I’ve talked before about my dislike of the modern toilet. It just doesn’t make much sense to contaminate clean water with human waste, then expend lots of money and resources treating it to remove the waste. Compost toilets are the way forward!
But this got me thinking – what actually happens to our waste once we flush it? Since I clearly have nothing better to do, I decided to do some research.
As it turns out, solids and liquids are separated by allowing the solids to sink to the bottom of a large tank, where it becomes ‘sludge’. Simply put, the water goes through a cleaning process before being returned to rivers. But I was more interested in what happens to the sludge.
According to the UK government, 52% of sludge is spread on agricultural land as fertiliser, usually in the form of solid ‘cake’. This is seen as the most environmentally friendly option, though sludge can only be used on certain crops. It’s claimed to be perfectly safe, though there are some concerns.
Another 21% is incinerated, widely recognised as being bad for the environment, while 17% goes to landfill. The disposal of the remaining 10% is vaguely classified as ‘Other’.
Further reading gave me some insight into what this might be. Thames Water apparently uses sludge to generate renewable energy, an interesting concept. They list three ways of doing this:
- Heating sludge so that bacteria eat it (anaerobic digestion). The resulting biogas can be burned to create heat and thus electricity.
- As above, but the biogas is cleaned more thoroughly and put into the national gas grid.
- Sludge is dried into blocks, which are burned to generate heat (I don’t know about you, but I wouldn’t want to be downwind of that!). The heat is then turned into electricity.
More information on the use of sludge to generate energy, including its environmental impact, can be found here.
I was glad to discover that dumping sludge at sea was banned in 1998. However, our methods of dealing with human waste still seem a bit dubious to me. Do you think the current system is a sensible one? Should we be composting our waste instead? Leave a comment below!