Worms for our waste water treatment

As there is no sewage system in Pahi we need an onsite waste water treatment system for both grey (all household wastewater from showers, baths, laundry, washing basins) and black water (kitchen sink, dishwasher and toilets).

Options are a sceptic tank or more advanced multi chamber oxygen based (aerobic) systems. The more advanced multi chamber systems are safer for human health and most councils will only allow multi chamber systems these days so I haven’t considered installing a sceptic tank.

The multi chamber options seem to be divided over:

  • Aerated Treatment Systems
  • Textile filter treatment systems
  • Wormorators

The price tag of the different systems doesn’t seem to differ much at roughly $12k but they work in different ways. The aerated and textile options require an electrical connection and consume energy for the mechanical aerators and pump to oxygenate the waste water or pump the water over the textile filter. When looking at an aerated system the amount of different plastic parts and chambers seemed not very robust.

In a wormorator, a colony of tiger worms, in a chamber, filters solids from the toilet waste. The leftover water is filtered and disposed of in underground trenches in a soakage field in the garden. There are no moving parts and the system doesn’t require any power. It uses natural processes and seems very simple and robust so we have chosen this system.

Naturalflow is one of the national suppliers of these systems who happen to be based close to Pahi in Maungaturoto. I know several people who have this system so it seems to be a fairly common used product up here for on-site waste water treatment.

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The system suitable for our home consists of two plastic tanks which will be buried under the surface in the garden with a chamber for black water which holds the tiger worms and a grey water tank. The soakage field to dispose of the filtered water needs to be rather large calculated at 200 m2 but can be planted with plants so will not be visible after a while. The tiger worms are bred in Cromwell on the South Island.


In our home the plumbing and water flushed toilet will be no different from a home connected to a sewer system. The only thing we should watch to keep our worms, plants and soil healthy and happy is the type of cleaning products we use in the toilets, dishwasher and kitchen sink. Cleaners and detergent high in chlorine, phosphorous, sodium or ammonia should not be used neither should toxic/strong chemicals. With a wide range of suitable products available these days with brands like Ecostore and Earthwise this should be no problem and should be the preferred product anyhow in any home.  Globally we have already surpassed safe levels of biochemical flows for nitrogen and phosphorous flows looking at the planetary boundaries assessment so a little help choosing the right products is a step in the right direction.


As we are currently preparing the drawings for building consent it still might take a while before we can welcome our new “pets” so we have to be a bit patient for their arrival and new home.


Margriet Geesink

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