Electrochemical oxidation of landfill leachate in a flow reactor: optimization using response surface methodology

Decolorization enhancement of basic fuchsin by UV/H2O2 process: optimization and modeling using Box Behnken design

The present work deals with the optimization of basic fuchsin dye removal from an aqueous solution using the ultraviolet UV/H2O2 process. Response Surface Modeling (RSM) based on Box-Behnken experimental design (BBD) was applied as a tool for the optimization of operating conditions such as initial dye concentration (10-50 ppm), hydrogen peroxide dosage (H2O2) (10-20 mM/L) and irradiation time (60-180 min), at pH = 7.4 under ultra-violet irradiation (254 nm and 25 W intensity). Chemical oxygen demand (COD abatement) was used as a response variable. The Box-Behnken Design can be employed to develop a mathematical model for predicting UV/H2O2 performance for COD abatement. COD abatement is sensitive to the concentration of hydrogen peroxide and irradiation time. Statistical analyses indicate a high correlation between observed and predicted values (R2 > 0.98). In the BBD predictions, the optimal conditions in the UV/H2O2 process for removing 99.3% of COD were found to be low levels of pollutant concentration (10 ppm), a high concentration of hydrogen peroxide dosage (20 mM/L), and an irradiation time of 80 min.

Design of experiments (DoE) to develop and to optimize extraction of psychoactive substances

The design of experiments (DoE) method was employed to optimize the adsorption processes of seven psychoactive substances in magnetic solid phase extraction. Fe₃O₄/GO/ZIF-8 was utilized as an adsorbent for the efficient extraction of psychoactive substances from environmental water samples. The analytes were ephedrine, methylephedrine, amphetamine, methamphetamine, morphine, papaverine, and thebaine, which were determined by ultrahigh performance liquid chromatography-tandem mass spectrometry. Plackett-Burman design was employed to identify the significant factors responsible for adsorption, and Box-Behnken design was used for further optimization to obtain the optimum values for each variable. The predicted and experimental values were found to be in good agreement. The coefficient of determination (R²) values of 0.9500-0.9976 indicated that the model was significant. The linear ranges were 1-100 ng mL^-1, and the correlation coefficient was good (r² ≥ 0.995). The EF with values of about 2.5 was obtained with recoveries in the range of 74.92-94.47%. The limits of detection (LOD) and limits of quantification (LOQ) were 0.086-0.353 ng mL^-1 and 0.286-1.175 ng mL^-1, respectively. The intra-day and inter-day RSDs were in the range of 0.17-1.87% and 0.06-2.21%, respectively. By using the DoE method, the errors associated with inferring the influence and interaction between various factors can be reduced. The combination of MSPE and DoE improves the recovery, precision, and simultaneous detectability of the target analytes. It has a high potential for psychoactive substance analysis in environmental water.

Treatment of wastewater from the washing process of a municipal solid waste collection container by electrochemical treatment using different anode materials: a statistical optimization

An underground municipal solid waste (MSW) container should be washed periodically to prevent/reduce odor and leachate production. In this study, the treatment process of wastewater derived from the washing process of an MSW container was investigated using the electrochemical (EC) treatment process with different anode materials (Fe, TiO₂, and graphite). Response surface methodology (RSM) was used to evaluate the effect of process parameters such as initial pH, applied current, and reaction time on chemical oxygen demand (COD), Tannin/Lignin, and color removals. According to the results obtained from the RSM models, all process parameters were significant. The optimum process parameters in terms of COD removal were derived from the models for each anode material. Under the optimized conditions, the COD removals were determined to be 93.25%, 75.95%, and 98.46% for Fe-Fe, TiO₂-Fe, and graphite-Fe electrode pairs, respectively. The color and Tannin/Lignin removals were determined as 98.12% and 77.78% for the Fe-Fe, 92.76% and 98.45% for the TiO₂-Fe and 94.50% and 79.56% for the graphite-Fe electrode pair, respectively. The specific energy consumption (SEC) values were found as 46.95, 300.02, and 32.95 kWh/m³ for each electrode combination given above, respectively. In terms of both removal efficiencies and SEC, the most effective anode material was determined as graphite, followed by iron.

Optimized Box-Behnken Design Combined Response Surface Methodology to Determine Calcium and Iron Contents Using Visible, Atomic Emission and Atomic Absorption Spectrophotometry in Vegetables and Wastewater Samples

BACKGROUND

Calcium and iron are crucial essential minerals. Iron is mainly responsible for transporting oxygen in the body and the immune system. In comparison, calcium's primary function is in human bones and teeth. Due to that, it is vital to quantify the amount in vegetables.

OBJECTIVE

Optimization and validation of three analytical procedures, visible, atomic emission spectrophotometry (AES), and atomic absorption spectrophotometry (AAS), were developed to determine calcium and iron in vegetables and wastewater samples using response surface methodology (RSM) via Box-Behnken design (BBD). The design helps to reduce experiment trials with selected variables to find a correlation between them and their respective dependent variables.

METHODS

Method I was developed to quantify calcium in vegetables mixed with concentrated 3M HNO3 and heated to reflux as per the BBD. Then it was cooled, filtered, and completed with 3M HNO3 to be carried out utilizing AES and AAS. For method II, vegetables were mixed with nitric acid and sulfuric acid solution with an optimized 5M KSCN solution, which was computed using the AAS and visible spectrophotometry.

RESULTS

First, percentage of water content was calculated for all vegetables, higher in malabar spinach and lower in peas. The calcium and iron contents were present within 0.59-2.68 mg and 35.8-211.5 mg, respectively, in 100 g of vegetables. The results showed a higher amount of iron was available in spinach and a lower amount in okra. In contrast, the highest calcium amount was present in broccoli and the lowest amount was in peas. The calcium and iron content were between 0.015-137.25 and 0.01-147.85 µg/mL in the wastewater samples.

CONCLUSIONS

These methods can help to determine the amount of calcium and iron for the quality control samples in research and development, food, and the environmental industry.

HIGHLIGHTS

Three validated analytical techniques quantify calcium and iron in vegetables and wastewater samples. The RSM-BBD optimized the method and determined its crucial factors.

Degradation of oxytetracycline in aqueous solution by heat-activated peroxydisulfate and peroxymonosulfate oxidation

Oxytetracycline (OTC) is a broad-spectrum antibiotic that resists biodegradation and poses a risk to the ecosystem. This study investigated the degradation of OTC by heat-activated peroxydisulfate (PDS) and peroxymonosulfate (PMS) processes. Response surface methodology (RSM) was used to evaluate the effect of process parameters, namely initial pH, oxidant concentration, temperature, and reaction time on the OTC removal efficiency. According to the results of the RSM models, all four independent variables were significant for both PDS and PMS processes. The optimum process parameters for the heat-activated PDS process were pH 8.9, PDS concentration 3.9 mM, temperature 72.9°C, and reaction time 26.5 min. For the heat-activated PMS process, optimum conditions were pH 9.0, PMS concentration 4.0 mM, temperature 75.0°C, and reaction time 20.0 min. The predicted OTC removal efficiencies for the PDS and PMS processes were 89.7% and 84.0%, respectively. As a result of the validation experiments conducted at optimum conditions, the obtained OTC removal efficiencies for the PDS and PMS processes were 87.6 ± 4.2 and 80.2± 4.6, respectively. PDS process has higher kinetic constants at all pH values than the PMS process. Both processes were effective in OTC removal from aqueous solution and RSM was efficient in process optimization.

Kinetics of the Organic Compounds and Ammonium Nitrogen Electrochemical Oxidation in Landfill Leachates at Boron-Doped Diamond Anodes

Electrochemical oxidation (EO) of organic compounds and ammonium in the complex matrix of landfill leachates (LLs) was investigated using three different boron-doped diamond electrodes produced on silicon substrate (BDD/Si)(levels of boron doping [B]/[C] = 500, 10,000, and 15,000 ppm—0.5 k; 10 k, and 15 k, respectively) during 8-h tests. The LLs were collected from an old landfill in the Pomerania region (Northern Poland) and were characterized by a high concentration of N-NH₄⁺ (2069 ± 103 mg·L⁻¹), chemical oxygen demand (COD) (3608 ± 123 mg·L⁻¹), high salinity (2690 ± 70 mg Cl⁻·L⁻¹, 1353 ± 70 mg SO₄²⁻·L⁻¹), and poor biodegradability. The experiments revealed that electrochemical oxidation of LLs using BDD 0.5 k and current density (j) = 100 mA·cm⁻² was the most effective amongst those tested (C_8h/C₀: COD = 0.09 ± 0.14 mg·L⁻¹, N-NH₄⁺ = 0.39 ± 0.05 mg·L⁻¹). COD removal fits the model of pseudo-first-order reactions and N-NH₄⁺ removal in most cases follows second-order kinetics. The double increase in biodegradability index—to 0.22 ± 0.05 (BDD 0.5 k, j = 50 mA·cm⁻²) shows the potential application of EO prior biological treatment. Despite EO still being an energy consuming process, optimum conditions (COD removal > 70%) might be achieved after 4 h of treatment with an energy consumption of 200 kW·m⁻³ (BDD 0.5 k, j = 100 mA·cm⁻²).

Statistical optimization of textile dye effluent adsorption by Gracilaria edulis using Plackett-Burman design and response surface methodology

Statistical optimization models were employed to optimize the adsorption of textile dye effluent onto Gracilaria edulis. Significant factors responsible for adsorption were determined using Plackett-Burman design (PBD) and were time, pH, and dye concentration. Box-Behnken (BB) design was used for further optimization. The predicted and the experimental values were found to be in good agreement, the coefficient of determination value 0.9935 and adjusted coefficient of determination value 0.9818 indicated that the model was significant. The results of predicted response optimization showed that maximum decolorization could be attained with time 131.51 min, pH 7.48, and dye concentration 23.13%. The model was validated experimentally with 92.65% decolorization efficiency. The experiment was confirmed using Fourier transform infrared spectroscopy (FTIR), high-resolution scanning electron microscope coupled with energy dispersive X-ray analysis (HR-SEM-EDX), X-ray diffraction spectrometry (XRD) and Brunauer-Emmett-Teller (BET) surface area and pore size analysis techniques. Desorption studies at various pH (2–14) were performed and a maximum of 23% of the dye was recovered from the adsorbed biomass.

Removal of natural organic matter from aqueous solutions using electrocoagulation pulsed current: optimization using response surface methodology

The use of the pulsed current can be an alternative to decrease the electrode polarization, as well as achieving lower energy consumption. This study investigated the electrocoagulation through pulsed current for the removal of natural organic matter from water. The experiments were carried out using Box-Behnken factorial design with the response surface methodology for the design of experiments, modeling and interpreting of the results. The electrocoagulation cell consisted of an acrylic reactor with 4 L capacity with four electrodes of aluminum, in parallel connection mode. The experimental independent variables studied were: current density (5.5 to 44.5 A m^-2), electrodes spacing (2 to 7.6 mm), stirring rate (200 to 1,000 rpm), frequency (500 to 5,000 Hz), humic acid concentration (5 to 20 mg L^-1) and NaCl (100 to 300 mg L^-1) as supporting electrolyte, evaluating the residual apparent color (RAC) and electric energy consumption (EEC). The pH of the solution increased during the experiments, reaching basic values. The response surface regression procedure was employed to fit the second-order polynomial, and the model fitted well to the obtained values, reaching R² 0.9995 (RAC) and R² 0.9989 (EEC). The lowest RAC was 11.8 Hazen units (96.2% color removal), where the EEC was 0.393 kWh m^-3.

Application of surface response method (RSM) to optimize ammonia nitrogen removal from fresh leachate using combination of ultrasound and ultraviolet

Ammonia nitrogen levels are very high in leachate. This study was conducted to optimize the removal of ammonia nitrogen from fresh landfill leachate using a combination of ultrasound waves and ultraviolet irradiation. A sample of fresh landfill leachate was obtained from a municipal landfill site, located in Shahroud (Semnan, Iran) and its ammonia nitrogen was measured by spectrophotometric method. Ultrasound and ultraviolet irradiation were simultaneously used to remove ammonia nitrogen. Box-Behnken design (BBD) based on response surface method (RSM) was applied to analyze and optimize ammonia nitrogen removal by different variables, including pH, contact time, ultrasound frequency and UV intensity. Based on this method, 29 samples with three replications were tested. The analysis of variance indicated quadratic model was significant for removal of ammonia nitrogen from leachate. According to the model, 99.7% removal efficiency (%) of ammonia nitrogen was obtained in the optimal conditions (pH at 9.7, contact time of 59.1 min, ultrasound frequency of 54 kHz and UV intensity of 40 W). The removal efficiency of ammonia nitrogen was obtained 98.6% from the laboratory experiment in these conditions, which agrees well with the predicted response value.

A High-Efficiency CuO/CeO2 Catalyst for Diclofenac Degradation in Fenton-Like System

An efficient Fenton-like catalyst CuO/CeO₂ was synthesized using ultrasonic impregnation and used to remove diclofenac from water. The catalyst was characterized by N₂ adsorption-desorption, SEM-EDS, XRD, HRTEM, Raman, and XPS analyses. Results showed that CuO/CeO₂ possessed large surface area, high porosity, and fine elements dispersion. Cu was loaded in CeO₂, which increased the oxygen vacancies. The exposed crystal face of CeO₂ (200) was beneficial to the catalytic activity. The diclofenac removal experiment showed that there was a synergistic effect between CuO and CeO₂, which might be caused by more oxygen vacancies generation and electronic interactions between Cu and Ce species. The experimental conditions were optimized, including pH, catalyst and H₂O₂ dosages, and 86.62% diclofenac removal was achieved. Diclofenac oxidation by ·OH and adsorbed oxygen species was the main mechanism for its removal in this Fenton-like system.

Coupled heat-activated persulfate - Electrolysis for the abatement of organic matter and total nitrogen from landfill leachate

This work analyzes the viability of a coupled heat-activated persulfate (PS) and electro-oxidation treatment toabatetheorganic matter and nitrogen from ahigh polluted landfill leachate (5500 mg L^-1 TOC; 5849 mg L^-1 TN, pH: 8.4). These characteristics makes PS as a suitable oxidant to deal with the recalcitrant organic matter. Under the optimal conditions (70 °C and 60% of the stoichiometric amount of PS), around 60% of the initial organic load was mineralized. On the contrary, the nitrogen removal was below 20%. A subsequent electrolytic stage using Ti/IrO₂-TaO₂ anode at 175 mA cm^-2 and 0.42 M NaCl during 60 min, led to overall organic matter and nitrogen removal above 85% and 90%, respectively, with energy requirement of 38 kWh per kg of nitrogen removed. In this sense, the combined process achieves a significant reduction in terms of energy consumption, up to one fifth in relation to sole electrolysis. These results confirm the feasibility of this combined process to treat landfill leachate.

Landfill leachate treatment by sequential combination of activated persulfate and Fenton oxidation

This work assesses the feasibility of sequential persulfate and Fenton oxidation for the decolorization and mineralization of landfill leachate (5600 mg L^-1 TOC; pH₀: 8.6) in a continuous batch-recirculation system. Firstly, it was analyzed the role of the operational conditions upon the persulfate activation evaluating the effects of electrolysis, ilmenite (FeTiO₃) as a source of Fe(II) and UV-LED (at 365 nm). The studied variables include current density (j) (50-200 mA cm^-2), persulfate dose (46.8-234 mM) and mineral concentration (500-1500 mg L^-1). The increase in j enhanced the hypochlorite generation and PS conversion to SO₄^- and, consequently, decolorization efficiency increasing the penetration of light through the solution and the photoreduction of Fe(III) to Fe(II) in the FeTiO₃ surface. The combined electrolysis/FeTiO₃/UV-LED showed synergetic effect compared to the individual processes, achieving mineralization around 53% under the optimum operating conditions (1 g L^-1 of FeTiO₃, using 234 mM of PS at 200 mA cm^-2 under UV-LED radiation). The subsequent Fenton oxidation once the pH decreased up to around 3, led to overall mineralization above 90% after 480 min, confirming the suitability of this combined treatment to deal with recalcitrant and highly colored effluents.

Electro activation of persulfate using iron sheet as low-cost electrode: the role of the operating conditions

This work assesses the role of the operational conditions upon the electro-activation of persulfate (PS) using sacrificed iron electrode as a continuous low-cost Fe²⁺ source. An aqueous phenol solution (100 mg L^-1) was selected as model effluent. The studied variables include current density (1-10 mA cm^-2), persulfate concentration (0.7-2.85 g L^-1), temperature (30-90°C) and the solution conductivity (2.7-20.7 mS cm^-1) using Na₂SO₄ and NaCl as supporting electrolyte. A mineralization degree of around 80% with Na₂SO₄ and 92% in presence of NaCl was achieved at 30°C using 2.15 g L^-1 PS at the lowest current density tested (1 mA cm^-2). Besides PS concentration, temperature was the main variable affecting the process. In the range of 30-70°C, it showed a positive effect, achieving TOC conversion above 95% (using Na₂SO₄ under the previous conditions) along with a significant increase in iron sludge, which adversely affects the economy of the process. A lumped and simplified kinetic model based on persulfate consumption and TOC mineralization is suggested. The activation energy obtained for the TOC decay was 29 kJ mol^-1. An estimated operating cost of US$ 3.00 per m³ was obtained, demonstrating the economic feasibility of this process.

Review on landfill leachate treatment by electrochemical oxidation: Drawbacks, challenges and future scope

Various studies on landfill leachate treatment by electrochemical oxidation have indicated that this process can effectively reduce two major pollutants present in landfill leachate; organic matter and ammonium nitrogen. In addition, the process is able to enhance the biodegradability index (BOD/COD) of landfill leachate, which make mature or stabilized landfill leachate suitable for biological treatment. The elevated concentration of ammonium nitrogen especially observed in bioreactor landfill leachate can also be reduced by electrochemical oxidation. The pollutant removal efficiency of the system depends upon the mechanism of oxidation (direct or indirect oxidation) which depends upon the property of anode material. Applied current density, pH, type and concentration of electrolyte, inter-electrode gap, mass transfer mode, total anode area to volume of effluent to be treated ratio, temperature, flow rate or flow velocity, reactor geometry, cathode material and lamp power during photoelectrochemical oxidation may also influence the system performance. In this review paper, past and present scenarios of landfill leachate treatment efficiencies and costs of various lab scale, pilot scale electrochemical oxidation studies asa standalone system or integrated with biological and physicochemical processes have been reviewed with the conclusion that electrochemical oxidation can be employed asa complementary treatment system with biological process for conventional landfill leachate treatment as well asa standalone system for ammonium nitrogen removal from bioreactor landfill leachate. Furthermore, present drawbacks of electrochemical oxidation process asa landfill leachate treatment system and relevance of incorporating life cycle assessment into the decision-making process besides process efficiency and cost, have been discussed.

Nanoscale Fe/Ag particles activated persulfate: optimization using response surface methodology

This work studied the bimetallic nanoparticles Fe-Ag (nZVI-Ag) activated persulfate (PS) in aqueous solution using response surface methodology. The Box-Behnken design (BBD) was employed to optimize three parameters (nZVI-Ag dose, reaction temperature, and PS concentration) using 4-chlorophenol (4-CP) as the target pollutant. The synthesis of nZVI-Ag particles was carried out through a reduction of FeCl₂ with NaBH₄ followed by reductive deposition of Ag. The catalyst was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) surface area. The BBD was considered a satisfactory model to optimize the process. Confirmatory tests were carried out using predicted and experimental values under the optimal conditions (50 mg L^-1 nZVI-Ag, 21 mM PS at 57 °C) and the complete removal of 4-CP achieved experimentally was successfully predicted by the model, whereas the mineralization degree predicted (90%) was slightly overestimated against the measured data (83%).

Distributed mixed-integer fuzzy hierarchical programming for municipal solid waste management. Part I: System identification and methodology development

Due to the existence of complexities of heterogeneities, hierarchy, discreteness, and interactions in municipal solid waste management (MSWM) systems such as Beijing, China, a series of socio-economic and eco-environmental problems may emerge or worsen and result in irredeemable damages in the following decades. Meanwhile, existing studies, especially ones focusing on MSWM in Beijing, could hardly reflect these complexities in system simulations and provide reliable decision support for management practices. Thus, a framework of distributed mixed-integer fuzzy hierarchical programming (DMIFHP) is developed in this study for MSWM under these complexities. Beijing is selected as a representative case. The Beijing MSWM system is comprehensively analyzed in many aspects such as socio-economic conditions, natural conditions, spatial heterogeneities, treatment facilities, and system complexities, building a solid foundation for system simulation and optimization. Correspondingly, the MSWM system in Beijing is discretized as 235 grids to reflect spatial heterogeneity. A DMIFHP model which is a nonlinear programming problem is constructed to parameterize the Beijing MSWM system. To enable scientific solving of it, a solution algorithm is proposed based on coupling of fuzzy programming and mixed-integer linear programming. Innovations and advantages of the DMIFHP framework are discussed. The optimal MSWM schemes and mechanism revelations will be discussed in another companion paper due to length limitation.

Optimization of phenol degradation by the microalga Chlorella pyrenoidosa using Plackett-Burman Design and Response Surface Methodology

Statistical optimization designs were used to optimize the phenol degradation using Chlorella pyrenoidosa. The important factor influencing phenol degradation was identified by two-level Plackett-Burman Design (PBD) with five factors. PBD determined the following three factors as significant for phenol degradation viz. algal concentration, phenol concentration and reaction time. CCD and RSM were applied to optimize the significant factors identified from PBD. The results obtained from CCD indicated that the interaction between the concentration of algae and phenol, phenol concentration and reaction time and algal concentration and reaction time affect the phenol degradation (response) significantly. The predicted results showed that maximum phenol degradation of 97% could be achieved with algal concentration of 4g/L, phenol concentration of 0.8g/L and reaction time of 4days. The predicted values were in agreement with experimental values with coefficient of determination (R(2)) of 0.9973. The model was validated by subsequent experimentations at the optimized conditions.

Cellulose nanofibril reinforced silica aerogels: optimization of the preparation process evaluated by a response surface methodology

CNF–silica composite aerogels with reinforced mechanical properties were prepared under an ambient pressure drying method and optimized by a response surface methodology.

Electrochemical treatment of mature landfill leachate using Ti/RuO2–IrO2 and Al electrode: optimization and mechanism

Today, improving the elimination of refractory pollutants in landfill leachate through electrochemical oxidation technology has attracted considerable attention.