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From the beginning we had intended to treat our own wastewater onsite, and commissioned an initial design that proposed three aerobic onsite systems using bioculture and natural media, each one to cater for around 10 houses.
However, when we sought initial approval for this scheme from WaterCare Services, the regional water management body, they opposed our application on the basis that the wastewater infrastructure was already in place.
[link to submission and appendices for more detailed info].
While not having a right of veto to the proposal, WaterCare's opposition meant that, even if we had achieved Resource Consent for the proposal, it was likely that they would challenge this through the Environment Court, a very costly and time consuming process.
By very good fortune, the 3 closest connections into the council sewer system were very near the proposed locations of the 3 on-site systems. We therefore chose not to incur delays and huge expense by seeking approval for onsite treatment at that time, but installed a standard system discharging into the existing council sewers. However we made sure that the network of pipes in the ground is laid in positions that will make diversion to future on-site wastewater treatment systems relatively easy.
The reality, however, is that even though the concept design from the wastewater consultants proposed that on-site treatment was technically feasible, Earthsong is a relatively densely-inhabited site. Almost all the unbuilt land area is quite intensively used for recreation space or food areas, and there is very little land left for any system that would require trickle irrigation of treated effluent. Being a medium density suburban site, we also have to be very mindful of our wider neighbours, and we would need a very robust system to safely handle the waste from nearly 70 people living and eating off only 3 acres.
One of the joint-venture projects we have undertaken with Waitakere City Council's 3-waters unit EcoWater is the installation of a dry composting toilet adjacent to the common house/Earthsong Centre, to trial the use of composting toilets for relatively heavy use within the metropolitan drainage area.
The model chosen is a Clivus Multrum CM14 (0.4 cubic metres), housed in a timber out-house adjacent to the common laundry. On the north side a large glazed hatch gives access to the composting chamber for periodic mixing and occasional removal of composted material. The glazing also acts as a glasshouse to keep the chamber warm and assist the composting process, and to demonstrate the system to interested visitors during our regular tours.
One consequence of dealing with our waste on-site is that toxins can be introduced into our otherwise organically-oriented system. Anyone who is on medication, therefore, is requested not to use the compost toilet, as it will all end up in our soil.
Leaf litter is added to the toilet with each deposit. As we are still fine-tuning the optimum operation of the system, the composted material removed to date has been added to large windrow compost heaps for further composting, before being added to non-food garden areas at Earthsong.
The compost toilet is only one of three toilets available for use in or near the common house by visitors and residents. Although every house has its separate flushing toilet, some residents make a point of using the compost toilet when possible. Usage has slowly grown from an average of 86 visits per month in 2007, to over 100 visits per month in 2010. As an alternative to a flushing toilet, the compost toilet is saving 600 litres of water a month, and retaining valuable nutrients to replenish the soil.