Aerated Wastewater Treatment Systems (AWTS)

In unsewered areas, the proper treatment and utilisation of household wastewater on-site is critical in preserving the health of the public and the environment. AWTSs have been developed as a way of achieving this.


What is an AWTS?

An AWTS does the job normally handled by a large Sewage Treatment Plant.  Instead of occupying large tracts of public land, it is a purpose built system used for the treatment of sewerage and liquid wastes from a single household or multiple dwellings.

It consists of a series of treatment chambers combined with an irrigation system. An AWTS enables people living in unsewered areas to treat and utilise their wastewater.


How does an AWTS work?

All water borne wastes from kitchen, laundry, bathrooms and toilets are treated in stages in several separate chambers. The first chamber is similar to a conventional septic tank. The wastewater enters the chamber where in the absence of oxygen (anaerobic) bacteria which thrive in these conditions reduce the toxicity of wastes.  The solids settle to the bottom and are retained in the tank forming a sludge layer. Scum collects at the top, and the partially treated wastewater flows into a second chamber.

Here oxygen is introduced to the mixture.  The oxygen, provided from a compact air pump (blower), together with nutrient present in the wastes, promotes the breeding of aerobic bacteria.

A third chamber allows clarification through the settling of solids, which are returned for further treatment to either the septic chamber or to the aeration chamber where it goes right back to work as activated material to assist in the treatment process.

The clarified effluent is disinfected in another chamber (usually by chlorinating).  From here a pump periodically sprays it into designated irrigation areas in the garden.

Bacteria in the first chamber break down the solid matter in the sludge and scum layers. Materials that cannot be fully broken down gradually build up in the chamber and must be pumped out periodically.


Regulations and recommendations

Local councils are primarily responsible for approving the smaller, domestic AWTSs in their area. The Environment Protection Authority (EPA) approves larger units, whilst the NSW Department of Health determines the design and structural requirements for all AWTSs.

At present AWTSs need to be serviced quarterly by an approved service provider at a cost to the owner. Local councils should also maintain a register of the servicing of each system within their area.

AWTSs should be fitted with an alarm having visual and audible components to indicate mechanical and electrical equipment malfunctions.


Maintaining your AWTS

The effectiveness of the system will, in part, depend on how it is used and maintained. The following is a guide on good maintenance procedures that you should follow:


Conserve Water

Water conservation is the single most beneficial action you can take to protect your AWTS (not to mention the environment as a whole!).  Your AWTS was designed to handle certain daily flows of wastewater.  Keeping your household's water usage well below your AWTS's "daily design flows" is a simple but powerful way to promote your AWTS's smooth functioning.  Consistently exceeding these flows impacts both the volume and quality of wastewater that enters your designated irrigation field.  The latter because higher flows disrupt the solids settling process and "push out" partially treated wastewater.  In fact water overuse is one of the leading causes of premature AWTS failure. 

The following are specific water conservation measures you can easily implement in your home:

• Fix leaky taps and toilets.  A leaky toilet can burden your AWTS with hundreds of wasted litres of water per day.
  
• Take sensible steps to curtail your water usage.  Limit showers to 5 minutes, fill bathtubs half full and remember not to let the tap run when you're shaving, brushing your teeth or washing dishes, vegetables, your hands, etc.
  
• Retrofit your showerhead with a water-saving (low flow) device.
  
• Retrofit your toilet with a water saving device, or, better yet, replace your toilet system, with a low volume dual flush system.
  
• Do laundry only when you have a full load, and try to spread laundry over the week rather than doing all your household's laundry at once.  If you're in the market for a new washing machine, consider a front-loading model rather than the more prevalent (but less water and energy efficient) top loading one.
  
• If you use a dishwasher, run it only when full.
  

• Limit your use of household cleaners such as bleach and detergents.  While most AWTS's can accommodate moderate amounts of such cleaners, large doses will destroy helpful bacteria populations in your AWTS and will pollute the environment. "Septic friendly" household cleaners can be purchased instead.  Better yet, use natural cleaning substances such as lemon, vinegar and baking soda where you can as substitutes for potential AWTS damaging commercial cleaners.
  
• If you have a clogged drain, use boiling water or a drain snake rather than caustic drain cleaners.
  
• Use low-phosphate detergents to avoid environmental damage.  Releasing phosphates into your local environment can spawn destructive algal blooms (including blue green algae) in the lakes and rivers nearby your house.
  
• Avoid anti-bacterial soaps and bathroom cleaners.  Used in excess, these can destroy bacterial populations in your septic tank.
  
• Don't flush medicines (over-the-counter and prescription) down the drain.  Here again, such substances have an adverse effect on your AWTS's bacteria..
  
• Don't discharge pool backwash into your AWTS..  Not only will this increase your water load, chlorides and salts in the discharge will harm your AWTS's bacteria.
  
• Biological septic system "additives" (e.g., bacteria, enzymes) sold to "jump-start" your system or "counter-act" the effects of household chemical usage are generally not actively harmful, but they are unnecessary.  Proper care and maintenance (including regular service), not septic additives, is the only sure way to promote a healthy AWTS.
  
• Never dispose of toxic chemicals in your AWTS. 
  

• Have your AWTS inspected and serviced four times per year by an accredited service provider. Assessment should be applicable to the system design.
  
• Have your system service include assessment of sludge and scum levels in all tanks, and performance of designated irrigation areas.
  
• Have your disinfection chamber inspected tested and cleaned quarterly to ensure correct disinfection levels.
  
• Keep a record of pump outs, inspections and other maintenance.
  
• Learn the location and layout of your AWTS and designated irrigation areas.
  

• Don't switch off power to the AWTS, even if you are going on holidays.
  

All copy and graphics in this website are Copyright © 2005 by Busy Bee Wastewater.  All party's wishing to use material from this website must obtain prior written approval from Busy Bee Wastewater.