The theory is simple and persuasive: biomethane can replace natural gas in homes and factories, bioethanol and biodiesel can replace fossil fuels for transport and biopower can meet baseload electrical demand. Realising these possibilities would drastically reduce dependence on (often) imported fossil fuels, improve energy security, create local jobs, and most importantly reduce greenhouse gas emissions. So, why the slow uptake?
Spelled out the issue and methodology seem simple, the reality is that cost issues and unwillingness to test new waters still remain as potent obstacles. Strong investment over the last decade has reduced production costs and industry has naturally concentrated on the simplest processes and cheapest raw materials, to ensure the highest profits.
This has largely meant crops producing sugars and starches (used by plants to 'burn' and store energy respectively), competing directly for land against food crops.
And therein lies the problem, since producing ethanol from starch (for example from corn) often uses natural gas to heat the process, so may hardly reduce greenhouse gas emissions at all.
Insensitive biomass removal in various parts of the world has also degraded soil fertility, reducing wildlife diversity and habitat, silting streams, causing flooding, and degrading water quality.
So the easiest, most profitable route happens to be little better for the environment than burning fossil fuels. Luckily as it turns out, biofuels have, over the last couple of years, been struggling against fairly low gas/diesel and high corn prices.
Idle first-generation biomass plants
California has set aggressive renewable and low carbon energy targets, part of which includes ambitious targets to produce its own biofuel. Production has concentrated on ethanol from Midwest corn grain along with biodiesel derived from waste grease, tallow, palm oil and other imported oils. Through most of 2009 and 2010, though, the ethanol and biodiesel production capacity was mainly idle from lack of demand.
To-date the demand is still not there, but the state is not rethinking its basic strategy. A 2011 draft Bioenergy Action Plan by the California Energy Commission recommends restarting idle plants, increasing production at other facilities, and building more.
The report concentrates on making its processes as a whole more efficient. For example, it aims to reduce the high costs of feedstock collection and transportation. That means bioenergy plants using multiple fuels, and being integrated with biomass collection, processing, and treatment. Small bioenergy projects will be located near forest biomass sources, waste disposal or biomass combustion sites to reduce treatment costs.
The action plan also stresses the need for next-generation technologies like cellulosic ethanol production, and could build up to 18 biorefineries.
Second generation biofuels don't compete against food
Cellulosic ethanol is the great hope for second-generation biofuels. It can be produced from a variety of materials including wood (woodchips, tree cuttings, paper mill residues), grasses (lawn grass, switch grass, miscanthus), dedicated energy crops, municipal paper waste, agricultural waste (sugarcane and corn crop residues), and other urban processes. It - potentially - solves the basic problem of sugar and starch based biofuels as it need not use food producing land and it does actually reduce greenhouse emissions - the US DoE calculates an 85% reduction over regular gasoline.
The issue with cellulose is that processes may not be able to compete in the long term. Cellulose needs more processing than corn and cane sugars to produce the simple sugars that are needed for efficient fermentation. Early commercial experience has not been encouraging, with early plants using more energy than they produced, or closing before they actually produced any ethanol.
Processes are continually being developed, though, which could yet play a major part. At the top of this list are gasification and hydrolysis.
Gasify or hydrolyse?
Feedstocks can be gasified - in effect partially combusted - into a CO/H2 synthesis gas, which is usually catalysed to produce the ethanol or other hydrocarbons. Choren's Carbo-V Fischer-Tropsch process can produce heat, power or transport fuels. The company's ethanol plant in Freiberg, south Germany, produces around 15,000t of biomass-to-liquid fuels year.
Hydrolysis is more widely used, and often broadly parallels the processes in the stomachs of cows and sheep to break down cellulose into sugars. Feedstocks are physically or chemically pretreated (cf. "chewing") to make the raw materials available to the hydrolysing enzymes. These can be fermented by yeast to produce ethanol, much as sucrose is fermented to give the ethanol in beer. Then, it is distilled to concentrate the ethanol.
SunOpta was an early player, but in late 2010 sold its fibre preparation and pretreatment to Mascoma Corporation. Mascoma is now building a 200 million litres a year wood-based cellulosic ethanol refinery with oil refiner Valero. It will use selectively harvested hardwood pulpwood.
Iogen Corporation uses a modified steam explosion pretreatment to increase the surface area of the plant fibre for the enzymes. Fermentation and distillation gives a yield of more than 340l of ethanol per ton of fibre. The lignin generates steam and electricity and so eliminates fossil fuel heating.
A wealth of possible processes
Bacteria, fungi and algae can all usefully hydrolyse. Feedstocks with high moisture content like dairy residues, animal manures and municipal solid wastes are already widely treated by bacteria using anaerobic digestion to produce methane biogas (although much of this is now wasted by being flared). Integrating anaerobic digestion with biorefining could reportedly produce nearly 8 billion litres of ethanol a year in the US alone.
Microalgae ('oilgae') are particularly interesting, with most algae using photosynthesis to produce oils. Oilgae promise to be more productive than other biofuel crops, and don't take up arable land or forests. They even have byproducts like plastics and cosmetics. That is actually a problem - they are so versatile that they are mainly being used for high-value products.
There are thousands of species of algae, and so a huge number of possible processes and many small start-up companies involved with R&D. California based Solazyme grows microalgae in the dark, converting plant derived sugars using standard industrial fermentation equipment. It accepts a wide range of feedstocks including cellulose, and can produce biofuel formulations virtually to order.
The potential rewards are huge, but risks are also high. One early promising startup, GreenFuel Technologies, developed a process to remove carbon dioxide from power station exhausts by bubbling the gases through algae and seawater. The company closed down in 2009, as a victim of the economic crash.
Will it all help?
Even if cellulosic ethanol is commercially viable, the much more serious question is whether we can produce enough feedstocks without stripping the land bare while doing so. Humans have always used biomass as a form of energy - usually by burning it. We've just never used it on such a scale.
Biofuels are best when they use waste from other processes, and agriculture and forestry residues (particularly from paper mills) already widely generate CHP. Specifically grown crops need water, pesticides and fertilisers, and harvesting them can lead to soil erosion.
Some crop residues must be left in place to protect land from erosion and to maintain organic carbon in the soil. In the US, the Department of Agriculture's Renewable Energy Assessment Project is for example studying harvest rates for corn stover, and how much residue must be left to maintain soil quality. Similarly, clearing dead trees from forests may help to prevent forest fires, but also reduces biodiversity since many species depend on them. Crops like miscanthus and switch grass are also invasive species which can themselves reduce biodiversity.
One of the most serious potential problems is hardly discussed: successfully refining biofuels on a huge scale will need significant genetic engineering advances. We cannot know the effects of the inevitable release of genetically engineered enzymes, bacteria, fungi and algae into the wild without prior testing. Having many small start-ups involved in the R&D only multiplies the dangers. Biomass projects need honest risk and life cycle evaluations, but these cannot be left to individual companies. Whatever 'the market' is good at, it is not good at protecting the environment.