Anaerobic bioaugmentation hydrolysis of selected nitrogen heterocyclic compound in coal gasification wastewater

Elucidating the role of sub-thermophilic temperature and pre-hydrolyzation for effective upgrading scheme of old swine manure digesters

Solids concentration, temperature, and digester configuration were subjected to biomethanation study to identify effective retrofitting schemes for old swine waste digesters. Batch assays were commenced to determine an appropriate scenario at 30-55 °C and total solids 1-3 %TS. Sub-thermophilic temperature (45 °C) was found desirable with an additional 11.1 % methane yield, while digestion at higher TS induced ammonium inhibition. Subsequent batch experiments lasted 72 hrs for hydrolytic-acidogenic assessment under various temperatures. Heating control at 45 °C and 55 °C for 24 hrs increased hydrolysis efficiency 4.6-5.7 folds above control but showed no significant difference (α = 0.05) between them. Limited heat supply from biogas engine dictated the continuous digestion study to operate pre-hydrolysis reactor at maximum temperature of 45 °C. The two-stage strategy demonstrated best overall performances at the sub-thermphilic combination, raising methane yield by 35.4 %. Next-Generation Sequencing indicated remarkable shifts in abundance and diversity, especially for hydrolytic organisms, which expanded from 54 to 70.2 % by sub-thermophilic temperature.

Energy recovery from syngas and pyrolysis wastewaters with anaerobic mixed cultures

The anaerobic digestion of aqueous condensate from fast pyrolysis is a promising technology for enhancing carbon and energy recovery from waste. Syngas, another pyrolysis product, could be integrated as a co-substrate to improve process efficiency. However, limited knowledge exists on the co-fermentation of pyrolysis syngas and aqueous condensate by anaerobic cultures and the effects of substrate toxicity. This work investigates the ability of mesophilic and thermophilic anaerobic mixed cultures to co-ferment syngas and the aqueous condensate from either sewage sludge or polyethylene plastics pyrolysis in semi-batch bottle fermentations. It identifies inhibitory concentrations for carboxydotrophic and methanogenic reactions, examines specific component removal and assesses energy recovery potential. The results show successful co-fermentation of syngas and aqueous condensate components like phenols and N-heterocycles. However, the characteristics and load of the aqueous condensates affected process performance and product formation. The toxicity, likely resulting from the synergistic effect of multiple toxicants, depended on the PACs' composition. At 37 °C, concentrations of 15.6 gCOD/gVSS and 7.8 gCOD/gVSS of sewage sludge-derived aqueous condensate inhibited by 50% carboxydotrophic and methanogenic activity, respectively. At 55 °C, loads between 3.9 and 6.8 gCOD/gVSS inhibited by 50% both reactions. Polyethylene plastics condensate showed higher toxicity, with 2.8 gCOD/gVSS and 0.3 gCOD/gVSS at 37 °C decreasing carboxydotrophic and methanogenic rates by 50%. At 55 °C, 0.3 gCOD/gVSS inhibited by 50% CO uptake rates and methanogenesis. Increasing PAC loads reduced methane production and promoted short-chain carboxylates formation. The recalcitrant components in sewage sludge condensate hindered e-mol recovery, while plastics condensate showed high e-mol recoveries despite the stronger toxicity. Even with challenges posed by substrate toxicity and composition variations, the successful conversion of syngas and aqueous condensates highlights the potential of this technology in advancing carbon and energy recovery from anthropogenic waste streams.

Two-stage conversion of syngas and pyrolysis aqueous condensate into L-malate

Hybrid thermochemical-biological processes have the potential to enhance the carbon and energy recovery from organic waste. This work aimed to assess the carbon and energy recovery potential of multifunctional processes to simultaneously sequestrate syngas and detoxify pyrolysis aqueous condensate (PAC) for short-chain carboxylates production. To evaluate relevant process parameters for mixed culture co-fermentation of syngas and PAC, two identical reactors were run under mesophilic (37 °C) and thermophilic (55 °C) conditions at increasing PAC loading rates. Both the mesophilic and the thermophilic process recovered at least 50% of the energy in syngas and PAC into short-chain carboxylates. During the mesophilic syngas and PAC co-fermentation, methanogenesis was completely inhibited while acetate, ethanol and butyrate were the primary metabolites. Over 90% of the amplicon sequencing variants based on 16S rRNA were assigned to Clostridium sensu stricto 12. During the thermophilic process, on the other hand, Symbiobacteriales, Syntrophaceticus, Thermoanaerobacterium, Methanothermobacter and Methanosarcina likely played crucial roles in aromatics degradation and methanogenesis, respectively, while Moorella thermoacetica and Methanothermobacter marburgensis were the predominant carboxydotrophs in the thermophilic process. High biomass concentrations were necessary to maintain stable process operations at high PAC loads. In a second-stage reactor, Aspergillus oryzae converted acetate, propionate and butyrate from the first stage into L-malate, confirming the successful detoxification of PAC below inhibitory levels. The highest L-malate yield was 0.26 ± 2.2 molL-malate/molcarboxylates recorded for effluent from the mesophilic process at a PAC load of 4% v/v. The results highlight the potential of multifunctional reactors where anaerobic mixed cultures perform simultaneously diverse process roles, such as carbon fixation, wastewater detoxification and carboxylates intermediate production. The recovered energy in the form of intermediate carboxylates allows for their use as substrates in subsequent fermentative stages.

Enhanced anaerobic biodegradation of typical phenolic compounds in coal gasification wastewater (CGW) using biochar: Focusing on the hydrolysis-acidification process and microbial community succession

The aim of this research is to investigate the effects of biochar (BC) on treatment performance (especially hydrolysis-acidification process) and microbial community shifts during anaerobic degradation of typical phenolic compounds in coal gasification wastewater. Compared to the control group, the removal of phenol, p-cresol and 3, 5-xylenol was gradually enhanced when increasing the BC addition within the test dosage (1-5 g/L). The biodegradation of phenol and p-cresol was significantly enhanced by BC addition while limited improvement for 3, 5-xylenol. The addition of BC significantly accelerated the hydrolysis-acidification process with the hydrolytic removal of phenol improved by 69.14%, the microbial activity was enhanced by 57.01%, and the key hydrolase bamA gene was enriched by 117.27%, respectively. Compared to 1-2 g/L dose, more protein-like and humic acid-like substances were secreted with 5 g/L BC, which probably contributed to higher extracellular electron transfer efficiency. In addition, phenol degrading bacteria (Syntrophorhabdus, Dysgonomonas, Holophaga, etc.) and electroactive microorganisms (Geobacter, Syntrophorhabdus, Methanospirillum, etc.) were enriched by BC addition. The functional genes related to carboxylation, benzoylation and ring cleavage processes of benzoyl-CoA pathway were potentially activated by BC.

Nitrification-denitrification co-metabolism in an algal-bacterial aggregates system for simultaneous pyridine and nitrogen removal

Photosynthetic oxygenation in algal-bacterial symbiotic (ABS) system was mainly concerned to enhance contaminant biodegradation by developing an aerobic environment, while the role of nitrification-denitrification involved is often neglected. In this study, an algal-bacterial aggregates (ABA) system was developed with algae and activated sludge (PBR-1) to achieve simultaneous pyridine and nitrogen removal. In PBR-1, as high as 150 mg·L-1 pyridine could be completely removed at hydraulic residence time of 48 h. Besides, total nitrogen (TN) removal efficiency could be maintained above 80%. Nitrification-denitrification was verified as the crucial process for nitrogen removal, accounting for 79.3% of TN removal at 180 μmol·m-2·s-1. Moreover, simultaneous pyridine and nitrogen removal was enhanced through nitrification-denitrification co-metabolism in the ABA system. Integrated bioprocesses in PBR-1 including photosynthesis, pyridine biodegradation, carbon and nitrogen assimilation, and nitrification-denitrification, were revealed at metabolic and transcriptional levels. Fluorescence in situ hybridization analysis indicated that algae and aerobic species were located in the surface layer, while denitrifiers were situated in the inner layer. Microelectrode analysis confirmed the microenvironment of ABA with dissolved oxygen and pH gradients, which was beneficial for simultaneous pyridine and nitrogen removal. Mechanism of nitrification-denitrification involved in pyridine and nitrogen removal was finally elucidated under the scale of ABA.

Bioelectrochemical anaerobic membrane bioreactor enables high methane production from methanolic wastewater: Roles of microbial ecology and microstructural integrity of anaerobic biomass

The disintegration of anaerobic sludge and blockage of membrane pores has impeded the practical application of anaerobic membrane bioreactor (AnMBR) in treating methanolic wastewater. In this study, bioelectrochemical system (BES) was integrated into AnMBR to alleviate sludge dispersion and membrane fouling as well as enhance bioconversion of methanol. Bioelectrochemical regulation effect induced by BES enhanced methane production rate from 4.94 ± 0.52 to 5.39 ± 0.37 L/Lreactor/d by accelerating the enrichment of electroactive microorganisms and the agglomeration of anaerobic sludge via the adhesive and chemical bonding force. 16 S rRNA gene high-throughput sequencing demonstrated that bioelectrochemical stimulation had modified the metabolic pathways by regulating the key functional microbial communities. Methanogenesis via the common methylotrophic Methanomethylovorans was partially substituted by the hydrogenotrophic Candidatus_Methanofastidiosum, etc. The metabolic behaviors of methanol are bioelectrochemistry-dependent, and controlling external voltage is thus an effective strategy for ensuring robust electron transfer, low membrane fouling, and long-term process stability.

Sequentially modified carbon felt for enhanced p-nitrophenol biodegradation through direct interspecific electron transfer

The widely applied aromatic nitration in modern industry leads to toxic p-nitrophenol (PNP) in environment. Exploring its efficient degradation routes is of great interests. In this study, a novel four-step sequential modification procedure was developed to increase the specific surface area, functional group, hydrophilicity, and conductivity of carbon felt (CF). The implementation of the modified CF promoted reductive PNP biodegradation, attaining 95.2 ± 0.8% of removal efficiency with less accumulation of highly toxic organic intermediates (e.g., p-aminophenol), compared to carrier-free and CF-packed biosystems. The constructed anaerobic-aerobic process with modified CF in 219-d continuous operation achieved further removal of carbon and nitrogen containing intermediates and partial mineralization of PNP. The modified CF promoted the secretion of extracellular polymeric substances (EPS) and cytochrome c (Cyt c), which were essential components to facilitate direct interspecies electron transfer (DIET). Synergistic relationship was deduced that glucose was converted into volatile fatty acids by fermenters (e.g., Longilinea and Syntrophobacter), which donated electrons to the PNP degraders (e.g., Bacteroidetes_vadinHA17) through DIET channels (CF, Cyt c, EPS) to complete PNP removal. This study proposes a novel strategy using engineered conductive material to enhance the DIET process for efficient and sustainable PNP bioremediation.

Detoxification of typical nitrogenous heterocyclic compound from pharmaceutical wastewater by mixed microbial consortia

Microbial consortia HY3 and JY3 with high degradation efficiency of 2-Diethylamino-4-hydroxy-6-methylpyrimidine (DHMP) were isolated from aerobic and parthenogenic ponds of DHMP-containing pharmaceutical wastewater, respectively. Both consortia were enriched and reached stable degradation performance with a DHMP concentration of 1500 mg L^-1. The DHMP degradation efficiencies of HY3 and JY3 were 95.66% ± 0.24% and 92.16% ± 2.34% under the condition of shaking at 180 r·min^-1 and the temperature of 30 °C for 72 h. And the removal efficiencies of chemical oxygen demand were 89.14% ± 4.78% and 80.30% ± 11.74%, respectively. High-throughput sequencing results indicated that three bacterial phyla of Proteobacteria, Bacteroidetes, and Actinobacteria were dominant in both HY3 and JY3, but their dominances varied. At the genus level, the richness of Unclassified Comamonadaceae (34.23%), Paracoccus (14.75%), and Brevundimonas (13.94%) ranked top three in HY3 whereas Unclassified Comamonadaceae (40.80%), Unclassified Burkholderiales (13.81%) and Delftia (13.11%) were dominant in JY3. The metabolites of DHMP degradation by HY3 and JY3 were analyzed in detail. Two pathways for cleavage of the nitrogenous heterocyclic ring were speculated, one of which was identified for the first time in this study.

New insight into fate and transport of organic compounds from pollution sources to aquatic environment using non-targeted screening: A wastewater treatment plant case study

A variety of chemicals discharged into the aquatic environment by the wastewater treatment plant (WWTP), which is a potential source of hazard to the ecological environment and human health. This study established a novel analytical method for all compounds using non-targeted screening to comprehensively explore the fate and transport of organic compounds from WWTP to aquatic environment. 3967 and 3636 features were detected in WWTP samples and river samples, respectively. Multi-level classification was applied to all identified compounds, and results showed that aliphatics were dominant in both abundance and response, accounting for an average of 35.49 % and 74.10 %, respectively. A total of 88 Emerging Contaminants (ECs), including 22 endocrine disrupting chemicals (EDCs), 12 pharmaceuticals and personal care products (PPCPs), 12 pesticides, 10 volatile organic compounds (VOCs), 5 persistent organic pollutants (POPs) and 27 chemicals with other uses, were identified from all compounds, and their traceability analysis was performed. Furthermore, the contribution rate of organic compounds from WWTP effluent to river was calculated to be 33.60 % by the analysis of source-sink relationship. An in-depth and comprehensive exploration of the fate and transport of all organic compounds will help to provide guidelines for the treatment technologies and achieve the traceability of pollutants.

Can a compact biological system be used for real hydraulic fracturing wastewater treatment?

Hydraulic fracturing wastewater (HFW), a byproduct of hydraulic fracturing oil extraction, contains a complex mixture of oil, aldehydes, and benzene compounds. Efficient and eco-friendly HFW treatment means are critical for the oil extraction industry, particularly in developing countries. In this study, two biological processes namely an anaerobic/anoxic/moving bed biofilm reactor (A²-MBBR) and an A²-MBBR with a microfiltration membrane (A²-MFMBBR) were established, and assessed for the real HFW treatment. Removal efficiencies of chemical oxygen demand (COD) and NH₄⁺-N were over 92% and 95%, respectively, in both processes with a hydraulic retention time of 72 h. The majority of organic compounds in both systems identified by GC-MS were degraded in the anaerobic units. In comparison, A²-MFMBBR demonstrated higher removal efficiencies for oil, total suspended solids, and complex compounds. The average relative abundances of refractory compound degrading bacteria were 43.4% and 51.6% in the A²-MBBR and A²-MFMBBR, respectively, which was consistent with the COD and oil removal, and suggested that the MBR could maintain a high diversity of microorganisms and contribute to deep recalcitrant organics degradation. This study sheds light on the potential of using a compact biological process for the real HFW treatment.

In-situ growth of Co/Ni bimetallic organic frameworks on carbon spheres with catalytic ozonation performance for removal of bio-treated coking wastewater

The Co/Ni-MOFs@CS composite derived from Co/Ni bimetallic organic framework was synthesized and characterized. Compared with a single O₃ system, the synergy between carbon sphere (CS) and metal organic frameworks (MOFs) improved the electron transfer efficiency and the formation rate of •OH. The coexistence of Co and Ni in various valence states might accelerate the cyclic process of Co(II)/Co(III) and Ni(II)/Ni(III), thereby improving the catalytic activity. Taking levofloxacin as a model pollutant, the mechanism of catalytic process was discussed, and the catalytic reaction was successfully applied to the removal of residual organics in bio-treated coking wastewater (BTCW). The removal rates of chemical oxygen demand (COD) and total organic carbon (TOC) in 60 min were 50.85%-53.71% and 39.98%-43.48%. From the perspective of UV absorption and 3D EEM, catalytic ozonation was more conducive to breaking the electronic protection of inert organic molecules such as heterocyclic compounds, and achieving higher efficiency of mineralization. It provides a new idea for catalytic ozonation technology of wastewater treatment in the future from theory, technology and application.

Insights into removal of sulfonamides in anaerobic activated sludge system: Mechanisms, degradation pathways and stress responses

The fate of antibiotics in activated sludge has attracted increasing interests. However, the focus needs to shift from concerning removal efficiencies to understanding mechanisms and sludge responding to antibiotic toxicity. Herein, we operated two anaerobic sequencing batch reactors (ASBRs) for 200 days with sulfadiazine (SDZ) and sulfamethoxazole (SMX) added. The removal efficiency of SMX was higher than that of SDZ. SDZ was removed via adsorption (9.91-21.18%) and biodegradation (10.20-16.00%), while biodegradation (65.44-86.26%) was dominant for SMX removal. The mechanisms involved in adsorption and biodegradation were investigated, including adsorption strength, adsorption sites and the roles of enzymes. Protein-like substance (tryptophan) functioned vitally in adsorption by forming complexes with sulfonamides. P450 enzymes may catalyze sulfonamides degradation via hydroxylation and desulfurization. Activated sludge showed distinct responses to different sulfonamides, reflected in the changes of microbial communities and functions. These responses were related to sulfonamides removal, corresponding to the stronger adsorption capacity of activated sludge in ASBR-SDZ and degradation capacity in ASBR-SMX. Furthermore, the reasons for different removal efficiencies of sulfonamides were analyzed according to steric and electronic effects. These findings propose insights into antibiotic removal and broaden the knowledge for self-protection mechanisms of activated sludge under chronic toxicities of antibiotics.

Enhanced anaerobic degradation of quinoline and indole with the coupling of sodium citrate and polyurethane

A coupling system of sodium citrate and biofilm based on polyurethane was prepared to analyse the coupling enhancement degradation on quinoline and indole. Four reactors (R1: sludge, R2: sludge + sodium citrate, R3: biofilm on polyurethane, and R4: biofilm + sodium citrate) were operated 120 days to compare the degradation efficiency. During whole running phases, R4 showed high degradation efficiency on quinoline (≥98.55%) and indole (≥95.44%). Analysis of bacterial colony showed anaerobic sludge reactors benefited the enrichment of Aminicenantes, Levilinea, and Longilinea, while anaerobic biofilm reactors benefited the enrichment of Giesbergeria and Comamonas. Furthermore, analysis of archaea colony showed acetic acid metabolism to produce methane was the main mode in anaerobic sludge reactors, while acetic acid and hydrogen metabolism to produce methane were both the main modes in biofilm reactors. This study can provide some references for the treatment of nitrogen heterocyclic wastewater.

Effects of polyurethane foam carrier addition on anoxic/aerobic membrane bioreactor (A/O-MBR) for coal gasification wastewater (CGW) treatment: Performance and microbial community structure

Coal gasification wastewater (CGW) is a typical toxic and refractory industrial wastewater with abundant phenols contained. Two identical anoxic/aerobic membrane bioreactors (with (R2) and without (R1) polyurethane (PU) foam) were carried out in parallel to investigate the role of PU foam addition in enhancing pollutants removal in CGW. Results showed that both systems exhibited effective removal of chemical oxygen demand (>93%) and total phenols (>97%) but poor ammonia nitrogen removal (<35%) constrained by ammonia oxidation process. GC-MS analysis revealed that aromatic and other refractory intermediates were dramatically reduced in R2. Moreover, the PU addition had negligible influence on the total soluble microbial products and extracellular polymeric substances contents but significantly alleviated membrane fouling with the operating time 33% prolonged. Microbial community revealed that Flavobacterium, Holophaga, and Geobacter were enriched on PU. Influent type might be a main driver for microbial community succession.

Synergy between pyridine anaerobic mineralization and vanadium (V) oxyanion bio-reduction for aquifer remediation

The co-occurrence of toxic pyridine (Pyr) and vanadium (V) oxyanion [V(V)] in aquifer has been of emerging concern. However, interactions between their biogeochemical fates remain poorly characterized, with absence of efficient route to decontamination of this combined pollution. In this work, microbial-driven Pyr degradation coupled to V(V) reduction was demonstrated for the first time. Removal efficiencies of Pyr and V(V) reached 94.8 ± 1.55% and 51.2 ± 0.20% in 72 h operation. The supplementation of co-substrate (glucose) deteriorated Pyr degradation slightly, but significantly promoted V(V) reduction efficiency to 84.5 ± 0.635%. Pyr was mineralized with NH₄⁺-N accumulation, while insoluble vanadium (IV) was the major product from V(V) bio-reduction. It was observed that Bacillus and Pseudomonas realized synchronous Pyr and V(V) removals independently. Interspecific synergy between Pyr degraders and V(V) reducers also functioned with addition of co-substrate. V(V) was bio-reduced through alternative electron acceptor pathway conducted by gene nirS encoded nitrite reductase, which was evidenced by gene abundance and enzyme activity. Cytochrome c, nicotinamide adenine dinucleotide and extracellular polymeric substances also contributed to the coupled bioprocess. This work provides new insights into biogeochemical activities of Pyr and V(V), and proposes novel strategy for remediation of their co-contaminated aquifer.

Unravelling nitrogen removal and nitrous oxide emission from mainstream integrated nitrification-partial denitrification-anammox for low carbon/nitrogen domestic wastewater

Stable supply of nitrite is often a major obstacle for achieving mainstream anammox due to washout failure of nitrite oxidizers (NOB) at low influent ammonia of municipal wastewater. In this study, an integrated nitrification, partial denitrification and anammox (INPDA) as a one-stage mainstream nitrogen removal alternative was established in a low-oxygen sequencing batch biofilm reactor treating synthetic sewage. The overall nitrogen removal and nitrous oxide (N₂O) emission were mainly investigated at 50 mg/L NH₄⁺-N influent with a low carbon/nitrogen (C/N) of 2.5. Continuous operation demonstrated that as high as 98.8% NH₄⁺-N and 94.1% TN were removed in SBBR system. Cyclic experiment verified sequential completion of nitrification, partial denitrification and anammox were responsible for high-rate TN removal. During one typical cycle, the trend of N₂O emission was characterized by firstly rapid rise, then fluctuant decrease followed by rapid decrease and finally slow disappearance. The maximum N₂O emission rate reached up to 6.7 μg/(L·min) occurred at 75 min. High-throughput sequencing revealed the co-existence of nitrifying, denitrifying and anammox species and large detection of key functional genes (Hzs, Hdh, Hao, Nor) in an oxygen-limited SBBR, thereby highly correlating nitrogen removal and N₂O emission characteristics. Nitrogen metabolic pathways analysis further suggest denitratation(NO₃^--N to NO₂^--N)-based anammox is a main route for mainstream nitrogen removal. Moreover, N₂O might be generated by both hydroxylamine oxidation step in nitrification and also heterotrophic denitrification pathway. The research findings provide more deep understandings of enhanced nitrogen removal and mitigated N₂O footprint from a single mainstream anammox-based system.

Investigation of hydrolysis acidification process during anaerobic treatment of coal gasification wastewater (CGW): Evolution of dissolved organic matter and biotoxicity

Coal gasification wastewater (CGW) contains several types of aromatic pollutants, which impart high biotoxicity and reduce the quality of anaerobic treatment. Two types of hydrolysis acidification processes, namely microaerobic hybrid reactor (HA-1) and upflow anaerobic sludge blanket reactor (HA-2), were developed for pre-treatment before the anaerobic treatment. The changes in the dissolved organic matter and biotoxicity were investigated to comprehensively understand the degradation process. The results showed that HA-2 coupled with an anaerobic reactor achieved a 12.3% and 13.4% higher removal efficiency for chemical oxygen demand and total phenols, respectively, compared with the coupled process with HA-1. Furthermore, HA-2 could transform macromolecules into small molecules more efficiently and produce fewer intermediates. The coupled process with HA-2 preferentially removed complex aromatic substances with absorption wavelengths of 285 and 254 nm, according to the sequential orders interpreted from two-dimensional correlation spectroscopy. In addition, the results of fluorescence excitation-emission-matrix with regional integration analysis revealed that the contents of typical cyclic compounds in CGW, such as phenolic, heterocyclic, and polycyclic aromatic compounds were remarkably reduced by HA-2. In addition, HA-2 reduced the toxic unit value of CGW by 67.5% and increased the resazurin dehydrogenase activity of the sludge by 37.5% during CGW treatment, thus improving the biotoxicity removal and biodegradability. However, the coupled process with HA-2 did not significantly affect the "indirect estrogenic activity" of CGW. A Pearson correlation analysis indicated that spectral indicators, such as UV₂₅₄ and Φ_T,n, presented a high positive correlation with the reduction of acute toxicity and organics.

Efficient degradation of indole by microbial fuel cell based Fe2O3-polyaniline-dopamine hybrid composite modified carbon felt anode

Indole is a high-toxic refractory nitrogen-containing compound that could cause serious harm to the human and ecosystem. It has been a challenge to develop economical and efficient technology for degrading indole. Microbial fuel cell (MFC) has great potential in the removal of organic pollutants utilizing microorganisms as catalysts to degrade organic matter into the nutrients. Herein, a novel anode of Fe₂O₃-polyaniline-dopamine hybrid composite modified carbon felt (Fe₂O₃-PDHC/CF) was prepared by electrochemical deposition. The degradation efficiency of indole by the MFC loading Fe₂O₃-PDHC/CF anode was up to 90.3 % in 120 h operation, while that of the MFC loading CF anode was only 44.0 %. The maximum power density of the MFC loading Fe₂O₃-PDHC/CF anode was 3184.4 mW·m^-2, increasing 113 % compared to the MFC loading CF anode. The superior performances of the MFC with Fe₂O₃-PDHC surface-modified anode owned to the synergistic effect of high conductive Fe₂O₃ and admirably biocompatible polyaniline-dopamine. MFC with the Fe₂O₃-PDHC/CF anode could produce considerable electricity and effectively degrade indole in water, which demonstrated a practical approach for the efficient degradation of refractory organic compounds in wastewater.

New insights of enhanced anaerobic degradation of refractory pollutants in coking wastewater: Role of zero-valent iron in metagenomic functions

Coking wastewater (CWW) has long been a serious challenge for anaerobic treatment due to its high concentrations of phenolics and nitrogen-containing heterocyclic compounds (NHCs). Herein, we proposed and validated a new strategy of using zero-valent iron (ZVI) to strengthen the anaerobic treatment of CWW. Results showed that COD removal efficiencies was increased by 9.5-13.7% with the assistance of ZVI. GC-MS analysis indicated that the removal of phenolics and NHCs was improved, and the intermediate 2(1H)-Quinolinone of quinoline degradation was further removed by ZVI addition. High-throughput sequencing showed that phenolics and NHCs degraders, such as Levilinea and Sedimentibacter were significantly enriched, and the predicted gene abundance of xenobiotic degradation and its downstream metabolic pathways was also increased by ZVI. Network and redundancy analysis indicated that the decreased oxidation-reduction potential (ORP) by ZVI was the main driver for microbial community succession. This study provided an alternative strategy for strengthening CWW anaerobic treatment.

Enhanced anaerobic degradation of nitrogen heterocyclic compounds with methanol, sodium citrate, chlorella, spirulina, and carboxymethylcellulose as co-metabolic substances

The aim of the study was to explore the feasibility of methanol, sodium citrate, chlorella, spirulina, and carboxymethylcellulose (CMC) as co-metabolic substances in strengthening the anaerobic degradation of selected nitrogen heterocyclic compounds (NHCs). Chlorella, spirulina, and CMC as co-metabolic substances were first introduced into the enhanced anaerobic treatment of refractory compounds. With the addition of 300 μg/L sodium citrate, chlorella, spirulina, and CMC, reactor 3, reactor 4, reactor 5, and reactor 6 had higher degradation ratios than reactor 2 with methanol as co-metabolic substance. The addition of sodium citrate, chlorella, spirulina, and CMC increased the number of bacterial sequences, promoted the richness and diversity of the bacterial community structure, and enriched the functional genera (Levilinea and Longilinea) responsible for the degradation of quinoline and indole.

The concept of anaerobic hydrolysis to produce clean and stable energy from the case study of utilization of three types of pollutants in coal pyrolysis wastewater

The purpose of the research was to explore the feasibility of anaerobic hydrolysis in the recycling of chemical wastewater. From the case study of utilization of coal pyrolysis wastewater (CPW), the concept of anaerobic hydrolysis to produce clean and stable energy was proposed. Compared with anaerobic methane production and hydrogen production, anaerobic hydrolysis was more suitable to realize the resource utilization of chemical wastewater. Typical pollutants in CPW could be hydrolyzed into short chain alkanes (or alkane alcohol) under the action of anaerobic hydrolysis. Furthermore, element N was released during the anaerobic hydrolysis of nitrogen heterocyclic compounds. The advantages and existing problems of anaerobic hydrolysis were also discussed. The conversion mechanism of pollutants in CPW can provide a theoretical basis for the utilization of chemical wastewater.

A novel enhanced anaerobic biodegradation method using biochar and Fe(OH)3@biochar for the removal of nitrogen heterocyclic compounds from coal gasification wastewater

Three identical lab-scale sequencing batch reactors (SBR) were operated for 120 days for raw (R₁), biochar (R₂), and Fe(OH)₃@biochar (R₃) enhanced anaerobic degradation of selected nitrogen heterocyclic compounds (NHCs). The occurrence of Fe-OH ensured the successful attachment of Fe(OH)₃ to biochar as evidenced by the Fourier transform infrared (FTIR) spectra of biochar and Fe(OH)₃@biochar. Acute biotoxicity experiments revealed that enhancing biochar and Fe(OH)₃@biochar effectively decreased the toxicity of microorganisms. Additionally, the introduction of biochar and Fe(OH)₃@biochar improved the settling performance of anaerobic sludge. Further, it was concluded that enriched Longilinea and Comamonas might be the major genera that function to degrade selected NHCs in anaerobic conditions.

Enhanced anaerobic degradation of quinoline, pyriding, and indole with polyurethane (PU), Fe3O4@PU, powdered activated carbon (PAC), Fe(OH)3@PAC, biochar, and Fe(OH)3@biochar and analysis of microbial succession in different reactors

The study was to explore the feasibility of polyurethane (PU), Fe₃O₄@PU, powdered activated carbon (PAC), Fe(OH)₃@PAC, biochar, and Fe(OH)₃@biochar as biological carriers in strengthening anaerobic degradation of quinoline, pyridine, and indole. When the concentrations of pollutants were 25 mg/L and 50 mg/L, reactors based on PAC and Fe(OH)₃@PAC had higher degradation ratios than the other reactors. However, when the concentrations of pollutants were 75 mg/L and 100 mg/L, with the addition of PU and Fe₃O₄@PU, reactors began to show their superiority in the degradation of the selected NHCs. Among these, the reactor based on Fe₃O₄@PU had the optimal degradation ratio on quinoline, pyridine, and indole. PU, PAC, Fe(OH)₃@PAC, biochar, and Fe(OH)₃@biochar benefited the enrichment of Acinetobacter, Comamonas, Levilinea, Longilinea, and Desulfomicrobium. The reactor with the carrier of Fe₃O₄@PU had some specificity, which benefited the enrichment of Zoogloea, Thiobacillus, Anaeromyxobacter, Sphingobium, Terrimonas, Parcubacteria genera incertae sedis, Bdellovibrio, Rhizobium, and Acidovorax.

Enhanced anaerobic degradation of selected nitrogen heterocyclic compounds with the assistance of carboxymethyl cellulose

Carboxymethyl cellulose (CMC) is a modified cellulose compound that is dispersible in water. Microbial anaerobic degradation of nitrogen heterocyclic compounds (NHCs) in wastewater treatment may be enhanced by CMC addition, but this remains uncertain due to a lack of experimental evidence. In this study, It was demonstrated that CMC is a suitable co-metabolic matrix in an enhanced anaerobic degradation of quinoline and indole in coal gasification wastewater. When the dosage of CMC was 0.5 mg/L, a reactor exhibited a high degradation efficiency on quinoline and indole, with ratios of 95.23 ± 1.99% and 94.33 ± 3.45%. The addition of CMC increased the concentration of extracellular polymeric substances in anaerobic sludge and increased the particle size of the sludge, which improved the microbial stability and sedimentation of anaerobic granular sludge. Analysis of high-throughput sequencing indicated that the addition of CMC improved the richness and diversity of bacterial and archaea communities. Acetic acid metabolism was the primary mechanism to produce methane during anaerobic degradation of NHCs wastewater.

Enhanced biodegradation of coal gasification wastewater with anaerobic biofilm on polyurethane (PU), powdered activated carbon (PAC), and biochar

The primary objective was to explore the feasibility of anaerobic biofilm on polyurethane (PU), powdered activated carbon (PAC), and biochar in strengthening anaerobic degradation of phenolic compounds and selected nitrogen heterocyclic compounds (NHCs) in coal gasification wastewater (CGW). When total phenols (TPh) was less than 300 mg/L, PAC-based biofilm was more efficient. Whereas, when the TPh concentration was more than 450 mg/L, PU-based biofilm performed the optimal degradation efficiency. Furthermore, microbial community structure analysis showed that PAC and biochar had little effect on the microbial community structure after 120 days of operation, while the addition of PU could lead to the enrichment of Giesbergeria, Caldisericum, Thauera, Methanolinea, and Methanoregula.

Study of pre-treatment of quinoline in aqueous solution using activated carbon made from low-cost agricultural waste (walnut shells) modified with ammonium persulfate

Activated carbon made from agricultural waste (walnut shells) was investigated as a suitable adsorbent for effectively removing quinoline from industrial wastewater. The activated carbon was treated with phosphoric acid and oxidized by ammonium persulfate and its ability to adsorb pyridine and quinoline in aqueous solution was investigated. Kinetic parameters for the adsorption process were determined through pseudo-first-order and pseudo-second-order kinetic models and intraparticle diffusion models. Equilibrium experiments and adsorption isotherms were analyzed using Langmuir and Freundlich adsorption isotherms. After reaching equilibrium, the activated carbon adsorbed quinoline in preference to pyridine: the equilibrium adsorptions from individual aqueous solutions (200 μL L^-1) of quinoline and pyridine were 166.907 mg g^-1 and 72.165 mg g^-1, respectively. Thermodynamic studies of quinoline adsorption were conducted at different temperatures and indicated that quinoline adsorption was an endothermic and spontaneous process. The column-adsorption of quinoline and pyridine was consistent with the Thomas model and the Yoon-Nelson model. The removal efficiency of quinoline reached more than 97% for a velocity of 6 mL min^-1 at the initial adsorption stage.

Isolation of a 3-hydroxypyridine degrading bacterium, Agrobacterium sp. DW-1, and its proposed degradation pathway

A 3-hydroxypyridine degrading bacterium, designated strain DW-1, was isolated from petroleum contaminated soil in Liao River China. 16S rRNA-based phylogenetic analysis indicates that strain DW-1 belongs to genus Agrobacterium. The optimal cultivation temperature and pH for strain DW-1 with 3-hydroxypyridine were 30 °C and 8.0, respectively. Under optimal conditions, strain DW-1 could completely degrade up to 1500 mg/L of 3-hydroxypyridine in 66 h. The 3-hydroxypyridine degradation pathway of strain DW-1 was suggested by HPLC and LC-MS analysis. The first reaction of 3-hydroxypyridine degradation in strain DW-1 was α-hydroxylation so that the major metabolite 2,5-dihydroxypyridine was produced, and then 2,5-dihydroxypyridine was transformed by a Fe2+-dependent dioxygenase to form N-formylmaleamic acid. N-Formylmaleamic acid will be transformed to maleic acid and fumaric acid through maleamic acid. This is the first report of the 3-hydroxypyridine degradation pathway and the utilization of 3-hydroxypyridine by a Agrobacterium sp. It may be potentially used for the bioremediation of environments polluted with 3-hydroxypyridine.