Development of a Mathematical Model for Sludge Build-up in Septic Tank

Septic tanks have been widely used as a basic decentralised wastewater treatment system (DWTS), especially in remote places where a direct connection to a centralised wastewater treatment plant is not available. Effluent from these septic tanks commonly empties into waterbodies, including rivers and oceans. However, in Brunei, there is yet to be a law and proper guidelines on the proper maintenance of a septic tank, despite the danger of improperly maintained septic tanks contaminating the environment. Currently, available sludge accumulation models in the literature may not be applicable to Brunei due to its tropical weather and high water usage. This study presents the development of a mathematical model that can predict sludge accumulation in septic tanks applicable in this region. Field studies were conducted on a sample of 25 septic tanks, and a mathematical model was developed, relating the sludge accumulation rate with the time between desludging and the number of people living in the household. The sludge accumulation rate in Brunei has been observed to decrease over time. The model has been shown to be better able to predict the sludge accumulation rate with the standard error of estimates of 281.7 compared to other existing models. This can be used to determine the appropriate sludging frequency for a septic tank. The research results are significant; government agencies can use them to shape their guidelines and policies related to wastewater management.