Effect of using different particle sizes of sand as filter media for dewatering faecal sludge

This research is aimed at investigating the effect of different particle sizes of sand for the dewatering of faecal sludge with respect to the dewatering time, contaminant load in the percolate, rate of clogging and quantity of biosolids produced. Three filter media FM1, FM2 and FM3 were used to dewater the faecal sludge. The experiment was conducted on bench scale consisting of miniature drying beds. Six cycles of dewatering were run where FM1, FM2, and FM3 showed average dewatering times of 10, 10 and 9 days respectively without significant differences (p > 0.05). However the percolate quality showed significant differences between them in the removal of TS, TVS, SS, COD, DCOD and NH3-N with FM1 having the highest removal for each parameter. Accumulation of organic matter in the top 10 cm of the filter bed indicated that FM1 was least likely to clog and it also generated the highest quantity of biosolids.

All the filter media with respect to particle size configuration used for the research were found to be able to improve the dewatering performance of the unplanted filter bed. However, FM1 was most efficient of all in terms of contaminant load removal while in terms of dewatering time they were statistically not different. The filter media with bigger particle sizes (FM3 and FM2) were relatively faster in accumulating organic matter and thus likely to clog faster than the FM1. FM1 had the added advantage of being able to generate more biosolids than the FM2 and FM3. Generally there were significant differences statistically, in the contaminant load removal between the different filter media. The different filter media were all not efficient in salts removal since they showed low EC reduction efficiencies. The pH and temperature were within favorable limits for microbial growth but the high ammonia levels in the percolate could be toxic to the microbes responsible for biological degradation. The contaminant load in the percolates from all the different filter media were all beyond permissible levels for discharge into the environment. Although high removal efficiencies were achieved by all the filter media, the parameters in the effluent needed to be treated further either through column filters, constructed wetlands or stabilization ponds for more polishing before final discharge. Having determined the particle sizes best suited for the sludge dewatering, further research into solid loading rate with respect to the mixing ratios of PTS and septage and other possible technologies (e.g. addition of physical conditioners like saw dust to the FS) to compliment the findings achieved for this studies will be effective approaches to improving the dewatering process of unplanted drying beds.