Suitability of sawdust as a dewatering material in sludge drying beds

Abstract

The increase in waste generation is contributed by the continued rise in population. Faecal sludge is one of the wastes generated and can have wide variations in its characteristics and consistency. Management of faecal sludge is an issue in developing countries where affordable sanitation facilities are not accessible. Bugoloobi waste water treatment plant (BWTP) in Kampala Uganda is a unique treatment plant that has both off-site and onsite systems. The plant receives high volumes of on-site faecal sludge which has high solids content but limited sludge drying space. This calls for optimization of sludge drying bed use (improving the sludge drying efficiency) by reducing sludge drying time. This study investigated the use of wood sawdust as a filtering and drying media in the faecal sludge drying process. Model beds were constructed at BWTP to carry out comparison of performance amongst sand and coarse and fine sawdust as filtering media. Moisture content variation (%) was the key parameter used in analyzing and determining the most ideal media for sludge dewatering. Faecal coliform lab analysis of the filtrate was carried out to characterize the extent of pathogen removal by the filtering media. The results showed that there was statistically significant difference in the moisture content of dry cake produced by sand, fine and coarse sawdust as drying media at 5% significance level (p = 0.0438). Coarse and fine sawdust produced the faecal sludge with the moisture content of 31.4% and 33.3% respectively whereas sand achieved the moisture content of 43.5% after 4 weeks of drying. However, sand removes much of the pathogens though slow in drying but the filtrate must be further treated to attain the standard levels before being discharged to the environment. In conclusion therefore, coarse sawdust achieved the dry cake with the lowest moisture content in the same drying period as the rest of the dewatering materials which means it dries faecal sludge faster than fine sawdust and sand.