Ramakrishna Mallampati

Apple peels--a versatile biomass for water purification?

The presence of anions such as chromate, arsenate, and arsenite in drinking water is a major health concern in many parts of the world due to their high toxicity. Removal of such anions from water using low cost biomass is an efficient and affordable treatment process. Owing to the easy availability and biodegradability, we chose to use apple peel as a substrate for our investigations. Zirconium cations were immobilized onto the apple peel surface and used for the extraction of anions. Zirconium loaded apple peels were used to extract anions such as phosphate, arsenate, arsenite, and chromate ions from aqueous solutions. The presence of Zr cations on the apple peel surface was characterized using XPS. The modified adsorbent was characterized using SEM, EDS, and FT-IR. Zr treated apple peels showed efficient adsorption toward AsO2(-) (15.64 mg/g), AsO4(3-) (15.68 mg/g), Cr2O7(2-) (25.28 mg/g), and PO4(3-) (20.35 mg/g) anions. The adsorption and desorption studies revealed the adsorption mechanism involves electrostatic interactions. Anion removal efficiency was estimated by batch adsorption studies. Adsorption kinetic parameters for all anions at different concentrations were described using pseudo-first-order and pseudo-second-order rate equations. Langumir and Freundlich isotherms were used to validate our adsorption data. Arsenate and chromate anions were strongly adsorbed at the pH range from 2 to 6, while arsenite was extracted efficiently between pH 9 and 10. Overall, the Zr immobilized apple peel is an efficient adsorbent for common anionic pollutants.

Application of tomato peel as an efficient adsorbent for water purification—alternative biotechnology?

Heavy metal ions and dissolved organic compounds in waste water are known to adversely affect human health, aquatic life and the overall ecosystem. Many hazardous pollutants need to be removed from drinking water; however, such technologies are not accessible for economically disadvantaged people around the world. Naturally abundant tomato peels or other biomembranes are used as an efficient biomaterial to remove toxic metal ions and organic pollutants from aqueous solution. The functional groups and morphologies of the tomato peels were characterized using FT-IR and FESEM, respectively. Factors such as pH, nature and amount of adsorbent used for extraction were studied to establish the optimum conditions. The maximum adsorption capacity was observed at different pH values for different pollutants. The equilibrium adsorption data were interpreted by using Freundlich and Langmuir isotherms and the adsorption mechanism was investigated by kinetic studies. Results showed that tomato peels have good potential as an efficient adsorbent to remove various pollutants from water.

Co-precipitation with calcium carbonate – a fast and nontoxic method for removal of nanopollutants from water?

Presence of nanosized contaminants such as engineered gold (Au), silver (Ag) nanoparticles and graphene oxide (GO) in many commercial products are creating environmental concerns owing to their high toxicity. Removal of such nanomaterials (NMs) from water using current technologies is not very efficient owing to the small size and shapes of such pollutants. Here we explore a fast method for the extraction of NMs from aqueous solutions based on in situ co-precipitation of calcium carbonate particles. Removal efficiency was estimated using batch adsorption studies. The co-precipitation method entraps and removes the nanomaterials in a fast and efficient manner to purify water. Microscopic observation and spectrophotometric analyses indicated the extraction and incorporation of NMs into the calcium carbonate precipitate. Complete removal (99%) of metal nanoparticles and graphene oxide was observed within 10 min during the co-precipitation and settling of the solids. This method is efficient to remove nanopollutants from water at low concentration (ppm) levels. Co-precipitation, a simple and scalable purification method using nontoxic material can be scaled up to treat contaminated industrial effluents.