Response surface optimization of chemical coagulation for solid-liquid separation of dairy manure slurry through Box-Behnken design with desirability function

Discharging livestock manure slurry without proper treatment causes various environmental and sociological problems. Chemical coagulation is a widely used and easily applicable method for treating such wastewater. However, the technique requires optimization to enhance coagulation efficiency while minimizing chemical usage. In this study, we propose an efficient, low-cost, and environmentally safe chemical coagulation method for solid-liquid separation of dairy manure slurry. Experiments were conducted in laboratory jar tests using dairy manure slurry to investigate the impact of coagulants, specifically polyaluminum chloride (PAC) and cationic polyacrylamide (CPAM), as well as pH, on the process of solid-liquid separation. Preliminary ranges of PAC, CPAM, and pH were estimated through single-factor experiments. Coagulation optimization and modeling were performed using the response surface methodology (RSM) with the Box-Behnken design (BBD), wherein the desired goal of each parameter was set to maximize solid-liquid separation efficiency while reducing chemical dosage to maintain residual aluminum (Al) concentrations below water quality standards. Numerical optimization predicted that the optimal dosages were 75 mg/L of PAC and 35 mg/L of CPAM at pH 7. Under these conditions, removal efficiencies of 99% for turbidity and 97% for chemical oxygen demand (COD) were achieved, with a minimal residual Al concentration of 0.045 mg/L. Positive zeta potential values in the treated water confirmed complete separation of negatively charged solids in the dairy manure slurry. The response values predicted by BBD aligned with the experimental results, and the analysis of variance (ANOVA) demonstrated the predictability and accuracy of the response models. Consequently, this study highlights the practical application of RSM with BBD in optimizing chemical coagulation using PAC and CPAM to achieve efficient solid-liquid separation in livestock wastewater while maintaining low residual Al concentrations.

Inoculum-to-substrate ratio and solid content effects over in natura spent coffee grounds anaerobic digestion

Coffee is the second most traded commodity worldwide, and its production is associated with the generation of a large number of residues, which are underused and disposed of in landfills. Notably, the coffee industry annually generates approximately 6 million tons of industrial spent coffee ground (ISCG) when extracting coffee flavorings to produce soluble coffee. That resource loss scenario has been highlighted in sustainable waste management contexts as an opportunity to improve the coffee circular economy. Despite ISCG bioconversion to methane potentially meets the waste-to-energy purposes of reducing residues disposal in landfills, decreasing greenhouse gas (GHG) emissions, and increasing renewable energy sources, data about anaerobic digestion (AD) of ISCG remains quite restricted. That limitation becomes more apparent owing to the lack of data focusing on AD key parameters for ISCG as substrate. This study assessed the influence of inoculum-to-substrate ratio (ISR) and the solid content influences on mesophilic (37 °C) ISCG-AD throughout the Response Surface Methodology (RSM) and Central Composite Design (CCD). Results revealed that both factors, ISR and solid content, should be kept above a certain threshold of 0.5 and 6.0 gTVS L^-1 to ensure experimental reliability, as well as reproductively and above 1.0 and 8.0 gTVS L^-1 to avoid underestimation on the MY potential achieved. Concerning ISCG-AD kinetics, the quadratic model optimum condition was at 1.36 and 14.83 gTVS L^-1 for ISR and solid content, respectively. This optimum range for ISR and solid content could guide further development of process configurations for mono- and co-digestion of ISCG, avoiding underestimation of the MY potential and extended incubation periods.

Synthesis of magnetic core-shell amino adsorbent by using uniform design and response surface analysis (RSM) and its application for the removal of Cu2+, Zn2+, and Pb2

The magnetic Fe₃O₄ was synthesized by using a one-step solvothermal method. Then, anhydrous ethanol as a solvent, tetramethyl ammonium hydroxide (TMAOH) as an auxiliary agent, tetraethyl orthosilicate (TEOS) as a silicon source, and (3-aminopropyl) triethoxysilane (APTES) as amino source were used to prepare Fe₃O₄@mSiO₂-NH₂ by using the sol-gel method. Uniform design U14*(14⁵) and the response surface method (RSM) were used to optimize the synthesis ratio. According to the results of TEM, SEM, N₂ adsorption-desorption test, VSM, and XRD, it found that the best coating effect obtained when the relative molar ratio of TMAOH:TEOS:APTES:Fe₃O₄ was 5:4:6:0.45. The results of EDS and elemental analysis confirmed the success of amino group coating; VSM magnetization after surface modification was 32 emu/g; BET results show that specific surface area is 236 m²/g, size 5 nm, and the pore volume is 0.126 cm³/g. The removal of Cu²⁺, Zn²⁺, and Pb²⁺ by Fe₃O₄@mSiO₂-NH₂ was studied at the optimal initial pH value 6 of the adsorption test system. The isothermal adsorption results show that the Langmuir model and Redlich-Peterson model are more suitable than the Freundlich model to describe the adsorption behavior, and Cu²⁺, Zn²⁺, and Pb²⁺ adsorption is mainly single molecular layer. The maximum adsorption capacity qm of the Langmuir model for Cu²⁺, Zn²⁺, and Pb²⁺ removal was 48.04 mg/g, 41.31 mg/g, and 62.17 mg/g, respectively. The adsorption kinetic rates of Cu²⁺, Zn²⁺, and Pb²⁺ on Fe₃O₄@mSiO₂-NH₂ relatively more suitable for pseudo-second-order kinetic model, i.e., R², were ranged between 0.995 and 0.999, and the suitable reaction time was 60 min. These results proved that Fe₃O₄@m-SiO₂-NH₂ prepared by using this method is easy to synthesize, has easy recovery, is ecofriendly, and can be potential adsorbent for Cu²⁺, Zn²⁺, and Pb²⁺ removal.

Optimization of ultrasonication curcumin-hydroxylated lecithin nanoemulsions using response surface methodology

Ultrasonication technology was used to enhance the solubility and availability of lipophilic compounds as curcumin. This study aimed to know the optimal conditions to produce ultrasonication curcumin nanoemulsions stabilized with hydroxylated lecithin using response surface methodology and to evaluate some physical characteristics. Nanoemulsions were produced according to a Central Composite Face-center Design: surfactant oil ratio (SOR, 0.33-1.17), amplitude (A, 8-92%), and ultrasonication time (t, 2-18.4 min). Dynamic light scattering was used to measure the droplet size and polydispersity index of the nanoemulsions. Our results showed that a second-order polynomial function of amplitude and ultrasonication time model fitted well with the mean droplet size and polydispersity of the emulsions. Predicted droplet size was 122.2 nm and polydispersity index was 0.13 obtained at optimal conditions: SOR = 0.72, A = 92%, and t = 12 min. The nanoemulsions remained stable during 15 days of storage at 20 °C. Nanoemulsion remained stable to the aggregation in the pH range from 7.0 to 3.0, while the droplet size increased at lower pH values due to a loss of charge of the lecithin. Nanoemulsion applied in a sugar-beverage showed a yellow-green translucent color, showing better stability on the droplet size than the beverage with the coarse emulsion. Nanoemulsion could be used as a natural colorant in beverages.

Increase of content and bioactivity of total phenolic compounds from spent coffee grounds through solid state fermentation by Bacillus clausii

Spent coffee grounds are waste material generated during coffee beverage preparation. This by-product disposal causes a negative environmental impact, in addition to the loss of a rich source of nutrients and bioactive compounds. A rotating central composition design was used to determine the optimal conditions for the bioactivity of phenolic compounds obtained after the solid state fermentation of spent coffee grounds by Bacillus clausii. To achieve this, temperature and fermentation time were varied according to the experimental design and the total phenolic and flavonoid content, antioxidant activity and antimicrobial activity were determined. Surface response methodology showed that optimum bioprocessing conditions were a temperature of 37 °C and a fermentation time of 39 h. Under these conditions, total phenolic and flavonoid contents increased by 36 and 13%, respectively, in fermented extracts as compared to non-fermented. In addition, the antioxidant activity was increased by 15% and higher antimicrobial activity was observed against Gram positive and negative bacteria. These data demonstrated that bioprocessing optimization of spent coffee grounds using the surface response methodology was an important tool to improve phenolic extraction, which could be used as an antioxidant and antimicrobial agents incorporated into different types of food products.

Combined effects of oregano essential oil and salt on the growth of Escherichia coli in salad dressing

There is a broad research interest in the search for alternatives to chemical additives for use as natural food preservatives. Although many natural compounds have biological in vitro properties evidenced, in situ studies are still scarce. This study evaluated the effect of oregano essential oil (OEO) and salt (NaCl) concentrations against Escherichia coli (ATCC 8739), in salad dressing, using the response surface methodology. The experiment included a 2² central composite rotatable design (CCRD) in a total of 11 formulations of salad dressings. Oregano essential oil was characterized by gas chromatography and salad dressings by ash, lipids, proteins and moisture. OEO was composed mainly by carvacrol (65.1%) and p-cymene (12.0%). Salad dressings showed similar chemical profiles. A mathematical model for the prediction of the antibacterial activity in salad dressing was obtained. The results revealed that the interaction between OEO and salt showed effect on the bacterial count. However, the effect of salt was negative suggesting that the highest NaCl concentrations decreases the bacterial count. Therefore, within the parameters studied, the use of OEO to control E. coli in salad dressing can be considered promising and allows reduction in the levels of salt to be incorporated in food.

Enhanced enzymatic saccharification of sugarcane bagasse pretreated by sodium methoxide with glycerol

Sodium methoxide (CH₃ONa) with glycerol pretreatment (CWGP) was performed to improve the enzymatic digestibility of sugarcane bagasse (SCB). Response surface methodology was utilized to optimize the CWGP parameters for pretreating SCB from the perspective of total fermentable sugar yield (TFSY) and total fermentable sugar concentration (TFSC). Under the optimal CWGP conditions, 0.5666g/g of TFSY (0.82% CH₃ONa, 1.11h, 150°C) and 17.75g/L of TFSC (0.87% CH₃ONa, 1.38h, 149.27°C) were achieved, corresponding to delignification of 79.05% and 79.34%, respectively. Compared the pretreatment using glycerol or CH₃ONa alone, the CWGP has significant synergies to enhance the enzymatic efficiency of SCB. The physical and chemical characteristics of untreated and pretreated SCBs were analyzed using FT-IR, XRD, and SEM, and the results suggest that CWGP significantly increased the susceptibility of the substrates to enzymatic digestibility. Ultimately, CWGP might be a prospective candidate for the pretreatment process of enzyme-based lignocellulosic biorefineries.

Synthesis and characterization of polysulfone/graphene oxide nano-composite membranes for removal of bisphenol A from water

Bisphenol A (BPA) is an emerging contaminant of water resources that disrupts endocrine function. Attempts are continuing to develop cost-effective methods to remove BPA from water environments. The aim of this study was to prepare and characterize polysulfone/graphene oxide nano-composite membranes for removal of BPA from water. Three membranes were synthetized using phase inversion method: polysulfone membrane as PSF and two polysulfone/graphene oxide nano-composite membranes with graphene oxide (GO) weight ratios of 0.4 and 1.0% as PSF/GO 0.4% and PSF/GO 1.0%, respectively. The membrane characteristics including morphology, surface roughness, pore size, zeta potential and presence of functional groups were determined using field emission scanning electron microscopy, atomic force microscopy, streaming potential, and attenuated total reflectance Fourier transform infrared spectroscopy techniques. Inclusion of GO remarkably increased permeate flux of the membranes, so that pure water flux of PSF, PSF/GO 0.4% and PSF/GO 1.0% at operating pressure of 2 bar was determined 226, 449 and 512 L/m² h, respectively. The membrane PSF/GO 0.4% with the most negative zeta potential (-10.46 mV) and the highest BPA removal efficiency was determined as the optimal membrane. The optimum conditions of input pressure, operating time, initial concentration of BPA, and pH for BPA removal efficiency by PSF/GO 0.4% were determined using surface response methodology to be 1.02 bar, 10.6 min, 7.5 mg/L, and 5.5, respectively. By optimizing the conditions of operating parameters, experimental BPA removal efficiency by PSF/GO 0.4% reached to as high as 93%.

Vacuum-assisted alkaline pretreatment as an innovative approach for enhancing fermentable sugar yield and decreasing inhibitor production of sugarcane bagasse

Sodium hydroxide pretreatment of sugarcane bagasse under vacuum conditions was established and evaluated in this study. Compared to pretreatment under conventional moderate pressure conditions, only half of the total phenolic compounds and less than half of the formic acid were produced under vacuum conditions, while the yield of total fermentable sugar was significantly increased by 31.38%. The pretreatment parameters: NaOH concentration, pretreatment time, and pretreatment temperature, were optimized using response surface methodology based on the response values of the total fermentable sugar yield (TFSY) and the total fermentable sugar concentration (TFSC), respectively. Under the optimal conditions, the TFSY of 0.5146g/g and the TFSC of 17.37g/L were achieved, respectively. By adjusting the ratio of cellulases to xylanase, the TFSY reached a maximum of 0.5213g/g when the ratio was 1:1, while the maximum TFSC of 17.71g/L was achieved when the ratio was 1:4.

Design of experiments for microencapsulation applications: A review

Microencapsulation techniques have been intensively explored by many research sectors such as pharmaceutical and food industries. Microencapsulation allows to protect the active ingredient from the external environment, mask undesired flavours, a possible controlled release of compounds among others. The purpose of this review is to provide a background of design of experiments in microencapsulation research context. Optimization processes are required for an accurate research in these fields and therefore, the right implementation of micro-sized techniques at industrial scale. This article critically reviews the use of the response surface methodologies in pharmaceutical and food microencapsulation research areas. A survey of optimization procedures in the literature, in the last few years is also presented.

Evolution of Zinc Oxide Nanostructures Grown on Graphene by Ultrasonic Spray Pyrolysis and Its Statistical Growth Modelling

The evolution of zinc oxide nanostructures grown on graphene by alcohol-assisted ultrasonic spray pyrolysis was investigated. The evolution of structures is strongly depended on pyrolysis parameters, i.e., precursor molarity, precursor flow rate, precursor injection/deposition time, and substrate temperature. Field-effect scanning electron microscope analysis, energy dispersive X-ray spectroscopy, X-ray diffraction, and transmission electron microscopy were used to investigate the properties of the synthesized nanostructures and to provide evidence for the structural changes according to the changes in the pyrolysis parameters. The optimum parameters to achieve maximum density and well-defined hexagonally shaped nanorods were a precursor molarity of 0.2 M, an injection flow rate of 6 ml/min, an injection time of 10 min, and a substrate temperature of 250-355 °C. Based on the experimental results, the response surface methodology (RSM) was used to model and optimize the independent pyrolysis parameters using the Box-Behnken design. Here, the responses, i.e., the nanostructure density, size, and shape factor, are evaluated. All of the computations were performed using the Design-Expert software package. Analysis of variance (ANOVA) was used to evaluate the results of the model and to determine the significant values for the independent pyrolysis parameters. The evolution of zinc oxide (ZnO) structures are well explained by the developed modelling which confirms that RSM is a reliable tool for the modelling and optimization of the pyrolysis parameters and prediction of nanostructure sizes and shapes.

Multiple responses optimization in the development of a headspace gas chromatography method for the determination of residual solvents in pharmaceuticals

An efficient generic static headspace gas chromatography (HSGC) method was developed, optimized and validated for the routine determination of several residual solvents (RS) in drug substance, using a strategy with two sets of calibration. Dimethylsulfoxide (DMSO) was selected as the sample diluent and internal standards were used to minimize signal variations due to the preparative step. A gas chromatograph from Agilent Model 6890 equipped with flame ionization detector (FID) and a DB-624 (30 m×0.53 mm i.d., 3.00 µm film thickness) column was used. The inlet split ratio was 5:1. The influencing factors in the chromatographic separation of the analytes were determined through a fractional factorial experimental design. Significant variables: the initial temperature (IT), the final temperature (FT) of the oven and the carrier gas flow rate (F) were optimized using a central composite design. Response transformation and desirability function were applied to find out the optimal combination of the chromatographic variables to achieve an adequate resolution of the analytes and short analysis time. These conditions were 30 °C for IT, 158 °C for FT and 1.90 mL/min for F. The method was proven to be accurate, linear in a wide range and very sensitive for the analyzed solvents through a comprehensive validation according to the ICH guidelines.