The Composting of Brewery Sludge

Sludge produced from a trickling filter effluent treatment plant dedicated to the treatment of brewery wastewater was flocculated with cationic polyelectrolytes and dewatered by centrifugation to produce a cake of around 16% (w/w) solids. This cake was mixed with spent grains, shredded office paper and straw to produce an initial mix of 34% (w/w) dried solids with a carbon: nitrogen ratio of 21:1. Temperatures of over 45°C were achieved for around 9 days in a purpose built, laboratory scale, composting unit equipped with temperature and aeration control. Dried solids (DS) were increased to about 65% (w/w) and the volatile solid fraction was reduced from 80% to 60% (w/w) of DS by microbial degradation. The compost was rich in nitrate and phosphate and was used as a peat substitute in qualitative, comparative growth trials where geranium and tomato plants were successfully grown.