Report of the 6th National Conference

A trial of biological treatment system in an Aboriginal community in coastal NSW

Page last updated: 07 July 2008

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James Allwood, Tim Short and Tait Farram, Aboriginal Environmental Health Branch, NSW Health, Greater Southern Area Health Service Merriman's LALC, SEC health.

James Allwood

Good afternoon and on behalf of colleagues I would like to acknowledge the traditional owners of the land on which we meet. I would also like to thank the conference organisers and all of you for the opportunity to present today in this beautiful country. I hope to take the rain back to southern NSW when I go as it so green here. This is my first national conference, and it is great to come here to network with new people and particularly catch up with old friends. This afternoon we are going to talk about a trial of biological treatment system in an Aboriginal community in coastal NSW. I will go into the background of the trial and my colleague, Tim, will go into what a biological system is, and a little bit of the methodology of the trial. Tait is going to look at some of the results we got from the trial, and draw some conclusions from there.

Background:

  • Discrete Aboriginal community with 32 homes located on the south coast of NSW.
  • Currently all homes rely on septic tanks and onsite disposal.
  • The community has a known history of poor onsite sewage management due to a number of reasons, such as topography. The community is on a ridge line. The slopes on which the houses are built are extensive, soil quality isn’t conducive to onsite disposal, and there are loadings issues, ie, the community has a reticulated water supply.
  • A reticulated sewerage supply has been proposed by government on a number of occasions over the last decade, but it hasn’t come to fruition.
During the Housing for Health Project carried out in the community in 2005 to 2006, it was reaffirmed that the current onsite waste disposal system (which are septic tanks and absorption trenches) were overflowing, and could be contributing to ill health in the community.

While carrying out the Housing for Health Project, three of the worst affected properties were considered for interim solutions using project funds to retain the existing septic tanks, and perhaps renew the land application areas.

A geotechnical report was commissioned, and quotations for the work sought. The report recommended evapotranspiration beds (due to the poor clay soils) to replace the existing failing absorption trenches.

When tenders were received it was found that costs were high, due mainly to the amount of soil that would be required to be imported and contoured. This was unfortunately beyond the Housing for Health budget, and therefore not able to be done.

At this time the local Council and Department of Commerce (DoC) were engaged with the community looking at options for a community-wide scheme that would include offsite treatment and disposal. One of the options being considered was the installation of a biological Treatment System (installed at each house to replace each existing septic tank, with the waste being pumped to off-site disposal).

In consultation with community, Department of Commerce, NSW Department of Aboriginal Affairs and Council, it was agreed to install a biological treatment system at one of the worst affected houses. This was done. The use of a biological treatment system as a trial would allow an:
  • Immediate improvement in treatment and disposal for residents.
  • Opportunity for residents of the community to view a biological treatment system first hand, and see how the system works.
  • Evaluation of a biological treatment system as an onsite waste water disposal option for Indigenous communities – looking at both treatment and disposal.
  • Evaluation of the effectiveness of the system to treat waste water prior to further treatment and disposal off-site – on a community-wide scale. This point was of particular interest to Department of Commerce, NSW Department of Aboriginal Affairs and Council, because one of the disposal options being considered is waste water from the entire community to be reused at a local farm”.
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Tim Short

“Good afternoon everybody. I think my wife summed up best what a biological sewerage system is - the poo goes in one end, the worms eat it, and you get waste water out the back end of it, so in the context of that.

What is a Biological Wastewater Treatment System? (Wet Composting Toilet):
  • Main components are a tank, filter bed, a sump in the base of the tank and centrally located pump well. It also requires an external pump for distribution to land application area which can have an alarm at the house, or be linked to a telemetry system, which means a phone goes off somewhere if the pump fails.
  • You can have further additional treatment such as UV that can allow for the waste water to be used for above ground disposal, or irrigation under the ground which is the case in this presentation.
  • What makes them different (and you probably have them in Queensland) is the structured arrangement of layers of geotextile material and media.
  • The filter bed is made up of three layers of coco peat filled modular geotextile bags, 250 mm deep, each section laid over with shade cloth. Between each layer there is a further barrier made up of agricultural drainage pipes that helps to support it, and helps to allow air to circulate around it.
  • A final geotextile filter moves suspended solids down to about 90 microns, and a sump below that is filled with agricultural drainage pipes, again to support the beds above.

Installation of the system:
  • The tank is initially inoculated with worms, beetles, mites and other soil fauna.
  • The biological treatment system and evapotranspiration area was installed in July 2006, and approved by the local shire council.
  • Design based on AS/NZS 1547.
  • LAA System is based on a peak hydraulic load of 1,400 litres per day, requiring evapotranspiration area of 400 m2 and is accredited for use in NSW. The subsurface drip irrigation lines are wrapped in a geotechnical cloth to prevent damage.
  • Our particular site, as James mentioned, was on heavy clay soil, with the initial design for up to 1000 sqm, based on a peak load of 1,400 litres per day. After 400 metres was installed we allowed for an increase up to 600 metres of lines for the land application area, and this amount was ultimately signed off by the local Council.
  • The system was designed to treat 1600 litres per day, and historic water use data indicated an average daily usage rate of 1,244 litres per day.
  • Water-saving devices were also installed throughout the house, which had about eight residents.
  • Primary focus of our work was to solve immediate onsite effluent disposal adsorption issues.

These various slides show:
  • Tank and external control box.
  • Inside the tank - inlet pipe for waste, important not to drown the worms in initial installation.
  • Servicing - about once a year, low technology, but lots of parts.
  • Not getting the results, though we were hopeful.

This is a photo of the central pump that sits inside the central well. You can see there that it is being serviced, and with this particular system this is required about once a year. As I was saying before, it’s basically coming in this side here, going down and comes back up the well and goes out there. In this particular instance we fitted a flowmeter on the downstream side of the tank, and there was also a flow meter on the house. We were curious as to what sort of difference there would be between the outlet to the house and the outlet to the tank, and initially we actually found the meter readings on the outlet of the tank were actually higher than the house. Part of this was because there’s a valve - a water rotor that splits water effluent across two line areas. Because the system is pressurised initially it comes back up, so there’s actually a valve that’s fitted there. When it reaches a certain pressure, it actually blocks off. However, after the initial installation there were some problems with that valve, and it was causing some effluent to re-enter the tank.

This is the first part of the land application - the initial 200 sqm - and you can see here what appears to be effluent actually running down the contour lines. Because it was such a slight grade (which was less than 10%) it shouldn’t have been a problem, but because the system was pressurised, there was equal distribution across that land application area. The second land application area was initially proposed down here. What actually happened was when it rained this actually created some drainage channels, and ultimately the effluent was escaping down and onto the road. This one down here was ultimately deactivated, and an additional 400 metres of irrigation lines had to be put across the slope at the back of the house.
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For what is considered a fairly low technology piece of equipment, there are a lot of bits and pieces. A full service was done a couple of months after the initial installation, and another one was done later. Again, at this stage it is probably not providing the results people had hoped for.

When we looked at what to sample for, we thought that because a tank was to be fitted to each house, ultimately the additional treatment that would be required by the Department of Commerce would be things like biological oxygen demand (BOD) and suspended solids. These are obviously important, because if you want to use the effluent above ground UV treatment would need to be fitted, or additional treatment would be required, as well as the normal parameters, E.coli, Ammonia, Nitrogen and Phosphate.

All the results were analysed at a NATA registered laboratory, and our sampling for the first six months of installation. We will continue the bi-monthly sampling for another six months. It is quite easy to take a sample, as you can see it’s just a priming pump and a container to take the sample after you let it run for a while.

Tait Farram

Results:
  • E_Coli and water usage results - only one week where the E_Coli is low.
  • Suspended solids - only passed the standard once.
  • Biochemical Oxygen Demand (BOD) - well over the scale.

Issues encountered:
  • Unusually high rainfall events resulted in subsurface water infiltrating the evapotranspiration area.
  • Consistent spikes in water usage since installation – for some periods an average daily flow > 2,000 litres per day, which was beyond the tank’s capacity.
  • Incorrect installation of drip lines led to seepages and run-off from the initial land application area.
  • High readings from test results from samples taken.
  • Grass would not grow for some time on land application area.
  • Lack of maintenance on land application areas.

Other problems that may arise:
  • Land application area may become damaged by vehicles.
  • Mowing of land application areas may not occur often enough, resulting in possible saturated areas being created.
  • Potential to overload the system as it’s connected to a reticulated water system.
  • Plastic top of tank may become damaged.
  • Homes may require extra tanks to cope with more people.
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Advantages of the system:
  • Residents were pleased there where no offensive odours released from the system, in comparison with the previous septic tank.
  • Apart from the initial, incorrect installation of the drip lines, no effluent has escaped from the land application area.
  • The system has the option of being upgraded to cope with more grey water use.
  • Once the system has been studied and tested for some time, it could prove to be a cheaper alternative for the community instead of a Sewage Treatment Plant - it is about half the cost of a sewerage treatment plant, but there are more costs associated with it if it has problems.
  • 20-year guarantee for performance and parts and requires only one service per year.
  • Manufacturer claims system costs less than $20 a year to operate.
  • Greenhouse-friendly, no chemicals and has a robust construction.

Conclusions:
  • Sampling – the system is not meeting the NSW Health CoA Standards, particularly for BOD and E.Coli.
  • Continued monitoring of tank and disposal areas is needed.
  • A system to maintain the land application areas needs to be developed.
  • Removal of waste pile to eliminate refuge for snakes.
  • Any above ground disposal or reuse will require further treatment.
  • It is good it was a trial - a ‘try before you buy’.

I would like to extend thanks to:
  • Traditional owners and Elders.
  • NATSIEH Conference organisers and sponsors.
  • NSW Health.
  • BVSC and ESC.
  • The Batchelor Institute.
  • Indigenous community involved in the trial
  • Everybody present today.

For Further Information

James Allwood
Senior Environmental Health Officer
PO Box 3095, Albury, NSW 2640
Ph: 02 6021 4799 Email: corporate@gsahs.nsw.gov.au
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