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What do I need to do to organise the installation and approval of my Household Sewerage Treatment Plant (HSTP)?

Step One - Investigate different types of HSTP's and make an initial decision on the type and brand you wish to install on your property.

There a number of HSTP's on the market today.  The following factors are worth considering in your decision process:

• Initial cost of HSTP.  Depending on the brand chosen the initial cost may vary from around $6 000 to $15 000 for a standard domestic installation.  Make sure you know what you are getting for your investment.  Compare the different brands and examine why there are cost differences.  The old adage of "you pay for what you get" has some merit in this instance.
• Inclusions/Exclusions.  This factor ties in strongly with the first point.  What exactly is included in the price you have been quoted and more importantly what do you have to do/provide yourself?  Key areas to look at include:  excavation of the tank hole(s), filling of the tank(s) with water (to prevent uplift), dispersal field, backfilling etc.  Make sure you compare "apples to apples" ie that each quote has the same inclusions so that you can compare on an equal basis.
•  Operating Costs can vary widely from system to system.  Key areas to look at include electricity consumption (from around $20/year up to $300/year), service requirements (quarterly, biannual, annual?), replacement parts (availability, cost), consumables (chlorine, UV lamps - how often? how much?) etc.
• Environmental Awareness.  How does this system affect the environment?  Can the treated effluent be re-used?  Is it chemical free?  Are there chemical by-products of the treatment process?  Are there any health and safety concerns?
• Aesthetics.  Is the HSTP's appearance pleasant, inconspicuous, intrusive etc?  Are there any limitations on activity in the vicinity of the HSTP?  

Some terminology you are likely to hear...

HSTP - Household Sewerage Treatment Plant or OSSF - On Site Sewerage Facility are the preferred alternative to the "old" septic system for domestic wastewater treatment.

Aerobic treatment (AWTS) uses natural aerobic bacteria to break down solids and treat effluent.  Aerobic bacteria as the name suggests require oxygen to survive.  HSTP's supply oxygen to this bacteria in a number of ways.

Where aerobic treatment is used inside the septic tank, the contents of the tank must be aerated to enable the bacteria to survive.  This is achieved by using aerators or "blowers" to blow air through the effluent.  Depending on the system chosen these aerators could operate up to 24 hours a day.  The energy consumption of this type of treatment system should be considered when choosing a HSTP.

Where aerobic treatment is used outside the septic tank it is generally in the form of a "polishing unit" or a sand media filter.  Polishing units are similar to the sand filtration units used on swimming pools.  They are generally a round ball-like object placed either on the tank or beside the tank.  

In - ground sand media filtration (like that used in Nature Flow Systems) utilise natural aerobic bacteria without the use of blowers or aerators.  Oxygen permeates through the top of the sand media bed which must remain open (ie not sealed with liner etc, may have lawn established over this area).  Depending on the system chosen, effluent may be either gravity or pressure fed to the sand media bed.

Gravity fed systems require the effluent to flow into the media bed without the use of a pump.  The advantage of this method is that it requires the use of a single pump only and thus reduces the operation cost of the system.  The disadvantages of gravity feeding is that it increases the occurrence of channelling and may not use the full area of the sand media bed to best effect.  Channelling occurs when the effluent flows via the path of least resistance ie where gravity dictates.  This may mean that effluent does not reach the end or edges of the bed and thus concentrates in one part of the bed or another.

Pressure fed systems provide some flexibility as to the location of the sand media bed as they do not require the assistance of gravity.  Generally however the sand media bed will be located higher than the tank.  The disadvantage of this method is obviously the requirement of a second pump and thus an increase in operation costs compared to gravity feeding.  The advantage is that the whole of the sand media bed is utilised to full effect resulting in a higher standard of treatment and also a longer life as the sand media bed is used evenly.

In-ground filtration provides a higher standard of aerobic treatment than effluent polishing units (EPU's) as the surface area of the media is greater increasing the retention time and treatment capacity.  The pressure fed pipe raft used within Nature Flow Systems also reduces the occurrence of channelling.  Energy consumption is significantly lower than in-tank aerobic treatment as aerators/blowers are not used.

Anaerobic bacteria are natural bacteria that assist with the breakdown of effluent particularly solids.  This bacteria does not require oxygen to survive.  It is commonly used "in-tank".  It is similar to the "old" septic system in that effluent is collected in septic tank, the anaerobic bacteria breakdown the effluent, the solids settle to the bottom of the tank as sludge, the treated wastewater continues through to disposal (generally trenches).  Periodically the tank requires pumping out to remove the build-up of sludge.

Disinfection describes the process of inactivating microbial organisms (bacteria, viruses etc).  There are a number of disinfection methods used for wastewater treatment.  Where surface disposal of treated wastewater is desired disinfection is compulsory.

Chlorine is probably the most common method of disinfection.  The use of chlorine varies from system to system however it should be noted that most systems use a slow dissolving type of chlorine block/tablet of a specific composition - generally not your standard swimming pool kind.  

There are two basic methods of releasing chlorine into the wastewater - immersion of chlorine blocks/tablet canister in the septic tank or "on-line" chlorination.  

The immersion of chlorine blocks/tablet canisters simply involves placing the block or canister inside the septic tank/compartment where chlorine will be gradually released by slowly dissolving.  This method makes it difficult to control the release of chlorine and may result in fluctuating dosages.  From an environmental and health and safety aspect this method could result in higher than necessary chlorine dosing.  From a household budget aspect this could also mean that replacement of chlorine blocks/tablets occurs more often than necessary - increasing the running costs of the treatment system.

 "On-line" chlorination operates similar to the chlorination of swimming pool (but on a much smaller scale).  Treated wastewater is pumped through a chlorinator on its way to disposal.  The chlorine tablets do not sit immersed in the effluent instead the effluent runs through the tablets (held in the chlorinator canister).  The dosage of chlorine is further controlled using a doser - "a dial up" chlorinator.  This ensures that only the minimum dose of chlorine necessary to provide the correct bacteria kill rate is used thus reducing the environmental impact of chemical treatment and saving your pocket.

Ultra Violet sterilisation is by no means a new technology however its use in mainstream wastewater treatment has only recently received stronger support.  The preference for chlorine use rather than UV historically was due to initial and ongoing costs, skills required to install/maintain, availability, limited public environmental awareness and public acceptance.

Nature Flow's patented self-cleaning UV technology provides effective and reliable wastewater treatment with minimal maintenance.  On-going costs are significantly lower than chlorinated systems with the added bonus of being chemical free.  Servicing requirements are greatly reduced due to the self-cleaning device unique to Nature Flow Systems.  The reactor design allows for easy and "unskilled" maintenance.  The effectiveness of UV against waterborne bacteria and viruses is certain and calculable - an advantage compared to free floating type chlorine canisters where dosage is largely uncontrolled and erratic.

Step Two - Get HSTP plans drawn up and submit to Local Authority.

Local Authority requirements differ from region to region.  

Some local authorities require the homeowner/builder to submit a "Site & Soil Evaluation" for your wastewater disposal system.  (This is a different type of assessment to a standard soil test done when you build a house although it can often be carried out by the same person who performs your soil test.)

A Site & Soil Evaluation will examine a number of factors on your property such as contours, soil type, permeability, property boundaries, the existence of wells, dams, bores, watercourses on your property etc.  The assessor will then compile a report with recommendations of the type of wastewater facility and disposal appropriate for your property including (in most cases) a site plan.  This report will be submitted to your Local Authority with the relevant forms to seek approval for the installation of the HSTP.  

It is worthwhile noting that when submitting your house plans to council you must include your proposed method of wastewater disposal.  Failure to do so will slow the approval process.  It is however possible to change the brand of HSTP chosen simply by putting the change in writing and sending it to council.  (Subject to the conditions of council approval.)

Other local authorities do not require "Site & Soil Evaluations" in every case.  (Although they may require evaluations where setback distances cannot be achieved or where there are environmental concerns.)  In this instance most suppliers of HSTP's are able to draw the plans for you.  (This may attract a fee however some suppliers will deduct this fee from your final invoice once installation is complete.)  They will normally require a scaled site plan with contours and often will inspect the site.  They need to be aware of a number of factors such as the location of buildings, swimming pools, dams, boundaries, easements, water courses etc - both existing and proposed as this will affect the placement of your HSTP and wastewater disposal field.  Serious thought should be given to this particularly to items such as proposed swimming pools, sheds etc as once your wastewater disposal field is installed and approved it will (to a certain extent) dictate placement of these future items.  See setback distances.

Once you have your HSTP plans ready you can submit them to your Local Authority along with the relevant forms (generally an :Application for an On-site Sewerage facility, Form 7 - Responsible Person, ).

Step Three - Installation of your HSTP

Installation of your HSTP cannot commence under any circumstances without Local Authority approval.  A copy of this approval must be given to your HSTP supplier/installer.  

Once a copy of approval has been received you or your builder should liase with your HSTP supplier/installer to plan installation.  The installation process may vary depending on the system chosen however generally it will proceed as follows:

1. Book in date for installation.  If you are organising HSTP installation independently of your builder, the HSTP supplier/installer will require permission from your builder to enter the site to complete the installation.
2. Site meeting to ensure that both you and the installer are in agreeance with siting of the HSTP.
3. Excavation of tank hole(s) and/or sand media bed.  Depending on the system chosen excavation may be included in the cost of the HSTP or it will be the responsibility of the Owner/Builder to organise.
4. Placement of tank(s) in hole(s).
5. Load and complete sand media bed (if required) OR placement and connection of Effluent Polishing Unit.
6. Plumbing associated with HSTP including disinfection method (if required).  Note that generally this does not include plumbing connection from your house to the system...this is the Owner/Builder's responsibility.
7. Complete treated wastewater disposal field (depending on local authority requirements this may be surface irrigation, subsurface irrigation, transpiration beds, retention mounds, trenches etc).
8. Fill tank(s) with water to prevent uplift.
9. Final check and test of installation.  (If electrical connection unavailable check can be done with a generator.  It is generally the Owner/Builder's responsibility to provide electrical connection for the HSTP.  Depending on  the system chosen this may mean hardwiring the HSTP or providing two double weatherproof powerpoint at the HSTP.)  Commission system.  Provide Owner/Builder and Local Authority with copy commissioning certificate.
10. Local Authority to inspect installation and issue approval notice when satisfied.
11. Owner to maintain a current service/maintenance agreement for the HSTP at all times and to ensure that they are conversant with their responsibilities in regard to operation of the HSTP.

Please note:  installation of a wastewater treatment system involves major earthworks.  While installations are completed as neatly as cost viability allows, owners should expect the area of the installation to have excess spoil (unless otherwise agreed within the purchase contract with supplier), evidence of machinery movement to, from and around the site of installation, visible trenching etc.  Particularly with changes in weather (ie long dry periods followed by rain etc), trenching and backfilled areas may develop depressions and be subject to subsidence.  Subsidence is a natural phenomenon that is highly unpredictable and as such remains the responsibility of the owner/builder and is not covered by warranty.

Step Four - Looking After Your HSTP

1. Ensure your HSTP is serviced according to manufacturer's requirements.  This is a Local Authority requirement and failure to comply does attract fines/prosecution.  Follow advice from your service agent - maintain your HSTP.  Replenish chlorine tablets, replace UV lamps etc.
2. Maintain your effluent disposal field - ie keep it mown, do not drive vehicles over it, remember to alternate irrigation areas (where required).
3. Use appropriate cleaning products - low or no phosphorus.  Stagger wash days.  Do not pour anti-bacterials, disinfectants, bleach etc down the sink.  Avoid pouring oil down the sink.
4. Do not "tinker" with your HSTP.  Your HSTP has been installed according to manufacturer's specifications - avoid altering or modifying your HSTP and dispersal field except at the direction of your local authority.

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Last modified: 06 January, 2008