Evaluating total organic carbon as an indicator for organic pollutant management in the marine environment: A case study on wastewater treatment plant effluent input into the coastal ocean

South Korea recently shifted its assessment indicator for organic matter in terrestrial environments from chemical oxygen demand (COD) to total organic carbon (TOC) due to the increase in refractory organic carbon levels. However, in the marine environment, where the inflow of refractory organic matter is also on the rise, COD is still used in some instances to assess organic pollution in contaminated areas. Our findings reveal that the main source of dissolved organic carbon (DOC) is terrestrial-derived refractory organic carbon, which enters through nearby wastewater treatment plant (WWPT) outlets. The low oxidation efficiency of COD to TOC (approximately 4 %) prevents it from being an accurate measure of terrestrial-derived refractory DOC. Contrasting results were observed when comparing the organic pollution index (OPI), which we calculated using TOC, with the currently employed water quality index (WQI) for ocean water quality evaluation, particularly in areas influenced by WWPTs. This discrepancy arises because the WQI primarily evaluates autochthonous organic carbon through chlorophyll measurements, whereas the OPI incorporates both autochthonous and allochthonous organic carbon through TOC measurements. Our findings demonstrate that TOC can effectively replace COD as an organic pollution indicator in marine environments.

Water pollution scenarios and response options for China

China has formulated several policies to alleviate the water pollution load, but few studies have quantitatively analyzed their impacts on future water pollution loads in China. Based on grey water footprint (GWF) assessment and scenario simulation, we analyze the water pollution (including COD, NH3-N, TN and TP) in China from 2021 to 2035 under different scenarios for three areas: consumption-side, production-side and terminal treatment. We find that under the current policy scenario, the GWF of COD, NH3-N, TN, and TP in China could be reduced by 15.0 % to 39.9 %; the most effective measures for GWF reduction are diet structure change (in the consumption-side area), and the wastewater treatment rate and livestock manure utilization improvement (in the terminal treatment area). However, the GWF will still increase in 8 provinces, indicating that the current implemented policy is not universally effective in reducing GWF across all provinces. Under the technical improvement scenario, the GWF of the four pollutants will decrease by 54.9 %-71.1 % via improvements in the current measures related to current policies and new measures in the production-side area and the terminal treatment area; thus, GWF reduction is possible in all 31 provinces. However, some policies face significant challenges in achieving full implementation, and certain policies are only applicable to a subset of provinces. Our detailed analysis of future water pollution scenarios and response options to reduce pollution loads can help to inform the protection of freshwater resources in China and quantitatively assess the effectiveness of policies in other fields.

Xylanase treatment of eucalypt kraft pulps: effect of carryover

The influence of pulp carryover on the efficiency of the xylanase (X) treatment of industrial unbleached and oxygen-delignified eucalypt kraft pulps (A1 and A2 pulps, with kappa number (KN) values of 16 and 10, respectively), collected at the same pulp mill, was studied regarding the consumption of bleaching chemicals and pulp bleachability. Another non-oxygen-delignified eucalyptus kraft pulp of KN 13 was received after the extended cooking from a different pulp mill (pulp B). The assays were performed with both lab-washed (carryover-free) and unwashed (carryover-rich) pulps. Both lab-washed and unwashed pulps with carryover were subjected to X treatment, the former being demonstrating considerably higher ClO2 savings than the pulps containing carryover. The savings of bleaching reagents were higher when the X stage was applied to the A1 pulp than to the A2 pulp. This advantage of A1 pulp, however, was not confirmed when using unwashed pulps. In contrast, the gains obtained from the X treatment of unwashed pulp A2 were practically as high as those observed for the lab-washed A2 pulp. Furthermore, a similar effect in X stage was recorded for unwashed pulps having close KN: oxygen-delignified A2 pulp and non-oxygen-delignified B pulp. The results suggest that pulp carryover and initial pH were the key factors relating to the effectiveness of X treatment. The application of X treatment to the A2 unwashed pulp (after the oxygen stage) not only saved 20% of the ClO2 and 10% of the sodium hydroxide, but also improved the brightness stability of the bleached pulp without affecting its papermaking properties. KEY POINTS: • Xylanase treatment boosts kraft pulp bleaching • Pulp carryover hinders the xylanase treatment • Nearly 20% of ClO2 and 10% NaOH savings can be reached using xylanase.

Integrated Fenton-like and ozonation based advanced oxidation processes for treatment of real-time textile effluent containing azo reactive dyes

The treatment of real-time textile effluent, collected from the Common Effluent Treatment Plant (CETP) of Kerala Industrial Infrastructure Development Corporation (KINFRA) at Kannur (District), Kerala (State), India, have been studied by utilizing the Fenton-like and ozone (O3) based advanced oxidation processes (AOPs). The Fenton-like AOP has been conducted as the pre-treatment of textile effluent involving the activation of persulfate (PS) and hydrogen peroxide (H2O2) as a single and the mixed oxidants by using the Flyash (FA)-Pd composite particles as the activator. The maximum chemical oxygen demand (COD) removal of 84% has been observed for a stand-alone O3 based treatment at an O3 flow rate of 5-6 g h-1. By conducting the pre-treatment of textile effluent with the PS, H2O2, and mixed oxidants (PS and H2O2) based Fenton-like AOPs, the COD removal after an O3 based post-treatment has been observed to be 83, 87, and 93% respectively at an O3 flow rate of 2, 3, and 5 g h-1. Hence, the Fenton-like pre-treatment involving the activation of mixed oxidants has been determined to be the best method for the highest COD removal of real-time textile effluent. The optimum values of initial oxidant-ratio (initial [H2O2]:initial [PS]), initial oxidant-dosage, and ozonation time, for the mixed oxidants based Fenton-like pre-treatment, have been determined to be 3 wt% mM-1, 6:2 wt% mM-1, and 60 min respectively. Under the most optimum conditions, the COD removal has been attributed to the combination of O2•- (for the pre-treatment) and •OOH (for the post-treatment) which possess relatively lower oxidation potential values.

The influence of various chemical oxygen demands on microbial fuel cells performance using leachate as a substrate

Microbial fuel cells (MFCs), hailed as a promising technology, hold the potential to combat various wastewater pollutants while simultaneously converting their chemical energy into electricity through biocatalysts. This study explores the applicability of a dual compartment MFC (DC-MFC) under varying conditions, targeting the removal of chemical oxygen demand (COD) from landfill leachate and electricity generation. In this setup, anaerobic sludge from a wastewater treatment plant serves as the inoculum in the anode compartment of the MFC, with a Nafion117 membrane acting as the separator between MFC units. The cathode compartments are filled with distilled water and continually aerated for 24 h to enhance air supply. The study assesses the MFC's performance across different COD concentrations, focusing on COD removal, power generation, and Coulombic efficiency. The findings reveal that COD removal efficiency is notably enhanced at higher concentrations of organic matter. Specifically, at a COD concentration of 3325.0 mg L-1, the MFC exhibited the highest COD removal efficiency (89%) and maximum power density (339.41 mWm-2), accompanied by a Coulombic efficiency of 25.5%. However, as the initial substrate concentration increased to 3825 mg L-1, the efficiency decreased to 72%, with a Coulombic efficiency of 13.56% and a power density of 262.34 mWm-2. Optical density levels increased due to bacterial growth at ambient temperature and neutral pH, reflecting the dynamic microbial response within the system.

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.

LX16 to simultaneously remove ammonia nitrogen, calcium, and chemical oxygen demand in reverse osmosis concentrates

In recent years, with the rapid development of industrial revolution and urbanization, the generation and treatment of a large number of salt-containing industrial wastewater has attracted wide attention. A novel salt-tolerant Zobellella denitrificans sp. LX16 with excellent nitrogen removal and biomineralization capabilities was isolated in this experiment. Kinetic experiments were conducted to determine the optimal condition. Under this condition, chemical oxygen demand (COD) can be entirely removed together with ammonia nitrogen, and the removal efficiency of calcium was 88.09%. Growth curves and nitrogen balance tests showed that strain LX16 not only had good HNAD and MICP capabilities, but also had high nitrite reductase and nitrate reductase activities during this process. Three-dimensional fluorescence results reflected that when external carbon sources were lacking or salinity was high, humic acid could effectively enhance the metabolic activity of heterotrophic nitrifying aerobic denitrifying microorganisms through extracellular electron transfer, and the substances produced in the metabolic process could promote biommineralization. Moreover, combined with SEM, SEM-EDS, XRD and FTIR analysis, it is concluded that the microbial surface can provide nucleation sites to form calcium salts, and with the increase of alkalinity to generate Ca5(PO4)3OH. The theoretical basis for the use of biological treatment in reverse osmosis wastewater have been proved by this experiment.

Characterizing and optimizing adsorption for olive mill wastewater processing in Loukkos, Morocco

The present research consists of studying the characterization and treatment of the olive mill wastewater (OMWW) resulting from the olive industries of the region of Loukkos, Morocco. According to the national plan for green Morocco, the annual volumes of OMWW discharges increase with the expansion of the areas of olive plantations compared to agricultural activities. The study of the organic, mineral, and microbiological composition of the obtained OMWW showed that they are rich in microbiological (FMAT, Let M., and B.L.), mineral (total Kjeldhal nitrogen, orthophosphate, total phosphorus, sodium, potassium, calcium, copper, iron, zinc, manganese, and lead ions), and organic (COD, BOD5, and polyphenols) micropollutants with very high percentages that are higher than the standards in force. The treatment used in this study is the combined process of aerated lagooning/adsorption using powdered activated carbon after optimization of the experimental parameters (mass concentration of activated carbon (AC) and agitation rapidity (Ar)) by experiment design method. The obtained physicochemical parameters, such as pH, total suspended solids (TSS), chemical oxygen demand (COD), rate of discoloration, and polyphenol content of raw OMWW, were 4.87, 0.63, 80.3, 0.8, and 1.45 g/l, respectively. The results of these parameters for the treated OMWW were obtained in the order of 6.10, 0.22, 28, 0.28, and 0.44 g/l for pH, TSS, COD, discoloration rate, and polyphenol content, respectively. These results show that the proposed treatment significantly reduced acidity, TSS, COD, discoloration rate, and polyphenol contents, with a performance of about 25.26, 65, 65.13, 65, and 69.65%, respectively. This indicates that there is significant performance in the processing of exploited OMWW.

Data fusion strategy based on ultraviolet-visible spectra and near-infrared spectra for simultaneous and accurate determination of key parameters in surface water

Chemical oxygen demand (COD), ammonia nitrogen (AN) and total nitrogen (TN) are the key parameters to reflect the degree of surface water pollution. Ultraviolet - visible (UV-Vis) spectroscopy and near - infrared (NIR) spectroscopy are ideal techniques for rapid monitoring of these indicators. In this study, a strategy based on the fusion of UV-Vis and NIR spectral data (UV-Vis-NIR) for water quality detection was proposed to further improve the quantitative analysis accuracy of spectroscopic methods. Seventy river samples with different levels of pollution were used for spectroscopic analysis. The UV-Vis-NIR fusion spectrum of each water sample was obtained by directly splicing sample's UV-Vis spectrum and NIR diffuse transmission spectrum. The UV-Vis-NIR fusion models were optimized through using different variable selection algorithms. The results show that the UV-Vis-NIR fusion models for surface water COD, AN and TN achieves better prediction results (the root mean square errors of prediction are 6.95, 0.195, and 0.466, respectively) than single-spectroscopic based models. Since better prediction performances were shown under different optimization conditions, the robustness of fusion models were also better than the single-spectroscopic based models. Therefore, the data fusion strategy proposed in this study has a promising application prospect for further accurate and rapid monitoring of surface water quality.

Electrochemical oxidation of tetrahydrofurfuryl acohol on boron-doped diamond anode: Influence of current density and electrolyte solution

Tetrahydrofurfuryl alcohol (THFA), a widely applied raw materials, intermediate and solvent in the fields of agricultural, industry (especially in nuclear industry), is a potentially hazardous and non-biodegradable pollutant in wastewater. In this study, the electrochemical degradation pathways of THFA by a boron-doped diamond (BDD) anode with different current density (jappl = 20, 40 and 60 mA cm-2) and electrolyte solution (KNO3, KCl and K2SO4) was carefully investigated. The results exhibit that high chemical oxygen demand (COD) removal and mineralization rates were achieved by rapid non-selective oxidation in electrolyte solutions mediated by hydroxyl radicals (∙OH) and active chlorine (sulfate) under constant current electrolysis. In-depth data analysis using the high performance liquid chromatography and liquid chromatography/mass spectroscopy, the underlying removal pathways of THFA in KNO3, KCl and K2SO4 electrolyte solutions are proposed according to the effect of different mineralization mechanisms.

Preparation and study of straw porous biochar with aromatic ring structure for adsorption performance and mechanism toward TNT red water

2,4,6-Trinitrotoluene (TNT) production processes generate a substantial amount of toxic wastewater. Therefore, it is crucial to identify efficient and sustainable methods for treating this wastewater. This paper explores the application of sustainable biomass-derived carbon produced from rice straw for the adsorption of 2,4,6-trinitrotoluene (TNT) red water. The rice straw-derived biochar (SBC) materials were synthesized by two-step reactions through hydrothermal carbonization and chemical activation with KOH. Characterization of the fabricated biochar was conducted using various techniques. Here, the chemical oxygen demand (COD) was used as an evaluation index for adsorption efficiency. The adsorption kinetics showed a good fit with the pseudo-second-order model, and the adsorption equilibrium was achieved in 30 min. The biochar's high surface area (1319 m2/g) and large pore volume (1.058 cm3/g) gave it a large adsorption capacity. The Langmuir model exhibited better correlation for equilibrium data analysis, with a maximum adsorption capacity of 173.9 mg/g at 298 K. The SBC was found to have a high removal effect over a wide pH range (from 1 to 13) and showed remarkable stability after undergoing five desorption-adsorption cycles using ethanol and acetone as eluent. The results provide a simple and low-cost method for the efficient treatment of TNT red water.

A new treatment step of bioelectrochemically treated leachate using natural clay adsorption towards sustainable leachate treatment

Standalone and combined leachate treatment mechanisms suffer from low treatment efficiencies due to leachate's complex, toxic, and recalcitrant nature. Bioelectrochemical system (BES) was used for the first time to investigate the treatment of leachate mixed wastewater (WW) (i.e., diluted leachate, DL) (DL ≈ L:WW = 1:4) to minimize these complexities. A natural clay (palygorskite) was used as adsorbent material for further treatment on the BES effluent (EBES) while using two different masses and sizes (i.e., 3 g and 6 g of raw crushed clay (RCC) and 75 μ of sieved clay (75 μSC)). According to bioelectrochemical performance, BES, when operated with low external resistance (Rext = 1 Ω) (BES 1), showed a high removal of COD and NH3-N with 28% and 36%, respectively. On the other hand, a high Rext (100 Ω, BES 100) resulted in low removal of NH3-N with 10% but revealed high COD removal by 78.26%. Moreover, the 6 g doses of 75 μSC and RCC showed the maximum COD removals of 62% and 38% and showed the maximum removal of NH3-N with an average range of 40% for both sizes. After efficient desorption, both clay sizes resulted in regeneration performance which was observed with high COD (75%) and NH3-N (34%) on EBES. Therefore, when BES and clay adsorption technique sequentially treated and achieved with combined removal of ~ 98% for COD and ~ 80% of NH3-N, it demonstrated an efficient treatment method for DL treatment.

Application of effective orifice jet length for treating SST effluent of STP by hydrodynamic cavitation

Advanced oxidation process in general and hydrodynamic cavitation, in particular, has emerged as a promising technology for the treatment of wastewater in the last few years as the process is energy-efficient and cost-effective. In this process, cavities are generated due to local pressure drops caused by constrictions. This work aimed to investigate the potential of hydrodynamic cavitation as a tertiary treatment to treat the secondary sedimentation tank effluent of a sewage treatment plant, with two laboratory-scale experimental setups having an orifice plate of a 1 mm diameter hole. The process dependency was estimated by optimizing inlet pressure (0.8 bar for setup I and 5 bar for setup II). Moreover, effective orifice jet length was varied to investigate the impact of fluid buoyancy force on expansion and collapse of a cavity on the chemical oxygen demand removal and disinfection potential. At L2 length (two-thirds of the original length), both setups can degrade the organic and inorganic pollutants to the maximum extent. With the optimum condition in setup II, maximum COD, TSS, and fecal coliform degradation were 80.47%, 62.83%, and 52.27%, respectively, compared to setup I.

A microbial flora with superior pollutant removal efficiency and its fermentation process optimization

Microbial flora plays an important role in microorganism-enhanced technology. The pollutant degradation ability and viable counts of these agents are crucial to guarantee their practical application. In this study, an efficient pollutant-degrading microbial flora was screened, its medium components and culture conditions were optimized, and its effect was verified in zeolite trickling filter towers. After a 24 h culture under the optimal conditions, the viable count reached 4.76 × 109 cfu/mL, with the degradation rates of ammonia nitrogen (NH4+-N), nitrate nitrogen (NO3--N), total nitrogen (TN), total phosphorus (TP), and chemical oxygen demand (COD) increased to 93.5%, 100%, 68.3%, 32.6%, and 85%, respectively. After optimizing the feeding strategy, the concentration of viable bacteria reached 5.80 × 109 cfu/mL. In the application effect verification experiment, the degradation rates of NH4+-N, TN, TP, and COD in the experimental group reached 96.69%, 75.18%, 73.82%, and 90.83%, respectively, showing a significant improvement compared to the results of the control group. The main components in the control group were Dokdonella, Brevundimonas, Alishewanella, Rhodobacter, Pseudoxanthomonas, and Thauera, whereas those in the experimental group were Dokdonella, Proteocatella, Rhodobacter, Dechlomonas, and Nitrospira. Proteocatella, Dechlomonas, and Nitrosra, which were unique to the experimental group, are common bacteria used for nitrogen and phosphorus removal. This explains the difference in the sewage treatment capacity between the two groups. This study provides an alternative sewage treatment microbial flora with a reasonable production cost and high degradation efficiency for NH4+-N, TN, TP, and COD.

Human and natural activities regulate organic matter transport in Chinese rivers

Rivers connect terrestrial and aquatic ecosystems and export approximately 55.47 % of the net terrestrial carbon fixation. However, due to unavailable high-frequency monitoring data, litter is known about diurnal variation in riverine carbon transport on a national scale. Based on daily measurements between March 2021 and February 2022 at 1491 stations across China, this study clarified the spatiotemporal variations in riverine organic matter indicated by chemical oxygen demand (COD). Spatially, COD content showed a spatial pattern with high values in the northwest (p < 0.05), and COD flux was determined by water discharge (84.01 %). Human activities explained 73.20 % of the spatial variations in riverine COD content; in particular, agricultural planting significantly elevated riverine COD (r = 0.73, p < 0.01). Seasonally, 95.53 % of stations showed significant seasonal variations in COD contents (p < 0.05); 69.72 % (25.81 %) were identified as Type II (III) typically had the maximum (minimum) COD in summer (autumn). Moreover, except for human activities (41.08 ± 22.94 %), natural factors also contributed 47.41 ± 24.04 % to the seasonal variations. In summer, high temperatures increased COD by promoting algal proliferation at Type II stations; however, heavy precipitation diluted COD contents at Type III stations. In these cases, seasonal measurements were essential for estimating riverine organic matter transport, especially the values measured in spring and winter. This study has significant implications for managing the aquatic environment, estimating riverine organic matter transport, and balancing the global carbon budget.

Sample Generation Method Based on Variational Modal Decomposition and Generative Adversarial Network (VMD-GAN) for Chemical Oxygen Demand (COD) Detection Using Ultraviolet Visible Spectroscopy

Ultraviolet visible spectroscopy can realize the detection of chemical oxygen demand (COD), especially for low concentration levels due to its high sensitivity, but the issue of insufficient real water sample data has always been a challenge owing to the low probability of occurrence of actual water pollution events. However, in existing methods, generated absorption spectra do not conform to actual situations as the former neglect the actual spectral characteristics. On the other hand, the diversity and complexity are restricted because the information in one-dimensional data is not enough for direct spectral generation. This study proposed a spectral sample generation method based on the variational modal decomposition and generative adversarial network (VMD-GAN). First, the VMD algorithm was utilized to separate principal components and residuals of absorption spectra. Among them, the GAN was used to generate new principal components to ensure that the major spectral characteristics of actual water samples are not lost. The corresponding residuals were then obtained by adjusting the parameters of a three-order Gaussian fitting function, which is more beneficial than the direct use of GAN in the aspect of diversity and complexity. Based on the spectral reconstruction with new principal components and residuals, various absorption spectra were generated more coincident with actual situations. Finally, the effectiveness of this method was evaluated by establishing regression models and predicting COD for actual water samples. In all, the insufficient water sample data can be expanded for a better performance in modeling and analysis of water pollution using the proposed method.

Empirical linkages of the construction sector, intensive energy consumption, and economic openness with chemical oxygen demand pollution

Though construction sector development and economic openness contribute to regional economic development, they have also been debated to pose some environmental challenges. Along these lines, we explored the long- and short-term connections of intensive energy consumption, economic openness, and construction sector development with the chemical oxygen demand throughout the scales of regional development of China's 30 provincial units over the 2004-2021 period. Theoretically, we contribute to the existing knowledge by incorporating chemical oxygen demand pollution, construction sector development, and economic openness to the Kaya identity's baseline framework. Empirically, we apply a series of advanced methods of panel data econometrics for robust results. Our key findings are as follows: First, we revealed a long-term stable cointegrating association among our variables of interest. Second, using the common correlated effect mean group estimator, we unfolded that the intensive energy consumption showed a chemical oxygen demand pollution reduction influence in both the long and short term, demonstrating the most substantial influence in the high regional development panel while expressing the least powerful influence the least regional development setting. Third, we unveiled that economic openness and construction sector development showed a linear chemical oxygen demand pollution enhancement influence in moderately and least developed regions. Nevertheless, both established an inverted U-shaped linkage with chemical oxygen demand pollution for the whole country as well as for high regional development data samples. Eventually, we found consistent estimates across long- and short-term investigations regarding signs of relationships; however, long-term effects remained more powerful than short-term ones. These findings would serve as factual scientific knowledge to help local as well as national governments create the optimal environmental regulations for the construction sector to achieve the sustainable development goals (SDGs), especially the Climate Action Plan (i.e., SDG-13).

Removal of chemical oxygen demand and ammonia nitrogen from high salinity tungsten smelting wastewater by one-step electrochemical oxidation: From bench-scale test, pilot-scale test, to industrial test

In recent years, electrochemical oxidation (EO) shows the characteristics of green and high efficiency in removing chemical oxygen demand (COD) and ammonia nitrogen (NH₃-N) from wastewater, which has been favored by researchers. However, at present, most of current studies on EO remain in laboratory stage, reports about pilot-scale or even industrial tests with large treatment capacity are few, which slowing down the use of the advanced technology to practical application. In this study, bench-scale tests, pilot-scale tests (treatment capacity 200-500 L/h), and industrial tests (treatment capacity 100 m³/h) were carried out by EO technology in view of the characteristics of tungsten smelting wastewater (TSW) with high salinity (NaCl), COD, and NH₃-N. Results showed that the removal of COD and NH₃-N was a competitive reaction in the EO process, and COD could be removed more preferentially than NH₃-N. When NH₃-N content was low, the influent pH had a minimal effect on its removal, and when NH₃-N content was high, increasing the influent pH was beneficial to its removal. Industrial tests showed that the one-step removal of COD and NH₃-N in TSW met the standard, and the power consumption per cubic meter of wastewater was only 4.2 kW h, and the treatment cost was much lower than the two-step process of "breaking point chlorination to remove NH₃-N and adding oxidant to remove COD". This study has successfully realized industrial application of EO technology in TSW treatment for the first time and provided a successful case, which is helpful to accelerate the popularization and application of this technology in the field of high salinity organic ammonia nitrogen wastewater treatment.

Efficient methane production from anaerobic co-digestion of poultry litter with wheat straw in daily sequencing batch reactor: Effects of carbon-to-nitrogen ratio, total solids, and hydraulic retention time

This study performed co-digestion of poultry litter (PL) with wheat straw in the daily anaerobic sequencing batch reactor considering operation parameters of carbon-to-nitrogen ratio (C/N, 11.6 to 28.4), total solids (TS, 2.6 to 9.4%), and hydraulic retention time (HRT, 7.6 to 24.4d). The inoculum with a diverse microbial community structure included 2% of methanogens (Methanosaeta) was chosen. Experimental performance by central composite design showed continuous methane production with the highest biogas production rate (BPR) obtained at C/N = 20, TS = 6%, and HRT = 7.6d, being (1.18 ± 0.14 L/L_R/d). A significant modified quadratic model (p < 0.0001) for predicting BPR was built (R²= 0.9724). The operation parameters and process stability both affected the release of nitrogen, phosphorus, and magnesium in the effluent. The results provided new support for the novel reactor operations for efficient bioenergy production from PL and agricultural wastes.

Green metal oxides coated biochar nanocomposites preparation and its utilization in vertical flow constructed wetlands for reactive dye removal: Performance and kinetics studies

Major causes of water pollution in the ecosystem are pollutants such as dyes which are noxious. The present study was based on the synthesis of the green nano-biochar composites from cornstalk and green metal oxide resulting in Copper oxide/biochar, Zinc oxide /biochar, Magnesium oxide/biochar, Manganese oxide/biochar, biochar for removal of dyes combined with the constructed wetland (CW). Biochar Augmentation in constructed wetland systems has improved dye removal efficiency to 95% in order of copper oxide/biochar > Magnesium oxide/biochar > Zinc oxide/biochar > Manganese oxide/biochar > biochar > control (without biochar) respectively in wetlands. It has increased the efficiency of pH by maintaining pH 6.9-7.4, while Total Suspended Solids (TSS) removal efficiency and Dissolved oxygen (DO) increased with the hydraulic retention time of about 7 days for 10 weeks. Chemical oxygen demand (COD) and colour removal efficiency increased with the hydraulic retention time of 12 days for 2 months and there was a low removal efficiency for total dissolved solids (TDS) from control (10.11%) to Copper oxide /biochar (64.44%) and Electrical conductivity (EC) from control (8%) to Copper oxide /biochar (68%) with the hydraulic retention time of about 7 days for 10 weeks. Colour and chemical oxygen demand removal kinetics followed second and first-order kinetic. A significant growth in the plants were also observed. These results proposed the use of agricultural waste-based biochar as part of a constructed wetland substratum can provide enhanced removal of textile dyes. That can be reused.

A state of the art review on the co-cultivation of microalgae-fungi in wastewater for biofuel production

The microalgae have a great potential as the fourth generation biofuel feedstock to deal with energy crisis, but the cost of production and biomass harvest are the major hurdles in terms of large scale production and applications. Using filamentous fungi to culture targeted alga for biomass accumulation and eventually harvesting is a sustainable way to mitigate environmental impacts. Microalgal co-culture method could be an alternative to overcome limitations and increase biomass yield and lipid accumulation. It was found to be the high feasibility for the production of biofuels from fungi and microalgae using wastewater. This article aimed to state the synergistic approaches, their culture protocols, harvesting procedure and their potential biotechnological applications. Additionally, algal-fungal consortia could digest cellulosic biomass, potentially reducing operating costs as part of industrial need. As a result of co-cultivation, biofuel production could be economically feasible owing to its excellent ability to treat wastewater and be eco-friendly. The implications of the innovative co-cultivation technology have demonstrated the potential for further development based on the policies that have been supported and implemented.

Co-composting poultry carcasses with wood-based, distillers' grain and cow manure biochar to increase core compost temperatures and reduce leachate's COD

Composting has been recognized as a viable method to dispose of animal carcasses. Common concerns related to the composting process include low core temperatures, leachate generation, and ammonia emissions. This study tested co-composting full-size poultry carcasses with commercially available biochars at an aeration rate of 0.8 L∙min^-1. Biochars prepared by gasifying wood pallets, distillers' grains, and cow manure were added to the composting bins at the 13% rate (by volume). Results showed that poultry carcasses with wood-based and cow manure biochar increased temperatures by 2.0 to 3.3 °C. All biochar-amended bins met the time-temperature criteria to eliminate avian influenza (H7N1) viruses, which could not be achieved without biochar addition. Wood-based biochar amendment lowered the cumulative chemical oxygen demand of the leachate samples by 87% (P = 0.02). At the rate studied, the biochar amendment did not significantly affect ammonia emissions (P = 0.56). BET surface area of wood-based biochar was 1.4 and 28 times greater than that of cow manure and distillers' grain biochar, respectively. Compared to no biochar addition, wood-based biochar resulted in significantly higher compost temperatures (P = 0.02), lower leachate COD values (P = 0.02), and a higher total nitrogen content (P = 0.01) while it did not cause an increase in sodium content (P = 0.94) of the finished compost. In conclusion, amending the poultry carcass composting process with wood-based biochar (13% by volume) is recommended, especially to eliminate disease-causing agents.

Converting synthetic azo dye and real textile wastewater into clean energy by using synthesized CuO/C as photocathode in dual-photoelectrode photocatalytic fuel cell

Cathode in photocatalytic fuel cell (PFC) plays a crucial role in degradation of organic contaminants. In this study, synthesized copper oxide (CuO) was loaded on carbon plate and used as photocathode in PFC for degradation of synthetic azo dye Reactive Black 5 (RB5) and real textile wastewater. Morphology and structural phase of the synthesized CuO were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. Several operating parameters had been investigated such as light irradiation, initial dye concentration, and pH of azo dye solution within 6 h of irradiation time. The lowest initial concentration of RB5 (10 mg L^-1) achieved 100% color removal compared to the highest initial concentration (40 mg L^-1) which only achieved 77.1% color removal within 6 h of irradiation time. The influence of external resistance was significant in electricity generation but trivial in dye degradation efficiency. The external resistance of 6000 Ω yielded highest maximum power density, with P_max of 0.2631 μW cm^-2, followed by 1000 Ω (0.2196 μW cm^-2) and 8000 Ω (0.1587 μW cm^-2), respectively. The real textile wastewater with dilution ratio (DR) 1:6 yielded the highest energy conversion efficiency, η (3.62%), followed by DR 1:4 (3.19%) and DR 1:2 (1.96%), respectively.

Removal of methylene blue and azo reactive dyes from aqueous solution and textile effluent via modified pulsed low-frequency ultrasound cavitation process

Organic dyes in the aqueous solutions and textile effluents cause severe environmental pollution due to their carcinogenic and mutagenic nature. Ultrasound (US) cavitation is one of the promising advanced oxidation processes (AOP) to remove the organic dyes from the aqueous solutions and textile effluents. Nevertheless, the conventional low-frequency US cavitation process exhibits very low efficiency in the dye removal process and demands effective modification to improve its performance. In this investigation, a conventional pulsed low-frequency (22 ± 2 kHz) US cavitation process has been modified by varying the US power (50-150 W), initial solution pH (2-10), and O₂ flow rate (1-4 L min^-1) to enhance the decomposition of cationic methylene blue (MB) dye in an aqueous solution. The operation of the classic Haber-Weiss reaction, both in the forward and backward directions, and the ozone effect have been observed, for the first time, under the modified US cavitation process, as confirmed via the radical trapping experiments. Moreover, the hydrothermally synthesized hydrogen titanate (H₂Ti₃O₇) nanotubes (HTN) have been utilized as sonocatalyst, for the first time, for 100% dye removal, with effective regeneration obtained via an in-situ thermal activation of persulfate (PS, S₂O₈^2-). The most optimum values of US power, initial solution pH, O₂ flow rate, HTN, and PS concentrations for 100% MB decomposition are observed to be 150 W, 2, 2 L min^-1, 0.3 g L^-1, and 10 mM, respectively. The decomposition of industrial azo reactive dyes in an aqueous solution as well as in a textile effluent has also been demonstrated using a modified pulsed low-frequency US cavitation process involving the thermal activation of PS without the use of HTN, which justifies its suitability for a commercial application.

Evolving tolerance of Yarrowia lipolytica to hydrothermal liquefaction aqueous phase waste

Hydrothermal liquefaction (HTL) is an emerging method for thermochemical conversion of wet organic waste and biomass into renewable biocrude. HTL also produces an aqueous phase (HTL-AP) side stream containing 2-4% light organic compounds that require treatment. Although anaerobic digestion (AD) of HTL-AP has shown promise, lengthy time periods were required for AD microbial communities to adapt to metabolic inhibitors in HTL-AP. An alternative for HTL-AP valorization was recently demonstrated using two engineered strains of Yarrowia lipolytica, E26 and Diploid TAL, for the overproduction of lipids and the polyketide triacetic acid lactone (TAL) respectively. These strains tolerated up to 10% HTL-AP (v/v) in defined media and up to 25% (v/v) HTL-AP in rich media. In this work, adaptive laboratory evolution (ALE) of these strains increased the bulk population tolerance for HTL-AP to up to 30% (v/v) in defined media and up to 35% (v/v) for individual isolates in rich media. The predominate organic acids within HTL-AP (acetic, butyric, and propionic) were rapidly consumed by the evolved Y. lipolytica strains. A TAL-producing isolate (strain 144-3) achieved a nearly 3-fold increase in TAL titer over the parent strain while simultaneously reducing the chemical oxygen demand (COD) of HTL-AP containing media. Fermentation with HTL-AP as the sole nutrient source demonstrated direct conversion of waste into TAL at 10% theoretical yield. Potential genetic mutations of evolved TAL production strains that could be imparting tolerance were explored. This work advances the potential of Y. lipolytica to biologically treat and simultaneously extract value from HTL wastewater. KEY POINTS: • Adaptive evolution of two Y. lipolytica strains enhanced their tolerance to waste. • Y. lipolytica reduces chemical oxygen demand in media containing waste. • Y. lipolytica can produce triacetic acid lactone directly from wastewater.

Anthropogenic impact on long-term riverine CODMn, BOD, and nutrient flux variation in the Pearl River Delta

In the Pearl River Delta (PRD), population growth and economic development have steadily increased the anthropogenic nutrient discharge into coastal waters. In this study, we employed the observed concentration and model reproduced runoff to quantify the interannual variation and the long-term (1985-2021) trends in riverine chemical oxygen demand (COD_Mn), biochemical oxygen demand (BOD), and nutrient fluxes. The annual COD_Mn and BOD fluxes increased slightly between 1999 and 2021. In comparison, the mean annual dissolved inorganic nitrogen (DIN) fluxes of the four eastern outlets increased significantly from 2.05 × 10⁵ t/a in 1985-1995 to 3.11 × 10⁵ t/a in 1999-2011 and then to 3.91 × 10⁵ t/a in 2014-2021. The outlets with the largest contributions to the COD_Mn, BOD, and DIN fluxes were Humen and Modaomen, which are both located near large cities. By calculating the COD_Mn fluxes upstream of the PRD, we found that the COD_Mn fluxes from downstream in the PRD increased faster than the fluxes from upstream. It follows that the increase in COD_Mn at outlets was mostly driven by the contributions of downstream major cities. In addition, the proportion of ammonia nitrogen flux in the DIN flux decreased from over 50 % to under 10 % at most outlets. This indicates that the toxicity of DIN fluxes has been mitigated. The DIN fluxes also showed a positive correlation with surface chlorophyll a and a negative correlation with bottom dissolved oxygen outside the Pearl River Estuary (PRE). This implies that the changes in phytoplankton growth and oxygen levels outside the PRE are closely linked to the variation in river-delivered nutrients, and the increasing riverine nutrient input may result in the expansion of intensified low-oxygen conditions outside the PRE.

Effects of synthesized AlFe2O4 and MgFe2O4 nanoparticles on biogas production from anaerobically digested sugar refinery wastewater

The application of magnetic nanoparticles (MNPs) toward sustainable water economy and bioenergy production has become a subject of great interest. Anaerobic digestion (AD) has been widely exploited in wastewater treatment settings, whereby utilization of MNP additives by microorganism response for degradation of organics into biogas is seen to be eco-friendly and economically viable. The present study investigated the impact of two synthesized MNPs such as aluminum ferrite (AlFe₂O₄) and magnesium ferrite (MgFe₂O₄) on biogas production via biochemical methane potential (BMP) tests. A BMP set-up of three (3) bioreactors was tested with a working volume of 0.8 L which comprises 0.5 L wastewater (WW) and 0.3 L activated sludge (AS) with 1.5 g of the MNPs and a control system without MNPs. The degradation of chemical oxygen demand (COD) was increased with set-ups that contained MNPs as compared to the control system, MgFe₂O₄ (93.96%) > AlFe₂O₄ (85.95%) > control (68.83%). In terms of biogas production, the methane yield was also recorded as MgFe₂O₄ (85.7%) > AlFe₂O₄ (84.3%) > control (65.7%). The physical and chemical stability of MNPs makes them more advantageous for application in biogas production. In the prospects of biogas enhancement and biodegradability, integrating MNPs in an anaerobic digestion system will result in a more efficient anaerobic process performance for biogas production.

Sustainable ceramic membrane for decontamination of water: A cost-effective approach

A sustainable ceramic membrane embedded with silver has been developed using quartz, kaolin and calcium carbonate. All the chemicals involved in this process were commonly available, non-toxic and cheap. The process was very simple, convenient and does not involve any wastage of water. Decoration of silver particles onto the porous ceramic membrane with the help of APTES as a connecting molecule leads to the formation of a durable material having strong antibacterial capacity. The fabricated membrane holds wide pore morphology with pore size of 4.4 μm and average porosity of 19.5% with an estimated cost of fabrication of about 60 dollar/m². The membrane was found capable in reducing the TDS, BOD and COD of water samples that confirms that it is efficient for water treatment applications.

A hybrid remote sensing approach for estimating chemical oxygen demand concentration in optically complex waters: A case study in inland lake waters in eastern China

Chemical oxygen demand concentration (C_COD) is widely used to indicate the degree of organic pollution of lakes, reservoirs and rivers. Mastering the spatiotemporal distribution of C_COD is imperative for understanding the variation mechanism and controlling of organic pollution in water. In this study, a hybrid approach suitable for Sentinel 3A/Ocean and Land Colour Instrument (OLCI) data was developed to estimate C_COD in inland optically complex waters embedding the interaction between C_COD and the absorption coefficients of optically active constituents (OACs). Based on in-situ sampling in different waters, the independent validations of the proposed model performed satisfactorily in Lake Taihu (MAPE = 23.52 %, RMSE = 0.95 mg/L, and R² = 0.81), Lake Qiandaohu (MAPE = 21.63 %, RMSE = 0.50 mg/L and R² = 0.69), and Yangtze River (MAPE = 29.34 %, RMSE = 0.83 mg/L, and R² = 0.64). In addition, the approach not only showed significant superiority compared with previous algorithms, but also was suitable for other common satellite sensors equipped same or similar bands. The hybrid approach was applied to OLCI images to retrieve C_COD of Lake Taihu from 2016 to 2020 and reveals substantial interannual and seasonal variations. The above results indicate that the proposed approach is effective and stable for studying spatiotemporal dynamic of C_COD in optically complex waters, and that satellite-derived products can provide reliable information for lake water quality management.

Environmental application of a cost-effective smartphone-based method for COD analysis: Applicability in the electrochemical treatment of real wastewater

This study aims to develop a cheap method for the evaluation of quality of water or the assessment of the treatment of water by chemical oxygen demand (COD) measurements throughout the use of the HSV color model in digital devices. A free application installed on a smartphone was used for analyzing the images in which the colors were acquired before to be quantified. The proposed method was also validated by the standard and spectrophotometric methods, demonstrating that no significant statistical differences were attained (average accuracy of 97 %). With these results, the utilization of this smartphone-based method for COD analysis was used/evaluated, for first time, by treating electrochemically a real water matrix with substantial organic and salts content using BDD and Pt/Ti anodes. Aiming to understand the performance of both anodes, bulk experiments were performed under real pH by applying current densities (j) of 15, 30, and 60 mA cm^-2. COD abatement results (which were achieved with this novel smart water security solution) clearly showed that different organic matter removal efficiencies were achieved, depending on the electrocatalytic material used as well as the applied current density (42 %, 45 %, and 85 % for Ti/Pt while 93 %, 97 % and total degradation for BDD by applying 15, 30, and 60 mA cm^-2, respectively). However, when the persulfate-mediated oxidation approach was used, with the addition of 2 or 4 g Na₂SO₄ L^-1, COD removal efficiencies were enhanced, obtaining total degradation with 4 g Na₂SO₄ L^-1 and by applying 15 mA cm^-2. Finally, this smartphone imaging-based method provides a simple and rapid method for the evaluation of COD during the use of electrochemical remediation technology, developing and decentralizing analytics technologies for smart water solutions which play a key role in achieving the Sustainable Development Goal 6 (SDG6).

Application of a membrane-less air cathode microbial fuel cell to treat municipal waste composting leachate

The adverse effects of high strength wastewaters on the microbial activities have created a challenge to biological treatments. Microbial fuel cell has been considered as a promising process because the electrical potential generation can stimulate microorganisms and overcome the inhibitory effect. However, several issues (e.g., scalability, high costs and maintenance) have prevented the process from the industrial applications. Elimination of the proton exchange membrane has been suggested as a remedy to the mentioned problems. In this work, a membrane-less microbial fuel cell was modified by putting the cathode within a thin sand layer (instead of the proton exchange membrane) to treat a high strength wastewater sample. The influences of the feed organic load and time of treatment in the modified system were studied in batch and continuous operations. It was revealed that the batch operation efficiency was higher for the lower feed loadings as a 5-day batch treatment removed 66 ± 4% of the 15,000 ± 500 mg/L initial chemical oxygen demand while the continuous process efficiency with 9-day hydraulic residence time was slightly more than 50%. However, the efficiency of the continuous operation for treatment of higher initial loading values was better than the batch mode with the removal efficiency of 41 ± 2% versus 12 ± 2% for a more concentrated leachate feed (45,000 ± 1000 mg/L). Finally, it was disclosed that the modified membrane-less MFC employed in this work can be effective in treatment of high strength wastewaters in larger scales with lower costs.

Heterogeneous electro-Fenton using three-dimension Fe-Co-Bi/kaolin particle electrodes for degradation of quinoline in wastewater

Wastewater containing quinoline has become a common pollutant in water and soil environments, which poses a threat to human health due to its carcinogenicity, teratogenicity, and mutagenicity. Quinoline's stability and toxicity hinders its degradation by conventional physicochemical and biological methods. In this contribution, Fe-Co-Bi/kaolin particle electrodes were prepared for the efficient degradation of quinoline in wastewater, and characterized by using scanning electron microscope, X-ray diffraction, pyridine-IR, Brunauer-Emmett-Teller, X-ray photoelectron spectroscopy, and four-probe resistivity test. Parameters affecting the degradation efficiency were optimized to be the particle electrode dosage of 40 g/L, pH 3.5, H₂O₂ addition of 67.6 mmol/L, electrical conductivity of 12.7 ms/cm, and voltage of 20 V. The constructed three-dimensional catalytic particle electrode system (3D-CPE) achieved 92.1% removal rate of chemical oxygen demand (COD) under the optimal conditions. Hydroxyl radicals (•OH) generated in the 3D-CPE process were identified by radical scavenging tests and electron spin response analysis. To unravel the degradation mechanism, the intermediate products were identified by using high performance liquid chromatography-mass spectrometry. The degradation mechanism was discussed with the help of theoretical calculation.

Recent progress in microbial fuel cells using substrates from diverse sources

Increasing untreated environmental outputs from industry and the rising human population have increased the burden of wastewater and other waste streams on the environment. The most prevalent wastewater treatment methods include the activated sludge process, which requires aeration and is, therefore, energy and cost-intensive. The current trend towards a circular economy facilitates the recovery of waste materials as a resource. Along with the amount, the complexity of wastewater is increasing day by day. Therefore, wastewater treatment processes must be transformed into cost-effective and sustainable methods. Microbial fuel cells (MFCs) use electroactive microbes to extract chemical energy from waste organic molecules to generate electricity via waste treatment. This review focuses use of MFCs as an energy converter using wastewater from various sources. The different substrate sources that are evaluated include industrial, agricultural, domestic, and pharmaceutical types. The article also highlights the effect of operational parameters such as organic load, pH, current, and concentration on the MFC output. The article also covers MFC functioning with respect to the substrate, and the associated performance parameters, such as power generation and wastewater treatment matrices, are given. The review also illustrates the success stories of various MFC configurations. We emphasize the significant measures required to fill in the gaps related to the effect of substrate type on different MFC configurations, identification of microbes for use as biocatalysts, and development of biocathodes for the further improvement of the system. Finally, we shortlisted the best performing substrates based on the maximum current and power, Coulombic efficiency, and chemical oxygen demand removal upon the treatment of substrates in MFCs. This information will guide industries that wish to use MFC technology to treat generated effluent from various processes.

Autochthonous sources and drought conditions drive anomalous oxygen-consuming pollution increase in a sluice-controlled reservoir in eastern China

Freshwater reservoirs are an important type of inland waterbody. However, they can suffer from oxygen-consuming pollution, which can seriously threaten drinking water safety and negatively impact the health of aquatic ecosystems. Oxygen-consuming pollutants originate from both allochthonous and autochthonous sources, and have temporally and spatially heterogeneous drivers. Datanggang Reservoir, China, is located in a small agricultural watershed; it is controlled by multiple sluice gates. Anomalously high oxygen consumption indicators were observed in this reservoir in March 2021. Here, it was hypothesized that autochthonous sources were the primary drivers of oxygen-consuming pollution in the reservoir under drought conditions. Datasets of water quality, precipitation, primary productivity, and sediment were used to analyze water quality trends in the reservoir and inflow rivers, demonstrating the effects of allochthonous inputs and autochthonous pollution. No correlation was found between reservoir oxygen consumption indicators and allochthonous inputs; reservoir oxygen consumption indicators and chlorophyll-a concentration were significantly positively correlated (p < 0.05). Substantially lower precipitation and higher water temperature and pH (compared to historical levels) were also observed before the pollution event. Therefore, during this period the hydrological conditions, water temperature, pH, and other variables caused by short-term drought conditions may have facilitated phytoplankton growth in the reservoir. This contributed to a large increase in autochthonous oxygen-consuming pollutants, as reflected by the abnormally high indicators. Sediments contaminated with organic matter may also have been an important contributor. As the effects of environmental management and pollution control continue to emerge, exogenous pollutants imported from the land to reservoirs are currently effectively controlled. However, endogenous pollutants driven by a variety of factors, such as meteorology and hydrology, will likely become the main drivers of short-term changes in oxygen-consuming pollution in freshwater reservoirs in the foreseeable future.

Controlling the formation of halogenated byproducts in the chlorination of source waters by oxidative pre-treatment with the Fe(II)/Fe(III)-S(IV)-air system

Breakpoint chlorination is a generally accepted method for removing ammonium ion from source waters in drinking water treatment technologies. This process is often accompanied by the formation of halogenated organic byproducts. The presence of these compounds in potable water is of primary concern. In this paper, we demonstrate that the concentration of the precursors of the halogenated species can sufficiently be decreased by oxidizing the organic pollutants with the Fe(II)/Fe(III) - S(IV) - air system. Pre-oxidative treatment of the source waters results in a substantial reduction of chemical oxygen demand, while the ammonium ion concentration remains unaffected. The breakpoint chlorination produces substantially less trihalomethanes (THMs) and adsorbable halogenated organic compounds (AOXs) in oxidatively pre-treated source waters than in raw waters. These results offer a possibility to improve drinking water treatment technologies for better controlling the formation of antagonistic byproducts. It is demonstrated that reaching the regulated concentration levels of THMs is feasible with this method even in source waters containing organic pollutants at relatively high concentration levels. The main advantage of the procedure is that the reagents used for the oxidative pre-treatment are converted into non-toxic products (Fe(III) and SO₄^2-) by the end of the process.

Estimation of chemical oxygen demand in different water systems by near-infrared spectroscopy

To monitor environmental water pollution effectively and meet human water needs, it is crucial to develop a fast, simple, and accurate method for monitoring chemical oxygen demand (COD) in various water systems. In this study, COD prediction models for different water systems were developed by combining near-infrared (NIR) spectroscopy with partial least squares regression (PLSR). Samples of wastewater, surface water, and seawater were collected from Guangzhou, Guangdong Province, China. Three pretreatment methods were used to preprocess the spectra in order to improve the accuracy and minimalism of the model. We investigate the performance of two variable selection algorithms, namely, binary gray wolf optimization (BGWO) and competitive adaptive reweighting sampling (CARS). The results show that both BGWO and CARS improved the performance of the model in terms of higher accuracy and less wavelength input; both of the combined model performances were better than that of PLSR alone, and CARS-PLSR achieved the best results. Using CARS-PLSR, surface water, wastewater, and seawater model inputs were reduced by 96 %, 96 %, and 82 % as compared to the PLSR results, respectively, and the testing sets R² reached 0.860, 0.815, and 0.692, respectively. The spectral variable selection algorithm could identify the important spectral variables between COD content and NIR spectra in three water systems, thereby improving the accuracy and simplicity of the PLSR model for COD prediction. Our results have important practical value for predicting COD content in different water systems by NIR spectroscopy.

Monitoring and assessment of Dracaena-based constructed vertical flow wetlands treating textile dye wastewater

The monitoring and assessment of multiple constructed vertical flow wetlands (CVFWs) treating textile dye wastewater (metanil yellow as dye) are studied covering three seasons. Three CVFWs (CVFW-1, dye-5 mg/l; CVFW-2, dye-50 mg/l; and CVFW-3, dye-100 mg/l) and a control (dye-5 mg/l) were used. The CVFWs with Dracaena (an ornamental plant) efficiently removed contaminants like dye, COD, NH₄⁺-N, and PO₄^3--P from the wastewater under varying inlet dye concentrations, indicating its dependence on meteorological conditions. Substantial dye removal was observed to be maximum in summer (control, 44.3%; CVFW-1, 75.1%; CVFW-2, 76.1%; CVFW-3, 46%), but lesser in winter (control, 45%; CVFW-1, 73.1%; CVFW-2, 76.8%; CVFW-3, 42.6%) and minimum in monsoon (control, 40.8%; CVFW-1, 63.5%; CVFW-2, 51.6%; CVFW-3, 37.1%), respectively. Efficiency was less in CVFW-3 as it observed plant stress due to higher inlet dye concentration. COD removal was higher in winter, followed by summer and monsoon. A first-order kinetic model was used to investigate the efficiency of the CVFW system w.r.t. contaminant removal. Various functional groups were characterized using Fourier transform infrared spectroscopy (FTIR) from the inlet and outlet water samples of different CVFWs. The Dracaena accumulated various elements and oxides during the treatment with no stress on its health. No effects on plant health highlight the suitability of Dracaena for textile wastewater treatment. The results were validated using statistical tools like the Mann-Whitney U test and principal component analysis (PCA).

Integrated approach of photo-assisted electrochemical oxidation and sequential biodegradation of textile effluent

Synthetic azo dyes are extensively used in the textile industries, which are being released as textile effluent into the environment presence of azo dyes in the environment is great environmental concern therefore treatment of textile effluent is crucial for proper release of the effluent into the environment. Electrochemical oxidation (EO) is extensively used in the degradation of pollutants because of its high efficiency. In this study, photo-assisted electrooxidation (PEO) followed by biodegradation of the textile effluent was evaluated. The pretreatment of textile effluent was conducted by EO and PEO in a tubular flow cell with TiO₂-Ti/IrO₂-RuO₂ anode and titanium cathode under different current densities (10, 15, and 20 mA cm^-2). The chemical oxygen demand level reduced from 3150 mg L^-1 to 1300 and 600 mg L^-1under EO and PEO, respectively. Furthermore, biodegradation of EO and PEO pretreated textile effluent shows reduction in chemical oxygen demand (COD) from 1300 mg L^-1 to 900 mg L^-1and 600 mg L^-1to 110 mg L^-1, respectively. The most abundant genera were identified as Acetobacter, Achromobacter, Acidaminococcus, Actinomyces, and Acetomicrobium from the textile effluent. This study suggests that an integrated approach of PEO and subsequent biodegradation might be an effective and eco-friendly method for the degradation of textile effluent.

Synchronous bio-degradation and bio-electricity generation in a Microbial Fuel Cell with aged and fresh leachate from the identical subtropical area

Seasonal leachate from both sealed and operating landfill in the identical district were employed as the sole substrate in the Microbial Fuel Cell (MFC) to evaluate the power output performance and aqueous organic waste disposal. The electrical performance was characterized to study the power generation, while the Chemical Oxygen Demand (COD) removal ratio and Coulombic Efficiency (CE) were calculated to illustrate the substrate disposal effect. In addition, Scanning Electron Microscope (SEM) on the operated anode was conducted to preliminarily explain the microbial community difference, and the phylogenetic tree constructed on the cultivated microorganism was an insight into the dominant bacteria suitable for leachate degradation. It was found that the MFCs inoculated with seasonal leachate from both sealed and operating landfill could generate electricity successfully. Although the fresh leachate-inoculated MFCs had better electrical output performance (22.7-25.6 W/m³ versus 6.61-7.48 W/m³) and COD removal efficiency (55.8%∼61.7% versus 47.7%∼51.4%), the CEs were only 4.3%∼7.6%, which were lower than the aged leachate inoculated group (5.9%∼11.3%). Based on the SEM images and the phylogenetic tree of the operated anode, the composition impacts on the microbial community and power output performance were verified, which was instructive for the leachate disposal in the MFC.

Electrocoagulation treatment of raw palm oil mill effluent: Optimization process using high current application

In the electrocoagulation wastewater treatment process, extremely polluted water treatment requires an effective technique, and using high current is one of those. This study aims to optimize electrocoagulation parameters such as operation time, electrodes gap and the initial pH by applying high current intensity to treat palm oil mill effluent (POME) via Box-Behnken design (BBD) method. Chemical oxygen demand (COD), biological oxygen demand (BOD), and suspended solids (SS) were used as the response variables in the quadratic polynomial model. Most of the selected models in the analysis of variance (ANOVA) have shown significant results. A high connection between the parameters and dependent variables was surprisingly discovered in this study which the obtained value of R² for removal percentage of COD, BOD and SS were 0.9975, 0.9984 and 0.9979 respectively. Optimal removal was achieved at 19.07 A of current intensity (equivalent to 542 mA/cm² of current density), 44.97 min of treatment time, 8.60 mm of inter-electrode distance and 4.37 of pH value, resulted in 97.21%, 99.26% and 99.00% of COD, BOD and SS removal respectively. This optimized scheme of operating parameters combination offers an alternate choice for enhancing the treatment efficiency of POME and also can be a benchmark for other researchers to treat highly polluted wastewater.

Improved water quality monitoring indicators may increase carbon storage in the oceans

Indicators related to organic matter are important when assessing aquatic environment quality. The chemical oxygen demand (COD) is widely used as a water quality reference. However, oxidizing agents used to determine the COD can oxidize refractory organic matter that is not pollutant and can persist in the ocean for thousands of years. This means the COD can misrepresent the water quality. The actual water quality can be indicated better by the biochemical oxygen demand (BOD) than the COD, but determining the BOD is time-consuming and gives variable results. In this study, the optical properties of dissolved organic matter in water samples from the Chinese coast that had been incubated for a long time or directly oxidized using COD oxidant were analyzed. The results indicated that the oxidizing agent rapidly oxidized 22.93% ± 4.96% of refractory dissolved organic matter (RDOM) that was resistant to microbial degradation, implying that RDOM made a marked contribution to the COD. Meanwhile, size-fractional fluorescence spectroscopy and COD measurements indicated that the COD of the >0.7 μm fraction and the fluorescence intensity of the protein-like component significantly positively correlated with the BOD of the bulk sample. This indicated that, for monitoring organic pollutants in coastal waters, the COD of the >0.7 μm fraction could be used as a proxy for the standard COD and that the fluorescence intensity of the protein-like component could be used as a convenient proxy for the BOD. The method can help retain recalcitrant organic matter in seawater to act as a carbon sink.

Propositure of maximum permissible limits for environmental assessment and classification of materials stabilized by solidification incorporated with oil waste

In the present work, oil sludge was subjected to the process of stabilization by solidification, the objective was to indicate maximum permissible limits of chemical demand for oxygen and oils and greases to evaluate the resulting material. A factorial design was used with the addition of three repetitions at the central point, to evaluate the performance of different percentage of residue and different curing times. The factors adopted were the percentage of oil sludge and the curing time. This material was evaluated using contaminants immobilization tests. From the leached and solubilized liquid, the concentration of the contaminants was determined and the environmental assessment was also carried out through the analysis of chemical demand for oxygen and oils and greases. One of the contributions of this work was to propose the maximum allowable limit for chemical oxygen demand, which is 1,000 (one thousand) milligrams per litre and, for oil and grease content, 100 (one hundred) milligrams per litre, both for the leaching test. For the solubilization test, 10 (ten) milligrams per litre were proposed for chemical oxygen demand and 1 (one) milligrams per litre for the oil and grease content. It was observed that the best results are obtained, when lower values of percentage of oil sludge were used and longer cure time. This work allows to affirm that the proposal of limits of environmental evaluation contributes to assure an adequate disposition and use of the cement matrix, that is the final product of the oily residue stabilized by solidification.

A shift from chemical oxygen demand to total organic carbon for stringent industrial wastewater regulations: Utilization of organic matter characteristics

From 2022, industrial wastewater discharge regulations in South Korea will replace chemical oxygen demand (COD_Mn) with total organic carbon (TOC). A shift from COD_Mn to TOC is a pioneering change in protecting water bodies from organic contaminants. However, several industries are struggling to meet these TOC requirements even though their effluents met the COD_Mn limits. Effluent COD_Mn/TOC ratios (1.28 ± 0.64) found in our study were lower than the COD_Mn/TOC coefficients (1.33-1.80) suggested by the Ministry of Environment in South Korea. Aliphatic and particulate organic matter contents in effluents likely influenced the COD_Mn/TOC ratio. Regardless of the industrial category, dissolved organic carbon often consists of low molecular weight neutrals, hydrophobic organic carbon, and protein-like substances in raw and treated industrial wastewaters. The present study also revealed that TOC and COD_Mn represented different organic matter fractions in the paper mill and oil refinery wastewater, whereas the industrial park wastewater showed similar dissolved organic matter characteristics. Specifically, COD_Mn was effective in the determination of humic content in paper mill wastewater but was underestimated in oil refinery wastewater. Additionally, only paper mill effluents exceeded the TOC requirements (4 of 6 samples) and required an additional post-treatment process owing to higher organic loads.

Enhanced biohydrogen production with low graphene oxide content using thermophilic bioreactors

Modern society envisions hydrogen (H₂) fuel to drive the transportation, industrial, and domestic sectors. Here, we explore use of graphene oxide nanoparticles (GO NPs) for greatly enhancing bio-H₂ production by a consortium based on Thermoanaerobacterium thermosaccharolyticum spp. Thermophilic batch bioreactors were set up at 60 ^OC and initial pH of 8.5 to assess the effects of GO NPs supplements on biohydrogen production. Under optimal GO NPs loading of 10 mg/L, the supplemented system yielded ∼ 300% higher H₂ yield (6.78 mol H₂/mol sucrose) than control. Such an optimized system offered 73% H₂ purity and 85% conversion efficiency by promoted the desirable acetate fermentation pathway. Miseq Illumina sequencing tests revealed that the optimal levels of GO NPs did not alter the microbial composition of consortium.

Innovative constructed wetland coupled with microbial fuel cell for enhancing diazo dye degradation with simultaneous electricity generation

A novel earthen separator-based dual-chambered unplanted core of constructed wetland coupled with microbial fuel cell was developed for studying the microbe-material interaction and their effect on treatment performance and electricity generation. The constructed wetland integrated microbial fuel cell was evaluated for the degradation of high molecular weight diazo Congo red dye as a model pollutant. The system exhibited 89.99 ± 0.04% of dye decolorization and 95.80 ± 0.71% of chemical oxygen demand removal efficiency from an initial concentration of 50 ± 10 mg/L and 750 ± 50 mg/L, respectively. Ultraviolet-Visible spectrophotometric and gas chromatography-mass spectrometric analysis revealed naphthalene and phenol as mineralized products. The developed system achieved high power density and current density generation of 235.94 mW/m³ and 1176.4 mA/m³, respectively. Results manifested that dual-chambered constructed wetland coupled with microbial fuel cell has a high capability of dye decolorization and toxicity abatement with appreciable simultaneous bioelectricity generation owing to the significantly low internal resistance of 100 Ω.

Influence of Free Chlorine and Contact Time on the Reduction of Salmonella Cross-Contamination of Tomatoes in a Model Flume System

ABSTRACT

The process of washing tomatoes in dump (flume) tanks has been identified as a potential source of cross-contamination. This study's objective was to assess the potential for Salmonella enterica cross-contamination at various inoculation levels in the presence of free chlorine (HOCl) and organic matter. Uninoculated tomatoes were introduced into a laboratory-based model flume containing tomatoes inoculated with a cocktail of five rifampin-resistant S. enterica serovars at 104, 106, or 108 CFU per tomato in water containing 0 or 25 mg/L HOCl and 0 or 300 mg/L chemical oxygen demand (COD). Uninoculated tomatoes exposed to the inoculated tomatoes were removed from the water after 5, 30, 60, and 120 s and placed in bags containing tryptic soy broth supplemented with rifampin and 0.1% sodium thiosulfate. Following incubation, enrichment cultures were plated on tryptic soy agar supplemented with rifampin and xylose lysine deoxycholate agar to determine the presence of Salmonella. HOCl and pH were measured before and after each trial. The HOCl in water containing 300 mg/L COD significantly declined (P ≤ 0.05) by the end of each 120-s trial, most likely due to the increased demand for the oxidant. Higher inoculum levels and lower HOCl concentrations were significant factors (P ≤ 0.05) that contributed to increased cross-contamination. At 25 mg/L HOCl, no Salmonella was recovered under all conditions from uninoculated tomatoes exposed to tomatoes inoculated at 104 CFU per tomato. When the inoculum was increased to 106 and 108 CFU per tomato, cross-contamination was observed, independent of COD levels. The results from this study indicate that the currently required sanitizer concentration (e.g., 100 or 150 mg/L) for flume water may be higher than necessary and warrants reevaluation.

HIGHLIGHTS

Elimination of oxacillin, its toxicity and antibacterial activity by using ionizing radiation

The chemical changes caused by electron beam and γ irradiations and the biochemical characteristics of degradation products of a frequently used antibiotic oxacillin were investigated and compared with those of cloxacillin by applying pulse radiolysis, chemical and biochemical oxygen demand, total organic carbon content, oxygen uptake rate, toxicity and antibacterial activity measurements. Oxacillin was found to be non-toxic, but poorly biodegradable by the mixed microbial population of the activated sludge of a wastewater treatment plant. Therefore, it can significantly contribute to the spread of β-lactam antibiotic resistant bacteria. However, the products formed by γ-irradiation were more easily biodegradable as they were utilized as nutrient source by the microbes of the activated sludge and the products did not show antibacterial activity. During irradiation treatment of aerated aqueous solutions mainly hydroxyl radicals induce the elimination of antimicrobial activity by making alterations at the bicyclic β-lactam part of these antibiotics. Since the β-lactam part is the same in oxacillin and cloxacillin, the biochemical characteristics of products of the two antibiotics are similar. The attack of hydrated electron takes place on the carbonyl groups. When the irradiation is made under anoxic conditions these reactions may also contribute considerably to alterations at the β-lactam part and thereby to the loss of antibacterial activity.

Long-term semi-continuous production of carbohydrate-enriched microalgae biomass cultivated in low-loaded domestic wastewater

The production of carbohydrate-enriched biomass from waste streams as a sustainable biofuel precursor is a noteworthy endeavor. This study investigates the long-term microalgae cultivated under low domestic wastewater loads and different hydraulic retention times (HRT) in a semi-continuous photobioreactor. The influence of operational conditions, the microalgae interaction with carbon, nutrients availability, and microbial population in terms of carbohydrate content were elucidated. The results revealed that the operation at similar low nutrients and carbon loads maintained at three different hydraulic retention times (HRT) of 10, 8, and 6 days caused different patterns in nutrients uptake and biomass composition. Particularly, the carbohydrate accumulation was greatly influenced by the unbalance in the N:P ratios than complete depletion of the nutrients. Hence, during the period operated at HRT of 10 d, high nutrients removal efficiencies were observed while gradually increasing carbohydrate content up to 57% in dry cell weight (DCW). Afterward, the decrease to 8 and 6 d of HRT showed lower nutrient consumption with depleted alkalinity, reaching an appreciably high carbohydrate accumulation of up to 46%, and 56%, respectively. The biomass concentration decreased in the order of HRT of 10, 8, and 6 days. This study demonstrated that microalgae adapted to low carbon and nutrient loads could still accumulate high carbohydrate at shorter HRT using domestic wastewater as substrate.

Intensified sonochemical degradation of 2-Picoline in combination with advanced oxidizing agents

2-picoline is a very important pyridine derivative with significant applications though it is also poisonous and harmful having considerable adverse influence on aquatic life, environment and organisms. The need for developing effective treatment methodologies for 2-Picoline directed the current work focusing on degradation of 2-Picoline using the combination of ultrasound and advanced oxidants such as hydrogen peroxide (H₂O₂), potassium persulphate (KPS), Fenton's reagent, and Peroxymonosulphate (PMS) along with the use of Titanium oxide (TiO₂) as catalyst. Ultrasonic bath having 8 L capacity and operating frequency of 40 ± 2 kHz has been used. The effect of parameters like power, initial pH, temperature, time and initial concentration of 2-Picoline were studied to establish best operating conditions which were further used in the combination treatment approaches of ultrasound with oxidising agents. The chemical oxygen demand (COD) reduction for the optimized approaches of ultrasound in combination with oxidizing agents was also determined. Degradation experiments were performed using oxidising agents also in absence of ultrasound to investigate the individual treatment capacity of the oxidants and also the synergetic index for the combination. Kinetic study demonstrated that second order model suited for all the treatment approaches except US/Fenton where first order model fitted better. Ultrasound in combination with Fenton reagent demonstrated a substantial synergy for the degradation of 2-Picoline compared to other treatment approaches showing highest degradation of 97.6 %, synergetic index as 5.71, cavitational yield of 1.82 × 10^-5 mg/J and COD removal of 82.4 %.

Eco-friendly bleaching of sugarcane bagasse with crude xylanase and pectinase enzymes to reduce the bleaching effluent toxicity

Bio-bleaching effect on bagasse pulp using xylano-pectinolytic enzymes produced by a bacterial species was studied in order to evaluate the potential of these enzymes in paper industry. In this study, action of enzymes was maximum with xylanase/pectinase dose 7/1.75 IU/g, pulp consistency 1:12.5 g/L, pH 8.5, temperature 50° C and 180 min of treatment time. Under the optimized bio-bleaching conditions, removal of reducing sugars (6.15±0.05 mg/L), brightness (16.08%), whiteness (25.54%) and release of chromophores (hydrophobic and phenolic compounds and lignin impurities) were maximum, along with decrease in kappa number (26.28%), and yellowness (27.88%) values were obtained. Improvement in the various physical properties like breaking length (10.28%), burst index (29.55%), tear index (5.02%), double fold (14.89%), Gurley porosity (15%) and viscosity (8.6%), along with the reduction of chlorine dioxide dose by 27%, was also observed. There is also reduction in COD and BOD values of bio-bleached effluents by 27.62% and 20.52%, respectively. This is the first report on bio-bleaching of bagasse pulp using xylano-pectinolytic enzymes.