The effect of different percentages of bulking agent (sawdust) on microbial quality of faecal sludge

The use of raw sludge spread on land as conditioner and fertilizer has been practised over the years in urban agriculture. However, this raw sludge (biosolids) is associated with a potential health risk as a result of the pathogenic microorganisms it contains. The study considered the dewatering of faecal sludge (FS) mixed with sawdust to produce biosolids that can be applied as manure for agricultural use. It assessed the bacterial and helminth egg qualities of the biosolids produced from FS–sawdust mixture. Bench-scale unplanted filter beds were used for dewatering of FS mixed with different percentages of sawdust. The sludge consisted of public toilet sludge and septage in the ratio of 1:3. An analysis of variance of the completely randomized design was undertaken and a P-value below 0.05 was considered statistically significant. The sawdust–FS mixture analysed after complete dewatering showed significant reduction in microbial (bacteria) content (P < 0.05) and helminth eggs, making the biosolids produced safe for farmers and the environment. The bulking agent improved the quality of the biosolids, with greatest pathogen removal observed in the 150% sawdust, whilst the least reduction was recorded in the 0% sawdust (control).