Integrating starch encapsulated nanoscale zero-valent iron for better chromium removal performance

[Display omitted] •Encapsulation over the bare nanoscale zerovalent iron was done successfully.•Encapsulated nanoscale zerovalent iron has better performance.•Integration with UV irradiation, aeration, Fenton reagent, improve the performance of S-nZVI.•Oxidation-reduction potential (ORP) and final pH can be used to monitor chromium removal performance. Hexavalent chromium removal from wastewater is a major challenge for researchers. The study attempts to use starch-modified nanoscale zero-valent iron for hexavalent chromium removal. Starch was used to reduce the agglomeration tendency of nanoparticle, which was evident in SEM micrographs. The effects of various process variables were investigated, including pH, nanoparticle dosage, initial chromium concentration, mixing rate, temperature. The results showed that all these variables, except pH, were positively correlated with removal efficiency. The pH played a vital role in Cr(VI) removal performance. The removal performance of bare nanoscale zero-valent iron was below 50 % for chromium concentration 50 mg/l. The starch encapsulated nanoscale zero-valent iron worked well for lower chromium concentration, but at higher concentration (50 mg/l), the performance stagnated to around 65 %. In order to improve the performance for higher chromium concentration, the nanoparticle was integrated with various other remedial methods like ultrasonication, irradiation, aeration, and Fenton system. All these remedial techniques generate reactive oxygen species in the system, which, together with nanoscale zero-valent iron, greatly enhance the removal performance. It was seen that among various systems created, the removal performance for US/nZVI system, UV/nZVI system, aeration/nZVI system, and Fenton/nZVI system increased to 92 %, 86.7 %, 91 %, 93 % respectively. The removal efficiency was seen to be strongly correlated with parameters like ORP and final pH of the system and thus can be used for monitoring removal performance.