Types of septic tank systems

These systems rely mostly on gravity and  consist of  a septic tank, normally 3200 litres, connected to a distribution pit followed by effluent (absorption) trenches which are generally slotted pipe laid underground in aggregate (usually scoria) filled trenches.  Length and width of these trenches is determined by the size of the development.

Solids settle in the bottom of the tank and liquid known as the effluent passes through the distribution pit to the trenches where it is absorbed by the soil.

These systems normally have two tanks and consist of a primary settling chamber with an aeration system which treats effluent with chlorination or ultra violet to an approved standard, 20/30, for use as onsite fixed underground irrigation.

These systems require power to operate and need to have an alarm fitted to warn you if it is not working properly.  Regular servicing is needed by a qualified service agent, generally every 3 months. 

It is important that you follow the manufacturer’s guidelines to make sure the system works properly at all times.

A composting on-site wastewater system is a type of domestic wastewater treatment system designed to treat toilet waste by breaking it down through a natural composting process rather than flushing it to a septic tank or sewer. These systems use aerobic decomposition (with oxygen) to safely compost human waste into a more stable, dry material over time. 

A worm farm on-site wastewater system is a type of domestic wastewater treatment system that uses worms and microorganisms to naturally break down and treat household wastewater, including sewage and greywater.

The system works by separating solids from liquids. The worms digest solid waste, breaking it down into compost-like material, while liquid waste is filtered through layers of soil, organic matter, and other media to assist with further treatment. The treated liquid is usually dispersed through a subsurface irrigation system.

These systems require care to ensure the composting system is operating properly and some systems require grey water to be treated separately, or a secondary treatment process.

These systems works in two stages:

1. Primary Treatment (Septic Tank)

Wastewater from the home first flows into the septic tank, where solids settle to the bottom and begin to break down. This process separates solids, scum, and liquid, providing basic treatment.

2. Secondary Treatment (Sand Filter)

The partially treated liquid from the septic tank then flows through a sand filter, which further treats the wastewater by filtering it through layers of sand and gravel. This process helps to remove nutrients, pathogens, and suspended solids. The treated effluent is then usually disposed of via subsurface irrigation or absorption trenches.

A septic tank with reed bed system uses natural processes to treat household wastewater. It combines the traditional septic tank with a constructed wetland (reed bed) to provide secondary treatment.

The system works in two main stages:

1. Primary Treatment (Septic Tank)

 Wastewater from the home flows into the septic tank, where solids settle to the bottom and begin to break down. This stage separates solids, scum, and liquid, providing basic treatment.

2. Secondary Treatment (Reed Bed)

 The partially treated wastewater from the septic tank is distributed through a reed bed — a gravel-filled basin planted with reeds and other wetland plants. Microorganisms around the plant roots break down remaining contaminants. The reeds help oxygenate the wastewater, supporting this natural filtration process. The treated effluent is usually disposed of via subsurface irrigation or an absorption area. Reeds need to be kept alive for this system to work.

A greywater system collects, treats, and reuses wastewater from non-toilet plumbing fixtures in your home, such as:

• Showers and baths
•  Bathroom sinks
•  Washing machines
•  Laundry troughs

Greywater does not include wastewater from toilets, kitchen sinks, or dishwashers (this is considered blackwater and must be treated separately via a septic system or sewer connection).

A greywater system is designed to either divert untreated greywater directly for garden irrigation (under specific conditions) or treat it for safer reuse, depending on the system type and level of treatment provided.