Kinetic and thermodynamic studies on biosorption of Cr(VI) on raw and chemically modified Datura stramonium fruit.

Biosorption of Cr(VI) on sulfuric and phosphoric acid-treated Datura stramonium fruit was investigated in batch mode. The various parameters that influence the biosorption process such as Cr(VI) initial concentration, biosorbent dosage, contact time, temperature, and pH value were optimized. Both linear and non-linear regression analysis of isotherm data suggest that Langmuir isotherm model mimics the behavior of Cr(VI) ion biosorption onto Datura stramonium fruit biosorbent. The maximum Cr(VI) ions adsorption capacity of 138.074 mg/g at pH 2 is achieved with phosphoric acid treated Datura stramonium (PDSF). The kinetics of adsorption process is well described by pseudo-second-order model with high R2 and low χ2 value. The estimated activation energy of < 8 kJ/mol obtained for both raw and chemically modified adsorbents suggests that the adsorption occurs mainly via physisorption. Besides, thermodynamic results reveal that biosorption of Cr(VI) on both treated and untreated Datura stramonium was endothermic, spontaneous, and randomness in nature.

Oxidative removal of stabilized landfill leachate by Fenton's process: process modeling, optimization & analysis of degraded products.

In this study, the stabilized landfill leachate which has a BOD : COD ratio of 0.045 was treated using Fenton's process. The effect of process parameters like reaction time, pH, dose of FeSO4 and dose of H2O2 was estimated using One Factor At a Time (OFAT) and the linear, interactive and quadratic effects between the factors were studied using Face Centered Central Composite Design (CCF). In the OFAT approach, reaction time: 5 minutes, pH: 3.0, dose of FeSO4: 30 mM, and dose of H2O2: 30 mM were optimized. In CCF, the statistically optimized model shows maximum removal of organic substances at an FeSO4 concentration of 14.44 mM, pH 3.0 and 29.12 mM of H2O2. The regression co-efficient R 2 = 0.9079, adj R 2 = 0.854 and adequate precision = 14.676. The degradation of organic substances was assessed by measuring the Chemical Oxygen Demand (COD). Total Organic Carbon (TOC) and Gas Chromatography-Mass Spectroscopy (GC-MS) were investigated for the sample corresponding to the maximum COD reduction.

Biosorption of chromium(VI) in aqueous solutions by chemically modified Strychnine tree fruit shell.

Chromium(VI) was removed from aqueous solution using sulfuric- and phosphoric-acid-activated Strychnine tree fruit shells (SSTFS and PSTFS) as biosorbents. Effects of various parameters such as adsorbent dose (0.02-0.1 g/L), temperature (303-333 K), agitation speed, solution pH (2-9), contact time, and initial Cr(VI) concentration (50-250 mg/L) were studied for a batch adsorption system. The optimum pH range for Cr(VI) adsorption was determined as 2. Equilibrium adsorption data were analyzed with isotherm models and the Langmuir and Freundlich models got best fitted values for SSTFS (R2 value - 0.994) and PSTFS (R2 value - 0.996), respectively. The maximum adsorption capacities of SSTFS and PSTFS were 100 and 142.85 mg/g, respectively. The biosorption process was well explained by pseudo-second-order kinetic model with higher R2 value (SSTFS - 0.996, PSTFS - 0.990) for both biosorbents. Characterization of biosorbents was done using Fourier transform infrared spectroscopy, scanning electron microscopy, elemental analysis, energy-dispersive X-ray analysis, and thermogravimetric analysis. Thermodynamic studies revealed the spontaneous, endothermic, and randomness in nature of the Cr(VI) adsorption process. Different concentrations of NaOH solutions were used to perform the desorption studies. The results demonstrated that both SSTFS and PSTFS can be used as an effective and low-cost biosorbent for removal of Cr(VI) from aqueous solutions.

Optimization of adsorption process parameters by response surface methodology for hexavalent chromium removal from aqueous solutions using Annona reticulata Linn peel microparticles.

Fruit peel microparticles of Annona reticulata Linn were used as biosorbent for the sequestration of hexavalent chromium (CR(VI)). Characterization of the biosorbent was done using scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDXS), Fourier transfer infrared spectroscopy (FTIR), gas chromatography-mass spectrometry (GCMS), carbon, hydrogen, nitrogen and sulphur (CHNS) elemental analysis, mercury intrusion porosimetry and point of zero charge. Influential parameters were optimized using response surface methodology (RSM) with a total of 17 experimental runs based on the Box-Behnken design and found to be pH 1.0, temperature 25 °C and 100 mg/L initial chromium concentration. pH and concentration were found to be more influential than temperature. The analysis of variance indicated that a second-order polynomial regression equation was the most suitable for fitting the experimental data. The experimental runs showed a good correlation with the predicted responses (R2 = 0.9956). The biosorption process fitted well with the Langmuir isotherm with an adsorption capacity of 108. 32 mg/g out of the other isotherms such as Freundlich and Dubinin-Radushkevich that were analyzed. Non linear pseudo first order, pseudo second order, and intraparticle diffusion kinetics were applied to describe the interaction between the biosorbent and Cr(VI). Desorption and regeneration performances showed that fruit peels of Annona reticulata Linn can be an environmental friendly option for hexavalent chromium removal from aqueous solutions.

Carbofuran removal in continuous-photocatalytic reactor: Reactor optimization, rate-constant determination and carbofuran degradation pathway analysis.

Carbofuran (CBF) removal in a continuous-flow photocatalytic reactor with granular activated carbon supported titanium dioxide (GAC-TiO2) catalyst was investigated. The effects of feed flow rate, TiO2 concentration and addition of supplementary oxidants on CBF removal were investigated. The central composite design (CCD) was used to design the experiments and to estimate the effects of feed flow rate and TiO2 concentration on CBF removal. The outcome of CCD experiments demonstrated that reactor performance was influenced mainly by feed flow rate compared to TiO2 concentration. A second-order polynomial model developed based on CCD experiments fitted the experimental data with good correlation (R2 ∼ 0.964). The addition of 1 mL min-1 hydrogen peroxide has shown complete CBF degradation and 76% chemical oxygen demand removal under the following operating conditions of CBF ∼50 mg L-1, TiO2 ∼5 mg L-1 and feed flow rate ∼82.5 mL min-1. Rate constant of the photodegradation process was also calculated by applying the kinetic data in pseudo-first-order kinetics. Four major degradation intermediates of CBF were identified using GC-MS analysis. As a whole, the reactor system and GAC-TiO2 catalyst used could be constructive in cost-effective CBF removal with no impact to receiving environment through getaway of photocatalyst.

Photocatalytic degradation of carbofuran by TiO2-coated activated carbon: Model for kinetic, electrical energy per order and economic analysis.

The photocatalytic removal of carbofuran (CBF) from aqueous solution in the presence of granular activated carbon supported TiO2 (GAC-TiO2) catalyst was investigated under batch-mode experiments. The presence of GAC enhanced the photocatalytic efficiency of the TiO2 catalyst. Experiments were conducted at different concentrations of CBF to clarify the dependence of apparent rate constant (kapp) in the pseudo first-order kinetics on CBF photodegradation. The general relationship between the adsorption equilibrium constant (K) and reaction rate constant (kr) were explained by using the modified Langmuir-Hinshelwood (L-H) model. From the observed kinetics, it was observed that the surface reaction was the rate limiting step in the GAC-TiO2 catalyzed photodegradation of CBF. The values of K and kr for this pseudo first-order reaction were found to be 0.1942 L  mg(-1) and 1.51 mg L(-1) min(-1), respectively. In addition, the dependence of kapp on the half-life time was determined by calculating the electrical energy per order experimentally (EEO experimental) and also by modeling (EEO model). The batch-mode experimental outcomes revealed the possibility of 100% CBF removal (under optimized conditions and at an initial concentration of 50 mg L(-1) and 100 mg L(-1)) at a contact time of 90 min and 120 min, respectively. Both L-H kinetic model and EEO model fitted well with the batch-mode experimental data and also elucidated successfully the phenomena of photocatalytic degradation in the presence of GAC-TiO2 catalyst.

Optimisation of radiolysis of Reactive Red 120 dye in aqueous solution using ionising (60)Co gamma radiation by response surface methodology.

In recent years, employing radiation technology is gaining great interest in degradation of industrial effluents. In this work the possibility of using gamma irradiation to degrade Reactive Red 120 (C.I.292775) was explored. The effects of pH, dose of gamma irradiation and concentration of dye were examined and their interaction were also established based on their response. For the analysis and optimisation of variables, three factor three level Box-Wilson face centred central composite design (CCF) was used. Analysis of variance with R(2) = 0.9988, adjusted R(2) = 0.9981 and the adequate precision value of 122.303 indicates that the CCF model can be used. The coefficient of variation (0.54%) indicates the reliability of the model. The dose of gamma irradiation (kGy) and the concentration of dye (mg/L) showed significant effects on the degradation of RR 120, while a difference of 6 to 10% degradation was observed in extending the pH towards the acid or alkali range from pH 7.00. The maximum concentration of dye degraded was observed as 347.509 mg/L at initial pH: 7.0, dose of gamma irradiation: 5.94 kGy and initial concentration of dye: 500 mg/L. This predicted value was found to be in agreement with the experimental value on the optimised conditions.

Adsorption of hexavalent chromium from synthetic and electroplating effluent on chemically modified Swietenia mahagoni shell in a packed bed column.

Packed bed column studies were carried out to evaluate the performance of chemically modified adsorbents for the sequestration of hexavalent chromium from synthetic and electroplating industrial effluent. The effects of parameters such as bed height (3-9 cm), inlet flow rate (5-15 mL/min), and influent Cr(VI) concentration (50-200 mg/L) on the percentage removal of Cr(VI) and the adsorption capacity of the adsorbents in a packed bed column were investigated. The breakthrough time increased with increasing bed height and decreased with the increase of inlet flow rate and influent Cr(VI) concentration. The adsorption column models such as Thomas, Adams-Bohart, Yoon-Nelson, and bed depth service time (BDST) were successfully correlated with the experimental data. The Yoon-Nelson and BDST model showed good agreement with the experimental data for all the studied parameter conditions. Results of the present study indicated that the chemically modified Swietenia mahagoni shell can be used as an adsorbent for the removal of Cr(VI) from industrial wastewater in a packed bed column.

Hexavalent chromium removal from aqueous solutions by a novel powder prepared from Colocasia esculenta leaves.

In this study, batch removal of hexavalent chromium from aqueous solutions by powdered Colocasia esculenta leaves was investigated. Batch experiments were conducted to study the effects of adsorption of Cr(VI) at different pH values, initial concentrations, agitation speeds, temperatures, and contact times. The biosorbent was characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier transform infrared spectrometer analysis. The biosorptive capacity of the adsorbent was dependent on the pH of the chromium solution in which maximum removal was observed at pH 2. The adsorption equilibrium data were evaluated for various adsorption isotherm models, kinetic models, and thermodynamics. The equilibrium data fitted well with Freundlich and Halsey models. The adsorption capacity calculated was 47.62 mg/g at pH 2. The adsorption kinetic data were best described by pseudo-second-order kinetic model. Thus, Colocasia esculenta leaves can be considered as one of the efficient and cheap biosorbents for hexavalent chromium removal from aqueous solutions.

Significance of exploiting non-living biomaterials for the biosorption of wastewater pollutants.

Industrial effluents from various sectors have become a matter of major environmental concern. The treatment of wastewater in recent year plays a significant role in order to remove the pollutants and to safeguard the water resource. The conventional wastewater treatment is considered costlier and associated with problem of sludge generation. Biosorption methods are considered as the potential solution due to their economical efficiency, good adsorption capacity and eco-friendliness. In this review, an extensive list of biosorbents from algae, bacteria, fungi and agricultural byproducts have been compiled. The suitability of biosorbents towards the eradication of heavy metals, textile dyes and phenolic compounds were highlighted. It is evident from the literature survey of recently published research articles that the biosorbents have demonstrated outstanding removal potential towards the wastewater pollutants. Therefore, biosorbents from the source of dead microbial and agricultural byproduct can be viable alternatives to activated carbon for the wastewater treatment.

A holistic approach combining factor analysis, positive matrix factorization, and chemical mass balance applied to receptor modeling.

Rapid urbanization and population growth resulted in severe deterioration of air quality in most of the major cities in India. Therefore, it is essential to ascertain the contribution of various sources of air pollution to enable us to determine effective control policies. The present work focuses on the holistic approach of combining factor analysis (FA), positive matrix factorization (PMF), and chemical mass balance (CMB) for receptor modeling in order to identify the sources and their contributions in air quality studies. Insight from the emission inventory was used to remove subjectivity in source identification. Each approach has its own limitations. Factor analysis can identify qualitatively a minimal set of important factors which can account for the variations in the measured data. This step uses information from emission inventory to qualitatively match source profiles with factor loadings. This signifies the identification of dominant sources through factors. PMF gives source profiles and source contributions from the entire receptor data matrix. The data from FA is applied for rank reduction in PMF. Whenever multiple solutions exist, emission inventory identifies source profiles uniquely, so that they have a physical relevance. CMB identifies the source contributions obtained from FA and PMF. The novel approach proposed here overcomes the limitations of the individual methods in a synergistic way. The adopted methodology is found valid for a synthetic data and also the data of field study.