Three-level Box-Behnken Experimental Design Research Articles

Sustainable Utilization of Mushroom By-Products Processed with a Combined Osmotic Dehydration Pretreatment and a Hot-Air-Drying Step.

Mushroom production and consumption are gaining increased interest due to their unique flavor and nutritional value. However, in the mushroom industry, large amounts of by-products are generated, which have a high negative environmental and economic impact. In this study, an osmotic dehydration process followed by hot-air-drying was applied to mushroom stems to produce dried mushrooms as the end product. The osmotic dehydration conditions (concentration of hypertonic solution, specifically, 10-30% maltodextrin and 20-40% oligofructose; a treatment time of 40-80 min; and a temperature range of 30-50 °C) were optimized using response surface methodology (RSM). The results showed that a four-factor three-level Box-Behnken experimental design was effectively implemented to evaluate the effect of the process parameters and identify the optimal osmotic dehydration conditions for producing osmotically dehydrated mushrooms. The main factor affecting mass transfer was the osmosis temperature, and the optimal conditions were found to be 38 °C, 40% oligofructose and 19.3% maltodextrin as the osmotic agents, and 80 min of immersion time. Moreover, the results showed that osmotic pretreatment, in the optimal conditions, significantly reduced the required drying time of the by-products compared to traditional hot-air-drying, especially at milder drying temperatures. Consequently, the required energy was also reduced by at least 40% at 50 °C.

An Optimization Study of Advanced Fenton Oxidation Methods (UV/Fenton–MW/Fenton) for Treatment of Real Epoxy Paint Wastewater

The use of various advanced oxidation methods in the treatment of wastewater has become the subject of many studies published in recent years. In particular, it is exceedingly significant to compare these treatment methods for industrial wastewater to reduce environmental effects and optimize plant operations and economics. The present study is the first to deal with the treatability of real epoxy paint wastewater (EPW) using MW- and UV-assisted Fenton processes within an optimization framework. A three-factor, three-level Box–Behnken experimental design combined with response surface methodology (RSM) was conducted for maximizing the chemical oxygen demand (COD) and color removal efficiencies of ultraviolet (UV)/Fenton and microwave (MW)/Fenton processes in the treatment of the real epoxy paint wastewater (EPW, initial COD = 4600 ± 90 mg/L, initial color = 114 ± 4 Pt-Co), based on 15 different experimental runs. Three independent variables (reaction time ranging from 20 to 60 min (UV) and from 5 to 15 min (MW), power ranging from 20 to 40 W (UV) and from 300 to 600 W (MW), and H2O2/Fe2+ ratio ranging from 0.2 to 0.6 (for both UV and MW)) were consecutively coded as A, B, and C at three levels (−1, 0, and 1), and four second-order polynomial regression equations were then derived to estimate the responses (COD and color removals) of two distinct systems. The significance of the independent model components and their interrelations were appraised by means of a variance analysis with 99% confidence limits (α = 0.01). The standardized differences of the independent variables and the consistency between the actual and predicted values were also investigated by preparing normal probability residual plots and experiment-model plots for all processes. The optimal operating conditions were attained by solving the quadratic regression models and analyzing the surface and contour plots. UV/Fenton and MW/Fenton processes, which constitute combined Fenton processes, were performed using advanced oxidation methods, while Fenton processes were utilized as the standard method for wastewater treatment. When UV/Fenton and MW/Fenton processes were applied separately, the COD removal efficiencies were determined to be 96.4% and 95.3%, respectively. For the color parameter, the removal efficiencies after the application of both processes were found to exceed 97.5%. While these efficiencies were achieved in 1 h with a 38 W UV unit, they were achieved in 15 min with a MW power of 570 W. According to the RSM-based regression analysis results, the R2 values for both processes were greater than 0.97 and p values were less than 0.003.

Effect of Operating Parameters on the Mulching Device Wear Behavior of a Ridging and Mulching Machine

To conduct an in-depth investigation of the impact of various operating parameters on mulching device wear during the operation of full-film dual-row ridging and mulching machine mulching, this paper employed EDEM software to create a 3D discrete element model of how a mulching device interacts with the soil on the seed bed and simulated the dynamic process of the interaction between the mulching device and the soil during the mulching operation. We analyzed the cladding wear process between the cladding device and the cladding sand particles, and two areas of impact wear on the overburden conveyor housing and areas of wear on the chute deflector scratches were detected. A three-factor, three-level Box–Behnken experimental design approach was used, with mathematical modeling of the relationship between the scraper conveyor lifting line speed, seed bed cover, scraper spacing, and wear of the cover device, finding the optimal combination of operating parameters for mulching devices. The results of the simulation test indicated that the mulching device experienced a minimum wear of 0.958 × 10−3 mm at a lifting line speed of 0.7 m·s−1 for the scraper conveyor, a mulching volume of 2.55 kg·s−1 for the seed bed, and a scraper spacing of 98 mm. The results of the field trial validation showed that, in a comparison between simulated wear parts and a mulching operation prototype of the same two wear parts, the established discrete element model appeared reasonable concerning the structural parameters, with a feasible abrasion mechanism process of sand particles on the soil-covering devices, demonstrating the model’s reliability and validity. It can serve as a guide for optimizing the design of mechanized full-film dual-furrow seed bed mulching operation.

A rapid optimization methodology of produced gas reinjection EOR in carbonate reservoirs

The Carboniferous carbonate reservoir of the Pre-Caspian basin has abundant oil and gas resources. The typical features of low porosity and low permeability and reservoir oil with high concentrations of H2S and CO2 and heavily dissolved gas-oil ratio allow produced gas reinjection as an effective and economic way to enhance oil recovery (EOR). However, the optimal design of injection/production parameters for gas injection processes is the premise for development scheme and technical decision. Compared to the conventional method of one-parameter-at-a-time approach with lack of interactions between various factors and tremendous challenge of main controlling factors identified, in this work we present a rapid optimization methodology to identify the main factors from numerous candidate parameters and obtain optimum levels of key factors. Our chosen methodology is a combination of experimental design with response surface method (RSM). Firstly, the two-level Plackett-Burman experimental design was used to screen and rank ten operational variables for the gas reinjection process. The top five significant parameters with the sum of their influencing weight greater than 94.3 % are bottomhole pressure for producers, reinjection ratio, injection period, injection gas timing and completion interval. Then the three-level Box-Behnken experimental design was employed to perform optimization exploration with the RSM. Regression models of the oil recovery factor (RF) were constructed by using these five key factors, which fits excellently with numerical simulation results. Finally, the optimal levels of controlling factors were determined to maximize oil recovery. This optimization procedure is very practical for reservoir engineers to guide a rapid evaluation of gas injection processes.

Optimization of Supercritical Carbon Dioxide Fluid Extraction of Medicinal Cannabis from Quebec

Research on cannabis oil has evolved to encompass the pharmaceutical industry for the therapeutic potential of the active compounds for pathologies such as Alzheimer, auto-immune disorders, and cancer. These debilitating diseases are best treated with cannabinoids such as tetrahydrocannabinol (∆9-THC), cannabigerol (CBG), and cannabinol (CBN), which relieve neuropathic pain and stimulate the immune system. We extracted cannabinoids from plants with supercritical CO2 and produced an extract with a total yield close to 26%. The three-level Box–Behnken experimental design considered four factors: Temperature, pressure, CO2 flow rate, and processing time, with predetermined parameters at low, medium, and high levels. The mathematical model was evaluated by regression analysis. The yield of ∆9-THC and CBG reached a maximum after 2 h and 15 g/min of CO2, 235 bar, 55 °C (64.3 g THC/100 g of raw material and 4.6 g CBG/100 g of raw material). After another 2 h of extraction time, the yield of CBN reached 2.4 g/100 g. The regression analysis identified pressure and time as the only significant factors for total yield while pressure was the only significant factor for ∆9-THC and CBG. Time, temperature, pressure, and flow rate were all significant factors for CBN.

Acoustic Characteristics of Jute and Coir Non-woven Fabric

Effective noise reduction is essential because it can influence the health and well-being of living organisms significantly, both physically and psychologically. This necessitates the use of appropriate absorbing materials to minimize the negative impact of noise. In recent years, there has been growing interest in using jute, coir and natural fibre-based acoustic materials in architectural and interior applications due to their exceptional acoustic properties, eco-friendliness, cost-effectiveness and widespread availability. The study focuses on analysing the effects of some scrutinised testing parameters of jute, coir and jute-coir blended non-woven fabric samples on noise reduction coefficient through observing sound absorption coefficient. The sound absorption coefficient was measured using the impedance tube method as per the ASTM E-1050 standard. The mean value of the sound absorption coefficient observed at frequencies 250 Hz, 500 Hz, 1000 Hz, and 2500 Hz was used to calculate the noise reduction coefficient. A three-factor & three-level Box–Behnken experimental design was used for designing research and non-woven jute, coir and jute coir blended fabric sample planning. The experimental work showed that with an increase in non-woven jute fabric sample thickness from 15 mm to 45 mm, blending jute 50 % with coir 50% and non-woven fabric samples tested by creating air gaps (15 mm to 30 mm) resulted in higher sound absorption coefficient and improved noise reduction coefficient. The experimental findings and statistical analysis revealed that blending jute with coir and increasing the thickness of non-woven fabric led to a significant improvement in the acoustic performance of the tested samples. However, increasing the air gap resulted in only a marginal improvement in acoustic performance.

Synthesis of Polyhydroxyurethanes-Experimental Verification of the Box-Behnken Optimization Model.

Polyurethanes are one of the most important groups of polymers for numerous sectors of industry. Their production involves using dangerous components (diisocyanates), thus, in the search for safer synthetic routes, alternative methods yielding non-isocyanate polyurethanes (NIPU) have been investigated. In this study, the synthesis of polyhydroxyurethane from cyclic carbonates was performed. A three-factor, three-level Box-Behnken experimental design was constructed and the reaction time, temperature and reagents' molar ratio were the independent variables. The built model revealed that the viscosity was influenced by all three independent factors, while the mechanical properties and glass transition temperature of the PHUs were affected by the reagents' ratios. An experimental verification of the model proved its accuracy as the mechanical strength and glass transition temperature deviated from the modeled values, by 15% and 7%, respectively.

Characterization of a novel chitinolytic Serratia marcescens strain TC-1 with broad insecticidal spectrum

The Gram-negative rod-shaped bacterium Serratia marcescens is an opportunistic pathogen of many organisms, including insects. We report the identification and optimal in vitro chitinase production conditions of a novel chitinolytic S. marcescens strain TC-1 isolated from a naturally infected white grub (Anomala corpulenta) collected from a peanut field at Nanyang city, Henan province, China. Strain identification was conducted by morphological, physiological, biochemical and molecular analyses. The amplified 16S rRNA gene of TC-1 showed a similarity greater than 99% with multiple strains of S. marcescens. Based on Neighbor-joining phylogenetic tree analysis of bacterial 16S rRNA gene sequences, TC-1 formed a clade with S. marcescens, clearly separated from other Serratia spp. The strain TC-1 showed larvicidal activities against five insect species (A. corpulenta, Plutella xylostella, Spodoptera exigua, Helicoverpa armigera, Bombyx mori) and the nematode Caenorhabditis elegans, but not against S. litura. The operating parameters of chitinase production by TC-1 were optimized by response surface methodology using a three-factor, three-level Box-Behnken experimental design. The effects of three independent variables i.e. colloidal chitin concentration (7–13 g l−1), incubation time (24–72 h) and incubation temperature (24–32 °C) on chitinase production by TC-1 were investigated. A regression model was proposed to correlate the independent variables for an optimal chitinase activity predicted as 20.946 U ml−1, using a combination of colloidal chitin concentration, incubation time and incubation temperature of 9.06 g l−1, 63.83 h and 28.12 °C, respectively. The latter agreed well with a mean chitinase activity of 20.761 ± 0.102 U ml−1 measured in the culture supernatants of TC-1 grown under similar conditions with a colloidal chitin concentration, incubation time and incubation temperature of 9 g l−1, 64 h and 28 °C, respectively. Our study revealed the S. marcescens strain TC-1 with potential as a biocontrol agent of insect pests and nematodes and demonstrated the proposed regression model's potential to guide chitinase production by this strain.

Response surface modeling with Box-Behnken design for strontium removal from soil by calcium-based solution.

Owing to its physicochemical similarity to strontium (Sr), calcium (Ca) was tested as a key component of a soil washing solution for Sr-contaminated soil collected near a nuclear power plant. A four-factor, three-level Box-Behnken experimental design combined with response surface modeling was employed to determine the optimal Sr washing condition for Ca-based solution. The Ca concentration (0.1-1M), liquid-to-soil ratio (5-20), washing time (0.5-2h), and pH (2.0-7.0) were tested as the independent variables. From the Box-Behnken design, 27 sets of experimental conditions were selected, and a second-order polynomial regression equation was derived. The significance of the independent parameters and interactions was tested by analysis of variance. Ca concentration was found to be the most influential factor. To determine whether the four variables were independent, three-dimensional (3D) response surface plots were established. The optimal washing condition was determined to be as follows: 1M Ca, L/S ratio of 20, 1h washing, and pH=2. Under this condition, the highest Sr removal efficiency (68.2%) was achieved on a soil contaminated with 90.1mg/kg of Sr. Results from five-step sequential extraction before and after washing showed that 84.0% and 82.9% of exchangeable and carbonate-bound Sr were released, respectively. In addition, more tightly bound Sr, such as Fe/Mn oxides-bound and organic matter-bound Sr, were also removed (86.2% and 64.5% removal, respectively).

Ultrasonic Delignification and Microstructural Characterization of Switchgrass

This present study was undertaken to investigate the ultrasonic delignification of switchgrass (Panicum virgatum L.) and the effects of ultrasonic irradiation on the molecular and microstructure of switchgrass. We investigated this question using response surface methodology (RSM) featuring a four-factor, three-level Box–Behnken experimental design with acoustic power (120, 180, and 240 W), solid–solvent ratio (1/25, 1/20, and 1/15 g/mL), hammer mill screen size (1.6, 3.2, and 6.4 mm), and sonication time (10, 30, and 50 min) as factors, while delignification (%) was the response variable. The native and treated switchgrass samples were further characterized through crystallinity measurements and electron microscopy. The results of lignin analysis show that the percent delignification ranged between 1.86% and 20.11%. The multivariate quadratic regression model developed was statistically significant at p < 0.05. SEM and TEM micrographs of the treated switchgrass grinds resulted in cell wall disruption at the micro- and nano-scales. XRD analysis revealed a reduction in the mean crystallite size and crystallinity index from 15.39 to 13.13 Å and 48.86% to 47.49%, respectively, while no significant change occurred in the d-spacings. The results of this investigation show that ultrasonic irradiation induces chemical and structural changes in switchgrass, which could enhance its use for biofuel and bioproducts applications.

Optimal design of a composite fibrous filter media through vertical integration of fibres in needle punched nonwoven

Present research work investigated the vertical integration of fibres by using newly proposed structural indices in needle punched nonwoven fabric. A new methodology was also proposed to measure the orientation of fibre in the Z direction of nonwoven fabric. The colour summarization technique was used to measure the percentage of fibre transfer from different layers and area covered by holes. The influence of punch density, needle penetration depth and stroke frequency on fabric structure and properties was studied and three-factor three-level Box-Behnken experimental design was used for sample preparation. The proposed structural indices provide useful information to explain the mechanism of vertical integration of fibres during punching operation. The bursting strength, mean flow pore size, filtration efficiency and pressure drop were highly influenced by considered punching parameters. A strong correlation was observed among measured properties and structural indices. Finally, punching parameters were optimised to achieve maximum filtration efficiency at minimum pressure drop.

Sensitive Determination of Imatinib Mesylate in Human Plasma Using DABCO-Based Ionic Liquid-Modified Magnetic Nanoparticles

In this research, new DABCO-based ionic liquid-modified Fe3O4 nanoparticles (NPs) were synthesized by the quaternization reaction. Modified magnetic NPs were characterized by different techniques. The functionalized magnetic NPs were utilized as a novel sorbent for magnetic SPE of imatinib mesylate (IMA) from human plasma samples followed with UPLC–MS–MS. Effective parameters on the extraction of IMA were studied by three-level Box–Behnken experimental design under response surface methodology. Under the optimized conditions, the proposed method was validated based on the principles of Guidance for Industry Bioanalytical Method Validation by the U.S. Food and Drug Administration. The linearity of the developed method was achieved within the range of 0.7–2500 ng mL−1. The LOD and lower limit of quantification were 0.68 and 0.21 ng mL−1, respectively. Satisfactory extraction recovery values ranged from 93 to 102% for human plasma samples with relative standard deviation values lower than 5.9%. The proposed analysis method was sensitive, efficient, rapid, and practical for the determination of IMA in biological samples.

An efficient optimization framework of cyclic steam stimulation with experimental design in extra heavy oil reservoirs

The Jurassic sandstone reservoir of the Pre-Caspian basin has abundant heavy oil resources. It has characteristics of high porosity, high permeability, shallow depth, and high crude oil viscosity. So the cyclic steam stimulation (CSS) is necessary to produce oil in an effective and economic way. However, the optimization of injection-production parameters for CSS is the premise of the technical strategies and development schemes. The conventional method usually adopts the one-parameter-at-a-time approach to perform sensitivity studies. This method is lack of interactions between different factors and difficult to determine the optimal level, in some situations even the main controlling factor is ignored.In our work, the experimental design method was used to consider the interactions of multiple injection-production parameters. The quantitative ranking of important factors was also determined. Based on geological characteristics and pilot test of the extra heavy oil reservoirs in Mortuk oilfield, the numerical simulation model was established. Firstly the two-level Plackeett-Burman experimental design was used to screen seven injection-production parameters for the CSS process. The first five parameters, the sum of their influencing weight larger than 98%, are steam injection intensity, production liquid rate, production time, steam quality and injection rate, respectively. Then the three-level Box-Behnken experimental design was used to perform optimizing studies. Two regression equations of cumulative oil production and cumulative oil steam ratio (COSR) were obtained on the basis of the response surface method, which fits very well with the numerical simulation results. Finally, the optimal values of uncertain factors were determined to maximize cumulative oil with relatively high COSR. This optimization framework is helpful for petroleum engineers to provide a quick evaluation of CSS.

Using Box-Behnken design approach to investigate benzo[a]anthracene formation in smoked cattle meat samples and its' risk assessment.

In present study, a novel approach was selected for benzo[a]anthracene determination from smoked cattle meat samples using solid phase extraction under various experimental conditions. To optimize experimental variables, a three factor, three-level Box-Behnken experimental design combining with response surface methodology and quadratic programming were employed to prevent excessive amount of benzo[a]anthracene formation in smoked meat based on different experimental parameters. The influence of some important process parameters including cooking time (10-30min), fat ratio (5-25%) and distance to the cooking source (5-25cm), which significantly affected the formation efficiency of benzo[a]anthracene were optimized. The analysis of variance was conducted for specifying the interactions of independent variables. The independent and the dependent variables interactions were investigated. The quadratic regression model and the response surface contour plots were used to determine optimum values for the selected variables. The results of study revealed that optimum cooking time of smoked cattle meat was determined as 24.9min, fat ratio 7.9% and the distance to the cooking source 21.8cm. Under optimum conditions, minimum benzo[a]anthracene was formed in meat and its amount was determined using high performance liquid chromatography-mass spectrophotometer as qualitative and quantitative. The limit of detection and limit of quantitation values were calculated as 0.4µgkg-1 and 1.1µgkg-1, respectively.

Optimization of Aqueous NH4+/NH3 Photodegradation by ZnO/Zeolite Y Composites Using Response Surface Modeling

Abstract In this study, ZnO/Zeolite Y composites were synthesized by the solid state dispersion method and employed in order to investigate their photocatalytic performance in NH4+/NH3 removal from an aqueous solution. FTIR spectroscopy, UV-vis diffuse reflectance spectroscopy, SEM and EDX analyses were applied to characterize these composites. The three-factor, three-level Box-Behnken experimental design (BBD), as one of the response surface methodology (RSM), was used to achieve maximum removal of aqueous NH4+/NH3 under optimum conditions by ZnO/Zeolite Y composites. The effects of parameters such as ZnO loading (10–50 wt %), initial pollutant concentration (25–315 mg/L) and solution pH (3–11) as well as their interactions were determined on removal of NH4+/NH3 by the mentioned method. It was found that pH of the solution with the percentage contribution of 86.79 %, was the most important parameter among the others. A second-order polynomial equation was well fitted on the experimental data with the determination coefficient value of 0.9932 and the adjusted determination coefficient value of 0.9864. It could not describe only 0.68 % of observed changes in the response. The predicted removal percentage of NH4+/NH3 at the optimal conditions (pH = 11, NH4+/NH3 initial concentration (207.21 mg/L) and ZnO loading (45.02 wt %)) was achieved 62.26 %, which was in agreement with its experimental value (65 %) obtained in similar conditions.

Response Surface Methodology of Pre-Concentration of Chorophenols from Seawater Samples by Molecularly Imprinted Stir Bar Sorptive Extraction Combined with HPLC: Box-Behnken Design.

A novel molecularly imprinted polymer coated stir bar was prepared using 2-chlorophenol (2-CP) as template molecule and used for selective extraction of phenolic compounds including chlorophenols (CPs) directly from seawater samples. Various parameters affecting extraction have been evaluated using one variable-at-a-time and Box-Behnken design. A three-level Box-Behnken experimental design by six factors, which combined the response surface methodology, was used to optimize the selective extraction of the CPs. Six independent variables, including the absorption and desorption times (ranging from 15 to 25 min), stirring speed (ranging from 550 to 650 rpm), pH of solution (ranging from 4.0 to 6.0), amount of NaCl (ranging from 0.30 to 0.40 mol/L) and temperature of extraction process (ranging from 40 to 50°C) were coded as A, B, C, D, E and F at three various levels (-1, 0 and 1). Under the optimum conditions, the detection limits calculated were 0.17, 0.33 and 0.38 μg/L, respectively, for 2-CP, 2,4-dichlorophenol and 2,4,6-trichlorophenol. The linear ranges of method were 1.0-100.0 μg/L for all CPs studied. This method was employed for the direct extraction and determination of three CPs in seawater samples.

Study of effective parameters for the polarization characterization of PEMFCs sensitivity analysis and numerical simulation

A three-dimensional model of a HT-PEMFC was simulated using Comsol Multiphysics software. Sensitivity was analyzed by using the three-level Box-Behnken experimental design. The effect of independent variables on the fuel cell performance including air and hydrogen velocity, temperature and amount of phosphoric acid doping level (PAdop) on the membrane was investigated. The results showed that the PAdop is the most important variable. The simulation results showed that with the increasing of the PAdop from 2 to 16, the current density (at a voltage of 0.4 V) increased from 0.3 to 0.9A/cm2, which confirms the importance of the PAdop factor on the fuel cell performance.

Sulforaphane-decorated gold nanoparticle for anti-cancer activity: in vitro and in vivo studies

This study aims to develop sulforaphane-loaded gold nanoparticles (SFN-GNPs) as a potential nanomedicine against the solid tumors. Citrate-mediated electrolysis optimized by four-factor three-level Box-Behnken experimental design was used to get nanoparticles of size <200 nm. The formulation was characterized and evaluated for cytotoxicity B16-F10, MCF-7, SW-620 and Caco-2 cell line. Single dose oral pharmacokinetics, gamma scintigraphy-based bio-distribution and tumor regression studies were conducted to evaluate the in vivo performance. Optimized SFN-GNPs showed spherical morphology with a particle size of 147.23 ± 5.321 nm, the zeta potential of −12.7 ± 1.73 mV, entrapment efficiency of 83.17 ± 3.14% and percentage drug loading of 37.26 ± 2.33%. With SFN-GNPs, both SFN (75.99 ± 2.36%) and gold (58.11 ± 2.48%) were able to permeate through the intestinal wall in 48 h. SFN-GNPs were able to bring LC50 of <100 µg/ml in all the cytotoxicity assays, more than 5-fold increase in AUC0−t, enhanced retention at tumor site as well as significant pre-induction tumor growth inhibition and post-induction tumor reduction as compared to plain SFN solution.

Development of preconcentration process of iron by using graphene adsorbent and experimental design methodology

In this study, a new method using graphene as an adsorbent was developed for the preconcentration of iron prior to its determination by flame atomic absorption spectroscopy. Graphene produced via electrochemical exfoliation showed great promise as an adsorbent for preconcentration of iron from environmental water samples due to its large surface area. The adsorbent was characterized by using Raman spectroscopy and scanning electron microscope (SEM). Preconcentration conditions of iron were investigated by using solid phase extraction method that graphene was packed in the extraction column. The pH, flow rate and eluent concentration parameters affecting the recovery yield were optimized using a three factor, three-level Box-Behnken experimental design combining with response surface methodology (RSM). The optimum conditions were determined as pH 7.0, sample flow rate 3 mL min−1, and eluent concentration 2 mol L−1. The detection limit (LOD) was 0.36 μg L−1 and the relative standard deviation (RSD) was % 1.79. Finally, the proposed method was successfully applied to the analysis of environmental water samples and its accuracy was evaluated by the analysis of certified reference material. The analysis of variance (ANOVA) was applied in the Box-Behnken experimental design and the statistic data showed adequate models.

Application of experimental design methodology to optimize antibiotics removal by walnut shell based activated carbon

Three-level Box-Behnken experimental design with three factors (pH, temperature and antibiotic initial concentration) combined with response surface methodology (RSM) was applied to study the removal of Metronidazole and Sulfamethoxazole by walnut shell based activated carbon. This methodology enabled to identify the effects of the different factors studied and their interactions in the response of each antibiotic. The relationship between the independent variable (sorption capacity) and the dependent variables (pH, temperature and antibiotic concentration) was adequately modelled by second-order polynomial equation. The pH factor exerted a significant but distinct influence on the removal efficiency of both antibiotics. The removal of Metronidazole is favoured by increasing pH values, with the maximum value obtained for pH 8 - upper limit of the study domain; while Sulfamethoxazole displays a maximum value around 5.5, with a decrease in the extent of adsorption as the pH increases. The best conditions, predicted by the model, for the removal of the antibiotic Sulfamethoxazole (106.9 mg/g) are obtained at a temperature of 30 °C, initial concentration of 40 mg/L and a pH value of 5.5. For the antibiotic Metronidazole, the highest removal value (127 mg/g) is expected to occur at the maximum levels attributed to each of the factors (pH = 8, Cin = 40 mg/L, T = 30 °C). The results of isotherm experiments (at 20 °C and pH 6) displayed a good agreement with the models predictions. The maximum sorption capacity, estimated by the Langmuir model, was 107.4 mg/g for Metronidazole and 93.5 mg/g for Sulfamethoxazole.