Assessment of total coliform removal and leaching of metal ions from sewage sludge-fly ash mixture at different pH and washing conditions

Abstract

Effectiveness of fly ash as a stabilising agent for heavy metals leaching was studied for different ratios of sewage sludge (SS)-fly ash (FA) mixtures at different pH and washing conditions. The supernatant liquid was analysed for total coliforms. The results obtained from the microbiological analysis of 1:1, 4:1, 1:4 sewage sludge and fly ash ratios showed that the initial concentration of total coliforms was 2.4 × 10⁴ MPN/100ml, 150 MPN/100ml and 120 MPN/100ml which were finally reduced to 28, 4 and 3 with successive washings. The leachate after shaking of the SS:FA mixture were analysed for heavy metals contents and the results showed that the maximum removal of heavy metals was achieved with SS/FA (1:1) mixture, while Co was absent in all the samples. Out of the three pH conditions (5, 6, 7), it was observed that the maximum removal of different heavy metals was achieved at the lower pH (5) conditions.

Key words: Fly ash, sewage sludge stabiliser, leaching, heavy metals, coliforms.