Influence of different bulking agents on the disappearance of polycyclic aromatic hydrocarbons (PAHs) during sewage sludge composting

In order to improve properties of compost produced from sewage sludge, a wide range of additives is used. The aim of the present study has been to determine the influence of fly ash and sawdust on the range of losses of 16 PAHs (US EPA). Composting was carried out in containers in which there was sewage sludge (100%), sewage sludge with fly ash added (20 or 30% w/w) and sewage sludge with sawdust added (30% w/w). Composting was carried out for 353 days. Then the compost obtained was stored for another 300 days. The content of 16 PAHs was determined using the HPLC-UV method. After composting, in all the experimental treatments, ie, with sludge alone, and with the additions of 20% and 30% fly ash, and sawdust, decreases in the total PAH load of 87.5, 83.4, 82.9 and 88.1% respectively, were found. The content of the total PAH load was mainly determined by 3-ring compounds. In the case of these last PAHs the highest level of their disappearance (> 90%) was noted after composting. In all composts obtained, the content of PAHs was within allowable limits for biosolids that can be used for agricultural purposes. A significant lowering of total concentration of the 16 PAHs after storage period was noted only in the experimental variant with 20% of fly ash. However, the process of composts storage influenced individual PAHs.