Potential priority pollutants in sewage sludge

Sewage sludge has been used as fertilizer for agricultural land over a long time. This is part of a sustainable practice utilizing and recycling the macronutrients back to land. During the last decades, questions have been raised concerning the risks related to heavy metals and xenobiotic organic compounds (XOCs) present in the sludge. Application on land used for agriculture is, therefore, not socially acceptable in some countries, e.g., Sweden. In this study, literature reviews showed that 541 XOCs potentially could be present in sewage sludge due to their presence in e.g. construction materials, pharmaceuticals, personal care products etc. 192 compounds have been quantified in sewage sludge, which indicate that, although many XOCs have been measured in sludge, there are potentially a vast number of compounds present that have not been analyzed for yet. In a hazard identification of the quantified compounds using their inherent properties and environmental fate it was shown that 99 XOCs could be classified as being hazardous with regard to the solid phase and 23 were found to be priority pollutants in the subsequent hazard assessment. The final selected priority pollutants can act as indicators when assessing sludge quality. They were compared with European legislations and discussed in regard for pointing out the need for mitigation such as substitution. Furthermore, the potential need for implementation of sludge treatment trains in order to meet the society’s needs was addressed.

Even though many pollutants have been measured in sewage sludge, there are a vast number of pollutants which have not been quantified yet that also could be present. Here it was found that out of 192 compounds found to be present in sewage sludge 24 compounds was identified as non-hazardous. 63 compounds could not be classified due to lack of available data and the remaining 99 compounds were identified as being hazardous and require further hazard assessment. In the hazard assessment was risk quotients calculated for 79 pollutants of which 23 were found to exceed 1, i.e., be classified as priority pollutants. Both the hazard identification and assessment were however hampered by the lack of data, especially of soil dwelling organisms. Experts applying CHIAT selected 14 priority pollutants. The selected priority pollutants can be used as a basis for evaluation of different strategies for handling sewage sludge application on land and for selection of priority pollutants to be included in monitoring programs or substitution by other compounds. In order to reduce the pollution load in sludge up stream mitigation procedures or advanced sludge treatment trains may The CHIAT methodology is a valuable tool for focusing the decision making process and the procedure for selecting pollutants is transparent and adaptive to specific scenario in focus.