Published on 18/05/2011
First Update 17/03/2017
Reuse and recycling of wastes has great economical promise. Industrial woody waste, agricultural wastes, pruned branches, bagasse and chaff can be gainfully recycled to produce Ethanol. The Technology centers round recycling, material recovery and fuel recovery. The acid hydrolysis process is used to decompose hemi cellulose to pentose with a main ingredient of Xylose. The remaining Cellulose is further hydrolyzed in presence of Sulphuric acid to hexose. Genetically modified Fungi are utilized to ferment the Pentose whereas Yeast is used to ferment the Hexose to Ethanol which is distilled. Pentose is unfermentable in its natural state but the use of genetically modified fungi enable the high yielding production of Ethanol. The basic research was started in 1989 and the demonstration held in 1996. The demonstration plant treated 4 tonnes per day of woody waste to produce 170 litres of Ethanol. On a commercial scale an 80000 tonnes per year of Bagasse treatment plant is likely to produce 10000 K.L. per year of Ethanol at an oil equivalent of 9,663 K.L. per year.
Woody construction wastes on account of various adhesives; paint etc. may have some limitations because of fungicidal properties. The technology has great promise in South East Asia and other areas where agricultural woody wastes are generated in large quantities.
Lignin is given off as waste. Lignin is a complex mixture of polymers. The molecular unit is partially aromatic with phenolic hydroxyl, methoxyl and carboxyl groups attached. It has found little use. A recent promising use is in the manufacture of Dimethyl Sulphide and Dimethyl Sulfoxide which is used as a spinning solvent in polyester yarn making. Other end uses for Lignin include as road binders for asphalt emulsions, adhesives for floor coverings, core binders in foundry practice and in the preparation of Levulinic acid. Activated Carbon can also be manufactured from the Lignins. Lignins can be removed from solutions by acidulation with either Carbon Dioxide or Sulphuric Acid.
It has been estimated that Canada could produce 5336 million litres of Bioethanol annually based on the recoverable fraction of crop residues produced in 2001.An estimated 6.22 million tonnes of Sugar can be produced from livestock manures and Municipal solids and sludges for subsequent conversion to Bioethanol. The long term benefits of using waste residues as lignocellulosic feed stocks will be to introduce a sustainable solid waste management strategy for a number of Ligno cellulosic waste materials and contribute to the mitigation of green house gases.
The Coskata Process promoted by General Motors uses a wide variety of different feedstocks to produce Ethanol. Agricultural wastes, purposefully grown crops and other waste materials like old tires and even municipal waste streams can be used with very little or Zero land fill waste. Anaerobic bacteria in a reactor are fed Carbon Monoxide and hydrogen produced by the gasification of the feed stock. The reactor is a sealed plastic tube with millions of filaments on which the bacteria live. Bacteria feed on the Carbon monoxide and hydrogen and produce ethanol. This process does not use genetically modified organisms and the microbes that are being used are not pathogenic. Being anaerobic they are poisoned as soon as they come into contact with air. The process is also less taxing on water. While other current methods of ethanol production take three to four times of water per unit of alcohol produced, the Coskata process needs less than a unit of water per unit of ethanol produced.
Coors Brewing Company, Aurora, Colorado Brewery is producing Alcohol from Beer waste. Ethanol is stripped from the waste Beer stream. They are also building a second unit to process waste biomass to ethanol. The brewing operations result in almost 87000 tonnes of brewers grains on a dry matter basis plus nine other byproducts that contain fermentable starches or some ethanol. The Biomass conversion plant will produce in excess of 4 million gallons of ethanol per year through enzymatic conversion of starches to fermentable sugars, yeast fermentation, stripping, distillation and dehydration of Ethanol. The residual wet distillers grains and solubles are utilized as cattle feed and in Dairy operations.
Star Techs Plasma Converter system contains a plasma field that reaches temperatures up to 30000 degrees Celsius. The plasma breaks down feedstock materials such as waste coal, used tires, wood wastes, raw sewage, municipal solid wastes, biomass, discarded roof shingles, coal waste, discarded corn stalks, and other agricultural by products to their core elements. The Synthesis gas thus produced can be used as feed stock for anaerobic bacteria to produce ethanol or heat, pressure and a catalyst can be used to convert the gas to alcohol.
Some researchers have pointed out that Ethanol and Bio diesel from agriproducts do not provide as much energy as it takes to create them.
Researchers at the Delft Institute of Technology have isolated a gene from a fungus found in the faeces of Elephants. This gene has been inserted into bakers yeast allowing it to convert Xylose into Ethanol thereby making the production of bioethanol from left over materials possible.
Animal manures are truly renewable feedstocks for Ethanol production. The quantity of Swine manure produced in the U.S. estimated at 5 billion tones dry matter per year is sufficient to contribute substantially to Ethanol production. With a conversion efficiency of 40% there is a theoretical yield of 500 million gallons a year.
Citrus waste materials are rich in pectin, cellulose and hemicellulose polysaccharides which can be hydrolyzed into sugars and converted to Ethanol. The process is all the more economical because of the recovery of Limonene and use of the residue (containing more protein than the original waste) after conversion to alcohol as cattle feed. Potato peels can also be converted. Rice and Tofu waste has been successfully fermented with bakers yeast to give Ethanol.
Industries that are likely to be benefited from the waste to Ethanol services include food and beverages, breweries and wineries, biotechnology, pharmaceutical, chemical and consumer goods and agriproducts.
Tokyo Gas has built a plant to produce both Ethanol and methane from organic waste in the ward of Koto, Tokyo. Organic waste from school lunches is mashed and then taken to saccharisation tanks. Enzymes are added to the tank to breakdown starch into sugars. The suspension is then separated into the soluble and insoluble portions. The soluble part is rich in glucose which is fermented and distilled to give Ethanol. The solids are mixed with the distillation wastes and used for the generation of methane.
It takes one dry tonne of municipal organic waste to give 400 liters of alcohol. The European Union creates 65 million tones of organic waste per year which is enough to produce about 12 million tones of Ethanol. The European Unions target is to get 20% of its road fuel coming from biofuels by the year 2020.