We spend a large amount of money of treating organic waste—sewage—so that it is safe and non-polluting so that it can then be released back into the water system. There are a variety of ways in which this treatment happens but the main technology is bacterial oxidisiation. Essentially a sewage plant is system for producing a large surface area of water and pumping oxygen through that water.
But should we be treating sewage as waste? It could be considered to be a resource, in the form of a GeneratingSewageSystem. There is already signficiant work being performed on developing AnaerobicDigestionPlants, and BacterialFuelCells. These work on pretty much the same principle as a traditional sewage system; but, by excluding Oxygen, large amounts of Methane and Hydrogen are released.
One of the nice things about this idea, is that it can be implemented in a migratory fashion. Obviously, we already have a lot of sewage and a mature sewage system as well as sewage treatment plants. A AnaerobicDigestionPlant is actually fairly low tech 2, the BacterialFuelCell only somewhat more so. These could be added to existing sewage plants, taking as much sewage as they are capable of dealing with, while the rest is released to existing capacity. Over time, more Anaerobic capacity could be added. Further more, productive use of the Hydrogen and Methane produced, would be straightforward enough. Most sewage systems are near to towns or cities, so the existing domestic gas system could be used; again, over time, more capacity and electricity plants might be added.
As it stands, this is not a bad idea, but it has a more significant implication than just recovery of Energy from sewage. If we turn waste into a useful resource, we also turn that sewage system from a waste removal system, to a resource redistribution. Considered in this way, we can now do something that would otherwise be perverse; we can artifically produce more of it.
The average house produces quite a lot of non sewage based organic waste. In the US, waste disposal units are quite widespread 1, while in the UK, they are not. If we were using a GeneratingSewageSystem, these would be more widely encouraged, because instead of pointless landfill sites, we would now be getting useful Energy out. For those areas where the sewage system were good enough, as well as house hold waste, garden waste might be added, although a fairly good chopping system would be needed for anything larger than grass.
Even here, though, we are still recycling waste. However, it could be produced using a BioFuelReactor. In most cases, this might be quite a large amount of apparatus, but it could also be small. Think of a house with a small system on the roof through which water drips and algae come out the other end. In general, this system would not produce a huge amount of energy and the material might not be worth collecting. However, if we can just drop the algae straight into the sewage system, there is only a small additional capacity cost. But now, potentially every rooftop because a SolarPower generating system. All with few moving parts, few chemicals and augmenting a system that already exists.
This system is particularly nice, because it's a good example of a MicroGeneration scheme, which I think is going to get increasingly important as time goes on.
1. Actually, waste disposal units are not present throughout the US. They are illegal in some states or cities. I suspect that this is because in some of the more densely populated areas, the sewage system can't cope with the quantity or get blocked.
2. This is a good thing! Low tech is often cheap, reliable, and easy to produce in bulk.