Impact of aging on quality of sewage sludge from lubigi sewage treatment plant

Abstract

The global goal regarding sanitation aims at ensuring availability of adequate sanitation for everyone and increase the proportion of treated wastewater and safe reuse. Wastewater treatment produces sludge as a residue of the primary and secondary treatment processes. Application of sludge known to have high concentration of nutrients has been proved in different places to provide a cheap solution to declining soil fertility. This study was conducted to assess the Impact of aging on the quality of sewage sludge from Lubigi Sewage Treatment Plant. The Study was arranged in a randomized complete block design (RCBD) with age of sludge as the blocking factor with a total of five blocks: Block 1 represented the fresh sludge, block 2 represented the settling sludge, block 3 represented maturing sludge, block 4 represented mature covered sludge, and block 5 represented mature uncovered sludge. 6 composite samples were obtained from each block making a total of 30 composite samples. Sewage sludge samples obtained were analyzed for pH, OC, total N, total P, K, Na and Ca concentration. The data were subjected to analysis using the Gen Stat Statistical software at 5% probability level. The impact of aging on pH, OC, total N, total P, K, Na, and Ca concentration of sludge was significant. The highest pH (7.4±0.11) was in the fresh sludge whereas the lowest (5.9±0.07) was in the mature sludge that was covered. The mature covered sludge tended to have the highest (13.41±2.323) % OC concentration whereas fresh sludge tended to have the lowest (5.31±0.634) %. The highest (0.91±0.058) % total N concentration was in the mature sludge that was uncovered whereas the lowest (0.352 ±0.007) % was in the fresh sludge. The highest (0.428±0.109) % total P concentration was in the mature sludge that was covered whereas the lowest (0.094±0.003) % was in the fresh sludge. The highest K, Na, and Ca concentration (0.24±0.054, 0.19±0.038, 0.12±0.012 respectively) % was in the mature sludge that was covered whereas the lowest (0.04±0.005, 0.03±0.005, 0.01±0.003 respectively) % was in the fresh sludge. Sludge from Lubigi Sewage Treatment Plant is of relatively low quality. However, there is undoubted high potential for improving the quality of this sludge owing to its pH. Raising roofs above the 30 open air drying beds, renovation of roofs that are above the covered drying beds, and application of liming material such as limestone at different stages of sludge should be done to improve sludge quality.