Chemical Oxygen Demand Removal Research Articles

Enhancing bioretention efficiency for pollutant mitigation in stormwater runoff: Exploring ecosystem cycling dynamics amidst temporal variability

In this study, three distinct bioretention setups incorporating fillers, plants, and earthworms were established to evaluate the operational efficiency under an ecosystem concept across varying time scales. The results revealed that under short-term operating conditions, extending the drying period led to a notable increase in the removal of NO3–-N, total phosphorus (TP), and chemical oxygen demand (COD) by 5 %–7%, 4 %–12 %, and 5 %–10 %, respectively. Conversely, under long-time operating conditions, the introduction of plants resulted in a significant boost in COD removal by 10 %–20 %, while the inclusion of earthworms improved NH4+-N and NO3–-N removal, especially TP removal by 9 %–16 %. Microbial community analysis further indicated the favorable impact of the bioretention system on biological nitrogen and phosphorus metabolism, particularly with the incorporation of plants and earthworms. This study provides a reference for the operational performance of bioretention systems on different time scales.

High-performance internal circulation anaerobic granular sludge reactor for cattle slaughterhouse wastewater treatment and simultaneous biogas production

This research investigates the efficacy of a high-performance pilot-scale Internal Circulation Anaerobic Reactor inoculated with Granular Sludge (ICAGSR) for treating cattle slaughterhouse wastewater while concurrently generating biogas. The primary objective is to assess the efficiency and performance of ICAGSR in terms of organic pollutant removal and biogas production using granular anaerobic sludge. The research methodology entails operating the ICAGSR system under ambient conditions and systematically varying key parameters, including different Hydraulic Retention Times (HRTs) (24, 12, and 8 h) and Organic Loading Rates (OLRs) (3.3, 6.14, and 12.83 kg COD/m³. d). The study focuses on evaluating pollutants’ removal and biogas production rates. Results reveal that the ICAGSR system achieves exceptional removal efficiency for organic pollutants, with Chemical Oxygen Demand (COD) removal exceeding 74%, 67%, and 68% at HRTs of 24, 12, and 8 h, respectively. Furthermore, the system demonstrates stable and sustainable biogas production, maintaining average methane contents of 80%, 76%, and 72% throughout the experimental period. The successful operation of the ICAGSR system underscores its potential as a viable technology for treating cattle slaughterhouse wastewater and generating renewable biogas. In conclusion, this study contributes to wastewater treatment and renewable energy production by providing a comprehensive analysis of the ICAGSR system’s hydrodynamic properties. The research enhances our understanding of the system’s performance optimization under varying conditions, emphasizing the benefits of utilizing ICAGSR reactors with granular sludge as an effective and sustainable approach. Identifying current gaps, future research directions aim to further refine and broaden the application of ICAGSR technology in wastewater treatment and renewable energy initiatives.

Enhanced degradation of enrofloxacin in mariculture wastewater based on marine bacteria and microbial carrier

This study aimed to isolate marine bacteria to investigate their stress response, inhibition mechanisms, and degradation processes under high-load conditions of salinity and enrofloxacin (ENR). The results demonstrated that marine bacteria exhibited efficient pollutant removal efficiency even under high ENR stress (up to 10 mg/L), with chemical oxygen demand (COD), total phosphorus (TP), total nitrogen (TN) and ENR removal efficiencies reaching approximately 88%, 83%, 61%, and 73%, respectively. The predominant families of marine bacteria were Bacillaceae (50.46%), Alcanivoracaceae (32.30%), and Rhodobacteraceae (13.36%). They responded to ENR removal by altering cell membrane properties, stimulating the activity of xenobiotic-metabolizing enzymes and antioxidant systems, and mitigating ENR stress through the secretion of extracellular polymeric substance (EPS). The marine bacteria exhibited robust adaptability to environmental factors and effective detoxification of ENR, simultaneously removing carbon, nitrogen, phosphorus, and antibiotics from the wastewater. The attapulgite carrier enhanced the bacteria's resistance to the environment. When treating actual mariculture wastewater, the removal efficiencies of COD and TN exceeded 80%, TP removal efficiency exceeded 90%, and ENR removal efficiency approached 100%, significantly higher than reported values in similar salinity reactors. Combining the constructed physical and mathematical models of tolerant bacterial, this study will promote the practical implementation of marine bacterial-based biotechnologies in high-loading saline wastewater treatment.

Breaking hydrogen bond in metal free carbon nitride to induce peroxymonosulfate nonradical activation: Surface-mediated electron transfer

Breaking hydrogen bond in metal free carbon nitride (CN) to increase peroxymonosulfate (PMS) adsorption for surface-mediated electron transfer has been challenging. Herein, we incorporated N−CN monomer into CN to break hydrogen bond by the introduction of polyvinylpyrrolidone (PVP). The developed nonradical oxidation system achieved selective decomposition of highly hydrophilic contaminants and efficient removal of chemical oxygen demand (58.0%), total phosphorus (88.1%), ammonia nitrogen (100.0%) and total nitrogen (67.8%) from the secondary effluent in a continuous flow reactor. This was attributed to that the breakage of hydrogen bond accelerated the redistribution of electron densities at C and N sites, leading to an increase in the adsorption energy of N site to PMS. This promoted the formation of PVP/CN-PMS* complex for the selective and efficient removal of organics and inorganics. This work provided a new perspective for the selective and long-term treatment of practical wastewater.

Potencial de Verrucodesmus verrucosus en la remoción de estructuras de nitrógeno y fósforo de aguas residuales de granjas porcinas

Verrucodesmus verrucosus in residual water from a pig farm located in Suchiapa, Chiapas, Mexico, was evaluated as a mixotrophic culture medium. The evaluation was carried out for 40 days, under the 12:12 light / dark cycle, two growth stages were evaluated (piglet and fattening) and the 50:50 mixture of these, as well as to the residual water two pre-treatments were applied, this consisted of a filtration process using a 15 µm diameter nylon filter and a sterilization process. The microalgal species Verrucodesmus verrucosus was shown to have bioremediation potential by growing in wastewater and producing biomass, demonstrating high efficiency in removing contaminants. The maximum Chemical Oxygen Demand (COD) removal was in the Ps treatment (sterile piglet) where the removal of 96.8 % was reached, while the Biochemical Oxygen Demand (BOD) had a maximum removal of 96.7 % in the Pf treatment (filtered piglet). The removal of total nitrogen, ammonia and nitrate was demonstrated with a percentage of 85.5 %, 74 % and 91 % respectively. As for the maximum removal of phosphorus and phosphate, they reach values of 97.9 % and 82 % respectively. On the other hand, it was possible to demonstrate the antagonistic capacity of this microalga with respect to Escherichia coli, where 100 % elimination was achieved.

Removal of melanoidin from baker yeast plant wastewater: A comparative study on chemical and biological processes

Dark brown color and large quantities of chemical oxygen demand (COD) are challenging for the successful treatment of molasses-based baker's yeast (BY) wastewater. In this study, the sequential biological and chemical coagulation processes were compared in terms of their ability to remove color and COD from industrial molasses-based BY wastewater. In the sequential chemical-biological processes, using the desired dosages of ferric chloride (FeCl3, 4 g/L) and calcium oxide (CaO, 2 % (w/v)) as coagulating agents, the color and COD removal were 90.6 % and 57 %, respectively. The COD removal of the samples from chemical pre-treated wastewater in an aerated biological reactor (reactor A) was improved to 78 %. In sequential biological-chemical processes with extended aeration (bioreactor A), the COD and color removal were 89.1 % and 93.7 %, respectively. The chemical post-treating of the effluent of the combined anaerobic-aerobic system (reactor C) led to COD and color removal of 80.8 % and 94.65 %, respectively. According to experimental findings, the chemical post-treatment was more efficient than the chemical pre-treatment process. This study offers new insights into the utilization of combined systems for the efficient removal of color and COD from industrial wastewater.

Ammonia nitrogen removal from coal gasification wastewater using a falling-film dielectric barrier discharge reactor: Process optimization and toxicity analysis

The continuous use of coal gasification technology for green energy generation to supplement the dwindling energy reserves generates significant amounts of wastewater containing ammonia nitrogen, posing a significant risk to the finite drinking water sources and aquatic lives. Herein, two falling-film dielectric barrier discharge (DBD) reactors with copper and titanium high-voltage electrodes, respectively, were designed to remove ammonia nitrogen (NH3−N) and chemical oxygen demand (COD) simultaneously from coal gasification wastewater. The operational parameters were screened using the Plackett-Burman design, and the significant parameters were further optimized via the response surface methodology. The results showed that the power parameter significantly influenced NH3-N removal, and COD removal was influenced considerably by power and treatment time. Under the optimum conditions (treatment time = 20.32 min, pH = 3, airflow rate = 1 L/min, power = 116 W, and recirculating flow rate = 50.02 mL/min), a removal ratio of 62.33 % and 37.35 % was achieved for NH3-N and COD for the reactor with the copper electrode, and 67.66 % and 44.90 % for NH3-N, and COD for the reactor with the titanium electrode. Additionally, the concentrations of O3, ·OH, and H2O2 produced by the reactors were quantified, and their crucial roles in the removal process of NH3-N were evaluated. Although smaller concentrations of NO2− and NO3− were detected in the treated wastewater, over 97 % of N2 selectivity encompassed NH3-N removal. Finally, acute phytotoxicity tests were performed, and the results indicated that at 100 mL/L dosage, the treated wastewater from both reactors did not restrict Barbarea verna growth.

Exploring the improving role of MWCNTs on the electrochemical behavior of electrophoretically prepared Ti/nanoZnO metal oxide electrode: A comparative study

In recent years, a growing amount of attention has been paid to the investigation and modification of metal oxide anodes as a critical parameter in electrochemical removal. In this way, this research attempts to bring out an effective comparison between modified Ti/nanoZnO electrode by multi-walled carbon nanotubes (MWCNTs) and base Ti/nanoZnO electrode. The electrophoretic deposition (EPD) method was used to prepare electrodes. The morphological and chemical composition of the surface for both electrodes were obtained by using characterization tests including field emission scanning electron microscope - energy dispersive spectrometer (FESEM-EDS), elemental mapping, and X-ray diffraction (XRD). Furthermore, the electrochemical behavior of Ti/nanoZnO as well as Ti/nanoZnO-MWCNTs electrodes were compared using linear sweep voltammetry (LSV), chronopotentiometry (CP), and chronoamperometry (CA) analysis. In the final step, the chemical oxygen demand (COD) removal in addition to the decolorization rate of a dyes mixture was used to evaluate the electrochemical performance in the same conditions. Presented results in this study showed the importance of metal oxide anode modification by improved deposited coating properties of Ti/nanoZnO-MWCNTs electrode compared with base ZnO electrode.

Study on the removal of high nitrate-nitrogen concentration from pig farm wastewater by heterotrophic and sulphur autotrophic synergistic denitrification filter process

Following the anaerobic fermentation process in a lagoon, the effluent from pig wastewater exhibited elevated levels of total nitrogen and nitrate nitrogen. The utilization of simple sulphur-limestone autotrophic denitrification resulted in a sluggish reaction rate and relatively moderate removal load. To enhance the efficacy of the sulphur autotrophic denitrification process, a strategy was implemented involving the introduction of a limited quantity of corncobs as a slow-release carbon source. This addition was made to a sulphur-limestone autotrophic denitrification reactor that was being operated continuously and stably. Furthermore, the volume ratio of the corncobs added was progressively increased. This study examines the alterations in nitrate nitrogen, chemical oxygen demand (COD), sulphate, and alkali consumption within the sulphur-limestone autotrophic denitrification reactor, both prior to and after the introduction of corncobs. This study examines the operational efficiency and reaction mechanism of a sulfur-limestone autotrophic denitrification reactor that is enhanced by the utilization of corncobs as a slow-release carbon source. The findings of the study indicate that the inclusion of maize cob carbon source in the sulphur limestone autotrophic denitrification process resulted in improved effectiveness in removing nitrate and nitrogen. Additionally, when considering the three different ratios of corncob carbon source, the process exhibited a chemical oxygen demand (COD) removal rate exceeding 42%. The observed trend in the consumption of alkalinity in both the pure sulphur limestone autotrophic denitrification process and the sulphur limestone autotrophic denitrification process augmented by the three types of corncob slow-release carbon sources indicated an increase with time. The concentration of nitrate-nitrogen in the influent water exhibited a negative correlation with the length of the reactor flow-through. The addition of a slow-release carbon source derived from corncob greatly enhanced the autotrophic denitrification and denitrification impact in the three reactors. Moreover, there was an observed increase in the trend of heterotrophic denitrification as the amount of carbon source added increased. The efficacy of the mixotrophic denitrification process surpassed that of the sulphur-limestone autotrophic denitrification method in the treatment of nitrate-nitrogen wastewater characterized by a high concentration of nitrate-nitrogen. The former exhibited a higher denitrification rate and resulted in lower levels of sulphate ions and alkalinity production.

Insights into the response mechanisms of activated sludge system under long-term dexamethasone stress

Dexamethasone (DEX) is a hormone drug that is often detected in wastewater treatment plants, but its impact on activated sludge systems is unknown. This study explored the long-term effects of DEX on nutrient removal, microbial activities, microbial assembly, and microbial interactions in the activated sludge system. During the 90-day DEX exposure experiment, both chemical oxygen demand and total nitrogen removal efficiencies were initially inhibited and then recovered. Microbial activities, i.e., specific oxygen uptake rate and denitrification, did not differ significantly from that of the control reactor (p > 0.05), possibly due to the secretion of extracellular polymers that act as a protective barrier against excess reactive oxygen species induced by DEX. This barrier protects cell membrane integrity and ensures stable treatment performance. Analysis of microbial assembly identified the drift of stochastic processes (from 92.7 % to 51.8 %) and homogeneous selection of deterministic processes (from 1.6 % to 38.7 %) as the main driving forces of microbial community structure succession under long-term DEX stress. Although long-term exposure to 1000 μg/L DEX did not significantly increase the abundance levels of functional bacteria (Nitrosomonas and 996-1) and key genes (AmoCAB and Hao), the ammonia oxidation capacity of the activated sludge system was enhanced. Analysis of microbial interactions indicated that streamlining of functional subnetworks and increased cooperation were the primary reasons. This is the first study to explore the long-term effects of DEX on activated sludge and provide insights into microbial interaction and assembly. Moreover, the findings of this study broaden our knowledge and lay an experimental foundation for reducing risks associated with hormone drugs.

Simultaneous degradation of pharmaceutical contaminants and sterilization in real hospital wastewater by a highly efficient electrocatalytic ozonation process: Performance, mechanism and application

Herein, this work investigated an electrocatalytic ozonation (ECO) strategy using stainless steel-graphite plates as cathode–anode for the degradation of the pharmaceutical pollutant dexamethasone (DXMS) and the treatment of real hospital wastewater. The reaction kinetic constant of the ECO degradation of DXMS (0.387 min−1) was 4 times higher than that of single ozone (0.087 min−1). The established efficient ECO system successfully degraded pharmaceutical contaminants and had excellent bactericidal effects against pathogenic microorganisms (Escherichia coli). The results of scavenging experiments, chemical probe experiments, and electron paramagnetic resonance (EPR) analysis indicated that the newly generated 1O2 in the ECO system achieved the synergistic effect of the combined EC-ozonation process. More to the point, the ECO system has a high removal rate of chemical oxygen demand (COD) and total organic carbon (TOC) for real hospital wastewater treatment. After 60 min treatment of the ECO system, the COD removal of hospital wastewater ranged from 70 % to 88.91 %, and the TOC removal ranged from 52.05 % to 71.81 %. The ECO system developed in this work has the capacity for simultaneous degradation of pharmaceutical contaminants and sterilization of pathogenic microorganism for hospital wastewater treatment.

Optimization of pollutants removal from anaerobically digested dairy wastewater by electro-oxidation process: a response surface methodology modeling and validation

AbstractThe release of anaerobically digested dairy wastewater (ANDDW) without a treatment can lead to severe environmental pollution, prompting the exploration of effective and sustainable treatment methods. Amidst various wastewater treatment approaches, the electro-oxidation (EO) process is considered as a promising, clean, and adaptable solution. In this study, the major operational parameters viz. current density, electrolyte concentration, treatment time, and mixing speed of an EO comprising Ti/PbO2 anode and stainless-steel cathode, were optimized using response surface methodology (RSM) for efficient removal of chemical oxygen demand (COD), ammonia nitrogen (NH3-N), total phosphorus (TP), orthophosphate (OP), total nitrogen (TN), and total Kjeldahl nitrogen (TKN) from ANDDW. Optimal conditions were identified as a current density of 90 mA cm−2, 0.08% electrolyte concentration, 180 min treatment time, and 400 rpm mixing speed. Under the optimum conditions, the COD, NH3-N, TP, OP, TN, and TKN removal efficiencies were 78.36, 63.93, 87.41, 92.39, 67.01, and 81.42%, respectively. Furthermore, the reaction rate followed the first-order kinetic model for the pollutants removal with correlation coefficients (R2) close to 1. The findings highlight the potential of using the EO process to treat high pollutant-laden ANDDW and encourage further studies to confirm the corresponding outcomes on a pilot scale. Graphical abstract

Exploring the role of domesticated resistors in batch-mode microbial desalination cell

Microbial Desalination Cells (MDCs) are an electrochemical process that harnesses microbial reactions to simultaneously treat wastewater, generate power, and desalinate water. By utilizing microbial decomposition of organic pollutants in wastewater, MDCs offer a sustainable and energy-efficient alternative to conventional desalination technologies. The technical framework of MDCs emphasizes the integration of water-electricity principles, making them promising for future applications in seawater desalination, wastewater treatment, resource recovery, and water softening. This study investigates the impact of acclimation resistance, represented by four different domesticated resistors values of 1 kΩ, 100Ω, 51Ω, and 10Ω, on the performance of MDCs. Larger acclimation resistors exhibit higher power performance, with the case of 100Ω achieving a power density of 0.33 mA/m2 and the case of 1 kΩ achieving the highest current density of 1.90 mA/m2. Furthermore, the case with an acclimation resistance of 1 kΩ exhibits superior performance in terms of chemical oxygen demand (COD) removal, achieving a removal rate of 76.3% on day 1. Conversely, the case with an acclimation resistance of 10Ω demonstrates the best desalination performance, achieving a desalination rate of 9.0%. It should be noted that the optimal performance in terms of COD removal and desalination capacity varies due to the various operational mechanisms involved. . The findings of this study provide valuable insights for enhancing the performance of MDCs in future applications, enabling further improvements in their efficiency and effectiveness.

Downflow sponge biofilm reactors for polluted raw water treatment: Performance optimisation, kinetics, and microbial community

Water outages caused by elevated ammonium (NH4+-N) levels are a prevalent problem faced by conventional raw water treatment plants in developing countries. A treatment solution requires a short hydraulic retention time (HRT) to overcome nitrification rate limitation in oligotrophic conditions. In this study, the performance of polluted raw water treatment using a green downflow sponge biofilm (DSB) technology was evaluated. We operated two DSB reactors, DSB-1 and DSB-2 under different NH4+-N concentration ranges (DSB-1: 3.2–5.0 mg L−1; DSB-2: 1.7–2.6 mg L−1) over 360 days and monitored their performance under short HRT (60 min, 30 min, 20 min, and 15 min). The experimental results revealed vertical segregation of organic removal in the upper reactor depths and nitrification in the lower depths. Under the shortest HRT of 15 min, both DSB reactors achieved stable NH4+-N and chemical oxygen demand removal (≥95%) and produced minimal effluent nitrite (NO2−-N). DSB system could facilitate complete NH4+-N oxidation to nitrate (NO3−-N) without external aeration energy requirement. The 16S rRNA sequencing data revealed that nitrifying bacteria Nitrosomonas and Nitrospira in the reactor were stratified. Putative comammox bacteria with high ammonia affinity was successfully enriched in DSB-2 operating at a lower NH4+-N loading rate, which is advantageous in oligotrophic treatment. This study suggests that a high hydraulic rate DSB system with efficient ammonia removal could incorporate ammonia treatment capability into polluted raw water treatment process and ensure safe water supply in many developing countries.

Isolation and characterization of Stenotrophomonas pavanii GXUN74707 with efficient flocculation performance and application in wastewater treatment.

The identification of microorganisms with excellent flocculants-producing capability and optimization of the fermentation process are necessary for the wide-scale application of bioflocculants. Therefore, we isolated and identified a highly efficient flocculation performance strain of Stenotrophomonas pavanii GXUN74707 from the sludge. The optimal fermentation and flocculation conditions of strain S. pavanii GXUN74707 was in fermentation medium with glucose and urea as the carbon and nitrogen sources, respectively, at pH 7.0 for 36 h, which treatment of kaolin suspension with 0.5 mL of the fermentation broth resulted in a flocculation rate of 99.0%. The bioflocculant synthesized by strain S. pavanii GXUN74707 was found mainly in the supernatant of the fermentation broth. Chemical analysis revealed that the pure bioflocculant consisted of 79.70% carbohydrates and 14.38% proteins. The monosaccharide components of MBF-GXUN74707 are mainly mannose (5.96 μg/mg), galactose (1.86 μg/mg), and glucose (1.73 μg/mg). Infrared spectrometric analysis showed the presence of carboxyl (COO-), hydroxyl (-OH) groups. The SEM images showed clumps of rod-shaped bacteria with adhesion of extracellular products. Furthermore, the strain decolored dye wastewater containing direct black, direct blue, and Congo red by 89.2%, 95.1%, 94.1%, respectively. The chemical oxygen demand (COD) and biological oxygen demand (BOD) removal rates after treatment of aquaculture wastewater with the fermentation broth were 68% and 23%, respectively. This study is the first to report the performance and application of strain Stenotrophomonas pavanii in wastewater flocculation. The results indicate that strain S. pavanii is a good candidate for the production novel bioflocculants and demonstrates its potential industrial practicality in biotechnology processes.

Promising membrane photobioreactor for continuous flow treatment of Low C/N wastewater: Treating process, community structure, and cooperation mechanism

Low carbon/nitrogen (C/N) wastewater treatment is an emerging issue for conventional treatment technologies. To achieve this goal, a novel membrane photobioreactor (MPBR), integrating microalgae consortium (MC) and activated sludge (AS) phases, was investigated. The separation of the MC and AS phases could improve the removal of pollutants in low C/N wastewater, which could achieve the rapid denitrogenation through NH4+-N assimilation in MC phase, and effectively reduce organic matter concentration in AS phase, resulting in better nutrient recovery, lower costs, and stable pH. The results in phase I showed that the pollutants, such as chemical oxygen demand (COD), ammonium (NH4+-N), and total phosphorus (TP), met the Environmental Quality Standards for Surface Water (GB3838–2002) by MPBR. The AS phase with low DO, which could enrich heterotrophic bacteria (e.g., Bacteroidetes vadinHA17, Spirochaeta and Ahniella) and nitrogen cycling bacteria (e.g., Mycobacterium, Bacillus and Ellin6067), could promote the removal of COD and NO3--N in the continuous effluent. Based on the co-occurrence pattern analysis, the main influencing factor of MC and AS phases was the reduction of COD, which also illustrated the synergistic removal of organic matter by the cooperative interaction of microalgae and heterotrophic bacteria. From a genetic perspective, the internal circulation mode also enhanced microbial nitrogen metabolism in the MPBRs, with higher abundances of nitrification- and denitrification-related functional genes in the MC phase, and higher abundances of nitrification, dissimilatory nitrate reduction, and denitrification genes in the AS phase. This study provided an experimental and theoretical basis for MPBR in low-C/N wastewater treatment.

Enhanced anaerobic digestion of landfill leachate based on a novel redox mediator: Synergistic mechanism of enhancing extracellular electron transfer

The presence of recalcitrant compounds and toxic substances in landfill leachate results in low anaerobic digestion (AD) efficiency and poor methane production performance. Strengthening the extracellular electron transfer of microorganisms represents an effective approach to promote the AD of landfill leachate. In this study, a novel redox mediator (FeNC-RM) was synthesized through the combination of metal and non-metal doping, intensifying the stable operation of the landfill leachate AD system. Through characterization techniques including X-ray photoelectron spectroscopy and X-ray diffraction, it was observed that FeNC-RM possesses a larger specific surface area, abundant functional groups, and exceptional electrochemical performance. By adding FeNC-RM, the stability and efficiency of the medium-temperature AD system in the treatment of landfill leachate were improved: Obtained a high removal of chemical oxygen demand which was increased by 30 % compared to the control group and enhanced the specific methanogenic activity by 57.5 % compared to the control group. The electron transport system (ETS) activities of the experimental groups with the addition of RMs were all significantly higher than those of the control group, and the ETS activity of the sludge from the FeNC-RM group was 79.6 % higher than that of the control group. Through a comprehensive analysis of the underlying mechanism, it was determined that three aspects synergistically facilitated electron transfer: FeNC-RM, endowed with electrochemical capabilities, assumed a pivotal role in establishing a conduit for electron transport, thus promoting the synthesis of extracellular humic substances and augmenting electron transport activity. Furthermore, the microbial community was optimized by FeNC-RM, thereby fostering a co-nutritional mechanism between hydrolytic acidification bacteria and methanogens, establishing a direct interspecific electron transport pathway. In this study, an “endogenous + exogenous” electron transport model based on the enhanced extracellular electron transport pathway facilitated by FeNC-RM was proposed. This study offered valuable contributions to the advancement of anaerobic treatment technology for landfill leachate.

Catalytic ozonation of reverse osmosis concentrate from coking wastewater reuse by surface oxidation over Mn-Ce/γ-Al2O3: Effluent organic matter transformation and its catalytic mechanism

Degradation of organics in high-salinity wastewater is beneficial to meeting the requirement of zero liquid discharge for coking wastewater treatment. Creating efficient and stable performance catalysts for high-salinity wastewater treatment is vital in catalytic ozonation process. Compared with ozonation alone, Mn and Ce co-doped γ-Al2O3 could remarkably enhance activities of catalytic ozonation for chemical oxygen demand (COD) removal (38.9%) of brine derived from a two-stage reverse osmosis treatment. Experimental and theoretical calculation results indicate that introducing Mn could increase the active points of catalyst surface, and introducing Ce could optimize d-band electronic structures and promote the electron transport capacity, enhancing HO• bound to the catalyst surface ([HO•]ads) generation. [HO•]ads plays key roles for degrading the intermediates and transfer them into low molecular weight organics, and further decrease COD, molecular weights and number of organics in reverse osmosis concentrate. Under the same reaction conditions, the presence of Mn/γ-Al2O3 catalyst can reduce ΔO3/ΔCOD by at least 37.6% compared to ozonation alone. Furthermore, Mn-Ce/γ-Al2O3 catalytic ozonation can reduce the ΔO3/ΔCOD from 2.6 of Mn/γ-Al2O3 catalytic ozonation to 0.9 in the case of achieving similar COD removal. Catalytic ozonation has the potential to treat reverse osmosis concentrate derived from bio-treated coking wastewater reclamation.

Optimizing hydraulic retention time of high-rate activated sludge designed for potential integration with partial nitritation/anammox in municipal wastewater treatment

The integration of high-rate activated sludge (HRAS), an effective carbon redirection technology, with partial nitritation/anammox (PN/A) is a novel AB treatment process for municipal wastewater. In this study, an airlift HRAS reactor was operated in the continuous inflow mode for 200 d at a wastewater treatment plant. The balance between potential PN/A system stability and peak HRAS performance under decreasing hydraulic retention time (HRT) was optimized. Energy consumption and recovery and CO2 emissions were calculated. The results showed that the optimal HRT suitable with the PN/A process was 3 h, achieving 2–3 g/L mixed liquor volatile suspended solid, 67.8 % chemical oxygen demand (COD) recovery, 81 % total COD removal efficiency, 2.27 ± 1.03 g COD/L/d organic loading rate, 62 % aeration reduction, and 0.24 kWh/m3 power recovery potential. Such findings hold practical value and contribute to the development of the optimal AB process capable of achieving energy autonomy and carbon neutrality.

Low voltage electric field mediating gravity-driven membrane bioreactor in treating saline wastewater: removal improvement and membrane fouling control

Gravity-driven membrane bioreactor (GDMBR) endowed with low maintenance and energy consumption owing to its combinations between biological degradation and membrane rejection, however, has not been reported in treating the saline wastewater due to the potential biological inhibition. This study investigated the effects of salt on GDMBR performance, and introduced a novel low voltage electric field (eGDMBR) with hopes to mediate the biological activity and improve the filtration performance. The influence of different low voltage electric fields (0.25 V, 0.50 V, and 0.75 V) on the flux variations and contaminants removal of eGDMBR were investigated. The results demonstrated that integrating low voltage electric field into GDMBR would not impact the appearance of flux stabilization, but delivered a significant influence on its stabilized flux level, and 0.50 V was the optimized voltage, contributing to a substantial flux improvement of 47.10 % in eGDMBR-0.50. Moreover, with the assistance of low voltage electric fields, eGDMBR process obtained an effective removal of chemical oxygen demand (COD), ammonia nitrogen (NH4+-N) and total phosphorus (TP), accounting for average removal efficiency of 54.01 %, 73.08 % and 25.74 %, respectively. Compared to the control, coupling 0.50 V voltage electric field to GDMBR was beneficial to engineer a loose, porous and heterogeneous structure of membrane biofilm and also reduce the accumulation of extracellular polymeric substance (EPS), significantly contributing to alleviating the membrane fouling. Furthermore, with the assistance of low voltage electric fields, the Proteobacteria was enriched by a relative abundance of 58.58 % in the membrane biofilm of eGDMBR-0.50, which was in favor of the degradation of COD and NH4+-N. Therefore, these findings indicated that eGDMBR conferred significant superiorities in treating the saline wastewater and mitigating membrane fouling.