A Filter in Sheep's Clothing

A while back I bought two large bags of sheep's wool for £1 each from a farm just outside of Bath, intending to try using them as filtration media for the pond. I finally got round to using some of one bag.

The problem with raw sheep's wool is that it's a) full of lanolin, which is a form of grease that I don't want sitting on top of the pond, and b) it's contaminated with the odd bit of sheep poo, which I also don't want contaminating the pond. The fleeces don't fetch much on the open market these days, so that's why they're so cheap.

Not having an industrial washing machine, I looked up how poor, Scottish crofters used to clean their wool before it was sent to market. Apparently they trod it like grapes in either huge vats or running water in a stream. Had I been downstream of the locations these were washed, I certainly wouldn't have wanted to use the resulting water for domestic purposes.

Anyway, I put a bag of wool in a large tank I have, applied a bit of washing up liquid and then trod it for a while, with the garden hose playing over it.

It came out fairly clean, although I smelled a bit sheepish myself. Adding more washing up liquid and treading for longer would have resulted in the wool felting, where the fibres interlock, which is not necessarily a bad idea, as it would form a natural mat.

I transferred the reasonably cleaned wool to the top box of my test filter and then put the pump outlet hose into it. Being finer than the plastic filter I originally had in the box, the water started to back up and threaten to overflow; however, the level of filtration was excellent.

The overflow problem was solved by simply making the holes in the bottom of the top box larger and adding a few more. Wringing out the wool will be a bit more difficult than wringing out a plastic mat, but as I said, if I felted the wool it would be much easier to wring out.

There again, wool is biodegradable, so I could merely put the algae soaked wool in the compost after having used it for a week or two.

I also managed to get on the large filter tubs into the filtration shed, but God alone knows how I'm going to support it.

The pipework at the very bottom has to be clear of the floor so that the effluent can be decanted every week or two, and the only way I can think of doing it (bearing in mind the tub will be full of water) would be to use breeze blocks. I will probably also need to slide some bearers under the shed in way of the tub. If necessary, I can remove a section of the floor to have the breeze blocks on the concrete pad.

The really difficult operation will be marrying up the pipes from the large pump I have to the inlet on the tub. The outlet won't be too much of a problem, as I'll merely use the same sized pipe as the outlet - which is at the top, which will be gravity fed back to the pond.

To prevent any chance of overflow, I will insert the UV-C system lower down than the outlet (its capacity is lower than the capacity of the pump), so the majority returns to the pond via the UV-C system and the tub outlet will take the rest. The combined exit capacity to the UV-C and the top exit will be greater than the input, preventing any overflow.

Of course, the entire system will have to be drained down over the winter to prevent freezing, but the algae production over winter is zero anyway due to the short daylight hours and the cold.

Watch this space.