This one caught my eye from a link sent by Bill (ngepro). A company in Portland, Oregon is recovering the energy in the sewer water. Original article here.
The basic idea is pretty simple – there’s water (and other stuff) flowing in the sewers anyway, and if you put a turbine in the pipe you can recover some of the energy you put in to pumping that water to the customers’ houses and use it to offset the energy put in.
There are maybe a few downsides to this. I know that sewers in London collect “fatbergs” where various fatty materials put down the sink from restaurants and fast-food establishments (and to some extent most kitchens) collects in large enough clumps to block the sewer. People have to go down and clear the pipes every so often and although that fat could be rendered down to a Diesel substitute it is normally just blasted further down the pipes and is finally extracted at the treatment works.
If you have a sewer turbine in the tube as illustrated, then this may end up as a centre of such blockage. Since you won’t be able to send a robot down the pipes to de-block them (they won’t pass the turbine) then things may get a little more difficult. Of course, they may have fixed the underlying problem in Portland by banning people putting fats down the sink, but once it’s done it’s going to be hard to identify the culprit.
Although I see this as somewhat of a niche application that requires specific conditions to be successful, where it’s applicable it could well be a good idea and be a worthwhile money-saving idea for the local water company.