Biological Treatment Processes Research Articles

A new strategy for greenhouse gas emission reduction in the anaerobic/anoxic/oxic biological treatment process using exogenous N-acyl-homoserine lactones, a quorum-sensing signaling molecules

ABSTRACT In this study, the impact of exogenous N-acyl-homoserine lactones (AHLs) on greenhouse gas (GHG) emissions in anaerobic/anoxic/oxic (A/A/O) systems was analyzed by manipulating the type and dosage of AHLs. The mechanism behind AHLs’ effects on GHG emissions was explored through changes in microbial community structure. Findings revealed that N-octanoyl-homoserine lactone (C8-HSL) and high-dose N-dodecanoyl-homoserine lactone (C12-HSL) increased GHG emissions, while low-dose C12-HSL decreased them. Moreover, C8-HSL and high-dose C12-HSL promoted methane (CH4) and nitrous oxide (N2O) production by affecting sludge particle size. Bacterial community analysis highlighted Acinetobacter and Flavobacterium's roles in N2O emissions and acetate methanogens in methane synthesis. Metabolic pathway analysis showed that the acetic acid (CH3COOH) methanogenic pathway was the main methanogenic pathway; C8-HSL and C12-HSL influenced methane emission by affecting the methanogenic pathway and N2O emission by changing nitrous oxide reductase (Nos) abundance. This research underscores AHL-based quorum sensing's potential in mitigating GHG emissions during activated sludge wastewater treatment, offering insights into their application and impact on key microbial activities. Limitations include the absence of methane emission reduction by signaling molecules and the need for further investigation into their effects on sludge accumulation.

Electrochemically Coupled Anaerobic Membrane Bioreactor Facilitates Remediation of Microplastic-Containing Wastewater

Ubiquitous microplastics (MPs) severely affect the efficiency of anaerobic membrane bioreactors (AMBR) for wastewater treatment and energy recovery by inhibiting the metabolic activity of anaerobic microorganisms. The electrochemical system can not only accelerate waste metabolism but also improve microbial resistance by promoting interspecies electron transfer within the system, which has broad application potential in the remediation of MPs wastewater. This paper attempts to evaluate the effect of electrical stimulation on the efficiency of biological wastewater treatment processes containing MPs employing an electrochemical system coupled to an anaerobic membrane bioreactor (ECAMBR). The results showed that although MP exposure inhibited methanogenic performance, electrical stimulation effectively alleviated this inhibitory effect. Further analysis showed that microplastics increased cell damage and affected enzyme activity, but electrical stimulation could affect the stress response of microorganisms, leading to changes in their cell viability and enzyme activities. The 16S-rRNA sequencing indicated that the highest abundance of hydrolytic–acidogenic bacteria Firmicutes and Bacteroidota was found at the phylum level, whereas at the genus level, it was Christensenellaceae_R-7_group, and methanogens were dominated by Methylomonas, Methyloversatilis, and Methylobacter. Functional prediction analysis indicated that carbohydrate metabolism, amino acid metabolism, and energy metabolism were the dominant metabolic pathways and that electrical stimulation could enhance their activities. This study demonstrated the important role of electrochemical stimulation in the remediation of wastewater containing high concentrations of MPs.

Decolorization and degradation of azo dyes in thermophilic biological wastewater treatment process: A mini-review

Decolorization and degradation of azo dyes in thermophilic biological wastewater treatment process: A mini-review

Enhancement of stress resistance of electroactive biofilms against hypersaline shock via exogenous electron mediator addition

Unexpected hypersaline shock from saline wastewater poses a common challenge in the biological treatment processes of WWPTs. Bioelectrochemical systems (BESs) possess an inherent advantage for treating hypersaline wastewater. The elevated salinity enhances the wastewater’s conductivity, which in turn significantly accelerates the electron and proton transfer within the system. However, excessive increases in salinity can impede electron transport capacity, potentially resulting in cell plasmolysis and system failure in severe instances. Here, we investigated the impact of electron mediator (EM) addition on the resilience of electroactive biofilms (EB) to hypersaline environments in BESs. The EB developed under anthraquinone-2,6-disulphonic disodium salt (AQDS) addition obtained preferable electrochemical properties (e.g., current output, redox peak current, conductivity, electron transfer capacity) under hypersaline shock and showed superior recovery post-hypersaline stress. Partial least squares path modeling (PLS-PM) analysis indicated that the enhanced secretion of extracellular polymeric substances (EPS) and the elevated ratio of proteins to polysaccharides are likely pivotal in the formation of EB with high electrochemical activity. Meanwhile, AQDS addition constructed more complex microbial network and enriched halotolerant bacteria (e.g., Solibacillus). Higher mean function abundance of replication & repair, stress tolerance, and biofilm formation were achieved by EM addition. The results of this study present a promising approach to augment the pressure tolerance of EBs, thereby broadening the practical applications of BESs.

Insights into the efficiencies of different biological treatment systems for pharmaceuticals removal: A review.

This review presents a comprehensive analysis of current research on biological treatment processes for removing pharmaceutical compounds (PhCs) from wastewater. Unlike previous studies on this topic, our study specifically delves into the effectiveness and drawbacks of various treatment approaches such as traditional wastewater treatment facilities (WWTP), membrane bioreactors (MBRs), constructed wetlands (CW), and moving bed biofilm reactors (MBBR). Through the examination and synthesis of information gathered from more than 200 research studies, we have created a comprehensive database that delves into the effectiveness of eliminating 19 particular PhCs, including commonly studied compounds such as acetaminophen, ibuprofen, diclofenac, naproxen, ketoprofen, indomethacin, salicylic acid, codeine, and fenoprofen, amoxicillin, azithromycin, ciprofloxacin, ofloxacin, tetracycline, atenolol, propranolol, and metoprolol. This resource provides a depth and scope of information that was previously lacking in this area of study. Notably, among these pharmaceuticals, azithromycin demonstrated the highest removal rates across all examined treatment systems, with the exception of WWTPs, while carbamazepine consistently exhibited the lowest removal efficiencies across various systems. The analysis showcases the diverse results in removal efficiency impacted by factors such as system configuration, operation specifics, and environmental circumstances. The findings emphasize the critical need for continued innovation and research, specifically recommending the integration of advanced oxidation processes (AOPs) with existing biological treatment methods to improve the breakdown of recalcitrant compounds like carbamazepine. PRACTITIONER POINTS: Persistent pharmaceuticals harm aquatic ecosystems and human health. Biological systems show varying pharmaceutical removal efficiencies. Enhancing HRT and SRT improves removal but adds complexity and costs. Tailored treatment approaches needed based on contaminants and conditions.

Removal of contaminants in paper dyeing wastewater by Fenton and photo-Fenton processes with biological treatment

Due to the production of huge quantity of potentially toxic and recalcitrant pollutants, which cannot be completely decomposed with conventional biological wastewater treatment processes, in the paper industry, reliable treatment processes are highly required. This study conducted effective experiments of different series of processes to decompose persistent contaminants in the paper wastewater under controlled conditions of the used processes to meet the effluent quality standards of Korea Ministry of Environment in terms of CODMn (< 130 mg/L). For Biological treatment, Fenton, and photo-Fenton processes, various operational parameters were adjusted to determine the optimal conditions for CODMn value. Due to large quantity of refractory contaminants in the wastewater, single treatment process was not enough to meet the requirement of CODMn. Herein, we achieved the goal with two approaches: (1) secondary Fenton oxidation after biological and primary Fenton treatments, and (2) photo-Fenton treatment after biological treatment alone. The secondary Fenton oxidation process is an additional process operated under the same condition of the primary Fenton treatment to treat the effluent from the primary Fenton treatment. Ultimately, the residual CODMn concentrations of the secondary Fenton and single photo-Fenton treatment were 62.7 and 85.3 mg/L, respectively. However, the secondary Fenton required larger amounts of reagents and produced significant amounts of sludge, which require post-treatment, compared to single photo-Fenton treatment. Therefore, it suggests that the application of photo-Fenton was more efficient than the secondary Fenton in terms of economic feasibility and post-treatment requirement.

Adsorben dari Lumpur Limbah untuk Penyisihan Kromium pada Fixed Bed Column

Sewage sludge is a major by-product of the wastewater biological treatment process. Wastewater Treatment Plants at Palm Oil Mills (PKS) produce a lot of sewage sludge and until now it has not been optimally utilized. This study aims to examine the potential of PKS sewage sludge as an adsorbent for the removal of kromium (Cr) by the fixed bed column method. The study will also analyze the effect of recirculation on the reduction of kromium levels. The sludge was carbonized in a furnace at 300°C for 2 hours. Synthetic kromium wastewater was made at three concentrations of 2000 ppm, 3000 ppm, and 4000 ppm. The sludge adsorbent used was 100 grams which was filled into the fix bed column. Recirculation of kromium wastewater was performed 3 times. Adsorption isotherms were analyzed using Langmuir and Freundlich models. The results showed that the best removal without recirculation occurred at a kromium concentration of 3000 ppm with a removal efficiency of 48.07%. Furthermore, recirculation was carried out 3 times and resulted in varying removal values at the 1st, 2nd, and 3rd recirculation of 37.9%, 40.06% and 35.4%. The highest removal occurred in the second recirculation. The addition of recirculation led to a decrease in the sorption of chrome as the adsorbent had reached saturation point. This allows the release of kromium ions that have been adsorbed and causes the removal efficiency to decrease. A suitable adsorption isotherm model for sludge adsorbent is the Langmuir model, where the adsorption process occurs in a single layer and is homogeneous.

Coupling Iron Coagulation and Microalgal–Bacterial Granular Sludge for Efficient Treatment of Municipal Wastewater: A Proof–of–Concept Study

The rapid expansion of global urbanization and industrialization has significantly increased the discharge of municipal wastewater, leading to issues of carbon emissions and energy consumption when using traditional biological treatment processes. This study proposes an innovative process that couples iron coagulation with microalgal–bacterial granular sludge (MBGS), with optimization and regulation based on operational conditions. The study found that the coagulation performance achieved optimal levels at an iron concentration of 25 mg/L and an anionic polyacrylamide concentration of 1 mg/L, which could remove approximately 61% of the organics and over 90% of phosphorus from raw wastewater. By relying on heterotrophic microorganisms, such as Proteobacteria, Bacteroidota, and Chloroflexi, along with the synergistic interaction between algae and bacteria, the subsequent MBGS process could further effectively remove organics over the day-night cycles. Moreover, the addition of inorganic carbon sources of NaHCO3 increased the abundance of denitrification-related genes, reduced the accumulation of nitrite within MBGS, and led to effective total nitrogen removal. These results indicate that the iron coagulation–MBGS coupling process can efficiently treat municipal wastewater, offering potential for environment-sustainable pollutant removal with reduced energy consumption. These findings provide valuable insights for the practical engineering application of MBGS in wastewater treatment systems aiming for carbon-neutral wastewater treatment.

Comparation on the responses and resilience of single-Anammox system and synergistic partial-denitrification/anammox system to long-term nutrient starvation: Performance and metagenomic insights

Starvation disturbance was a common problem in biological sewage treatment processes. However, understanding about the responses and resilience of different active anammox biomass in autotrophic and heterotrophic systems to long-term nutrient starvation remains limited. This study compared responses and potential recovery mechanisms of autotrophic single-Anammox and heterotrophic synergistic partial-denitrification/anammox (PD/anammox) systems to prolonged starvation (31–40 days). After starvation, total inorganic nitrogen (TIN) removal efficiency of single-Anammox and synergistic PD/anammox systems decreased to 62.16 % and 78.52 %, respectively, of their original level. After the nutrient resupply, the performance of both systems gradually recovered to a similar-to-pre-starvation level at the rate of 1.26 %/day and 1.89 %/day, respectively. Compared with single-Anammox system, complex synergistic relationship of microorganisms and effective quorum sensing (QS) regulation strategies might mitigate the negative influences were caused by starvation and ensure the performance quickly return of synergistic PD/anammox system. This study would contribute to promote the application of Anammox technology.

Sludge carbon quantum dots-activated peroxymonosulfate oxidation for sludge conditioning

Large amounts of waste activated sludge (WAS) are produced from biological treatment processes in wastewater treatment plants, and its effective disposal and reutilization are considered to be inevitable challenges in the world. In this work, carbon quantum dots derived from WAS (SCQDs) were successfully synthesized via hydrothermal method, which had a significant photoluminescence effect, excellent water solubility, and graphite structures with main elements of C, N, and O. Subsequently, its potential for peroxymonosulfate (PMS) activation under visible light for WAS conditioning was investigated. The results showed that SCQDs-activated PMS (SCQDs-PMS) system could effectively improve sludge dewaterability. Under experimental conditions, capillary suction time reduction and water content of sludge cake after conditioning were 81.2% and 72.6%, respectively. Reactive oxygen species including SO4·-, ·OH, and 1O2 produced in SCQDs-PMS system could effectively degrade extracellular polymeric substances (EPS) (especially tyrosine-like and tryptophan-like substances in tightly bound-EPS), inactivate microbial cells, and destruct α-helix structure of protein molecule, which resulted in the desirable release of EPS-bound water, consequently improving sludge dewaterability. This result was well supported by the variations in the transverse relaxation time of protons at low field nuclear magnetic resonance. Thus, this work explored a potential pathway of reutilizing sludge and a new activator for PMS activation. However, it should be noticeable that this work was the first attempt using SCQDs-PMS system for sludge conditioning, the future studies about system optimization and its wider application scenarios should be further investigated.

Advances in the Separation and Removal of Microplastics in Water Treatment Processes

In this review, we comprehensively analyzed the distribution of microplastics （MPs） in major water ecosystems in China and the fate of MPs during the water treatment process. The removal efficiency of MPs with different colors, sizes, shapes, and materials was also discussed. The results showed that the abundance of microplastics in the aquatic environment was geographically variable and closely related to human activities. Fibrous and transparent （white） microplastics were the most common features in China's water ecosystems and water treatment plants, with polypropylene （PP）, polyethylene （PE）, and polystyrene （PS） being the most common polymer types of microplastics. The removal efficiency of MPs varied from different treatment processes significantly. Pre-treatment and primary treatment in wastewater treatment plants （WWTPs） contributed the most to the removal. In the secondary treatment, the sedimentation tank showed more efficiency than the biological treatment processes. Tertiary treatment processes demonstrated remarkable effectiveness in achieving terminal control of MPs, especially membrane technologies. On the contrary, aeration and hydrodynamic effects may have increased the abundance of MPs in WWTPs. In drinking water treatment plants （DWTPs）, coagulation-sedimentation processes were found to be the most effective in removing MPs, followed by filtration and disinfection processes. Further, both pre-treatment and post-treatment steps also made significant contributions to MPs removal.

Response to shock load of titanium dioxide nanoparticles on aerobic granular sludge and algal-bacterial granular sludge processes

Titanium dioxide nanoparticles (TiO2 NPs) are extensively used in various fields and can consequently be detected in wastewater, making it necessary to study their potential impacts on biological wastewater treatment processes. In this study, the shock-load impacts of TiO2 NPs were investigated at concentrations ranging between 1 and 200 mg L−1 on nutrient removal, extracellular polymeric substances (EPSs), microbial activity in aerobic granular sludge (AGS), and algal-bacterial granular sludge (AB-AGS) bioreactors. The results indicated that low concentration (≤10 mg L−1) TiO2 NPs had no effect on microbial activity or the removal of chemical oxygen demand (COD), nitrogen, and phosphorus, due to the increased production of extracellular polymeric substances (EPSs) in the sludge. In contrast, the performance of both AGS and AB-AGS bioreactors gradually deteriorated as the concentration of TiO2 NPs in the influent increased to 50, 100, and 200 mg L−1. Specifically, the ammonia‑nitrogen removal rate in AGS decreased from 99.9 % to 88.6 %, while in AB-AGS it dropped to 91.3 % at 200 mg L−1 TiO2 NPs. Furthermore, the nitrate‑nitrogen levels remained stable in AB-AGS, while NO3-N was detected in the effluent of AGS at 100 and 200 mg L−1. Microbial activities change similarly as smaller decrease in the specific ammonia uptake rate (SAUR) and specific nitrate uptake rate (SNUR) was found in AB-AGS compared to those in AGS. Overall, the algal-bacterial sludge exhibited higher resilience against TiO2 NPs, which was attributed to a) higher EPS volume, b) smaller decrease in LB-EPS, and c) the favorable protein to polysaccharide (PN/PS) ratio. This in turn, along with the symbiotic relationship between the algae and bacteria, mitigates the toxic effects of nanoparticles.

Continuous self-circulating up-flow granular sludge fluidized bed process treating low-strength real municipal wastewater at high hydraulic loads

Conditions conducive to aerobic granular sludge (AGS) growth and maintenance are very difficult to realize in continuous-flow biological treatment processes. This study conducted a continuous-flow self-circulating up-flow granular sludge fluidized bed (Zier process) treating real urban wastewater approximately one year. The substantial self-circulating multiple times (RSCMT, 8–15 times) and up-flow velocity (8–15 m/h) generated by aeration, the only power equipment in Zier process, facilitated pollutant removal, particle granulation and stabilization. With hydraulic retention time of 5 h, RSCMT of 9.3–14.4 times and chemical oxygen demand (COD)/total nitrogen (TN) ratio of 5.9 ± 1.0, the effluent COD, ammonia nitrogen and TN were 28.6 ± 7.7, 1.1 ± 1.2, and 13.3 ± 1.7 mg/L, respectively. The median particle size was 150–250 μm and effluent suspended solids concentration was 33.4 ± 14.5 mg/L. It is unnecessary to set up sludge reflux which simplifies the subsequent mud-water separation facilities. The Zier process provides a new process structure for implementation of continuous-flow AGS process.

The fate of severe acute respiratory syndrome coronavirus-2 and pepper mild mottle virus at various stages of wastewater treatment process

This study investigated the efficiency of the treatment processes of wastewater treatment plants (WWTPs) to remove severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and pepper mild mottle virus (PMMoV) from the wastewater and sewage sludge, as well as the influence of the mode of operation on the quality of the treated wastewater. SARS-CoV-2 and PMMoV were detected and quantified at different stages of the wastewater and sludge treatment process of three major WWTPs in Stockholm, Sweden. The results showed that primary, biological, and advanced membrane treatment processes are effective in removing SARS-CoV-2 from the wastewater with removal efficiencies of 99–100 % for all WWTPs, while the virus was accumulated in the primary and waste-activated sludges due to higher affinity to biosolids. Operation strategies such as bypass reintroduced the virus into the treated wastewater. The WWTPs achieved relatively low PMMoV removal efficiencies (63–87 %) most probably due to the robust capsid structure of the virus. Anaerobic digestion could not completely remove SARS-CoV-2 and PMMoV from the sludge leading to increased levels of SARS-CoV-2 and PMMoV in dewatered sludge. The study gives an overview of WWTPs’ role in tackling pathogen spread in society in the event of a pandemic and disease breakout.

Strategy to mitigate substrate inhibition in wastewater treatment systems

Global urbanization requires more stable and sustainable wastewater treatment to reduce the burden on the water environment. To address the problem of substrate inhibition of microorganisms during wastewater treatment, which leads to unstable wastewater discharge, this study proposes an approach to enhance the tolerance of bacterial community by artificially setting up a non-lethal high substrate environment. And the feasibility of this approach was explored by taking the inhibition of anammox process by nitrite as an example. It was shown that the non-lethal high substrate environment could enhance the nitrite tolerance of anammox bacterial community, as the specific anammox activity increasing up to 24.71 times at high nitrite concentrations. Moreover, the system composed of anammox bacterial community with high nitrite tolerance also showed greater resistance (two-fold) in response to nitrite shock. The antifragility of the system was enhanced without affecting the operation of the main reactor, and the non-lethal high nitrite environment changed the dominant anammox genera to Candidatus Jettenia. This approach to enhance tolerance of bacterial community in a non-lethal high substrate environment not only allows the anammox system to operate stably, but also promises to be a potential strategy for achieving stable biological wastewater treatment processes to comply with standards.

Assessment of wastewater ecotoxicity in a large hybrid sewer system in Lodz (Poland)

ABSTRACT Municipal wastewater may contain toxic substances that have a negative impact on biological treatment processes and receiving waters. This paper presents the wastewater toxicity test results from the Lodz hybrid sewage system. Wastewater is discharged to surface waters through a treatment plant, but also during wet weather, partially without treatment by combined sewer overflows. The research was carried out using the ToxTrakTM method with the use of the microbial community of activated sludge from the wastewater treatment plant in Lodz. The median toxicity, expressed as the degree of inhibition, ranged from 16.0% to 30.7%, but sometimes exceeded 50%. Higher toxicity was observed in wet weather than in dry weather. Seasonal variability was found but typical daily variability was not observed. In the case of sewage samples with the degree of inhibition above 40%, a significant correlation was found with chromium concentration and non-ionic surfactants (Pearson’s coefficient correlation above 0.7).

Two-stage partial nitrification-denitrification and anammox process for nitrogen removal in vacuum collected toilet wastewater at ambient temperature

Vacuum collected toilet wastewater (VCTW) contains high and fluctuating contents of organics and nitrogen, which exerts technological challenges to biological treatment processes. A partial nitrification–denitrification and anammox (PND-AMX) process was developed in sequencing batch reactor (SBR) and moving bed biofilm reactor (MBBR) to achieve effective nitrogen removal in VCTW at low ambient temperature. Stable PND was achieved, and nitrogen removal efficiency in SBR could be manipulated by adjusting influent COD/N ratios. As temperature ≥18 °C, 91.0% nitrogen was removed in PND-AMX process. In spite of the decreased anammox activity at 13–18 °C, more than 90% nitrogen removal could be obtained by adjusting SBR influent COD/N to 2.43 ± 0.32 with methanol. In MBBR reactor, Candidatus Kuenenia was the dominant anammox bacteria and contributed to more than 90% nitrogen removal capacity. Co-existing anammox and denitrifying bacteria synergistically contributed to the removal of ammonium, nitrite, nitrate, and COD in MBBR.

Performance evaluation of integrated Upflow Anaerobic Sludge Blanket reactor with trickling filter used for municipal wastewater treatment and effluent reuse potential for agriculture

Effluent reuse is a rapidly growing field of research where assessing the quality of effluent is one of the focus areas. This research examines the viability of using wastewater in agriculture by testing an integrated Upflow Anaerobic Sludge Blanket (UASB) reactor with a trickling filter (TF) system during the dry season. Compliance monitoring was conducted for 30 days from May 11 to June 9 of 2021. Samples were collected, handled, and analyzed following standard wastewater analysis procedures for biological oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), volatile suspended solids (VSS), cations, anions, heavy metals, E. coli, and helminth egg. The UASB-TF system in Kality wastewater treatment performed well in removing COD, BOD5, and TSS with average removal rates of 80.5%, 82.9%, and 80.9%, respectively, compared well with similar treatment configurations. The effluent quality satisfied the national inland discharge limit with a residual concentration of 125.1 mg/L for COD, 61.7 mg/L for BOD5 and 85.8 mg/L for TSS. On the other hand, high concentrations of chromium, nitrate-nitrogen, and helminth egg count restricted effluent reuse for agricultural purposes due to high health risks and environmental contamination. We found out that discharging industrial sewage into the domestic sewer network could inhibit microbial growth and affect the biological treatment processes. Furthermore, adopting integrated treatment systems in developing countries might face operational challenges and monitoring nitrate, helminth egg, and heavy metals would help provide timely operational feedback. An appropriate tertiary treatment unit—constructed wetlands or polishing ponds—is therefore needed to be introduced to ensure effluent reuse for agricultural purposes.

Insights into the role of electrochemical stimulation on sulfur-driven biodegradation of antibiotics in wastewater treatment

The presence of antibiotics in wastewater poses significant threat to our ecosystems and health. Traditional biological wastewater treatment technologies have several limitations in treating antibiotic-contaminated wastewaters, such as low removal efficiency and poor process resilience. Here, a novel electrochemical-coupled sulfur-mediated biological system was developed for treating wastewater co-contaminated with several antibiotics (e.g., ciprofloxacin (CIP), sulfamethoxazole (SMX), chloramphenicol (CAP)). Superior removal of CIP, SMX, and CAP with efficiencies ranging from 40.6 ± 2.6 % to 98.4 ± 1.6 % was achieved at high concentrations of 1000 μg/L in the electrochemical-coupled sulfur-mediated biological system, whereas the efficiencies ranged from 30.4 ± 2.3 % to 98.2 ± 1.4 % in the control system (without electrochemical stimulation). The biodegradation rates of CIP, SMX, and CAP increased by 1.5∼1.9-folds under electrochemical stimulation compared to the control. The insights into the role of electrochemical stimulation for multiple antibiotics biodegradation enhancement was elucidated through a combination of metagenomic and electrochemical analyses. Results showed that sustained electrochemical stimulation significantly enriched the sulfate-reducing and electroactive bacteria (e.g., Desulfobulbus, Longilinea, and Lentimicrobiumin on biocathode and Geobactor on bioanode), and boosted the secretion of electron transport mediators (e.g., cytochrome c and extracellular polymeric substances), which facilitated the microbial extracellular electron transfer processes and subsequent antibiotics removal in the sulfur-mediated biological system. Furthermore, under electrochemical stimulation, functional genes associated with sulfur and carbon metabolism and electron transfer were more abundant, and the microbial metabolic processes were enhanced, contributing to antibiotics biodegradation. Our study for the first time demonstrated that the synergistic effects of electrochemical-coupled sulfur-mediated biological system was capable of overcoming the limitations of conventional biological treatment processes. This study shed light on the mechanism of enhanced antibiotics biodegradation via electrochemical stimulation, which could be employed in sulfur-mediated bioprocess for treating antibiotic-contaminated wastewaters.

Impact of copper and sulfamethazine stress on microbial community and antibiotic resistance genes in denitrification systems: Comparison between heterotrophic and sulfur autotrophic denitrification processes

As common pollutants in wastewater, heavy metals and antibiotics have negative effects on the performance, microbial community and antibiotic resistance genes (ARGs) propagation of biological treatment processes. This study investigated the differential responses of heterotrophic denitrification (HD) and sulfur autotrophic denitrification (SAD) process to Cu(II) and sulfamethazine (SMZ) stress. Exposure to 12 mg/L Cu(II) and 25 mg/L SMZ, either alone or combined, reduced nitrogen removal efficiency by 4.22 % to 32.6 % for HD and 38.7 % to 63.2 % for SAD, respectively. HD exhibited greater robustness and microbial cooperation compared to SAD under stress. Cu(II) and SMZ intensified bacterial reactive oxygen species (ROS) responses, inhibited cell activity, and reduced extracellular polymeric substance secretion. Interestingly, microbially reduced sulfides (e.g., H2S and S2−) in SAD alleviated the cellular oxidative stress induced by Cu(II) and SMZ through ROS neutralization and CuS precipitation. Under stress, the relative abundance of ARGs increased significantly more in HD than in SAD compared to their respective control groups. Network analysis revealed more potential ARGs hosts in HD than in SAD. This study underscored the potential of the microbially reduced sulfides generated in the SAD process to effectively mitigate the spread of ARGs under selective pressure from heavy metals and antibiotics.