Onsite wastewater treatment
in Greener Homes on 6 February 2011
Homeowners in unsewered areas can choose greener systems than septics.
MANY years ago, John Eldridge decided to retrofit the septic tank on his Red Hill property with a worm farm treatment system. The system, made by A & A Worm Farm Waste Systems in Hastings, works the same way as the forest floor, he says. “In the forest you’ve got all sorts of things dropping out of the trees – twigs, bird poo, the odd dead bird – and the water that falls is filtered through it.
“At the top of the pile the material is coarse, but as it moves down it is broken down more finely.”
His worm farm mimics the natural composting process. “The material disintegrates in the liquid. We never need to pump it out and there is absolutely no smell at all,” he says. “We noticed a huge difference.”
Septic tanks are still the most common wastewater system in unsewered parts of Australia, but they don’t actively treat the wastewater to remove pathogens. The effluent must be disposed in trenches more than a foot deep, and the tanks regularly pumped out.
Like a septic tank, Mr Eldridge’s worm farm is classified as a primary treatment system.
Sarah West, from Environment Protection Authority Victoria, says secondary treatment systems are best for recycling the nutrients found in wastewater, by way of sub-surface irrigation. There are many kinds available, including aeration systems, reed beds, sand filters and trickle filters and some worm farms.
“With any of those higher quality secondary treatment systems, you are permitted to irrigate the effluent through the garden in the topsoil layer, where plants reuse the nutrients in the water,” Ms West says.
“Those nutrients are a resource, but septic tank trenches are too deep in the soil for most plants to access them.”
If you are planning a wastewater system in an unsewered area, Ms West suggests you first consider how you’d like to reuse the treated effluent. “Do you want to irrigate the garden, or use it in the home for toilet flushing?” she asks. “To recycle it back into the house, you need to choose a greywater treatment system approved for toilet flushing.”
But if you just want the treated water to irrigate the garden, you can use an all-waste method such as those listed above. Be aware that you must only use an EPA-approved onsite treatment system, and must obtain a permit from your local council.
The various technologies have very different ongoing costs. “Find out how often the system has to be serviced and how much electricity it consumes,” Ms West recommends. “Ask about the cost of spare parts and consumables – some need chlorine tablets or a new UV lamp every year.”
In Red Hill, Mr Eldridge opted for the worm farm system because it requires minimal ongoing maintenance and no chemical additives, and uses little power. “We have a small pump at the bottom of the tank, but it doesn’t run for very long,” he says. “The other advantage for us is that we can put any other organic matter in there, so it is an easy way to reduce our waste to landfill.”
The worms chomp through black and greywater, together with organic material such as vegie scraps, paper, cardboard and garden clippings. For a typical three-bedroom house, a new system costs about $8000 to $9000, including installation.