1.1 Introduction
The septic tank is pivotal to wastewater treatment as well as public health especially in developing countries where central treatment plants are not affordable. Early septic tanks were cast in situ while there are now available precast septic tanks which can be made of materials ranging from concrete to fibre glass. The usual configuration is the rectangular type. All the wastewater from the home is routed to the septic tank through pipes that merge into one that conveys wastewater to the tank. The tank is usually provided with a concrete cover with air vents to allow the escape of gaseous products of anaerobic digestion. There are also manholes on the cover, near the inlet and outlet for inspection and desludging of the tank. In some case, the tank could have two or more compartments to enhance the treatment efficiency of the tank. The bottom of the tank may be flat, or it may slope towards inlet to enhance pumping of sludge.
As a prelude to other parts of this study, this chapter will discuss the background upon which this study was initiated, the statement of problems that led to this study, the Aim and Objectives of the study. Others are Significance of the study, Scope of work, Limitations of the Study and Definition of technical terms.
1.2 Background of 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 (Collicket al., 2006).
According to Fidelia (2004, in Burubaiet 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.
A properly functioning septic tank system should be able to reduce the pollutional level of wastewater to such a level as is within local and international standards for wastewater disposal. The septic tank system consists of a water tight tank for removal of solids and partial digestion of organic matter, and a drain field which is a secondary treatment system. The tank is an anaerobic system while the drain field is mostly aerobic which further treats the effluent before channeling it to the groundwater. In some cases, the drain field could be a gravity type or a dosing type.
All things being equal, the septic tank system does not pose much problem and requires little maintenance. However when the system is not working properly, it merely serves as a route for recycling pathogens and deadly chemicals through the ecosystem. According to Cogger (1988), nearly 40% of groundwater attributed disease outbreaks can be traced to the failure of onsite disposal systems. Weissman et al. (1976), Bidgmanet al. (1995) and Taylor et al. (1981) among others, reported cases of disease outbreak resulting from groundwater contamination due to septic tank failure. In Africa where most people depend on streams, shallow wells and boreholes, the case is even more severe.
Therefore, in Nigeria where the research was carried out, the activities that was conducted is to investigate the Anaerobic Processes in Septic Tank as a Wastewater Treatment Option.
1.3 Statement of Problems
Investigate the waste water flowing into the septic tank does not receive adequate treatment; it is simply passed on to the groundwater unnoticed thus wreaking havoc on public health. Researchers have shown that most septic tanks especially in developing countries do not even attain an average performance throughout their lifetime. The result is that most septic tanks only act as a conduit for conveying raw / under treated sewage into the soil leading to massive fouling of our groundwater. And because the groundwater is the main source of potable water in most communities, man constantly stands the risk of water borne and water related diseases.
Most times, the groundwater is used without treatment on the common assumption that it is “always clean”. The menace of such diseases as typhoid fever, diarrhea, giardiasis, gastroenteritis, hepatitis, methemoglobinamia, samonellosis, dysentery, etc will continue to plague humanity until a systematic approach to the design, construction and maintenance of the septic tank system is adopted.
The foregoing indicates that the septic tank system requires proper design, construction, use and maintenance. The cardinal aspect of septic tank maintenance which is of interest in this research is desludging. The absence of a deterministic equation for the prediction of desludging interval has usually led to too frequent desludging or excessive accumulation of sludge in the septic tank. Too frequent desludging increases cost of operation while excessive accumulation of sludge drastically reduces the efficiency of the septic tanks.
The problem at the heart of this research is to develop a systematic and rational approach to the design of septic tanks and also to provide suitable guidelines for the maintenance of the septic tank system in order to ensure the protection of public and environmental health as well as enhance anaerobic processes.
1.4 Aim and Objectives of Study
The aim of the study is to investigate the Anaerobic Processes in Septic Tank as a Wastewater Treatment Option. In achieving this aim, the following specific objectives were laid out as follows:
- To derive a model to predict the rate of sludge accumulation in septic tanks;
- To compare the sludge accumulation model to existing models;
- To calibrate the model using field data; and
- To predict the desludging interval of septic tanks by relating sludge accumulation to reduction in detention time.
1.5 Research Questions
The study came up with research questions so as to be able to ascertain the above stated objectives. The specific research questions for the study are stated below as follows:
- What is the model to predict the rate of sludge accumulation in septic tanks?
- What is the sludge accumulation model to existing models?
- What is the model using field data?
- What is the desludging interval of septic tanks by relating sludge accumulation to reduction in detention time?
1.6 Justification of the Study
The septic tank is pivotal to public health and yet one of the most overlooked and least maintained waste treatment facilities. Research has shown that most outbreaks of water borne epidemics result from fecal contamination. In most developing countries, people are not aware of the crucial role of the septic tank as they merely view it as a sewage pit that needs no special design, construction and maintenance considerations. The result is the ubiquity of malfunctioning septic tanks. This is why this subject deserves a serious intellectual attention.
1.7 Scope of Study
The scope of the research is focused on the Investigation of Anaerobic Processes in Septic Tank as a Wastewater Treatment Option.
1.8 Limitations of the Study
During the course of this study, many things militated against its completion, some of which are:
- Time Constraint: The time frame given to accomplish this project was very short due to school academic calendar and it was carried out under pressure which made the researcher not to implement some necessary features.
- Research material: availability of research material is a major setback to the scope of the study.
- Frequent power failure: This made the researcher append more money on fuel to ensure sustainable power.
- Financial Constraint: Insufficient fund tends to impede the efficiency of the researcher in sourcing for the relevant materials, literature or information and in the process of data collection (internet).
