Chemical Oxygen Demand Ratio Research Articles

Enhanced bioenergy production through dual-chamber microbial fuel cells: Utilizing citric acid factory wastewater and grape waste as substrates

IntroductionMicrobial fuel cell (MFC) is a variant of the bio-electro-chemical system that uses microorganisms as biocatalysts to generate bioenergy by oxidizing organic matter. Due to its two-prong feature of simultaneously treating wastewater and generating electricity, it has drawn extensive interest by scientific communities around the world. However, the pollution purifying capacity and power production of MFC at the laboratory scale have tended to remain steady, and there have been no reports of a performance breakthrough. Problem statementThis research was conducted to produce electricity and evaluate the efficiency of chemical oxygen demand (COD) removal from wastewater containing Citric Acid using a two-chamber microbial fuel cell without an intermediary. MethodologyIn this research, citric acid factory wastewater was used as the substrate, graphite as the electrode, Nafion membrane for proton transfer from anode to cathode, and grape waste as a carbon source. These Experiments were performed at room temperature and neutral pH. Also, the effect of three independent variables mixed liquor suspended solid (MLSS), Carbon: Nitrogen: Phosphorus stoichiometric ratio (COD:TKN:P), and grape waste on electricity production and wastewater treatment was investigated. Then, the optimal values of each variable were determined under favorable conditions for electricity generation and COD reduction. ResultsThe MFC was conducted at the optimal values of MLSS 1400 mg/L, the stoichiometric ratio of COD:TKN:P 140:10:1, and the grape waste dose of 1.4 g/L. At these conditions, the obtained maximum power density and current density were 18228.10 µW/m2 and 244.44 mA/m2, respectively. The maximum COD removal was 72% achieved in the values of MLSS 1400 mg/L, the stoichiometric ratio of COD:TKN:P equal to 260:10:1, and 1.4 g/L of grape waste. The maximum open circuit voltage was also recorded as 678 mV, obtained at MLSS 3000 mg/L, the stoichiometric ratio of COD:TKN:P equal to 200:10:1, and for a grape waste dose of 2 g/L. ConclusionThe results of this research showed that the use of grape waste to supply glucose to microorganisms in the MFC system has a significant effect on increasing energy production and COD removal, and it is recommended to conduct additional research in the future to improve the efficiency. However, scalability and practical application potential of these integrated technologies are the challenges towards their real-world applications in small scale trials.

Experimental Study on Tribological, Rheological and Bio-degradability Characteristics of Canola Oil with TiO2 Nanoparticles as Bio-nanolubricants

In response to growing environmental concerns about the adverse effects of conventional lubricants, there has been a surge in the demand for eco-friendly alternatives. Biodegradable lubricants, crafted from renewable sources, represent a sustainable solution to address these environmental apprehensions. This research describes the tribological, rheological properties and biodegradability of rapeseed oil with 0.25 to 1.25 weight percent TiO2 nanoparticles as additives. The lubricant samples were prepared using a magnetic stirrer and an ultrasonic device. Friction and wear properties such as coefficient of friction and wear scar diameter were determined using a four-ball tester. In comparison with SAE20W40, samples 1 (0.25 weight percentage of TiO2) and sample 2 (0.5 weight percentage of TiO2) shown remarkably improved tribological performance, with 73.32% and 66.76% decreases in coefficient of friction (COF), respectively. Shear stress, shear rate and dynamic viscosity are analyzed using a rheometer. The acquired results are juxtaposed with both pure canola oil and various mineral oils for comparison. The nano-lubricant synthesized in this study emerges as a viable alternative to SAE10, DXT3 (steering fluid), and SAE20W50 grade oils, demonstrating lower friction and a reduced wear scar diameter. Biodegradability tests were performed on all generated samples using the Biochemical Oxygen Demand (BOD) apparatus, and all samples exhibited a BOD to Chemical Oxygen Demand (COD) ratio better than 0.5, indicating biocompatibility. The findings of the research investigation indicate that the combination of canola oil with TiO2 blends holds significant promise as an alternative to conventional synthetic lubricant oils.

Integrated process of Tetrasphaera-dominated in-situ waste activated sludge fermentation, biological phosphorus removal and endogenous denitrification in single reactor for treatment of wastewater with limited carbon sources

An integrated process of sludge in-situ fermentation, biological phosphorus removal and endogenous denitrification (ISFPR-ED) was developed to treat low ratio of chemical oxygen demand to nitrogen (COD/N) wastewater and waste activated sludge (WAS) in a single reactor. Nutrient removal and WAS reduction were achieved due to Tetrasphaera-dominated sludge fermentation provided organic carbon in extending the anaerobic duration. The WAS reduction efficiency, effluent orthophosphate (PO43−-P) and total inorganic nitrogen reached 28.1 %, less than 0.4 and 7.2 mg/L, respectively. While organic carbon was reduced by 67 %. Tetrasphaera, conventional polyphosphate accumulating organisms (PAOs) stored glycogen, amino acids, and PHA for nutrient removal. Excess energy from fermentation enhanced anaerobic PO43−-P uptake by Tetrasphaera. Tetrasphaera was the dominant PO43−-P removal and fermentation bacteria, working synergistically with conventional PAOs and fermenting microorganisms. This integrated process improves nutrient removal efficiency and reduces operating costs for carbon addition and WAS disposal in wastewater treatment.

Fast development of purple nonsulfur bacteria (PNSB) in a bubble column photobioreactor: Influence of carbon source and dissolved O2 availability on wastewater treatment performance

Photobioreactors with purple nonsulfur bacteria (PNSB) constitute a promising technology for wastewater treatment, gas purification, and high value-added bioproducts. In this work, different operational strategies were tested to investigate their impacts on photobioreactor performance, biomass properties, and microbial community. It showed that the operational conditions significantly influence the performance and microbial composition of PNSB photobioreactors. Anaerobic conditions favored the dominance of Rhodopseudomonas spp. and moderate COD removal efficiency (36.7 %), while aerobic conditions significantly enhanced COD removal efficiency (91.7 %) but altered the microbial community composition from PNSB to aerobic heterotrophic microorganisms, such as Delftia sp. and Microbacterium sp.. The removal ratio of chemical oxygen demand (COD):N:P was 100:10:2 under anaerobic conditions with continuous CO2 supply, while it was 100:1:1 under aerobic conditions with continuous supply of a CO2/O2 mixture. Net CO2 removal efficiencies of 2.8 % and 5.4 % were recorded under anaerobic conditions with and without the addition of organic carbon, respectively. The outlet CO2 concentration showed that CO2 uptake occurred under dark and anaerobic conditions without organic carbon. The reduced production of extracellular polymeric substances (EPS) was observed after COD was removed from the influent, preventing granule formation.

Biodegradability index (BDI) as an indicator for effluents quality measurement; a case study based on different industry sectors in Matara District, Sri Lanka

ABSTRACT This study addresses the crucial need for appropriate indicators to characterize aquatic pollution, given the challenges posed by unrestricted effluent discharge globally. Focusing on wastewater from hotel and tourism industries and vehicle service stations in Matara District, Sri Lanka, we explored the relationship between biological oxygen demand (BOD) and chemical oxygen demand (COD) through the biodegradability index (BDI). Monthly water samples were collected from January 2019 to December 2022, analyzed using standard methods, and statistically evaluated. Results revealed a significant spatial variation in BDI among industry sites, with a modest temporal change. The BOD:COD ratio exhibited a slight increasing trend over time, suggesting factors beyond temporal influence. BDI correlated significantly with temperature, alkalinity, and total suspended solids (TSS), emphasizing its potential as an indicator. The study underscores the importance of complementing the BOD:COD ratio with other indicators for a comprehensive assessment of industrial effluent quality. This research contributes valuable insights into understanding wastewater characteristics, facilitating informed pollution reduction and control strategies in aquatic systems.

Fate of organic nitrogen in amino acids during alternating denitrification and nitrification

Nitrogen-containing organic compounds, such as amino acids in soybean-processing wastewater, can be used as electron donors to drive denitrification, but their biodegradation releases ammonium nitrogen that must be nitrified and denitrified to maintain total-nitrogen removal. We evaluated glutamate, isoleucine, and methionine as example amino acids to explore the fate of nitrogen when they are used as electron donor to drive denitrification during two stages of alternating denitrification and nitrification. The experimental results documented that each amino acid enabled complete removal of exogenous NO3− in the first stage of denitrification and complete NO3− removal in the second stage. After two alternations of denitrification and nitrification, the TN concentration in effluent was less than 5 mgN/L for all amino acids, and COD in the effluent was less than 25 mg/L. Based on stoichiometry and the ratio of chemical oxygen demand (COD) to organic N in each amino acid, 57%–66% of the COD from the amino acids had to be oxidized to reduce the endogenous NO3−–N in the first stage. N from the amino acids was nitrified and denitrified in the subsequent nitrification and denitrification stages, and the percentages of COD used for denitrification from both stages were 72%–85%. The residual NH4+-N concentrations were slightly higher with methionine, possibly due to inhibition from sulfide released from methionine.

Electrochemically regulating COD/TN ratio of aged landfill leachate via rapid chlorine-mediated ammonia oxidation with RuO2-IrO2/Ti anode

Electrochemical oxidation process was employed to regulate the ratio of chemical oxygen demand to total nitrogen (COD/TN ratio) of aged landfill leachate, aiming to meet the requirement of biological treatment. The results indicate that the ammonia nitrogen can be rapidly removed through electrogenerated chlorine radicals over a typical chlorine evolution RuO2-IrO2/Ti anode. The increased input current and decreased flow rate are beneficial to COD/TN ratio improvement, and COD/TN ratio can be increased to more than 16 at 1000 mA (input current) and 0.3 L/h (flow rate). According to the obtained experimental data, we present a strategy for COD/TN ratio increase: (i) determining the COD/TN ratio balance coefficient (B) of aged landfill leachate, and selecting the anode with COD/TN ratio adjustment coefficient (TN) >B, where TN represents the ability to regulate COD/TN ratio, and B represents the specific TN to keep the same COD/TN ratio; (ii) performing the wastewater treatment experiments at different control parameters during electrochemical process; (iii) calculating the k of control parameter sensitivity curves to achieve different tolerance abilities, and further preferentially regulating the reaction process to high average current efficiency (ACE) of ammonia nitrogen and low ACE of COD. This work validates that the electrochemical process can increase the COD/TN ratio together with enhancing the biodegradability of such refractory wastewater, and also provides an effective tool for regulation of the COD/TN ratio via complete ammonia oxidation.

The Performance of Iron Nanocomposites as Persulfate Activators in Permeable Reactive Barrier Technology for Treatment of Landfill Leachate

Landfill leachate contains a large organic load and a wide spectrum of pollutants, and it needs appropriate treatment to reduce the severity of these contaminants. Therefore, the present study aimed to remove chemical oxygen demand (COD) and ammonia (NH3 ) as target contaminants from the landfill leachate. To this end, the zero-valent iron nanofibers/reduced ultra-large graphene oxide (ZVINFs/rULGO) and converter sludge (CS) were used as persulfate (PS) activators in permeable reactive barrier (PRB) technology for removing COD and NH3 . The Box–Behnken design (BBD) was employed to determine the possibility of using each activator and optimize three parameters: activator, pore volume (PV), and flow (mL/min) using target contaminants. In the Batch process, the effects of pH, activator concentration, and PS/COD mass ratio on COD removal were examined. The BBD experiments provided a satisfactory predictive model, indicating that ZVINFs/rULGO is superior to CS when used as activators of PS in PRB technology. The biochemical oxygen demand (BOD5 )/COD ratio increased from 0.24 in raw leachate to 0.67 in treated leachate, and leachate toxicity was reduced by more than 85%. Additionally, the ZVINFs/rULGO and CS contributed to the activation of PS.

Application of environmentally friendly technologies for the management of nanofiltration concentrate from landfill leachate

In this study, the treatability of leachate nanofiltration (NF) concentrate using the modified Fenton process was investigated. The modified Fenton process employs an environmentally friendly oxidant (sodium percarbonate, SPC), an environmentally friendly catalyst (Fe2+), and environmentally friendly activators (electrooxidation-ultraviolet, EO-UV). The study aimed at enhancing the biological degradability of leachate NF concentrate and was conducted in two stages. In the first stage, the process variables of the SPC/Fe2+ process were optimized. In the second stage, combined processes were applied under optimum conditions. With the SPC/Fe2+ process under optimum conditions (pH: 5, SPC dose: 10 mM, Fe2+ concentration: 50 mM, reaction time: 60 min, pre-catalyst dosing), removal efficiencies of 53.5%, 47.1%, and 61.6% were obtained for chemical oxygen demand (COD), UV254, and color, respectively. After optimizing the operational parameters of the SPC/Fe2+ process, combined processes of EO/SPC/Fe2+ and UV/SPC/Fe2+ were applied, and higher pollutant removal efficiencies were achieved with the EO/SPC/Fe2+ process. Under optimum conditions, removal efficiencies of 75.3%, 80.5%, and 85.6% were achieved for COD, UV254, and color, respectively. The first-order reaction rate constant was 0.022 1/min for the EO/SPC/Fe2+ process. The biochemical oxygen demand (BOD)/COD, which increased from 0.040 to 0.080 with the SPC/Fe2+ process, reached 0.455 with the EO/SPC/Fe2+ process. Additionally, with the EO/SPC/Fe2+ process, the biologically degradable COD ratio of leachate NF concentrate increased from 16.7% to 83.5%, and the soluble COD fraction increased from 72.7% to 89.5%.

Using Mean Oxidation Number of Organic Carbons to Count Theoretical Chemical Oxygen Demand

Chemical oxygen demand and mean oxidation number of organic carbons are two important concepts in redox chemistry. The former is used for counting pure or mixed organic matters in aqueous solution. The latter is a redox metric for water treatment, organic combustion, and anaerobic digestion. Currently the calculation of theoretical chemical oxygen demand of neutral organic matter is based on the number of moles of molecular oxygen (O2). However, the calculation of theoretical chemical oxygen demand of ionic organic matter has seldom been studied. The purpose of this article is to develop a simple mathematical equation for doing so by using mean oxidation number of organic carbons. To develop the equation, relationships among chemical oxygen demand, mean oxidation number of organic carbons, number of organic carbons, and formula mass of organic matter are identified. The mathematical equations for chemical oxygen demand, total organic carbon, and the ratio of chemical oxygen demand to total organic carbon are also established for any molecule(s).

Advanced nitrogen and phosphorus removal in pilot-scale anaerobic/aerobic/anoxic system for municipal wastewater in Northern China

Removing nitrogen and phosphorus from low ratio of chemical oxygen demand to total nitrogen and temperature municipal wastewater stays a challenge. In this study, a pilot-scale anaerobic/aerobic/anoxic sequencing batch reactor (A/O/A-SBR) system first treated 15 m3/d actual municipal wastewater at 8.1–26.4 °C for 224 days. At the temperature of 15.7 °C, total nitrogen in influent and effluent were 45.5 and 10.9 mg/L, and phosphorus in influent and effluent were 3.9 and 0.1 mg/L. 16 s RNA sequencing results showed the relative abundance of Competibacter and Tetrasphaera raised to 1.25 % and 1.52 %. The strategy of excessive, no and normal sludge discharge enriched and balanced the functional bacteria, achieving an endogenous denitrification ratio more than 43.3 %. Sludge reduction and short aerobic time were beneficial to energy saving contrast with a Beijing municipal wastewater treatment. This study has significant implications for the practical application of the AOA-SBR process.

Prediction of heavy metal removal performance of sulfate-reducing bacteria using machine learning

A robust modeling approach for predicting heavy metal removal by sulfate-reducing bacteria (SRB) is currently missing. In this study, four machine learning models were constructed and compared to predict the removal of Cd, Cu, Pb, and Zn as individual ions by SRB. The CatBoost model exhibited the best predictive performance across the four subsets, achieving R2 values of 0.83, 0.91, 0.92, and 0.83 for the Cd, Cu, Pb, and Zn models, respectively. Feature analysis revealed that temperature, pH, sulfate concentration, and C/S (the mass ratio of chemical oxygen demand to sulfate) had significant impacts on the outcomes. These features exhibited the most effective metal removal at 35 °C and sulfate concentrations of 1000–1200 mg/L, with variations observed in pH and C/S ratios. This study introduced a new modeling approach for predicting the treatment of metal-containing wastewater by SRB, offering guidance for optimizing operational parameters in the biological sulfidogenic process.

Study of BOD: COD Ratio as an Indicator for Wastewater of Rubber Industry Sector

When considering the rubber industry sector, the most significant challenge is the efficient wastewater treatment before discharging it into the natural environment. The rubber industry is considered to be highly chemical and water-intensive: and involves enormous quantitative s of waste production. The ratio between Biological Oxygen Demand (BOD5) and Chemical Oxygen Demand (COD) is a widely used parameter in characterising wastewater and then the same was used in this study as an indication to measure the efficiency of wastewater treatment plant operated in the rubber industry sector. Data for the study was extracted from samples collected from 10 wastewater treatment plants of rubber industries in the Sabaragamuwa Province; two samples from each representing before and after treatment. The samples were tested in two replicated for BOD5, COD, pH, and conductivity. These selected rubber factories contain lagoon/pond type wastewater treatment systems or activated sludge wastewater treatment systems. The results showed that the treated wastewater samples were within the range of 0.1–0.4 of BOD5: COD and were below the BOD5: COD permissible level as per CEA standards. (General standards for rubber in inland surface waters; Latex-BOD 60, COD 400; Lanka rubber/crepe rubber–BOD 50, COD 400) comparing the BOD, COD, pH, and conductivity influent and effluent of the treatment process proves the effectiveness of each treatment plant of the relevant industry. Tested samples show a high BOD5: COD ratio in influent and effluent of wastewater treatment system indicate that wastewater of the industry is easily biodegradable. However, more research comparing the characteristics of different rubber manufacturing processes is needed to develop this approach further. 
 Keywords: BOD, COD, BOD: COD ratio, Wastewater treatment plant

Iron-based autotrophic denitrification driven by sponge iron for nitrite removal in an anaerobic bioreactor: Effect of iron and carbon source.

The study investigated the denitrification effect of the iron autotrophic denitrification process for removing nitrite under anaerobic conditions, utilizing sponge iron as the electron donor. When the C/N ratio equaled 1, defined as the ratio of chemical oxygen demand to total nitrogen (TN), and the influent nitrite nitrogen (NO2--N) was at 80 mg/L, the average steady-state TN effluent concentration of this system was 41.94 mg/L during the 79-day experiment. The TN value exhibited a significant decrease compared to both the sponge iron system (68.69 mg/L) and the carbon source system (56.50 mg/L). Sponge iron is beneficial for providing an electron donor and ensuring an anaerobic system, fostering an environment that promotes microorganism growth while effectively inhibiting the conversion of nitrite to nitrate. In addition, carbon sources play a vital role in ensuring microorganism growth and reproduction, thereby aiding in TN removal. The optimal parameters based on the effectiveness of TN removal in the iron autotrophic denitrification system were determined to be s-Fe0 dosage of 30 g/L and C/N = 1.5. These results suggest that the iron autotrophic denitrification process, driven by sponge iron, can effectively remove nitrite under anaerobic conditions.

Biodegradability enhancement and sequential treatment of real chemical industry wastewater by chemical coagulation and Electro-Fenton processes

A sequential treatment with chemical coagulation in the first step and Electro-Fenton (EF) in the second step was applied to chemical industry wastewater. By coagulation using Poly Aluminum Chloride (PAC) as a coagulant, 57.5% chemical oxygen demand (COD), 96.8% total suspended solids (TSS), and 90.5% color index (CI) removal were obtained. In the EF process applied after chemical coagulation, the design parameters were optimized by the central composite design. Two quadratic models of the four factors were established with the COD and CI as two responses. Optimized conditions of the EF were pH 2.5, Fe2+ dose 5 mM, applied current 1 A, and reaction time 60 min. Under these conditions, the COD removal from the validation experiments was 63.5%. In total, 84.5% COD removal was achieved with the two-step treatment. By extending the reaction time in EF to ensure the discharge limits, 89.5% COD removal was reached, and the COD concentration decreased to 193 mg/L after 240 min. At the same time, the 5-day biochemical oxygen demand (BOD5)/COD ratio increased from 0.1 to 0.57 after 240 min. Consequently, the discharge limit was provided and the biodegradability was improved.

Physical and chemical characterization and pollution index applied in the assessment of the polluting potential of leachate from urban landfills.

During the operation of the landfills, leachate should be managed with caution to avoid possible negative environmental impacts. Considering this, the present study aims to evaluate the relationship between different variables in the leachate composition and elucidate the transformation processes through which this effluent passes during the landfill's period of operation. The study was conducted with eight sanitary landfills from the state of Minas Gerais, in southeastern Brazil, and used descriptive statistical analysis, principal component analysis (PCA), correlation analysis, and calculation of the leachate pollution index (LPI). The biochemical oxygen demand (BOD5)/chemical oxygen demand (COD) ratio was between 0.20 and 0.60. We also observed a significant correlation of 0.45 between Cl- and N-NH4+, which reflects the biological degradation processes that contribute to the presence of both variables. The PCA showed that inorganic variables and organic matter dominated the first component, with coefficients above 0.65, indicating the importance of those variables in determining the general data variability. The LPI values were between 15.26 and 25.97, with BOD5, COD, and N-NH4+ having sub-indexes above 35, being the main variables that increase the pollution potential of the leachate. On the other hand, trace metals present sub-indexes below 7 due to precipitation caused by increased pH and the characteristics of the waste discarded in landfills. The study provides essential information regarding the landfill leachate characteristics and its variation over time, which can contribute to the definition of treatment technologies for this affluent in different scenarios.

Achievement of partial denitrification in SBR treating acidic wastewater: Performance and mechanism of nitrite accumulation

Partial denitrification (PD) can provide stable electron acceptors for anaerobic ammonium oxidation; however, PD operates mostly under alkaline conditions (pH >7), limiting its application in acidic wastewater treatment. In this study, PD with nitrate-to-nitrite transformation ratio (NTR) of 69.7 % was achieved using a sequencing batch reactor (SBR) by decreasing the pH (7.5 to 5.5) and the ratio of chemical oxygen demand to nitrate nitrogen (COD/NO3−-N) (4.5 to 3.5). Paracoccus (22.68 %) and Thauera (11.53 %) were the dominant microbes in this study. The ratio of COD/N consumed in the SBR was as high as 5.2 ± 0.6, and the content of extracellular polymeric substances (EPS) increased from 36.5 to 128.4 mg g−1 VSS. In a single cycle, a maximum NTR of 86.7 % was obtained at 90 min, and the NTR was maintained at 70 % even when the reaction time was prolonged to 300 min. Further studies confirmed that acidic pH decreased the rate of nitrate reduction, which increased the duration of nitrate presence and inhibited the reduction of nitrite. More importantly, during nitrate reduction, COD was transformed into glycogen and poly-β-hydroxybutyrate, and further converted to EPS, resulting in nitrite reduction limitation due to carbon source scarcity. This study provides a newfound basis for low consumption treatment of acidic nitrogenous wastewater, such as mining and nuclear industry production.

Insights on sequential changes to the ratios of Biochemical Oxygen Demand and Chemical Oxygen Demand

Insights on sequential changes to the ratios of Biochemical Oxygen Demand and Chemical Oxygen Demand

Advanced treatment of low-pollution and poor biodegradability sewage by combined process

A system was developed for the treatment of low-pollution sewage with poor biodegradability and a low ratio of chemical oxygen demand (CODCr) to nitrate-nitrogen (COD/NO3−-N (C/N)) ratio to achieve high efficiency. This system combines the anaerobic-oxic (AO) process with the biological aerated filter (BAF) and introduces the Fenton advanced oxidation process. A pilot test system was established, and feasibility investigations were conducted using a continuous flow of 500 L/h. The results showed that the optimal conditions for removing nitrate from sewage were achieved with a C/N ratio of 5.5–6 and a hydraulic retention time (HRT) of 4 h. Under these conditions, the average nitrate removal efficiency was 83.36%, and the average concentration of total nitrogen (TN) in the effluent was reduced to 6.68 mg/L. Additionally, the Fenton oxidation treatment was effective in reducing the COD content of sewage, with an average removal efficiency of 82.47% and a decrease in CODCr from 55.24 mg/L to 9.68 mg/L. The combined process successfully met the stringent discharge standards after advanced treatment. Microbial community analysis revealed that the dominant genera in anoxic BAFs were Trichococcus, Comamonadaceae, Lentimicrobium, and Thauera, while the dominant genera in aerobic BAFs were mainly Acinetobacter, Thiothrix, Gemmobacter, and Caldilineaceae. The synergistic effect of various nitrifying and denitrifying bacteria in BAFs effectively removed nitrate from the sewage. Furthermore, GC-MS analysis indicated that the Fenton oxidation significantly reduced the concentration of refractory organic compounds in the sewage, including long-chain organic compounds and acrylic acid maleic acid copolymer (MA/AA). After upgrading and renovating the factory's sewage treatment facilities, the impact of the discharged effluent on the receiving drainage basin will be minimized.

Modification of a plant-scale semi-centralized wastewater treatment system to enhance nitrogen and phosphorus removal from black water.

Owing to the low ratio of chemical oxygen demand to total nitrogen (SCOD/TN), effective removal of nutrient pollutants from black water is difficult. In this study, to enhance nitrogen and phosphorus removal from such wastewater, a series of operational modification strategies was investigated and applied to a plant-scale semi-centralized system used for black water treatment. The results showed that 21 mg Fe3+/L was the optimal dosage for the chemical-enhanced pretreatment process, achieving average removal efficiencies of 51.1 and 74.1% for organics and phosphorus, respectively, with a slight enhancement in nitrogen removal by 2.3%. However, nitrogen and phosphorus removal could be further enhanced to 88 and 96%, by the addition of carbon sources in the post-anoxic zone of the reversed anaerobic-anoxic-aerobic process. Contrastingly, neither the addition of carbon sources in the pre-anoxic zone nor the prolongation of the time for pre-denitrification could significantly improve the nitrogen and phosphorus removal efficiencies. Furthermore, reducing the aeration intensity promoted simultaneous nitrification and denitrification in aerobic reactors, thereby making it a potential energy-saving method for system operation.