Complete Chemical Oxygen Demand Removal Research Articles

Sustainable utilization of anthraquinone-rich Rheum officinale as electron shuttle in microbial fuel cell: Strategy for stimulating monohydric phenols degradation and bioelectricity generation

In an aim to completely degrade refractory phenolic compounds for effective wastewater treatment, a sustainable strategy using anthraquinone-rich herbal plant contents as electron shuttles is presented. This study is the first attempt of treating four different chemical structures of monohydric phenols, while simultaneously generate low-carbon electricity in a microbial fuel cell. An electron shuttle-mediated strategy was introduced to investigate the effect of electron shuttle against the degradation of phenolic pollutants and bioelectricity generation, by employing Rheum officinale extract as electron shuttle. Results revealed that there was a two-fold increase in chemical oxygen demand (COD) removal, degradation extent of phenol and cresol isomers, output voltage and power density of MFC, compared to the mediator-free MFC system. The degradation of phenol yielded higher COD removal, degradation efficiency, output voltage and power generation over cresol isomers, with and without the application of electron shuttle. A complete removal of COD and phenol, with output voltage of 620.06 mV and power density of 252.49 mW/m2 were obtained. Phenol outperformed cresol isomers with regard to its sole activating hydroxy (−OH) group, lower dipole moment and higher electronic conductivity (8.53 mS/cm). Conversely, meta-cresol exhibited the lowest removal efficiency and power generation, ascribed to greater inductive influence of methyl group in meta position on the dissociation energy of the − OH group. Moreover, detection of the phenolic intermediates by gas chromatograph-mass spectrometer analysis was conducted, and detailed degradation pathways were presented.

Treatment of laundry wastewater by different processes: Optimization and life cycle assessment

Wastewater from industrial laundries is often difficult to treat because it usually presents high turbidity and chemical oxygen demand (COD). We studied several processes for the treatment of laundry wastewater which was provided by a hotel in the south of Gran Canaria, Spain. More specifically, we studied coagulation with iron (III) sulphate, Fenton, photo-Fenton and a biological treatment (using a biofilter, and a granular activated carbon, GAC, filtration). The coagulation and Fenton processes produced large amounts of sludge and could not meet the required standards for water reuse in Spain. The use of photo-Fenton and the BF resulted in complete turbidity removal and high COD removal. However, we found that the effluent from the BF did not meet the COD removal criteria for water reuse, and thus a GAC filtration post-treatment was employed to reduce COD to acceptable levels. The photo-Fenton process alone did meet the criteria for water reuse. The estimated cost to treat 1 m3 of wastewater was 6.72 € for photo-Fenton and 0.71 € for BF + GAC. The cost and life cycle assessment analyses that were also performed revealed that the acquisition of the necessary reagents is the main contribution to the overall economic and environmental costs for both options, and that the BF + GAC option is notably cheaper. Additionally, this option also causes much lower environmental impacts than photo-Fenton.

Treatment of textile industry wastewater based on coagulation-flocculation aided sedimentation followed by adsorption: Process studies in an industrial ecology concept

This study examines the feasibility of treatment of textile industry wastewater using a two-step process that includes coagulation-flocculation aided sedimentation and adsorption. It also aims at finding reuse potential of the generated sludge while making the treated water recyclable for the same industry in an industrial ecology concept. The wastewater was collected from a small-scale textile plant with a discharge of 400 L/week, where more than 70 similar textile plants are located in and around the area. FeCl3 was selected as the coagulant for the initial step in the treatment process, and a bimetallic oxide Graphene Oxide (GO) hybrid was selected as the adsorbent for the latter step of the treatment process. The experimental conditions for the coagulation process included the optimization of dose, stirring speed, stirring time, and settling time. For the adsorption process it included the optimization of stirring time, dose, and rate. The parameters like Chemical Oxygen Demand (COD) and color were checked during the treatment process and near complete removal of COD and color were achieved using the suggested materials and process. The treated water was found fit for recycling - towards making zero liquid discharge plant. Later, the sludge generated from both the steps in the processes was sundried and mixed with cement and tested for 7 days and 28 days of compressive strength. A total of 26 kg of cement was replaced, by using sludge generated from treating 100 L of textile wastewater, in the sludge-cement mix. In addition to solving the sludge problem, the process can help in reducing the requirement of cement in concrete. Finally, a detailed economic assessment for the entire study was also performed and is reported.

Application of Sequential Combination of Electro-Coagulation/Electro-Oxidation and Adsorption for the Treatment of Hemodialysis Wastewater for Possible Reuse

Reusing hemodialysis wastewater (HWW) is more difficult due to its higher conductivity (salinity) and the need for an iterative RO or adsorption process. It can therefore be challenging and technologically laborious. In this context, this study aimed to investigate the possibility of treating HWW by combining electro-coagulation (EC) and electro-oxidation (EO) processes and adsorption as the best technologies to achieve efficient removal of dissolved micropollutants. In this work, the application of electro-coagulation/electro-oxidation processes using, respectively, aluminum and platinum electrodes combined with adsorption onto active carbon to treat HWW was studied. In the EC process, high removal of phosphate ions and chemical oxygen demand (COD) was observed. In the EO process, the COD removal performance, total nitrogen, and Mg were significant and reached 100, 83, and 89%, respectively, after 100 min of treatment. The estimated energies required to treat HWW by EC and/or EO were approximately 0.7 kWh/m3 and 0.05 kWh/m3, respectively. While the EO and EC processes used for COD removal from HWW showed almost similar performances, the EO process seems to consume less energy. Therefore, electrochemical removal of HWW can be successfully performed using the EO process and activated carbon (AC) for the complete removal of COD and the mineralization of pharmaceutical residues. The experimental results showed that the coupling of the three processes (EC–EO–AC) provides treated water that can be reused in agriculture due to its less sodium absorption ratio (SAR) value and might be an alternative method of wastewater treatment responding to the concept of green dialysis.

Reuse Potential of Refinery Wastewater Treated Using a Two‐Stage Submerged Membrane Bioreactor

AbstractRefinery wastewater treatment was performed using a novel submerged tubular ceramic membrane bioreactor (STMBR) with the oleaginous hydrocarbonoclastic bacterium Rhodococcus opacus. A membrane‐based flux study with the STMBR was carried out to assess the performance of the tubular ceramic membrane. Continuous experiments with the STMBR achieved a maximum chemical oxygen demand (COD) removal of 84 %, with an average flux of 0.4 × 10−3 m3m−2s−1. To further enhance the COD removal efficiency, two STMBR were operated under the optimum conditions. Complete COD removal along with 2.98 g L−1 biomass growth was achieved during two‐stage STMBR operation. Furthermore, a toxicity assessment of the permeate water established its reuse potential.

Treatment of Synthetic Wastewater Containing Diethyl Phthalate through Photo-Fenton Method by Box-Behnken Design

Background & Aims of the StudyDiethyl phthalate (DEP) cannot be proficiently degraded by ultraviolet (UV) radiation and hydrogen peroxide (H2O2) oxidation separately; however, the photo-Fenton method is verified to be operative and can completely degrade this pollutant. Currently, advanced oxidation methods have been growing to be employed for the remediation of industrial wastewater. In the present study, the photo-Fenton process investigated the degradation and mineralization of the aqueous solution containing DEP.Materials and MethodsSynthesized wastewater was used in this study. In addition, the effects of operative factors, such as the initial concentrations of H2O2, ferrous ion, and DEP, have been studied. The response surface methodology and Box-Behnken design of experiments were applied to examine the effects of three sovereign variables on the response functions to obtain the optimum circumstances.ResultsThe analysis of variance was carried out to determine the importance of the effects of independent variables on the response function. Various amounts of variables were optimized for the removal of DEP. At optimum conditions (i.e., H2O2 concentration of 400 mg/l, ferrous concentration of 75 mg/l, and DEP concentration of 50 mg/l) and 60 min following the reaction, the rates of degradation efficiency for DEP and chemical oxygen demand (COD) were 100% and 85.3%, respectively.ConclusionAccording to the obtained results, the suggested quadratic model showed good correctness. The statistical analysis of the model indicated that the model was satisfactory to predict the performance of the processes. The obtained findings demonstrated that the photo-Fenton processes can be used for the complete and partial removal of DEP and COD from wastewater, respectively. The benefits of the photo-Fenton process were less sludge formation, fewer chemicals, and time obligation but at the cost of consumed power. The power consumption can be reduced by employing sunlight instead of artificial UV light to a larger amount. The photo-Fenton procedure was influential in the degradation of DEP and can considerably decrease COD.

Decolorization and Degradation of a Mixture of Industrial Azo Dyes by Anodic Oxidation Using a Ti/Ru0.3Ti0.7O2 (DSA‐Cl2) Electrode.

AbstractThe electrochemical treatment of wastewaters from the textile industry is a promising alternative for the elimination of organic pollutants. This study approach the decolorization and chemical oxygen demand (COD) removal from synthetic water (0.91 mM Acid Yellow 25 dye ‐ and ‐ 0.42 mM Acid Blue 29 dye), by anodic oxidation (AO) in batch mode using a Ti/Ru0.3Ti0.7O2 (DSA‐Cl2) electrode as anode and an AISI 304 stainless steel plate as cathode. The influence of pH (3, 7 and 10), type of supporting electrolyte (50 mM Na2SO4, 50 mM NaCl and 100 mM NaCl) and applied current density (10 < j < 80 mA cm–2) on COD removal and mineralization current efficiency was analyzed. The best AO test in terms of energy consumption was performed at pH 7, 50 mM NaCl and j=30 mA cm–2, obtaining a complete decolorization and COD removal. These operating parameters have an energy consumption between 0.41 and 0.82 kWh m–3. High performance liquid chromatography (HPLC‐MS/MS) analyses indicated the presence of several organic intermediates and carboxylic acids.

A hybrid treatment process for product recycling from tannery process effluent and soak liquor

The sulfate rich saline tannery effluent (SRSTE) was treated effectively using halophilic bacterial pretreatment followed by electrochemical oxidation (hybrid treatment). Aerobic degradation was done using halophilic bacterial consortia isolated from the tannery soak effluent, resulted in 76 % COD removal after 6 days. The remaining COD was reduced by electrochemical oxidation (EO). In electro oxidation process (without aerobic pretreatment), 24 h of electro-oxidation was needed to complete COD removal. The process efficiency was analysed through Fourier transform infrared spectroscopy (FTIR), high performance liquid chromatography (HPLC), total organic carbon (TOC) and chemical oxygen demand (COD). The reduction of sulfate could not be noticed in presence of halophilic bacteria in aerobic treatment. The energy consumption for COD removal was about 0.343 and 0.020 kW h/g1 in electrochemical oxidation and hybrid treatment process respectively. Besides, chloride loss was also higher in EO when compared to hybrid approach. Hybrid treatment process was proved to be an effective method for treating SRSTE. The mixed salt was recovered and used for dyeing purpose.

Applicability of electrochemical methods to paper mill wastewater for reuse. Anodic oxidation with BDD and TiRuSnO2 anodes

The electrochemical oxidation of paper mill wastewater belonging from Halfa industries (Tunisia) was performed by galvanostatic electrolysis using boron-doped diamond (BDD) anodes and Ti-Ru-Sn ternary oxide (TiRuSnO2). The effect of several operating parameters, such as applied current density, flow rate, temperature, initial pH value and addition of NaCl was evaluated. Chemical oxygen demand (COD) and ammonium measurements were carried out to study the treatment of the actual wastewater. The energy consumption analysis has been also discussed. The experimental results exhibited that galvanostatic electrolyses with BDD always allowed efficient COD removal in any conditions thanks to the reaction with hydroxyl radicals electrogenerated on BDD surface during electrolysis. On the contrary, using the TiRuSnO2 anode, the complete COD removal was only obtained in the presence of chloride ions. Comparison of the results of the two electrodes showed that BDD provided a faster removal with higher efficiency and lower energy consumption, while TiRuSnO2 was more efficient for ammonium removal.

Veratric acid removal from water by electrochemical oxidation on BDD anode

The efficiency of boron doped diamond (BDD) in the electrochemical treatment of synthetically contaminated water with veratric acid (VA), one kind of polyphenolic type compounds, is investigated in this work. A BDD electrode was practically fabricated using hot filament chemical vapor deposition (HFCVD). Later on, the BDD electrode was implemented as an anode in a batch electrolytic reactor. The effect of operating factors such as the initial concentration of VA, NaCl addition, and supporting electrolyte type (H2SO4, H3PO4 and Na2SO4) was studied. The chemical oxygen demand (COD) measurements were conducted to study the VA electrolysis kinetics. The experimental data suggested that sodium sulfate was the best supporting electrolyte as the COD removal reached a percentage of 100% using 1 mmol/dm3 as VA concentration. The kinetics of the COD decay of the VA electrolysis were found to obey the pseudo-first order model. Remarkably, the electrolysis process is significantly speeded up once chloride is added to the reaction. The complete COD removal was achieved in 60 minutes of treatment.

Electrochemical mineralization and detoxification of naphthenic acids on boron-doped diamond anodes.

Electrochemical oxidation (ELOX) with boron-doped diamond (BDD) anodes was successfully applied to degrade a model aqueous solution of a mixture of commercial naphthenic acids (NAs). The model mixture was prepared resembling the NA and salt composition of oil sands process-affected water (OSPW) as described in the literature. The initial concentration of NAs between 70 and 120mg/L did not influence the electrooxidation kinetics. However, increasing the applied current density from 20 to 100A/m2 and the initial chloride concentration from 15 to 70 and 150mg/L accelerated the rate of NA degradation. At higher chloride concentration, the formation of indirect oxidative species could contribute to the faster oxidation of NAs. Complete chemical oxygen demand removal at an initial NA concentration of 120mg/L, 70mg/L of chloride and applied 50A/m2 of current density was achieved, and 85% mineralization, defined as the decrease of the total organic carbon (TOC) content, was attained. Moreover, after 6h of treatment and independently on the experimental conditions, the formation of more toxic species, i.e. perchlorate and organochlorinated compounds, was not detected. Finally, the use of ELOX with BDD anodes produced a 7 to 11-fold reduction of toxicity (IC50 towards Vibrio fischeri) after 2h of treatment.

Anodic oxidation of slaughterhouse wastewater on boron-doped diamond: process variables effect.

A non-sacrificial boron-doped diamond electrode was prepared in the laboratory and used as a novel anode for electrochemical oxidation of poultry slaughterhouse wastewater. This wastewater poses environmental threats as it is characterized by a high content of recalcitrant organics. The influence of several process variables, applied current density, initial pH, supporting electrolyte nature, and concentration of electrocoagulant, on chemical oxygen demand (COD) removal, color removal, and turbidity removal was investigated. Results showed that raising the applied current density to 3.83 mA/cm2 has a positive effect on COD removal, color removal, and turbidity removal. These parameters increased to 100%, 90%, and 80% respectively. A low pH of 5 favored oxidants generation and consequently increased the COD removal percentage to reach 100%. Complete removal of COD had occurred in the presence of NaCl (1%) as supporting electrolyte. Na2SO4 demonstrated lower efficiency than NaCl in terms of COD removal. The COD decay kinetics follows the pseudo-first-order reaction. The simultaneous use of Na2SO4 and FeCl3 decreased the turbidity in wastewater by 98% due to electrocoagulation.

Treatment of chemical cleaning wastewater and cost optimization by response surface methodology coupled nonlinear programming

The real alkaline cleaning wastewater (ACW) was treated by a process consisting of neutralization, NaClO oxidation and aluminum sulfate (AS) coagulation, and a novel response surface methodology coupled nonlinear programming (RSM-NLP) approach was developed and used to optimize the oxidation-coagulation process under constraints of relevant discharge standards. Sulfuric acid neutralization effectively removed chemical oxygen demand (COD), surfactant alkylphenol ethoxylates (OP-10) and silicate at the optimum pH of 7.0, with efficiencies of 62.3%, >82.7% and 94.2%, respectively. Coagulation and adsorption by colloidal hydrated silica formed during neutralization were the major removal mechanisms. NaClO oxidation achieved almost complete removal of COD, but was ineffective for the removal of surfactant OP-10. AS coagulation followed by oxidation can efficiently remove OP-10 with the formation of Si-O-Al compounds. The optimum conditions for COD ≤100 mg/L were obtained at hypochlorite to COD molar ratio of 2.25, pH of 10.0 and AS dosage of 0.65 g Al/L, with minimum cost of 9.58 $/m3 ACW. This study shows that the integrative RSM-NLP approach could effectively optimize the oxidation-coagulation process, and is attractive for techno-economic optimization of systems with multiple factors and threshold requirements for response variables.

Performance analysis of a continuous serpentine flow reactor for electrochemical oxidation of synthetic and real textile wastewater: Energy consumption, mass transfer coefficient and economic analysis

A continuous flow electrochemical reactor was developed, and its application was tested for the treatment of textile wastewater. A parallel plate configuration with serpentine flow was chosen for the continuous flow reactor. Uniparameter optimization was carried out for electrochemical oxidation of synthetic and real textile wastewater (collected from the inlet of the effluent treatment plant). Chemical Oxygen Demand (COD) removal efficiency of 90% was achieved for synthetic textile wastewater (initial COD - 780 mg L−1) at a flow rate of 500 mL h−1 (retention time of 6 h) and a current density of 1.15 mA cm−2 and the energy consumption for the degradation was 9.2 kWh (kg COD)−1. The complete degradation of real textile wastewater (initial COD of 368 mg L−1) was obtained at a current density of 1.15 mA cm−2, NaCl concentration of 1 g L−1 and retention time of 6 h. Energy consumption and mass transfer coefficient of the reactions were calculated. The continuous flow reactor performed better than batch reactor with reference to energy consumption and economy. The overall treatment cost for complete COD removal of real textile wastewater was 5.83 USD m−3.

Biological removal of selenate and ammonium by activated sludge in a sequencing batch reactor

Wastewaters contaminated by both selenium and ammonium need to be treated prior to discharge into natural water bodies, but there are no studies on the simultaneous removal of selenium and ammonium. A sequencing batch reactor (SBR) was inoculated with activated sludge and operated for 90days. The highest ammonium removal efficiency achieved was 98%, while the total nitrogen removal was 75%. Nearly a complete chemical oxygen demand removal efficiency was attained after 16days of operation, whereas complete selenate removal was achieved only after 66days. The highest total Se removal efficiency was 97%. Batch experiments showed that the total Se in the aqueous phase decreased by 21% with increasing initial ammonium concentration from 50 to 100mgL−1. This study showed that SBR can remove both selenate and ammonium via, respectively, bioreduction and partial nitrification-denitrification and thus offer possibilities for treating selenium and ammonium contaminated effluents.

Identification of Chlorophene in a Backwater Stream in Kerala (India) and its Sonochemical Degradation Studies

Chlorophene, a chlorinated phenolic compound and a well‐known emerging pollutant due to its extensive use as an antimicrobial agent, has been identified in a local backwater stream using liquid chromatography quadrupole time of flight MS (LC‐Q‐TOF‐MS). The concentration of chlorophene has been calculated as 6 × 10−7 mol L−1 (0.132 ppm). In order to develop a suitable treatment protocol, ultrasound mediated oxidative degradation has been carried out. Prior to the investigation of chlorophene in the backwater sample, the degradation in pure water has been investigated at 620 kHz and 40.25 W mL−1. Complete disappearance of chlorophene was observed within 40 min of sonication. The presence of various inorganic ions had no significant influence on the degradation. A complete chemical oxygen demand removal in the local backwater samples was achieved within 3 h of sonication. Three major intermediate products have been identified by LC‐Q‐TOF‐MS and a plausible mechanism of the degradation is proposed. The same method was applied for the backwater sample containing chlorophene with a concentration of 6 × 10−7 mol L−1. Complete disappearance of chlorophene and nearly 85.7% COD removal was observed in this system as well.

Applicability of an electrochemical Fenton-type process to actual wastewater treatment.

The applicability of an electrochemical Fenton-type process (EF-HOCl-ReFe) to the treatment of three actual wastewaters, namely wastewater from an automobile factory (automobile wastewater), metal scrap-cleansing wastewater, and municipal wastewater, is discussed in this research. The EF-HOCl-ReFe successfully removed the chemical oxygen demand (COD) from automobile wastewater pre-treated by a coagulation process without any inhibition. The apparent current efficiency reached 86%, 46% of which was ascribed to the electrochemical Fenton-type mechanism. The metal scrap-cleansing wastewater had a yellow colour and high concentrations of COD (6550 mg/L) and Cl(-) (1560 mM). The EF-HOCl-ReFe could achieve almost complete COD removal and decolourization after 48 h of treatment, although a temporary intensification of colour was observed before the decolourization. The EF-HOCl-ReFe was also effective in the removal of 1,4-dioxane from municipal wastewater pre-treated by activated sludge and coagulation processes, which were unable to remove 1,4-dioxane. The 1,4-dioxane removal efficiency after 30 min of treatment reached 68.5%. Thus, the EF-HOCl-ReFe was applicable to the treatment of these actual wastewaters.

Granular activated algae for wastewater treatment.

The study used activated algae granules for low-strength wastewater treatment in sequential batch mode. Each treatment cycle was conducted within 24 h in a bioreactor exposed to 235 μmol/m²/s light intensity. Wastewater treatment was performed mostly in aerobic conditions, oxygen being provided by microalgae. High removal efficiency of chemical oxygen demand (COD) was achieved (86-98%) in the first hours of the reaction phase, during which the indicator's removal rate was 17.4 ± 3.9 mg O₂/g h; NH(4)(+) was removed during organic matter degradation processes with a rate of 1.8 ± 0.6 mg/g h. After almost complete COD removal, the (O⁺) remaining in the liquor was removed through nitrification processes promoted by the increase of the liquor's oxygen saturation (O₂%), the transformation rate of NH4(+) into NO(3)(-) increasing from 0.14 ± 0.05 to 1.5 ± 0.4 mg NH4(+)/g h, along with an O₂% increase. A wide removal efficiency was achieved in the case of PO(4)(3)(-) (11-85%), with the indicator's removal rate being 1.3 ± 0.7 mg/g h. In the provided optimum conditions, the occurrence of the denitrifying activity was also noticed. A large pH variation was registered (5-8.5) during treatment cycles. The granular activated algae system proved to be a promising alternative for wastewater treatment as it also sustains cost-efficient microalgae harvesting, with microalgae recovery efficiency ranging between 99.85 and 99.99% after granules settling with a velocity of 19 ± 3.6 m/h.

Comparison of Pyridazinium Electro-oxidation on Boron-doped Diamond (BDD) and SnO2 in a Basic Medium

The eco-friendly ionic liquid 1-(2-ethoxy-2-oxoethyl) pyridazinium chloride's (EOPC) newly synthesised electro-oxidation behaviors of boron-doped diamond (BDD) and SnO 2 in an alkaline media were compared using galvanostatic electrolysis. Various pyridazinium and alkaline concentrations were studied. In addition, the temperature, and density current effect of pyridazinium oxidation were investigated. The BDD showed a higher activity toward pyridazinium oxidation than the SnO 2. This is mainly due to the higher characteristics and the relatively inert nature of the BDD. The bulk electrolysis tests have shown that the complete removal of COD can only be achieved using a boron-doped diamond and that SnO 2 only permits a partial oxidation of pyridazinium. On the basis of the chemical oxygen demand (COD) evolution released during the treatment, a total mineralization has been proposed. Finally, electrolysis has been performed in the presence of NaCl. Based on these results, it is concluded that BDD has less poisoning effects and higher activity than SnO2 for the selective electro-oxidation of pyridazinium.

Coupling digestion in a pilot-scale UASB reactor and electrochemical oxidation over BDD anode to treat diluted cheese whey.

The efficiency of the anaerobic treatment of cheese whey (CW) at mesophilic conditions was investigated. In addition, the applicability of electrochemical oxidation as an advanced post-treatment for the complete removal of chemical oxygen demand (COD) from the anaerobically treated cheese whey was evaluated. The diluted cheese whey, having a pH of 6.5 and a total COD of 6 g/L, was first treated in a 600-L, pilot-scale up-flow anaerobic sludge blanket (UASB) reactor. The UASB process, which was operated for 87 days at mesophilic conditions (32 ± 2 °C) at a hydraulic retention time (HRT) of 3 days, led to a COD removal efficiency between 66 and 97 %, while the particulate matter of the wastewater was effectively removed by entrapment in the sludge blanket of the reactor. When the anaerobic reactor effluent was post-treated over a boron-doped diamond (BDD) anode at 9 and 18 A and in the presence of NaCl as the supporting electrolyte, complete removal of COD was attained after 3-4 h of reaction. During electrochemical experiments, three groups of organochlorinated compounds, namely trihalomethanes (THMs), haloacetonitriles (HANs), and haloketons (HKs), as well as 1,2-dichloroethane (DCA) and chloropicrin were identified as by-products of the process; these, alongside free chlorine, are thought to increase the matrix ecotoxicity to Artemia salina.