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How does a Home Sewage Treatment Plant work?

Home sewage treatment plants, otherwise known as HSTPs, are the other option when it comes to wastewater treatment. It offers a system that treats both greywater and blackwater in one area, making it both a practical and functional arrangement in varying forms. HSTPs are based on whole community sewage treatment systems however, are in a smaller structure that are used by one household or family as opposed to the whole community. They are eco-friendly options that allow wastewater, once treated, to be immediately used in the environment (both above and below ground) and will not be a health threat to you or your property. As a HSTP is structured like any Municipal sewer system, a lot of people do not even know that they have a HSTP - the difference however lies in the fact that HSTPs allow you to use treated wastewater whereas Municipal systems do not.

If you currently have a septic system and it is causing problems, or you are wanting a higher-quality effluent to be created by your system, a HSTP is considered a better option than traditional septic systems.

How does a Home Sewage Treatment Plant work?

A HSTP works by enabling natural bacteria to treat wastewater in an environmentally-safe way, without including any chemicals in the process. A separation of solids and liquids occurs by transferring both the blackwater and greywater between varying chambers, which also allows the addition of anaerobic bacteria (bacteria that don’t need oxygen to survive!) and the aeration of the liquids. After this process is finished, the resulting water is safe for the environment and can be used for irrigation of your garden without posing a threat to you or those around you.

What makes up a HSTP?

There are various kinds of HSTPs, however the general parts of a HSTP include :

  • Primary treatment chamber : otherwise known as the ‘septic tank chamber’ or the ‘trash trap’ where water initially begins the treatment process
  • Secondary treatment chamber : otherwise known as the ‘aeration chamber’, aerating the wastewater to allow bacteria to do its cleaning job
  • Settling, disinfection and pump out chamber : the water is cleaner and lighter than before, allowing pollutants to settle on the bottom of this chamber
  • Irrigation Pump : transfers the treated water into the environment

Primary Treatment Chambers

Wastewater enters the plant in the primary treatment chamber. This chamber allows the settling of solids that can not be treated, such as oils, fats, grit and personal hygiene items, and the rising of lighter things to the top. This chamber has very low (or even zero) oxygen and is realistically the primary filter for wastewater. The lighter wastewater and matter leaves at around the mid-water level and then goes to the secondary pre-treatment chamber where anaerobic bacteria (otherwise known as bacteria that does not need oxygen to live) uses the nasties in the water as food and they begin to break them down.

Secondary Treatment Chamber(s)

The partially-treated wastewater then enters the second treatment phase. This chamber, otherwise known as the aeration chamber, releases air from the bottom of the area that is distributed throughout the water. This injects gaseous oxygen into the water, becoming dissolved oxygen, which then allows aerobic bacteria to get involved. This process is much quicker than stage one, as this kind of bacteria can multiply very quickly when a food source, such as that contained in the wastewater, is combined with lots of oxygen and time. The bacteria both eat the food and each other (this is part of nature, as harmful as it may sound), which then results in countless naturally-occurring bacteria cleaning the water contained within the chamber. The outcome is a very clear liquid which contains considerably less contaminants and nutrients.

Settling, Disinfection and Pump Out Chambers

After passing its way through the first and second treatment chambers, the water is cleaner and not as heavy as before. Any pollutants will therefore sink to the bottom and the clean water will remain at the top in the settling chamber. This water leaves by displacement, caused by any water entering the primary treatment chamber from your home. This water goes through a UV disinfection tube or a chlorine tablet dispenser, depending on the system, into the pump out chamber.

Irrigation Pump

The irrigation pump is the last step in the treatment process, automatically transferring the treated water from the pump out chamber into the environment for use in irrigation in your garden. The water is discharged in a ‘designated land application area’ and it is not completely devoid of pollutants, however it is at an acceptable environmental level for the particular discharge area.

What is a ‘designated land application area’?

If you have a HTSP, the water is required to be discharged into a designated land application area. This areas’ requirements will be set out in the relevant regulatory authority approval conditions that were provided when the system was installed, and are to ensure the health and safety of you and those around you. Some things to consider when looking for a designated land application area include :

  • The area must have suitable topsoil depth
  • The area must have vegetation cover, such as grass or other appropriate plants
  • Try and have your designated land application area in a sunny spot
  • The sprinkler discharging the effluent should be a coarse droplet type with a spray height no higher than 300mm

Handy tip - use additional mulch to ensure extra absorption and avoid any run-off!

What about maintenance and servicing of a HSTP?

Maintenance of a HTSP is the responsibility of the owner of the property on which it is located, and it must be serviced by a licenced service agent in accordance with the relevant regulatory authority approval conditions that were provided when the system was installed.

If you're based in south east Queensland and would like to know more, feel free to get in touch wit us.

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