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Ethanol from Rice Waste
Biofuel from plants could be a remedy to expensive petroleum products, but making it out of food crops poses problems emphasized by the current food crisis. Food prices hit record levels this year. A third of the increase, estimates the International Food Policy Research Institute in Washington, DC, is due to increasing demand in the US and elsewhere for maize (corn) to make ethanol for fuel. Increasingly many voices say that this imbalance should stop. There should be a moratorium on using food for fuel, as world food production is not enough to feed us all and at the same time to make fuel as well. For example, even if the US turned its entire annual maize crop into ethanol, it would barely supply 15% of the nation’s current petrol consumption.

With the advent of increasing crude prices worldwide, the search for alternative fuel has been booming, especially producing alternative biofuel from corn and sugar cane. However, there is now a re-allocation of both crops since they are forced to be redistributed for food and fuel production. Even now, land is being diverted from food production to fuel production.

It is no longer just a dream to make ethanol from cellulose, the main component of plant cell walls, which humans cannot digest. The planet produces 180 billion tonnes of cellulose per year, making it the biggest reservoir of carbon fixed into energy-rich organic molecules. Much of the biomass produced on farms is abundant in cellulose – rice straw alone accounts for half of the world’s farmed biomass – and other potential sources such as switchgrass can be grown on land that will not grow food.

Much innovative research is underway to use the tough inedible plants, or parts of plants, to produce fuel. In the past, this has been an expensive, multistage process.

That could change though, says one expert, if we produced genetically engineered fuel plants that make their own cellulose-digesting enzymes – a bit like oil that refines itself into petrol.

A promising approach is to employ a mixture of micro-organisms to produce bioethanol through a process called “cellulose degradation” on rice straw. Rice straw is a by-product of agriculture and is not used directly for food and most of the time it is burned or fed to the animals. The discovery of the potential of bioethanol from rice straws is timely.

The main barrier to making cellulosic ethanol profitably is that the cellulose first has to be broken down into sugars that can be fermented to alcohols.

Bacteria and fungi that attack wood and other plant matter convert cellulose using enzymes known as cellulases.

Currently, to make cellulosic ethanol, bacteria are genetically modified to produce cellulases and are then cultured in large tanks. The cellulose enzymes are then used to convert the cellulose in plant material into sugars, which can finally be fermented into ethanol fuel.

But this is an expensive process. Instead, why not put the gene for the enzyme into the biofuel plant itself?

The enzymes are stored in a cellular compartment away from the cell walls. Processes can produce enzymes that will only break down the cellulose when the plant is ground up and heated. The advantage is that it takes much less energy to produce the cellulose-degrading enzyme by growing it in the fuel plant itself than by brewing it in a tank. The enzymes have already been cloned into rice plants.

Rice straws have the potential to produce 205 billion liters of bioethanol per year. It is a source that does not directly influence the price of the rice itself as a food.

As an exampe, in 2007 in the USA, Arkansas produced over 4.5 million tons of rice, about half of all domestic rice production. Approximately 19 percent of Arkansas’ rice, or 900, 000 tons, consisted of rice hulls. Those hulls sell for up to $ 40 a ton, based on their use.

An estimated 108, 000 tons of rice hulls are bought annually by Arkansas poultry growers. Rice hulls are mixed with pine shavings for use as bedding in poultry houses. Chopped rice hulls are used as an ingredient in cattle feed. Many of Arkansas’ rice hulls are used as a fuel to generate electricity.

“It’s a way of getting us into cellulosic ethanol fairly quickly, because we have the raw material that’s already here, already gathered,” a state official said, referring to rice hulls, the husks that encapsulate rice kernels and are removed in the milling process. Using rice hulls as a feedstock raw material, it is possible to make ethanol for less than $ 1 a gallon. Ethanol currently sells for over $ 2.85 a gallon,

Furthermore, rice consists of a very large portion by weight of silica, which is worth about 20 cents a pound, and can be used in a number of applications ranging from silica wafers for the electronics industry to photovoltaic cells for the solar industry.

Ethanol from Rice Waste