Removal of high concentration of sulfate from pigment industry effluent by chemical precipitation using barium chloride: RSM and ANN modeling approach

Global research trends of uranium-containing wastewater treatment based on bibliometric review

The generation of uranium-containing wastewater (UCW) during different stages of uranium mining, processing, and utilization presents a significant ecological and biospheric threat. Consequently, it is crucial for both sustainable development and the protection of human health to adopt appropriate methods for the treatment of UCW as well as the separation and enrichment of uranium. This study conducted a comprehensive search of the Web of Science Core Collection (WOSCC) database for publications related to UCW treatment between 1990 and 2022 to gain insight into current trends in the field. Subsequently, the annual publications, WOSCC categories, geographical distribution, major collaborations, prolific authors, influential journals, and highly cited publications were the subjects of a biliometric analysis that was subsequently carried out. The study findings indicate a significant rise in the overall number of publications in the research field between 1990 and 2022. China, India, and the USA emerged as the primary contributors in terms of publication count. The Chinese Academy of Sciences, the East China University of Technology, and the University of South China were identified as the key research institutions in this field. Furthermore, a majority of the publications in this field were distributed through prestigious journals with high impact factors, such as the Journal of Radioanalytical and Nuclear Chemistry. The top 3 journals were Radioanalytical and Nuclear Chemistry, Chemical Engineering Journal, and Journal of Hazardous Materials. The keyword co-occurrence and burst analysis revealed that the current research on UCW treatment mainly focuses on adsorption-based treatment methods, environmentally functional materials, uranium recovery, etc. Furthermore, the study of the adsorption efficiency of different adsorbent materials, as well as the strengthening and improvement of adsorbent material selectivity and capacity for the recovery of uranium, represents a research hotspot in the field of UCW treatment in the future. This study conducts a comprehensive overview of the current status and prospects of the UCW treatment, which can provide a valuable reference for gaining insights into the development trajectory of the UCW treatment.

The co-adsorption of sulfate and metal ions on Al-doped graphene: a first principles study

CONTEXT

The co-adsorption of sulfate and metal ions on intrinsic and Al-doped graphene is investigated through first principles calculations. When SO42- ions exist only, both of intrinsic and Al-doped graphene can form stable adsorption configurations with SO42-. However, the presence of Cu2+/Ca2+/Zn2+/Mg2+ ions attenuates the interaction between intrinsic graphene and SO42-, resulting in weak physical adsorption between them, while Al-doped graphene can still constitute co-adsorption chemically with both SO42- and Cu2+/Ca2+/Zn2+/Mg2+ ions simultaneously. The sensitivity of Al-doped graphene towards co-adsorbed ions is in the order of SO42--Cu2+ > SO42--Zn2+ > SO42--Ca2+ > SO42--Mg2+. The research indicates Al-doped graphene could be a promising material for sensing sulfate ions under the presence of various metal ions.

METHODS

All of the calculations were carried out by using a first principles method based on density functional theory (DFT). The generalized gradient approximation (GGA) with the Perdew-Burke-Ernzerhof (PBE) functional was selected to describe electron exchange-correlation energy. The double numerical plus polarization (DNP) was employed as the basis set. The conductor-like screening model (COSMO) was implemented to simulate the aqueous solvent effect.

Advancements of sequencing batch biofilm reactor for slaughterhouse wastewater assisted with response surface methodology

Slaughterhouse wastewater (SWW) contains a significant volume of highly polluted organic wastes. These include blood, fat, soluble proteins, colloidal particles, suspended materials, meat particles, and intestinal undigested food that consists of higher concentrations of organics such as biochemical oxygen demand (BOD), chemical oxygen demand (COD), nitrogen and phosphorus hence an efficient treatment is required before discharging into the water bodies. The effluent concentrations and performance of simultaneous sequential batch biofilm reactor (SBBR) with recycled plastic carrier media support are better than the local single-stage sequential batch reactor (SBR), which is lacking in the literature in terms of COD, NH₃, NO₃, and PO₄ treatment efficiency. The present study reports a novel strategy to remove the above mentioned contaminants using an intermittently aerated SBBR with recycled plastic carrier media support along with simultaneous nitrification and denitrification. The central composite design was evaluated to optimize the treatment performance of seven different process variables including; different alternating conditions (Oxic/anoxic) for aeration cycles (3/2 h in a 6 h cycle, 6/5 h in a 12 h cycle and 9/8 h in an 18 h cycle) and hydraulic retention time (6, 12 and 18 h). The average removal efficiencies are 94.5% for NH₃, 93% for NO₃ and 90.1% for PO₄, and 99% for COD. The study reveals that the denitrification in the post-anoxic phase was more efficient than the pre-anoxic phase for pollutant removal and maintaining higher quality effluent. The effluent concentrations and performance of simultaneous SBBR with recycled polyethylene carrier support media were better than local SBR system in terms of COD, NH₃, NO₃ and PO₄ treatment efficiency. Results stipulated the suitability of SBBR for wastewater treatment and reusability as a sustainable approach for wastewater management under optimum conditions.

Removal of High-Concentration Sulfate from Seawater by Ettringite Precipitation

Due to the worldwide scarcity of fresh water, seawater becomes an alternative base fluid in hydraulic fracturing for oil and gas production. However, the injection of seawater that contains high concentration of sulfate will induce the scale formation and thus reduce hydrocarbon production. One of the most effective ways to solve this problem is to remove sulfate ions from seawater before fracturing application. The objective of this study is to develop an effective and environment-friendly approach to remove sulfate ions from seawater based on coprecipitation of SO42− with NaAlO2 and CaO as ettringite (Ca6Al2(SO4)3(OH)12·26H2O). Residual sulfate concentration in treated seawater was determined when NaAlO2 and CaO dosed at different molar ratios to sulfate. Results showed the efficiency of sulfate removal was more than 90% (4290 ppm to ∼400 ppm) when Al : Ca : S = 2 : 6 : 1. It was found the sulfate precipitation completed in 15 mins with stirring under an alkaline condition (pH ≈ 12) and was not affected by temperature (15°C to 45°C). Increasing the Na+ concentration from 0 to 25,000 ppm in waters resulted in the increment of residual sulfate concentration from 250 to ∼600 ppm, decreasing the removal efficiency. Besides, the analysis of Ca2+ and Mg2+ in treated seawater showed the Ca2+ concentrations were on the similar level as that before the treatment and Mg2+ was removed in the precipitation process, which is beneficial to the application of the treated seawater. The morphology and element analysis of the collected precipitates showed that the ettringites were in a layered shape with composition between Ca6Al2(SO4)3(OH)12 and Ca4Al2(SO4)(OH)12 at the optimized chemical dosage; therefore, the developed ettringite precipitation method could effectively remove sulfate from seawater without toxic chemicals involved, which benefits seawater hydraulic fracturing in an economic way, and this contributes to water sustainability.

Fabrication and characterization of a novel Ba2+-loaded sawdust biochar doped with iron oxide for the super-adsorption of SO42- from wastewater

Biochar is a low-cost adsorbent used in the treatment of contaminated wastewater. We investigated the potential of an Fe-impregnated, Ba²⁺-loaded biochar (Fe-(Ba-BC)) for the removal of SO₄^2- from aqueous solutions. The Ba²⁺-loaded biochar was synthesized from sawdust impregnated with iron oxide via pyrolysis at 600 °C. The porous structure of the Fe-(Ba-BC) was identified by scanning electron microscopy before sulfate was adsorbed onto the adsorbent. Functional groups were determined by energy-dispersive spectrophotometry and Raman spectrometry.. The Fe-(Ba-BC) Raman peaks before the experiment were higher than after, suggesting the precipitation of BaSO₄. The presence of BaCl₂ on the surface of the biochar was confirmed by X-ray diffraction. Batch sorption results showed that Fe-(Ba-BC) strongly adsorbed aqueous SO₄^2- with a removal efficacy of 96.7% under the optimum conditions of 0.25 M BaCl₂, a contact time of 480 min, a pH of 9 and an adsorbent dose of 2 g. The optimum condition for removal and reaction rate kinetics analysis indicated that adsorption curve fitted well with PSO, k₂ 0.00015 confirmed the removal of SO₄^2- via chemisorption. Thus, Fe-(Ba-BC) was found to be a favorable adsorbent for removing SO₄^2-.

Physicochemical analysis of wastewater generated from a coating industry in Mauritius

The coating industry is one of the most important consumers of water and chemicals and consequently is a major water polluter in Mauritius. The focus of this study was to characterise wastewater generated by a coating industry in Mauritius. The objectives were to develop a wastewater sampling strategy and to analyse the pollutant parameters as per Mauritian regulations. The wastewater samples were analysed for physicochemical properties and metal abundances over a period of 6 months. The physicochemical parameters analysed were pH, electrical conductivity (EC), true colour, total suspended solids (TSS), biological oxygen demand (BOD₅), chemical oxygen demand (COD), nitrate, phosphate, sulphate and free chlorine. The wastewater samples were also analysed for metal ions such as sodium, potassium, arsenic, cadmium, chromium, cobalt, copper, iron, lead, manganese, mercury, molybdenum, nickel and zinc. The results of the physicochemical parameters indicated the presence of biologically resistant organic matters in all the wastewater samples with elevated values of BOD₅ and COD, and low biodegradability index, respectively. The coating industry wastewater samples were acidic and saline in nature. Moreover, they presented high concentrations of TSS, free chlorine and sodium ions compared to standard limits promulgated by the Mauritian Government. Spearman's rank correlation matrix with non-linear regression analysis showed significant associations among the measured parameters which were found to have a common origin in the coating industry wastewater. This research will be useful for regular monitoring and setting up an adequate coating industry wastewater treatment for the potential reuse in production processes in Mauritius.

Treatment of real industrial wastewater with high sulfate concentrations using modified Jordanian kaolin sorbent: batch and modelling studies

In the present study, BaCl₂ modified Jordanian kaolin sorbent (obtained from Mahis, Jordan) was used to remove sulfate-contaminated industrial wastewater. The kaolin sample was pretreated to enhance its adsorption capacity and then characterized using X-Ray fluorescence (XRF) and Fourier Transform Infrared Spectroscopy (FTIR). Equilibrium isotherms for the adsorption parameters were carried out experimentally, and the adsorption data correlated very well with Freundlich and Temkin and Dubinin-Radushkevich models. Furthermore, the adsorption kinetics followed the pseudo-first-order and intraparticle diffusion models perfectly. The estimated value of the maximum adsorption capacity qm = 85.08 mg/g indicates that kaolin has a very high capacity to adsorb sulfate ions at studied parameters. The estimated value of the mean free energy (4.87 kJ/mol) is very low, confirming physical type adsorption. The study results established that modified Jordanian kaolin could serve as a safe and effective natural adsorbent for sulfate-contaminated industrial wastewater.

Over-sulfated soils and sediments treatment: A brief discussion on performance disparities of biological and non-biological methods throughout the literature

High sulfate concentrations in industrial effluents as well as solid materials (excavated soils, dredged sediments, etc.) are a major hindrance for circular economy outlooks. SO₄^2- acceptability standards are indeed increasingly restrictive, given the potential outcomes for public health and ecosystems. This literature review deals with the treatment pathways relying on precipitation, adsorption and microbial redox principles. Although satisfactory removal performances can be achieved with each of them, significant yield differences are displayed throughout the bibliography. The challenge here was to identify the parameters leading to this variability and to assess their impact. The precipitation pathway is based on the formation of two main minerals (ettringite and barite). It can lead to total sulfate removal but can also be limited by aqueous wastes chemistry. Stabilizer kinetics of formation and equilibrium are highly constrained by background properties such as pH, Eh, SO₄^2- saturation state and inhibiting metal occurrences. Regarding the adsorption route, sorbents' intrinsic features such as the q_max parameter govern removal yields. Concerning the microbial pathway, the chemical oxygen demand/SO₄^2- ratio and the hydraulic retention time, which are classically evoked as yield variation factors, appear here to be weakly influential. The effect of these parameters seems to be overridden by the influence of electron donors, which constitute a first order factor of variability. A second order variability can be read according to the nature of these electron donors. Approaches using simple monomers (ethanol lactates, etc.) perform better than those using predominantly ligneous organic matter.

Enhancing arsenic sequestration on ameliorated waste molasses nanoadsorbents using response surface methodology and machine-learning frameworks

The development of a novel nanobiosorbent derived from waste molasses for the adsorptive removal of arsenic (As) has been attempted in this study. Waste molasses were chemically ameliorated through a solvothermal route for the incorporation of iron oxide, thereby producing iron oxide incorporated carbonaceous nanomaterial (IOCN). Synthesis of IOCN was confirmed through transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and atomic emission spectroscopy (AES) analysis. The surface area and porous behavior of IOCN were elucidated by Brunauer-Emmett-Teller (BET) assessments. The experimental conditions for adsorption were first modeled using response surface methodology (RSM) based on the central composite design (CCD), considering the parameters: adsorbate dosage, adsorbent dosage, pH, and contact time. RSM optimizations were improved upon using a three-layer feed-forward multilayer perceptron (MLP) based Artificial Neural Network (ANN) model. Optimization through ANN model resulted in the increase of the maximal As adsorption efficiency to ~ 96% for IOCN. The IOCN isotherm plots show the best fit for the Sips isotherm, and the reaction kinetics follows the pseudo-second-order model, indicating the chemisorption mechanism for As adsorption. Evidence for direct coordination of As to the surface of adsorbents was further confirmed by FTIR spectroscopic studies before and after As adsorption. The high adsorption efficiencies and the low-cost facile synthesis of the IOCN nanosorbent from agro-industrial waste indicate their potential for commercial applications.

Advanced and Intensified Seawater Flue Gas Desulfurization Processes: Recent Developments and Improvements

Seawater flue gas desulfurization (SWFGD) is considered to be a viable solution for coastal and naval applications; however, this process has several drawbacks, including its corrosive absorbent; low vapor loading capacity since the solubility of sulfur oxides (SOx) in seawater is lower than that of limestone used in conventional methods; high seawater flowrate; and large equipment size. This has prompted process industries to search for possible advanced and intensified configurations to enhance the performance of SWFGD processes to attain a higher vapor loading capacity, lower seawater flowrate, and smaller equipment size. This paper presents an overview of new developments as well as advanced and intensified configurations of SWFGD processes via process modifications such as modification and optimization of operating conditions, improvement of spray and vapor distributors, adding internal columns, using square or rectangular shape, using a pre-scrubber, multiple scrubber feed; process integration such as combined treatment of SOx and other gases, and waste heat recovery; and process intensification such as the use of electrified sprays, swirling gas flow, and rotating packed beds. A summary of the industrial applications, engineering issues, environmental impacts, challenges, and perspectives on the research and development of advanced and intensified SWFGD processes is presented.

Enhanced removal of trichlorfon and Cd(II) from aqueous solution by magnetically separable chitosan beads immobilized Aspergillus sydowii

Simultaneous removal of heavy metals and organics from wastewater has always been an environmental problem with great concern. In this study, a novel ecofriendly bioborbent, magnetic chitosan beads immobilized Aspergillus sydowii (MCBAs) were synthesized and used to simultaneously remove trichlorfon (TCF) and Cd(II) from aqueous solution. MCBAs showed an increased special surface area (55.38 m²·g^-1) through immobilizing A. sydowii and its saturation magnetization reached 14.62 emu·g^-1. The equilibrium removal capacities of TCF and Cd(II) were 135.43 mg·g^-1 and 56.40 mg·g^-1 in the co-system with 200 mg·L^-1 TCF and 50 mg·L^-1 Cd(II), respectively. The removal capacities of TCF and Cd(II) were strongly depended on the immobilized A. sydowii spore concentration, initial concentrations of TCF and Cd(II), and MCBAs dose. TCF biodegradation intermediates were identified by gas chromatography-mass spectrometry system. Fourier transform infrared spectra displayed that -OH and -NH groups on MCBAs mainly participated in the Cd(II) sequestration and the CO stretching vibration was possibly related to the degradation intermediates of TCF. MCBAs exhibited excellent recyclability upto four cycles. Therefore, MCBAs are suitable and effective for the simultaneous removal of TCF and Cd(II) from wastewater.

Degradation of bisphenol A by persulfate coupled with dithionite: Optimization using response surface methodology and pathway

The degradation efficiency of bisphenol A (BPA) was investigated in the process of persulfate (PS) coupled with dithionite (DTN) as a function of concentration of BPA, PS, DTN and solution pH. A simple response surface methodology (RSM) based on central composite design (CCD) was employed to determine the influence of individual and interaction of above variables and the optimum processing parameters. It is satisfactory of a quadratic model with low probabilities (<0.0001) at a confidence level of 95% to predict the BPA degradation efficiency. The model was well fitted to the actual data and the correlation coefficients of R² and R²-adj were 0.9270 and 0.8885, respectively. In addition, the obtained optimum conditions for BPA degradation were 1.79 μM, 131.77 μM, 93.64 μM for BPA, PS, DTN and pH = 3.62, respectively. It achieved a degradation efficiency >90% within 150 min. Moreover, the trapping experiment of active species demonstrated that SO₄^·- and ·OH were the dominant species and natural water matrix showed an obvious inhibition effect on BPA degradation. The BPA degradation pathway was predicted based on GC-MS results in this study.

Tackling environmental challenges in pollution controls using artificial intelligence: A review

This review presents the developments in artificial intelligence technologies for environmental pollution controls. A number of AI approaches, which start with the reliable mapping of nonlinear behavior between inputs and outputs in chemical and biological processes in terms of prediction models to the emerging optimization and control algorithms that study the pollutants removal processes and intelligent control systems, have been developed for environmental clean-ups. The characteristics, advantages and limitations of AI methods, including single and hybrid AI methods, were overviewed. Hybrid AI methods exhibited synergistic effects, but with computational heaviness. The up-to-date review summarizes i) Various artificial neural networks employed in wastewater degradation process for the prediction of removal efficiency of pollutants and the search of optimizing experimental conditions; ii) Evaluation of fuzzy logic used for intelligent control of aerobic stage of wastewater treatment process; iii) AI-aided soft-sensors for precisely on-line/off-line estimation of hard-to-measure parameters in wastewater treatment plants; iv) Single and hybrid AI methods applied to estimate pollutants concentrations and design monitoring and early-warning systems for both aquatic and atmospheric environments; v) AI modelings of short-term, mid-term and long-term solid waste generations, and various ANNs for solid waste recycling and reduction. Finally, the future challenges of AI-based models employed in the environmental fields are discussed and proposed.

A novel carbon monoxide fed moving bed biofilm reactor for sulfate rich wastewater treatment

In this study, a moving bed biofilm reactor was used for biodesulfuruization using CO as the sole carbon substrate. The effect of hydraulic retention time (HRT), sulfate loading rate and CO loading rate on sulfate and CO removal was examined. At 72, 48 and 24 h HRT, the sulfate removal was 93.5%, 91.9% and 80.1%, respectively. An increase in the sulfate loading reduced the sulfate reduction efficiency, which, however, was improved by increasing the CO flow rate into the MBBR. Best results in terms of sulfate reduction (>80%) were obtained for low inlet sulfate and high CO loading conditions. The CO utilization was very high at 85% throughout the study, except during the last phase of the continuous bioreactor operation it was around 70%. An artificial neural network based model was successfully developed and optimized to accurately predict the bioreactor performance in terms of both sulfate reduction and CO utilization. Overall, this study showed an excellent potential of the moving bed biofilm bioreactor for efficient sulfate reduction even under high loading conditions.

The Effect of Multi-Walled Carbon Nanotubes-Additive in Physicochemical Property of Rice Brand Methyl Ester: Optimization Analysis

Biodiesel as an alternative to diesel fuel produced from vegetable oils or animal fats has attracted more and more attention because it is renewable and environmentally friendly. Compared to conventional diesel fuel, biodiesel has slightly lower performance in engine combustion due to the lower calorific value that leads to lower power generated. This study investigates the effect of multi-walled carbon nanotubes (MWCNTs) as an additive to the rice bran methyl ester (RBME). Artificial neural network (ANN) and response surface methodology (RSM) was used for predicting the calorific value. The interaction effects of parameters such as dosage of MWCNTs, size of MWCNTs and reaction time on the calorific value of RBME were studied. Comparison of RSM and ANN performance was evaluated based on the correlation coefficient (R2), the root mean square error (RMSE), the mean absolute percentage error (MAPE), and the average absolute deviation (AAD) showed that the ANN model had better performance (R2 = 0.9808, RMSE = 0.0164, MAPE = 0.0017, AAD = 0.173) compare to RSM (R2 = 0.9746, RMSE = 0.0170, MAPE = 0.0028, AAD = 0.279). The optimum predicted of RBME calorific value that is generated using the cuckoo search (CS) via lévy flight optimization algorithm is 41.78 (MJ/kg). The optimum value was obtained using 64 ppm of < 7 nm MWCNTs blending for 60 min. The predicted calorific value was validated experimentally as 41.05 MJ/kg. Furthermore, the experimental results have shown that the addition of MWCNTs was significantly increased the calorific value from 36.87 MJ/kg to 41.05 MJ/kg (11.6%). Also, the addition of MWCNTs decreased flashpoint (−18.3%) and acid value (−0.52%). As a conclusion, adding MWCNTs as an additive had improved the physicochemical properties characteristics of RBME. To our best knowledge, no research has yet been performed on the effect of multi-walled carbon nanotubes-additive in physicochemical property of rice brand methyl ester application so far.

Thermodynamic Simulations for Determining the Recycling Path of a Spent Lead-Acid Battery Electrolyte Sample with Ca(OH)2

By utilizing thermodynamic calculations, the possible removal path of spent lead-acid battery electrolytes was modeled. The process was divided into precipitation and carbonation processes. In the carbonation process, two scenarios were discussed, namely carbonation with and without pre-filtration of the precipitates resulted from the precipitation process. The results showed that in the precipitation process, the theoretical limit for the chemical removal of SO42− was 99.15%, while in the following carbonation process without filtration, only 69.61% of SO42− was removed due to the fact that CO2 reacts with Ca2+ ion in the solution, and thus leads to the production of CaCO3 and SO42− ions in the solution. In the carbonation process without filtration, with the increase of CO2 in the solution the removal ratio of SO42− further decreases. Thermodynamic simulation was effective in predicting the theoretical removal limits and helps in understanding and optimizing the removal process.

Sulphur compounds removal from an industrial landfill leachate by catalytic oxidation and chemical precipitation: From a hazardous effluent to a value-added product

This study focused on the removal of sulphur compounds from a high-strength leachate of a hazardous industrial waste landfill. Firstly, sulphides (0.5 g L^-1) and sulphites (2.5 g L^-1) were catalytic oxidised at natural pH (8.7). Air or H₂O₂ were applied as oxidants and metals present in the leachate were used as catalysts. Distinct air flow rates and H₂O₂:sulphur molar ratios were tested. Concentrations of sulphide and sulphite lower than 1.0 mg L^-1 (emission limit value - ELV) were obtained after 5-h oxygenation or 1-min peroxidation under the best conditions, i.e. air flow rate of 1 L_air L_leachate^-1 min^-1 and H₂O₂:sulphur stoichiometric ratio. Aeration was considered unsafe since >33 volatile organic compounds (VOCs) and hydrogen sulphide (H₂S) were released to the atmosphere. Thus, only the H₂O₂-oxidised leachate pursued treatment. Sulphates (13 g L^-1) were removed by chemical precipitation as ettringite or barite applying different reactants contents and pH values. Without pH correction, sulphate contents below 2.0 g L^-1 (ELV) were achieved using a [Ca²⁺]:[Al³⁺]:[SO₄^2-] molar ratio of 12:4:3 (2-fold stoichiometry) and a [Ba²⁺]:[SO₄^2-] molar ratio of 1.0:1.0 (1-fold stoichiometry). The analysis of precipitates by X-ray diffraction (XRD) showed a three-phase ettringite (only 67% corresponding to ettringite itself) and single-phase barite. Barite precipitation proved to be more appealing since a value-added product was obtained and, furthermore, less reactants were required. After sulphur compounds removal using H₂O₂-driven catalytic oxidation and chemical precipitation through barite, the leachate was suitable for biological treatment, despite the high salinity, and a high fraction of the organic load (46%) could be biologically oxidised.

Effects of barium on the pathways of anaerobic digestion

The sufficient presence of trace elements (TE) is essential for anaerobic digestion. Barium (Ba) is considered a non-essential trace element that can be collaterally added to digesters as part of low-cost trace element sources or because of its presence in some feedstocks, such as crude glycerol. In the present study, the impact of Ba supplementation (2-2000 mg/L) on each stage of the anaerobic digestion (AD) process was evaluated using pure substrates (i.e., cellulose, glucose, a mixture of volatile fatty acids, sodium acetate and hydrogen) as well as a complex substrate (i.e., dried green fodder). Hydrolytic activity was affected at dosages higher than 200 mg Ba/L, whereas cellulose degradation was completely inhibited at 2000 mg Ba/L. The negative effects of the addition of Ba to methane production were observed only in the hydrolytic activity, and no effects were detected at any barium dosage in the subsequent anaerobic steps. Because Ba does not have a reported role as a cofactor of enzymes, this response could have been due to a direct inhibitory effect, a variation in the bioavailability of other trace elements, or even the availability of CO₂/SO₄ through precipitation as Ba-carbonates and sulphates. The results showed that the addition of Ba modified the chemical equilibrium of the studied system by varying the soluble concentration of some TEs and therefore their bioavailability. The highest variation was detected in the soluble concentration of zinc, which increased as the amount of Ba increased. Although little research has shown that Ba has some utility in anaerobic processes, its addition must be carefully monitored to avoid an undesirable modification of the chemical equilibrium in the system.

Biosorptive removal of Zn(II) ions by Pongamia oil cake (Pongamia pinnata) in batch and fixed-bed column studies using response surface methodology and artificial neural network

Design of experiment and artificial neural networks (ANN) have been effectively employed to predict the rate of uptake of Zn(II) ions onto defatted pongamia oil cake. Four independent variables such as, pH (2.0-7.0), initial concentration of Zn(II) ions (50-500 mg/L), temperature (30ºC-50 °C), and dosage of biosorbent (1.0-5.0 g/L) were used for the batch mode while the three independent variables viz. flowrate, initial concentration of Zn(II) ions and bed height were employed for the continuous mode. Second-order polynomial equations were then derived to predict the Zn(II) ion uptake rate. The optimum conditions for batch studies was found to be pH: 4.45, metal ion concentration: 462.48 mg/L, dosage: 2.88 g/L, temperature: 303 K and on the other hand the column studies flow rate: 5.59 mL/min, metal ion concentration: 499.3 mg/L and bed height: 14.82 cm. Under these optimal condition, the adsorption capacity was 80.66 mg/g and 66.29 mg/g for batch and column studies, respectively. The same data was fed to train a feed-forward multilayered perceptron, using MATLAB to develop the ANN based model. The predictive capabilities of the two methodologies were compared, by means of the absolute average deviation (AAD) (4.57%), model predictive error (MPE) (4.15%), root mean square error (RMSE) (3.19), standard error of prediction (SEP) (4.23) and correlation coefficient (R) (0.99) for ANN and for RSM AAD (16.27%), MPE (21,25%), RMSE (13.15%), SEP and R (0.96) by validation data. The findings suggested that compared to the prediction ability of RSM model, the properly trained ANN model has better prediction ability. In batch studies, equilibrium data was used to determine the isotherm constants and first and second order rate constants. In column, bed depth service time (BDST) and Thomas model was used to fit the obtained column data.

Removal of High-Concentration Sulfate Ions from the Sodium Alkali FGD Wastewater Using Ettringite Precipitation Method: Factor Assessment, Feasibility, and Prospect

The feasibility of removal of sulfate ions from the sodium alkali FGD wastewater using the ettringite precipitation method was evaluated. Factors affecting the removal of sulfate ions, such as NaAlO2 dosage, Ca(OH)2 dosage, solution temperature, anions (Cl−, NO3− and F−), and heavy metal ions (Mg2+ and Mn2+), were investigated, and the optimal experimental conditions for the removal of sulfate ions were determined. Experimental results indicate that the ettringite precipitation method can effectively remove SO42− with removal efficiency of more than 98%. All the investigated factors have influences on the removal of sulfate ions, and among them, the dosage of reagents, solution temperature, and fluoride ions have the strongest influence. In addition, the method can effectively synergistically remove F− and heavy metal ions with removal efficiencies of more than 90% and 99%, respectively; meanwhile, Cl− and NO3− also can be removed minimally by the method. The result of actual wastewater treatment shows that the method is feasible for treating high-concentration sulfate wastewater. The ettringite precipitation method has the potential to be a commercial application in the future.