On Site Waste Water

We design wastewater treatment and land application systems for residential use.

We can work with conventional technology like septic and AWTS.

We also use more innovative methods like reed beds, compost toilets, greywater diversion and using waste water for home crops.

To read more about how we design for water, check out the blog topic “22 water conservation techniques”.

If your land can’t be connected to council sewer, then waste water needs to be treated and disposed of on site. Council will require a design which conforms to Australian standards. Designs are site specific, considering the dwelling capacity, terrain, soil and surrounding water movement.

On site waste water regulations have toughened over time, so many systems that were allowed in the past will no longer cut it. It’s common for people who extend their house to get a nasty shock when council requires a new or dramatically upgraded system.

Primary treatment

The good old (sometimes not so good and sometimes too old) septic tank. Household wastewater goes to septic tank and then to sullage trenches. These are relatively simple and cheap. To get approval these days they require large areas of favourable land with fairly good soil, well away from water courses or ground water.

Secondary treatment

If any one of the above factors (land size, slope, soil type, proximity to permanent or ground water) is unfavourable, further treatment is required. This involves an intermediate step between the septic tank and sullage trenches – secondary treatment. You can use an AWTS or reed beds.

AWTS

(Aerated Wastewater Treatment System) is a series of chambers, pumps, filters, perhaps chlorinators within a big plastic unit. There are a range of brand names, e.g. envirocycle. They have high running costs due to power use, replacement parts and a compulsory maintenance contract with the agent costing $600- $1200/ year.

Reed beds

A reed bed is a gravel filled tank with plants. The outlet pipe is well below the gravel surface, so the top of the reed bed is dry and mosquitoes should not be an issue. Treatment is mostly through the biological action of bacteria and micro organisms hosted by the aquatic plant roots. Although the reed bed ecology is vulnerable to toxic agents, so to is an AWTS, as both systems rely on bacterial action. An advantage is that compared to AWTS, it is a simple system which is far cheaper to run and maintain. I usually recommend reed beds instead of AWTS.

Black water

Is faecies mixed with water, produced by a flush toilet. Primary treated black water requires sullage trench disposal areas approximately three times the size of secondary treated black water.

Grey water

Is all other water – bathroom, laundry, kitchen. It is approximately the same quality as secondary treated black water.

Compost toilets

Believe it or not, this is the most progressive form of on site waste water treatment because there is no black water. No toilet flushing means reduced water consumption and less land required for on site treatment. The ideal system is two large (at least 1 cubic metre each) chambers rotated as a long period batch system. Unfortunately there is no commercially available unit like this. The best alternative is a pair of Clivus Multrum units. They include large, compartmentalised chambers with baffles and small fans.

This system requires an allowance in the bathroom design for plenty of space in plan, under floor and accessibility for emptying.

Using grey water in the garden

In NSW, you are allowed to divert greywater to a garden without council approval or a plumber, provided a range of conditions are met. The conditions include; greywater must be delivered sub surface, not affect neighbours and not be stored in a tank. For the full set of conditions, google “Local Government (General) Amendment (Domestic Greywater Diversion) Regulation 2006”.

Sullage trenches

If soil is OK and slope is less than about 20%, sullage trenches are an economic form of “land application” (where the waste water ends up). These are level, gravel filled trenches topped with geotextile fabric and about 20cm of soil. Plants are active in absorbing and transpiring water, so an open, sunny location is best. Crops can be strategically located for uptake, but don’t plant so close that root systems invade and block or puncture the trenches. Also avoid blocking solar access to the trenches. Directly on top of the trenches is usually grwon grass, which could be cut in cycles and used for mulch. On the south side of trenches you could plant hungry crops like citrus, banana, lychee, macadamia, jakfruit, sugar, jaboticaba, coffee, pumpkin, zuchini or mulch crops. Root crops aren’t recommended around trenches for health reasons.

Many trenches fail because they are driven on by a vehicle. Even a ride on mower can ruin a trench and will certainly compact the soil around the trench such that absorption is restricted.

Sub surface dripper irrigation

Steeper slopes or shallow soils require dripper irrigation. These are more complex, expensive and have some issues. By law the drippers must be buried, making them vulnerable to clogging and hard to inspect. A pretty toxic herbicide is added to the water to stop roots blocking the drippers. Ants shove particles in the dripper holes regardless.