Remediation potential of Compost and Vermicast

Dale A. Fuertes (MS Graduated: 2nd Sem 2008-2009)

Abstract

Compost and vermicast were evaluated as sorbents for the removal of heavy metals (Cu2+, Cr6+, and Fe2+) from acidic mine water. Characterization revealed high action exchange capacity, total organic matter content, calcium carbonates, high moisture and water holding capacity, irregular morphology, surface functional groups, and colonies of microorganisms. In addition to these, samples have high base saturation and slightly acidic pH.

Sorption was significantly affected by pH. Compost has highest adsorption intensity for Cu2+ (0.8318 dm-3g-1at pH 3), and vermicast with Fe2+ (1.884 dm-3g-1at pH 2.5). All metals followed Freundlich isotherm model which suggested physisorption mechanism. This was supported by calculated heats of adsorption values. The best fir kinetic model was pseudo-second order indicative of surface adsorption as rate limiting reaction. Intra-particle diffusion model was obeyed by Cu2+ and Fe2+.

Column experiments showed 99% removal of Cu2+and higher than 84% in the presence of Cr6+. With Fe2+, precipitation of Fe(OH)3 occurred. The column breakthrough time to meet the 2008 DENR Proposed Effluent standard for Cu2+ was 18.23 min (25g compost and 1000 mg L. -1feed at 5 mL min-1). Sequential extraction of contaminated samples revealed that Cu2+and Cr6+ were at least 40% mobile and available once sorbed in the samples while Fe2+was released mostly only when reduced.