Composting of anaerobic sludge: an economically feasible element of a sustainable sewage sludge management.

An investigation into the feasibility of anaerobic sludge composting, as a sustainable treatment of sewage sludge management, was carried out under actual Slovenian environmental conditions. In order to demonstrate successful composting, five pilot plant experiments were performed during the summer and winter conditions. The first three experiments were performed with pile aeration, while experiments 4 and 5 were carried out by pile turning. Anaerobic sludge to bulking agent ratios were set at 1-6.4:1. The composting was successful and thermophilic temperature being achieved in all cases. In winter conditions, the composting process was prolonged; and low ambient temperatures had a significant impact in pile turning experiments. During winter, a temperature drop of 30 °C during turning of the material doubled the necessary time for an adequate composting process. Five scenarios were considered within an economic feasibility study and in the most favourable scenario, where 60% of compost was commercialised and 40% was used as landfill cover. The payback period in this scenario was 2.9 years. The study of compost quality showed that it can be used in variety of civil engineering applications, especially as a landfill cover and for recultivation of degraded areas.