate and/or electron availability among different reaction steps. Bioelectrochemical anaerobic digestion (BEAD) is a promising concept that has demonstrated potential for balancing the electron transfer rates and enhancing the methane yield in AD during shocks. While great progress has been made, a wide range of, and sometimes inconsistent engineering and technical strategies were attempted to improve BEAD. To consolidate past efforts and guide future development, a comprehensive review of the fundamental bioprocesses in BEAD is provided herein, followed by a critical evaluation of the engineering and technical optimizations attempted thus far. Further, a few novel directions and strategies that can enhance the performance and practicality of BEAD are proposed for future research to consider. This review and outlook aim to provide a fundamental understanding of BEAD and inspire new research ideas in AD and BEAD in a mechanism-informed fashion.

Influence of electrostatic field and conductive material on the direct interspecies electron transfer for methane production

The influence of electrostatic field on the direct interspecies electron transfer (DIET) pathways for methane production was investigated in a batch bioelectrochemical anaerobic digester (BEAD). The ultimate methane production and methane yield in the BEAD reactor saturated to 925 ± 29 mL/L and 309.9 ± 9.6 mL CH₄/g COD, respectively, which were much higher than 616 ± 3 mL/L and 205.4 ± 205.4 mL CH₄/g COD in the anaerobic digester (AD). In the cyclic voltammogram (CV) for bulk solution, the oxidation peak current was 0.52 mA in the BEAD reactor, which was higher than 0.24 mA of AD reactor. This shows that the oxidizing ability of microorganisms was greatly improved in the BEAD reactor. Anaerolineaceae, a well-known electroactive bacterial family, was well enriched in the BEAD reactor. It indicates that the electrostatic field can enrich the electroactive bacteria and activate the DIET pathways for methane production. Moreover, the conductive material (activated carbon) further improved the performance of BEAD reactor, implies that the conductivities of bulk solution is one of the important parameters for the DIET pathways.

Effect of low-intensity electric current field and iron anode on biological nitrate removal in wastewater with low COD to nitrogen ratio from coal pyrolysis

Mixotrophic nitrate removal in wastewater from coal pyrolysis was achieved in microbial electrolysis cell with iron anode (iron-MEC). The effect of voltage, iron anode and conductivity were investigated. The effluent TN concentration was 8.35 ± 1.94 mg/L in iron-MEC when the conductivity of the wastewater was adjusted to 3.97 ± 0.08 mS/cm, which was lower than that in no-treated reactor. The increase of current density, which was resulted from the elevation of conductivity, promoted the iron corrosion and Fe2+ ion generation. Therefore, more Fe2+ ion was utilized by nitrate reducing ferrous oxidation bacteria (NRFOB) used to reduce nitrate. The microbial community analysis demonstrated that NRFOB, including Acidovorax and Bradyrhizobium, possessed a higher abundance in iron-MEC. The enrichment of Geobacter in iron-MEC might imply that the part of Fe(III) produced by ferrous oxidation was reduced by Geobacter, which established an iron cycle. Moreover, the production of N2O was decreased by the formation of Fe2+ ion.

Corrosion Behavior of API-X120 Carbon Steel Alloy in a GTL F-T Process Water Environment at Low COD Concentration

The effect of temperature, time and rotation speed of FT-GTL process water on the corrosion rate of API X-120 carbon steel was investigated. Electrochemical impedance spectroscopy and potentiodynamic polarization techniques were used to determine the carbon steel corrosion rate under temperatures ranging from 293 to 323 K and rotation speed of 0, 500, 1000, 2000 rpm when the immersion time was 0.5, 1, and 2 h. The corrosion rate increased with temperature and rotation speed but decreased with immersion time. SEM, XRD, and XPS analyses of the corroded surfaces confirmed the formation of iron oxide and ferric oxide as the main components of the protective layer.

Bioelectrochemical Ammoniation Coupled with Microbial Electrolysis for Nitrogen Recovery from Nitrate in Wastewater

Nitrate-N in wastewaters is hard to be recovered because it is difficult to volatilize with an opposite charge to ammonium. Here, we have proved the feasibility of dissimilatory nitrate reduction to ammonia (DNRA) by the easy-acclimated mixed electroactive bacteria, achieving the highest DNRA efficiency of 44%. It was then coupled with microbial electrolysis to concentrate ammonium by a factor of 4 in the catholyte for recovery. The abundance of electroactive bacteria in the biofilm before nitrate addition, especially Geobacter spp., was found to determine the DNRA efficiency. As the main competitors of DNRA bacteria, the growth of denitrifiers was more sensitive to C/N ratios. The DNRA microbial community contrarily showed a stable and recoverable ammoniation performance over C/N ratios ranging from 0.5 to 8.0. A strong competition of the electrode and nitrate on electron donors was observed at the early stage (15 d) of electroactive biofilm formation, which can be weakened when the biofilm was mature on 40 d. Quantitative PCR showed a significant increase in nirS and nrfA transcripts in the ammoniation process. nirS was inhibited significantly after nitrate depletion while nrfA was still upregulated. These findings provided a novel way to recover nitrate-N using organic wastes as both electron donor and power, which has broader implications on the sustainable wastewater treatment and the ecology of nitrogen cycling.

Applying potentials to conductive materials impairs High-loading anaerobic digestion performance by affecting direct interspecies electron transfer

In order to illustrate the impact that application of positive or negative potential to conductive materials can have on direct interspecies electron transfer (DIET) and reactor performance under high organic loading rates, three continuous laboratory-scale reactors with carbon-cloth electrodes poised at +0.7 V, -0.7 V (vs. Ag/AgCl) and no-potential were fed high concentrations of ethanol wastewater. While exoelectrogens and methanogens that are capable of DIET were significantly enriched in poised reactors, they performed worse than the non-current control. Volatile fatty acids (VFAs) accumulated more rapidly in the positively then negatively poised reactor, but neither could withstand high-loading rates. These results demonstrate that applying potential to conductive materials had a negative effect on anaerobic digestion under high-loading conditions.

Effect of low-intensity direct current electric field on microbial nitrate removal in coal pyrolysis wastewater with low COD to nitrogen ratio

The coupling of bioelectrochemical system with the biological denitrification process (R1) was constructed for nitrate removal in coal pyrolysis wastewater (CPW) and the effect of low-intensity direct current electric field was investigated. Compared with control reactor (R2), the total nitrogen (TN) removal efficiency in R1 at the optimized voltage of 0.9 V was 94.20 ± 2.14%, which was 14.42% higher than that in R2. The biofilm on the cathode of R1 enhanced the nitrate reducing, however, nitrite was only reduced by bacteria in suspended activated sludge, which was confirmed by cyclic voltammetry measurement (CV). Microbial community network analysis revealed that exoelectrogenic bacteria of Pseudomonas was enriched on the anode of R1, and the "small world", including Zoogloea, Pseudomonas and Arenimonas, was established under the stimulation of voltage. Therefore, Pseudomonas transferred electron to anode, and Arenimonas could utilize electron from anode to reduce nitrate, which enhanced TN removal in R1.

Direct current triggering enhanced anaerobic treatment of acetyl pyrimidine-containing wastewater in up-flow anaerobic sludge blanket coupled with bioelectrocatalytic system

In this study, the novel up-flow anaerobic sludge blanket coupled with bioelectrocatalytic system (UASB-BEC) was developed with the attempt to enhance treatment of acetyl pyrimidine-containing wastewater. The results revealed that higher current applied had a positive effect on acetyl pyrimidine (AP) degradation but a negative impact could be followed by the overhigh current (>1.26 A m^-3). Removal efficiencies of AP and total organic carbon (TOC) were as high as 96.3 ± 2.6% and 92.9 ± 3.2% while methane production reached up to 0.70 ± 0.03 NL-CH₄ L^-1-reactor d^-1 at applied current of 1.26 A m^-3, which were significantly higher those in control system. Moreover, high-throughput 16S rRNA gene pyrosequencing further indicated that Desulfovibrio and Methanimicrococcus species were specially enriched in suspended sludge and cathodic biofilm with current involvement. It could be reasonably speculated that enrichment of Desulfovibrio and Methanimicrococcus species could promote biotransformation of AP and final H₂-depended methylotrophic methanogenesis. This study could shed light on better understanding of AP transformation in bioelectrocatalytic system and provide a valuable reference to practical application of anaerobic AP-containing wastewater treatment.

New insights into pollutants removal, toxicity reduction and microbial profiles in a lab-scale IC-A/O-membrane reactor system for paper wastewater reclamation

In this study, an internal circulation-anoxic/aerobic (IC-A/O) process followed by ultrafiltration (UF) and reverse osmosis (RO) system was applied for paper wastewater reclamation. The IC-AO system presented a stable and efficient performance, achieving high removal of chemical oxygen demand (COD), total organic carbon (TOC) and total nitrogen (TN) with methane production rate of 132.8 mL/d. Acute toxicity to Daphnia magna (D. magna) was reduced significantly (83.2%) and the spearman's rank correlation analysis indicated that the toxicity of effluents from each reactor were positively correlated with COD and TOC. Hexadecanoic acid, octadecanoic acid and benzophenone were the main toxic contributors for biological effluent. Microbial community revealed that Anaerolinea was significantly related with organic pollutants. The UF-RO system further removed pollutants and toxicity with the final effluent COD, TOC, ammonium nitrogen (NH₄⁺-N) and TN of 32.6, 18.8, 0.3 and 9.2 mg/L, respectively, which proved that it was feasible for paper wastewater reuse. This study presented an efficient, practical and environmentally competitive system, and paved a foundation for the treatment and reuse of paper wastewater.

NMR analysis of the Fischer-Tropsch wastewater: Combination of 1D selective gradient TOCSY, 2D DOSY and qNMR

The Fischer-Tropsch (FT) process is a practical approach to convert synthesis gas (CO and H₂) into hydrocarbons and oxygenates, and these product mixtures are usually well-characterized. However, the analysis of Fischer-Tropsch waste water (FTW) is still somewhat underdeveloped and the exact composition of FTW remains unclear. Herein, various qualitative NMR techniques, especially diffusion-ordered spectroscopy (DOSY) and one dimension (1D) selective gradient total correlation spectroscopy (SelTOCSY) were strategically applied in the analysis of FTW. The NMR results show that the DOSY technique can pseudo-separate most of components in complex mixtures over the diffusion dimension. The SelTOCSY technique is used as a supporting method in the cases where the DOSY technique cannot clearly distinguish overlapped signals. Moreover, the quantitative ¹H NMR (qNMR) was further used to quantify the components of the sample. These routine and advanced qualitative and quantitative NMR technique utilized here provide a fast, effective and feasible method for the identification of complex mixtures in FTW, which might be a powerful and fast alternative to gas chromatography or high performance liquid chromatography for FTW research.

Selective adsorption and bioavailability relevance of the cyclic organics in anaerobic pretreated coal pyrolysis wastewater by lignite activated coke

This study originally investigated the selective adsorption of cyclic organics in APCPW by LAC, corresponding to the change of the bioavailability. As a product from low rank coal, LAC showed more oxygen (O)-containing groups and mesoporous structure than PAC. Adsorption mechanisms were analyzed by equilibrium isotherms and kinetics models combined with physicochemical properties of adsorbent and adsorbates. The results indicated that selectivity of LAC was dominated by chemical interaction and its mesoporous, and was enhanced by hydrophobicity of adsorbates. In addition, PAC and LAC were applied for the treatment of APCPW. Compared with PAC, LAC adsorption exhibited superior removal efficiency of Tph, TOC and TN at 85.90%, 91.15% and 51.64%, respectively. Furthermore, preferential adsorption of biotoxic and bioresistant cyclic organics by LAC was further proved by GC-MS analysis, resulting in increased bioavailability of APCPW. Specifically, LAC exerted sustained detoxication capacity until 86.50% reduction of TU by D. magna evaluation, and lowered toxicity rank (TU = 4.51, classIII) to T. pyriformis than that after PAC adsorption (TU > 10, ClassIV). Meanwhile, biodegradability was also improved by 9.17% after LAC adsorption. Lastly, LAC would exhibit great economic benefits as an alternative for PAC in subsequent process after anaerobic pretreatment.

Enhanced Degradation of Waste Activated Sludge in Microbial Electrolysis Cell by Ultrasonic Treatment

This study investigates the feasibility of ultrasonic pretreatment for improving treatment efficiency of waste activated sludge (WAS) in microbial electrolysis cell (MEC). Results showed that at applied voltage of 0.5 V, biogas production and cathodic hydrogen recovery enhanced 3.68-fold and 2.56-fold, respectively. Due to the transformation of soluble COD accelerated by the pretreatment, the removal rates of suspended solids and volatile suspended solids were significantly enhanced by 1.38-fold and 1.48-fold, respectively. Various kinds of organics, including VFAs (volatile fatty acids), proteins and carbohydrates, could be utilized in sequence. The primary biodegradable substance in MEC was hydrophilic fraction from sludge organics and the pretreatment effectively resulted in an elevated concentration of this fraction. The 16S rRNA pyrosequencing analysis demonstrated multiple syntrophic interactions between fermentative bacteria, exoelectrogenes, and methanogenic archaea in MEC for WAS.

The mechanism of synergistic effect between iron-carbon microelectrolysis and biodegradation for strengthening phenols removal in coal gasification wastewater treatment

A novel iron-carbon microelectrolysis (ICME) inoculated with activated sludge (AS) process was specifically designed to look into the roles of microelectrolysis and biodegradation as well as their synergistic effect on phenols removal in coal gasification wastewater (CGW) treatment. The results indicated that the removal efficiency of COD, phenols and TOC in integrated ICME-AS process reached 87.36 ± 2.98%, 92.62 ± 0.76% and 84.45 ± 0.65%, respectively. Moreover, phenols-degrading bacteria and electrochemical-active bacteria presented better adaptability to phenolic impact. Meanwhile their syntrophic interaction was driven under the simulation of microelectrolysis. Furthermore, electrochemical redox efficiency was significantly improved, and the corresponding maximum power output reached 0.043 ± 0.01 mW/cm². Apparently, the synergistic effect between microelectrolysis and biological action effectively strengthened phenols degradation and electricity generation. The results proved that the integrated ICME-AS process was a promising technology applied for CGW and other refractory industrial wastewater treatments.

Microbial nitrate removal in biologically enhanced treated coal gasification wastewater of low COD to nitrate ratio by coupling biological denitrification with iron and carbon micro-electrolysis

Mixotrophic denitrification coupled biological denitrification with iron and carbon micro-electrolysis (IC-ME) is a promising emerging bioprocess for nitrate removal of biologically enhanced treated coal gasification wastewater (BECGW) with low COD to nitrate ratio. TN removal efficiency in R1 with IC-ME assisted was 16.64% higher than R2 with scrap zero valent iron addition, 23.05% higher than R3 with active carbon assisted, 30.51% higher than R4 with only active sludge addition, 80.85% higher than R5 utilizing single IC-ME as control. Fe²⁺ generated from IC-ME decreased the production of N₂O and enriched more Nitrate-reducing Fe(Ⅱ) oxidation bacteria (NRFOB) Acidovorax and Thiobacillus, which could convert nitrate to nitrogen gas. And the presence of Fe³⁺, as the Fe²⁺ oxidation product, could stimulate the growth of Fe(III)-reducing strain (FRB) that indicated by redundancy analysis. Microbial network analysis demonstrated FRB Geothrix had a co-occurrence relationship with other bacteria, revealing its dominant involvement in nitrate removal of BECGW.

New insights into enhanced anaerobic degradation of Fischer-Tropsch wastewater with the assistance of magnetite

In this study, magnetite (Fe₃O₄), as the typical conductive material, was supplemented in anaerobic sequential batch reactor (ASBR) with the attempt to enhance pollutants removal and methane production during Fischer-Tropsch wastewater treatment. The results showed that COD removal efficiency and cumulative methane production with the addition of optimum magnetite dosage (0.4 g) were as high as 84.3 ± 2.0% and 7.46 ± 0.24 L, which were higher than other test groups (0, 0.2 and 0.6 g). Furthermore, the combination of high-throughput 16S rRNA gene pyrosequencing and metagenomic analysis in this study further confirmed that the Geobacter and Methanosaeta species were specially enriched in bacterial and archaeal community at the optimum magnetite dosage, suggesting that magnetite-mediated direct interspecies electron transfer (DIET) between Geobacter and Methanosaeta species was likely a crucial reason to promote syntrophic metabolism of propionic acid and butyric acid, and further enhance final methanogenesis.

Granulation and microbial community dynamics in the chitosan-supplemented anaerobic treatment of wastewater polluted with organic solvents

The effect of chitosan on the development of granular sludge in upflow anaerobic sludge blanket reactors (UASB) when treating wastewater polluted with the organic solvents ethanol, ethyl acetate, and 1-ethoxy-2-propanol was evaluated. Three UASB reactors were operated for 219 days at ambient temperature with an organic loading rate (OLR) of between 0.3 kg COD m^-3 d^-1 and 20 kg COD m^-3 d^-1. One reactor was operated without the addition of chitosan, while the other two were operated with the addition of chitosan doses of 2.4 mg gVSS^-1 two times. The three reactors were all able to treat the OLR tested with COD removal efficiencies greater than 90%. However, the time required to reach stable operation was considerably reduced in the chitosan-assisted reactors. The development of granules in the reactors with chitosan was accelerated and granules larger than 2000 μm were only observed in these reactors. In addition, these granules exhibited better physicochemical characteristics: the mean particle diameter (540 and 613 μm) was approximately two times greater than in the control reactor (300 μm), and the settling velocities exceeded 35 m h^-1. The extracellular polymeric substances (EPS) in the reactors with the chitosan was found to be higher than in the control reactor. The protein-EPS content has been correlated with the granule size. The analyses of the microbial communities, performed through denaturing gradient gel electrophoresis and high-throughput sequencing, revealed that the syntrophic microorganisms belonging to genus Geobacter and the hydrogenotrophic methanogen Methanocorpusculum labreanum were predominant in the granules. Other methanogens like Methanosaeta species were found earlier in the chitosan-assisted reactors than in the control reactor.

A novel bio-electrochemical system with sand/activated carbon separator, Al anode and bio-anode integrated micro-electrolysis/electro-flocculation cost effectively treated high load wastewater with energy recovery

A novel bio-electrochemical system (BES) was developed by integrating micro-electrolysis/electro-flocculation from attaching a sacrificing Al anode to the bio-anode, it effectively treated high load wastewater with energy recovery (maximum power density of 365.1 mW/m³ and a maximum cell voltage of 0.97 V), and achieving high removals of COD (>99.4%), NH₄⁺-N (>98.7%) and TP (>98.6%). The anode chamber contains microbes, activated carbon (AC)/graphite granules and Al anode. It was separated from the cathode chamber containing bifunctional catalytic and filtration membrane cathode (loaded with Fe/Mn/C/F/O catalyst) by a multi-medium chamber (MMC) filled with manganese sand and activated carbon granules, which replaced expensive PEM and reduced cost. An air contact oxidation bed for aeration was still adopted before liquid entering the cathode chamber. micro-electrolysis/electro-flocculation helps in achieving high removal efficiencies and contributes to membrane fouling migration. The increase of activated carbon in the separator MMC increased power generation and reduced system electric resistance.

Enhanced treatment of Fischer-Tropsch wastewater using up-flow anaerobic sludge blanket system coupled with micro-electrolysis cell: A pilot scale study

The coupling of micro-electrolysis cell (MEC) with an up-flow anaerobic sludge blanket (UASB) system in pilot scale was established for enhanced treatment of Fischer-Tropsch (F-T) wastewater. The lowest influent pH (4.99±0.10) and reduced alkali addition were accomplished under the assistance of anaerobic effluent recycling of 200% (stage 5). Simultaneously, the optimum COD removal efficiency (93.5±1.6%) and methane production (2.01±0.13m³/m³·d) at the lower hydraulic retention time (HRT) were achieved in this stage. In addition, the dissolved iron from MEC could significantly increase the protein content of tightly bound extracellular polymeric substances (TB-EPS), which was beneficial to formation of stable granules. Furthermore, the high-throughput 16S rRNA gene pyrosequencing in this study further confirmed that Geobacter species could utilize iron oxides particles as electron conduit to perform the direct interspecies electron transfer (DIET) with Methanothrix, finally facilitating the syntrophic degradation of propionic acid and butyric acid and contributing completely methane production.