Anaerobic Wastewater Treatment Research Articles

Coupling Fe3O4 and micro-hydrogen for enhancing the anaerobic bio-conversion of phenol: Methanogenesis pathway and interspecies electron transfer

Low anaerobic biological conversion rate is a challenge in the anaerobic biological treatment of phenol wastewater. The dominant syntrophic acetate oxidation and hydrogenotrophic methanogenesis (SAO-HM) pathway is expected to solve the problem. However, there are raw studies on artificially simulating a dominant SAO-HM pathway for enhancing the anaerobic bio-conversion of phenol. In this study, Fe3O4 and micro-hydrogen (Fe3O4/H2) was used to strengthen the anaerobic bio-conversion of phenol by simulating the dominant SAO-HM pathway. The results suggested Fe3O4 and H2 had a coupling promotion on the anaerobic bio-conversion of phenol and Fe3O4/H2 increased the relative abundance of Syntrophus (29.35%), Syntrophorhabdu (3.27%), Clostridium (3.01%) and Methanobacterium (65.74%), indicating Fe3O4/H2 formed a dominant SAO-HM pathway. However, Fe3O4/H2 obviously reduced the conductivity of sludge, the extracellular protein and the functional gens pilA, pilB and OmcS, implying direct interspecies electron transfer (DIET) generated by Fe3O4 was interfered by micro hydrogen in extracellular electron transport process which reduced the efficiency of extracellular electron transport. This study remind that extracellular electron transport cannot be ignored in the dominate SAO-HM pathway for the anaerobic bio-conversion of phenol.

Microbial community response to temperature reduction during anaerobic treatment of long chain fatty acids-containing wastewater

Acclimating mesophilic biomass to low temperatures have been used to start-up psychrophilic anaerobic reactors, but limited microbial information is available during the acclimation. To investigate microbial responses to temperature reductions, duplicate lab-scale anaerobic digestion (AD) reactors were operated for 166 days, with the temperature being reduced from 37°C to 15°C, using synthetic long chain fatty acid (LCFA)-containing wastewater as the feedstock. The acclimated biomass at 15°C exhibited efficient removal of organic matter (total COD>75%, soluble COD>88%, and LCFA>99%). Temperature reductions lead to significant reductions in microbiome diversity. Fermentative bacteria were highly dynamic and functional redundant during temperature reductions. Smithella was the dominant syntrophic bacteria involved in LCFA degradation coupled with Methanothrix and Methanocorpusculum at 15°C. Membrane modifications and compatible cellular solutes production were triggered by temperature reductions as microbial response to cold stress. This study provided molecular insights in microbial acclimation to low temperatures for psychrophilic AD.

Impact of gentamicin on the performance and antimicrobial resistance in the anaerobic treatment of pharmaceutical wastewater

Impact of gentamicin on the performance and antimicrobial resistance in the anaerobic treatment of pharmaceutical wastewater

An in-depth analysis of microbial response to exposure to high concentrations of microplastics in anaerobic wastewater fermentation

The impact of microplastics (MPs) in anaerobic wastewater treatment on microbial metabolism is significant. Anaerobic granular sludge (AS) and biofilm (BF) are two common ways, and their responses to microplastics will have a direct impact on their application potential. This study investigated the microbial reactions of AS and BF to three types of MPs: polyethylene (PE), polyvinyl chloride (PVC), and a mixture of both (MIX). Results exhibited that MPs reduced methane output by 44.65 %, 55.89 %, and 53.18 %, elevated short-chain fatty acid (SCFA) levels by 95.93 %, 124.49 %, and 110.78 %, and lowered chemical oxygen demand (COD) removal by 28.77 %, 36.78 %, and 33.99 % for PE-MP, PVC-MP, and MIX-MP, respectively, with PVC-MP showing the greatest inhibition. Meanwhile, microplastics also facilitated the relative production of reactive oxygen species (ROS, 40.29 %–96.99 %), lactate dehydrogenase (LDH, 20.01 %–75.02 %), and adenosine triphosphate (ATP, 26.64 %–43.80 %), while reducing cytochrome c (cyt c, 23.60 %–49.02 %) and extracellular polymeric substances (EPS, 17.44 %–26.58 %). AS and BF displayed distinct enzymatic activities under MPs exposure. Correspondingly, 16S-rRNA sequencing indicated that AS was mainly involved in acetate generation by Firmicutes, while BF performed polysaccharide degradation by Bacteroidota. Metatranscriptomic analysis showed AS to be rich in acetogens (Bacillus, Syntrophobacter) and methanogens (Methanothrix, Methanobacterium), while BF contained more fermentation bacteria (Mesotoga, Lentimicrobium) and electroactive microorganisms (Clostridium, Desulfuromonas) under MIX-MP. Moreover, BF exhibited higher glycolysis gene expression, whereas AS was more active in methane metabolism, primarily through the acetoclastic methanogenic pathway's direct acetate conversion. This study provides new insights into understanding the microbial response produced by microplastics during anaerobic wastewater digestion.

Long-term performance and activity study of a two-stage anaerobic EGSB reactors system treating complex and toxic industrial wastewater.

Anaerobic treatment of industrial wastewater using upflow anaerobic reactors is an extended trend due to its high efficiency and biogas production potential, but its implementation in some sectors is limited due to the complexity and toxicity of the wastewaters. In this study, a two-stage expanded granular sludge bed (EGSB) reactors system has been investigated at both bench and pilot scale for the treatment of complex and toxic real wastewater from a petrochemical industry. The effect of different operational parameters including organic loading rate (OLR), hydraulic retention time (HRT) and influent characteristics over COD removal and biogas production and composition have been studied. Additionally, biomass specific methanogenic activity (SMA) and wastewater toxicity have been evaluated after long-term operation. Optimum total HRT of 24 h has been determined resulting in total COD and SO4 2- removal of 56.30 ± 5.25% and 31.68 ± 14.71%, respectively, at pilot scale, and average biogas production of 93.47 ± 34.92 NL/day with 67.01 ± 10.23 %CH4 content and 5210.11 ± 6802.27 ppmv of H2S. SMA and toxicity tests have confirmed inhibitory and toxic effects of wastewater over anaerobic biomass with average maximum inhibition of 65.34% in the unacclimated anaerobic inoculum while chronic toxicity produced a decrease of an order of magnitude in SMA after 600 days of operation. This study demonstrates the feasibility of applying an anaerobic treatment to this wastewater using EGSB reactors between a 0.97-1.74 gCOD/L/day OLR range. Nonetheless, periodic reinoculation would be necessary for long-term operation due to chronic toxicity of the wastewater exerted on the anaerobic biomass. PRACTITIONER POINTS: A two-stage EGSB reactors system has been operated at bench and pilot scale to treat complex and toxic petrochemical wastewater. Optimal total HRT of 24 h resulted in average COD removal ranging from 40% to 60%. SMA and toxicity tests have been performed to study long-term acclimation, detecting an activity depletion of an order of magnitude.

Comparative study on the effects of anionic, cationic, and nonionic polyacrylamide surface modified magnetic micro-particles (MMP) for anaerobic digestion treatment of vegetable waste water (VWW)

Anaerobic digestion provides a solution for the treatment of vegetable waste water (VWW), but there are currently limited targeted treatment methods available. Building upon previous studies, this research investigated the effects of polyacrylamide-modified magnetic micro-particles (MMP) on anaerobic digestion (AD) of VWW. Three variations of these particles were created by grafting anionic, cationic, and non-ionic polyacrylamide (PAM) onto the MMPs’ surfaces, resulting in aPAM-MMP, cPAM-MMP, and nPAM-MMP, respectively. In AD experiments, the addition of aPAM-MMP notably enhanced the degradation of chemical oxygen demand (COD) in VWW. COD decreased to 1290 mg/L in the reactor with aPAM-MMP by day 12 and remained low, while the other reactors had COD concentrations of 4137.5, 5510, and 3010 mg/L on the same day, decreasing thereafter. This modification also improved the production and utilization of hydrogen gas and volatile fatty acids (VFAs), along with the conversion of methane. When tested for bioaffinity using fluorescent GFP-E.coli bacteria, the aPAM-MMP, cPAM-MMP, and nPAM-MMP demonstrated increases in fluorescence intensity by 51.66%, 36.13%, and 37.02%, respectively, compared to unmodified MMP when attached with GFP-E.coli. Further analyses of microbial community revealed that the reactor with aPAM-MMP had the highest microbial richness and enriched bacteria capable of organic matter degradation, such as Bacteroidota, Synergistota, Chloroflexi, Halobacterota phyla, and Parabacteroides, Muribaculaceae, and Azotobacter genera. In conclusion, our experiment verifies that APAM-MMP promotes anaerobic treatment of VWW and provides a novel reference point for enhancing VWW degradation.

Enhancing assimilatory sulfate reduction with ferrihydrite-humic acid coprecipitate in anaerobic sulfate-containing wastewater treatment

Sulfide produced from dissimilatory sulfate reduction can combine with hydrogen to form hydrogen sulfide, causing odor issues and environmental pollution. To address this problem, ferrihydrite-humic acid coprecipitate was added to improve assimilatory sulfate reduction (ASR), resulting in a decrease in sulfide production (190.2 ± 14.6 mg/L in the Fh-HA group vs. 246.3 ± 8.1 mg/L in the Fh group) with high sulfate removal. Humic acid, adsorbed on the surface of ferrihydrite, delayed secondary mineralization of ferrihydrite under sulfate reduction condition. Therefore, more iron-reducing species (e.g. Trichococcus, Geobacter) were enriched with ferrihydrite-humic acid coprecipitate to transfer more electrons to other species, which led to more COD reduction, an increase in electron transfer capacity, and a decrease in the NADH/NAD+ ratio. Metagenomic analysis also indicated that functional genes related to ASR was enhanced with ferrihydrite-humic acid coprecipitate. Thus, the addition of ferrihydrite-humic acid coprecipitate can be considered as a promising candidate for anaerobic sulfate wastewater treatment.

Electric stimulation mitigated the mixed microplastic inhibition to anaerobic digestion during wastewater treatment

The presence of mixed microplastics (MPs) in anaerobic wastewater treatment processes has been shown to impede fermentation performance by suppressing microbial activity. Microbial electrosynthesis (MES), with its extensive potential, offers a promising solution for refractory substances management and methane recovery, achieved through the enhancement of microbial metabolism and interspecies electron transfer. This study, therefore, delves into the functional impacts and the microbial response to MES in the remediation of wastewater contaminated with mixed-MPs. Results indicated that mixed-MPs could inhibit methane production (−52.38%) and substance removal (−26.59%), and MES could effectively mitigate this inhibitory effect (−22.86%, −19.01%). Concurrently, MES also boosts enzymatic activities pivotal for electron transfer, such as cytochrome c and nicotinamide adenine dinucleotide (NADH), as well as those linked to energy metabolism like adenosine triphosphate (ATP). Furthermore, MES bolsters microbial resistance to mixed-MPs, as evidenced by an increase in extracellular polymeric substances (EPS), albeit with a minor rise in reactive oxygen species (ROS) production and lactate dehydrogenase (LDH) release. Correspondingly, electric stimulation promoted the enrichment of functional microorganisms associated with fermentation, acetate production, electrogenesis, and methanogenesis, and stimulated elevated expression levels of genes related to methane metabolism. Notably, the Methanothrix-mediated acetoclastic pathway emerges as the predominant methanogenic route, succeeded by the Methanobacterium-driven hydrogenotrophic pathway. Lastly, the study underscores the supportive role of applied voltage and carriers in energy metabolism and substance transport, which are associated with methanogenesis. Overall, MES demonstrates efficacy in mitigating the biotoxicity induced by mixed-MPs exposure and in enhancing anaerobic wastewater treatment and methane recovery.

Full-scale study on high-rate low-temperature anaerobic digestion of agro-food wastewater: process performances and microbial community.

The fast-growing global population has led to a substantial increase in food production, which generates large volumes of wastewater during the process. Despite most industrial wastewater being discharged at lower ambient temperatures (<20 °C), majority of the high-rate anaerobic reactors are operated at mesophilic temperatures (>30 °C). High-rate low-temperature anaerobic digestion (LtAD) has proven successful in treating industrial wastewater both at laboratory and pilot scales, boasting efficient organic removal and biogas production. In this study, we demonstrated the feasibility of two full-scale high-rate LtAD bioreactors treating meat processing and dairy wastewater, and the microbial communities in both reactors were examined. Both reactors exhibited rapid start-up, achieving considerable chemical oxygen demand (COD) removal efficiencies (total COD removal >80%) and generating high-quality biogas (CH4% in biogas >75%). Long-term operations (6-12 months) underscored the robustness of LtAD bioreactors even during winter periods (average temperature <12 °C), as evidenced by sustained high COD removal rates (total COD removal >80%). The stable performance was underpinned by a resilient microbial community comprising active acetoclastic methanogens, hydrolytic, and fermentative bacteria. These findings underscore the feasibility of high-rate low-temperature anaerobic wastewater treatment, offering promising solutions to the zero-emission wastewater treatment challenge.

Enhanced methane production from anaerobic wastewater treatment by carbon nanotubes: Surface defect mediated interfacial electron transfer

Interfacial electron transfer, a crucial process in direct interspecies electron transfer (DIET) between exo-electrogenic microorganisms and conductive materials, has played a vital role in enhancing methane production in anaerobic wastewater treatment. To improve interfacial electron transfer, the construction of surface defect has been identified as an effective approach. In this study, a range of metals and non-metals were used to dope carbon nanotubes (CNTs), which were served as the conductive materials and added into anaerobic wastewater treatment systems. The effect of surface defect of CNTs on methane production were investigated. The results demonstrated that all the doped CNTs can significantly increase methane production rate in anaerobic systems. Among them, boron and iron doped CNTs (B-CNTs and Fe-CNTs) exhibited the most promising performance as non-metal and metal doped CNTs. The addition of B-CNTs and Fe-CNTs led to impressive increase of 101.6% and 149.8% in the methane production rate of the anaerobic systems. Furthermore, this study elucidated the underlying mechanisms responsible for the enhanced methane production in the anaerobic wastewater treatment with doped CNTs. The introduction of doped CNTs enriched exo-electrogenic bacteria and archaea, thereby promoting the DIET process. Additionally, the CNTs also acted as the capacitor, storing and discharging electrons, which contributed to the maintenance of a stable methane production in anaerobic wastewater treatment.

Using the kriging method based on cross-validation stepwise variable selection to optimize anaerobic wastewater treatment process

In this study, process parameters for wastewater treatment are optimised in order to improve the efficiency of energy recovery from wastewater treatment. In order to identify process parameters that have a significant impact on carbon recovery, we propose a stepwise forward variable selection method based on K-fold cross kriging to validate the loss ER.The results show that for complex wastewater treatment systems, the cross-validated kriging-based stepwise variable selection method can predict carbon recovery quickly and accurately. Finally, this paper combines the kriging prediction model with the PSO optimisation strategy to determine the optimal set points of process parameters with the objective of maximising carbon recovery.

The important role of high sludge concentration in anaerobic biological systems with low COD/SO42- sulfate-containing wastewater predicted by machine learning: Insights from microbial community and metabolic pathways

In anaerobic biological systems, sulfate reduction efficiency is influenced by multiple factors synergistically, particularly under low chemical oxygen demand-to-sulfate ratio (COD/SO42-) conditions. Enhancing sulfate reduction efficiency under low COD/SO42- conditions is challenging due to the deficiency of electron donors. In this study, two anaerobic systems were operated with a gradual decrease in COD/SO42-. The primary objective was to investigate the correlations among various influential factors, the efficacy of sulfate reduction, and the progression of microbial communities. The results showed that even with a decrease in COD/SO42- to 0.1, the sulfate reduction efficiency could reach 70% under high sludge concentration. Machine learning predictions identified sludge concentration as the most influential factor under low COD/SO42- conditions. The functional gene analysis confirmed that the sulfate reduction under high sludge concentration was primarily governed by the dissimilatory pathway and exhibited minimal reliance on COD/SO42-. These findings provide theoretical support and a novel approach for the anaerobic biological treatment of sulfate-containing wastewater under low COD/SO42- conditions.

Synergetic effect of biochar and intermittent electricity stimulation on mitigating the adverse effects of tannic acid on anaerobic granular sludge in wastewater

Tannic acid (TA), a common industrial contaminant in sectors such as papermaking and leather production, affects the anaerobic treatment of wastewater by forming complexes with proteins in sludge granules, thereby inhibiting microbial efficiency and promoting sludge deflocculation. Although techniques such as intermittent electricity can promote microbial growth, they do not effectively resolve sludge deflocculation. Additionally, although biochar (BC) enhances the abundance of microbes, it does not significantly improve microbial activity or treatment performance. This study aimed to alleviate the adverse effects of TA on anaerobic granular sludge (AnGS) by synergistically applying intermittent electrical stimulation and BC. Co-treatment with 1 h-on/off intermittent electricity and 3 g/L BC notably reduced granular sludge deflocculation. Consequently, the chemical oxygen demand (COD) removal efficiency in wastewater reached 91.73 %, with a maximum methane production per cycle of 230.59 mL/g COD, 16.95 % higher than that of the control reactor (197.17 mL/g COD). This improvement was attributed to the synergistic action of intermittent electricity and BC, which enriched the functional microorganisms and stimulated their activity, thereby facilitating direct interspecies electron transfer. Additionally, enhancing the polysaccharide and protein levels in extracellular polymeric substances improved the stability of granular sludge, ultimately mitigating the adverse effects of TA on AnGS.

Performance of anaerobic dynamic membrane bioreactor treatment of wastewater from food waste pretreatment: Dissolved organic matter changes and overloading effects

Food waste requires pretreatment before composting due to its high moisture, oil, and salt content. Wastewater from pretreatment (FWPW) has high organic content (COD > 80 g/L) and requires further treatment. The performance and variations in dissolved organic matter (DOM) in an anaerobic dynamic membrane bioreactor (AnDMBR) treating FWPW were investigated along with the impact of the organic loading rate (OLR) of the system. The results showed that, at the stable stage, when the OLR reaches 6.07 kg COD m−3d−1, the average COD removal efficiency was 95.3 %, with a methane production of 0.21 L g−1COD removed. The effluent volatile fatty acid concentration was below 560 mg L−1 and primarily comprised from acetate and propionate. The proportion of DOM with a large (100–500 kDa) and medium (10–100 kDa) molecular weight (MW) in the mixed liquor decreased by 7.0 and 5.5 %, respectively, whereas the MW (> 500 kDa) in the effluent decreased by 14.8 %. The fluorescence spectra revealed only one humic-like peak in the samples, exhibiting a higher fluorescence intensity and humification index in the effluent and mixed liquor than in the influent. At the shock loads stage, the system could withstand a maximum OLR of 11.71 kg COD m−3d−1, and further increases in OLR caused reactor acidification and methane production failure. This study offers new strategies for optimal FWPW treatment and holds promise for guiding the industrial application of AnDMBRs.

Anaerobic treatment of fruit and vegetable wastewater using EGSB: From strategies for regulating over-acidification to microbial community

Fruit and vegetable waste (FVW) are characterized by high-water content. Solid-liquid separation of FVW by crushing-extrusion physical pre-treatment provides fruit and vegetable wastewater (FVWW), and then for anaerobic biological treatment to recover methane, which is considered a cost-effective approach. However, anaerobic treatment of FVWW faces difficulties with low methane productivity and over-accumulation of volatile fatty acids (VFAs). In this study, the expanded granular sludge bed (EGSB) reactor was used for the anaerobic treatment of FVWW and the regulatory strategy to alleviate over-acidification was proposed. When the influent chemical oxygen demand (COD) concentration was 10000 mg/L, the hydraulic retention time (HRT) was 2 days, the organic loading rate (OLR) reached 5 g COD/L/d, the maximum methane productivity reached 301.14 ± 2.32 mL/g COD with a COD removal rate of 96 % ± 2 %. Lower VFAs accumulation was observed when decreasing the influent COD concentration to the same OLR compared with extending HRT, resulting in 38.5 % higher methane productivity. Decreasing the influent COD concentration not only benefited the enrichment of acetogens and hydrogenotrophic methanogens but also specifically enriched syntrophic bacteria. The enhanced syntrophic acetogenesis and hydrogenotrophic methanogens maybe the main reasons for promoting the degradation of propionate and butyrate and improving the methane productivity.

Heterogeneous g-C3N4/polyaniline composites enhanced the conversion of organics into methane during anaerobic wastewater treatment

In this study, g-C3N4/PANI was prepared by in situ oxidative polymerization. Graphite-phase carbon nitride (g-C3N4) with surface defects was deposited onto the surface of conductive polyaniline (PANI) to form a p-n heterojunction. This construction aimed to create an efficient heterogeneous catalyst, increasing the surface defect level and active sites of the composite, and augmenting its capability to capture and transfer extracellular electrons under anaerobic conditions. This addresses the challenge of low efficiency in direct interspecies electron transfer between bacteria and archaea during anaerobic digestion for methane production. The results showed that the prepared g-C3N4/PANI increased the CH4 yield and CH4 production rate by 82% and 96%, respectively. Notably, the conductivity and XPS test results showed that the ratio of g-C3N4 to PANI was 0.15, and the composite exhibited favorable conductivity, with a uniform distribution of pyrrolic nitrogen, pyridinic nitrogen, and graphitic nitrogen, each accounting for approximately 30%. Furthermore, g-C3N4/PANI effectively enhanced the metabolic efficiency of intermediate products such as acetate and butyrate. Analysis of the microbial community structure revealed that g-C3N4/PANI led to a significant increase in the abundance of hydrogenotrophic methanogen Methanolinea (from 48% to 64%) and enriched Clostridium (a rise of 1%) with direct interspecies electron transfer capability. Microbial community function analysis demonstrated that the addition of g-C3N4/PANI boosted the activities of key enzymes involved in anaerobic digestion, including phosphate transacetylase (PTA), phospho-butyryl transferase (PTB), and NAD-independent lactate dehydrogenase (NNLD), by 47%, 135%, and 153%, respectively. This acceleration in enzymatic activity promoted the metabolism of acetyl-CoA, butyryl-CoA, and pyruvate. Additionally, the function of ABC transporters was enhanced, thereby improving the efficiency of material and energy exchange among microorganisms.

Anaerobic biodegradation enables zero liquid discharge of two-stage nanofiltration system for microelectronic wastewater treatment

Nanofiltration (NF) is a promising technology in the treatment of microelectronic wastewater. However, the treatment of concentrate derived from NF system remains a substantial technical challenge, impeding the achievement of the zero liquid discharge (ZLD) goal in microelectronic wastewater industries. Herein, a ZLD system, coupling a two-stage NF technology with anaerobic biotechnology was proposed for the treatment of tetramethylammonium hydroxide (TMAH)-contained microelectronic wastewater. The two-stage NF system exhibited favorable efficacy in the removal of conductivity (96 %), total organic carbon (TOC, 90 %), and TMAH (96 %) from microelectronic wastewater. The membrane fouling of this system was dominated by organic fouling, with the second stage NF membrane experiencing a more serious fouling compared to the first stage membrane. The anaerobic biotechnology achieved a near-complete removal of TMAH and an 80 % reduction in TOC for the first stage NF concentrate. Methyloversatilis was the key genus involved in the anaerobic treatment of the microelectronic wastewater concentrate. Specific genes, including dmd-tmd, mtbA, mttB and mttC were identified as significant players in mediating the dehydrogenase and methyl transfer pathways during the process of TMAH biodegradation. This study highlights the potential of anaerobic biodegradation to achieve ZLD in the treatment of TMAH-contained microelectronic wastewater by NF system.

Hydrolytic enzyme activity in high-rate anaerobic reactors treating municipal wastewater in temperate climates

Particulate matter hydrolysis is the bottleneck in anaerobic treatment of municipal wastewater in temperate climates. Low temperatures theoretically slow enzyme-substrate interactions, hindering utilization kinetics, but this remains poorly understood. β-glucosidase, protease, and lipase activities were evaluated in two pilot-scale upflow anaerobic sludge blanket (UASB) reactors, inoculated with different sludges and later converted to anaerobic membrane bioreactors (AnMBRs). Despite similar methane production and solids hydrolysis rates, significant differences emerged. Specific activity peaked at 37 °C, excluding the predominance of psychrophilic enzymes. Nevertheless, the Michaelis-Menten constant (Km) indicated high enzyme-substrate affinity at the operational temperature of 15–20 °C, notably greater in AnMBRs. It is shown, for the first time, that different seed sludges can equally adapt, as hydrolytic enzymatic affinity to the substrate reached similar values in the two reactors at the operational temperature and identified that membrane ultrafiltration impacted hydrolysis by a favourable enzyme Michaelis-Menten constant.

Effectiveness of low-intensity ultrasound on anaerobic bioaugmentation of phenolic wastewater: Model optimization and system stabilization

The study optimized the parameters of low-intensity ultrasound (LIUS), including ultrasound density (0.25 W·mL−1), duration (12 min), and interval time (48 h), through a combination of uniform experiments and response surface prediction. The optimized parameters were aimed at enhancing the removal efficiency of phenolic wastewater to approximately 80%. Furthermore, they facilitate the production of hydrolytic gases in anaerobic digestion, resulting in methane accumulation of up to 237.3 mL·(g VS)−1. Following the long-term experiment, LIUS has been demonstrated to effectively enhance the enzyme activity of anaerobic organisms while also damaging the bacterial structure of microorganisms. However, microbiological analysis indicates that the ultrasound-induced screening mechanism effectively increases the relative abundance of dominant bacterial communities. This facilitated the removal of persistent phenolic contaminants and stabilized the balanced development of the overall anaerobic environment. These findings suggest that LIUS can enhance biological activity and improve the anaerobic treatment of phenolic wastewater.

Anaerobic treatment of low-strength municipal wastewater with electroactive magnetite-embedded granules under mainstream conditions

This study examined the potential for the anaerobic treatment of low-strength wastewater (250 mg chemical oxygen demand/L) using expanded granular sludge bed (EGSB) with conductive magnetite-embedded granules (MEGs) under mainstream conditions (25°C). The inclusion of magnetite, with high specific gravity and conductivity, enhanced the settleability, structural stability, and electron transfer capability of MEGs compared to granules without it. Within the hydraulic retention time (HRT) range of 4–12 h, the MEG-EGSB reactors maintained superior treatment performance, along with comparable or higher methane production, compared to the control EGSB reactors lacking MEGs. This performance enhancement was more pronounced under conditions of higher hydraulic and organic loading. The MEG-EGSB reactors achieved approximately 90% organic removal efficiency at 8–12-h HRTs, a range comparable to that of the aerobic activated sludge process, with minimal loss of magnetite. The results from RNA-based microbial community analysis, alone with the consistently higher methane content in the biogas from MEG-EGSB reactors, supported the potential development of electric syntrophy between exoelectrogenic bacteria and electrotrophic methanogens in electroactive MEGs. This capability of MEGs to promote electro-syntrophic methanogenesis could potentially enhance methanogenic degradation of organic matter. The overall findings suggest that the MEG-EGSB process is a promising candidate for anaerobic municipal wastewater treatment.