RESUMEN

Microbial fuel cell technology draws attention with its ability to directly recover electrical energy from various organic materials. In this study, the operating conditions affecting the oxidation-reduction and electricity generation efficiency of MFC were optimized using the Taguchi Experimental Design model. Optimization was carried out for maximum power density, coulombic efficiency, azo dye removal, and COD removal. With the determined optimum conditions (cathode pH of 3.0, cathode oxygen status of anaerobic, anode substrate of pre-treated, external resistance of 100 Ω, cathode electrode type of plain carbon, cathode electrode surface of 22 cm2, cathode conductivity of 20 µs/cm), 177.03 mW/m2 power density, 7.50% coulombic efficiency, 91.26% azo dye removal efficiency and 21.61% COD removal efficiency were obtained. By Pareto analysis, it was determined that the power density, coulombic efficiency and COD removal efficiency were most affected by the substrate type at the anode, and the azo dye removal was most affected by the catholyte pH. The maximum power density and internal resistance of the MFC operated under optimum conditions were determined as 145.11 mW/m2 and 243.30 Ω, respectively by the polarization curve. Cyclic voltammetry was also performed for the electrochemical characterization of MFC operated under optimum conditions. An anodic peak at -183.2 mV and a cathodic peak at -181.2 mV was visible in the CV curve.

RESUMEN

In this study, regeneration of spent granular activated carbon (GAC) with reactive dye by hydroxyl and sulfate radical-based advanced oxidation processes (microwave (MW) +persulfate (PS)), (Fe(II)+ PS), and (O3 + H2O2) were evaluated. The adsorption of the dye to the GAC surface was characterized by chemisorption and Langmuir isotherm. Regeneration processes have been optimized by the response surface methodology to determine the operating conditions that will provide the highest adsorptive capacity. The optimum conditions of (MW + PS), (Fe (II) + PS), and (O3 + H2O2) processes were process PS anion of 45.52 g/L, pH of 11.4, MW power of 126 W, and duration of 14.56 min; Fe (II) of 3.58 g/L, PS anion of 73.5 g/L, duration of 59.8 min, and pH of 10.9; and H2O2 of 2.8 mole/L, flow rate of 8.14 mg ozone/L, duration of 32.8 min, and pH of 5.3, respectively. For (MW + PS), (Fe (II) + PS), and (O3 + H2O2) processes, the adsorptive capacity under optimum conditions was found as 4.36, 8.89, and 8.12 mg dye/g GAC, respectively. For (Fe (II) + PS) and (O3 + H2O2) processes, these values are approximately equal to the adsorptive capacity of raw GAC (8.01 mg dye/g GAC). The predicted values of the adsorption capacities by the obtained models were in good agreement with the actual experimental results. Preference Ranking Organization Method for Enrichment Evaluation approach was used in the preference of the appropriate regeneration process. The adsorptive capacity of regenerated GAC, operating cost of the regeneration process, change in the adsorptive capacity during the regeneration cycle, and carbon mass loss criteria were taken into account. The order of preference of regeneration processes was determined as (Fe (II) + PS)> (MW + PS)> (O3 + H2O2) considering all criteria.

Asunto(s)

RESUMEN

Diclofenac sodium (DCF) is a non-steroidal anti-inflammatory drug. It has been classified as ecotoxic even at low concentrations. In this study, adsorption of DCF on coconut shell-based granular activated carbon (GAC) and regeneration of spent GAC with hydrochloric acid (HCl) were investigated. The results showed that GAC with heterogeneous surface structure adsorbs DCF endothermically with both chemical and physical forces. Adsorption and regeneration processes were optimized with Taguchi Experimental Design. The effects of all parameters affecting the adsorption and regeneration processes were determined by analysis of variance and Pareto analyses. DCF removal of 79.80% was obtained at optimum conditions and the most effective parameter was evaluated as GAC size. At optimum regeneration conditions, 6.85 mg DCF/g GAC adsorption capacity was found with an operating cost of €0.05 g GAC. The amount of HCl was the most effective parameter. It was determined that the regenerated GAC had an adsorptive capacity higher than the adsorptive capacity of the raw GAC during at least three regeneration cycles. Raw, spent and regenerated GACs were characterized by Fourier transform infrared spectrometry and scanning electron microscopy analysis.

Asunto(s)

RESUMEN

In this study, a multi-response optimization method using Taguchi's robust design approach is proposed for imidacloprid removal by reverse osmosis. Tests were conducted with different membrane type (BW30, LFC-3, CPA-3), transmembrane pressure (TMP = 20, 25, 30 bar), volume reduction factor (VRF = 2, 3, 4), and pH (3, 7, 11). Quality and quantity of permeate are optimized with the multi-response characteristics of the total dissolved solid (TDS), conductivity, imidacloprid, and total organic carbon (TOC) rejection ratios and flux of permeate. The optimized conditions were determined as membrane type of BW30, TMP 30 bar, VRF 3, and pH 11. Under these conditions, TDS, conductivity, imidacloprid, and TOC rejections and permeate flux were 97.50 97.41, 97.80, 98.00% and 30.60 L/m2·h, respectively. Membrane type was obtained as the most effective factor; its contribution is 64%. The difference between the predicted and observed value of multi-response signal/noise (MRSN) is within the confidence interval.

Asunto(s)

RESUMEN

In this study, surfactant-modified natural zeolite was used to remove Bisphenol A (BPA) from aqueous solutions. Kinetics, equilibrium and thermodynamics of BPA adsorption on the adsorbent surfaces were investigated. The experimental data were described with the Temkin isotherm and the pseudo-second- order kinetic model. Taguchi's robust design approach was used to optimize adsorption of BPA. Experimentation was planned as per Taguchi's L27 orthogonal array. Tests were conducted with different adsorbate amount, pH, time, initial concentration of BPA, temperature and agitation speed. The optimum levels of control factors for maximum total organic carbon removal were defined (adsorbate amount at 0.25 g, pH at 7, time at 30 min, initial concentration of BPA at 50 mg/L, temperature at 30°C and agitation speed at 200 rpm). The ANOVA analysis shown that the most effective control factor is adsorbent dosage; its contribution is 56.4%. Contribution of pH and mixing rate are 7.5% and 7.6%, respectively. A confirmation experiment was conducted to verify the feasibility and effectiveness of the optimal combination. The observed value of S/N (ηobs = 39) ratio is compared with that of the predicted value (ηopt = 48). The prediction error, that is, ηopt - ηobs = 9, is within CI value.

Asunto(s)

RESUMEN

Ciprofloxacin hydrochloride (CIP) is the second generation of fluoroquinolone antibiotics whose residues are found in wastewater and surface water. CIP has high aqueous solubility under different pH conditions and high stability in the soil system. In this study, bentonite was used as a potential sorbent for the removal of CIP from aqueous solutions using batch experiments. The effects of various parameters such as contact time, pH, adsorbent dosage, agitation speed, ionic strength and initial concentration of CIP in aqueous solution on the adsorption capacity were investigated. The optimum contact time, pH, agitation speed and adsorbent dosage were found to be 30 min, 4.5 pH, 150 rpm and 2.5 g L(-1), respectively. When the ionic strength was increased from 5 to 50 mM, the adsorption of CIP decreased from 97.8 to 93.4%. The isotherm adsorption data fitted well with the Langmuir model, Kl and qe were found to be 0.27 L mg(-1) and 147.06 mg g(-1), and the data fitted well with the pseudo-second order kinetics, whereby k was found to be 2.19 g mg(-1) h(-1).

Asunto(s)

RESUMEN

Nitrification and carbon removal are investigated in aerobic batch digestion of various sludges. The experiments are carried out with activated sludge (Test 1) and with a mixture of activated and primary settling sludge (Test 2). The nitrification rate was monitored, measuring the NO2- concentration. At the 3rd day of the digestion 40.7 mgNO2-N/l and 3.89 mgNO2-N/l were found in Tests 1 and 2 respectively. In a digestion process, the degradation of biomass indicates the beginning of the endogenous phase. Our measure for biomass content of the sludge was protein analysis. In Test 1, the first day values of 50.93 mgTOC/ g(dry) matter/day and 138.53 mg(protein)-C/g(dry) matter/day for specific TOC and protein-C removal rates showed, that the digestion process began in the endogenous phase. For Test 2, since the endogenous phase began after removal of raw organic matter in primary settling sludge, specific TOC and protein-C removal rates were observed to be 60.12 mgTOC/g(dry) matter/day and 26.72 mg(protein-C/g(dry)matter/day, respectively.

Asunto(s)

RESUMEN

Wet oxidation process is specially effective for wastes with a high organic matter which can not be removed by conventional treatment methods. The digested and raw activated sludges of PAKMAYA yeast factory are treated by wet oxidation process. The liquid-phase organic matter concentration [as total organic carbon (TOC)] was increased by 16.5% in 10 min during the wet oxidation in the presence of Cu as catalyst and H2O2. Lenghtening the period of the wet oxidation, the TOC-concentration was increased by 66% in 120 min. The biodegradability of the sludge after wet oxidation process was also examined. A very little development in the biodegradability was observed, when wet oxidation was applied as pre-treatment to the digested sludge (5% decrease as TOC, in the presence of Cu catalyst and H2O2). However, in the case of digestion of the raw sludge after the application of wet oxidation, the biodegradability increased significantly (approximately 75%, as TOC). Moreover, wet oxidation improved the ability of settling of sludge solids, as well as enhancing the treatment efficiency. Finally, the volume of settled solids was decreased by 80% in the presence of Cu and H2O2. NH3+-N, NO2(-)-N and NO3(-)-N concentrations in the supernatant decreased with the wet oxidation. pH value of the sludge increased from 6.6 to 7.8-8.0. Since stable sludge was taken from the digester where the nitrification process was progressing, a decrease in the nitrite concentration, with an increase in nitrate was observed in the digestion continuing after the wet oxidation pre-treatment. However, in the raw activated sludge, there was a nitrite formation only in the non-pretreated sludge.

Asunto(s)