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How Do Septic Tanks Work?

By January 11, 2022No Comments

For homes in rural areas or those that are not connected to a sewerage system, a septic tank is of vital importance as they provide a safe means to dispose wastewater. In this article, we break down all the information about septic tanks, common problems and how to take care of your septic tank.

What is a septic tank?

A septic tank is an underground container or chamber where household wastewater flows for basic treatment process. This process involves the separation of solids from liquids and the decomposition of solids and organics through anaerobic (without oxygen) biological action.

Septic tanks are considered as a type of simple onsite sewage facility (OSSF) as the treatment process is minimal.

Septic tanks are usually installed 50 metres away from the household and are made from concrete, fibreglass, or plastic. They are watertight containers, mostly rectangular or round, and usually have a T-shaped outlet that prevents scum (fats) and sludge (solids) from escaping from the tank.

How does a septic tank work?

An inlet pipe will transport wastewater from the house and collect it in the septic tank where the solids, floatable matter like oils and grease, and liquid waste get separated.

Biological anaerobic processes, also known as anaerobic digestion, take care of the organic waste matter by decomposing the waste. In this process, microorganisms in the tank break down biodegradable matter in the absence of oxygen.

A healthy septic tank is a well-balance living ecosystem where bacteria thrive in the right amount to digest biodegradable waste and treat effluent water. When wastewater collects in a healthy septic tank, it begins to separate into 3 layers:

  • Scum

This is a layer of fat which floats on the surface of the liquid waste. Lighter substances like grease and oil will float to the surface to form this top layer. The scum prevents odours from escaping and stops air from entering the septic tank.

  • Sludge

This is the layer of heavier solids that sinks to the bottom of the tank. The bacteria living in the septic tank will work to break down some of the organic solids into liquid components and thus help to reduce the build-up of sludge in the tank.

  • Effluent

This is the layer of clear liquid waste found between the scum and sludge layers. The effluent contains large amounts of pollutants, salts and nutrients, such as nitrogen and phosphorous, at this point. It also contains viruses, bacteria and other pathogens that can cause diseases and illness.

An outlet pipe will transport the pre-processed liquid effluent from the septic tank to the septic drain field, which typically comprises trenches containing perforated pipes and gravel covered with a layer of soil. Here, the partially treated wastewater further breaks down some pathogens and harmful nutrients through natural soil processes.

Common problems associated with septic tanks

The following are potential problems that can cause septic tanks to malfunction, or break down:

Ground movement: Any ground movement can put pressure on the septic tank, which can cause fractures or cracks in the walls of the tank. As a result, groundwater to get in affecting the separation process in the tank.

Damage from roots: If a septic tank is located close to trees, shrubs and bushes, then roots can grow through tank walls and even get through the pipes, leading to cracks which allow liquid to escape from the tank, or groundwater to get in.

Lack of regular maintenance: This is quite a common problem. The septic tanks need to be emptied regularly to avoid problems from arising.

A collapsed baffle or damaged dip pipe: A septic tank will have either a dip pipe or a baffle, or both, which acts as a barrier within the tank making sure that solid waste does not escape with the liquid effluent into the drain field or cause a blockage. A collapsed baffle or dip pipe will cause problems, and blockages will mean that wastewater backs up into your house.

Pressure: Excessive pressure can cause damage to the septic tank. Excess applied pressure can occur from vehicles such as tractors and farm equipment that drive or park over the septic tank.

Sometime hydro-static pressure can occur when the volume of water beneath the tank is high. Although this is a rare occurrence, this kind of pressure can push the tank out of the ground.

Excess water: When excess water gets into the tank, it can cause solid particles to rise that try to escape through the outlet, thus blocking the tubes.

Excessive detergent: Phosphates from dishwashing liquids and laundry detergents can spur algae growth. This blocks the perforations in the tank’s distribution pipes.

Harsh chemicals: Chemicals and products such as motor oil, paint thinners and solvents kill bacteria in the tank that are necessary for decomposing organic waste. These chemicals also leach into the surrounding soil through the septic tank, which pollutes the environment and affects plant growth.

Non-biodegradable items: Items like paper towels, wet wipes and sanitary napkins should never get flushed as they enter the septic tank causing blockage. They do not break down naturally and cause the water inside the tank to rise, forcing particles of non-biodegradable items into the distribution system.

Old septic tank: Septic tanks are susceptible to damage, and wear and tear as they age, causing clogs, breakage and other kinds of problems.

Signs of septic tank problems

There are a few warning signs you must look out for that can indicate problems with your septic tank:

  • Wastewater backing up into household drains.
  • Wastewater draining slowly.
  • Unpleasant odour around the septic tank.
  • Bright, lush, and spongy grass growing around the drain field, especially in the summer.
  • Pooling water or damp spots around the septic system.
  • Gurgling sounds from the plumbing.

How to take care of the septic tank?

Septic tanks need to be drained regularly, which helps to keep them clean. On an average, the sludge in the tank needs to be pumped out every 3 to 5 years. But some tanks may require pumping every year.

It’s vital to regularly check the septic tank with professional inspections every six months.

Other things you can do to look after the septic tank are:

  • Don’t overload your tank with wastewater, which mostly comes from washing machines, dishwashing machines, toilets, and bathrooms.
  • Run the dishwasher and washing machines when loads are full.
  • Don’t empty large volume of water into the tank, like from a spa pool.
  • Never flush non-flushable items or expired medicines.
  • Reduce the use of strong bleaches and disinfectants
  • Don’t put fats, grease, and oils down the drain.
  • Don’t put any other chemicals, paints and weed killers down the drain.