Asok Adak

Organoarsenicals in poultry litter: Detection, fate, and toxicity

Arsenic contamination in groundwater has endangered the health and safety of millions of people around the world. One less studied mechanism for arsenic introduction into the environment is the use of organoarsenicals in animal feed. Four organoarsenicals are commonly employed as feed additives: arsanilic acid, carbarsone, nitarsone, and roxarsone. Organoarsenicals are composed of a phenylarsonic acid molecule with substituted functional groups. This review documents the use of organoarsenicals in the poultry industry, reports analytical methods available for quantifying organic arsenic, discusses the fate and transport of organoarsenicals in environmental systems, and identifies toxicological concerns associated with these chemicals. In reviewing the literature on organoarsenicals, several research needs were highlighted: advanced analytical instrumentation that allows for identification and quantification of organoarsenical degradation products; a greater research emphasis on arsanilic acid, carbarsone, and nitarsone; identification of degradation pathways, products, and kinetics; and testing/development of agricultural wastewater and solid treatment technologies for organoarsenical-laden waste.

Adsorption of anionic surfactant on alumina and reuse of the surfactant-modified alumina for the removal of crystal violet from aquatic environment

Abstract The adsorption characteristics of sodium dodecyl sulfate (SDS), an anionic surfactant on neutral alumina were studied in detail. Alumina was found to be an efficient adsorbent for SDS and could be used for the removal of SDS from its highly concentrated (several thousand ppm) solution. The equilibrium time found was 2 h. Though the removal efficiency was low (∼65%) at neutral pH, but in slightly acidic condition and in the presence of NaCl the efficiency could be increased dramatically (up to >98%). The adsorption isotherm study showed distinct four regions. The effects of various other parameters such as adsorbent dose, time, and the presence of different ions (Cl- NO- 3, SO2- 4, and Fe3+), and nonionic surfactant on the SDS adsorption were also studied. It was observed that the adsorption capacity was increased due to the presence of these ions in general. After the adsorption of SDS on alumina, the surfactant-modified alumina (SMA) was used for the removal of crystal violet (CV), a well-known cationic dye from aquatic environment. The kinetic studies showed that 1 h shaking time was sufficient to achieve the equilibrium. The removal of CV followed the second order kinetics. Studies were conducted to see the effects of adsorbent dose and initial CV concentration on the removal of CV using SMA. The pH was maintained at 6.7 ± 0.1. SMA was found to be very efficient, and ∼99% efficiency could be achieved under optimised conditions for the removal of CV when present even at a high concentration (200 ppm). To test whether the removal of CV was possible from real water using SMA, the adsorption study was conducted using CV spiked samples using distilled water, tap water, and synthetically prepared wastewater. It was interesting to note that the removal efficiency was even better for tap water and much better for wastewater when compared to that using distilled water. Desorption of both SDS and CV from the SMA surface was possible using 1 M sodium hydroxide solutions.

Sorption kinetics of arsenic on laterite soil in aqueous medium

The efficiency of a locally available laterite soil in removing both arsenite and arsenate from aqueous medium by adsorption was evaluated. It was observed that in batch experiment conducted at 0.5 mg/L initial concentration of arsenic, laterite soil could remove up to 98% of arsenite and 95% of arsenate under optimized conditions. The kinetic profiles under various conditions were developed. Both arsenite and arsenate removal followed pseudo—second order reaction kinetic model. Pore and film diffusion coefficients were determined from the half-time equation and film diffusion appeared to be the rate-limiting. This was further supported by multiple interruption tests.

Modeling and fixed bed column adsorption of As(V) on laterite soil

Laterite soil, an abundant locally available natural adsorbent, has been evaluated for As(V) removal from aqueous solutions in column mode operation. The column studies were conducted using columns of 10, 20, 30 cm bed depth with 2 cm internal diameter. Initial As(V) concentration was 0.5 mg/L and flow rate was 7.75 mL/min. Bohart and Adams sorption model was employed for the determination of different parameters like height of exchange zone, adsorption rate, time required for exchange zone to move, and the adsorption capacity. Effect of flow rate and initial concentration was studied. The adsorption capacity of the laterite soil for 0.5 mg/L of As(V) was found to be 62.32 mg/L, and the adsorption rate constant was 1.0911 L/mg h for the minimum bed depth of 8.47 cm. The column was designed by the BDST model. Freundlich isotherm model was used to compare the theoretical and experimental breakthrough profile in the dynamic process. The bed saturation obtained was 36–80%. Regeneration of the exhausted column was possible with 1M NaOH.

Problem of arsenic in groundwater - a feasible solution

West Bengal in India and Bangladesh achieved remarkable successes in providing drinking water at low cost to the rural population through sinking of shallow tubewells in floodplain aquifers. Unfortunately arsenic contamination of shallow tubewell water in excess of the acceptable limit has become a major public health problem in both the countries. The contamination scenario in West Bengal and Bangladesh appears to be the worst detected so far worldwide, both in terms of area and population. The probable source of arsenic has been reported to be through geological formation. Thousands of people have already shown the symptoms of arsenic poisoning and several millions are at risk of arsenic contamination from drinking tubewell water. Arsenic toxicity has no known effective medicine for treatment, but drinking of arsenic–free water can help the arsenic–affected people to get rid of the symptoms of arsenic toxicity. Hence, provision of arsenic–free water is urgently needed to mitigate arsenic toxicity and protection of health and well–being of rural people living in acute arsenic problem areas of Bangladesh and India. The most commonly used technologies include oxidation, co–precipitation and adsorption onto coagulated flocs, adsorption onto sorptive media, ion exchange resin, and membrane techniques. In this chapter the above methods have been discussed along with a very low–cost adsorbent called CalSiCO developed in our laboratory at the Indian Institute of Technology, Kharagpur.

Effect of Operating Conditions and Interfering Substances on Photochemical Degradation of a Cationic Surfactant

ABSTRACT This work investigates the degradation kinetics of a recalcitrant organic pollutant, cetyltrimethylammonium bromide (CTAB), using direct UV and UV–H2O2 advanced oxidation processes. Direct photolysis at 253.7 nm showed only 55% degradation up to fluence dose of 40.65 J/cm2 for an initial CTAB concentration of 100 mg/L. The apparent fluence-based pseudo-first-order rate constant and quantum yield were 2.29(±0.325) × 10−5 cm2/mJ and 0.305(±0.043) mol/Einstein, respectively. In case of UV–H2O2, >99% degradation was observed up to a fluence dose of 0.79 J/cm2. The rate constant was ∼200 times higher compared to direct photolysis, which was due to hydroxyl radical generation in the UV–H2O2 process. The second-order hydroxyl radical rate constant for CTAB was found to be 1.59(±0.18) × 109 M−1 s−1. The effects of H2O2 dose, initial CTAB concentration and relevant water quality parameters (pH, alkalinity and nitrate concentrations) were studied; all of these influenced the rate constants. CTAB degradation was also examined in the municipal wastewater matrix. It is concluded that UV–H2O2 represents an efficient treatment process for CTAB in environmental matrices.

Application of silica gel factory waste for methyl orange dye removal

The silica gel waste (SGW), after its collection from a local factory (at Kolkata, India), was modified with cationic surfactant and was utilised as an adsorbing media for the removal of methyl orange dye from aquatic environment. In batch mode, the effect of different dissolved salts, solution pH, and surfactant surface coverage on SGW were studied. Presence of electrolyte and solution pH was found to affect performance of the adsorbent. The adsorption capacity could be increased by increasing the surfactant surface coverage. In continuous mode, the SMSGW packed fixed column was run to find the height of adsorption zone, rate of movement of adsorption zone and its saturation at breakthrough. The column was analysed by Logit model to determine the adsorption capacity constant and adsorption rate constant. Desorption of methyl orange from the surface of SMSGW was efficiently done using ethanol.