Discharge Of Untreated Wastewater Research Articles

CeO2 NANOTANECİKLERİNİN SENTEZİ, KARAKTERİZASYONU VE FOTOKATALİTİK AKTİVİTESİ

The discharge of untreated wastewater from unplanned industrial activities using dyes can cause serious environmental pollution and affect the aquatic environment. Semiconductor photocatalysis is a favorable technology widely used for degrading organic dyes in wastewater. This study dealt with the preparation of CeO2 nanoparticles via a simple precipitation technique. Information on the structural and morphological features of the developed CeO2 nanoparticles were determined using Fourier transform infrared with attenuated total reflectance (FTIR-ATR), Raman spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM) spectroscopic methods. The presence of the characteristic bands of CeO2 in the FTIR spectrum provided evidence of successful CeO2 formation. The calculated crystallite particle size utilizing the Scherrer equation was 10 nm. SEM images revealed that the morphology of CeO2 consisted of almost spherical particles with slight agglomeration. Brunauer-Emmett-Teller (BET) technique was also used to find out the specific surface area of CeO2 nanoparticles (11 m2/g). The efficiency of CeO2 nanoparticles was also confirmed in terms of their photocatalytic activity against Rhodamine B (Rh B) under UV-A light. The results indicated that CeO2 nanoparticles could be a promising catalyst candidate for industrial wastewater treatment.

Spatiotemporal distribution, source apportionment, and ecological risk of bisphenol analogues in a highly urbanized river basin

Bisphenol analogues (BPs), as one of the endocrine disruptors, have received wide attention due to their adverse impacts on ecosystems. However, the seasonal spatiotemporal distribution, source apportionment, and ecological risk of BPs in natural basins are poorly understood. Especially in highly urbanized river basins with the extensive economic development and anthropogenic activities threaten these critical but ecologically fragile regions. In this study, field investigations of BPs in the waters of the entire Qinhuai River Basin (QRB) were conducted in June (before the annual flood period) and August (after the annual flood period) 2023. The Qinhuai River, an important primary tributary of the lower Yangtze River, is located in eastern China and the QRB is characterized by a high population density and dense urbanization. Thirty-two sites were sampled for six types of BPs known to be ubiquitous in the surface water of the QRB. Significant differences in the concentrations of those BPs were found. Specifically, the concentration of total BPs (ΣBPs) was significantly higher before than after the flood period: 20.3–472 ng/L (mean = 146 ng/L) and 14.1–105 ng/L (mean = 35.9 ng/L), respectively. BPA was the main contributor to ΣBPs before the flood, and BPB followed by BPA after the flood. ΣBP concentrations were 12–241 % higher downstream than upstream of wastewater treatment plants (WWTPs). The results of a principal component analysis followed by multiple linear regression (PCA-MLR) suggested that untreated wastewater discharge from the WWTPs is an important source of BPs in the basin, with urban rainfall runoff as another potential source after the flood period. An assessment of the ecological risk of BPs, based on a calculation of the risk quotient, showed that BPA and BPS should be given due attention, and overall ecological risk of BPs pose a low risk to local algae but high and medium risks to invertebrates and fish, respectively.

Construction of wetlands in La Piedad Lagoon: a strategy to mitigate climate change in Mexico

ABSTRACT The freshwater systems located within the Metropolitan Area of Mexico City (Mexico City and the State of Mexico) are depleted. La Piedad Lagoon is recognized as a critical water resource as it serves as a run-off reservoir during the rainy season. However, the Lagoon is highly contaminated by untreated wastewater discharge due to disorderly and unplanned urban development. Inadequate sanitation has caused significant biodiversity loss and negatively impacted the population's health. Climate change models estimate that surface water availability could be reduced by over 30% in the short term, increasing the risk of a regional water crisis. This complex situation is urgent and demands the ecological restoration of La Piedad Lagoon as it provides an alternative source of water for Mexico City. Here, the intervention and efforts currently performed to rescue La Piedad Lagoon are described, involving its transformation and analysis of the environmental conditions of the area, land uses and ownership, as well as available infrastructure. Finally, it examines key environmental parameters for the construction of wetlands in the Lagoon. The removal contamination capacities of Eichhornia crassipes and Lemna minor, two aquatic plants in the area, were assessed. The lessons learned from this intervention can provide valuable lessons.

Coagulation/Floculation Of Slaughter Effluent Using Moringa Oleifera Lam as A Coagulant

Objective: In view of the growing need for low-cost, easily accessible alternative wastewater treatments, this study aimed to evaluate the influence of a natural product (Moringa oleifera lam), when used as a coagulant, on the removal of turbidity and color from a pig slaughterhouse effluent. Method/design/approach: The coagulant was prepared in saline solution (NaCl - 1M) and saline solution (KCl - 1M), all the coagulant solutions were prepared at the time of the test. In order to assess the effect of the coagulant on the effluent, coagulation/flocculation tests were carried out using the Jar- test apparatus, evaluating the effects of dosages of 200, 500, 1000, 1500 and 2000 mg/L of Moringa in saline solution (NaCl and KCl). The parameters analyzed were color and turbidity. Results and conclusion: According to the results of the statistical analysis, the optimum dosages obtained for the coagulants Moringa NaCl and Moringa KCl were 1000 and 1500 mg/L, respectively. With these dosages, removal of 63.9% for turbidity and 56.3% for color was observed when using NaCl saline solution and removal of 57.4% for turbidity and 45.2% for color when using the coagulant in KCl saline solution. Implications of the research: The main implication of the study is a proposal to evaluate the efficiency of the coagulation/flocculation/decantation process of pig slaughterhouse effluent, using natural coagulants, in the removal of organic matter. Due to the many problems caused by the use of chemical coagulants, such as aluminum sulfate and aluminum polychloride, which are used worldwide, there is a great demand for an alternative coagulant that is mainly natural. Originality/value: The study seeks to contribute to improving the management of water resources, in terms of local management. The use of natural coagulants, produced locally and at a low cost, can alleviate the problems linked to the discharge of untreated wastewater into receiving water bodies and the consumption of non-potable water.

Understanding phosphorus fractions and influential factors on urban road deposited sediments

Phosphorus (P) is a primary pollutant that builds-up on urban road surfaces. Understanding the fraction and load characteristics of P, as well as their relationship with urban factors, is helpful for assessing the ecological risk of urban receiving water bodies. This study presents the characteristics of build-up loads of P fractions in road-deposited sediments (RDS) in Guangzhou, China, analyzes their correlation with three urban factors (road, traffic, and land-use area), and then estimates the exceedance probability of P in stormwater runoff over the past 10 years. The results showed that detrital apatite phosphorus (De-P) performed the highest build-up load on urban road surfaces, followed by apatite phosphorus (Ca-P), iron-bound phosphorus (Fe-P), exchangeable phosphorus (Ex-P), aluminum-bound phosphorus (Al-P), organophosphorus (POP), dissolved inorganic phosphorus (DIP), occluded phosphorus (Oc-P), and dissolved organic phosphorus (DOP). Depression depth, road materials, and land-use fractions affected the P fractions. The P in the RDS may have originated from three distinct sources: road background, domestic waste, and untreated wastewater discharge. In the most recent 10 years, the event mean concentrations of total P in the RDS have had a 30 % probability of exceeding 0.4 mg L−1, which indicates a serious threat of P to receiving water bodies. The outcomes of this study are expected to provide valuable guidance for elucidating the principal categories of urban non-point source P pollution and enhancing the ecological health of urban water environments.

Impact of abattoirs and local textile (Adire and Kampala) effluents on Yemoja River in Abeokuta, Nigeria.

Discharge of untreated wastewater into water bodies pollutes the receiving waters. This study assessed the impact of abattoir and Kampala designers' effluent discharge on the water quality of the Yemoja River in Abeokuta, Nigeria. Twenty-seven water samples collected at three points, covering 180 m length, for 6 months were assessed for physicochemical parameters and metals and compared with the World Health Organization (WHO) and Standard Organization of Nigeria (SON) permissible standards. Most discharge point levels were found to be higher than their corresponding upstream and downstream values. Temperature, turbidity, magnesium, alkalinity, DO, TSS, phosphate, lead, BOD and potassium were found to be higher than normal levels for river water as prescribed by the WHO and SON while parameters like TDS, TS, calcium, chloride, nitrate, sulphate, iron and COD were lower than the standards. The total coliform values were higher than both national and international permissible limits, indicating contamination by human sewage or animal droppings. The water quality index indicated polluted water that is unfit for consumption. Findings from this research indicate that butchering and tie-and-dye activities have impacted river Yemoja water quality. Therefore, wastewater from the abattoir and textile industries be treated before discharge into water bodies.

Addressing Marine Pollution in the Context of the UN Ocean Decade

The United Nations Decade of Ocean Science for Sustainable Development (2021-2030), known as the “Ocean Decade”, represents a significant global initiative aimed at mobilising ocean science to foster sustainable development. One of the key challenges highlighted by this initiative is marine pollution, which poses severe threats to ocean ecosystems, biodiversity, and human livelihoods. Marine pollution has escalated over the past decades, primarily driven by anthropogenic activities, including plastic waste, chemical runoff, oil spills, and untreated wastewater discharges. Addressing these challenges requires not only robust scientific research but also coordinated international efforts to implement practical and long-term solutions.

Evaluation of the physicochemical and bacteriological quality of groundwater in the Nihit rural commune of the Moroccan Anti-Atlas

Our study evaluated the physico-chemical and bacteriological quality of water wells and boreholes in the rural commune of Nihit in the Moroccan Anti Atlas. In this study, we assessed the physico-chemical qualities of the water such as pH, temperature, conductivity, turbidity, nitrate, nitrite, sulfate, mineral elements, and heavy metals. We also studied the bacteriological quality of the water in terms of microbial germs represented by Total Coliforms, Fecal Coliforms, Escherichia coli (E. coli), Intestinal Enterococci, and sulfito-reducing Clostridium.Apart from two points located upstream of the Douars, nitrate concentrations range from 60 to 290 mg.L-1, well above the permissible value according to the World Health Organization (50 mg.L-1). At some points, values reach concentrations of 4.1.103 CFU/100 mL, 1.9.102 CFU/100 mL, 60 CFU/100 mL, 1.8.103 CFU/100 mL, and 90 CFU/100 mL, respectively for total coliforms, fecal coliforms, Escherichia, intestinal enterococci and sulfito-reducing Clostridium. The presence of Total Coliforms, Fecal Coliforms, and E. coli in the water tested is an indicator of contamination by human or animal fecal matter, which may come from conventional septic tanks, untreated wastewater discharges, animal manure leaching, or runoff. On the other hand, the values of the other physicochemical parameters tested remain compliant with potable water standards.

Assessing the Transboundary Water Pollution Possibly Produced By an Armed Conflict

The impact of armed conflicts can be direct and indirect, highlighted by population displacement and casualties, infrastructure destruction, together with social and economic hiatus, but also the movement of air, water and soil pollutants across regional and national borders. There are numerous possible contamination sources of the water bodies and aquatic ecosystems that may appear during armed conflicts, including projectile composition, use of chemical weapons, discharge of untreated wastewater due to damage to sewage lines or wastewater treatment plants, unregulated waste management (improper disposal of industrial, hospital and municipal waste), oil spills, and deliberate poisoning of water resources. Thus, a comprehensive study from a multidisciplinary perspective of the armed conflicts is a sine qua non condition. In accordance, to properly assess the effects of pollution in the study area (Black Sea and coastal area) and to establish further strategies that can hinder the impact, water samples from various points of interest were analyzed to determine the water quality of the aquatic ecosystem and to possibly identify contaminants in the analyzed water bodies. Higher concentration values were observed for Pb in MB3 (27.9 μg/L) and Zn in MB1 (232 μg/L) and MB2 (53.1 μg/L), exceeding the maximum concentration limits set by the national legislation (10 μg/L for Pb and 50 μg/L for Zn).

Health Risk Assessment of Nitrate in Drinking Water with Potential Source Identification: A Case Study in Almaty, Kazakhstan.

Infant mortality in Kazakhstan is six times higher compared with the EU. There are several reasons for this, but a partial reason might be that less than 30% of Kazakhstan's population has access to safe water and sanitation and more than 57% uses polluted groundwater from wells that do not comply with international standards. For example, nitrate pollution in surface and groundwater continues to increase due to intensified agriculture and the discharge of untreated wastewater, causing concerns regarding environmental and human health. For this reason, drinking water samples were collected from the water supply distribution network in eight districts of Almaty, Kazakhstan, and water quality constituents, including nitrate, were analyzed. In several districts, the nitrate concentration was above the WHO and Kazakhstan's maximum permissible limits for drinking water. The spatial distribution of high nitrate concentration in drinking water was shown to be strongly correlated with areas that are supplied with groundwater, whereas areas with lower nitrate levels are supplied with surface water sources. Based on source identification, it was shown that groundwater is likely polluted by mainly domestic wastewater. The health risk for infants, children, teenagers, and adults was assessed based on chronic daily intake, and the hazard quotient (HQ) of nitrate intake from drinking water was determined. The non-carcinogenic risks increased in the following manner: adult < teenager < child < infant. For infants and children, the HQ was greater than the acceptable level and higher than that of other age groups, thus pointing to infants and children as the most vulnerable age group due to drinking water intake in the study area. Different water management options are suggested to improve the health situation of the population now drinking nitrate-polluted groundwater.

Study on Nutrients Concentration Trends in Tukad Badung River Toward Nutrient Recovery Potential

This study addresses the urgent concern of water quality degradation resulting from untreated domestic wastewater discharge, with a specific focus on nutrient trends within an aquatic ecosystem. The investigation centres on ammonium (NH4 +) as a significant contaminant sourced from residual foods, hygiene practices, and fertilizers, known for its association with eutrophication—characterized by excessive algae growth and oxygen depletion. The study aims to offer comprehensive insights by meticulously analysing water quality parameters across six distinct sampling points. Data collection encompassed total suspended solids (TSS), ammonia (NH4 +), nitrite (NO2 −), nitrate (NO3 −), total phosphate (PO4 −), and total nitrogen (TN). Notable variations were observed: TSS concentrations ranged from 9.00 mg/L to 20.00 mg/L, NH4 + concentrations spanned 0.00 mg/L to 1.96 mg/L, NO2- and NO3 − levels varied from 0.00 mg/L to 0.16 mg/L and 1.19 mg/L to 1.91 mg/L, respectively, PO4 3- content ranged from 0.01 mg/L to 0.65 mg/L, and TN concentrations fluctuated between 1.36 mg/L and 3.31 mg/L. These findings underscore the complexity of water quality dynamics and highlight the need for integrated management strategies to mitigate nutrient pollution’s impact on aquatic ecosystems.

Technology Selection for Wastewater Treatment in the Maldives

In the Maldives, the discharge of untreated wastewater into the sea poses a significant threat to public health and the marine environment. This study proposes technically feasible, sustainable, and economical wastewater treatment technologies appropriate for small islands in the Maldives. Out of the 187 residential islands in the Maldives, three islands (HA. Dhidhdhoo, HA. Hoarafushi, and HA. Ihavandhoo) were selected as study areas. This study characterized the wastewater from these islands using physiochemical and microbiological water quality assessment parameters. The Water and Wastewater Treatment Technologies Appropriate for Reuse (WAWTTAR), an open-source software developed by the Humbolt State University in 1993, was used to simulate the performance of different wastewater treatment processes to treat the characterized wastewater. The feasible alternatives identified from these simulations were analyzed using a Multi-Criteria Analysis (MCA), considering various indicators that influence the decision-making process. The wastewater quality assessment revealed that the wastewater generated in the three islands produced low concentrations of chemical and biological oxygen demand (COD and BOD), with concentrations ranging from 267 – 309 mg/L and 128 – 219 mg/L, respectively. Nitrate and phosphate concentrations were also low (5.7 – 18.0 mg/L and 2.8 – 14.9 mg/L, respectively), where these concentrations in Dhidhdhoo and Hoarafushi were already within the maximum allowable limits of 15 mg/L and 10 mg/L, respectively, for discharge into the deep sea. Based on the findings, secondary treatment technologies such as membrane bioreactors (MBR) and sequencing batch reactors (SBR) with Ultraviolet (UV) disinfection were found to be the most feasible options for treating the wastewater. These results were further checked for robustness using a sensitivity analysis. This study demonstrates that the proposed methodology is suitable for technology selection and can provide valuable information for policymakers and stakeholders in the country and serve as a basis for future studies.

Investigation of reusability of effluents from an organized industrial zone wastewater treatment plant using a pressure-driven membrane process

Abstract The quantity of wastewater being discharged into the environment due to the rise in industrial activities is progressively growing over time. Aside from large environmental risk posed by untreated wastewater discharge, the reuse of treated water prevents wastage of large amounts of water. For this reason, in this study, the reuse potential of an organized industrial zone wastewater was investigated by membrane processes. The appropriate membrane type and rejection performance were determined for various pollutant parameters including conductivity, chemical oxygen demand (COD), total nitrogen (TN), chloride, and sulfate. Laboratory-scale batch membrane filtration experiments were performed by using three different membrane types (BW30, XLE, and X20). The experiments were conducted at 15 and 20 bar pressures and flux data were collected during the operations. The results showed that BW30 and X20 membranes could be operated comfortably with 80% recovery for the wastewater containing low and high sulfate concentrations. For the wastewater with low sulfate concentration, the fluxes of BW30 and X20 at 20 bar were 19.7 and 16.4 L/m2/h, respectively, at 80% recovery. On the other hand, for the wastewater with higher sulfate concentration, the fluxes of BW30 and X20 at 20 bar were 8.6 and 11.5 L/m2/h, respectively.

A comparative study between low- and high-tech methods for the detection and mitigation of illicit connections in stormwater systems.

Illicit connections of wastewater to stormwater systems are the main drawback of separate sewer systems, as they lead to a direct discharge of untreated wastewater to the aquatic environment. Consequently, several inspection methods have been developed for detecting illicit connections. This study simultaneously applied several low- and high-tech methods for the detection of illicit connections in the same catchment (De Heuvel, the Netherlands). The methods included mesh wire screens for capturing coarse contamination, measurements of electroconductivity and temperature, sampling and quantification of Escherichia coli and extended-spectrum ß-lactamase-producing E. coli (ESBL-EC), DNA analysis via quantitative polymerase chain reaction for human-, dog-, and bird-specific fecal indicators, and distributed temperature sensing. Significant illicit connections could be identified using all methods. Nonetheless, hydraulic conditions and, predominantly, the sewage volume determine whether a misconnection can be detected by especially the low-tech methods. Using these results, the identified misconnections were repaired and biological and DNA analyses were repeated. Our results demonstrate that there were no changes in E. coli or ESBL-EC before and after mitigation, suggesting that these common markers of fecal contamination are not specific enough to evaluate the performance of mitigation efforts. However, a marked decrease in human wastewater markers (HF183) was observed.

Low-cost materials for swine wastewater treatment using adsorption and Fenton's process.

Untreated swine wastewater (SW) discharge leads to serious consequences such as water quality decreasing related to eutrophication and proliferation of harmful algae containing cyanotoxins, which can cause acute intoxication in humans. The use of untreated pig farming effluent as fertilizer can lead to the accumulation of polluting compounds. Biological treatments can degrade organic matter but have the disadvantage of requiring large areas and high retention times and demonstrating low efficiencies in the degradation of refractory compounds such as pharmaceutical compounds. In this ambit, the performance of four low-cost materials was evaluated for treatment of a swine wastewater using physical-chemical processes such as adsorption and Fenton's process. The tested materials are two natural resources, red volcanic rock from Canary (RVR) Islands and black volcanic rock (BVR) from Azores, and two industry residues, red mud (RM) and iron filings (IF). Among the tested materials, only IFs are catalytically active for Fenton's peroxidation. Still, RVR, BVR, and RM were efficient adsorbents removing up to 67% of COD. The combination between adsorption followed by Fenton's process using IF as catalyst showed interesting results. When RM is applied as adsorbent in the diluted effluent, it was able to remove 67% and 90% of COD for adsorption and adsorption followed by IF Fenton, respectively. At those conditions, the resultant treated effluent accomplishes the requirements for direct discharge in the natural water courses as well as the parameters for water reusing.

Occurrences, sources and health hazard estimation of potentially toxic elements in the groundwater of Garhwal Himalaya, India

High concentrations of potentially toxic elements (PTEs) in potable water can cause severe human health disorders. Present study examined the fitness of groundwater for drinking purpose based on the occurrence of nine PTEs in a heavy pilgrim and tourist influx region of the Garhwal Himalaya, India. The concentrations of analyzed PTEs in groundwater were observed in the order of Zn > Mn > As > Al > Cu > Cr > Se > Pb > Cd. Apart from Mn and As, other PTEs were within the corresponding guideline values. Spatial maps were produced to visualize the distribution of the PTEs in the area. Estimated water pollution indices and non-carcinogenic risk indicated that the investigated groundwater is safe for drinking purpose, as the hazard index was < 1 for all the water samples. Assessment of the cancer risk of Cr, As, Cd, and Pb also indicated low health risks associated with groundwater use, as the values were within the acceptable range of ≤ 1 × 10−6 to 1 × 10−4. Multivariate statistical analyses were used to describe the various possible geogenic and anthropogenic sources of the PTEs in the groundwater resources although the contamination levels of the PTEs were found to pose no serious health risk. However, the present study recommends to stop the discharge of untreated wastewater and also to establish cost-effective as well as efficient water treatment facility nearby the study area. Present work’s findings are vital as they may protect the health of the massive population from contaminated water consumption. Moreover, it can help the researchers, governing authorities and water supplying agencies to take prompt and appropriate decisions for water security.

Comparison of aerobic and anoxic-oxic sequential batch reactors for treating textile wastewater

ABSTRACT The discharge of untreated textile dyeing wastewater containing azo dyes has significant ecological consequences. The incomplete biodegradation of these dyes can produce harmful and carcinogenic aromatic amines (AAs), which pose a threat to the environment. This study evaluates the treatment of real textile dyeing wastewater containing azo dyes by two different systems: an anoxic sequential batch reactor (A/O-SBR) and an aerobic sequential batch reactor (A-SBR). The effects of hydraulic retention time (HRT) on both systems were investigated in terms of chemical oxygen demand (COD), total nitrogen (TN), color, and AAs removal. Ranging between 85% and 92%, the COD removal efficiency was almost similar in the A/O-SBR and A-SBR systems, suggesting that the aerobic phase is primarily responsible for COD removal. However, A/O-SBR showed higher removal of color (90%) than A-SBR (75%) due to the presence of an anoxic phase. HRT has a significant impact on color removal in both systems. However, there was no significant effect on COD removal when HRT exceeded 12 h. According to LC-MS/MS analysis, increasing the HRT from 12 h to 24 h increased the AAs concentration in the anoxic phase, from 253 ng/L to 261 ng/L and slightly decreased the AAs concentration in the aerobic phase from 107 ng/L to 102 ng/L. This resulted in an overall improvement in both dye and AAs removal. The presence of aerobic phase in A/O-SBR and A-SBR demonstrates strong AAs removal capacity. GC-MS/MS analysis indicated that as the HRT of A/O-SBR and A-SBR increased, the number of by-products increased.

Critical State of the Art of Sugarcane Industry Wastewater Treatment Technologies and Perspectives for Sustainability.

The worldwide pressure on water resources is aggravated by rapid industrialization, with the food industry, particularly sugar factories, being the foremost contributor. Sugarcane, a primary source of sugar production, requires vast amounts of water, over half of which is discharged as wastewater, often mixed with several byproducts. The discharge of untreated wastewater can have detrimental effects on the environment, making the treatment and reuse of effluents crucial. However, conventional treatment systems may not be adequate for sugarcane industry effluent treatment due to the high organic load and variable chemical and mineral pollution. It is essential to explore pollution-remediating technologies that can achieve a nexus (water, energy, and food) approach and contribute to sustainable development. Based on the extensive literature, membrane technologies such as the membrane bioreactor have shown promising results in treating sugarcane industry wastewater, producing treated water of higher quality, and the possibility of biogas recovery. The byproducts generated from this treatment can also be recovered and used in agriculture for food security. To date, membrane technologies have demonstrated successful results in treating industrial wastewater. This critical review aims to evaluate the performance of traditional and conventional processes in order to propose sustainable perspectives. It also serves to emphasize the need for further research on operating conditions related to membrane bioreactors for valuing sugarcane effluent, to establish it as a sustainable treatment system.

Progress in the Preparation of Metal Oxide Electrodes for the Electrochemical Treatment of Organic Wastewater: A Short Review

The direct discharge of untreated organic wastewater poses significant threats to the environment and to human health. To address these threats, electrocatalytic oxidation technology has emerged as a key solution for organic wastewater treatment. Building on research conducted over the past three years, this review highlights the considerable advantages of electrocatalytic oxidation technology in the context of organic wastewater treatment, with a particular emphasis on the application of metal oxide electrodes. The review also provides a summary of the primary methods used in the preparation of such electrodes. Subsequently, the applications of both single-metal-oxide electrodes and metal oxide composite electrodes in organic wastewater treatment are summarized. Finally, we discuss the future development of metal oxide electrodes.

Nitrate Migration and Transformation in Low Permeability Sediments: Laboratory Experiments and Modeling

The excessive application of fertilizers and the uncontrolled discharge of untreated wastewater on land contribute to the nitrogen pollution of groundwater. Low permeability sediment plays an important role in slowing down the migration of nitrate in groundwater systems. This study focuses on the mechanisms that affect nitrate transport in the low permeability layer. A soil column experiment was conducted and an MT3D transport model (a modular three-dimensional multispecies transport model) of nitrate was proposed. The results show that a low permeation layer could act as a strong barrier to nitrate migration and transportation, as demonstrated by the column soil experiment. The denitrification rates were controlled by many other factors, including nitrate concentration, flow rate, pH values and sediment particle characteristics. This indicated that denitrification is the most important factor in the attenuation of nitrate in low permeability sediments. This study clarified the law of migration and transformation of nitrate in low permeability soils and the factors that influence these processes. The results not only provide a basis for large-scale nitrate simulations, but also provide a reference for nitrate treatment in low permeability layers.