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Sewage water quality

On-site sewerage facilities

Treating wastewater isn’t as simple as some people believe, and a particular level of sewage water quality is required in treating water through these systems. There are two major on-site sewerage facilities, namely septic tanks and home sewage treatment plants (HSTP), which are used to treat wastewater. Both systems have their pros and cons and work in different manners to achieve a suitable result.

Septic tanks

A septic tank is known as a primary system as it provides limited treatment, which treats wastewater through biological processes before releasing the end product into a below-ground system. The system a septic tank utilizes is that fats and grease are buoyed to the surface and form scum, and the solids settle at the bottom of the tank forming sludge. Irrigation is not possible with water treated by septic tanks alone, however, if combined with an aerated system the treatment standard increases and irrigation is a possibility.

Home Sewage Treatment Plant (HTSP)

A HTSP is also known as an on-site sewage treatment plant which releases treated wastewater through both above and below-ground irrigation systems, using a combination of filtration, biological and mechanical processes. The process is environmentally sustainable, as it allows different bacteria strains to thrive in varying components of the plant, ‘treating’ the water naturally and without harmful products or chemicals. There are secondary, advanced secondary and tertiary systems, which vary in compliance characteristics depending on the process utilized, and treat wastewater produced in the same location as the HTSP is located.

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What’s the difference between septic tanks and home sewage treatment plants?

There are a few differences between the systems, which pose positives and negatives for each facility :

Process Utilized

Septic tanks use a biological process to treat wastewater which can only be released below ground once the process is complete due to its nature. HTSPs however use more complicated filtration, biological, and mechanical processes and the wastewater, once treated, can be released both above and below ground.


The effluent, otherwise known as the treated wastewater, that is released from a HTSP is non-polluting, meaning it is clean water which can be released directly into a watercourse. On the other hand, the effluent from a septic tank is of a polluting nature, meaning it can only be released into a soakaway for further treatment. This, therefore, means that a HSTP is generally better for the environment than a septic tank.


The installation of a septic tank requires approval from your local council but does not require chief executive approval. If you have not obtained the required approval from the council, you will not be permitted to install a septic tank on your property. Additionally, you are not permitted to install a septic tank in water catchment areas or coastal areas where effluent may run into waterways.

On the other hand, a HTSP requires both local government approval and chief executive approval (or its equivalent) in accordance with Part 5 of the Plumbing and Drainage Act 2002 before it can be installed.

Cleaning, emptying and servicing

When it comes to cleaning and maintenance, HSTPs require servicing in accordance with their State Accreditation Approval however septic tanks do not, therefore it is wise to enquire regarding servicing charges whilst considering HSTPs. Septic tanks do however require emptying around once a year, and HTSPs have emptying requirements that range depending on the model and process, making the upkeep requirements a little different between the systems.


A septic tank is a much cheaper option than a HTSP, however, both are relatively cost-effective to run relative to their respective dimensions. Septic tanks do not require electricity to run and HTSPs do though, with the level needed depending on the model and type.

If you have any questions regarding sewage quality, septic tanks or home sewage treatment plants, please give us a call at 1300 722 517 and we discuss all available options with you.