Achieving carbon-neutral municipal wastewater treatment remains a critical challenge amid global climate change. Microalgae possess advantages in carbon capture and nutrient recovery, and their integration into municipal wastewater treatment systems is emerging as an active research area. This study developed an integrated process coupling anaerobic treatment and a membrane photobioreactor (MPBR) with CO2 supplementation for synthetic municipal wastewater treatment to achieve nutrient recovery, and carbon emission reduction. After anaerobic treatment, 96.0 ± 1.8% of the total organic carbon (TOC) was removed, resulting in an effluent TOC to total nitrogen (TN) ratio was approximately 0.14. Varied CO2 supplementation strategies were evaluated during MPBR operation, finding that moderate CO2 supplementation (10%) enhanced microalgal ammonium assimilation and achieved TN removal efficiency of 75.4 ± 6.9%. Nitrogen removal predominantly occurred through assimilation during light periods, while in the dark period, assimilation accounted for 42.6%. These were supported by molecular and enzymatic evidence, including increased activity of Rubisco and glutamine synthesis (GS) enzymes, along with upregulated expression of the glnA gene. Furthermore, 51% and 66% of influent carbon and nitrogen, respectively, were recovered into biomass, indicating effective carbon fixation and nitrogen recovery. Overall carbon emission assessment revealed a net carbon emission of 0.07 g CO2 equivalent/L wastewater, suggesting its carbon neutrality potential. This performance was attributed to energy recovery from biogas, efficient microalgal carbon fixation and additional energy recovery from lipid-rich biomass. Overall, the integrated anaerobic and microalgal-bacterial process is a promising strategy for simultaneous nitrogen recovery, and carbon sequestration for municipal wastewater treatment.

Conventional aerobic composting is limited by incomplete organic matter degradation, long composting times, and low product quality. Hyperthermophiles have been applied in composting, but systematic studies on their storage conditions and inoculation strategies are lacking. In this study, the hyperthermophilic microbial consortium, designated as NJ, maintained higher post-storage regrowth capacity after 6-month storage at 25 °C and 4 °C than at -80 °C. Furthermore, inoculated at the medium-temperature stage, NJ enhanced organic matter decomposition and shortened the composting time by 50% compared with high-temperature stage inoculation (>55 °C). Compared with a commercial inoculant, NJ shortened composting time by 67%, increased the germination index from 70% to 85%,raised DTN by 40%, and led to humic substance accumulation by the end of composting, indicating improved product quality. Consequently, medium-temperature stage inoculation of NJ enhances composting efficiency and product quality by enabling earlier functional expression and effective ecological niche occupation.

Microbial quorum sensing (QS) triggers substantial membrane biofouling formation that restricts the application of membrane bioreactors (MBRs). This study employed predatory Bdellovibrio-and-like organisms (BALOs) to mitigate biofouling, with particular emphasis on their effects on QS inhibition throughout the fouling process. Herein, BALO addition reduced the total concentrations of N-acyl homoserine lactones (AHLs) as the QS signals in both mixed liquor and membrane-attached biofilm by a maximum of (29.7 ± 0.7) % and extended the filtration period by up to 86.4%, with greater effects at higher inoculation dosages. BALO introduction slowed the accumulation of 8 out of 10 detected AHLs during the MBR operation, with the strongest effects occurring from the middle to final fouling stages in the mixed liquor and from the early to middle stages in the biofilm. BALOs also decreased the levels of precursors for polysaccharide and protein in extracellular polymeric substances (EPS) and biofilm biomass compared with the control, and altered the microbial composition and reduced the relative abundances of QS-related genera and genes. Positive correlations between typical AHL concentrations and EPS content or biofilm biomass supported a close association between QS activity and foulant accumulation. Collectively, BALOs functioned as living predatory quorum quenchers that mitigated dynamic membrane biofouling through persistent QS interference, reduction of foulant precursors, alteration of microbial community composition, and inhibition of biofilm formation.

In this study, the enhanced natural attenuation was investigated in a sandbox system which composed of the coarse, medium and fine sand layers for nitrobenzene contaminated groundwater treatment. The screened nitrobenzene degradation consortium X2 and the oxygen-releasing material OCRT-2W were applied to investigate their migration behavior and effects on nitrobenzene degradation. X2 exhibited upstream-to-downstream migration within the sandbox and achieved a maximum nitrobenzene removal efficiency of 49.0 % in the coarse sand layer within 40 days (HRT=2.5 days). The DO levels throughout the sandbox decreased from 1.6 to 0.2 mg/L after only X2 was inoculated, which led to a 65.4-80.0 % decline in liquid-phase microbial biomass. The addition of OCRT-2W consistently promoted the upstream DO levels to 2.1 mg/L without altering ambient conditions and the oxygen subsequently diffused downstream. By day 40, the DO levels represent 7.0-fold and 9.5-fold increases relative to the scenario with X2 alone, confirming the continuous oxygen-releasing capacity of OCRT-2W. Adequate oxygen supplementation enhanced liquid-phase microbial biomass to 1.4-2.5 x 108 cells/ mL by day 40. The combined application of consortium X2 and OCRT-2W yielded the highest nitrobenzene removal efficiency in the coarse sand layer, improving the removal efficiency by 51.2 % and 7.9 % compared to the control and X2 alone within 40 days. This study systematically investigated the migration patterns of microbial consortia in sandbox and analyzed the effectiveness of combined oxygen-releasing materials and microbial consortium for nitrobenzene removal, providing fundamental support for implementing Enhanced Natural Attenuation in risk management of temporarily undeveloped contaminated groundwater sites.

Food waste (FW) could be valorized through anaerobic digestion (AD) to produce bioenergy. However, it is necessary to develop an effective pretreatment method for FW to promote the methane production. To this end, this study investigated the effects of thermal-alkaline pretreatment (TAP) on the physicochemical characteristics of FW. An optimal condition (TAP, 80 °C and 0.10 g NaOH/g TS for 1 h) was adopted to pretreat FW prior to semi-continuous anaerobic digestion for methane production. Results showed that the TAP improved the solubilization of particulate organic matters. Meanwhile, the concentration of total volatile fatty acids (TVFA) increased by 40.6

The increasing accumulation of sulfates in groundwater, caused by industrial discharges, agricultural activities, and natural processes, has raised significant ecological and health concerns. Microbial bioremediation technologies offer distinct advantages, including environmental compatibility, the ability to degrade pollutants sustainably, minimal ecosystem disruption, and low costs. Sulfate-reducing bacteria (SRB), known for their metabolic versatility and environmental resilience, have emerged as a promising tool for the bioremediation of complex environments contaminated not only with sulfate but also with diverse pollutants such as hydrocarbons and chlorinated organics. This review summarizes the current knowledge on SRB diversity, distribution, and metabolic activities, critically examines the key factors influencing their bioremediation efficiency, the corresponding regulatory strategies, and addresses their current applications in soil and groundwater, as well as potential challenges. Particular attention is given to SRB applications in the treatment of co-contaminated sites with both organic and sulfate contamination, the mitigation of secondary pollution caused by in situ chemical treatment, and the regulation of sulfur transformation for targeted production or resource recovery. Meanwhile, the review discusses the key priorities to accelerate research and practical implementation in this field.

High-concentration sulfate and benzene, toluene and ethylbenzene (BTE) co-contamination in groundwater poses severe ecological risks. In situ bioremediation utilizing sulfate-reducing bacteria (SRB) consortia is a promising strategy. This study evaluated the environmental adaptability of an SRB consortium. The SRB consortium maintained activity across pH 5–9, 10–30 °C, sulfate concentrations up to 5000 mg/L, and chloride concentrations up to 10,000 mg/L. Sodium lactate was identified as the optimal carbon source, whereas SRB activity was inhibited at C/S ratios below 2 because of electron-donor limitation. To address this limitation, the feasibility of utilizing benzene, toluene, and ethylbenzene as alternative electron donors was evaluated. The SRB consortium successfully drove sulfate reduction using benzene, toluene, or ethylbenzene individually (100 mg/L), achieving removal efficiencies of 81.04%, 97.00%, and 87.12%, respectively, within 10 days. In a mixed system containing benzene, toluene, and ethylbenzene, multi-substrate co-metabolism enhanced simultaneous pollutant removal, following a preferential degradation sequence of toluene, ethylbenzene, and benzene. However, sulfate reduction efficiency remained low (approximately 10%) when the three compounds were the sole carbon sources. Consequently, sodium lactate biostimulation markedly enhanced remediation performance, increasing sulfate removal from 7.22% to 27.21% and benzene removal from 53.68% to 86.78% within 10 days. Community, enzyme, and functional-gene analyses showed increased APS and benzoyl-CoA reductase activities, alongside aprA and bcrA abundances. It also shifted dominant microbial genera from Desulfosporosinus to Clostridium and Desulfovibrio, enhancing electron transfer and metabolic coupling. Ultimately, combining SRB consortia with sodium lactate biostimulation offers immense potential for remediating such sites.

The occurrence of biofouling restricts the large-scale application of membrane bioreactor (MBR) in wastewater treatment. Herein, predatory Bdellovibrio-and-like organisms (BALOs) were introduced into MBR to alleviate membrane fouling without impairing treatment performance. BALO addition prolonged the MBR's filtration period by up to 335.1 % compared to the control and reduced extracellular polymeric substances (EPS) levels by up to 65.7 ± 2.2 % in both sludge and membrane phases. Additionally, nine typical N-acyl homoserine lactones (AHLs) were detected, with C4-HSL being most abundant and 3-oxo-C10-HSL least abundant. BALO inoculation shifted dominant AHL profiles and reduced six key AHLs by up to 68.0 ± 2.0 %. BALOs may alter the relative abundances of quorum sensing (QS) and quorum quenching related genera, including Nitrospira, Sphingomonas, Pseudomonas, Flavobacterium, and Rhodobacter, contributing to QS inhibition and EPS reduction. Consequently, BALO supplementation represents a promising biological strategy for mitigating membrane fouling by reducing foulant, disrupting QS, and reshaping microbial communities.

The effects and mechanisms of extracellular polymeric substances (EPS) on the sludge biolysis by parasitic Bdellovibrio-and-like organisms (BALOs) for dewatering and reduction were investigated. The studied BALOs successfully biolyzed the sludge for dewaterability improvement with the specific resistance of filtration value decreased by (67.0 +/- 4.4)% for the sludge of 15 g/L. Soluble EPS (S-EPS), loosely-bound EPS (LB-EPS), and tightly-bound EPS (TB-EPS) were utilized during BALOs' predation, and TB-EPS showed the highest protein and polysaccharide removal rates of (47.7 +/- 3.5)% and (37.5 +/- 4.3)%, respectively. Additionally, sludge floc structure formed by EPS were found to hinder BALOs' predation, and S-EPS likely played a key role in EPS's blocking effect. BALOs displayed a longer proliferation cycle but a higher cell density in the sludge with EPS removed, suggesting the great possibility of BALOs using EPS as energy sources. BALOs were speculated to secret hydrolases and lyases to degrade EPS, notably the protein, and adenosine triphosphate (ATP) synthase helped energy's transmission and utilization to promote BALOs' activities and proliferation. These findings indicated that BALOs could balance EPS's "dual effects" of both the negative steric hindrance effect for their movements and the positive energy sources for predation activities, providing new insights to explain the mechanisms underlying BALOs' sludge biolysis and facilitate the subsequent sludge biolysis accurately and controllably.

Wastewater treatment plants are recognized as "hotspots" for the emergence and dissemination of antibiotic resistance genes (ARGs). Bdellovibrio-and-like organisms (BALOs), as obligatory predatory bacteria, simultaneously remove ARGs when lysing sludge for dewaterability improvement. Quantitative polymerase chain reaction (qPCR) results revealed the significant removal of typical ARGs and mobile genetic elements (MGEs). Then, metagenomic analysis further indicated that the relative abundances of 61.5 and 63.3% of the detectable ARGs and MGEs gradually decreased during the 36 h sludge biolysis process, with more than half of the ARG and MGE subtypes achieving their highest degradation rates at the optimal reaction time of 16 h, ranging from (32.4 +/- 0.5) to 100%. The main potential antibiotic-resistant bacteria as BALOs' hosts were probably within the seven genera, Rhodoferax, Hydrogenophaga, Lutimaribacter, Variovorax, Ideonella, Xenophilus, and Rubivivax, whose lysis would contribute to ARG degradation in the sludge. Moreover, the enhanced proteases, nucleases, and hydrolases encoded genes' expressions highly emphasize the importance of replication and repair, nucleotide, energy, and amino acid metabolism activities for ARG degradation during the biolysis process. Consequently, the application of BALOs in sludge biolysis could limit the spread of ARGs in the environment.

Sludge treatment with sulfide has emerged as a potential solution for nitrite-oxidizing bacteria (NOB) inhibition, facilitating partial nitritation for efficient nitrogen removal in municipal wastewater treatment. The N2O emission in sulfide treatment (S-treatment) established PN (partial nitritation) has not been systematically characterized, resulting in the impact of S-treatment on carbon emissions being uncovered. In this study, S-treatment on enriched nitrifying sludge was investigated for selective inhibition of NOB and N2O emission characteristics. It was found that NOB was more significantly suppressed by S-treatment as compared with ammonia-oxidizing bacteria (AOB). An 82.8% inhibition of NOB activity was observed at the S-treatment concentration of 4.0 mg H2S-S/g VSS, leading to nitrite accumulation rates up to 90%. S-treatment also inhibited N2O production, especially from the nitrifier denitrification (ND) pathway under both low and high DO levels. At 0.5 and 2.0 mg DO/L, N2O emission rates via the ND pathway decreased by 63.6% and 50.0%, respectively. Further, even with elevated NO2- levels from 2.5 to 15 mg N/L, N2O emission was not significantly stimulated, likely due to the inhibitory effect of S-treatment on nitrite reductase (NIR) activity. Finally, an anaerobic treatment and mainstream deammonification process integrated with ex situ S-treatment was proposed for simultaneous NOB repression and reduction of N2O emission.

The mainstream deammonification of municipal wastewater has been recognized as one of the greatest challenges in wastewater engineering. The conventional activated sludge process has disadvantages of high energy input and sludge production. To tackle this situation, an innovative A-B process, where an anaerobic biofilm reactor (AnBR) functioned as the A stage for energy recovery, and a step-feed membrane bioreactor (MBR) functioned as the B stage for mainstream deammonification, was constructed for carbon-neutral wastewater treatment. For addressing the challenge associated with selective retention of ammonia-oxidizing bacteria (AOB) over nitrite oxidizing bacteria (NOB), a multi-parameter control-based operation strategy was developed with synergistic control of influent COD redistribution, dissolved oxygen (DO) concentration and sludge retention time (SRT) in the innovative AnBR - step-feed MBR system. Results showed that more than 85% of wastewater COD could be removed with the direct production of methane gas in the AnBR. A relatively stable partial nitritation, which is a prerequisite of anammox, was achieved with the successful suppression of NOB, leading to 98% of ammonium-N and 73% of total nitrogen removed. Anammox bacteria could well survive and enrich in the integrated system, and the contribution of anammox to the total nitrogen removal was more than 70% at optimal conditions. Reactions network involved in the nitrogen transformation in the integrated system was further constructed through the mass balance and microbial community structure analyses. Consequently, this study demonstrated a practically feasible process configuration with high operation and control flexibility towards stable mainstream deammonification of municipal wastewater.

Sewage sludge treatment and disposal remains a challenging problem. Composting of sewage sludges is gaining increasing attention due to its cost-effectiveness, operation convenience, advantages in lifecycle management, and low greenhouse gas emissions. Disadvantages, such as long reaction time, significant land area occupation requirement, potential risks of residual heavy metals, and emerging contaminants, have restricted wider application. Here we review applications of hyperthermophiles in composting , focusing on the unique improvements provided by hyperthermophiles in composing temperatures, product safety, nitrogen preservation and humification. Inoculation of hyperthermophiles allows temperature of composting to reach over 80°C. Specific metabolic strategies are critical in hyperthermophiles-inoculated composting. High-temperature resistance in the metabolism of hyperthermophiles and their roles in temperature rising during composting is often overlooked. This review discusses both aspects, allowing for a deeper understanding of the functions and influences of hyperthermophiles in sludge composting. Additionally, this review highlights the policy challenges associated with the hyperthermophiles-inoculated sludge composing technique and provides potential directions for future research in this field.

Aerobic composting of conventional municipal sludge has always had the problems of nitrogen loss and low humification. In this study, biolysed sludge (BS), polyacrylamids-added sludge (PS) and Fe (III)/CaO-added sludge (FS) were used for composting, respectively, and their effect on the physical-chemical parameters, nitrogen conversion and humification during composting were investigated. The results showed that the dissolved organic matter (DOM) concentration of the BS pile (23.1 ± 0.4 g/kg) was 48.4% and 48.4% higher than the PS (15.5 ± 0.4 g/kg) and FS piles (15.5 ± 0.0 g/kg) in the initial stage of composting and became the lowest after composting, suggesting that the degradation of DOM was promoted in the BS pile. BS can also increase the retention rate of total nitrogen (TN) (27.8% ± 0.8%), higher than that in PS (22.7% ± 1.1%) and FS (24.6% ± 0.5%), which may be due to the lower production of ammonia nitrogen in the BS pile. Compared with PS and FS, BS provided more humic substance (HS) and humic acid (HA) for composting and the HA contents of the compost products were 34.4 ± 1.0, 35.4 ± 0.2 and 34.0 ± 0.3 mg/g in the PS, BS and FS treated piles, respectively. Fourier transform infrared and the excitation-emission matrix revealed that BS and FS promoted the aromaticity and stability of HA. The degree of polymerization (DP) of the products from the BS (1.48) and FS piles (1.56) was higher than that of the PS pile (1.36). However, the germination index (GI) value (133.4% ± 6.0%) of FS was lower than that of PS (152.3% ± 6.2%) and BS (158.3% ± 0.8%), showing that the products of FS composting contain more plant biotoxicity. Thus, compared with PS and FS, BS can increase the nitrogen retention rate and the maturity of the compost.

Freshwater resilience is facing to an increasing challenge, while carbon neutral wastewater reclamation has been put onto agenda in more and more countries. The activated sludge-microfiltration (MF)-reverse osmosis (RO) process has been currently adopted for reclamation of municipal wastewater to high-grade product water (e.g. NEWater). However, the conventional activated sludge (CAS) unit in this process has the drawbacks of excessive sludge generation, high energy consumption, greenhouse gases (GHGs) emissions etc. To address these emerging issues, an integrated anaerobic fixed-film membrane bioreactor (AnfMBR)-RO-chlorination process was developed in this study. Results showed that about 99.9% of COD, 99.3% of phosphate and 95.3% of NH4+-N were removed in the AnfMBR-RO process, while breakpoint chlorination served as a polishing step when the NH4+-N concentration in RO permeate exceeded the typical NH4+-N concentration (e.g. 1 mg/L) of NEWater. The net energy consumption and total GHG emissions in the proposed integrated process were estimated to be 0.33 kWh/m(3) and 310.2 g CO(2)e/m(3) influent wastewater treated, respectively, which were 64% and 74% less than those in the current municipal wastewater reclamation process. Consequently, this study offers an alternative path to bring municipal wastewater reclamation one step closer to carbon neutrality and water sustainability.

With the speedy evolution of global climate change and water shortage, there is a growing need for the energy and carbon neutral wastewater reclamation technology. To tackle this challenge, an innovative anaerobic membrane bioreactor (AnMBR)-biochar adsorption-RO process was developed for reclaiming municipal wastewater to high-grade product water with the aims for achieving the energy and carbon neutrality. It was found that about 95.6% of influent COD was removed by AnMBR with direct generation of biomethane, while ammonium-N in AnMBR permeate was fully recovered through biochar adsorption. The effluent from biochar adsorber with significantly lowered divalent ions concentrations was further reclaimed by RO at reduced cost and energy consumption. The energy demand and the total carbon emissions in the proposed process were estimated to be 0.50 kWh/m3 and 633 g CO2e/ m3 against 0.86 kWh/m3 and 1101 g CO2e/ m3 in the current conventional activated sludge (CAS)-microfiltration-RO process. It was further shown that the ammonium recovery via biochar adsorption could offset about 0.503 kWh/m3 that was originally utilized for chemically producing recovered ammonia by the Haber-Bosch method, equivalent to a carbon offsetting of 498 g CO2e/m3, leading to a net carbon emission of 135 CO2e/m3 in the proposed process, which was only about 12% of that in the current CAS-MF-RO process. These suggested that a carbon-neutral municipal wastewater reclamation might be achievable through concurrent carbon reduction and offsetting, while carbon offsetting via ammonia recovery appeared to be a game-changer towards the carbon-neutral operation. Consequently, it is expected that this study can shed lights on how energy- and carbon-neutrality would be achieved by innovating municipal wastewater reclamation technology.

Various anaerobic processes have been explored for the energy-efficient treatment of municipal wastewater. However, dissolved methane in anaerobic effluent appears to be a barrier towards the energy and carbon neutrality of wastewater treatment. Although several dissolved methane recovery methods have been developed, their engineering feasibility and economic viability have not yet been assessed in a holistic manner. In this perspective, we thus intend to offer additional insights into the cost-benefit of dissolved methane recovery against its emission.

Novel sandwich-structured carriers were developed for fast immobilizing anammox sludge, with which a fixed film membrane bioreactor was further established for treating municipal wastewater. Results showed that fast start-up of the fixed-film reactor with anammox bacteria could be achieved without lag phase, indicated by the respective nitrogen removal efficiency and rate of 70.58 +/- 0.66% and 0.12 g N/(L.d). Meanwhile, low membrane fouling 0.0017 bar/hour was also observed. The activity of anammox sludge fixed in the novel carriers gradually stabilized at the level of 6.59 mg N/(g VSS.h), while Candidatus Kuenenia as the dominant anammox bacteria were enriched from the initial abundance of 15.16% to 39.12% after a long-term operation. Consequently, it was demonstrated that the sandwich-structured carriers developed in this study could offer a promising alternative for fast immobilization and start-up of mainstream anammox process.

In this study, four groups of microalgal-bacterial granules with averaged diameters of about 356, 760, 951 and 1,444 mu m were used to investigate their characteristics and performance in treating wastewater. A strong correlation between extracellular polymeric substances of microalgal-bacterial granules and the granule size was observed. Moreover, granule size showed a positive effect on the specific organics removal rate, but being negative for ammonium and phosphorus removal. It appeared that granule size could be used as a useful index to reflect the synergistic interactions between microalgae and bacteria in terms of the abundances, distributions and functional species in the microalgal-bacterial granules. This study is expected to offer new insights into the sizedependent performances of microalgal-bacterial granules for wastewater treatment.

Tetracycline has been frequently detected in municipal wastewater due to its extended use for various purposes. This study investigated the influence of tetracycline on non-aerated microalgal-bacterial granular sludge cultivated for municipal wastewater treatment. It was found that ammonia-N removal rate decreased at the tetracycline concentrations of 1 and 10 mg/L. A mass balance on nitrogen further revealed that the observed ammonia-N removal could be mainly attributed to microalgal assimilation which was inhibited by tetracycline at the concentrations studied. In fact, reduced production of chlorophyll in microalgae was observed in the presence of tetracycline, leading to decreased ammonia-N removal rate. Meanwhile, decreased dissolved oxygen (DO) concentration at high tetracycline concentration also indicated inhibition of microalgae. Furthermore, the relative abundances of microalgae containing green algae and cyanobacteria were inhibited by tetracycline. The results gathered in this study indicated the tetracycline-induced decoupling of symbiosis in microalgal-bacterial granular sludge. It is expected that this study can shed lights on the behaviors of non-aerated microalgal-bacterial granules in response to the presence of tetracycline during municipal wastewater treatment.