High Levels Of Chemical Oxygen Demand Research Articles

Desain Sumur Resapan Pengolahan Limbah Cucian Mobil X

Car washes have become increasingly popular in some areas, but this growth has also had a negative impact on environmental quality, as untreated wash water is often discharged directly into car wash drainage systems without any prior treatment. This discharge of unfiltered wastewater can lead to high levels of COD (chemical oxygen demand) and surfactants in nearby water sources if carried out intensively. Much of the wastewater is often classified as waste. It is discharged by car wash operators into the drainage system and eventually into smaller waterways. In 2014, the Minister of the Environment highlighted the importance of managing cleaning waste due to its harmful effects on the environment and health. Based on the Pekanbaru Municipality's Regional Regulation No. 8 of 2003 on the payment of liquid waste treatment control permit, which stipulates that every industry must carry out waste treatment before discharging into the environment and each industry must also pay a fee, this study will allow the design of absorption wells, which will be used to treat liquid waste from car washes, so that the wastewater absorbed into the ground is no longer a contaminated liquid waste. By treating the waste by the method of infiltration pits, it is hoped that the environment and the health of the residents around the laundry will be well preserved.

Assessment of Water Quality Parameters and Their Correlations in the Kalimas River, Surabaya: Implications for Health Risks

The Kalimas River, which flows through industrial and residential areas, faces significant pollution pressure due to diverse anthropogenic activities. This study evaluates the water quality parameters of the Kalimas River in Surabaya, Indonesia, and investigates the correlations among these parameters to assess potential health risks. Key parameters assessed include temperature, pH, dissolved oxygen (DO), biochemical oxygen demand (BOD), chemical oxygen demand (COD), and total suspended solids (TSS). Sampling was conducted along ten strategically selected segments. The results reveal varying levels of pollution, with elevated BOD5, COD, and TSS values indicating organic and chemical pollution, and low DO levels signalling oxygen depletion in certain sections. Statistical analysis using Spearman’s correlation demonstrated significant relationships among variables, such as a negative correlation between temperature and DO. Health risks are evident, as high COD and BOD levels promote pathogen growth, increasing the risk of waterborne diseases, while elevated TSS may carry pollutants that further threaten public health. The presence of low DO levels also disrupts aquatic ecosystems, which can exacerbate bacterial growth, posing additional health hazards to communities using the river for daily activities. These findings highlight the need for urgent interventions to mitigate pollution and protect both ecological health and public safety.

Development of a portable electrocoagulation unit for on-site treatment of washing machine wastewater

This study evaluated the effectiveness of the electrocoagulation method in treating wastewater from two laundries in the Huancavelica district of Peru, focusing on reducing chemical oxygen demand (COD) and monitoring temperature and pH levels. Over two weeks, treatments were conducted with varying current intensities (15 and 30 Amp/m²) and durations (15 and 40 minutes), mixing speed + time (20 and 40 rpm) alongside a control with 0 Amp/m² and 0 minutes. The initial untreated samples showed high COD levels, highlighting significant organic pollution. The results demonstrated substantial COD reductions across all treatments, with the most effective reduction observed at 15 Amp/m² for 15 minutes, achieving COD levels of 366.50 mg/L in Laundry 1 and 348.50 mg/L in Laundry 2. This significant decrease complies with Supreme Decree No. 010-2019-VIVIENDA, which mandates COD levels below 1000 mg/L for non-domestic wastewater discharges. Temperature and pH variations were also analyzed, revealing that the electrocoagulation process increased the temperature moderately, with averages ranging from 15.15°C to 36.80°C in Laundry 1 and 15.65°C to 34.80°C in Laundry 2. The pH levels remained slightly alkaline, ranging from 8.47 to 10.55 in Laundry 1 and 9.47 to 10.62 in Laundry 2, indicating that the process maintains acceptable alkalinity. In conclusion, the electrocoagulation method effectively reduces COD, maintains moderate temperature increases, and slightly alters pH levels, making it a viable option for treating industrial wastewater. These findings support the potential for electrocoagulation to enhance wastewater management practices, promoting environmental sustainability and regulatory compliance.

The Modifying Effects of Lifestyle Behaviors on the Association Between Drinking Water Micronutrients and BMI Status Among Children and Adolescents Aged 7~17: A Population-Based Regional Surveillance in 2022.

This study aims to investigate the potential modifying effects of lifestyle behavior on the association between drinking water micronutrients and body mass index (BMI) in a large population of children and adolescents. Data of the present analysis came from a comprehensive regional large-scale surveillance study in 2022, involving 172,880 children and adolescents (50.71% boys vs. 49.29% girls) aged seven to seventeen. A restricted cubic spline (RCS) analysis was utilized to examine the exposure-response association of regular drinking water indices (including fluoride, nitrate nitrogen, pH, chloride, sulfates, and total dissolved solids (TDS), total hardness (TH), and chemical oxygen demand (COD)) with BMI. Generalized linear model and logistic regression were conducted to relate BMI and quartiles of drinking water micronutrients. Our findings reveal a nonlinear association between nitrate nitrogen (P for nonlinear < 0.001) and pH (P for nonlinear < 0.001) with BMI. High TH and COD levels significantly increase BMI. Notably, fluoride and chloride were associated with BMI Z-scores but not with overweight and obesity (OB). The BMI Z-score showed a more pronounced association with low and high pH levels in girls. For urban participants, increased TH levels were associated with a higher risk of OB. This study also found that adopting healthy lifestyles could mitigate the negative effects of fluoride, chloride, and sulfate on BMI Z-scores. This large surveillance study provides new insights into the complex interplay between drinking water micronutrients and BMI in children and adolescents. The association of various drinking water parameters on BMI varies, necessitating ongoing focus on their effects, particularly among girls and urban individuals. Healthy lifestyle behavior could mitigate the effects of fluoride, chloride, and sulfate on BMI Z-score.

Application of electrochemical flow-through oxidation technology in the treatment of concentrated water from nanofiltration and reverse osmosis in the coal chemical industry

In the coal chemical industry, the concentrated waters produced by nanofiltration and reverse osmosis are usually evaporated and crystallized. During the evaporation crystallization process, high COD levels can lead to problems such as the entrainment of liquid droplets and excessive amounts of mother liquor. Therefore, there is an urgent need to develop efficient, stable, and engineering-applicable organic matter degradation technologies before the evaporation crystallization process. In this study, Ti-ENTA/SnO2-Sb and GF-5 were combined as cathodes to form an electrochemical flow-through oxidation system to treat nanofiltration concentrate (NFCs) and reverse osmosis concentrate (ROCs). The experimental results show that within the current density range of 10–20 mA·cm−2, the chemical oxygen demand (COD) removal rates of NFCs and ROCs are 55.3 %–85.2 % and 49.9 %–93.6 %, respectively. And the oxidation system can be used stably for a long time, fully meeting the practical application needs. In addition, this article further analyzed the effects of current density, initial organic matter concentration, pH value, and electrode spacing on COD removal. The results indicate that the COD removal efficiency is mainly affected by current density and initial organic matter concentration. Finally, a comprehensive comparison was made on the efficiency and cost of various advanced oxidation technologies in treating wastewater. The results indicate that the electrochemical flow-through oxidation system has significant cost advantages. The cost of processing NFCs and ROCs per cubic meter is $0.96 and $1.23, respectively. These findings indicate that the electrochemical flow-through oxidation system proposed is an advanced oxidation technology with economic benefits and practical application prospects.

Integrated A/O-MBR–NF process for treating high COD content wastewater from traditional Chinese medicine

Traditional Chinese medicine (TCM) wastewater poses a significant environmental challenge due to its high chemical oxygen demand (COD) and complex components. This study demonstrates a highly effective treatment approach for complex TCM wastewater using a combination of hydrolysis-acidification (HA) pre-treatment, anaerobic-aerobic membrane bioreactor (A/O-MBR), and nanofiltration (NF). Pudilan Xiaoyan Oral Liquid (PDL) wastewater, characterized by high COD (around 5500 mg/L) and baicalin content, served as the model feedstock. The A/O-MBR demonstrated removal rates of 23.6 mg COD g biomass−1 h−1 and 1.0 mg NH3-N g biomass−1 h−1. The combined A/O-MBR-NF process achieved exceptional COD removal exceeding 99 %, significantly reducing the wastewater's environmental impact. Importantly, the treated effluent exhibited no biological toxicity in zebrafish acute toxicity tests, demonstrating the effectiveness of this approach in detoxifying PDL wastewater. Analysis of the A/O-MBR's bacterial community further elucidates the treatment mechanism. This study indicates that MBR treatment for complex TCM wastewater is feasible and holds promising industrial prospects, offering a fresh perspective on the treatment of TCM wastewater with high COD levels.

Using ultrasonic washing combined with UV-LEDs as a novel chemical-free method to disinfect fresh ready-to-eat produce

The consumption of ready-to-eat fresh produce raises the issue of food-borne pathogen infections; thus, disinfecting ready-to-eat produce for commercial use, such as in homes and restaurants, is important to ensure food safety. Chemical sanitizers are typically used for disinfection. Ultraviolet-light emitting diodes (UV-LEDs) are a novel non-thermal disinfection technology that consumes less energy and generates less heat than traditional UV lamps, making them more appealing to consumers. In this study, we combined ultrasonic (US) washing method with UV-LEDs (US-UV-LEDs) to develop a technique for disinfecting fresh produce without using chemical sanitizers and compared its efficacy with three common household sanitizers (“84” (sodium hypochlorite) disinfectant, kettle descaler (citric acid), and vinegar (acetic acid)). In addition, we investigated the efficacy of this method in controlling pathogen numbers in the water used to wash (washing water) the produce to prevent cross-contamination between water and produce. Cherry tomatoes and lettuce were selected as produce models and Salmonella Typhimurium and Escherichia coli O157:H7 were used as the bacterial models. The results showed that US-UV-LEDs reduced the numbers of S. Typhimurium and E. coli O157:H7 on produce by 2.1–2.2 log CFU/g, consistent with the results achieved by the three household sanitizers; however, kettle descaler and vinegar had a limited effect (2.6–3.5 log CFU/mL) on residual pathogens in the washing water. Furthermore, we created washing water with low (754 mg/L) and high (1425 mg/L) chemical oxygen demand (COD) levels and determined the disinfection efficacy of “84” disinfectant and US-UV-LEDs. The results showed that US-UV-LEDs reduced the number of S. Typhimurium and E. coli O157:H7 by 2.0–2.1 and 1.8–2.1 log CFU/g under low and high COD levels, respectively, which was similar a result to that of “84” disinfectant. However, the residual pathogen numbers in the washing water were reduced to 1.4–1.9 log CFU/mL after treatment with US-UV-LED under high COD, whereas the pathogens were undetected in the washing water disinfected with “84” disinfectant. These results suggest that US-UV-LEDs have better application potential than acidic household sanitizers, but chlorine sanitizer remains the most effective disinfecting method.

Naturally derived organic biochar as an alternative to commercially activated carbon in the oxygen removal of seafood processing wastewater

AbstractBACKGROUNDThe seafood processing industries are tremendously increasing in numbers which eventually discharge a large quantity of wastewater with a high range of biochemical oxygen demand (BOD) and chemical oxygen demand (COD), directly into the aquatic environment. A high level of BOD and COD in wastewater pertains to a higher level of pollution which must be reduced to prevent hazardous impacts on ecosystems. The main objective of the research aimed to develop cost‐effective biochar and to remove BOD and COD from processing wastewater using two natural biomasses: water hyacinth and sugarcane bagasse.RESULTSNaOH‐treated and non‐treated biochar for both water hyacinth as well as sugarcane bagasse were prepared through the process of pyrolysis carried out at 600 °C with three different residence times of 30, 45 and 60 min. The wastewater was initially analyzed for BOD and COD levels. The results showed that among all the groups of biochars, the water hyacinth NaOH‐treated biochar pyrolyzed at 600 °C for 60 min exhibited significantly (P &lt; 0.05) higher levels of reduction in BOD (86.6 ± 0.03%) and COD (94.3 ± 0.05%) at a residence time of 60 min in D2 (0.5 g (250 mL)−1). The maximum removal efficiency was observed for water hyacinth NaOH‐treated biochar pyrolyzed at 600 °C for 60 min.CONCLUSIONThe removal efficiencies of organic load revealed that the treated biochars exhibited a better reduction of nutrients. The biochar efficiencies when compared with those of activated carbon exhibited a higher removal level. The present research can be used to reduce BOD and COD levels in wastewater treatments. © 2024 Society of Chemical Industry (SCI).

Hydrodynamic Cavitation – A Promising Technology for Water Treatment

In today's context, water treatment assumes paramount importance due to the scarcity of potable water and the escalating needs of the global population. Hydrodynamic Cavitation (HC) emerges as a promising application in wastewater treatment, particularly when integrated with Advanced Oxidation Processes (AOPs). The study begins with a critical examination of the literature on combined approaches involving hydrodynamic cavitation, followed by experimental findings. The primary objective was to mitigate the chemical oxygen demand (COD) of the sample through HC in conjunction with hydrogen peroxide and Fenton reagent. Subsequently, each run was executed, and the output value obtained from HC was determined. Throughout the research, samples of river water were procured from the Mula-Mutha River in Pune. HC treatment reduced the COD of river water by approximately 60.83 % at 3 pH. Notably, the highest degradation was observed at 9 pH with the use of Sodium persulphate, with the optimal concentration estimated to be 600 ppm. Moreover, a COD reduction exceeding 89 % with a dosage of 15 mM H2O2. Treatment with Fenton reagent for 60 min demonstrated a remarkable COD decrease of up to 93 %, with an optimal H2O2 to FeSO4 molar ratio of 10:1 and at 3 pH. The Fenton procedure alone or in combination with H2O2 and HC proved to be the most efficient for river water characterized by extremely high COD levels, yielding the greatest reduction during experimental trials. The kinetics of HC degradation conformed to a first-order rate law, with the value of a rate constant (K = 7.21 × 10-4 s−1).

Response surface methodology optimization of the effect of pH, contact time, and microbial concentration on chemical oxygen removal potential of vegetable oil industrial effluents.

The vegetable oil refinery industry generates highly polluted effluents during oil production, necessitating proper treatment before discharge to prevent environmental hazards. Treating such wastewater has become a major environmental concern in developing countries. Chemical oxygen demand (COD) is a key parameter in assessing the wastewater's organic pollutant load. High COD levels can lead to reduced dissolved oxygen in water bodies, negatively affecting aquatic life. Various technologies have been employed to treat oily wastewater, but microbial degradation has gained attention due to its potential to remove organic pollutants efficiently. This study aims to optimize the biodegradation treatment process for vegetable oil industrial effluent using response surface methodology (RSM). The wastewater's physicochemical properties were characterized to achieve this, and COD removal was analyzed. Furthermore, RSM was used to investigate the combined effects of pH, contact duration, and microbial concentration on COD removal efficiency. The result showed that the microbial strain used recorded a maximum COD removal of 92%. Furthermore, a quadratic model was developed to predict COD removal based on the experimental variables. From the analysis of variance (ANOVA) analysis, the model was found to be significant at p < 0.0004 and accurately predicted COD removal rates within the experimental region, with an R2 value of 90.99% and adjusted R2 value of 82.89%. Contour plots and statistical analysis revealed the importance of contact duration and microbial concentration on COD removal. PRACTITIONER POINTS: Response surface methodology (RSM) optimization achieved a significant chemical oxygen demand (COD) removal efficiency of 92% in vegetable oil industrial effluents. The study's success in optimizing COD removal using RSM highlights the potential for efficient and environmentally friendly wastewater treatment. Practitioners can benefit from the identified factors (pH, contact time, and microbial concentration) to enhance the operation of treatment systems. The developed predictive model offers a practical tool for plant operators and engineers to tailor wastewater treatment processes. This research underscores the importance of sustainable practices in wastewater treatment, emphasizing the role of microbial degradation in addressing organic pollutant loads.

Assessment of Greenhouse Gas Emissions and Water Quality in Relation to Tourism and Human Activities at Kenyir Lake, Terengganu

This study assesses the impact of tourism and human activities on greenhouse gas (GHG) emissions and water quality at Kenyir Lake, Terengganu. Kenyir Lake, a tourist destination in Malaysia, faces environmental challenges due to increased anthropogenic activities. The research quantifies GHG emissions from various sources such as forest land management, land conversion to flooded areas, aquaculture, domestic wastewater, and solid waste disposal using IPCC guidelines. The total GHG emissions from these activities amounted to 151,527 tCO2-eq/year, highlighting the substantial contribution of tourism and human activities to climate change. Water quality was evaluated through the analysis of parameters including Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Suspended Solids (TSS), ammonia nitrogen (NH3N), total phosphorus (TP), and total nitrogen (TN). Samples were collected from resorts, houseboats, aquaculture farms, and parks during wet and dry seasons. The findings indicate that houseboat areas significantly contribute to high levels of BOD (up to 8.73 mg/l), COD (up to 69.23 mg/l), TSS (up to 303.39 mg/l), and NH3-N (up to 2.64 mg/l), with seasonal variations reflecting the influence of runoff and water volume on pollutant concentrations. These results underscore the need for effective pollution control and sustainable tourism practices to preserve Kenyir Lake’s ecological balance and reduce its GHG footprint.

Energy balance survey for the design and auto-thermal thermophilic aerobic digestion of algal-based membrane bioreactor for Landfill Leachate Treatment(under organic loading rates): Experimental and simulation-based ANN and NSGA-II

Although algal-based membrane bioreactors (AMBRs) have been demonstrated to be effective in treating wastewater (landfill leachate), there needs to be more research into the effectiveness of these systems. This study aims to determine whether AMBR is effective in treating landfill leachate with hydraulic retention times (HRTs) of 8, 12, 14, 16, 21, and 24 h to maximize AMBR's energy efficiency, microalgal biomass production, and removal efficiency using artificial neural network (ANN) models. Experimental results and simulations indicate that biomass production in bioreactors depends heavily on HRT. A decrease in HRT increases algal (Chlorella vulgaris) biomass productivity. Results also showed that 80% of chemical oxygen demand (COD) was removed from algal biomass by bioreactors. To determine the most efficient way to process the features as mentioned above, nondominated sorting genetic algorithm II (NSGA-II) techniques were applied. A mesophilic, suspended-thermophilic, and attached-thermophilic organic loading rate (OLR) of 1.28, 1.06, and 2 kg/m3/day was obtained for each method. Compared to suspended-thermophilic growth (3.43 kg/m3.day) and mesophilic growth (1.28 kg/m3.day), attached-thermophilic growth has a critical loading rate of 10.5 kg/m3.day. An energy audit and an assessment of the system's auto-thermality were performed at the end of the calculation using the Monod equation for biomass production rate (Y) and bacteria death constant (Kd). According to the results, a high removal level of COD (at least 4000 mg COD/liter) leads to auto-thermality.

A comparison between iron and mild steel electrodes for the treatment of highly loaded grey water using an electrocoagulation technique

In the last years, the electrocoagulation (EC) process has been widely used as a potential technique for grey water treatment. However, only a few studies have focused on treating highly loaded GW (HLGW) by EC. In this study, the EC technique was used to compare iron and mild steel electrodes for the treatment of HLGW under different current densities (CDs) (5, 10, 15, and 20 mA/cm2) during 10 min of EC time. The performance criteria included chemical oxygen demand (COD) and turbidity removal efficiencies, current efficiency, energy consumption, and operational costs. It was found that EC using iron or mild steel can be effective electrodes for removing high levels of COD and turbidity from HLGW. At optimum conditions, the study demonstrated that at a CD of 5 mA/cm2, mild steel-based electrodes reduced COD by 86.5% while iron-based electrodes achieved 85.3% reduction at 10 mA/cm2. In conjunction with these removals, the turbidity removals were 92% and 94% achieved by steel and iron electrodes, respectively. The current efficiency of all the conducted experiments exceeded 90% but was generally higher for iron electrodes. At optimum conditions, analysis of operating costs in terms of energy consumptions and electrode materials requirements were 0.054 $/m3 and 0.097 $/m3 achieved by steel and iron electrodes, respectively. Thus, mild steel-based electrodes are considered superior to iron electrodes. Based on the obtained results, the study recommends that further investigations should give attention to the effect of metal alloy type or physical properties of electrodes as performance criteria and designing aspects when studying EC technology for HLGW treatment due to its notable effect on removal efficiency and operational costs.

Co-treatment of stabilized landfill leachate and municipal wastewater in a granular activated carbon-sequencing batch reactor (GAC-SBR)

A laboratory-scale granular activated carbon-sequencing batch reactor (GAC-SBR) was used to co-treat stabilized landfill leachate with municipal wastewater. GAC-SBR was studied for the different mixing ratios of leachate and municipal wastewater at different hydraulic retention time (HRT). GAC dose (5, 10, 15 and 20 g/L) was optimized for COD reduction with a contact time of 22 h. GAC-SBR treatment efficiency was assessed on mixed liquor suspended solids (MLSS), mixed liquor volatile suspended solids (MLVSS), turbidity, chemical oxygen demand (COD), ammonia, nitrate, and phosphate removal. Univariate ANOVA was applied to test the statistical significance of treatment at different leachate:wastewater ratios. Results showed that the increase in GAC concentration led to an increase in the removal of COD and ammonia from stabilized landfill leachate. Adsorption efficiency decreased or remained constant after 15 g/L GAC. GAC-SBR was efficient in removing COD (83%) and nutrients (80–90%) from stabilized landfill leachate at 10 d HRT. Univariate analysis of variance (ANOVA) highlighted that there was a statistically significant difference in the treatments for the mixing ratio tested. GAC-SBR results showed that treatment efficiency was dependent on landfill leachate concentration and hydraulic retention time (HRT). Coupled treatment tested exhibited a high potential for co-treatment of leachate and municipal wastewater. However, the effluent after treatment could not achieve a complete or very high level of COD, nutrients and turbidity removal which necessitates the incorporation of physico-chemical processes such as coagulation, electrocoagulation, membrane filtration etc. as post-treatment options. Further studies in this direction along with exploring the longevity of GAC in SBR would provide useful information for effective landfill leachate treatment.

Evaluation of Pollutant Discharge from Slaughterhouses on Receiving Water Bodies

Aim: The aim of this study is to appraisal the consequences of slaughterhouse wastewater discharge into surface water of selected slaughterhouse environment.&#x0D; Study Design: Three (3) main stream/surface water discharged slaughterhouses was analyzed. Water samples were collected at the Middle Course (MC) of the receiving water body. Sampling was be carried out between the hours of 10.00 am and 11.00 am when the discharge of effluent into the rivers/streams always occur.&#x0D; Methodology: Wastewater samples were collected from the different slaughterhouses in order to determine the quality of the effluent before it was discharged into nearby stream/river. The MC samples will be collected from about 40 m from the point of entry of the slaughterhouse waste. Waste samples were collected from each sampling site with a clean polyethylene bottles. The containers was washed with diluted HCl and then rinsed with the wastewater from the slaughterhouse so as to neutralize or reduce the effect of external contaminants. The samples were appropriately labeled and transported to the laboratory, stored in the refrigerator at 4⁰C prior to being analyzed for the physical, chemical and biological parameters present.&#x0D; Results: The parameters assessed include, Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Solids (TS), Phosphate, pH, Magnesium, Zinc, Iron, Manganese, Cadmium and Lead. High level of BOD, COD, and TS was revealed on receiving streams with minimum values of 1001mg/l, 1120mg/l, and 990mg/l.&#x0D; Conclusion: The physico-chemical parameters showed the negative impact of the abattoir effluent on the stream thus rendering the water of worthless value to humans. Furthermore, the abattoir urgently needs an effluent treatment facility to be installed to reduce the health hazard its effluent poses on the abattoir users and users of the streams receiving the effluent.

Potential of Chlorella sp As A Bioremediation Agent in Tofu Liquid Waste: Literature Review

Tofu liquid waste that contains high levels of COD (Chemical Oxygen Demand), BOD (Biological Oxygen Demand), and TSS (Total Suspended Solid) is usually discharged directly into the waters, causing a foul odor in community drainage and contaminating rivers. This study aims to determine the potential of Chlorella sp as a bioremediation agent in tofu wastewater. This type of research is research that uses the literature review method. The stages of literature collection used in this study refer to the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) guidelines. This stage consists of four procedures, namely, identification, screening, eligibility, and acceptance. This study shows that the microalgae Chlorella sp. can increase population growth and lipid levels, Chlorella sp. Can reduce COD and Nitrate levels contained in tofu liquid waste, and increase the pH from acidic to neutral. Based on the results of the study found, it can be concluded that Chlorella sp has the potential as a bioremediation agent in tofu liquid waste.

Water quality changes and shift in mechanisms controlling hypoxia in response to pollutant load reductions: A case study for Shiziyang Bay, Southern China

Shiziyang Bay, located in the upstream of the Pearl River Estuary, has frequently suffered from hypoxia since 2000, which has persisted in recent years despite effective controls on anthropogenic pollutant loads. To explore the underlying causes, changes in dissolved oxygen (DO), nutrients, chemical oxygen demand (COD), and chlorophyll a (Chl a) along the bay in response to altered pollutant inputs were investigated using observations collected in summers of 2015–2019 and historical data during 2000–2008. In addition, DO sources and sinks were calculated based on data from August 2020 and laboratory incubations for water column respiration (WCR) and sediment oxygen uptake, and were compared with their equivalents in August 2008 to elucidate changes in primary processes controlling hypoxia. The results showed that ammonia has decreased significantly with pollutant control, while other parameters responded in different trends, especially for Chl a (with a substantial increase over time). The intensified eutrophication contributed to high COD levels, leading to a strong WCR (as dominant oxygen depletion) close to that in the 2000s and thereby maintaining low-oxygen conditions despite reduced effluent discharges. The shifted primary oxygen-consuming substances from allochthonous inputs to in-situ phytoplankton production were also evidenced by significant correlation between oxygen consumption rate and Chl a in recent data. Simultaneously, the enhanced algal blooms could also modulate oxygen supply, resulting in higher photosynthetic oxygen production and lower air-sea reaeration compared with the past. Furthermore, the impact of major environmental changes on exacerbated eutrophication was explored and it was speculated that notable declined sediment loads would be important by improving light conditions to promote phytoplankton proliferation in the bay. Collectively, substantial control on eutrophication as well as tracking DO source-to-sink processes is of great importance to mitigate hypoxia in Shiziyang bay.

A critical review of state-of-the-art electrocoagulation technique applied to COD-rich industrial wastewaters.

Electrocoagulation (EC) is one of the emerging technologies in groundwater and wastewater treatment as it combines the benefits of coagulation, sedimentation, flotation, and electrochemical oxidation processes. Extensive research efforts implementing EC technology have been executed over the last decade to treat chemical oxygen demand (COD)-rich industrial wastewaters with the aim to protect freshwater streams (e.g., rivers, lakes) from pollution. A comprehensive review of the available recent literature utilizing EC to treat wastewater with high COD levels is presented. In addition, recommendations are provided for future studies to improve the EC technology and broaden its range of application. This review paper introduces some technologies which are often adopted for industrial wastewater treatment. Then, theEC process is compared with those techniques as a treatment for COD-rich wastewater. The EC process is considered as the most privileged technology by different research groups owing to its ability to deal with abundant volumes of wastewater. After, the application of EC as a single and combined treatment forCOD-rich wastewaters is thoroughly reviewed. Finally, this review attempts to highlight the potentials and limitations of EC. Related to the EC process in batch operation mode, the best operational conditions are found at 10 V and 60 min of voltage and reaction time, respectively. These last values guarantee high COD removal efficiencies of >90%. This review also concludes that considerably large operation costs of the EC process appears to be the serious drawback and renders it as an unfeasible approach for handling of COD rich wastewaters. In the end, this review has attempted to highlights thepotential and limitation of EC and suggests that vast notably research in the field of continuous flow EC system is essential to introduce this technology as a convincing wastewater technology.

Bio-assessment of wastewater effluent conditions with algal pollution index and multivariate approach

Water scarcity and water pollution are important issues in the world. Therefore, reusing treated wastewater for irrigation can be a crucial approach in arid and semi-arid regions. There are still some concerns about the sustainability of wastewater irrigated agriculture. Thereby, the present study is aimed to evaluate responses of algal species to stressors in the central wastewater treatment plant using the modified algae pollution index and multivariate approaches to assess healthy sustainability of wastewater effluent quality and to give the suggestion for reusing such kind of waters, especially for irrigation. Samplings of water and algae were carried out twice a month between October 2019 and August 2020. Canonical correspondence analysis (CCA) explained 94.1% of the relationships between environmental factors and species. Water and air temperatures, precipitation, chemical oxygen demand (COD), electrical conductivity (EC), pH, and NO3 played important roles in the temporal occurrence/succession of algae composition in the wastewater treatment plant. Ordination of commonly encountered algae species relatively near the center of the CCA indicates their wide range of tolerance levels to the changes in environmental conditions in the system. Of the species, Navicula aitchelbee, Nitzschia fonticola, and Euglena oxyuris preferred high EC levels; Brachysira exilis, Chlorella vulgaris, G. parvulum, and C. ovata associated with high COD levels, and Navicula tripunctata, Nitzschia umbonata and C. vulgaris related to high NO3 levels (>75% of the percentile). The modified pollution index developed in the present study indicated that the wastewater treatment plant had mainly high organic pollution (>3.00) in the summer and fall seasons, when it had moderate organic pollution (>2.50) in the winter and spring seasons. Results of the study suggest that crucial algae-stressors relationships can be used as an assessment tool to ensure sustainable water supply for the irrigation purpose in arid and semi-arid regions.

Bacterial community evolution along full-scale municipal wastewater treatment processes.

Sewage pollution is a major threat to public health because sewage is always accompanied by pathogens. Generally, wastewater treatment plants (WWTP) receive and treat sewage to control pathogenic risks and improve environmental health. This study investigated the changes in the bacterial community over the course of treatment by a WWTP. Illumina MiSeq high-throughput sequencing was performed to characterize the bacterial communities in the WWTP. This study found that potential pathogens in the WWTP, especially the genera Arcobacter and Acinetobacter, were greatly reduced. In addition, high chemical oxygen demand levels provided excessive growth substrates for the genera Hyphomicrobium and Rhodoplanes, the abundance of which could exceed autotrophic bacteria, increasing the ammonium removal. According to the network analysis, the bacterial assemblage was not randomly arranged in the WWTP, and various defined processes led to higher intra-phylum (such as Proteobacteria) coexistence than expected. Moreover, the metabolic functions of bacterial communities significantly improved in the WWTP compared with the influent. Together, the data in this study emphasize the need to understand the bacterial community of WWTPs better. When analyzing the risks of WWTP drainage systems to the environment and human health, these data should be considered.