Experimental study on electrocoagulation of textile wastewater by continuous horizontal flow through aluminum baffles

We investigated the feasibility of applying a continuous textile wastewater (TWW) treatment, which was accomplished by using electrocoagulation (EC) unit with zigzag horizontal flow across a series of mono-polar aluminum plate baffles. The effects of operating parameters such as current density (20-80 A/m²) and detention time (5-40 min) on turbidity, color, chemical oxygen demand (COD), total suspended solids (TSS) and total dissolved solids (TDS) removal were studied. The optimum conditions were determined as 60 A/m² and 20min by monitoring zeta potential (ζ) of effluent. At the optimum conditions, removal efficiencies for turbidity (97.63%), color (87.87%), COD (93.3%), TSS (94.02%), and TDS (52.13%) were observed. Further, addition of 4mg/L of NaCl dose in the TWW modified conductivity suitably, thereby reducing electrical energy consumption per cubic meter of waste water and specific electrical energy consumption (SEEC) from 13.33 to 2.67kWh/m³, and 23.84 to 4.77kWh/kg Al, respectively. Comparing the EC with conventional coagulation process, EC showed better pollutant removal efficiency.     

Multi-Response Optimization of Parameters for the Electrocoagulation Treatment of Electroplating Wash-Water using Aluminum Electrodes

This present study investigates Ni and Mg removal from electroplating wash-water employing electrocoagulation with aluminum electrodes. The simultaneous effects of various operating parameters were evaluated and optimized using a central composite design in terms of Ni, Mg removal, COD removal, energy consumption, and operating cost. At these optimum conditions (current density = 86.23 A/m², pH = 7.5, operating time = 60 min, and NaCl dose = 0.5 g/l), 97% Ni removal and 90% Mg removal was achieved with energy consumption of 22.45 kWh per kg Ni removed and operating cost being 4 $ per kg Ni removed. X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis were on the residue obtained.     

Anaerobic biogas generation from sugar industry wastewaters in three‐phase fluidized‐bed bioreactor

In the present study, attempts are made to optimize digestion time, initial feed pH, feed temperature, and feed flow rate (organic loading rate, OLR) for maximum yield of methane gas and maximum removal of chemical oxygen demand (COD) and biological oxygen demand (BOD) of sugar industry wastewaters in three‐phase fluidized‐bed bioreactor. Methane gas is analysed by using flame‐ionisation detector (FID). The optimum digestion time is 8 h and optimum initial pH of feed is observed as 7.5. The optimum temperature of feed is 40°C and optimum feed flow rate is 14 L/min with OLR 39.513 kg COD/m³ h. OLR is calculated on the basis of COD inlet in the bioreactor at different flow rates. The maximum methane gas concentration is 61.56% (v/v) of the total biogas generation at optimum biomethanation process parameters. The maximum biogas yield rate is 0.835 m³/kg COD/m³ h with maximum methane gas yield rate (61.56%, v/v) of 0.503 m³/kg COD/m³ h at optimum parameters. The maximum COD and BOD reduction of the sugar industry wastewaters are 76.82% (w/w) and 81.65% (w/w) at optimum biomethanation parameters, respectively.     

Comparison of an Ion Exchanger and an In‐House Electrodialysis Unit for Recovery of L‐Lactic Acid from Fungal Fermentation Broth

Lactic acid has long been widely used in many applications. Currently, the worldwide market is increasing due to the discovery of biodegradable polylactic acid. In this work, L‐lactic acid separations from filamentous fungal fermentation broth using ion‐exchange chromatography and in‐house electrodialysis, were studied and compared. Dowex Marathon WBA was used for the lactic acid separation. The adsorption equilibrium followed a Langmuir isotherm. The optimal conditions for lactic acid adsorption in a fixed‐bed column were at pH 6.0, and 0.8 mL/min and elution by a mixture of 1.0 M sulfuric acid and 1.0 M phosphoric acid in a ratio of 30:70 at 0.3 mL/min. The final lactic acid recovery was 76 % with 90 % purity. A laboratory scale in‐house electrodialysis apparatus was constructed with an effective membrane area of 2.925 · 10^–3 m². The effects of feeding solution concentration, flow rate, pH of the fermentation broth, and applicable voltage were studied. Under the optimal conditions, lactic acid recovery was 92 % with 100 % purity and a specific energy consumption of 0.6122 kWh/kg.     

Comparative study of electrocoagulation and electrochemical Fenton treatment of aqueous solution of benzoic acid (BA): Optimization of process and sludge analysis

Benzoic acid containing synthetic solution was pretreated by acid precipitation at various pH (1-3) and temperature (15-60 °C). Pre-treated solution was further treated by electrocoagulation (EC) and electrochemical Fenton (EF) processes using iron anode and graphite cathode. Optimization of independent operating parameters, namely, initial pH: (3-11), current density (A/m²): (15.24-76.21), electrolyte concentration (mol/L): (0.03-0.07) and electrolysis time (min): (15-95) for EC process and pH: (1-5), current density (A/m²): (15.24-76.21), H₂O₂ concentration (mg/L): (100-500) and electrolysis time (min): (15-95) for EF process, was performed using central composite design (CCD) in response surface methodology (RSM). Maximum removal efficiencies of BA- 76.83%, 88.50%; chemical oxygen demand (COD) - 69.23%, 82.21% and energy consumption (kWh/kg COD removed) - 30.86, 21.15 were achieved by EC and EF processes, respectively, at optimum operating conditions. It was found that EF process is more efficient than EC process based on removal of BA and COD with lower energy consumption. The sludge obtained after EC and EF treatments was analyzed by XRD, FTIR, DTA/TGA and SEM/EDX techniques.     

Characterization of the removal of Chromium(VI) from groundwater by electrocoagulation

A batch electrocoagulation system has been evaluated for the removal of Cr(VI) from brackish groundwater under different operating conditions. The influence of electrode type, applied current density, initial pH, initial chromium concentration, conductivity and temperature were evaluated. The experimental results indicated that chromium removal increased with increasing the applied current density and conductivity. The efficiency of different electrode arrangements (iron, aluminum) was also assessed, and indicated that Fe–Fe electrode pair was the most efficient arrangement and was able to achieve 100% Cr removal at an electrocoagulation time of 5 min, a current density of 7.94 mA/cm², and pH of 8 at room temperature 25 °C. The generated sludge for the iron electrodes was characterized using EDS, X-ray fluorescence (XRF) and FE-SEM. The analysis confirmed the formation and precipitation of Fe(OH)₃ and Cr(OH)₃ as solids. Overall, the study affirmed that electrocoagulation is a reliable technique for the purification of groundwater with an estimated energy consumption of 0.6 kWh/m³.     

Mineralization of the Pharmaceutical β-Blocker Atenolol by Means of Indirect Electrochemical Advanced Oxidation Process: Parametric and Kinetic Study

Atenolol is a β-blocker that can be found in urban wastewaters and which is not removed efficiently by conventional wastewater treatments. In the present study, electro-Fenton (EF) process was used to assess the degradation and mineralization of pharmaceutical atenolol in aqueous solutions. Electrolyses of 250 mL of atenolol solution (0.17 mM), at initial pH 3, were carried out in an undivided electrolytic cell in galvanostatic mode. Influence of material cathode (graphite, stainless steel, and platinized titanium), applied current (100–500 mA), sulfate dosage (0.01–0.5 M), and catalyst ferrous ions concentration (1–10 mM), on the oxidation efficiency was studied. Atenolol mineralization was monitored by COD dosage. Kinetic analysis indicated that atenolol mineralization followed a pseudo-first order model and the rate constant increased with rising current, ferrous ions concentration (up to 5 mM) and electrolyte concentration. Results showed that graphite cathode, 0.5 M Na₂SO₄ electrolyte, 0.3 A and 5 mM FeSO₄ catalyst were the best conditions for atenolol mineralization. In these optimal conditions, after 240 min more than 87% of the initial COD was removed. The corresponding current efficiency (CE) and specific energy consumption (SEC) were 22.33% and 0.194 kWh/kg COD, respectively. This latter corresponds to 0.078 kWh/m³ of treated wastewater.     

Removal of trace Cu from aqueous solution by foam fractionation

A system for removal of Cu²⁺ from aqueous solution by foam fractionation is proposed. The effects of pH, gas flow rate, surfactant concentration and froth/solution ratio on the removal rate and the enrichment ratio were studied to optimize the conditions. The results show that the removal rate increased with gas flow rate decreased, surfactant concentration increased and the froth/solution ratio increased, and was higher at pH4.0-5.0 than at other pH value. The optimum separation conditions were pH5.0, 200 mL/min of gas flow rate, 0.15 g/L of surfactant concentration and 1.1 of froth/solution ratio. Under the optimum conditions, the removal rate was 97.2% and the enrichment was 53.0.     

用硫酸改性粉煤灰处理含磷废水的研究

以硫酸对粉煤灰进行改性用于含磷废水的净化,考察了pH值,吸附剂用量,磷初始浓度,反应时间、反应温度对净化过程的影响。通过实验发现溶液pH值在8~11范围内对磷的吸附过程影响不显著,改性粉煤灰可以在较宽的pH值范围内进行脱磷处理;随着粉煤灰加入量的增加和初始溶液中磷酸根浓度的降低,磷的净化率逐渐增加。对于含磷<80 mg/L的溶液,当粉煤灰的投加量为3%时,反应温度40℃,磷的吸附效率可达97.6%。改性粉煤灰对水中磷的净化过程速度较快,30~40 min可达到最大净化率。     

Comparison of electrocoagulation,peroxi-electrocoagulation and peroxi-coagulation processes for treatment of simulated purified terephthalic acid wastewater: Optimization,sludge and kinetic analysis

This study mainly focuses on a comparative study of electrocoagulation (EC), peroxi-electrocoagulation (PEC) and peroxi-coagulation (PC) processes for the treatment of aqueous solution containing major toxic components of purified terephthalic acid wastewater: benzoic acid (BA), terephthalic acid (TPA), para-toluic acid (p-TA) and phthalic acid (PA). The solution was initially treated by acid treatment method at various pH (2-4) and temperature (15-60 °C). The supernatant was further remediated by EC, PEC and PC methods independently. Process variables such as pH (4-12) and pH (1-5), current density (45.72-228.60 A/m²), electrolyte concentration (0.04-0.08 mol/L), electrode gap (1-3 cm), H₂O₂ concentration (600-1,000 mg/L) and reaction time (20-100 min) during EC, PEC and PC treatment were effectively optimized through central composite design under Design Expert software. Maximum COD removal of 60.76%, 73.91%, 66.68% with energy consumption (kWh/kg COD removed) of 95.81, 49.58, 69.26 was obtained by EC, PEC and PC treatments, respectively, at optimum conditions. Electrochemical methods were compared by removal capacities, consumption of energy, operating cost, degradation kinetics and sludge characteristics. PEC treatment was found most effective among EC, PEC and PC processes due to its highest removal capacity and lowest energy consumption features.     

Heavy oil processing in steam and hydrogen plasmas

Heavy oil in the form of finely divided spray was reacted with steam and hydrogen plasmas respectively. The heavy oil was preheated to 473 K at a pressure of 2 MPa and fed through pressure atomizers at flow rates between 0.002 and 0.08 m³/h into a dc plasma jet contained in a reactor 20 cm in diameter and 1.5 m long. The hydrogen and steam plasmas had maximum initial temperatures of 6000 K and 3450 K respectively and specific net energy inputs between 0.4 and 12.6 kWh/kg oil were used. With a hydrogen plasma, the heavy oil reacted to form acetylene, ethylene, methane, soot, and pitches, while with a steam plasma, carbon monoxide and dioxide were formed as well. Light liquid hydrocarbons were not in evidence. Increases in the hydrogen (or steam)-to-oil ratio and specific energy consumption increased the oil-to-gas conversions.     

Cathodic Decolourisation of Dyes in Concentrates from Nanofiltration and Printing Pastes

Direct cathodic reduction of dyes which contain an azo-goup in the chromophore was successfully used for decolourisation of intensively coloured concentrates from Nanofiltration treatment of textile effluents. Based on laboratory scale experiments, a technical multi-cathode electrolyser was applied for full scale decolourisation experiments at cell currents from 40 to 80 A. The absorbance of the treated wastes decreased from 60 to 80% of the initial value at an energy consumption of 2–8 kWh m^–3. Experiments with addition of redox mediator indicate a significant increase in decolourisation rate; however chemical consumption is increased for 0.5–1.5 kg m^–3 of waste. The decolourisation of reactive dye containing printing pastes was also achieved at the laboratory scale, where decolourisation of 60–80% was achieved.     

Characteristics of phosphate adsorption on ferric hydroxide synthesized from a Fe<Subscript>2</Subscript>(SO<Subscript>4</Subscript>)<Subscript>3</Subscript> aqueous solution discharged from a hydrometallurgical process

Ferric hydroxide adsorbent was prepared by a chemical treatment process with H₂O₂, NaOH, and aeration from a Fe₂(SO₄)₃ aqueous solution as a side product discharged from the hydrometallurgical process used to extract neodymium. The ferric hydroxide was used as an adsorbent to prevent eutrophication in water. At the time of synthesis, the most important process variable is the pH condition, which, in this experiment, was changed from pH 3 to 13. The cost of synthesizing ferric hydroxide was sharply reduced by using ferric sulfate, which is considered a side product of the aforementioned hydrometallurgical process, as a starting material, and an adsorbent with high adsorption ability was prepared by controlling the pH level. Microstructural characterization of the synthesized ferric hydroxide revealed particles with a specific surface area of 194.2 m²/g and an average pore diameter of 2.66 nm at pH 6 and 298 K. A column-type packed-bed adsorption experiment was conducted under the following conditions: a flow rate of 0.567 BV/min (3.2 mL/min), 298 K, and atmospheric pressure. The results of the adsorption performance test indicated that the adsorption efficiency of phosphate at concentrations of 10 ppm was 100% at a flow rate of 0.567 BV/min within a contact time of 2 min, and the maximum adsorption capacity for phosphate ions was 65 mg/g.     

DECOMPOSITION OF 4-NITROPHENOL BY OZONATION IN A HOLLOW FIBER MEMBRANE REACTOR

The effect of initial pH, liquid flow rate, gas flow rate, and gaseous ozone concentration on the ozonation of 4-nitrophenol in a membrane reactor was investigated. The results showed that the disappearance of 4-nitrophenol increased with the increase of liquid flow rate, gas flow rate, and gaseous ozone concentration. The rise of the initial pH value led to an increase in 4-nitrophenol removal rate, but the increase became negligible after initial pH exceeded 9.5. The highest removal efficiency of 4-nitrophenol achieved was 94% after 100 min reaction when gaseous ozone concentration was 0.51 mmol L^?1, gas flow rate was 57 mL min^?1, liquid recirculation rate was 72 mL min^?1, and initial pH was 10.3. The membrane reaction system could be modeled based on the lumped kinetics of 4-nitrophenol removal, and the corresponding rate constant of 4-nitrophenol removal was determined from the model.     

Comparison of cost and treatment efficiency of solar assisted advance oxidation processes for textile dye bath effluent

The study investigated the efficiency and cost effectiveness of solar-assisted photochemical processes in comparison with advance oxidation processes (AOPs) for the textile effluents treatment. Efficiency of UV irradiation alone for one hour in removing color was almost double in comparison to solar radiation alone for effluents of different dye concentrations (E1>E2>E3). For coupled UV/H₂O₂ process, there was higher color removal efficiency obtained for effluent E₃ (85%) as compared to E₂ (70%) and E₁ (57%), while E1 showed higher COD removal efficiency (70%) as compared to E₂ (50%) and E₃ (62%). However, the efficiency of solar/H₂O₂ for COD removal was comparable to UV/H₂O₂, i.e., E₂ (57%) and E₃ (53%). In the case of UV and solar-assisted photo-Fenton processes, removal efficiency of the UV process was further increased as approached to almost 90% removal for E₁; on the other hand, the solar-assisted process efficiency remained the same. The relative efficiencies of AOPs were found to be in the order of UV assisted photo-Fenton process>UV/H₂O₂>UV alone. Although, solar-assisted Fenton treatments were relatively low and slow but without any energy consumption in comparison to high energy consumption of UV. Among the UV processes, UV assisted photo-Fenton treatment appeared to have better color removal efficiency with energy requirements of 5 kWh/m³, 8 kWh/m³ and 3 kWh/m³ for E₁, E₂ and E₃, respectively.     

含十二烷基苯磺酸钠废水的多级泡沫分离研究

采用多级泡沫分离装置对水中十二烷基苯磺酸钠(SDBS)进行分离富集,考察了表面活性剂溶液的浓度、离子强度、pH值、分离时间、气体流速等因素对水中十二烷基苯磺酸钠脱除率的影响。进一步采用四因素三水平正交实验进行分离条件的优化,结果表明溶液浓度为20 mg/mL,气体流速为20L/min,pH=10,离子强度为2×10-5mol/L时,分离5 min,可使SDBS的脱除率最高达到97%,三次平行试验SDBS的脱除率分别为96.61%、97.04%和93.93%。与单级环流泡沫分离塔(其脱除率为82%)相比,多级泡沫分离装置具有能耗比低、分离效率高的优点,具有更好的推广应用价值。     

Development of the electrochemical scale removal technique for desalination applications

The possibility of alkaline scale precipitation and removal by electrolytic devices has long been recognized. The scale removal principle of the electrochemical technique is based on the creation of a high pH environment around the cathode by water and oxygen reduction reactions which release hydroxyl ions. The alkaline environment induces precipitation of the calcium hardness in the form of CaCO₃ and of the magnesium hardness, in the form of Mg(OH)₂. Despite the commercial availability of such equipment, the use of electrochemical scale control methods is quite limited. Currently, the main field of application of electrolytic devices is for reducing the hardness of water recirculating in cooling towers. The lack of authoritative technical information on electrochemical scale removal reflects the paucity of research and development efforts in a technology which holds considerable promise for expanding the rather limited scope of viable scale control techniques. The objectives of this research project are to evaluate the potential of the electrochemical technique for RO desalination processes in general and for increasing water recovery levels in particular. The paper summarizes results of the first phase of the research. Models describing cell resistance in the absence and in the presence of a deposit on the cathode are presented. The effects of several parameters on the deposition rate and on the electric energy consumption are investigated. Results show that the higher the water hardness, the higher the scale precipitation rate and the lower the specific energy consumption. An increase in the flow velocity augments the scale deposition rate. Analysis of the velocity effect data indicates that the scale precipitation reaction is mass transfer controlled. The main optimization parameter is the current density. As may be anticipated, a low specific electrical energy is consumed when the electrolyzed solution is exposed to a large electrode surface and a high specific energy is consumed when the solution is exposed to a small electrode surface. The energy consumption can be rather low. For instance, in the electrolysis of a typical concentrate stream of a brackish desalination plant at a current density of 25 A/m², the energy consumption is of the order of 4 kWh per kg of precipitated CaCO₃ and the scale precipitation rate is of the order of 25 g CaCO₃/h m². Finally, a flow scheme is presented indicating the possibility of beneficial increase of the water recovery level in brackish water RO desalination, by partial recycle of the concentrate after electrochemical precipitation of the scale forming ions held in solution by the anti-scalant.     

水箱中水的电化学法处理

利用研制的电极电解水产生强氧化剂,进行杀灭微生物、除铁改善水箱中水质的实验。结果表明,水流单程通过处理,杀菌率＞99％,电耗≤0．1kWh/m^3;除铁率＞99％,电耗≤0.08kWh/m^3。通过检测水中溶解氧含量的变化确认杀藻效果。循环处理水中的水,水中总铁含量从14mg／L降至≤0.3mg/L,细菌总数从10^4个／mL降至≤个／mL。用处理后的水冲洗小便池,消除了尿垢。     

Investigation of sour gas desulfurization process by nano absorber and under magnetic field in a packed tower; experimentally and theoretically

ABSTRACT

Hydrogen sulfide is a major contaminant that is expelled into the atmosphere by chemical industry. So, the mechanism for absorption of sulfur from sour gas by carbon nano-tubes in a packed bed under a magnetic field is considered, in this paper. Therefore, empirical and theoretical studies have been done to obtain the sulfur content in the outlet gas stream. The independent variables studied in this paper include: the magnetic field (1.5 amperes), initial sulfur content (0, 0.003, 0.008, 0.013, 0.05 and 0.1?mole/m³) and gas temperature (33°C, 37°C and 40°C). The gas flow rate is (0.18, 0.2 and 0.22?m³/min). The minimum amount of hydrogen sulfide in the output stream is selected as the aim of the experiments and related conditions as optimal operating conditions. Results indicate that the sulfur oxidation curves contains an approximately linearly increasing segment when the applied field intensity increases from 90 to 160?Oe, and that the sulfur oxidation percentage is improved by nearly 5.8% when the magnetic field is increased from 90 to 400?Oe. Obtained results state the optimum flow rate and temperature for maximum desulfurization is 0.22?m³/min and 40°C, respectively. Results show, the increase in the initial concentration under the operating temperature and magnetic field increases the effective mass transfer coefficient from 2.2–8.3. In addition the effective mass flux of hydrogen sulfide removal can be extended to 5.9, in this state. Finally, the experimental results have a fairly good fit with theoretical results.     

Treatment of potato chips manufacturing wastewater by electrocoagulation

Treatment of wastewater from potato chips manufacturing by electrocoagulation (EC) was investigated. Experiments were conducted to determine the optimum operating conditions such as electrode type, pH, current density and retention time. Aluminium and iron electrodes were used, and aluminium electrodes were found to be more suitable since it had a higher removal rate of COD, turbidity and suspended solids than the iron electrode. The removal efficiencies of COD and turbidity were high, being 60% and 98%, respectively, with retention time < 40 min. 0.05–1.75 kg (per kg COD removed) of dried sludge was removed. COD removal kinetics during EC process was described by a macro-kinetics model. Results from the kinetic studies showed that the kinetic data fit the second-order kinetic model well. The operating costs investigated in the present study were the energy cost of EC and the material cost due to the consumption of aluminium electrode. Operating costs were varied in the range of 0.48 to 5.42 $/m³ and 0.62 to 6.32 $/m³ wastewater treated at 20–300 A/m² and 5–40 min, respectively. The energy consumption was 4 kWh/m³ for wastewater treated less than 8 min under typical operating conditions.