Electrocatalytic nitrate removal from water using Ag- microparticles and Ag-Poly vinyl alcohol beads: a comparative study.

Excessive application of fertilisers and illegal land disposal of untreated industrial wastewater leads to mounting nitrate content in surface and ground water sources. Conventionally explored methods have their own limitations giving rise to the need for advanced methods which are cost-effective and cause complete destruction of nitrate. In the present study, electrocatalysis has been carried upon synthetic nitrate solutions and actual ground water samples containing nitrate. Silver microparticles (Ag-MP) and silver immobilised on poly vinyl alcohol (Ag-PVA beads) were applied at current density of 15 mA/cm2, 33–35°C and initial pH in a two-compartment cell with Cation Exchange Membrane (CEM) as separator, which is a completely novel approach. Scanning Electron Microscope (SEM) observation of the Ag-PVA beads was done to understand the composition and characterisation of the beads. Three concentrations of silver nitrate solutions i.e. 3.3 mM, 6.6 mM and 9.9 mM were used for the fabrication of silver catalyst. Maximum removal (96% for Ag-MP and 90% for Ag-PVA beads) was obtained with largest concentration (9.9 mM) of silver nitrate synthesised catalyst for synthetic nitrate solutions in both the cases. Selectivity of end product was towards nitrogen gas with sparse nitrite and negligible ammonical nitrogen formation. The destruction of nitrate was due to the nucleophile AgHx generated by Ag0 and the nascent hydrogen on catalystsurface. Conversion was higher using nanoparticles than by use of immobilised beads due to more specific surface area in the former. For ground water sample, tests were carried out at 15 mA/cm2 using 6.6 mM Ag-PVA beads and gave 63% of nitrate reduction with substantial formation of nitrate and some ammonia. [ABSTRACT FROM AUTHOR]