On-site Wastewater Management

Primary Treated Systems

Septic Tanks: A septic tank is a wastewater treatment device that provides the first stage of treatment for wastewater. This tank is connected to a disposal area, such as a transpiration bed or absorption trench. The disposal area must be big enough to manage the wastewater generated by the system.

Wastewater from the household enters the septic tank. The solids settle to the bottom of the tank and form a sludge layer. The fats & greases collect at the surface, forming a scum layer. Micro-organisms break down the matter in both the scum and sludge layers. Any material that cannot be broken down will gradually build-up resulting in the tank needing to be pumped out periodically.

Wastewater then flows, or is pumped, to the disposal area and distributed along the length of the bed or trench through pipework. Wastewater is absorbed by the soil and plant roots around the absorption area.

Secondary Treated Systems

Aerated Wastewater Treatment Systems (AWTS): An AWTS consists of one or two wastewater tanks, which contain a series of chambers. Wastewater enters the primary chambers where solids settle to the bottom to form a sludge layer. The scum layer, containing fats and grease, collects at the top of the chamber and clarified water flows from between the two layers to the aeration chamber. In the second chamber, the wastewater is aerated and broken down further by biological activity. The treated effluent is finally disinfected in a chlorination or UV chamber and irrigated across lawns or via a subsurface system.

All AWTS need to be serviced by a suitably qualified technician every three (3) months. Copies of the service reports are required to be submitted to Council within two (2) weeks of the date of servicing, via electronic PDF format. These service reports can be emailed to This email address is being protected from spambots. You need JavaScript enabled to view it..

Alternative Wastewater Management Systems

Composting Toilets

Composting toilets can have either a dry or wet composting process. They rely on the principle of aerobic composting or bio degradation of organic matter. They work by providing an enclosed environment for the natural decomposition process which is aided by microorganisms (aerobic bacteria). If properly composted according to the accredited manufacturer’s standards, the end product is a nutrient rich fertiliser that can be used on plants thereby reducing the need for commercial fertiliser while also saving water.

Sand Filter System

Sand filter systems generally use a sand bed with a gravel or geotextile base, all protected by an impermeable liner, to filter wastewater. Wastewater from a treatment tank is piped to the filter system, and the wastewater then filters through the sand layer, after which it may be disinfected prior to being piped to a management area. Sand filter systems may also be recirculating, and be located above, partially above, or below the ground. The surface may be mounded to help divert rainwater from the surface of the system.

Mound

A mound system is a soil absorption system which is raised above the natural soil surface. Wastewater from the dwelling is sent to a holding tank (septic or AWTS), and the effluent is then pressure dosed to the mound. Mounds generally use a fill material such as a sand media. Mound systems can overcome many site restrictions including shallow permeable soils over a porous bedrock, permeable soils with a high-water table and slowly permeable soils.

Biological Filter Systems

A biological filter system involves the combination of two treatment techniques. The waste is first made to pass through filter beds and is then subjected to aerobic decomposition with the aid of biological microorganisms such as worms, beetles, mites and other soil fauna. The treated effluent is then disposed of by sub-surface irrigation or absorption trenches.

It is a requirement of the NSW Health Accreditation and the Approval to Operate that all AWTS be serviced quarterly by a suitably qualified service technician.
The system operator shall enter into a service agreement with the manufacturer, distributor or other person accepted by Penrith City Council to service the AWTS every three (3) months from the date of commissioning (or for a period as required by the NSW Health accreditation).

The three-monthly service shall include a check on all mechanical, electrical and functioning parts of the aerated system including:

• the chlorinator
• replenishment of the disinfectant
• the UV disinfection unit (where applicable)
• all pumps and switches
• the air blower, fan or air venturi
• the alarm system
• the EMA and irrigation spray outlets and/or sub-surface irrigation lines and filters
• the slime growth on the filter media, and the operation of the sludge return system.

The following field tests are to be carried out at every service:

• free residual chlorine using DPD colorimetric or photometric method
• pH from a sample taken from the irrigation chamber
• dissolved oxygen from a sample taken from the final aeration or stilling chamber (recommended but optional).

On the anniversary date of the commissioning of the system, the service shall also include a check on the sludge accumulation in the AWTS.

For systems which use the sewage treatment principle of activated sludge or contact aeration, a sludge bulking test, known as a SV30 Test, shall also be conducted on an annual basis. This test is to determine whether the accumulated sludge is bulking, indicating that the aeration compartment(s) will require de-sludging.

On completion of each service, a legible service report sheet is to specify:

• all service items and test result figures
• detailed description of any tests and observations undertaken on the effluent management area (including all distribution lines, sprinklers and associated plumbing)
• amount of chlorine compound provided OR specific actions taken for other forms of disinfection
• date and time the service was conducted, and
• technician’s name and contact details.

A copy of the service report is to be:

• given to the system operator, and
• provided to Penrith City Council electronically via This email address is being protected from spambots. You need JavaScript enabled to view it., no later than 14 days from the service date. Service agents are required to submit individual electronic PDF service reports to Council. Multiple service reports within a single document will not be accepted.

If Council receives a service report that does not comply with the above requirements, the report may be returned to the system operator or service provider requesting further information or the carrying out of an inspection. Processing fees may be charged to service agents for each system/property that does not comply with the above electronic/individual requirement.

Council’s On-site Wastewater Management Policy

Decommissioning Requirements for OWM Systems

Onsite Wastewater Management Guidelines

The Easy Septic Guide