Septic Tanks vs HSTPs : How do they compare?

If you are considering introducing a wastewater treatment arrangement to your property, there are different options available depending on your household and its needs. From septic tanks to home sewage treatment plants, wastewater treatment has come a long way in ensuring environmentally friendly and safe choices for both blackwater and greywater treatment.

But which option is best?

To help you decide on a system, we have compared two of the most common wastewater treatment solutions - septic tanks and home sewage treatment plants - and looked at the advantages (and disadvantages) of each option. Give the Express Wastewater team a call on 1300 722 517 if you would like further assistance.

Septic tanks

What is a septic tank?

Septic tanks are the most widely-known part of a septic system. They are, in essence, a buried watertight container that can be made out of concrete, fibreglass or polyethylene plastic and their main responsibility is to collect and store all the wastewater from the plumbing in your home before dispensing it through a drain field. Depending on the system, some septic tanks may treat either just blackwater (toilet discharge) or both grey and blackwater (all household wastewater).

Diagram of a septic tank — Diagram of a Septic Tank

How does a septic tank work?

The steps a septic tank takes are quite simple - some of the matter that drains into a tank (ie. fats and grease) floats to the top of the tank and forms a scum layer, whilst the rest of the broken-down solids (known as sludge) drops to the bottom. The water that has been treated then drains through an outlet and enters a trench or disposal area.

Pros of a septic tank

Requires approval from your local council but does not require chief executive approval when installing, making it a quicker/easier process.
More common option.
Cheaper to purchase.
Much cheaper running costs and do not require electricity to run.
Environmentally friendly.
Low maintenance requirements (pumping needed every 3-5 years).
Long-lasting.

Cons of a septic tank

Effluent from a septic system is of a polluting nature, meaning treated wastewater can only be released below ground once the process is complete due to the levels of contaminants still present.
If you are located in water catchment areas or coastal areas where discharge may run into waterways, you will not be permitted to install a septic system.
Can have foul odours if not maintained properly.
Poor maintenance can cause soil contamination.
Excessive rain can cause the tank to overflow.
Some systems only treat blackwater.
A larger area is required to install.

Home Sewage Treatment Plant

What is a home sewage treatment plant?

Home sewage treatment plants, also known as HSTPs, are another option when it comes to wastewater treatment. They offer 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 but have been condensed down into smaller forms that are used by one household or family (as opposed to the whole community). HTSPs are an eco-friendly choice that allows wastewater, once treated, to be immediately used in the environment (both above and below ground) and do not pose a threat to the health of you or your property.

As a home sewage treatment plant is constructed just like any Municipal sewer system, many people do not even know that they have a HSTP - the difference between the two lies in the fact that HSTPs allow you to use treated wastewater (whereas Municipal systems do not).

How does a HSTP work?

A home sewage treatment plant works by allowing natural bacteria to treat wastewater in an eco-friendly way, without involving any chemicals in the process. The division of solids and liquids occurs by transferring both the blackwater and greywater between different chambers, which also introduces 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.

Although there are different types of HSTPs, there are a few common parts that all share:

Primary treatment chamber.
Secondary treatment chamber.
Settling, disinfection and pump out chamber.
Irrigation pump.

Pros

Unlike the septic system, the HSTP has three stages to treat wastewater to a higher level.
Use a more complicated filtration, biological and mechanical process.
The effluent or ‘treated wastewater’ that is released from a HSTP is non-polluting, meaning it can be released both above and below ground.
Relatively cost-effective to run.
Treats both blackwater and greywater.
Environmentally friendly.
Suits properties of all shapes and sizes

Cons

HSTPs require more approvals to be installed, as they need both local government approval and chief executive approval (or its equivalent) in accordance with Part 5 of the Plumbing and Drainage Act 2002 before they can be installed.
HSTPs require servicing in accordance with their State Accreditation Approval (it is suggested to enquire regarding servicing charges when looking at installing a HSTP).
More expensive to purchase.
Higher running costs and require electricity to run.

Septic Tanks vs HSTPs: which is best?

A home sewage treatment plant is generally considered a better option than traditional septic systems, as it provides higher quality effluent than septic tanks and treats water in 3 stages. In saying this, however, it is always suggested that you speak to a qualified wastewater professional who will be able to assist in choosing the most appropriate option for your needs.

‍If you would like further information, give Express Wastewater a call at 1300 722 517 and we can discuss all the septic tanks or HTSPs suitable for your property.

Resources:

Taylex (Frequently Asked Questions): https://taylex.com.au/wastewater/faq/

Taylex (What is a Home Sewage Treatment System?): https://taylex.com.au/wastewater/secondary-wastewater-treatment-systems/

Moreton Bay Regional Council (Your Guide to Wastewater & Sewerage Systems): https://www.moretonbay.qld.gov.au/files/assets/public/services/building-development/building-plumbing/wastewater-and-sewerage-systems-brochure.pdf