COD Removal Research Articles

Disinfection of synthetic human urine by mixed metal oxide anode through photo/electrochemical oxidation

This study investigates the electrooxidation treatment of synthetic urine (SU) using quaternary mixed metal oxide (d-MMO) anodes in both batch and continuous modes. We combine photocatalysis (PC) and electrooxidation (EO) to enhance pollutant degradation. The impact of treatment time, pH, Na/Cl ratio, and current density on COD removal and the specific energy consumption is examined. Optimized parameters for batch EO treatment yield a desirability value (D) of 0.941, with COD removal of 90.55 % and energy consumption of 20.851 kWh/kg of COD removed. Treatment time is reduced from 10.05 h to 6.5 h with PEC (Photoelectrocatalysis) incorporation. The stability and durability of anodes are confirmed through XRD and FE-SEM/EDS analysis, even after 500 recycling cycles. This research stands out for utilizing innovative d-MMO anodes for EO and PEC, capturing molecular hydrogen gas during scale-up trials for SU. Through this study, we are proposing for the first time, the novel composition of d-MMO (Ti/IrO2/Ta2O5/SnO2/Sb2O5) for the treatment of SU on a pilot-scale in continuous mode with solar panels, thus making the process cost effective with less energy consumption.

Yeast-enhanced activated sludge for improved nitrogen removal in wastewater treatment: Focus on dissolved organic nitrogen degradation

Dissolved organic nitrogen (DON) in effluent of wastewater treatment plants (WWTP), particularly hydrophilic DON, is usually more effective than dissolved inorganic nitrogen (DIN) in stimulating phytoplankton growth and increases the risk of eutrophication in receiving waterbodies. Proteins, amino acids, and nucleic acids, which are the main sources of DON in the effluent, are produced during the hydrolysis of extracellular polymeric substances (EPS) in activated sludge. Herein, a yeast strain Candida tropicalis O2, which was highly efficient in degrading DON in EPS was screened. Within 48-hour batch experiments, the DON removal rates of the extracted hydrophilic and hydrophobic EPS reached 68.26% and 59.27%, respectively. During the continuous 35-day operation of sequencing batch bioreactor (SBR) fed with synthetic wastewater, the yeast-enhanced activated sludge (AS-Y) reactor demonstrated a marked improvement in removing various pollutants compared to the traditional activated sludge (AS) reactor. Specifically, DON removal increased by 1.53 mg/L (24.75%), hydrophilic DON by 1.24 mg/L (27.13%), hydrophobic DON by 0.28 mg/L (12.08%), and COD removal by 4.04 mg/L (6.48%). Although the DIN removal decreased by 0.38 mg/L (3.86%), it did not attenuate the overall TN removal from the system, and an additional TN reduction of 1.15 mg/L (7.13%) was achieved. Metagenomic analysis showed that adding strain O2 slightly inhibited the DIN metabolism, and the relative abundances of napB, nirK/S, norB/C, and nosZ involved in denitrification somewhat decreased. Kyoto Encyclopedia of Genes and Genomes and Carbohydrate-Active Enzymes annotations revealed that adding strain O2 promoted amino acid and carbohydrate metabolism. The increased relative abundance of Candida indicated that strain O2 was able to colonize the sludge in AS-Y reactor, which was conducive to synergistic interactions with other microorganisms. This study provided a novel method for in situ improving nitrogen removal in WWTP and reducing the eutrophication risk of the effluent to receiving waterbodies.

Advanced oxidation enhanced microbial electrolysis cell coupled with anaerobic digestion: A novel approach to coal gasification wastewater treatment

Coal gasification wastewater (CGW) contains a range of refractory and toxic organic pollutants with low biodegradability and significant biological toxicity. This study synthesized a hemin-graphene (H-graphene) catalyst for permonosulfate (PMS) activation. The MEC-AD (Microbial electrolysis cell- Anaerobic digestion) reactor (K1) was designated as the control group. The experimental groups were the MEC-AD reactor (K2) with PMS and H-graphene, and the MEC-AD reactor (K3) with advanced oxidation as a synthetic CGW pretreatment. The results demonstrated that the COD removal rates of K1, K2 and K3 reactors were 76.7%, 79.5% and 87.4%, while the total phenol removal rates were 74.1%, 90.1% and 100%, respectively. Quinoline and indole were removed at rates greater than 90% in the microbial electrolytic cell reactors K2 and K3, and 100% in the K3 reactor. In K2 and K3, there was a considerable decrease in the abundance of unclassified _ f _ Alcaligenaceae, Arenimonas and unclassified _ f _ Gracilibacteraceae as compared to K1. The abundance of unclassified _ p _ Zixibacteria, Candidatus _ Caldatribacterium, unclassified _ c _ JS1 and JGI-0000079-D21, which are responsible for promoting the anaerobic degradation of long-chain fatty acids and anaerobic fermentation of acid production increased.

Enhanced hydrolytic acidification with Zero-Valent Iron for efficient treatment of comprehensive wastewater from industrial parks: mechanistic insights and toxicity reduction

In this study, a laboratory-scale zero-valent iron (ZVI)-enhanced hydrolytic acidification system was established to treat the comprehensive wastewater from Nanjing Jiangbei New Material Science Technology Park. Results indicated that the ZVI-enhanced hydrolytic acidification system achieved a maximum COD removal efficiency of 95.0%, surpassing the performance of the system without ZVI by 12.2%. Microbial community analysis revealed the enrichment of electrogenic bacterium Bacteroidetes_vadinHA17 and typical hydrogenotrophic methanogen Methanobacterium due to ZVI addition. High-throughput sequencing combined with PICRUSt2 analysis demonstrated acetate production was promoted, and butyrate and propionate production was inhibited. Additionally, Oxygen Uptake Rate-based toxicity assays revealed the hydrolytic acidification system transitioned the wastewater of three enterprises from low toxicity to non-toxic status and two from high to low toxicity. While the ZVI-enhanced hydrolytic acidification system successfully reduced the toxicity of all highly and low toxic wastewaters to non-toxic levels.

Construction of efficient S-scheme TiO2/Bi3.84W0.16O6.24 heterojunction with abundant O vacancies: Kinetics, performance and mechanism insight

The photocatalytic oxidation of Tetracycline hydrochloride (TC) under visible light irradiation is an economically viable solution to address energy and pollution concerns. Herein, an oxygen vacancies (Ovs) defecting-TiO2/Bi3.84W0.16O6.24 S-scheme heterostructure with strong redox ability was constructed, exhibiting superior catalytic capability for TC destruction. 30 % Ov-TiO2/Bi3.84W0.16O6.24 (Ov-TBW30) composite demonstrated the highest activity, with the constant (0.872 min−1). The results indicated that Ov is conducive to the reduced bandgap and promoting effective charge transfer. In the ligand-metal charge transfer (LMCT) effect, charge transferred from the Highest Occupied Molecular Orbital (HOMO) of the TC to the conduction band (CB) of the heterojunction, which enables the heterogeneous structure to be much more light-responsive. Furthermore, the variable cycling of Ti4+/Ti3+ facilitated charge balance and quickened the charge transport rate on the heterojunction surface. Noteworthy, the work function calculation, differential charge density, and XPS results jointly confirmed that electrons flowed from Bi3.84W0.16O6.24 to the TiO2 side. O2-TPD and NH3-TPD demonstrate that Ov-TBW30 has a strong catalytic oxidation ability for pollutants. Additionally, the calculated AQE value for COD removal is 0.08 %. 3DEEMs results confirmed that the Ov-TBW photocatalysis system has a strong mineralization capacity for TC. This work provides new perspectives on the design of S-scheme photocatalysis with efficient photocatalytic performance.

Native microorganisms for sustainable dye biodegradation in wastewaters from jeans finishing.

The textile mill is one of the most water-consuming industries. Wastewater production is very high, and among the main generated pollutants are dyes. In particular, jeans finishing, which is performed all over the world, generates wastewater with indigo dye that has to be eliminated before discharge. This work studies the biological treatment of this type of wastewater using native microorganisms, i.e., without the need for external seed sludge to start-up the process. Two strategies for starting up the biological treatment using laboratory sequencing batch reactors have been compared: the addition of seed sludge from a biological reactor of a wastewater treatment plant and the non-addition of seed sludge, which means that native microorganisms (those in wastewater coming from the industry facilities) are responsible for COD and color degradation. Special attention is paid to biomass shift in both reactors, analyzing both bacterial and fungal populations. Results yielded more than 90% of COD and color removal after 25days in both reactors. MLSS increased in both reactors during the operation, reaching very similar values (around 1840mg/L). Rozellomycota was the predominant phylum in the reactors. Concerning bacteria, Planctomycetota abundance increased considerably in both reactors, which shows the important role of these bacteria in the treatment. It can be concluded that the lower bacterial diversity in the native population in comparison with the seeded sludge was shifting to a higher microbial diversity during the process, achieving a similar microbial population in reactors. It implies that it is not necessary to either work with isolated cultures or seeded sludge, which leads to a simpler and more sustainable solution for textile wastewater treatment in areas all over the world.

Biogas Production from a Solar-Heated Temperature-Controlled Biogas Digester

This research paper explores biogas production in an underground temperature-controlled fixed dome digester and compares it with a similar uncontrolled digester. Two underground fixed-dome digesters, one fitted with a solar heating system and a stirrer and the other one with an identical stirrer only, were batch-fed with cow dung slurry collected from the University of Fort Hare farm and mixed with water in a ratio of 1:1. The solar heating system consisted of a solar geyser, pex-al-pex tubing, an electric ball valve, a water circulation pump, an Arduino aided temperature control system, and a heat exchanger located at the centre of the digester. Both the digesters were intermittently stirred for 10 min every 4 h. The digester without a heating system was used as a control. Biogas production in the two digesters was compared to assess the effect of solar heating on biogas production. The total solids, volatile solids, and the chemical oxygen demand of the cow dung used as substrate were determined before and after digestion. These were compared together with the cumulative biogas produced and the methane content for the controlled and uncontrolled digesters. It was observed that the temperature control system kept the slurry temperature in the controlled digester within the required range for 82.76% of the retention period, showing an efficiency of 82.76%. Some maximum temperature gradients of 7.0 °C were observed in both the controlled and uncontrolled digesters, showing that the stirrer speed of 30 rpm was not fast enough to create the needed vortex for a uniform mix in the slurry. It was further observed that the heat from the solar geyser and the ground insulation were sufficient to keep the digester temperature within the required temperature range without any additional heat source even at night. Biogas yield was observed to depend on the pH with a strong coefficient of determination of 0.788 and 0.755 for the controlled and uncontrolled digesters, respectively. The cumulative biogas was 26.77 m3 and 18.05 m3 for controlled and uncontrolled digesters, respectively, which was an increase of 33%. The methane content increased by 14% while carbon dioxide decreased by 10% from the uncontrolled to the controlled scenario. The percentage removal of the TS, VS, and COD was 66.26%, 76.81%, and 74.69%, respectively, compared to 47.01%, 60.37%, and 57.86% for the uncontrolled situation. Thus, the percentage removal of TS, VS, and COD increased by 19.25%, 16.44%, and 16.89%, respectively.

Acclimatation of Microbial Biomass to Effluents From a Swine Slaughterhouse in Batch Reactors

Objective: To evaluate the acclimatization of microbial biomass in sequential reactors to optimize the treatment of wastewater from pig slaughterhouses. Theoretical framework: The meat industry generates highly contaminated wastewater. Biological treatments, such as aerobic and anaerobic systems, are more efficient and sustainable than physicochemical ones. Materials and methods: Industrial effluents were collected in a pig slaughterhouse and then characterized. The microbial biomass was collected from the same slaughterhouse and was subjected to an acclimatization process in a sequential batch reactor. Results and discussion: The results showed that the wastewater from the pig slaughterhouse had high levels of BOD, COD and suspended solids, exceeding the limits established by local regulations. During the acclimatization process, the microbial biomass demonstrated a gradual improvement in its COD removal capacity, reaching efficiencies greater than 70%. The positive correlation observed between volumetric organic load and organic matter removal efficiency indicates that acclimated biomass has a greater capacity to treat effluents with high levels of organic load. Research implications: Biomass acclimatization is essential to improve the efficiency of biological treatment in slaughterhouse effluents, reducing its environmental impact and the need for costly treatments. Value/originality: This study proposes a more sustainable and efficient solution for the treatment of slaughterhouse wastewater, highlighting the importance of biomass acclimatization.

Application of Central Composite Design for Commercial Laundry Wastewater Treatment by Packed bed Electrocoagulation using sacrificial iron electrodes.

This research paper deals with a novel method utilizing packed bed electrocoagulation (PBEC) comprising of sacrificial iron electrodes and coupled with extracellular polymeric substances (EPS) used as flocculent agents for the treatment of commercial laundry wastewater (LWW). The study employs stainless steel cathodes, graphite anodes, and scrap iron pieces as sacrificial electrodes, ensuring efficient treatment in dynamic batch mode operation with enhanced contact time facilitated by serpentine flow. The initial characteristics of LWW were COD 579 ± 30 mg/L, TSS of 60 ± 10 mg/L, TS of 622 ± 20 mg/L, turbidity of 110 ± 5 NTU, pH of 9 ± 0.5, NPEOs of 570 ±150 μg/L and conductivity of 494 ± 20 mS/cm. The results demonstrate effective removal of turbidity (98 ± 2%), TS (95 ± 3%), COD (89 ± 5%), and NPEOs (53 ± 2%) under optimized current intensity: 2.99A, treatment time: 58.8 minutes and enhanced EPS dose from 5.8 mg/L to 8.0 mg/L. The economic feasibility analysis reveals energy consumption as the primary expenditure, with a treatment cost of 1.20$CAN/m3. This research introduces sustainable treatment for commercial LWW, meeting Quebec's reuse standards, implying reuse potential and responsible wastewater management.

Improved treatment of coking wastewater and higher biodiversity through immobilization of Comamonas sp. ZF-3 supplemented microbial community.

The aim of this study was to investigate the relationship among pollutant removal performance, microbial community structure and potential gene function of immobilized microorganisms in coking wastewater (CWW) treatment process. The results showed that the immobilized biomass containing strain Comamonas sp. ZF-3 displayed greater resistance to CWW and higher COD, NH4+-N removal efficiency (92%, 60%) than free cells (48%, 7%), meanwhile, the results from GC-MS proved main organic pollutants in CWW including phenolic compounds, heterocyclic compounds and polycyclic aromatic hydrocarbons were basically removed by immobilized microorganisms. During 123 days of degradation experiment, high-throughput 16S rRNA gene sequencing analysis of immobilized carriers showed more stable and diverse microbial community, which was consistent with simultaneous removal of COD and NH4+-N observed in carrier experiment. Among them, Comamonas sp. ZF-3 continuously remained at the highest proportion (23.25%) in immobilized carrier, while Nitrosomonas (1.47%) and Nitrospira (1.90%) were simultaneously detected. Moreover, microbial community of immobilized carriers showed higher relative abundance of potential function in membrane transport and xenobiotics biodegradation and metabolism, which may indirectly displayed biodegradation activity of immobilized functional microorganisms. This work illustrated the survival status and potential gene function of immobilized microorganisms, and provided basis for practical application of immobilized carriers in CWW treatment.

Treatment of sugarcane vinasse in AnMBR and UASB: process performance and microbial community comparison

Vinasse is a by-product of sugarcane processing which is often used in fertigation; however, the direct use of vinasse harms the environment and reduces soil productivity due to its physicochemical properties. Anaerobic digestion (AD) offers an alternative to mitigate part of the negative effects. Anaerobic high-rate reactors, which mainly rely on sludge granulation, are mostly used in AD of vinasse wastewater. However, the composition of vinasse such as high concentration of solids and organic matter, high salinity, low pH, and high concentrations of sulfate, affect granule formation, leading to sludge washout. Anaerobic membrane bioreactors (AnMBR) present an alternative for vinasse treatment, eliminating the need for sludge granulation and producing a nutrient-rich effluent with minimal residual organics and no suspended solids. Research on sugarcane vinasse treatment using AnMBRs is limited. Most studies have employed submerged internal membrane modules, highlighting the need for further research with different reactor configurations to enhance process performance. In this study, an AnMBR equipped with an external inside-out crossflow ultrafiltration membrane was compared to an upflow anaerobic sludge blanket (UASB) reactor for the treatment of sugarcane vinasse. At a volumetric organic loading rate of up to 6 g COD. L-1.d-1, the UASB reactor reached 75% ± 7% of COD removal efficiency whereas the AnMBR generated a solids-free effluent and reached 88% ± 2% of COD removal efficiency. Microorganisms such as Clostridia, Bacteroidia, Mesotaga, Syner-01, Dehalococcoidia, Bacteroidia-DMER64, and Methanolinea were found as the most abundant. The results highlight the AnMBR potential as an effective alternative for treating sugarcane vinasse while overcoming the challenges posed by unsatisfactory sludge granulation.

Enrichment of Methanothrix species via riboflavin-loaded granular activated carbon in anaerobic digestion of high-concentration brewery wastewater amidst continuous inoculation of Methanosarcina barkeri

Effective treatment of high-concentration brewery wastewater through anaerobic digestion (AD) has always been a challenging issue. Enhancing direct interspecies electron transfer (DIET) was demonstrated to increase methane production during AD under high organic loading rate (OLR). Herein, the feasibility of enhancing DIET with the addition of riboflavin-loaded granular activated carbon (RF-GAC) as well as co-addition with Methanosarcina barkeri (Rf-GAC+M.barkeri) was investigated (M.barkeri is well-known to be capable of DIET with electroactive bacteria). During the whole process, the Rf-GAC and the Rf-GAC+M.barkeri group both achieved average COD removal rates above 97 %, which was 14 % higher than that of the control. The average methane production in the Rf-GAC group and the Rf-GAC+M.barkeri group respectively reached 0.334 ± 0.02 L(stp)/g COD and 0.345 ± 0.02 L(stp)/g COD, 1.35 and 1.39 times higher than the 0.247 ± 0.03 L(stp)/g COD reached by the control. The control reactor deteriorated at an OLR of 12 kg COD/(m3·d), whereas the Rf-GAC and the Rf-GAC+M.barkeri group maintained stable as the OLR reached as high as 17.5 kg COD/(m3·d) and the volatile fatty acids concentration was consistently below 10 mM. The RF-GAC performed better than Rf-GAC+M.barkeri in enriching Methanothrix, whose relative abundance was 60.6 % in the former group. Metabolic pathway analysis revealed the addition of RF-GAC upregulated genes related to DIET in Methanothrix species, including hdrA and fpoD. Furthermore, Methanothrix remained the dominant archaea even continuously inoculating pure strains of M.barkeri during the entire operational period. Pure culture experiments proved that GAC inhibited M.barkeri growth. The results of this study can be optimized for practical application of AD treating high-concentration brewery wastewater.

Effects of Zn(II) on the simultaneous nitrification and denitrification (SND) process: performance and microbial community

Simultaneous nitrification and denitrification (SND) is considered an attractive alternative to traditionally biological nitrogen removal technology. Knowing the effects of heavy metals on the SND process is essential for engineering. In this study, the responses of SND performance to Zn(II) exposure were investigated in a biofilm reactor. The results indicated that Zn(II) at low concentration (≤ 2 mg·L−1) had negligible effects on the removal of nitrogen and COD in the SND process compared to that without Zn(II), while the removal of ammonium and COD was strongly inhibited with an increasing in the concentration of Zn(II) at 5 or 10 mg·L−1. Large amounts of EPS, especially PN, were secreted to protect microorganisms from the increasing Zn(II) damage. High-throughput sequencing analysis indicated that Zn(II) exposure could significantly reduce the microbial diversity and change the structure of microbial community. The RDA analysis further confirmed that Azoarcus-Thauera-cluster was the dominant genus in response to low exposure of Zn(II) from 1 to 2 mg·L−1, while the genus Klebsiella and Enterobacter indicated their adaptability to the presence of elevated Zn(II). According to PICRUSt, the abundance of key genes encoding ammonia monooxygenase (EC: 1.14.99.39) was obviously reduced after exposure to Zn(II), suggesting that the influence of Zn(II) on nitrification was greater than that of denitrification, leading to a decrease in ammonium removal of SND system. This study provides a theoretical foundation for understanding the influence of Zn(II) on the SND process in a biofilm system, which should be a source of great concern.

Nanoconfined Cu clusters-activated peroxodisulfate for efficient wastewater decontamination via polymerization

In water treatment, the transition from mineralization to polymerization of organic pollutants is an essential step towards carbon and energy recovery. However, achieving efficient polymerization through the construction of heterogeneous catalysts remains a great challenge. In this work, we prepared Cu clusters nanoconfined in ZIF-derived carbon hollow structure to activate peroxodisulfate (PDS), achieving efficient wastewater decontamination via polymerization. The reaction rate is increased by a factor of 62. It shows excellent performance under different conditions (pH, anions, aqueous) as well as stability. Experiments and DFT calculations show that the removal of Bisphenol A was mainly by the direct oxidative transfer process, Cu–N and Cu clusters were involved in the catalytic oxidation. The removal of COD and TOC could reach 80% and 63.50%, respectively. This work provides technical support for the accelerated mechanism of oxidative polymerization during the treatment of toxic organic wastewater.

Enhanced Photocatalytic Degradation of Ciprofloxacin Antibiotics using Fe3O4-SiO2-EN@Zn-Al Layered Double Hydroxide Nanocomposites under the COVID-19 pandemic

A novel layered double hydroxide nanocomposite, Fe3O4-SiO2-EN@Zn-Al-LDH, was synthesized and employed as a photocatalyst for the degradation of ciprofloxacin (CIP) in aqueous solutions. Characterization of the photocatalyst was performed using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET) techniques. The results indicated successful synthesis of particle with specific surface area of 28.67 m²/g, pore size of 1.64 nm, and pore volume of 6.58 cm³/g. Optimal degradation of CIP was observed under the following conditions: pH 5, photocatalyst dosage of 0.6 g/L, initial CIP concentration of 25 mg/L, and an irradiation duration of 60 minutes. Comparative experiments demonstrated that incorporating Zn-Al LDH with core-shell nanoparticles (Fe3O4-SiO2-EN) enhanced removal efficiency by 2.5 to 6 times compared to individual materials. The composite exhibited efficient activation under UV, visible light, and solar radiation, resulting in 100% degradation of CIP under UV, 100% under visible light, and 81.4% under solar radiation. Biodegradability, indicated by the BOD5/COD ratio, increased from 0.28 to 0.73 after 120 minutes of photocatalytic oxidation under visible light, with 80.83% COD removal and 74.17% TOC removal. Reactive species generation, such as •OH, •O2-, and h+, was confirmed by introducing scavengers (TBA, BQ, and TEOS) into the reaction medium. The photocatalytic activity of the nanocomposite was slightly decreased over 5 consecutive CIP treatment cycles. Toxicity assessment of treated wastewater using E. coli and Daphnia magna bioassays revealed a significant decrease in E. coli growth inhibition rate with prolonged treatment time. The EC50 percentage improved from 1.27% to 97.4% after 4 hours of CIP treatment under visible light. In conclusion, the development of the Fe3O4-SiO2-EN@Zn-Al-LDH presents a noteworthy advancement in photocatalysis for the degradation of CIP in aqueous solutions.

Optimal carbofuran degradation via CWPO in NOM-doped water by a framework Cu-doped aluminate perovskite catalyst derived from aluminum saline slags

This study is the first to propose the synthesis of LayAl1–xCuxO3–δ perovskite catalysts using Al recovered from acid leaching of saline slags. The effect of parameters such as the La/Al molar ratio was explored during the synthetic process. A suite of characterization techniques—including XRF, XRD, N2 adsorption, H2-TPR, FTIR, TGA-DTA, TEM, SEM, EDX, and XPS—confirmed the successful synthesis of high-purity (up to 90 %) perovskites with La and O vacancies, and a high concentration of Cu(I) active sites dispersed within the perovskite lattice. The best catalyst was used to optimize the degradation of carbofuran (CBF) in water doped with synthetic dissolved natural organic matter (NOM) using the Fenton-like catalytic wet peroxide oxidation (CWPO) approach. The effects of catalyst concentration, H2O2 dose, and pH on catalytic performance were investigated. Degradation, mineralization (COD removal), and H2O2 consumption were maximized, while Cu leaching was minimized using a statistical desirability function for multiple responses. Optimal conditions were found to be a catalyst concentration (mg Cu/mg H2O2) of 0.234 (2.0 g L–1), an H2O2 dose of 73.3 % (0.73 times the stoichiometric dose for full COD mineralization), and a remarkable circumneutral pH of 6.2. Under these conditions, degradation reached 94.1 %, and COD mineralization was 51 % under room temperature. Notably, the perovskite catalyst exhibited remarkable stability during reuse in up to three cycles, as demonstrated by the low Cu leaching (<1.30 mg L–1).

Effect of substrate concentration on sulfamethoxazole wastewater treatment by osmotic microbial fuel cell: Insight into operational efficiency, dynamic changes of membrane fouling and microbial response.

To solve the problems of antibiotic pollution, water resources and energy shortage, an osmotic microbial fuel cell (OsMFC) was adopted innovatively to treat antibiotic wastewater containing sulfamethoxazole (SMX), and achieved SMX removal, water production and electricity generation. Substrate concentration was a key factor affecting the performances of OsMFC, which was often ignored by researchers. This study explored the effect of substrate concentration on system performances, clarified the dynamic changes of membrane fouling under different substrate concentrations, and further revealed the response of microbial communities. The results showed that the stable removal efficiency of SMX exceeded 98.8 % due to the efficient interception of forward osmosis (FO) membrane. Compared with the 1.0 g/L NaAc system, the SMX degradation efficiency and maximum output voltage in the 2.0 g/L NaAc system were only increased by 3.9 % and 6.3 %, respectively. However, the initial water flux decreased by 30.1 % in the 7th cycle due to more serious FO membrane fouling. In addition, there were significant differences in the dynamic formation process of FO membrane fouling. Higher substrate concentration increased the relative abundance of Desulfobacterota and Geobacter. Functional prediction analysis showed that increasing substrate concentration promoted carbohydrate metabolism pathways and relative abundance of sulfur respiration functional groups, thereby improving COD and SMX removal rates. However, the biosynthesis of other secondary metabolites was significantly improved, resulting in increased contents of EPS and SMP, which aggravated membrane pollution. Overall, the system performed better when the substrate concentration was 1.0 g/L. This study would provide certain guidance for the performance optimization and membrane fouling mitigation of OsMFC, thereby promoting its practical application in antibiotic wastewater treatment.

Intensification of flocculation efficiency in multi-stage reactors by optimizing the multi-cone segment configuration

Flocculation is widely used in water treatment, and creating an optimal environment for floc growth is essential to enhancing flocculation efficiency. In this paper, we developed a multi-stage flocculation reactor (MFR) with strong, moderate, and weak mixing zones. Specifically, multi-cone structures with varying diameter ratios (DR) were incorporated in the moderate zone to promote floc growth. Computational simulations revealed that an MFR with a DR of 0.5 generated a uniform and symmetric flow field, reducing zero-velocity zones and forming distinct vortices within cones. This environment facilitated gradual floc growth while minimizing breakage. When applied to treating fracturing flowback fluid, a complex and challenging wastewater, the MFR produced larger and denser flocs, with an average chord length of 180 μm and a fractal dimension of 1.7170. These flocs exhibited high viscoelasticity, with a strength factor of 68.22 and a recovery factor of 47.77, indicating superior shear resistance and recovery ability after breakage. Consequently, the MFR achieved COD and turbidity removal rates of 92.05% and 93.61%, respectively, outperforming a stirred flocculation reactor, which achieved rates of 72.29% and 83.53% for the same parameters. Additionally, the MFR demonstrated excellent pollutant removal efficiency for both mineral processing wastewater and dyeing wastewater. With gradually decreasing energy along the flow direction, the MFR provided appropriate mixing intensities for different stages of floc growth, promoting efficient formation. These findings underscore the MFR’s potential as a highly effective solution for wastewater treatment applications.

Valorization of paper-mill sludge laden with 2-chlorotoluene using hydroxyapatite@biochar nanocomposite to enrich methanogenic community: A techno-economic approach

While several studies have investigated the anaerobic digestion of paper-mill sludge (PMS), this technology suffers from nutrient insufficiency, inhibition by aromatic compounds, and low bio-CH4 yield. Hence, PMS was anaerobically co-digested with chicken manure (CM) and supplemented by hydroxyapatite@biochar (HAP@BC) nanocomposite for enhancing 2-chlorotoluene degradation and enriching the methanogenic archaea. Multiple continuous stirred tank reactors (CSTRs) were operated at 12.6 h hydraulic retention time (HRT), using PMS (R1), CM (R2), PMS + CM (R3), PMS + CM+100 mg HAP/L (R4), and PMS + CM+100 mg HAP@BC/L (R5). The maximum bio-CH4 yield of 147.5 ± 9.1 mL/g COD and 2-chlorotoluene removal of 91.2 ± 6.8 % were obtained from R5, experiencing a sufficient C/N ratio of 14.7 and the highest activities of acidogenesis (42.0 %), acetogenesis (37.9 %), and methanogenesis (42.1 %). The abundances of Euryarchaeota, Bacteroidota, and Chloroflexi at the phylum level, and Pseudomonas, and Bacillus at the genus level could highly contribute to the dechlorination mechanism and acetate transformation into CH4. This biomass-to-bioenergy project (10 m3/d capacity) could benefit from pollution reduction, biogas recovery, and carbon credit, giving 5.6 yr payback-period, 3503 USD net present value, and 12.1 % internal rate of return. Because R5 exhibited an efficient techno-economic anaerobic biodegradation performance, future studies are required to optimize its HRT condition and HAP@BC dosage.

Thermophilic and mesophilic anaerobic digestion of soybean molasses: A performance vs. stability trade-off

One of the factors that has a direct impact on anaerobic digestion is the applied organic loading rate (OLRA). Increasing OLRA can boost methane production but can also cause process failure. As a result, establishing the appropriate OLRA for the procedure is critical. This study evaluated the effect of increasing the OLRA using soybean molasses in a thermophilic anaerobic reactor (R-Thermo), as well as the effect of feeding strategy and co-processing with okara. Furthermore, the performance versus stability trade-off between R-Thermo and mesophilic anaerobic digestion (R-Meso) was investigated. The increase of OLRA from 10 to 15 and 20 kg-COD/m³/d led to a decrease in COD removal efficiency (90, 86, and 75%), methane yield (12.0, 11.6, and 9.9 mol-CH4/kg-COD) and an increase in total volatile acids concentration (251, 456, and 1393 mg-HAc/L, respectively). At 15 kg-COD/m³/d, R-Meso performed similarly to R-Thermo, and at 20 kg-COD/m3/d, R-Meso outperformed (81% COD removal efficiency, 9.3 mol-CH4/kg-CODrem and 154.5 mol-CH4/m3/d). Temperature greatly influenced the distribution of metabolic pathways, as shown by thermodynamic and kinetic analyses, thus impacting bacterial diversity. At 55 °C, amongst the bacterial genera, Tepidiphilus stood out (>28.2%), followed by Acetomicrobium, Coprothermobacter and Candidatus_Caldatribacterium. The OLRA clearly impacted the archaeal community; Methanothermobacter (77.4%) was favored over Methanosarcina (14.8%). Under thermophilic temperature, it seems that syntrophic acetate oxidation (SAO) bacteria might have competed for substrate with acetoclastic methanogens, while in R-Meso microorganisms responsible for the initial steps of organic matter breakdown, such as members of the Firmicutes and Proteobacteria phyla (at least 67%), were dominant. In summary, R-Meso, characterized by a more uniform distribution of metabolic pathways, as well as a diverse and well-adapted microbial consortium, have exhibited enhanced stability and outperformed R-Thermo at high-loads.