(739d) Toxicity Study of Powdered and Cast Incinerated Sewage Sludge Ash - Chemical Treatment, Leaching Patterns and Marine Toxicity

Disposal of ash obtained from thermal treatment of solid waste has been a cause of concern due to its toxic content and potential leaching of these toxins into the environment, such as if it is used in land reclamation applications. In this study, bottom ash from the incineration of sewage sludge was subject to acid treatment to facilitate removal of heavy metals. A phosphate treatment was also explored to fix heavy metal from leaching. The treated samples were examined for heavy metal leaching using a standard protocol (EN 12457). A relatively mixed leaching profile was observed, with different heavy metals leaching out more or less compared to raw untreated ash. Malonic acid, an organic acid, was found to remove more heavy metals compared to nitric acid, a strong inorganic acid. When evaluated for marine eco-toxicity, acid treated ash was found to be more toxic as compared to untreated raw ash, with malonic acid-treated samples being the most toxic; whilst phosphate treated ash displayed a similar toxicity profile to that of untreated raw ash. Raw ash was compared also against concrete sand, a commonly used land reclamation material. There was relatively low toxicity toward microalgae, barnacles and brine shrimp. However, raw ash triggered toxicity responses in the sea urchin egg fertilization assay indicating presence of toxic substances not present in sand. The raw ash was tested against human cell lines also, where it showed size and dose-dependent toxicity, with greater toxicity at higher doses and smaller sizes. This study demonstrates the importance of evaluating the toxicity of post-treatment of ash if it will be used for environment applications such as coastal reclamation. Appropriate treatments are required to minimize the potential leaching of harmful contaminants. Further studies will be pursued with to investigate the effect on mechanical properties if fresh or aged sewage sludge ash is used as a substitute for cement as compared to Ordinary Portland Cement concrete tiles. Further studies on the leaching patterns in seawater and effect on microbial communities will also be pursued.