Organic Pollutants of Sewage Sludge, Fate in Soil and their Analytical Methods

Sewage sludge is a semisolid residual material resulting from the sedimentation of the suspended solid during the wastewater-treatment processes. Since large amounts of sludge are being produced, different ways of disposal have been introduced. One tempting option is to use it as fertilizer in agricultural fields due to its high contents of inorganic nutrients and organic materials. However, the presence of contaminants considerably restricts the application of sewage sludge for the fertilisation and reclamation of soils. Because of the high toxicity of organic pollutants and their irreparable effects on the environment, the aim of this study was to investigate the diversity of organic pollutants in sewage sludge, their limit values for agricultural lands, and the fate of them in the soil. Also methods of analysis of organic trace compounds have been compiled. Some of the most frequently detected contaminants in sewage sludge are polycyclic aromatic hydrocarbons, polychlorinated biphenyls, di-ethylhexylphthalate, nonylphenol and nonylphenol ethoxylates, linear alkylbenzene sulphonates, adsorbable organic halides, polychlorinated dibenzodioxins and furans. These pollutants in the soil may undergo sorption by mineral particles, degradation by soil organisms or transportation with water or soil particles over long distances. Extraction of the sludge sample, subsequent clean-up of the extract and final analysis by either gas or liquid chromatography are methodologies for determining the concentration of organic pollutants in sewage sludge. Novel techniques in extraction such as ultrasonic extraction, microwave-assisted extraction, and pressurized liquid extraction require less solvents reagents and smaller sample siz, are more automated and reduce the number of analytical steps. This study show a better understanding of variety of organic pollutants in sewage sludge, their analytical methods and limit values that is imperative to restricting legislation and specification suitable properties of sludge for land application.