Bioethanol Production
Technologies: Anaerobic Digestion, Bioethanol Production, Incineration
Introduction
Bioethanol production from organic material is a technology that has been well researched and is implemented globally using a variety of different feedstocks. The requirements for an organic material to be used for the production of bioethanol is a composition high in starch and sugar. Due to a significant proportion of municipal waste containing organic material it is possible to apply the bioethanol producing process to this fraction of municipal waste. The treatment of waste to create bioethanol creates an end product which can act as an almost complete alternative to traditional fossil fuels as a fuel to power vehicle engines. Given the governmental targets to reduce the emissions of carbon dioxide the production of bioethanol from municipal waste may prove an extrememely benfitial technology and an additional solution to waste management.
The Process
The process of bioethanol production is similar to that of methane production by anaerobic digestion. The organic feedstock requires enzymatic hydrolysis to break down the carbohydrates, proteins and fats to sugar, fatty and amino acids. To allow this process to occur the waste requires pre-hydrolysis treatment to increase the enzymatic digestability of the material [1], the common pre-hydrolysis treatment technologies are dilute acid pre-hydrolysis, steam treatment and microwave treatment. Following the production of sugars from hydrolysis the next stage depends upon the waste type however fermentation is commonly used. Prior to fermentation of the sugars distillation is required to segregate the ethanol from the remaining prodcuts.
Application for Municipal Solid Waste
Despite being a well researched technology in terms of crop feedstocks (sugar cane, corn) it is an extremely underdeveloped technolgy in terms of organic waste as a feedstock.
Municipal waste requires segregation to provide a completely organic waste stream. Further research into the efficiencies of various fractions within organic waste will provide detail as to whether the feedstock should be further segregated.
The feedstock requires transportation to the bioethanol refinery and from there input to the reactor at the optimal loading rate for pre-hydrolysis treatment.
The feedstock will then be subject to dilute acid treatment followed by steam treatment to increase the digestibility of the material. The cellulose enzyme is then added to allow hydrolysis to occur. Once the cellulose has been broken down fermentation and distillation will be caused with the addition of a yeast enzyme and an increase in temperature producing ethanol and carbon dioxide. The ethanol may then be seperated and with sufficient purity provide a fuel resource to be utilized
Current Research
Due to the limited research concerning the production of bioethanol from an organic waste feedstock the majority of research covers the economic possibilities of the technology in addition to possible improvements to the processes involved.
The efficiency of various pre-hydrolysis treatment technologies is one of the areas of the bioethanol production which has been researched. The pre-hydrolysis treatments being examined were dilute-acid treatment, steam treatment and microwave treatment. The glucose yield values for the use of each treatment or combination of treatments was recorded to obtain the optimum pre-hydrolysis process. The results showed that the ideal treatment was dilute acid (sulphuric acid) with a 1% concentration followed by steam treatment at 121 degress. Additionally it was found that the enzyme loading and acid concentration provided a greater factor than temperature of steam treatment in bioethanol yield. [2]
The competitiveness of ethanol dervied from municipal waste has also been compared to ethanol produce from traditional feedstocks. The effects of production of crops to produce bioethanol has put significant strain on the economic strength of food crops and therefore signifies a possible need to derive ethanol from alternative sources. With further research involving bioethanol derived from organic waste it is possible that waste may be capable of providing a sustainable alternative to bioethanol production. [3]
References
1-Antizar-Ladislao, B; Turrion-Gomez, J. L. (2008)Second-generation biofuels and local bioenergy systems; Biofuels, Biproducts and Biorefining
2-Aiduan, Li; Antizar-Ladislao, B; Khraisheh, M; (2007) Bioconversion of Municipal Solid Waste to Glucose for Bio-ethanol Production; Bioprocess Biosyst Eng; 30:189:196
3-Broder, J.D (2001) Using MSW and Residue as Ethanol Feedstock; Biocycle; Renewable Energy
Pictures courtesy of
1-E85 Fuel - www.e85bio.org/
2-Bioethanol Plant - www.clubofpioneers.com
Anaerobic Digestion Technologies Incineration
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