Effective biosorption of As(V) from polluted water using Fe(III)-modified Pomelo (Citrus maxima) peel: A batch, column, and thermodynamic study.

Pomelo, Citrus maxima, peel was chemically modified with lime water and then loaded with Fe(III) to develop anion exchange sites for effective sequestration of As(V) from water. Biosorbent characterizations were done by using FTIR, SEM, XRD, EDX, and Boehm's titration. The batch biosorption studies were carried out at various pHs using modified and non-modified biosorbents and optimum biosorption of As(V) occurred at acidic pH (3.0-5.0) for both the biosorbents. A kinetic study showed a fast biosorption rate and obtained results fitted well with the pseudo-second-order (PSO) model. When isotherm data were modeled using the Langmuir and Freundlich isotherm models, the Langmuir isotherm model fit the data better and produced maximal As(V) biosorption capacities of 0.72 ± 03, 0.86 ± 06, and 0.95 ± 05 mmol/g at temperatures 293± 1K, 298± 1K and 303± 1K, respectively. Desorptionof As(V) was effective using 0.1 M NaOH in batch mode. Negative values of ΔG° for all temperatures with positive ΔH° confirmed the spontaneous and endothermic nature of As(V) biosorption. The existence of co-existing chloride (Cl-), nitrate (NO3 -), sodium (Na+), and calcium (Ca2+) showed insignificant interference whereas a high concentration of sulphate (SO4 2-) and phosphate (PO4 3-) significantly lowered As(V) biosorption percentage. Arsenic concentrations in actual arsenic polluted groundwater could be reduced to the WHO drinking water standard (10 µg/L) by using only 1 g/L of investigated Fe(III)-SPP. The dynamic biosorption of As(V) in a fixed bed system showed that Fe(III)-SPP was effective also in continuous mode and different design parameters for fixed bed system were determined using Thomas, Adams-Bohart, BDST, and Yoon-Nelson models. Therefore, from all of these results it is suggested that Fe(III)-SPP investigated in this study can be a potential, low cost and environmentally benign biosorbent material for an effective removal of trace amounts of arsenic from polluted water.

Thermochemical study of Cr(VI) sequestration onto chemically modified Areca catechu and its recovery by desorptive precipitation method.

A new biosorbent for Cr(VI) sequestration was investigated from betel nut waste (BNW), Areca catechu, by H2SO4 charring. Aqueous insolubility and Cr(VI) uptake capacity of native BNW were potentially improved after H2SO4 modification due to cross-linking reaction of betel nut cellulose, thereby creating suitable complexation sites for Cr(VI) ion removal. Langmuir isotherm and pseudo second order (PSO) kinetic models described well with the experimental data. A trace amount of Cr(VI) was effectively removed below the safe drinking water standard (WHO, 0.05 mg/L) using charred BNW (CBNW). The negative value of ΔG° evaluated for all the temperatures suggested the spontaneous nature of Cr(VI) sequestration and positive value of ΔH° (42.43±0.13 kJ/mol) confirmed an endothermic reaction. Co-existing NO 3 - , Cl-, Na+ and Zn2+ ions showed negligible interferences, whereas SO 4 2 - and PO 4 3 - notably reduced Cr(VI) uptake capacity of CBNW. More than 98% of adsorbed Cr(VI) was desorbed using 1M NaOH solution. A light yellow precipitate of BaCrO4 was recovered from the desorbed solution after precipitation with BaCl2 solution. Therefore, the CBNW biosorbent investigated in this work is expected to be a promising material for Cr(VI) sequestration and its recovery from polluted water.

Assessing volatile organic compound level in selected workplaces of Kathmandu Valley.

Volatile organic compounds (VOCs) are one of the major contributors to poor indoor air quality. Due to advancements in sensor technologies, continuous if not regular monitoring total VOC (TVOC) and or some specific VOC in potential high risk workplaces is possible even in resource limited settings. In this study, we implemented a portable VOC sensor to measure concentration of TVOC and formaldehyde (HCHO) in six types of potential high risk workplaces (n = 56 sites) of Katmandu Valley. For comparison, concentration was also measured in immediate surroundings (n = 56) of all the sites. To get preliminary information on safety practices, a survey study was also conducted. The mean TVOC and HCHO concentration in the sites ranged from 1.5‒8 mg/m3 and <0.01-5.5 mg/m3, respectively. The indoor: outdoor TVOC and HCHO ratio (I/O) was found to be significantly higher (I/O > 1.5 and p < 0.05) in 34 (~61%) and 47 sites (∼84%), respectively. A strong positive correlation between HCHO and TVOC concentration was observed in furniture industry (R = 0.91) and metal workshops (R = 0.98). Interestingly, we found TVOC and HCHO concentration higher than WHO safe limit in ∼64% and ∼32% sites, respectively. A rough estimate of chronic daily intake (CDI) of formaldehyde showed that CDI is higher than WHO limit in four sites. These findings suggested that indoor air quality in the significant number of the workplaces is poor and possible measures should be taken to minimize the exposure.