Contaminated Site Investigation and Remediation Using Modified Nano Zero Valent Iron Particles

Abstract

Rapid industrialization has boosted economic growth but also increased contaminants in air, water, and soil. Improper disposal of municipal solid waste and industrial effluents has rendered many groundwater sources unfit for domestic use. The Ministry of Environment, Forest, and Climate Change (MoEFCC), with World Bank support, has identified contaminated sites, revealing 35% are polluted with chromium and lead. The Peenya industrial area in Bengaluru, classified as critically polluted by the Central Pollution Control Board (CPCB) in 2019, was studied for groundwater and soil contamination. A study across 28 groundwater sampling locations showed 78% of samples unfit for drinking due to elevated Cr(VI) levels, with water primarily of Ca·Mg-HCO3 and mixed Ca·Mg-Cl·SO4 types. Health risk assessments revealed non-carcinogenic risks, particularly to children, at most sites. The non-carcinogenic impact of trace metals on adults and children was in the order Cr >Mn > Ni>Zn >Fe>Cu =Pb. Nearly 71% and 53.5 % of samples showed a potential carcinogenic impact for Cr(VI) and Ni, respectively, in adults and children through the oral ingestion route. Soil analysis indicated high pollution levels, with copper and chromium being the main contributors. Toxicity Characteristic Leaching Procedure (TCLP) results showed significant leaching of Cu, Cr, and Ni, necessitating targeted remediation for six high-risk sites. Furthermore, among the twelve locations analyzed, one site presented a carcinogenic risk to adults, while all sites posed a carcinogenic risk to children. The research evaluated the efficacy of sulfidated carboxymethyl cellulose stabilized nano zerovalent iron (S-CMC-nZVI) for Cr(VI) removal. Batch experiments indicated Cr(VI) removal efficiency increased from 73.89% to 99% with an S/Fe molar ratio of 0.4. Adsorption followed Langmuir isotherm and pseudo-second-order kinetics, with an adsorptive capacity of 311.02 mg/g. The study assessed the effectiveness of carboxymethyl cellulose (CMC) stabilized and sulfidated CMC-stabilized nano zero-valent iron (nZVI) in immobilizing Cr, Cu, and Ni in spiked soil samples. Dosages ranging from 0% to 6% were tested, and SEP and TCLP analyses revealed that higher nZVI dosages significantly reduced heavy metal leaching. S-CMC-nZVI showed greater efficiency in immobilizing Cr and Cu compared to CMC-nZVI. The impact assessment showed higher environmental impacts for nZVI production (GWP: 55 kg CO2 eq.) compared to coal granular activated carbon (9.52 kg CO2 eq.) and coconut shell granular activated carbon (7.54 kg CO2 eq.) due to chemical-intensive synthesis. For the pump-and-treat system (PTS), the GWP was similar for nZVI (6.72E+05 kg CO2 eq.), coal GAC, and coconut shell GAC (6.63E+05 kg CO2 eq.), driven by raw materials and energy use. This study highlights the risks associated with heavy metal contamination and provides a basis for developing remediation strategies to address environmental challenges. Six sites were identified as high-priority due to significant carcinogenic risks to children, warranting detailed analysis. The findings offer critical insights into heavy metal pollution, enabling policymakers to prioritize hotspots for remediation. Moreover, the application of S-CMC-nZVI demonstrated promising potential in remediating Cr(VI)-contaminated groundwater and soil effectively.