Comparative studies of subcritical water extraction of polycyclic aromatic hydrocarbons in municipal sewage sludge

Abstract

The quantitative determination of organic contaminants in sewage sludge has received little attention so far, as compared to the voluminous amount of information that is available for the analysis of inorganic compounds in sludge. Many organic chemicals, termed as 'priority pollutants' due to their potentially toxic effects, are known to occur in sludge. In the specific context of wastewater and sewage sludge, polycyclic aromatic hydrocarbons (PAHs) are generally regarded among the most critical in terms of toxicity. Land application of sludge as fertilizers is a way of disposal and recycling of sludge. However, public concern has arisen due to the fact that organic contaminants in sludge may ultimately enter the food chain. Hence the need to analyse the organic contaminants such as PAHs in sludge. Therefore, in this study, subcritical water extraction (SWE) was utilised as a viable extraction method for the analysis of PAHs from municipal sludge samples. Various extraction procedures, such as pure SWE, surfactant-modified SWE and SWE coupled with membrane discs were attempted. Several factors were investigated for the pure SWE procedure coupled with SPE extract clean-up, which yielded the best recovery in comparison with the other methods. Recovery studies of PAHs from spiked sludge samples were performed using gas chromatography with flame ionisation detection. Although a recovery range of 38.84 - 56.06 % was obtained using the above mentioned method, the results indicated the usefulness- of the technique as an alternative to Soxhlet extraction for the analysis ofPAHs in sludge samples.