Marty McFly: "Wait a minute, what are you doing Doc?"
Doc Brown: "I need fuel!"
At the end of the 1985 film, Back To The Future, Doc Brown famously starts picking through Marty McFly's trash for materials to drop into a Mr. Fusion device attached to a DeLorean time machine. The Mr. Fusion is used to generate the 1.21 gigawatts of electricity needed to run the flux capacitor and the time circuits for the time machine so that the doctor no longer has to steal plutonium from the Libyans. In other words, the makers of Mr. Fusion have figured out how to convert common garbage (matter) into energy. Sadly, the engineers of the world have not yet given us Mr. Fusions to power our time machines or our toasters or anything else.
While we cannot convert any old matter directly into energy, however, some innovators have been working to make the most of the easily-available energy resources in what would otherwise be common waste matter, and they are using bacteria to do the work.
Sharp's Brewery in Cornwall, UK, is currently installing an anaerobic digestion system that will use bacteria to convert the brewery's liquid waste into power and keep it from pouring into the local water treatment plant. All that liquid wastewater will be diverted into a "digester" tank where anaerobic bacteria (the kind that don't need oxygen) will eat the organic material in the water and produce loads of biogas. Generally, anaerobic digesters are useful simply for their ability (like big composters) to break down waste matter and recycle nutrients. Because the brewery is using anaerobic digestion to deal with its waste matter on a large scale, the biogas produced can be collected and used like natural gas to provide heat and energy. According to Brian Scheffe, associate director of H2OK Water and Energy, the company installing the system, 300 cubic meters of brewery waste per day should generate more than 1300Nm³ a day of biogas.
Biogas produced in anaerobic digesters contains high amounts of methane (50%–80%) and carbon dioxide (20%–50%), along with trace levels of other gases such as hydrogen, carbon monoxide, nitrogen, oxygen, and hydrogen sulfide. Methane is the major component of natural gas, and when biogas is burned, the number of BTUs it yields depends on the percentage of methane it contains.
Dairies are another source of liquid waste that is well suited for anaerobic digestion. BV Dairy in Dorset, UK has a system for processing the liquid residues and food waste from the dairy's food and drink processing sites. When the dairy makes cheese, for instance, the whey heads into a digester, where anaerobic bacteria are kept at the optimum temperature to happily convert the particulates into biogas. Not only is the dairy cutting down on its sewer costs, it is generating energy that can be used on site.
Waste management systems that harvest biogas can be useful in a large number of sectors, including HVAC, food, chemical, pharmaceutical, and municipal water supply.
Converting Carbon Monoxide:
LanzaTech, a company based in New Zealand, specializes in converting factory waste emissions to biofuels and biochemicals. Anaerobic bacteria come into the picture again, this time using a gas-liquid fermentation process to create ethanol from carbon monoxide emissions.
In large amounts, carbon monoxide is a harmful gas that will attach to hemoglobin, preventing it from carrying oxygen through the blood stream to the cells. LanzaTech technology captures the carbon monoxide before it escapes from steel mills, factories, or oil refineries and pumps the emissions into a bioreactor mixed with liquid and nutrients. Bacteria feed on the mixture, producing ethanol, which can be used as a fuel. LanzaTech is also working to produce jet fuel from industrial waste.
Gas From Seaweed:
Move aside corn. A young biotech start-up called Bio Architecture Lab is working to produce energy from brown seaweed. The company uses a designer strain of E coli to produce ethanol from the sugars in macro algae from the ocean. Not only does seaweed cost radically less than corn to grow and harvest, but according to the company, the seaweed can also yield 1500 gallons of ethanol per acre– three times as much as corn.
One major difficulty with using seaweed as an energy source is that it produces a significant amount of alginate, which most bacteria cannot digest. In fact, there are only a few ocean microbes that can metabolize this specific sugar. To deal with this problem, a team of Bio Architecture Lab researchers did a bit of genetic engineering to take genes from an ocean microbe that metabolizes alginate and spliced them into the genetic code of E coli so that it too can digest alginate and produce fuel. Depending on its exact genetic programming, the E coli could be used to produce ethanol or jet fuel or butanol.
While we often associate bacteria with stuffy noses and sore throats, these vital one-celled creatures provide a host of necessary benefits and allow life on Earth to persist. They aid in digestion and produce important nutrients in our guts, they give us wine from grapes and cheese from milk curd, and they break down our garbage so that it doesn't pile over our heads. What's more, as they digest our waste, their own waste matter can be collected to produce fuel for our heat and energy needs. The world may have high energy requirements and no Mr. Fusions available just yet, but when oil supplies run low – at least we still have bacteria.