Introduction
1.1 Background Of The Study
The septic tank system is the most widely used onsite treatment system for domestic wastewater. In fact, most developing countries (Nigeria inclusive) lack the technology and economic power to construct and operate sewerage systems for conveyance of domestic wastewater to central sewage treatment facilities, so a greater population rely on the septic tank system for sewage treatment. It is an enclosed receptacle designed to collect wastewater, segregate settleable and floatable solids (sludge and scum), accumulate, consolidate and store solids, digest organic matter and discharge treated effluent (Bounds, 1997).
In the United States only, over 50 million people use the septic system (Collick et al., 2006). According to Fidelia (2004, in Burubai et al., 2007), over 46% of the Nigerian population use the septic tank system. The septic tank system was once thought to be a temporary solution to domestic wastewater treatment and disposal. This was true until 1997 when the United States Environmental Protection Agency and Congress officially recognized the system as a sustainable, long-term solution for treating wastewater.
The septic tank is an anaerobic reactor due to the insufficiency of oxygen concentration to act as electron acceptor. The wastewater is degraded by micro-organisms aerobically while the C, CO2 SO4 act as electron acceptors to form CO2, H2, CH4 and S2- (sulphides). At the same time, most of the organic N is converted to NH+4 (inorganic). The effluent flows into the drain field where aerobic degradation occurs due to abundance of oxygen in the unsaturated soil layer. The C in the wastewater is now oxidized to CO2 while NH4+ is oxidized to NO2- thus raising the nitrate level of the sewage to about seven times the limit acceptable for dumping water (10mg/l). The H+ released from the oxidation of NH4+ now reduces the pH of the effluent.
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