Box-Wilson Statistical Experiment Design Research Articles

Disintegration of sewage sludge using pulsed electrical field technique: PEF optimization, simulation, and anaerobic digestion

ABSTRACT A Pulsed Electrical Field (PEF) reactor was developed to process biological sludge as a pretreatment method prior to anaerobic digestion. This study focuses on the effects of operational parameters such as applied voltage, pH, conductivity, flow-rate, and temperature affecting the treatment of waste active sludge (WAS) by PEF, the simulation of reactor process conditions and anaerobic biodegradation of PEF pretreated sludge. The effects of the sludge conductivity, flow-rate, and temperature on the Soluble Chemical Oxygen Demand (SCOD) of WAS treated by PEF reactor were investigated by using a Box–Wilson statistical experiment design. Simulations of the PEF process conditions were performed to verify experimental results. After PEF optimization study, the PEF operational conditions for maximum SCOD were obtained at 4 mS/cm conductivity, 5 mL/min flow-rate, and 40 °C temperature during PEF treatment. The measured and predicted SCOD showed a good consistency (R 2 = 0.92). After it was pretreated by the PEF, the SCOD, total nitrogen, total phosphorus, polysaccharide and protein contents of WAS increased. However filterability property also decreased. In the anaerobic digestion study, the reactor fed with the PEF pretreated WAS provided 1.70 times higher methane production compared with raw sludge. In addition to this situation, 18% and 19% improvements, respectively, were observed in SCOD and VSS reductions when it was compared with raw sludge in the 23 days of anaerobic operation. Sixteen percent decrease in CST showed that the PEF enhanced the filterability of WAS during the anaerobic stabilization.

Optimization of particle number, substrate concentration and temperature of batch immobilized reactor system for biohydrogen production by dark fermentation

Immobilized cell bioreactor was operated in batch mode for biohydrogen generation by dark fermentation from acid hydrolyzed waste wheat powder. It was aimed to optimize the fermentation conditions with the purpose of obtaining the highest hydrogen yield (YH2) and production rate (HPR) by applying Box–Wilson statistical experimental design method. Particle number (PN = 120–240; X1), initial total sugar concentration (TS0 = 10–30 g/l; X2) and fermentation temperature (T = 35–55 °C; X3) were selected as independent variables. Polyester fibers with particle diameter “Dp” = 0.5 cm were used as support material to immobilize microorganisms with heat-pretreated sludge. Quadratic equations for production yield and rate were developed by using experimental results. The maximum YH2 (3.21 mol H2/mol glucose) and HPR (73.3 ml H2/h) were predicted at the optimum conditions of PN = 240, TS0 = 10 g/l and T = 44.9 °C. Also, analysis of variance, as well as sum of ranking difference test results demonstrated that fitting models were statistically significant.

Glucose and 5-hydroxymethylfurfural production from cellulosic waste by sequential alkaline and acid hydrolysis

Glucose and 5-hydroxymethylfurfural production from waste paper towel was evaluated by sequential alkaline and acid hydrolysis. Effects of alkali/acid doses, treatment time and temperature on hydrolysis performance were investigated by using Box-Behnken and Box-Wilson statistical experiment design methods. Operation parameters for alkaline hydrolysis were percent NaOH, treatment time and temperature and for acid hydrolysis percent acid and treatment time. Total paper conversion of the sequential process was 72% indicating significant waste reduction beside glucose and 5-hydroxymethylfurfural formation. The maximum yields for glucose and 5-hydroxymethylfurfural were 61.23% and 19.70% in acid and alkaline hydrolysis, respectively. Main products in the effluent of alkaline hydrolysis were glucose and 5-hydroxymethylfurfural. Highest glucose concentration (25.2 gL−1) in alkaline hydrolysis was obtained at 16% NaOH, 119 °C, and 74 min. The 5-hydroxymethylfurfural concentration and paper conversion at this condition was 7.22 gL−1 and 28.47%, respectively. When the solid residue of alkaline hydrolysis was treated with 5% H2SO4 at 135 °C for 120 min then 30.7 gL−1 glucose and 0.87 gL−1 5-hydroxymethylfurfural was obtained with 44.35% paper conversion.

Optimization of coal flocculation with an anionic flocculant using a box-wilson statistical design method

In this study, the Box-Wilson statistical experimental design method was employed to evaluate suspension pH, salt (CaCl2·2H2O) concentration and anionic flocculant (A-150) amount in flocculation of coal. Response function coefficients were determined by the regression analysis of experimental data and the predictions were found to be in good agreement with the experimental results. The optimum pH, salt (CaCl2·2H2O) concentration and anionic flocculant (A-150) amount were determined as 9.8, 0.0009 M and 791 g/Mg respectively, when minimum turbidity and maximum settling rate are considered.

Effects of operating parameters on acid hydrolysis of ground wheat starch: Maximization of the sugar yield by statistical experiment design

AbstractFuels and chemicals production from carbohydrate rich waste materials has received considerable attentions in recent years. Pretreatment and hydrolysis are required stages during processing the waste materials for this purpose. Therefore, the objective of this study was to determine the optimum operating conditions in acid hydrolysis of ground wheat (GW) starch for maximum yield of total sugar (TS) formation. Hydrolysis reaction was realized by dilute sulfuric acid and heat treatment in an autoclave. Factorial experiment design was used to determine the significant variables affecting the yield of hydrolysis. The independent variables were particle size (Dp = <74 and 220 µm), acid concentration (A = 0.98–196 g/dm3), GW concentration (GW = 10–20 g/dm3), hydrolysis temperature (T = 90–130°C), and time (t = 5–60 min). The dependent variables were final TS concentration and hydrolysis yield (YH). The significant factors in the hydrolysis of GW were determined as GW concentration, acid (A) concentrations, and hydrolysis temperature (T). Box–Wilson statistical experimental design was used for optimization of hydrolysis conditions by considering the signficant factors. The optimal conditions, maximizing the hydrolysis yield (YH = 0.94) were A = 49 g/dm3 (0.5 M), T = 90°C, GW = 35 g/dm3 and t = 15 min. The most suitable A/GW ratio for the maximum hydrolysis yield of 94% was 1.3.

Application of Box–Wilson experimental design method for 2,4-dinitrotoluene treatment in a sequential anaerobic migrating blanket reactor (AMBR)/aerobic completely stirred tank reactor (CSTR) system

A sequential aerobic completely stirred tank reactor (CSTR) following the anaerobic migrating blanket reactor (AMBR) was used to treat a synthetic wastewater containing 2,4-dinitrotoluene (2,4-DNT). A Box–Wilson statistical experiment design was used to determine the effects of 2,4-DNT and the hydraulic retention times (HRTs) on 2,4-DNT and COD removal efficiencies in the AMBR reactor. The 2,4-DNT concentrations in the feed (0–280mg/L) and the HRT (0.5–10 days) were considered as the independent variables while the 2,4-DNT and chemical oxygen demand (COD) removal efficiencies, total and methane gas productions, methane gas percentage, pH, total volatile fatty acid (TVFA) and total volatile fatty acid/bicarbonate alkalinity (TVFA/Bic.Alk.) ratio were considered as the objective functions in the Box–Wilson statistical experiment design in the AMBR. The predicted data for the parameters given above were determined from the response functions by regression analysis of the experimental data and exhibited excellent agreement with the experimental results. The optimum HRT which gave the maximum COD (97.00%) and 2,4-DNT removal (99.90%) efficiencies was between 5 and 10 days at influent 2,4-DNT concentrations 1–280mg/L in the AMBR. The aerobic CSTR was used for removals of residual COD remaining from the AMBR, and for metabolites of 2,4-DNT. The maximum COD removal efficiency was 99% at an HRT of 1.89 days at a 2,4-DNT concentration of 239mg/L in the aerobic CSTR. It was found that 280mg/L 2,4-DNT transformed to 2,4-diaminotoluene (2,4-DAT) via 2-amino-4-nitrotoluene (2-A-4-NT) and 4-amino-2-nitrotoluene (4-A-2-NT) in the AMBR. The maximum 2,4-DAT removal was 82% at an HRT of 8.61 days in the aerobic CSTR. The maximum total COD and 2,4-DNT removal efficiencies were 99.00% and 99.99%, respectively, at an influent 2,4-DNT concentration of 239mg/L and at 1.89 days of HRT in the sequential AMBR/CSTR.

Optimization of TiO 2/Fe(III)/solar UV conditions for the removal of organic contaminants in pulp mill effluents

Solar degradation of effluents of pulp mill industry containing toxic chemicals has been studied using TiO 2/Fe(III) (Degussa P25 TiO 2 was used as a catalyst). Effects of some operating parameters such as the initial oxidant and catalyst concentrations and circulation rates of wastewater on TOC, color and AOX removals were investigated using the Box–Wilson statistical experimental design method. The highest color, TOC and AOX removals of 78%, 64% and 68% were obtained at TiO 2 concentration of 188 mg/L and Fe (III) concentration of 0.5 mM, respectively.

COD, para-chlorophenol and toxicity removal from synthetic wastewater using rotating tubes biofilm reactor (RTBR)

Para-chlorophenol (4-chlorophenol, 4-CP) containing synthetic wastewater was treated using a rotating perforated tubes biofilm reactor (RTBR). Box-Wilson statistical experiment design and response surface methodology (RSM) were used to investigate the effects of the feed COD, 4-CP contents and the A/Q (biofilm surface/flow rate) ratio on percent COD, 4-CP and toxicity removals. Increases in A/Q ratio and the feed COD contents improved COD, 4-CP and toxicity removals. High feed 4-CP contents adversely affected the system performance due to toxic effects of 4-CP on microorganisms. High A/Q ratio and feed COD contents were required for effective 4-CP and toxicity removals at high feed 4-CP contents. More than 95% 4-CP and toxicity removals were obtained with an A/Q ratio of 186 m(2) d m(-3), and feed COD of 6000 mg L(-1) with the feed 4-CP content of 1000 mg L(-1). The RTBR was proven to be more efficient than the RBBR used for the same purpose in our previous studies.

Optimization of media composition for hydrogen gas production from hydrolyzed wheat starch by dark fermentation

Effects of N/C, P/C and Fe(II)/C ratios in fermentation medium on biohydrogen production by dark fermentation of acid-hydrolyzed wheat starch was investigated. The powdered wheat was autoclaved at pH = 3 and 90 °C for 15 min and the resulting sugar solution was fermented after external addition of N, P and Fe(II) to overcome nutrient limitations. Box–Wilson statistical experiment design was used by considering the N/C (0–0.05, w w −1), P/C (0–0.02) and Fe(II)/C (0–0.03) ratios as the independent variables while the hydrogen yield and specific hydrogen production rate (SHPR) were the objective functions to be optimized. A quadratic response function was used to correlate the response functions with the independent variables. Low levels of the variables (N/C < 0.02, P/C < 0.01, Fe(II)/C < 0.01) resulted in low hydrogen yield and SHPR due to nutrient limitations and high levels of nutrients caused inhibitions. The optimum conditions yielding the maximum hydrogen yield ( Y = 2.84 mol H 2 mol −1 glucose) were N/C = 0.02, P/C = 0.008 and Fe(II)/C = 0.015. The maximum SHPR (96 mL H 2 g −1 biomass h −1) was obtained at N/C = 0.025, P/C = 0.008 and Fe(II)/C = 0.015 (w w −1).

Biohydrogen production by dark fermentation of wheat powder solution: Effects of C/N and C/P ratio on hydrogen yield and formation rate

The effects of C/N and C/P ratio on hydrogen yield and specific production rate were investigated in dark fermentation of wheat powder solution (WPS) by external addition of N and P since the wheat powder was N and P deficient. A Box–Wilson statistical experiment design approach was used. C/N ratio was varied between 20 and 200 while C/P ratio was between 50 and 1000. A quadratic response function was used to correlate the objective functions with the independent variables and the response function coefficients were determined by regression analysis. Hydrogen yield increased with increasing C/N and C/P ratios. Low nitrogen concentrations required low phosphorous contents for high hydrogen yields. A C/N ratio of 200 and C/P ratio of 1000 yielded the highest H 2 yield of 281 ml H 2 g - 1 starch at STP. SHPR also increased with increasing C/N and C/P ratios. Again the highest SHPR ( 98 ml H 2 g - 1 biomass h - 1 at STP) was obtained at C/N and C/P ratios of 200 and 1000, respectively. The C/N/P ratio maximizing the yield and formation rate of hydrogen was 100/0.5/0.1 ( w w - 1 w - 1 ) .

Application of a statistical technique for olive oil mill wastewater treatment using ultrafiltration process

Ultrafiltration process was used for olive oil mill wastewater treatment in this work. Filtration experiments were performed with raw wastewater and no pretreatment was applied. Effects of major operating variables such as the transmembrane pressure, feed flow rate and operation time were investigated. A Box–Wilson statistical experiment design method was used by considering the transmembrane pressure (1–3 bar), recycling flow rate (100–200 L/h) and operation time (30–120 min) variables while COD removal and permeate flux variation were the objective functions. The results were correlated by a response function and the coefficients were determined by regression analysis. COD removal efficiency and permeate flux variation determined from the response functions were in good agreement with the experimental results. The optimum set of flow rate and pressure for COD removal was 100 L/h and 1 bar with 89.5% COD removal efficiency. On the other hand, optimum set was 200 L/h and 3 bar for permeate flux with 34.4 L/(m 2 h) flux value. Since optimum sets are just at opposite corners of operation region (pressure, flow rate), first of all objective (COD removal or permeate flux) should be determined and then optimum operation parameters can be selected.

Biological treatment of 2,4-dichlorophenol containing synthetic wastewater using a rotating brush biofilm reactor

A newly developed rotating brush biofilm reactor was used for DCP, COD and toxicity removal from 2,4-dichlorophenol (DCP) containing synthetic wastewater at different feed COD, TCP concentrations and A/ Q (biofilm surface area/feed flow rate) ratios. A Box–Wilson statistical experiment design was used by considering the feed DCP (50–500 mg l −1), COD (2000–6000 mg l −1) and A/ Q ratio (73–293 m 2 d m −3) as the independent variables while percent DCP, COD, and toxicity removals were the objective functions. The experimental data were correlated by a quadratic response function and the coefficients were determined by regression analysis. Percent DCP, COD and toxicity removals calculated from the response functions were in good agreement with the experimental data. DCP, COD and toxicity removals increased with increasing A/ Q ratio and decreasing feed DCP concentrations. The optimum A/ Q ratio resulting in the highest COD (90%), DCP (100%) and toxicity (100%) removals with the highest feed COD (6000 mg l −1) and DCP (500 mg l −1) contents was nearly 210 m 2 d m −3.

Application of a statistical design method to the shear flocculation of celestite with Na-Oleate

In this study, the Box–Wilson statistical experimental design method was employed to evaluate the effects of important variables such as amount of Na-Oleate, salt (MgCl 2) concentration and stirring speed on the shear flocculation of celestite. Response function coefficients were determined by the regression analysis of experimental data and the predictions were found to be in good agreement with the experimental results. The optimum Na-Oleate amount, MgCl 2 concentration and stirring speed were determined as 1.5 kg/t, 0.1 M and 500 rpm, respectively, when considering flocculation recovery.

Biological treatment of para-chlorophenol containing synthetic wastewater using rotating brush biofilm reactor

A novel rotating brush biofilm reactor (RBBR) was used for para-chlorophenol (4-chlorophenol, 4-CP), COD and toxicity removal from synthetic wastewater containing different concentrations of 4-CP. Effects of major operating variables such as the feed 4-CP and COD concentrations and A/ Q (biofilm surface area/feed flow rate) ratio on the performance of the biofilm reactor were investigated. A Box–Wilson statistical experiment design method was used by considering the feed 4-CP (0–1000 mg l −1), COD (2000–6000 mg l −1) and A/ Q ratio (73–293 m 2 day m −3) as the independent variables while the 4-CP, COD and toxicity removals were the objective functions. The results were correlated by a response function and the coefficients were determined by regression analysis. Percent 4-CP, COD and toxicity removals determined from the response functions were in good agreement with the experimental results. 4-CP, COD and toxicity removals increased with decreasing feed 4-CP and increasing A/ Q ratio. Optimum conditions resulting in maximum COD, 4-CP and toxicity removals were found to be A/ Q ratio of nearly 180 m 2 day m −3, feed COD of nearly 4000 mg l −1 and feed 4-CP of less than 205 mg l −1.

Application of the Box-Wilson experimental design method for the spherical oil agglomeration of coal

In this study, the Box-Wilson statistical experimental design method was employed to evaluate the effects of important variables such as bridging liquid (oil) concentration, salt (CaCl 2·2H 2O) concentration and stirring speed on the agglomeration of bituminous coal. Response function coefficients were determined by the regression analysis of experimental data and the predictions were found to be in good agreement with the experimental results. The optimum kerosene concentration, CaCl 2·2H 2O concentration and stirring speed were determined as 30 wt%, 1 M and 1683 rpm, respectively, when considering combustible recovery and ash content. In addition, contact angle and solution surface tension measurements were carried out to evaluate of agglomeration success with the contact angle values and surface tension values. The surface tension of CaCl 2 2H 2O solutions and the average contact angle increased with increasing CaCl 2·2H 2O concentration.

Para-Chlorophenol inhibition on COD, nitrogen and phosphate removal from synthetic wastewater in a sequencing batch reactor

COD, nitrogen, phosphate and para-chlorophenol (4-chlorophenol, 4-CP) removal from synthetic wastewater was investigated using a four-step sequencing batch reactor (SBR) at different sludge ages and initial para-chlorophenol (4-CP) concentrations. The nutrient removal process consisted of anaerobic, oxic, anoxic and oxic phases with hydraulic residence times (HRT) of 1/3/1/1 h and a settling phase of 0.75 h. A Box–Wilson statistical experiment design was used considering the sludge age (5–25 days) and 4-CP concentration (0–400 mg l −1) as independent variables. Variations of percent COD, NH 4-N, PO 4-P and 4-CP removals with sludge age and initial 4-CP concentration were investigated. Percent nutrient removals increased with increasing sludge age and decreasing 4-CP concentrations. Low nutrient removals were obtained at high initial 4-CP concentrations especially at low sludge ages. However, high sludge ages partially overcome the adverse effects of 4-CP and resulted in high nutrient removals. COD, NH 4-N, PO 4-P and 4-CP removals were 76%, 72%, 26% and 34% at a sludge age of 25 days and initial 4-CP concentration of 200 mg l −1. Sludge volume index (SVI) also decreased with increasing sludge age and decreasing 4-CP concentrations. An SVI value of 104 ml g −1 was obtained at a sludge age of 25 days and initial 4-CP of 200 mg l −1.

Removal of 2,4-dichlorophenol and toxicity from synthetic wastewater in a rotating perforated tube biofilm reactor

Chlorinated aromatic compounds present in many industrial effluents are usually removed by a combination of physical and chemical processes. Biological oxidation of chlorophenol compounds is difficult because of toxic effects of those compounds on microorganisms. A newly developed rotating perforated tubes biofilm reactor (RTBR) was used in continuous mode for removal of 2,4-dichlorophenol (DCP) and toxicity from synthetic wastewater. A special culture of Pseudomonas putida capable of degrading DCP supplemented activated sludge culture was used for this purpose. A Box–Wilson statistical experiment design method was used to investigate the effects of major operating parameters such as A/ Q ratio, feed chemical oxygen demand (COD) and feed 2,4-dichlorophenol concentrations on COD, DCP and toxicity removals. Experimental data were used for determination of the response function coefficients. Percent COD, DCP and toxicity removals determined from the response functions were in good agreement with the experimental data. A Resazurin method based on dehydrogenase activity was used for assessment of the toxicity for the feed and effluent wastewater. Low feed COD and DCP contents and high A/ Q ratios were found to be favorable for effective removal of DCP, COD and toxicity. Maximum percent DCP removal (nearly 100%) was obtained with a feed DCP concentration of 50 mg l −1, A/ Q ratio of 200 m 2 d m −3 and a feed COD of 2000 mg l −1, which resulted in COD and toxicity removal efficiencies of 96 and 79%, respectively.

Nutrient removal performance of a five-step sequencing batch reactor as a function of wastewater composition

Nutrient removal from synthetic wastewater was studied as a function of nutrient composition in a five-step sequencing batch reactor (SBR) in order to determine the most suitable nutrient ratios maximizing nutrient removal. The nutrient removal process consisted of anaerobic, anoxic, oxic, anoxic, oxic phases. Hydraulic residence times (HRT) of the aforementioned phases were kept constant at 2/1/4.5/1.5/1.5 h with 1/2 h of settling phase. Solids retention time (SRT) was constant at 10 days in all experiments. COD/N and COD/P ratios in the nutrient medium were considered as independent variables with a constant initial chemical oxygen demand (COD) of 1200 mg l −1. Box–Wilson statistical experiment design was used to determine the effects of independent variables on COD, NH 4-N, and PO 4-P removal efficiencies. The results were correlated by a response function and the coefficients determined by regression analysis. COD/N/P ratio resulting in maximum COD, NH 4-N and PO 4-P removal efficiencies was found to be 100/2/0.54 yielding COD, NH 4-N and PO 4-P removal efficiencies of 95, 94 and 99%, respectively.

Functionalization of atactic polypropylene by succinyl-fluorescein: A two-step process of chemical modification in the melt

Chemical modification of an industrial waste (atactic polypropylene) using a two-step process to obtain a fluorescent-modified polyolefin is the subject of this article. For these purposes, a Box–Wilson statistical experimental design has been used. The product was obtained by a condensation reaction after a previous one via a radical reaction had taken place in the melt. Furthermore, the nature of this product reveals that only single succinic anhydride groups were previously grafted onto polymers coming from the previous radicular reaction. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 689–696, 1998

Optimization of sucrose and inorganic nitrogen concentrations for somatic embryogenesis of birch (Betula pendula Roth.) callus cultures: A statistical approach

The effects of different concentrations of sucrose and inorganic nitrogen on somatic embryogenesis of birch (Betula pendula Roth.) callus cultures were studied using Box-Wilson statistical experimental design. The experimental results were processed by regression analysis, and mathermatical models describing the effects of the selected variables were derived. On the basis of the modeling, maximum embryo production can be achieved with 35 mM total inorganic nitrogen and 20.8 g 1-1 sucrose in the medium.