Removal of alpha-picoline, beta-picoline, and gamma-picoline from synthetic wastewater using low cost activated carbons derived from coconut shell fibers

Low-temperature synthesis of functionalized activated carbon from blackboard (Alstonia scholaris) with improved selectivity for 2-methylpyridine removal: batch and column analyses

Coal tar industry has been reported to discharge 2-methylpyridine (2Mp) in concentrations up to 150 mg L^-1. For removal of 2Mp, activated carbon was synthesized from blackboard tree ground bark (BA) by the novel technique of prior cooling (which helped decrease heat generation and volatile gas emission). The material was successfully functionalized with carboxylic group which enhanced 2Mp uptake. Batch sorption of 2Mp was carried out on both BA and carboxyl functionalized BA (CFA). Acetonitrile-water (55:45) was used as eluent in uHPLC quantification of 2Mp. Interaction mechanism of 2Mp with both sorbents was studied by using characterization techniques (SEM, FTIR and EDS). Carboxyl groups present on CFA were found to interact with 2Mp molecules, leading to their removal from synthetic solution. Carboxylation helped in lowering the intrinsic moisture content of the sorbent. Proton leaching from carboxyl groups of CFA was found to be negligible. Specific surface areas for CFA and BA were found as 211.15 m² g^-1 and 156.32 m² g^-1, respectively. Batch experimentation showed that CFA had twice the adsorption capacity compared to BA (27.0 and 15.5 mg g^-1, respectively). Pseudo-second-order kinetics and Langmuir isotherm-based equilibria were observed. Intraparticle diffusion was the rate-limiting step. Top-down fixed bed studies were performed using a 2-cm-diameter column by varying flow rate, bed depth and 2Mp concentration, respectively. The Thomas model could successfully emulate the steep slopes of the breakthrough curves, implying good sorbent saturation.

Sonochemical degradation of 3-methylpyridine (3MP) intensified using combination with various oxidants

3-Methyl pyridine (3MP) is a toxic and hazardous organic compound having considerable negative impact on environment and living organisms. The objective of this work to report a novel treatment strategy based on sonochemical degradation of 3MP, in combination with oxidants such as hydrogen peroxide, Fenton's reagent, peroxymonosulphate (PMS), and potassium persulphate (KPS) as well as solar irradiations. A bath sonicator operating at 25 kHz frequency and rated power dissipation of 100 W was applied in the work to study different approaches with an objective to enhance the removal of 3MP in lesser time. Effect of operating parameters such as pH (over the range of 2-10), treatment time, temperature (25-55 °C) and ultrasonic power (25 W to 150 W) on the degradation has been studied and the best conditions were used in subsequent combination approaches. It was demonstrated that ultrasound in combination with PMS, ferrous sulphate (FeSO₄) and solar irradiations (approach of US/PMS/FeSO₄/solar irradiation) is the best treatment strategy yielding maximum degradation as 97.4% with highest cavitational yield as 1.920 × 10^-4 mg/J and highest synergetic Index as 2.70. Kinetic analysis revealed that first order mechanism fitted well to all the approaches involving different combinations of ultrasound, oxidising agents and solar irradiation. Degradation products were also analysed that established the degradation mechanism as C₂ and C₃ ring cleavages forming 1, 4-dihydro3-methylpyridine followed by Levulinic acid as non -toxic main by-product. Overall the work clearly demonstrated an effective treatment approach involving combined sonication with oxidants for remediation of 3MP also providing insights on kinetics and mechanism of degradation.

Coconut-based biosorbents for water treatment--a review of the recent literature

Biosorption is an emerging technique for water treatment utilizing abundantly available biomaterials (especially agricultural wastes). Among several agricultural wastes studied as biosorbents for water treatment, coconut has been of great importance as various parts of this tree (e.g. coir, shell, etc.) have been extensively studied as biosorbents for the removal of diverse type of pollutants from water. Coconut-based agricultural wastes have gained wide attention as effective biosorbents due to low-cost and significant adsorption potential for the removal of various aquatic pollutants. In this review, an extensive list of coconut-based biosorbents from vast literature has been compiled and their adsorption capacities for various aquatic pollutants as available in the literature are presented. Available abundantly, high biosorption capacity, cost-effectiveness and renewability are the important factors making these materials as economical alternatives for water treatment and waste remediation. This paper presents a state of the art review of coconut-based biosorbents used for water pollution control, highlighting and discussing key advancement on the preparation of novel adsorbents utilizing coconut wastes, its major challenges together with the future prospective. It is evident from the literature survey that coconut-based biosorbents have shown good potential for the removal of various aquatic pollutants. However, still there is a need to find out the practical utility of such developed adsorbents on commercial scale, leading to the superior improvement of pollution control and environmental preservation.

Functional Groups and Interactions Controlling the Adsorption of Bisphenol a onto Different Polymers

The behaviour of different polymers in the adsorption and removal of bisphenol A (BPA) from aqueous solutions was examined in order to identify the mechanism controlling the process. Three polymers with different functional groups were prepared and employed in our laboratory; they were characterized both texturally and chemically in terms of their surface areas, pore-size distributions, total exchange capacities and other parameters. The adsorption isotherms of bisphenol A were obtained and accurately modelled by the three-parameter Langmuir–Freundlich (LF) isotherm, the binding parameters calculated directly by the LF fitting coefficients indicating that increasing temperature was helpful in causing the adsorption process to move from positive cooperativity to negative cooperativity.

The kinetic data were found to be well represented by the pseudo-second-order kinetic model, indicating that the functional groups of the polymers had a significant influence on the adsorption mechanism of BPA. The adsorption of BPA basically depended on the chemical nature of the polymers and the pH value of the solution. The adsorption process was favoured by the molecular form of bisphenol A, since this controlled the surface complexes produced between the polymer surface and the bisphenol A molecules, with the resulting increase in adsorbent–adsorbate interactions being positively influenced by the temperature.

Pyridine sorption from aqueous solution by rice husk ash (RHA) and granular activated carbon (GAC): parametric, kinetic, equilibrium and thermodynamic aspects

The present study deals with the adsorption of pyridine (Py) from synthetic aqueous solutions by rice husk ash (RHA) and commercial grade granular activated carbon (GAC) and reports on the kinetic, equilibrium and thermodynamic aspects of Py sorption. Batch sorption studies were carried out to evaluate the effect of various parameters, such as adsorbent dose (m), initial pH (pH0), contact time (t), initial concentration (C0) and temperature (T) on the removal of Py. The maximum removal of Py is found to be approximately 96% and approximately 97% at lower concentrations (<50 mg dm(-3)) and approximately 79.5% and approximately 84% at higher concentrations (600 mg dm(-3)) using 50 kg m(-3) and 30 kg m(-3) of RHA and GAC dosage, respectively, at 30+/-1 degrees C. Adsorption of Py is found to be endothermic in nature and the equilibrium data can be adequately represented by Toth and Redlich-Peterson isotherm equations. Py can be recovered from the spent adsorbents by using acidic water and 0.1 N H2SO4. The overall adsorption of Py on RHA and GAC is found to be in the order of GAC>RHA. Comparative assessment of adsorbents used by various investigators available in literature showed the effectiveness of BFA and RHA over other adsorbents. Spent RHA can simply be filtered, dried and used in the boiler furnaces/incinerators. Thus, its heating value can be recovered.

Arsenic removal from water/wastewater using adsorbents--A critical review

Arsenic's history in science, medicine and technology has been overshadowed by its notoriety as a poison in homicides. Arsenic is viewed as being synonymous with toxicity. Dangerous arsenic concentrations in natural waters is now a worldwide problem and often referred to as a 20th-21st century calamity. High arsenic concentrations have been reported recently from the USA, China, Chile, Bangladesh, Taiwan, Mexico, Argentina, Poland, Canada, Hungary, Japan and India. Among 21 countries in different parts of the world affected by groundwater arsenic contamination, the largest population at risk is in Bangladesh followed by West Bengal in India. Existing overviews of arsenic removal include technologies that have traditionally been used (oxidation, precipitation/coagulation/membrane separation) with far less attention paid to adsorption. No previous review is available where readers can get an overview of the sorption capacities of both available and developed sorbents used for arsenic remediation together with the traditional remediation methods. We have incorporated most of the valuable available literature on arsenic remediation by adsorption ( approximately 600 references). Existing purification methods for drinking water; wastewater; industrial effluents, and technological solutions for arsenic have been listed. Arsenic sorption by commercially available carbons and other low-cost adsorbents are surveyed and critically reviewed and their sorption efficiencies are compared. Arsenic adsorption behavior in presence of other impurities has been discussed. Some commercially available adsorbents are also surveyed. An extensive table summarizes the sorption capacities of various adsorbents. Some low-cost adsorbents are superior including treated slags, carbons developed from agricultural waste (char carbons and coconut husk carbons), biosorbents (immobilized biomass, orange juice residue), goethite and some commercial adsorbents, which include resins, gels, silica, treated silica tested for arsenic removal come out to be superior. Immobilized biomass adsorbents offered outstanding performances. Desorption of arsenic followed by regeneration of sorbents has been discussed. Strong acids and bases seem to be the best desorbing agents to produce arsenic concentrates. Arsenic concentrate treatment and disposal obtained is briefly addressed. This issue is very important but much less discussed.