Optimization of complex conditions by response surface methodology for APAM-oil/water emulsion removal from aqua solutions using nano-sized TiO2/Al2O3 PVDF ultrafiltration membrane

Hydrothermal carbonization of food waste: Process parameters optimization and biomethane potential evaluation of process water

Food waste (FW) is one of the major biomasses produced in large quantities in urban areas, which contributes to more than one-third of global greenhouse gas emissions. FW must be properly managed to minimize its environmental consequences. Hydrothermal carbonization (HTC) of FW is a promising technology compared to conventional methods. The objective of the present study is to maximize the mass yield (MY), higher heating value (HHV) and energy yield (EY) of FW by optimizing the operational variables of HTC process. Additionally, process water generated during HTC of FW under optimal conditions was evaluated for methane yield using anaerobic digestion. To optimize the HTC process, three operational variables, including solid-to-liquid (S/L) ratio, temperature, and reaction time, were manipulated using response surface methodology (RSM). According to RSM studies, the optimum operating conditions are 198.5 °C for 150 min with a 0.2 S/L ratio, resulting in MY, HHV and EY as 62.5%, 21.24 MJ/kg and 81.71%, respectively. Proximate and elemental analysis for the hydrochars synthesized at various operating conditions reveals that the temperature and reaction time have a significant impact on fixed carbon and carbon percentage. The anaerobic digestion results showed that the combination of process water and hydrochar, yielded a maximum cumulative methane production of 298.5 ± 16.34 mL/g COD. To mimic methane production, the modified Gompertz model was utilized. Thus, this finding contributes towards the commercialization of the HTC process to produce solid fuel (hydrochar) and provides a way to find an alternative energy source that enhances the HTC process and tackles the problem of process water disposal.

Statistical Simulation, a Tool for the Process Optimization of Oily Wastewater by Crossflow Ultrafiltration

This work aims to determine the optimized ultrafiltration conditions for industrial wastewater treatment loaded with oil and heavy metals generated from an electroplating industry for water reuse in the industrial process. A ceramic multitubular membrane was used for the almost total retention of oil and turbidity, and the high removal of heavy metals such as Pb, Zn, and Cu (>95%) was also applied. The interactive effects of the initial oil concentration (19−117 g/L), feed temperature (20−60 °C), and applied transmembrane pressure (2−5 bar) on the chemical oxygen demand removal (RCOD) and permeate flux (Jw) were investigated. A Box−Behnken experimental design (BBD) for response surface methodology (RSM) was used for the statistical analysis, modelling, and optimization of operating conditions. The analysis of variance (ANOVA) results showed that the COD removal and permeate flux were significant since they showed good correlation coefficients of 0.985 and 0.901, respectively. Mathematical modelling revealed that the best conditions were an initial oil concentration of 117 g/L and a feed temperature of 60 °C, under a transmembrane pressure of 3.5 bar. In addition, the effect of the concentration under the optimized conditions was studied. It was found that the maximum volume concentrating factor (VCF) value was equal to five and that the pollutant retention was independent of the VCF. The fouling mechanism was estimated by applying Hermia’s model. The results indicated that the membrane fouling given by the decline in the permeate flux over time could be described by the cake filtration model. Finally, the efficiency of the membrane regeneration was proved by determining the water permeability after the chemical cleaning process.

Effects of pollutants in alkali/surfactant/polymer (ASP) flooding oilfield wastewater on membrane fouling in direct contact membrane distillation by response surface methodology

The characteristic pollutants in alkali/surfactant/polymer (ASP) flooding oilfield wastewater are complex [e.g., NaCl, sodium dodecyl sulfate (SDS), petroleum, and polyacrylamide (PAM)]; thus, membrane distillation (MD) applied to treat this wastewater will be fouled and wetted easily. In this study, response surface methodology (RSM) was used to analyze the effects of pollutant interactions in ASP flooding oilfield wastewater on membrane fouling. The response model showed quantitative relationships between the membrane flux and the pollutant concentrations. The analysis of variance (p-value of the model < 0.0001, p-value of lack of fit > 0.05, R² = 0.9750 and R²_adj = 0.9500) showed that the regression equation fit the empirical data well. The results also indicated that the interactions of pollutants (NaCl and SDS; petroleum and PAM) had significant influence on the flux decline in the simulated ASP flooding oilfield wastewater. The characterization of Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) revealed that the MD membrane was fouled by simulated ASP flooding oilfield wastewater to a certain degree. Moreover, the membrane flux was restored to 86.9% after hydraulic cleaning.

The underlying mechanism in gel formation and its mathematical simulation during anionic polyacrylamide solution ultrafiltration process

A dead-end ultrafiltration cup was continuously operated to investigate the underlying mechanisms of membrane fouling caused by gel layer in this paper. Anionic polyacrylamide was used as a model foulant for gel formation process in various ultrafiltration processes by two kinds of ultrafiltration membrane, e.g., polyvinylidene fluoride (PVDF) membrane (OM) and TiO₂/Al₂O₃-PVDF membrane (MM); then, a gel formation model was established and systematically assessed. The results show that the gel formation process in ultrafiltration can be divided into three stages: "slow-rapid-slow" flux decay curve. The R² value of the simulation curve was still higher than 0.90 for both OM and MM. Based on the current cognition, the proposed gel layer formation mechanism and mathematical model were feasible.

A Review on Current Development of Membranes for Oil Removal from Wastewaters

The current situation with the problems associated with the removal of oil from wastewaters by membranes is being explored. Many types of membranes have been investigated—organic polymers, inorganic or ceramic species and hybrids of the two. Polymeric membranes can be designed to facilitate the passage of oil, but the more successful approach is with hydrophilic types that encourage the passage of water. Ceramic membranes have an advantage here as they are less often irreversibly fouled and give a higher recovery of oil, with a lower flux decline. Furthermore, they can be cleaned up by a simple heating procedure. More attention should be given to understanding the mechanism of fouling so that operating conditions can be optimised to further reduce fouling and further decrease the flux decline, as well as assisting in the design of antifouling membranes. Another obstacle to ceramic membrane use is the high cost of manufacture. Cheaper starting materials such as clays have been surveyed.

Treatment of High-Concentration Wastewater from an Oil and Gas Field via a Paired Sequencing Batch and Ceramic Membrane Reactor

A sequencing batch reactor (SBR) and a ceramic membrane bioreactor (CMBR) were used in conjunction (SBR+CMBR) to treat high-concentration oil and gas field wastewater (HCOGW) from the China National Offshore Oil Corporation Zhanjiang Branch (Zhanjiang, Guangdong, China). The chemical oxygen demand (COD) and the oil concentrations in the wastewater were 20,000–76,000 and 600–2200 mg/L, respectively. After the SBR+CMBR process, the effluent COD and oil content values were less than 250 mg/L and 2 mg/L, respectively, which met the third level of the Integrated Wastewater Discharge Standards of China (GB8978-1996). Through microbiological analysis, it was found that the CMBR domesticated a previously unreported functional microorganism (JF922467.1) that successfully formed a new microbial ecosystem suitable for HCOGW treatment. In conjunction with the SBR process, the CMBR process effectively reduced pollutant concentrations in HCOGW. Moreover, economic analyses indicated that the total investment required to implement the proposed infrastructure would be approximately 671,776.61 USD, and the per-unit water treatment cost would be 1.04 USD/m³.

Pilot study on the effects of operating parameters on membrane fouling during ultrafiltration of alkali/surfactant/polymer flooding wastewater: optimization and modeling

Alkali/surfactant/polymer (ASP) flooding wastewater is commonly produced in enhanced oil extraction processes and needs to be properly treated prior to reuse due to the potential threat of formation damage. Ultrafiltration (UF) is an effective technique for treating ASP flooding wastewater to meet the requirements for reinjection water. Membrane fouling is the major challenge to UF application. In this study, the operating parameters were modified to research their effects on membrane fouling in a UF pilot study in Daqing, China. The effects of trans-membrane pressure (TMP), cross-flow velocity (CFV), concentration factor (CF) and temperature on membrane flux were systematically investigated, and optimal operating conditions were established by an orthogonal experiment. A temperature of 22 °C, TMP of 2.12 bar, CFV of 3.00 m s⁻¹ and CF of 5 were the most feasible operating conditions for the membrane types and raw water quality parameters in the study. The quality of the permeate met the water quality standards for injection to oilfield low-permeability layers. The results could provide a reference and guidance for practical operations. To learn more about the influences of the operating parameters, a model including external and internal pollution factors was developed based on the Hagen–Poiseuille equation and classical membrane fouling theory. The operating parameters had a more significant effect on external pollution than on internal pollution. The fouling on the membrane surface was much affected by TMP and CFV.

Ultrafiltration (UF) is an effective technique for treating ASP flooding wastewater to meet the requirements for reinjection water.

Adsorption Mechanism of Oil-in-Water on a TiO2/Al2O3-Polyvinylidene Fluoride (PVDF) Ultrafiltration Membrane

For the sake of gaining a clear idea of the adsorption mechanism involved with an oil emulsion-membrane system, Daqing crude oil emulsion and two types of polyvinylidene fluoride (PVDF) ultrafiltration membranes made in our laboratory were used as the objects to pursue the adsorption characteristics in this system. Several isotherm and kinetics models were used here to simulate the adsorption process; the effect of variables such as time, initial concentration, temperature, as well as scanning electron microscopy (SEM) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectra were investigated to assist in understanding the mechanism. The results show that the Redlich-Peterson model and the pseudo-first-order kinetic model are the best fitting models, with all of the models exhibiting correlation coefficient ( R²) values of >0.98, suggesting an endothermic adsorption process that involves a combination of chemical and physical mechanisms. Moreover, the thermodynamic parameters, such as Δ_r G_m^θ, Δ_r H_m^θ, and Δ_r S_m^θ were also calculated from the temperature dependence, indicating a nonspontaneous process, and increases in temperature had a negative effect on the oil-in-water (o/w) adsorption. Ultimately, further evidence is obtained from the microstructural and infrared spectral analyses.

Radiation induced in-situ cationic polymerization of polystyrene organogel for selective absorption of cholorophenols from petrochemical wastewater

A new in-situ cationic polymerization was performed to synthesize a cross-linked (91%) polystyrene (PS) organogel through tetrachloroethylene radiolysis assisted by ⁶⁰Co gamma rays. Hoernschemeyer diagram and swelling capacity test show a better selectivity of PS organogel to chlorinated molecules compared to ester, hydrocarbons and alcohols organic molecules by 80-184 folds. Response surface modeling (RSM) of CPs (2,4,6-trichlorophenol) sorption from artificial wastewater confirm superiority of PS organogel to absorb 1746 μmol CPs/g (∼345 mg CPs/g) at broad pH (4-10) and temperature (25-45 °C). Based on ANOVA statistic, simulated CPs absorption model onto PS organogel was successfully developed, with accuracy of prediction of R²≈ R_Adj² of 0.991-0.995 and lower coefficient of variation of 2.73% with F_model of 611.4 at p < .0001. Particularly, the usage of PS organogel for petroleum wastewater reclamation exhibited higher absorption affinities for all the organic contaminants especially for CPs (>99%) by non-covalent and/or dispersive interaction mechanisms with a well-term reusability and good stability up to 5 cycles.

Under-oil superhydrophilic wetted PVDF electrospun modified membrane for continuous gravitational oil/water separation with outstanding flux

Water in the world is becoming an increasingly scarce commodity and the membrane technology is a most effective strategy to address this issue. However, the fouling and low flux of the polymeric membrane remains the big challenges. Novel modified Polyvinylidene fluoride (PVDF) membrane was introduced, in this work, using a novel treatment technique for an electrospun polymeric PVDF membrane to be used in oil/water separation systems. The Characterizations of the modified and pristine membranes showed distinct changes in the phase and crystal structure of the membrane material as well as the wettability. The modification process altered the surface morphology and structure of the membrane by forming hydrophilic microspheres on the membrane surface. Therefore, the proposed treatment converts the membrane from highly hydrophobic to be a superhydrophilic under-oil when wetted with water. Accordingly, in the separation of oil/water mixtures, the modified membrane can achieve an outstanding flux of 20664 L/m². hr under gravity, which is higher than the pristine membrane by infinite times. Moreover, in the separation of the emulsion, a high flux of 2727 L/m². h was achieved. The results exhibited that the modified membrane can treat a huge amount of oily water with a minimal energy consumption. The corresponding separation efficiencies of both of oil/water mixtures and emulsion are more than 99%. The achieved characteristics for the modified and pristine membranes could be exploited to design a novel continuous system for oil/water separation with an excellent efficiency.

Molecular Mechanisms of Ultrafiltration Membrane Fouling in Polymer-Flooding Wastewater Treatment: Role of Ions in Polymeric Fouling

Polymer (i.e., anionic polyacrylamide (APAM)) fouling of polyvinylidene fluoride (PVDF) ultrafiltration (UF) membranes and its relationships to intermolecular interactions were investigated using atomic force microscopy (AFM). Distinct relations were obtained between the AFM force spectroscopy measurements and calculated fouling resistance over the concentration polarization layer (CPL) and gel layer (GL). The measured maximum adhesion forces (Fad,max) were closely correlated with the CPL resistance (Rp), and the proposed molecular packing property (largely based on the shape of AFM force spectroscopy curve) of the APAM chains was related to the GL resistance (Rg). Calcium ions (Ca(2+)) and sodium ions (Na(+)) caused more severe fouling. In the presence of Ca(2+), the large Rp corresponded to high foulant-foulant Fad,max, resulting in high flux loss. In addition, the Rg with Ca(2+) was minor, but the flux recovery rate after chemical cleaning was the lowest, indicating that Ca(2+) created more challenges in GL cleaning. With Na(+), the fouling behavior was complicated and concentration-dependent. The GL structures with Na(+), which might correspond to the proposed molecular packing states among APAM chains, played essential roles in membrane fouling and GL cleaning.

Response surface methodology for the modeling and optimization of oil-in-water emulsion separation using gas sparging assisted microfiltration

Response surface methodology (RSM) and central composite design (CCD) were used to develop models for optimization and modeling of a gas sparging assisted microfiltration of oil-in-water (o/w) emulsion. The effect of gas flow rate (Q G ), oil concentration (C oil ), transmembrane pressure (TMP), and liquid flow rate (Q L ) on the permeate flux and oil rejection were studied by RSM. Two sets of experiments were designed to investigate the effects of different gas-liquid two-phase flow regimes; low and high gas flow rates. Two separate RSM models were developed for each experimental set. The oil concentration and TMP were found to be the most significant factors influencing both permeate flux and rejection. Also, the interaction between these parameters was the most significant one. At low Q G , the more the gas flow rate, the higher the permeate flux; however, in the high gas flow rate region, higher Q G did not necessarily improve the permeate flux. In the case of rejection, gas and liquid flow rates were found to be insignificant. The optimum process conditions were found to be the following: Q G  = 1.0 (L/min), C oil  = 1,290 (mg/L), TMP = 1.58 (bar), and Q L  = 3.0 (L/min). Under these optimal conditions, maximum permeate flux and rejection (%) were 115.9 (L/m(2)h) and 81.1 %, respectively.

Optimization of cleaning conditions on a polytetrafluoroethylene (PTFE) microfiltration membrane used in treatment of oil-field wastewater

Membrane fouling is one of the main drawbacks of microfiltration technology during the treatment of oil-field wastewater.

Modelling and optimization of critical parameters by hybrid RSM-GA for the separation of BSA using a tubular configured MFI-type zeolite microfiltration membrane

A tubular MFI-type zeolite membrane exhibited good rejection (82%) of BSA with a permeate flux of 4.63 × 10⁻⁵m s⁻¹.

Photoinduced superwetting single-walled carbon nanotube/TiO(2) ultrathin network films for ultrafast separation of oil-in-water emulsions

A SWCNT/TiO2 nanocomposite ultrathin film that has superhydrophilic and underwater superoleophobic properties after UV-light irradiation is successfully prepared by coating TiO2 via the sol-gel process onto an SWCNT ultrathin network film. The robust and flexible SWCNT/TiO2 nanocomposite films with a thickness and pore size of tens of nanometers can separate both surfactant-free and surfactant-stabilized oil-in-water emulsions in an ultrafast manner with fluxes up to 30 000 L m(-2) h(-1) bar(-1), which is 2 orders of magnitude higher than commercial filtration membranes with similar separation performance, and with high separation efficiency. Most importantly, the films exhibit excellent antifouling and self-cleaning performance during multiple cycles with the aid of the photocatalytic property of TiO2 nanoparticles. This work provides a route for designing ultrathin and superwetting films for effective separation of oil-in-water emulsions. The SWCNT/TiO2 ultrathin film is potentially useful in treating emulsified wastewater produced in industry and daily life and for purification of crude oil and fuel.

Novel polyethersulfone (PES)/hydrous manganese dioxide (HMO) mixed matrix membranes with improved anti-fouling properties for oily wastewater treatment process

The improvement in flux recovery from ∼42% in pristine PES membranes to >75% in PES/HMO-2 mixed matrix membranes indicated the greater anti-fouling properties of the PES/HMO-2 membrane in treating synthetic wastewater.