Bio-septic system offers relief for the effluent society

Out of sight, out of mind, and far too often, out of order - that malodorous monster, the septic tank, lurks just below the ground in the back yards of more than 450,000 homes around Australia's eastern seaboard, from Queensland to Victoria. Another 200,000 households around New Zealand are unsewered.

Overflowing septic tanks are a chronic problem in environmentally sensitive areas, contaminating ground and surface waters in water catchments. When storms saturate the leafy bushland suburbs around major cities, the creeks often reek from the leaks.

Environmentalist, permaculturist and inventor Dean Cameron, 45, who founded and now manages small Queensland company Biolytix Australasia, has devised a novel way of keeping raw sewage out of the environment: run it through a self-contained ecosystem in a septic tank, then network the treated effluent.

Cameron's eco-friendly septic tank came out of his studies of nature's own phenomenally efficient system of dealing with waste. He believes his eco-septic tank will turn a problem into an asset, saving local governments and homeowners millions of dollars and billions of litres of water, while creating free fertiliser for gardens, ovals and parklands.

The Biolytix system could also be a boon to Australia's ecotourism industry, and for remote Aboriginal settlements in Australia's arid interior, where lack of sewerage and water scarcity cause health problems, says Cameron.

The Biolytix system is far more efficient than either a passive septic tank or any of the new-generation aerated septic tank systems that, like large-scale sewage-treatment works, use oxygen to accelerate digestion of organic material.

That efficiency might be attractive to alpine resorts, where low temperatures limit sewage treatment rates, and there are strict controls over environmental discharges.

Cameron says that normal septic tanks and sewage-treatment works rely principally on a community of microbes to digest relatively small amounts of organic matter suspended in an enormous volume of water.

"Wastewater treatment plants struggle to deal with a tiny amount of organic material - typically, around 1 per cent," says Cameron. "It takes a lot of energy to pump all that water around and aerate it.

"Historically, nearly all sewage-treatment systems have gone the aquatic route, yet it makes no sense.

"In nature, every tree drops many kilograms of litter onto the soil each year, where it is processed to humus without odour, with little water, and without mechanical aeration."

Cameron studied how soil and aquatic life forms conspired to perform this magic, and re-created nature's own system in a septic tank.

His system works in air, not water, and where conventional sewage-treatment systems play with only the low cards from the biological pack, the Biolytix system deals out a full royal flush.

The tanks are pre-installed (or existing septic tanks can be retro-fitted) with a fixed medium incorporating a complex community of both macro- and microorganisms, spanning multiple trophic levels, from decomposers through grazers to top predators.

At the micro-level, bacteria and actinomycete fungi and do the primary digestion, and in turn, nourish protozoans, and single celled algae, including rotifers.

These microbes in turn nourish an array of grazers and their predators, such as leeches, flatworms, earthworms, and arthropods, including collembola, pronurans, mites, flies, tardigrades, and copepods (water fleas) and beetles.

Snails, spiders, and even the odd lizard or frog washed down a gully trap or flushed down a toilet, join the feast, and with time, says Cameron, each tank will develop a unique, troglodytic community of pre-installed and locally recruited organisms.

The "dry", or more correctly, moist, environment accelerates decomposition of organic material by at least a factor of two over a conventional septic tank, says Cameron. It also rapidly digests vegetable peelings and other household scraps processed through an "insinkerator".

The clear liquid effluent contains about 20mg/l of nitrate, around 12mg/l of phosphate, depending on what detergents are used in the household, and variable amounts of potassium. It can be used to irrigate gardens, and Cameron has used it successfully, undiluted, as a hydroponic nutrient for growing vegetables, herbs and strawberries.

Neighbourhood network

Aerated septic systems produce the same effluent, and householders buy them for the advantage of irrigating gardens or lawns with ready-made liquid fertiliser. But excess effluent can be a problem in winter, or after heavy rainfall saturates gardens and lawns.

Cameron says the Biolytix system solves this problem by linking households together into a neighbourhood network; small pumps on each property can deliver excess effluent to a central storage point for irrigating community parklands or ovals.

"The most economical cluster size is around 1000 homes, but it could be adapted for a township of 100, or a city of 20,000," he said.

"Conceptually, it's like the shift from a mainframe computer to a distributed PC network. It's a lot cheaper to install and operate an individual treatment plant, and have a small connection to a network that operates somewhat like a modem, storing the effluent offsite if the need arises."

He says Sydney Water has a multi-million dollar program to provide sewerage to a huge backlog of unsewered homes in the Sydney area, to protect its catchment areas. Bega, the largest town in the state's south-east, has 2000 unsewered homes.

Cameron has developed his Biolytix system over the past seven years; he has patented it, and two years ago took on a South African partner who has helped its commercialisation with a $2.5 million capital injection.