COD Removal Rate Research Articles

Study on the electrochemical oxidation mechanism of sulfamethoxazole using three-dimensional boron-doped diamond

In this study, we prepared a novel three-dimensional boron-doped diamond (BDD) electrode. Subsequently, we systematically conducted an electrochemical oxidation reaction on sulfamethoxazole (SMX) using a BDD anode and a platinum plate (Pt) cathode. The effects of initial concentration, current density, initial pH, and carrier electrolyte on SMX degradation were investigated. The SMX was completely removed after 4 h of electrolysis at a current density of 30 mA/cm2, 0.1 mol sodium sulphate as the supporting electrolyte, and a pH of 7. Additionally, the COD removal rate was 65.6 %, while the energy consumption was 40.1 %. Compared with two-dimensional BDD electrode degradation, the energy saving was 54 %. Density functional theory (DFT) and high-performance liquid chromatography (HPLC) were used to analyse the SMX degradation mechanism. Three possible degradation pathways were proposed: ·OH substitution of the amino group in the aromatic ring, oxidation of the amino group to nitrogen dioxide, and addition of ·OH to the isoxazole ring. The active sites detected in the reaction corresponded closely with the calculated results using DFT. Moreover, ECOSAR toxicity analysis was applied to evaluate the toxicity of the intermediates produced during electrolysis. We discovered that the toxicity of SMX and its intermediates decreased significantly during electrolysis.

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.

Mathematical model of dissolved microbial products in sewage treatment system

Water is the source of life, but all kinds of water resources in the world are suffering from different degrees of pollution. Water pollution leads to a serious shortage of available fresh water resources, and sewage treatment is the main way to solve water pollution. For the sewage after biological treatment of activated sludge, the organic matter contained in the effluent is mainly the dissolved microbial products (SMPs) produced in the process of microbial metabolism. The composition of SMPs is complex, mainly including macromolecular substances such as protein, polysaccharide, humic acid and DNA and cell fragments. The mathematical model of activated sludge is a quantitative description of the mathematical relationship between substrate degradation parameters and microbial growth. Starting from the Monod equation representing the relationship between substrate consumption and microbial growth, it combines the reactor theory and microbiology theory in the chemical field. Based on the principle of conservation of materials and Monod equation, the mathematical expression of organic degradation model was determined according to the collected data and empirical values of parameters. The general idea of activated sludge model No.1 (ASM1) for activated sludge process simulation was introduced, and the influence of sludge concentration on SBR process water treatment was explored. It was found that the removal rate of COD, ammonia nitrogen, total nitrogen and total phosphorus increases with the increase of sludge concentration. When C/N=8, the removal rate of ammonia nitrogen increased from 62% to 81%, and the removal rate of total nitrogen increased from 64% to 82%, with the most obvious effect.

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.

Magnesium Bicarbonate-Walnut Shell Dual-Template Synthesis of Multifunctional Layered Porous Carbon for Enhanced Adsorption of Aqueous Chlorinated Organic Compounds.

Chloride ions readily react with organic matter and other ions, resulting in the formation of disinfection by-products (DBPs) that exhibit heightened levels of toxicity, carcinogenicity, and mutagenicity. This study creatively employed waste walnut shells as self-templates and low-cost magnesium bicarbonate as a rigid template to successfully synthesize multifunctional porous carbon derived from walnut shells. Employing a series of characterization techniques, it was ascertained that the porous carbon material (WSC/Mg) synthesized via the dual-template method exhibited a distinct layered microscopic surface structure, with a predominance of C and O elements on the surface. The material displayed a high degree of graphitization, significant specific surface area, and abundant oxygen-containing surface functional groups. The incorporation of magnesium bicarbonate as a hard template improved the structure of the walnut shell porous carbon, resulting in a significant enhancement in mass transfer efficiency for the target product on the adsorbent and a substantial improvement in removal efficiency. In comparison with walnut shell-derived carbon using only self-templating, WSC/Mg exhibited a 17.26-fold increase in adsorption capacity for 2,4-dichlorophenol. Furthermore, even after four adsorption-desorption cycles, WSC/Mg-12 maintained an adsorption efficiency above 90%. It is remarkable that WSC/Mg-12 demonstrated exceptional resistance to interference from natural organic matter and pH variations. Moreover, the adsorbed saturated WSC/Mg-12 effectively treated real coke wastewater, resulting in an 80% color removal rate, 20% COD removal rate, and 15% ammonia nitrogen removal rate. In conclusion, this study presents an innovative approach for cost-effective and versatile porous carbon materials with extensive applications in water environment purification and biomass utilization.

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.

Characteristics of Nitrogen Removal from an Integrated Fixed-Film Activated Sludge (IFAS) System and the Relationship Between Activated Sludge and Biofilm Interactions

In order to investigate the enhancement mechanism of modified three-dimensional elastic filler (MTEF) on the nitrogen removal performance of the integrated fixed-film activated sludge (IFAS) process, and to clarify the interactions between competition and synergy between activated sludge and biofilm in the IFAS system, an IFAS reactor (T2) filled with MTEF was employed for the study, while a sequencing batch reactor activated sludge process (SBR) reactor (T1) was utilized for comparison. IFAS and SBR reactors were operated over an extended period at ambient temperature to assess the enhancement of pollutant removal performance with the addition of the filler to investigate the competitive dynamics between activated sludge and biofilm under varying influent water qualities (C/N, N/P, and organic loading), and to analyze the synergistic relationship between activated sludge and biofilm at the microbial level using high-throughput sequencing technology. The results demonstrate that throughout the entire operational phase, reactor T2 exhibited superior pollutant removal efficiency. Compared to reactor T1, reactor T2 achieved an average increase in the removal rates of COD, ammonia nitrogen, and total nitrogen by 13.07%, 12.26%, and 28.96%, respectively. The findings on the competitive dynamics between activated sludge and biofilm indicate that the nitrification volumetric load of the IFAS system is significantly higher than that of a pure activated sludge system, suggesting that the IFAS system possesses enhanced nitrification capabilities. Furthermore, when dealing with wastewater characterized by low C/N ratios and high phosphorus pollution, or under substantial organic loads, the biofilm holds a competitive edge and the IFAS system exhibits improved stability. High-throughput sequencing data reveal that the microbial community structures in activated sludge and biofilm can influence each other, thereby enabling the IFAS system to effectively enrich denitrification-related functional microbial populations. Additionally, the biofilm has a certain enhancing effect on the expression levels of nitrogen metabolism-related functional genes in the activated sludge phase microorganisms, indicating that, in addition to competitive interactions, there is also a synergistic effect between the biofilm and activated sludge.

Electrochemical removal of ethylene glycol monobutyl ether in aviation industry wastewater using a porous Ti4O7/Ti electrode

Titanium alloy chemical milling wastewater contains a significant amount of ethylene glycol monobutyl ether (EGBE), which is toxic and difficult to be degraded by microorganisms, and the emission will lead to severe environmental pollution. To solve this problem, the electrocatalytic oxidation method was employed to remove EGBE in the wastewater, in which a porous Ti4O7/Ti electrode were prepared and employed as the anode, while stainless steel acted as the cathode. The effects of current density, interelectrode distance, and stirring mode on the COD removal rate were also investigated. Results show that the COD of the wastewater significantly decreases from 12410 to 15 mg L−1 after 16 h of electrolysis at 10 mA cm−2 and electrode spacing of 1.0 cm as well as aeration stirring at 100 mL min−1. Moreover, pilot-plant scale testing reveals that the COD decreasing from 11980 to 183 mg L−1 after 24 h of electrolysis. Consequently, the utilization of porous Ti4O7/Ti electrode as anode in the electrocatalytic oxidation method presents significant potential in removal of EGBE in aviation industry wastewater.

Electrical stimulation improves the efficiency of treating typical reclaimed water in biofilters

ABSTRACT To conduct advanced treatment on reclaimed water with a low C/N ratio and a low content of biodegradable organic matter, this paper established an biofilter-microbial electrolysis cell (BF-MEC). Through two-stage influent, the influence of electrical stimulation and electrochemical structure on the nitrogen and carbon removal of the system was explored, and the following results were obtained. The optimal externally applied voltage for the BF-MEC system is 0.55 V. The optimal structure of the BF-MEC system is an electrode spacing of 100 mm, and the optimal electrode position is when the electrode is located at the bottom of the system. Compared with the BF system, in the first stage, the removal rates of chemical oxygen demand, total ammonia nitrogen (TAN), and total nitrogen (TN) in the optimal structure BF-MEC system are increased by 13.4, 118.1, and 273.65%, respectively. In the second stage, COD, TAN, and TN removal rates are increased by up to 277.98, 115, and 722.98%, respectively. The optimal electrode position is when the electrode is located at the lower part of the system. At this time, the microbial community is more abundant, the microbial activity and lifespan are longer, and the system efficiency is optimal.

Extended photoperiods enhance the production and water treatment performance of algal-bacterial bioflocs from aquaculture wastewater

Reducing pollution and converting wastewater nutrients into useful biomass are major challenges of intensive aquaculture. We investigated the nitrogen and phosphorus metabolism, nutrient composition, and microbial community of algal-bacterial bioflocs (ABBs) produced under glucose addition and different photoperiods. This biomass was used for aquaculture wastewater treatment for 18 days. ABBs produced under longer photoperiods were smaller and more numerous, which facilitated nitrogen recovery and reduced nitrogen loss. Additionally, nitrogen and phosphorus-metabolizing enzyme activities, as well as the activity of overall microorganisms were positively correlated with the light duration. The removal rates of COD (96.89 %), DTN (93.57 %), and DTP (93.67 %) from wastewater by ABBs were highest when the photoperiod was 16L:8D during the production period. Moreover, the crude protein content (41.77 ± 0.11 %) was highest under a photoperiod of 12L:12D, and the rich amino acid and fatty acid profile of the ABB under this photoperiod enhanced its utility as a feed additive for aquaculture species. The high-throughput sequencing analysis revealed a high abundance of Hydrogenophaga at the genus level, highlighting its denitrification capacity of ABBs under the 16L:8D photoperiod. Redundancy analysis (RDA) demonstrated that photoperiod, as a key driver in the formation of microbial communities in ABBs, exerted a direct influence on water treatment efficiency and nutrient accumulation. This study provides new insights into the effects of photoperiod on the properties of ABBs, which has implications for the treatment and subsequent application of aquaculture wastewater.

Nutrient removal efficacy and microbial dynamics in constructed wetlands using Fe(III)-mineral substrates for low carbon-nitrogen ratio sewage treatment.

This study evaluated the roles of two common sources of Fe(III)-minerals-volcanic rock (VR) and synthetic banded iron formations from waste iron tailings (BIF-W)-in vertical flow-constructed wetlands (VFCWs). The evaluation was conducted in the absence of critical environmental factors, including Fe(II), Fe(III), and soil organic matter (SOM), using metagenomic analysis and integrated correlation networks to predict nitrogen removal pathways. Our findings revealed that Fe(III)-minerals enhanced metabolic activities and cellular processes related to carbohydrate decomposition, thereby increasing the average COD removal rates by 10.7% for VR and 5.90% for BIF-W. Notably, VR improved nitrogen removal by 1.70% and 5.40% compared to BIF-W and the control, respectively. Fe(III)-mineral amendment in bioreactors also improved the retention of denitrification and nitrification bacteria (phylum Proteobacteria) and anammox bacteria (phylum Planctomycetes), with increases of 3.60% and 3.20% using VR compared to BIF-W. Metagenomic functional predictionindicated that the nitrogen removal mechanisms in VFCWs with low C/N ratios involve simultaneous partial nitrification, ANAMMOX, and denitrification (SNAD). Network-based analyses and correlation pathways further suggest that the advantages of Fe(III)-minerals are manifested in the enhancement of denitrification microorganisms. Microbial communities may be activated by the functional dissolution of Fe(III)-minerals, which improves the stability of SOM or the conversion of Fe(III)/Fe(II). This study provides new insights into the functional roles of Fe(III)-minerals in VFCWs at the microbial community level, and provides a foundation for developing Fe-based SNAD enhancement technologies.

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.

Development of a horizontal seepage test system of constructed wetland and research on the seepage characteristics based on micro-pollution water

Horizontal subsurface flow constructed wetlands (HSFCW) were widely used as an effective biotechnology for wastewater treatment. However, clogging of the substrate bed was a key factor restricting its application. In this study, a horizontal seepage test system was independently developed, which was used to reveal the development trends of hydraulic resistance in HSFCW, as well as changes in permeability coefficients with time. The relationship between the average permeability coefficient and purification effect was further analyzed. The results showed that the new test system has proved the law of resistance development in HSFCW. The distribution characteristics of the isobaric surface indicate that the blockage of the HSFCW gradually spreads from the lower part to the lower part. The seepage resistance of homogeneous subbed in HSFCW was mainly concentrated in the front end. The growth rate of hydraulic loss in the core zone ranged from 0.685 to 19.515 cm·month−1, the growth rate in the transition zone ranged from 0.223 to 0.695 cm·month−1, and little change occurred in the safety zone. At the end of the HSFCW operation, the widths of the core, transition, and safety zones account for approximately 20–30 %, 50–70 %, and 10–20 % of the entire wetland length, respectively. Meanwhile, the SS removal rate stabilized at over 92 %, when the average permeability coefficient reached 41.45 m·d−1. The removal rate of COD and TN was higher when the average permeability coefficient is between 59.45 and 41.45 m·d−1 and 27.08–59.45 m·d−1, respectively. This study provided a horizontal testing method to accurately understand the changes in the seepage field in HSFCW.

Innovative Treatment of Urban Wastewater by Flocculation Combined with Ozone Pre-Oxidation and Denitrification

In this study, urban wastewater was treated by flocculation, ozone pre-oxidation and denitrification for efficient purification. Polymeric aluminum chloride (PAC) and polymeric aluminum ferric sulfate (PAFS) were added to the wastewater at different levels to remove the COD, turbidity, TP and TN of the wastewater. A better flocculant was selected and its optimum ozone pre-oxidation concentration was determined by changing the ozone concentration and measuring the effluent quality. Denitrification was further enhanced by varying the C/N ratio of the wastewater. The results show that, with the increase in flocculant dosage, the removal rates of COD, turbidity, TP and TN by PAC and PAFS were improved. The purification effect of PAC was better than that of PAFS and the optimum removal of COD, turbidity, TP and TN was obtained at a dosage of 80 mg L−1 by PAC, at 55.9%, 55.6%, 90.0% and 13.3%, respectively. Ozone pre-oxidation enhanced the removal of COD, turbidity and TN by PAC, and the optimal ozone dosage was 1.2 mg L−1, which resulted in 64.8%, 57.1% and 24.8% removal of COD, turbidity and TN, respectively. With the increase in the C/N ratio from 2.0 to 4.0, the NO3−-N concentration of PAC-treated water gradually decreased, but when the C/N ratio was 4.0, the COD concentration increased, so the optimal C/N ratio should be 3.5. Overall, the combination of ozone pre-oxidation, denitrification and flocculation was an effective method to treat urban wastewater, which has a strong application prospect.

Nitrogen reducing mechanism by microporous aeration based on microbial population characteristics: water temperature factor

ABSTRACT The formation of black odour water is primarily attributed to the elevated concentration of organic pollutants, along with an excessive amount of nitrogen and phosphorus, ultimately leading to an anoxic aquatic environment. The water temperature influence mechanism on black-odorous water restoration by microporous aeration is still lacking depth study. This paper selected (15–18) ℃ (spring and autumn), (22–25) ℃ (summer), (8–11) ℃ (winter) as temperature conditions, and investigated temperature influence on nitrogen reduction. Researches showed that: (1) The removal rates of COD, NH4 +-N and TN were significantly positively correlated with temperature (r = 0.99, 0.96, 0.97), the lowest removal rates were 83.16%, 95.68%, 58.7% ((8–11) ℃), the highest values were 92.67%, 98.27%, 70.96% ((22–25) ℃), respectively. (2) At a temperature range of 22–25°C, the microbial community exhibited the highest levels of abundance, diversity, and uniformity. Notably, Proteobacteria dominated this temperature range with a relative abundance of 79.72%. Furthermore, temperature positively correlated with the majority of dominant bacterial species, suggesting that conditions at 22–25°C are highly conducive to the growth of most bacterial communities. Among these, Limnohabitans, Alsobacter, and Candidatus_Aquirestis, which possess key functions in denitrification and nitrogen removal, displayed significantly higher abundances. It explains the positive correlation between temperature and removal rates of COD, TN and NH4 +-N from microbial population’s perspective. Thus, the best temperature for repairing black-smelly water is (22–25) ℃. This study provides technical reference for mechanism research and practical application of microporous aeration.

Increased oxygen partial pressure enhances toxicity reduction by membrane aerated biofilm reactor treating oil and gas industrial wastewater

Wastewater produced during oil and gas extraction processes is one of the largest residual water streams. Also known as produced water (PW), it has a complex composition and is typically toxic to aquatic ecosystems. This study explores the use of membrane aerated biofilm reactors (MABR) for biological removal of dissolved organic compounds and associated toxicity. Three different oxygen partial pressures (0.2, 0.6 and 1 bar), the last two mimicking subsea pressures at 20 and 40 m below the sea level, respectively, were tested at three different hydraulic retention times (HRT of 24, 12 and 6 h). Reactors were fed both with onshore and offshore PW. Removal rates for organic carbon increased at decreasing HRT. Highest oxygen partial pressure led to best performance at 6 h HRT (30.1 ± 3.0 g-COD m−2 d−1) when treating onshore PW and at all HRT when treating offshore PW, with highest COD removal rate still at 6 h HRT (9.4 ± 1 g-COD m−2 d−1). Removal efficiencies ranged from 78 % when treating onshore PW at 24 h HRT to 36–49 % when treating offshore PW at 6 h HRT. All treatments led to a reduction in toxicity (>92 % reduction for offshore PW), with 0.2 bar oxygen partial pressure showing worst performance, while 0.6 and 1 bar did not show significant differences. The biofilms were dominated by hydrocarbonoclastic, responsible of hydrocarbons biodegradation, and sulfur cycling bacteria. Overall, MABR were effective treating PW and operating at higher oxygen partial pressures yield to better performance, especially at high volumetric loading rates.

Catalytic Ozonation Treatment of Coal Chemical Reverse Osmosis Concentrate: Water Quality Analysis, Parameter Optimization, and Catalyst Deactivation Investigation.

Catalytic ozone oxidation, which is characterized by strong oxidizing properties and environmental friendliness, has been widely used in organic wastewater treatments. However, problems such as a low organic pollutant removal efficiency and unstable operation during the catalytic ozone treatment process for wastewater remain. To address these disadvantages, in this study, the treatment efficacy of catalytic ozone oxidation on a coal chemical reverse osmosis concentrate was investigated. The basic water quality indicators of the chemical reverse osmosis concentrate were analyzed. The effects of initial pollutant concentration, pH, ozone concentration, and catalyst concentration on the COD removal rate from the coal chemical reverse osmosis concentrate were explored. Water quality indicators of the chemical reverse osmosis concentrate before and after the catalytic ozone treatment were studied using spectroscopic analysis methods. The RO concentrate demonstrated large water quality fluctuations, and the catalytic ozonation process removed most of the pollutants from the treated wastewater. A possible deactivation mechanism of the ozone catalyst was also proposed. This study provides a theoretical reference and technical support for the long-term, efficient, and stable removal of organic pollutants from coal chemical reverse osmosis concentrate using a catalytic ozone oxidation process in practical engineering applications.

Enhanced performance of coal-based adsorbents in removing phenols from highly concentrated coking wastewater: Targeting large-scale applications

Coking wastewater threatens the ecology and environment significantly, but it still has challenges in the efficient removal of organic contaminants due to its complex composition and inadequate biochemical properties. Low-cost coal-based material has potential in treating coking wastewater due to its special structure and surface oxygenic functional groups. In this work, gangue-based materials were modified in different ways and applied to coking wastewater treatment. Combined with the comprehensive analysis of the adsorbents' morphology, structure, and composition with SEM, XRD, FT-IR, XPS, etc., the adsorption behaviors and regeneration properties were extensively investigated. Notably the adsorption and regeneration capacity of the adsorbents are significantly enhanced after modification, BY-C2 exhibits a remarkable COD removal rate of 90.2 % from real coking wastewater, which remains stable at 72.0 % even after 10 cycles. The pseudo-second-order kinetic model and Freundlich isotherm model are found to fit well with the adsorption processes of phenolic compounds in coking wastewater. The adsorption mechanism involves hydrogen bonding, van der Waals' force, capillary forces and electrostatic attraction. This work paves the way for the large-scaled application of coal-based adsorbents in coking wastewater treatment and the subsequent recycling of high-valued organic pollutants.

Leaching behavior of microplastics during sludge mechanical dewatering and its effect on activated sludge

Dewatering is an indispensable link in sludge treatment, but its effect on the microplastics (MPs) remains inadequately understood. This study investigated the physicochemical changes and leaching behavior of MPs during the mechanical dewatering of sludge, as well as the impact of MP leachates on activated sludge (AS). After sludge dewatering, MPs exhibit rougher surfaces, decreased sizes and altered functional groups due to the addition of dewatering agents and the application of mechanical force. Meanwhile, plastic additives, depolymerization products, and derivatives of their interactions are leached from MPs during sludge dewatering process. The concentration of MP-based leachates in sludge is 2–25 times higher than that in water. The enhancement of pH and ionic strength caused by dewatering agents induces the release of MP leachates enriched with protein-like, fulvic acid-like, and soluble microbial by-product-like substances. The reflux of MP leachates in sludge dewatering liquor to the wastewater treatment system negatively impacts AS, leading to a decrease in COD removal rate and inhibition of the extracellular polymeric substances secretion. More importantly, MP leachates cause oxidative stress to microbial cells and alter the microbial community structure of AS at the phylum and genus levels. These findings confirm that MPs undergo aging and leaching during sludge dewatering process, and MP leachates may negatively affect the wastewater treatment system.

Optimized Design of Modular Constructed Wetland for Treating Rural Black–Odorous Water

In recent years, the phenomenon of black–odorous water has occurred frequently, and constructed wetlands have been widely used as an effective means of treating black–odorous water. In order to achieve the goal of low-carbon and high-efficiency long-term clean-up of black–odorous water, the modular constructed wetland system was optimized in this study. The optimized modular constructed wetland consisted of aeration, denitrification, and phosphorus removal, of which the denitrification module was a sulfur–iron autotrophic denitrification unit and the phosphorus removal module was a polyaluminum chloride composite filler phosphorus-removal unit. Experimental findings indicated that modular systems with layout ratios of 1:3:1 (A) and 1:2:2 (B) exhibit outstanding performance in remediating contaminants from black–odorous water. Notably, system B demonstrated superior treatment efficiency. Under conditions of high pollution loading, system B consistently achieved stable removal rates for COD (95.79%), TN (91.74%), NH4+-N (95.17%), and TP (82.21%). The combination of along-track changes and high-throughput sequencing results showed that the synergies among the units did not produce negative effects during the purification process, and each unit realized its predefined function. Changes in the substrate and internal environment of the wetland units caused changes in the microbial populations, and the unique microbial community structure of the units ensured that they were effective in removing different pollutants.