One of the benefits of embracing ecological realities in business, are the opportunities presented by the new perspectives required. One such example is anaerobic digestion as a power generation strategy. I have toured two different facilities, with two different approaches, and utilize different waste streams. Capitalizing on waste is not a new concept, heap leach mining for example is used to reprocess discarded tailings in order to extract more gold ore.
Unlike extractive efforts, the processes involved with anaerobic digestion solves more problems than it creates. AD focuses on either food and other organic wastes (Dry) or house hold waste water (Wet). The Dry AD facility was located on a household waste management transfer site, where it generated ten percent of the facilities total power consumption needs while diverting less then 1% of available appropriate waste. (lots of room for expansion). The wet system I toured was located at a waste water treatment center, and wasn't generating at the time, but once repaired, could significantly reduce the facilities total power consumption.
Using a process not dissimilar to traditional organic composting, Dry AD harvests the gases produced through normal decomposition. Some technological solutions are used to create an air tight vessel and to distribute dairy farm waste over the top of the heap to facilitate more complete bacterial saturation. But for the most part, mother nature has already done billions of years worth of research and development to optimize the system. Best of all, after processing the spent raw stock is often safe enough to reintroduce to the agricultural industry as a soil amendment.
Wet AD systems require integration with municipal waste treatment systems, and as such might be better handled by local governments. But the concept is simple, basically cap a cistern with a floating lid, and harvest the gasses as the water is allowed to settle. While designing entire systems to optimize integration would produce the highest returns, the argument that undertakings of this kind would reduce the amount of other much more potent green house gasses that would ordinarily be vented by open topped settling ponds might make energy generation a happy byproduct of environmental protection.
From a larger perspective, AD (wet or dry) as a lot of potential in the future of the green grid. The raw material is produced in houses, commercial kitchens and grocery stores by the ton every day. This raw stock is currently incurring a second big slice on an industrial nations carbon budget as major cities consume tens of thousands of barrels of oil every day shipping household waste away from city centers. Much of the weight they are moving is ideal for Dry AD and with only a slight change in habit for the "producers" could be diverted using existing infrastructure.
Solar power's daily cycle of production and wind power's occasional unpredictability are ideally matched to the low but constant output available through AD. AD bio-gas could also compete directly for market with CNG the compressed natural gas produced through hydro-fracturing or fracking. Other benefits would include the local jobs that would be created, as bio-gas or co-gen plants pop up in neighborhoods. These system are easily replicated and can be scaled to meet the needs of growing or mature communities alike.
It is hard not to see a win here.,