How Your Septic Tank Works

All wastewater from your toilets, showers, sinks, washing machines and dishwashers runs into your septic tank. Solid materials sink to form the sludge layer while oils and fats float above to create the scum layer.

Anaerobic bacteria inside the septic tank break down organic waste pollutants. The clarified liquid that is left is called effluent. The filtered liquid exits the septic tank through a pipe into your septic drain field. Contact Septic Tank Armadale for professional help.

All of the wastewater generated by your toilets, shower, tub, sinks and appliances (called blackwater or greywater) drains into a septic tank. Solid materials in the wastewater sink to the bottom of the septic tank where anaerobic bacteria live, and these organic waste pollutants are broken down by the bacteria. The liquid portion of the wastewater, called effluent, floats to the top of the septic tank where fats, oils and greases collect in a layer known as scum. Effluent passes through a septic tank outlet into a septic system’s soil absorption field (also referred to as a drain field).

The drainage field is a network of perforated pipes in gravel trenches buried under the ground that treats the wastewater, converting it to sludge and water. Solids must be removed from the wastewater before it enters the drain field, or it may clog and flood the septic tank or the house.

A properly designed septic tank-soil absorption system can be very effective for preventing groundwater contamination. However, there are a few situations where septic tanks are not suitable, including steep slopes, limited space or shallow groundwater table. In those cases, alternative septic systems are sometimes used.

Alternative septic systems, which are also known as package sewage treatment plants or off-mains septic system, typically consist of a multi-compartment tank called an Aerobic Treatment Unit or ATU. The ATU has a “trash compartment” that holds the solids for pretreatment and liquification, an aerobic chamber where anaerobic bacteria digest some of the organic waste material, and a clarifying chamber. Some ATUs do additional treatment with ultraviolet light or chlorine tablets.

A septic tank should be pumped out every 3 to 5 years depending on household size and usage. Regular pumping reduces accumulation of sludge and scum layers that can overflow the tank and into the drain field, plugging the pipe to the drainfield and causing premature drainfield failure. Avoid flushing anything other than toilet paper and human waste into a septic tank, as even things labeled as “flushable” can clog the plumbing system. If your septic system needs to be pumped out, contact a qualified septic tank professional for a safe and efficient job.

Sludge

Sludge is the thick, dark material that forms the bottom of a septic tank. It consists of the heaviest waste materials that don’t break down, such as human waste and toilet paper. The septic tank system allows the heavier solid waste to sink to the bottom of the tank while the lighter materials float up to the surface and form the scum layer. The septic tank system relies on this natural process to separate and purify the wastewater.

The septic tank also contains anaerobic bacteria that digest the organic waste materials that sink to the bottom of the septic tank and form the sludge. The by-products of this decomposition are soluble compounds and gases, which are carried away in the liquid effluent. If the septic tank isn’t pumped regularly, the sludge layer will gradually reduce the usable volume of the septic tank. This means the wastewater won’t spend enough time in the septic tank for proper separating and purifying, leading to pathogenic bacteria and dissolved organic pollutants that can clog drainfield soil and cause septic system failure.

When sludge and scum take up more than 35% of the tank’s volume, it’s time for pumping. Pumping removes the sludge and scum layers, leaving the clarified effluent layer at the top of the septic tank.

If a homeowner doesn’t get their septic tank pumped, the sludge layer may increase and start to block the septic system’s inlet and outlet pipes. This can lead to sewage backups and expensive repairs. To avoid a septic system failure, homeowners should learn what can and cannot be flushed down the toilets and other drains. Things like handi-wipes, coffee grounds, grease, paint, cleaning products, disinfectants, bleach, and other chemicals can clog pipes going out of the septic tank and contaminate groundwater.

A septic tank should be pumped every three to eight years, depending on the size of the tank and how often it’s used. Homeowners should also consider using a bacteria additive, which is a blend of live bacteria that help keep the septic system working as it should. The bacteria help to eliminate odors, reduce the buildup of sludge and scum layers, and keep the septic tank healthy.

Scum

The scum layer is where fats, oils and anything less dense than water goes as it drains into your septic tank. Eventually, these floating substances separate from the wastewater and sink to the top of the tank where the microorganisms break down any remaining solids.

Gravity causes this separation, but it’s also enhanced by the fact that scum is lighter than the wastewater. That makes it more likely to float. The fats, oils and floating solids are trapped in the scum layer while the heavier solids go to the sludge layer. This helps to reduce the amount of solids that reach your leach field and clog pipes.

Floating scum usually takes up 1/2 to 2/3 of your tank’s volume. The rest of the tank is filled with liquid wastewater that’s poured into the toilets and drains throughout your home.

The more people in your household, the faster your septic system will need to deal with solids. Excessive food waste and the use of a garbage disposal can also accelerate sludge accumulation. The local climate also plays a role in how quickly your septic system may need to deal with wastes. When it rains heavily, groundwater infiltrates your septic system and can increase the rate at which the sludge and scum layers build up.

Septic tanks need to be pumped on a regular basis. This is a cost-effective way to extend the life of your septic system and help it function as effectively as possible for as long as you own your home.

If your septic system isn’t properly maintained, you could need to replace it sooner than expected. That’s why it’s important to understand how your septic tank works and the signs that it needs to be pumped.

Keep in mind that any surface water or rainwater from your roof and gutters must be kept completely separate from your septic tank wastewater. That water should drain to the mains drainage system or a dedicated soakaway or stormwater attenuation tank. Avoid flushing anything down your septic system that’s listed as ‘flushable’. Items like Handi-Wipes aren’t safe for your septic system and can clog the pipes that lead out of your tank.

Effluent

All wastewater from your home’s toilets, showers and sinks flows through a sewer line that slopes down toward the septic tank. In the septic tank, all of this waste is temporarily held and separated by both settling and flotation. Substances lighter than water (oils, greases and soap scum) float to the top of the tank where anaerobic bacteria work to digest them. The heavier solids, called sludge, settle to the bottom of the tank. The clear liquid in between, known as effluent, flows through the septic tank outlet into the drain field.

A septic system’s drainage area, also known as the absorption field, is where the clean wastewater trickles through a series of trenches filled with gravel and/or sand that act as a filter to remove disease-causing pathogens and other pollutants before they are discharged to soil and groundwater. An advanced septic system may have one or more additional treatment systems installed between the septic tank and the drain field to further reduce contaminants like nutrients, pathogens and organic compounds.

The septic tank inlet and outlet baffle walls prevent the sludge layer from flowing out of the septic system, where it could clog the septic tank outlet pipe or the absorption field. These baffle walls are constructed of a concrete material that is strong enough to withstand the pressure of the liquids inside the septic tank.

To keep the sludge from getting too thick, it needs to be regularly stirred up or “desludged.” This is the process of injecting special chemicals into your septic tank that dissolve the fats, oils and other solids.

If you do not pump your septic tank on time, the scum and sludge layers build up. The liquid layer between them disappears, and septic solids like toilet paper and feces go out into the absorption field where they can clog pipes, soil and distribution boxes.

To avoid this, make sure to only flush human wastes, toilet paper and white household wastes down the drain. Also be careful not to wash diapers, sanitary products and cloth or paper towels down the toilet. These can cause the septic tank to become overloaded and require early pumping. You should also refrain from using drain cleaners, anti-bacterial products and other household chemicals that kill anaerobic bacteria in your septic tank.