The Investigation of COD Treatment and Energy Consumption of Urban Wastewater by a Continuous Electrocoagulation System

Electrochemical treatment of carwash wastewater using Fe and Al electrode: Techno-economic analysis and sludge characterization

Electro-oxidation is a promising technology for wastewater treatment with biorefractory organic and nitrogen pollutants; however, the high energy demand hinders its wide application. In this study, a novel method by regulating significant parameter during the electro-oxidation process in a timely manner for real dyeing wastewater treatment with energy savings was studied. Operating factors (i.e., flow rate, initial pH value, electrode distance, and current density) were investigated for chemical oxygen demand (COD) and ammonia removal, and the results indicated that current density was the key factor that obviously influenced the electrochemical performance. Indirect oxidation by active chlorine was then confirmed as the main reaction pathway for pollutant oxidation, and the relationship between the current density and the generation of active chlorine was established, suggesting that a large part of the generated active chlorine was not utilized effectively. Subsequently, a novel method of varying the current density in a timely manner based on the reaction mechanism was proposed; the results indicated that, with similar pollutant removal efficiencies, energy consumption could be reduced from 31.6 to 20.5 kWh/m3. Additionally, the novel system was further optimized by Box-Behnken design: The COD removal efficiency could reach 71.8%, and the energy demand could be reduced by 45.6%.

An electrocoagulation process has been used to eliminate the chemical oxygen demand (COD) from wastewaters discharged from the Al-Muthanna petroleum refinery plant. In this process, a circular aluminum bar was used as a sacrificial anode, and hallow cylinder made from stainless steel was used as a cathode in a tubular batch electrochemical Reactor. Impacts of the operating factors like current density (5-25mAcm-2), NaCl addition at concentrations (0-2g/l), and pH at values (3-11) on the COD removal efficiency were studied.Results revealed that the increase in current density increases the COD removal efficiency, whereas an increase in NaCl concentration results in a decline in the COD removal efficiency. Using a pH value higher or lower than 7 causes a lowering of the COD removal efficiency. A current density of 15mA/cm2, NaCl concentration of 1g/l, and pH value of 7 were found to be the best operating conditions in which COD removal efficiency of 95.3% was achieved at a treatment time 45 minutes with an energy consumption of 27.78kWh/kg COD. Based on these conditions, a COD value of 20 ppm could be obtained, which is below the standard limit for discharging petroleum refinery effluents.

Redox flow batteries (RFBs) allow independent control of energy capacity (system size) and power density (reactor design) making them suitable candidates for grid-scale energy storage. Such large-scale applications necessitate high performance and cost effective designs. Aqueous vanadium redox flow batteries are largely studied at laboratory scale, but their application to the grid is restricted by the poor electrochemical stability window of aqueous based system, high costs associated with the metal ions such as vanadium and ion selective membranes. Redox-active polymers (RAPs) are potential redox active molecules which mitigate the parasitic crossover phenomenon. Previous work [G. Nagarjuna et al., J. Am. Chem. Soc., 136, 16309 (2014)] has shown that RAP polymers of molecular weights ranging between 0.56kDa to 300kDa showed increasing rejection rates at the Celguard separators with molecular weight, the largest molecules being rejected 86% relative to supporting salt species in the electrolyte solution. Although large RAP molecules have low trans-separator permeability, the viscosity of the electrolytes increases drastically with RAP concentration. The viscosity of the electrolytes is also sensitive to the supporting salt concentration [ T. Janoschka et al., Polym. Chem., 6, 7801 (2015)]. Rheological properties of the electrolyte influence the flow distribution inside the reactor eventually effecting the reaction distribution. Therefore, it is important to study the flow rate effects on performance of RFBs and estimate the pressure drops inside the reactor since high pressures risk the mechanical integrity of the system and can enhance crossover. A two-dimensional model based on porous electrode theory is developed to simulate the performance of a RAP based RFB with inter digitated flow field. The tanks are modeled as perfectly mixed units and we show that the mixing in the tanks causes significant loss in capacity particularly at low flow rates. In addition to this, we developed a simplified model which predicts the charge utilization (%) and polarization of an RFB as a function of two dimensionless numbers: (1) tank-to-electrode volume ratio, and (2) ratio of flow rate to the stoichiometric flow rate,. With the help of these two models, we identify certain irreversibilities inherent to the conventional RFB design, apart from ohmic resistances, which arise due to thermodynamics of mixing in the tanks and non-uniform reaction current distribution within the reactor. Operating the RFB at high flow rates would enable high utilization and low polarization. Fig 1 (a) shows the development of charge/discharge voltages as a function of the cell’s average state-of-charge at low () and high () flow rates. The polarization, which is measured by the difference in average charge and discharge voltages, is high at low flow rates and low at high flow rates. The spatial variation of the pore scale reaction current density at halfway of charge/discharge process reveal that the reaction current is localized at the flow inlets of the electrodes leading to high polarization. At high flow rates, the reaction current is more uniformly distributed through the volume of the electrode leading to greater utilization and low polarization. Figure 1(b) shows the variation of the magnitude of the charge utilization (Fig 1(b)(i)) and polarization (Fig 1(b)(i)) with the non-dimensional flow rate, as predicted by the porous electrode model and the simplified model. For flow rates greater than twice the stoichiometric flow rate, , the utilization increases and polarization decreases with increasing flow rate. For flow rates close to stoichiometric value, , the RFB approaches a non-flowing battery, therefore polarization decreases with decreasing flow rate in that regime. A simplified transient model developed based on species conservation equation, agrees well with the porous electrode model and therefore can be used as a tool for performance predictions. On-going work is aimed at modeling crossover and determining the losses associated with it. The modeling results highlight the importance of flow rate and tank design. Results confirm that the RFBs should be operated at high flow rates from the perspective of electrochemical performance, but high pressures associated with high flow rates, particularly for viscous electrolytes such as RAPs, would require bulky reactor designs to ensure mechanical integrity and also the high pumping costs associated would reduce the effective energy stored by the entire system. This motivates optimization of RFB design, operating conditions and cost, the relative importance of which is dependent upon the scale of demonstration (lab or grid). We gratefully acknowledge the financial support of the Joint Center for Energy Storage Research (JCESR). Figure 1

A several-fold increase in the flow rate of liquids in synthetic and natural sandstone cores was observed upon application of direct electrical current. These results present the possibility of using direct electric treatment to stimulate wells or enhance water injectivity. Introduction Electroosmosis has long been applied in soil engineering, and there are several patents granted on the removal of water from clayey and silty soils by electroosmosis. These techniques have been used successfully in Germany, England, the U.S.S.R. and Canada in drying water-logged soils for heavy construction. Casagrande documented a good example of electroosmosis in a large-scale soil drying operation in Salzgitter, Germany, during the construction of a double-track railway cutting in a loose loam deposit. Well electrodes were 7.5 m deep and 10 m apart. Before the application of electrical potential, the water flow rate was 0.4 cu m/day/20 wells. potential, the water flow rate was 0.4 cu m/day/20 wells. An electrical potential of 180 v and 19 amps/well increased the flow rate to 60 cu m/day/20 wells, or 150 times the original rate. We and our colleagues have conducted extensive research on the effect of direct electrical current on permeability of sandstone cores. In some of these permeability of sandstone cores. In some of these earlier experiments the flow rate of water was increased by as much as 32-fold on application of direct electrical current, whereas in other cases the increase in flow rate was only about twofold. It was not clear as to why the volumetric rate of flow increased much more in some cases than in others. It was concluded that there is a possibility of using direct electrical current to enhance the injectivity of water in waterflood systems, or simply to increase the rate of production in tight formations. Amba et al. have discussed production in tight formations. Amba et al. have discussed the economics. Amba et al. reported a 175 percent increase in flow rate at 1.5 psi pressure drop upon application of a potential gradient of 4.5 v/cm and a current density of 0.28 milliamp/sq cm. Chilingar et al. reported a 33.7-fold increase in water flow rate at 3.0 psi pressure drop upon application of a potential gradient pressure drop upon application of a potential gradient of 7.5 v/cm and a current density to 20 milliamp/sq cm. Adding CaCl2 (0.1 to 0.5 percent by weight) to the flowing liquid increased the electrosmotic flow rate and resulted in electrochemical changes in the porous medium. These changes were evidenced by porous medium. These changes were evidenced by the higher final permeability upon discontinuation of the treatment (hysteresis effect). Chilingar et al. discovered, however, that the volumetric rate of flow increased to a lesser degree on using concentrated formation brines. Tikhomolova studied the displacement of immiscible liquids in a porous medium. She compared the effectiveness of displacement caused by capillary forces only (imbibition) with that of displacement owing to application of an electric field to the system (electroosmotic displacement) in relation to the capillary radii of powder systems. Based on her experiments, electroosmosis substantially increases the rate of displacement of nonpolar kerosene over the entire range of particle sizes studied (16 to 20, 12 to 16, 8 to 12, and 4 to 8 microns). The influence of electroosmosis increases with decrease in size of silica particles and with increase in backpressure applied to the system. JPT P. 830

Battery thermal management system (BTMS) is of great significance to keep battery of new energy vehicle (NEV) within favorable thermal state, which attracts extensively attention from researchers and automobile manufacturers. As one BTMS scheme, pumped two-phase system displays excellent cooling capacity owing to large amount of latent heat usage, while there is limited research efforts focusing on the feasibility of the BTMS scheme. This paper experimentally investigates thermal performance of a pumped two-phase BTMS heated by a dummy battery with relative high heat fluxes. The effects of heat fluxes, flow rates and cold source temperatures on thermal performance have been studied and conclusions have been drawn accordingly. The results show that the thermal performance of the system is generally enhanced with the increase of the refrigerant flow rates. When the heat flux and cold source temperature are 0.11 W/cm2 and 10°C, respectively, tavg and △tmax are decreased by 3.4°C and 0.5°C, respectively, when the refrigerant flow rate is increased from 0.20 to 1.67 L/min. Meanwhile, heat transfer coefficient is also improved with an increase of the flow rates, while the enhancements become less obvious under high heat flux. In addition, the tavg and △tmax of cold plate surface are increased when the heat flux is elevated, while the tavg at the low flow rate is increased slightly. However, the increase of △tmax is more obvious at the low flow rate, compared to that at high flow rate. When the heat flux is increased from 0.11 to 0.60 W/cm2, tavg is increased by 3.8°C under the flow rate of 0.2 L/min, while that at the flow rate of 1.67 L/min is almost doubled. Meanwhile, the heat transfer coefficient is increased monotonously at the low flow rate, while that at the high flow rate is first decreased and then increased. Besides, lower surface temperatures can be obtained with low cold source temperatures. However, cold source temperatures affect temperature uniformity less.

Combined electrocoagulation and electrochemical treatment on BDD electrodes for simultaneous removal of nitrates and phosphates

Solid‐waste management, particularly of aluminum (Al), is a challenge that is being confronted around the world. Therefore, it is valuable to explore methods that can minimize the exploitation of natural assets, such as recycling. In this study, using hazardous Al waste as the main electrodes in the electrocoagulation (EC) process for dye removal from wastewater was discussed. The EC process is considered to be one of the most efficient, promising, and cost‐effective ways of handling various toxic effluents. The effect of current density (10, 20, and 30 mA/cm2), electrolyte concentration (1 and 2 g/L), and initial concentration of Brilliant Blue dye (15 and 30 mg/L) on the efficiency of the EC process were examined in this study. The results show that removal efficiency increased with current density and sodium chloride (NaCl) concentration and decreased with initial dye concentration. The electrical power and electrodes consumed increased with an increase in current density and decreased notably with increased NaCl. The optimum current density and amount of NaCl were 20 mA/cm2 and 2 g/L, respectively to attain highest values of E133 brilliant blue dye removal. The EC process was examined using adsorption isotherms and kinetics models. Those results showed that the Langmuir isotherm matched the experimental data. Furthermore, the experimental data were followed the Elovich model kinetics.

Deciding on the priority of process parameters using the analytical hierarchy process in electrochemical wastewater treatment and investigation of paint wastewater treatability

Simulation of coupled heat and mass transport with reaction in PEM fuel cell cathode using lattice Boltzmann method

Comparison of COD removal from pharmaceutical wastewater by electrocoagulation, photoelectrocoagulation, peroxi-electrocoagulation and peroxi-photoelectrocoagulation processes

Advanced treatment of dye manufacturing wastewater by electrocoagulation and electro-Fenton processes: Effect on COD fractions, energy consumption, and sludge analysis

The color and Chemical Oxygen Demand (COD) reduction in distillery industrial effluent (DIW) was investigated utilizing photo (UV), sono (US), electrocoagulation (EC), UV + US, UV + EC, US + EC, and US + UV + EC technologies. The empirical study demonstrated that the UV + US + EC process removed almost 100% of color and 95.63% of COD from DIW while consuming around 6.97 kWh m−3 of electrical energy at the current density of 0.175 A dm−2, COD of 3600 mg L−1, UV power of 32 W, US power of 100 W, electrode pairings of Fe/Fe, inter–electrode distance of 0.75 cm, pH of 7, and reaction time of 4 h, respectively. The values found were much greater than those produced using UV, US, EC, UV + US, UV + EC, and US + EC methods. The influence of various control variables such as treatment time (1–5 h), current density (0.075–2.0 A dm−2), COD (1800–6000 mg L−1), inter-electrode distance (0.75–3.0 cm), electrode pairings (Fe/Fe, Fe/Al, Al/Fe, Al/Al), UV (8–32 W), and US (20–100 W) on the color and COD reduction were investigated to determine the optimum operating conditions. It was observed that, an increase in treatment time, current density, UV and US power, decrease in the COD, and inter-electrode distance with Fe/Fe electrode combination improved the COD removal efficiency. The UV and US + EC processes' synergy index was investigated and reported. The results showed that, the US + UV + EC treatment combination was effective in treating industrial effluent and wastewater.

The objective of this study was to determine the effectiveness of two-stage electro-coagulation (EC) process using multi-parameter optimization for treating bio-digested distillery spent wash by stainless steel (SS) and aluminum (Al) electrodes. Operating parameters have been optimized and treatment efficiency of SS and Al electrodes have been compared by central composite design of response surface analysis in terms of COD, color and total organic carbon (TOC) removal. Individual and interactive effects of four independent parameters namely initial pH (pHo: 2–10 and 4–10 for SS and Al electrodes, respectively), current density (j: 30.86–154.32 A m−2), inter-electrode distance (g: 0.5–2.5 cm) and electrolysis time (t: 30–150 min) on the COD, color and TOC removal efficiency were evaluated for both the electrodes. SS electrode was found to be more effective for the removal of COD, color and TOC with removal efficiencies of 70%, 93% and 72%, respectively, as compared to Al electrode, which showed respective removal efficiencies of 59%, 80% and 55%. A two-stage EC process was also conducted to study the predominance of different types of electrodes, and to increase the efficiency of EC process. Results shows that SS followed by Al electrode (with total COD, color and TOC removal efficiency of 81%, 94% and 78%, respectively) was found to be more effective than Al followed by SS electrode combination (with total COD, color and TOC removal efficiency of 78%, 89% and 76%, respectively). Present study shows that EC process can be used as an additional step to bio-methanation process so as to meet effluent discharge standards in distilleries.

An effective method for improving electrocoagulation process: Optimization of Al 13 polymer formation