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2 Journal of Ecological Engineering

2 2015

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Microbial Leaching of Chromium From Solidified Waste Forms – a Kinetic Study

Ayyappan C. S.

Journal of Ecological Engineering

2015

Vol. 16, nr 3

36--42

In this study, Thiobacillus thiooxidans (T. thiooxidans) was used to study the microbial stability / degradation of cement-based waste forms. The waste forms contained a chromium salt (CrCl3·6H2O), cement and other additives viz., lime and gypsum in two different proportions. The experimental samples of all the simulated waste forms showed evidence of microbial growth as indicated by substantial increase in sulfate. Chromium leached from the waste forms was found to be lowest in cement – lime solidified waste forms (0.061 mg·1-1) and highest in cement gypsum waste forms (0.22 mg·1-1) after 30 days of exposure. These values were lower than the toxicity characteristic leaching procedure (TCLP), regulatory limit (5 mg·1-1). Model equations based on two shrinking core models (acid dissolution and bulk diffusion model), were used to analyze the kinetics of microbial degradation of cement based waste forms. The bulk diffusion model was observed to fit the data better than the acid dissolution model, as indicated by good correlation coefficients.

A Novel Bio-Waste Incorporated Alginate Sorbent for De-Fluoridation of Water

Ayyappan C. S., Sreeja S., Bhalambaal V. M.

Journal of Ecological Engineering

2015

Vol. 16, nr 4

8--13

This study evaluates the feasibility of using tamarind (Tamarindus indica) seed powder for de-fluoridation of fluoride contaminated water. Batch study confirmed that tamarind seeds in dry powder form could remove 87% of fluoride from water. This bio-sorbent can be used effectively in areas where fluoride concentrations are above the permissible limits of 1.5 mg·l-1 as per WHO Standard, 1984. Tamarind seed powder was incorporated in a matrix of sodium alginate and made into gel-beads. The beads were tested for de-fluoridation efficiency by conducting column studies. The effect of various factors, such as flow rate, retention time, and the number of runs on the efficacy of fluoride removal was also studied. The results revealed that flow rate did not seem to have much effect on the percentage fluoride removal but the fluoride concentration decreased drastically upon greater retention time and multiple runs.