The septic system is a type of the Decentralized Wastewater Treatment Systems (DWTS), discussed in the previous article and possibly a missing piece in wastewater management for developing countries. The septic system is widespread in Africa, even in urban areas, and has prevented many public health crises by solving many African countries’ sanitation challenges. In Nigeria, the name “septic tank” and “soakaway” is used interchangeably, but the term “soakaway” is used more frequently among residents. It’s seen in almost every corner of the country, reducing open defecation in many parts of the country. I remember growing up in Nigeria and never knowing the difference between a soakaway and septic tank, which is the case for most Nigerians. Although used commonly, it is rarely understood by those who use it. Therefore, in most cases, not properly constructed or maintained.
The septic system consists of a septic tank and a drainfield or soil absorption field. While the septic tank is an enclosed vessel underneath the ground, designed to collect wastewater, separating it into settleable solids(sludge) and floatable solids (scum, e.g., oil and grease). The septic tank’s primary function is to accumulate, consolidate, and store solids, which are then digested as organic matter by bacteria. At the same time, the fluid is discharged as treated effluent into the drainfield or absorption field. It is a simple design that encourages natural decomposition without oxygen (anaerobic) and requires no additional chemical to treat wastewater, whereas the soakaway is a smaller tank that collects only liquid wastewater and not sludge. At times, the septic system might have a soakaway attached to the septic tank. The septic system was officially recognized by the EPA in 1997 as a sustainable, long-term solution for treating wastewater.
The septic system presents exciting possibilities for solving many developing countries’ sanitation challenges. It requires very little to no energy, especially if the system is gravity-fed. Once the water moves through the drain field, it is virtually clean, free of harmful pathogens, and replenishes groundwater. The cost of constructing a septic system is a bonus, as it is much more individually affordable and presents many entrepreneurial opportunities.
Cost of Constructing a Septic System
The initial cost of setting up a septic tank in Nigeria ranges from N150,000 to N500,000 ($429 – $1429). This can be considered high for a country where half the population lives under a dollar per day but pretty cheap considering the alternative option of a CWTS. Things to consider when constructing a septic system include:
- Size of the septic system: This depends on the size of the household expected to use it.
- Drainage(drainfield): The drainfield should have suitable soil conditions, i.e., “not too much” clay and “not too much” sandy soil.
- Material: Concrete is normally used in constructing septic tanks, but the ideal material should be a high-density polyethylene model. Although it cost more, but will outlast the concrete model.
- Labour: This can be expensive, depending on who is installing the septic tank.
Usually, constructing a functional septic system is affordable in urban areas but not in rural areas where poverty is still high. Due to the cost of installing a septic tank, septic tanks are not be built up to standard nor maintained in these countries experiencing high levels of poverty and illiteracy. One possible solution is to construct community septic tanks where a few houses are connected to a central septic tank. However, the septic system remains one of the cheapest ways to treat domestic wastewater. If not available, open defection and unkept pit latrines becomes the obvious choice.
Challenges of Having a Septic System
Although the septic system is an environmentally sustainable wastewater treatment option, the need to maintain the system is paramount to prevent an overload, which reduces the drainfield’s lifespan of effectiveness. Therefore, the septic system requires more mindfulness and maintenance than the centralized wastewater treatment system (CWTS). The septic system needs to be cleaned regularly, ideally (1-3years). The frequency depends on the tank’s size, condition of the drainfield, and number of users. If the system isn’t pumped regularly, they can leak, causing problems both ways. Either water from outside the tank infiltrates in and overburdens the system or untreated waste in the tank exfiltrates out, contaminating the soil with fecal coliform bacteria and overwhelms the drainfield. Also, if a septic tank is not cleaned regularly, toxins and antibacterial substances build up, killing the vital bacteria that break down the waste.
Additionally, septic systems do not do an excellent job of removing nitrogen, which can be a problem if the effluent eventually drains into a water body. Another issue with the septic tank is organisms can form a “biomat” near the side of the drainfield, covering the entire trench. When this happens, decomposition shifts from an aerobic to an anaerobic (i.e., stinky) process within the drainfield, and effluent cannot filter down instead ponds on top of the drainfield. In worst-case scenarios, sewage can back up into the house.
Innovative Solutions for The Septic System
Innovators in the field are coming up with innovative solutions to reinvent the septic system into a resource generating system. One such innovator I admire is Olatunbosun Obayomi, a Lagosian microbiologist and inventor. He came up with a brilliant way to transform the septic system into an energy generating system. He is a Ted fellow and has been recognized internationally for his cheap retrofitted household septic tank. His retrofitted septic tank is a simple way to convert septic tanks into biogas generators. This can be achieved by attaching cheap plastic pipes into existing septic tanks to collect methane and carbon dioxide used to power a household as electricity. According to him, an average street in Lagos using the retrofitted septic tank could produce 1,720 liters of biogas a day, enough for an engine-powered water pump to serve the daily domestic needs of at least 50 families.
Another solution would be the Septic Tank Effluent Pumping (STEP) system. In a STEP system, tanks are used to capture most of the solids, then the effluent is sent to a centralized system for further treatment. STEP systems ease the burden on treatment plants, so they can be smaller, which equates to less costly infrastructure. Additionally, combining a septic tank or system with an advanced treatment ensures wastewater is treated adequately, and nitrogen is removed before it is released into the drainfield.
An idea I am exploring is a mobile sludge drying unit that can dry sludge in a relatively short time at the site during the pumping of the septic tank. According to the UNESCO-IHE Institute for Water Education experiment, Microwave technology efficiently dried sludge in record time producing beneficial byproducts. Farmers and customers can use the byproducts from the sludge drying process as fertilizers, soil conditioners, and biofuels. A mobile sludge drying unit can eliminate the unnecessary and unhygienic transport of sludge to a facility for sludging drying; instead, transports the byproducts to where it is needed.
Anaerobic technologies like the septic system are the core of the sustainable decentralized wastewater treatment systems. They should be encouraged in developing countries where it could be a cost-effective option for solving sanitation challenges. It’s hard to tell when a septic system is in trouble. There is no warning signal once it’s at breaking point because it starts to smell unbearably, backing up sewage into the house. Therefore, policy enforcement is required to ensure regular maintenance and cleaning by citizens in developing countries. More than ever, sound policies and government support are needed to promote the septic system’s standard construction and maintenance. Like Olatunbosun Obayomi says, “Lack of political will is one of the greatest obstacles to solving the sanitation crisis. Limited access to the septic system is due to poor governance rather than poor infrastructure or insufficient finance”. I support his statement because innovative ideas like the retrofitted septic tank may never see the light of day without support from the government and investors.
- United States Environmental Protection Agency (EPA), (2020). How Your Septic tank Works. https://www.epa.gov/septic/how-your-septic-system-works
- United States Environmental Protection Agency (EPA), (2020). Types of Septic Tanks. https://www.epa.gov/septic/types-septic-systems
- George Webster (CNN). (2011). How Human Waste Could Power Nigeria’s Slums. https://www.cnn.com/2011/09/26/world/africa/nigeria-sewage-biogas/index.html
- Juilet Grable (2014). Better Wastewater Management. https://www.greenbuildermedia.com/blog/better-wastewater-treatment
- Nairaland Forum (2020). Cost of Soakaway(Septic Tank). https://www.nairaland.com/1904839/cost-soakaway-septic-tank
- Nnaji C. C.(2011) Improviong Septic Tank Performance by A New Rational Design Approach. http://www.unn.edu.ng/publications/files/images/Ph.D%20Thesis%20Latest%20printable.pdf
- Household Quotes uk. (2020). Septic Tank Costs: 5 Things you Need to Know in 2020. https://householdquotes.co.uk/5-factors-affecting-septic-tank-costs/
- Peter M. Mawioo, Hector A. Garcia, Christine M. Hooijmans, Konstantina Velkushanova, Marjana Simonič, Ivan Mijatović, Damir Brdjanovic,. (2017) A pilot-scale microwave technology for sludge sanitization and drying. https://www.sciencedirect.com/science/article/pii/S0048969717314079?via%3Dihub
Exploring Septic Systems as a Missing Piece in Wastewater Management