USING BIODEGRADABILITY TO ASSESS THE PERFORMANCE OF SEWAGE IN ORDINARY PIT LATRINES

Abstract

Biodegradability of sewage in ordinary pit latrine depends on deposition time and and layer depth. This research investigated using biodegradability of sewage in ordinary pit latrines to assess pit latrine performance for better design. The objective of this study was to measure both aerobic and anaerobic biodegradability of pit sludges to assess performance of such pits. Samples of fresh faecal sludges collected at six different vertical layers (surface, 0.2m, 0.4m, 0.6m, 0.8m and 1.0m depths) from pit latrines in selected households in Aku community using designed sampler. These samples were analysed in the laboratory for their physico-chemical and biological characteristics. Samples were taken across each pit layer to allow for heterogeneity of the contents. Collection was carefully done to ensure that bioactivity of the samples was least altered in the process. The samples were analyzed for their physico-chemical and biological characteristics namely moisture contents, temperature, volatile solids, BOD, COD, total solids, plate count, pH, suspended solids and phosphorous content using standard methods of measurement (ALPHA, 1998). Biodegradability of faecal sludge in the pit latrines was determined using the result of parameters from laboratory analyses. The result showed that in terms of BOD, twelve (12) pits had biodegradability of at least 80%. In terms of COD and SS, nine (9) pits had biodegradability of at least 80%. For the VS, eleven (11) pits had biodegradability of at least 80%. Ten (10) pits had ratio of VS: TS ranging from 0.90 – 2.93. Using COD: BOD ratio, eleven (11) pits had values ranging from 0.90 – 1.34 indicating that the pits sludges were readily biodegradable. Lower values showed lower organic contents and lower biodegradability. Result showed that Pit 6 had pH value of 7.98 at the surface and 6.42 at the bottom; Pit 11 had pH of 7.93 at the surface and 6.85 at the bottom. Pit 4 had pH of 7.77 and 8.77 at the surface and bottom respectively. The highest pH measured in this study was 8.96 and not too high to inhibit anaerobic process. In terms of BOD, 12 pits had biodegradability ranging from 80 - 97%. In terms of COD, Pits 9 and had biodegradability of 80% and 87.95% respectively. COD to BOD ratio ranged from 0.90 to 1.34. In terms of total solids, Pits 5, 8, 15 had biodegradability of 70% and above. In terms of volatile solids, 11 pits had biodegradability above 80%. TS: VS ratio ranged from 0.67 - 0.91. Temperature range was 51.67 - 66.67oC. Biodegradability in terms of BOD could not be used to effectively assess the performance of pit sludge at the lower part of the latrine since aerobic biodegradation prevailed at the surface and minimally down the profile. COD should be adopted to assess the biodegradability and performance of any pit latrine including user-education. data were analyzed using figures and model for biodegradability measurement.