An afternoon at the poo ponds

As part of a work training course, I spent quite a while this afternoon at the Christchurch wastewater treatment plant - colloquially knowns as the poo ponds. It was actually really interesting, although quite smelly in places. I have never before seen sewage in the process of being treated, and really it is far more efficient and cleaner than I had realised. It only takes a couple of hours for sewage to be fit to release into the oxidation ponds, where it spends another 21-25 days until it's clean enough to be pumped out into the sea (not drinking water quality, but usually bathing water quality at that point).

The first thing we saw was what they call "rag" - the solid material that is present in the sewage when it arrives. Apparently it is known as the Three Ts - tissue, turds, and tampons. Mmm, nice. Anyway, in reality it just looks like a grey pulpy mess with some identifiable bits in it. We could see a shower cap and half an onion, both of which I had not expected, but nothing particularly offensive.

When the really obvious gunk has been separated out, the sewage is solidified in some sort of process that I didn't really understand, but it starts out looking like brown water and a couple of metres further on the conveyor belt it looks like this - lumpy sludge.


We saw various other bits and pieces, including one section that was so pungent that I was nearly sick on the way out. It wasn't a sewage smell, exactly, but it was really hard to ignore and really unpleasant to breathe. (We didn't visit the smelliest part, which can make a person pass out very quickly, so I can only imagine how much worse that would have been.)

Outdoors, there were various settlement ponds for separating liquid from solid, and another conveyor belt thing that dumped the final solid result into a big pit. It is currently being put onto a closed landfill as a capping/fertiliser layer, but once that landfill is capped I am not sure what will be done with it.

The whole plant uses just natural gravity and microbes and oxygen and sunlight to clean the water and remove the dangerous material and the pollution. Also, it uses naturally produced methane gas to convert to electricity and power the entire plant, and usually generates enough to sell back to the national grid as well. It may not be everybody's idea of a fun afternoon out, but I found it both interesting and educational!