The production of an artificial soil from sewage sludge and fly-ash and the subsequent evaluation of growth enhancement, heavy metal translocation and leaching potential

Abstract

The combustion of coal in South Africa produces approximately 22 million tons of fly ash annually. This fly ash has to be handled and stored on ash dumps, which in turn have to be rehabilitated – increasing the cost of ash handling. Sewage sludge is classified as a hazardous, toxic waste. It requires expensive methods of treatment. This investigation was concerned with the co-utilisation of these otherwise waste products to form an odourless, pasteurised, soil-like product with only the beneficial characteristics of both components (high organic load and low levels of available heavy metals). The pasteurisation of the sewage sludge is achieved due to the exothermic reaction between the highly alkaline, lime amended, fly ash and the moisture of the sewage sludge. This process is sufficient to treat the sewage sludge to the USEPA PFRP (Process to Further Reduce Pathogens) levels. SLASH has been added to soil to determine whether the bound heavy metals, present in the product from the sewage sludge, are translocated to plants grown in a medium containing SLASH.

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