ABSTRACT
Processing sewage sludge can be problematic due to its potential environmental toxicity. It may contain high concentrations of pharmaceuticals, polycyclic aromatic hydrocarbons, and heavy metals, as well as pathogenic microorganisms. However, it is a good source of organic matter and rich in microbial communities and enzymatic activity. This study deals with composting and vermicomposting of pre-composted mixtures of two different kinds of sewage sludge blended with moulded pulp in an operating composting plant. Of the total number and concentration of pollutants detected in individual piles, a large percentage of them were reduced by the composting process. The composting 2 process resulted in the greatest reduction in contaminating substances--a total of 19 substances by 4.39-90.4%. Some pharmaceuticals accumulated in earthworm bodies during vermicomposting; a total of 11 substances were detected. Atorvastatin showed the highest percentage reduction in compost 2 (90.4%), vermicompost 1 (65.2%) and vermicompost 2 (97.3%). Both composting and vermicomposting appeared to be effective for removal of heavy metals. A higher content of microbial phospholipid fatty acids (PLFAs) was found in composts than vermicomposts. There was a significant reduction in the content of pathogenic microorganisms in both processes, but the reduction in enterococci was not significant.
