Vermicomposting as an Alternative Method of Sludge Treatment

The article presents the results of the research from several years of exploitation of the vermiculture plots located in the municipal wastewater treatment plant in Zambrów. It is the only facility in Poland where the vermicompost from municipal sewage sludge has been produced continuously since 2004 (for 16 years). The results of tests of ready-made vermicomposts conducted regularly twice a year (32 tests) were subjected to a simple statistical analysis. The vermicompost analyses of heavy metals, biogenic compounds, organic matter and selected macroelements were compared with the requirements for mineral-organic fertilizers. In terms of the heavy metals content, the highest total content was observed in the first year of plots exploitation, i.e. in 2004, when it amounted to over 1200 mg^-1 kg DM. The lowest sum content of heavy metals in vermicomposts, amounting to 398 mg^-1 kg DM, was recorded in 2017. The median total content of heavy metals from all observations was 821 mg^-1 kg DM. During the whole research period, the content of nutrients in vermicomposts was high, for nitrogen it ranged from 9.8 g^-1 kg DM to 31.1 g^-1 kg DM (median 14.3 g^-1 kg DM), whereas for phosphorus it ranged from 2.1 g^-1 kg DM to 14.5 g^-1 kg DM (median 5.5 g^-1 kg DM). The content of organic matter in the whole several-year study period was high and ranged from 21.3% DM to 59.0% DM (median 33.1% DM). The conducted research confirmed that the use of California earthworm in the process of municipal sewage sludge vermicomposting results in its good mineralization and humification, and the final product (vermicompost) may be a valuable mineral-organic fertilizer.