Liam talks sh*t: composting toilets for Wellington?

Liam talks sh*t: composting toilets for Wellington?

Today, we (mostly Liam) presented to the Wellington City Council Strategy and Policy Committee, to make the case for composting toilets to be considered in the Long-Term Plan. Don’t worry, we weren’t proposing that the Council do away with the flush toilet sewage system, but that the Council think about supporting research into some more resilient and ecological approaches to toileting that could help take pressure off the system. Our case is that there is a need to take source separated, decentralised systems seriously – fund the work and you never know what you might find.

Have a watch of the presentation here. It’s ten minutes long and starts at around 29:00. To get a bit of background about why The Rubbish Trip is talking about sludge and composting toilets, scroll down to below the video…

Why is sludge and composting toilets an issue for zero wasters?

You may or may not be aware that Wellington’s Southern Landfill is filling up fast, and so an extension into the valley behind (Carey’s Gully) is on the cards. The area is a Key Native Ecosystem, a stream will need to be diverted underground through piping, and habitats will be displaced, all in the name of our capital city’s rubbish.

Part of the reason for the pace at which Wellington’s landfill is filling up is that the landfill accepts “‘sewage sludge” (the surprisingly non-euphemistic term for all the solids extracted from the City’s wastewater after it’s gone through the treatment process).

The long and the short of it is that most Wellingtonians use a flush toilet, i.e. we poo into potable water. When we flush the toilet, the poo and water begin their journey through the underground highway of pipes to the wastewater treatment plant (Moa Point). At Moa Point the ‘biosolids’ are extracted from the water. These biosolids then get put back into more water to be piped on the next phase of their journey to the landfill (ALTHOUGH when sewer pipes break, as happened in the first half of 2020, biosolids/sludge must be trucked to the landfill overland in what locals affectionately call “turd taxis”). Upon arrival at the landfill, the sludge then goes through another dewatering process at the Southern Landfill before being landfilled.


Wellington landfills 15,000 tonnes of sludge a year. The thing is though, the sludge can only be landfilled with a 4-to-1 ratio of general waste to sludge, as this is required for stabilising the landfill. So, the Council needs to find lots of waste in order to landfill the sludge – 60,000 tonnes of waste, to be precise, which is the exact amount of waste that Wellington landfills each year…

What this means is that the continued landfilling of sludge goes directly against wider attempts to minimise waste in Wellington.

There’s no two ways about it, to solve the landfill problem, Wellington has to solve the sludge problem.

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