Septic Tank design:All you need to Know about Septic Tank
Septic Tank Design:
Definition of Septic Tank
Septic Tank is a water-tight receptacle which receives the discharge of a human waste from the toilets. It is an underground storage chamber made of concrete, fibreglass or plastic and is intends to control, manage and most importantly treat waste material. It also has some partial decomposition is based on anaerobic bacterial reaction solids and organics materials reduce to liquid. It’s basically a type of biodigester, only that it lacks the functionality of gas collection and waste treatment. Most septic tanks just separate the solid and liquid waste material. The wastewater will collect at the slung heap up at the bottom. As a result, the tanks will require emptying from time to time.
Septic tank Design
It has one end connected to an inlet from the toilets and sometimes an outlet connected to the drain field. Some septic tank design has 2 chambers while others have 3. A wall with openings between the floor and roof of the tank separates the chambers. As a result, the drainage pipes fill more evenly and preventing premature clogging of the drains, therefore, extending their life. Some septic tank designs include water pumps so as to increase the volume and velocity of water drainage.
A well-maintained septic system is odour-free and requires less emptying.
In addition, it should last for decades with no problems.
How a septic Tank Works
A septic tank works in four basic steps. Namely :
- Receives the wastewater from the house- all the house wastewater goes to the septic tank in through one inlet.
- Separates the solids from the liquids- The solid waste settles at the bottom of the tank. The wall separating the chambers allows for liquid only to move to the second chamber. The solids materials remain for degrading.
- Decomposes the solids- Bacteria is used to decompose the solid waste to liquid. The bacteria feed on solid waste and free it from pathogens. They further reduce them to water.
- Send the wastewater out to the drain field- the treated waste is released to the ground or left to percolate into the soil. Some tanks may include a pump to assist in pushing water out of the septic system.
Factors to Consider When Designing a Septic Tank
Septic Tank Capacity/Size
The septic tank capacity depends on the sewage flow and detention period. In addition, space for sludge and scum accumulation before emptying is also considered. Depending on the type of house and the number of the user, septic capacity can be customized. The table below shows capacity Viz a Vis number of users.
Amount of Sewage Flow
The amount of sewage flow highly depends on the number of users. The tank should be able to hold the total waste for all users during the detention period. If the design does not account for all users, the tank will block more often and require emptying more frequently. This, on the other hand, increases the cost for maintenance.
Sludge holding Period
The septic tank design should account for the sludge holding period. The minimum sewage detention period in a septic tank is 24 hours. However, due to the total volume requirement for sludge and scum accumulation, a septic tank is designed for a detention period of not less than 48 hours.
Septic Tank Construction
A septic tank construction should be perfect to prevent cracking and groundwater pollution. In addition, it should be strong enough to withstand the Earths movements and hold the weight of the waste. Most importantly, it is best to use plastic or reinforced concrete tanks.
A trench is dug and steel is placed where concrete is moulded on both sides to form a 4 inches thick wall. This provides the strength for the tank to hold pressure and also prevent the steel from rusting. The inlet and outlet pipe are put in place before pouring the concrete. It is very important you mix the concrete is well. Add little water to harden the concrete. Use a vibrator to ascertain that it has compacted properly with no air holes or cracks. After that, connect the pipe to the inlet and outlet and also install the manhole slab.
Septic Tank Maintenance
Similar to any other system, a septic tank may become faulty and requires maintenance. The main causes for a septic tank failure include:
- Too much disposal of grease and cooking oils may cause the drains to block. This is because they are difficult to decompose. It can also result in an odour.
- None biodegradable waste will cause the septic tank to fill up and clog. Do not flush these materials down the toilet.
- Some chemicals can damage the septic tank components. This includes inorganic material like paint and solvents, water softener, pesticides among others.
- Tree roots protruding may plunge and clog the pipes or even worse rupture septic tank. The trees tend to grow rapidly as a result of continuous nutrients supply from the septic system.
Other things that can make a septic tank to fail include high water table, biofilms which develop over time and covering the system with an impermeable surface
Sludge Withdrawal and Disposal
Emptying a septic tank happens once or twice a year. Individual home tanks can lust for 2 years. Note that disinfection agent like phenyl can kill the bacteria in the tank. As a result, do not use flush chemicals down the toilet. In addition, non-biodegradable waste material like condoms and sanitary pads cannot decompose when inside the tank. As a result, Do not throw them into the toilet because they may lead to blocking or fill the tank sooner.