Economics and environmental impact of bioethanol
production technologies: an appraisal (Part -3)

Anuj Kumar Chandel1,2, Chan ES3, Ravinder Rudravaram1, M. Lakshmi Narasu2, L.Venkateswar Rao1 and Pogaku Ravindra3*
Economics of ethanol production technologies

To be competitive, and find economic acceptance, the cost for bioconversion of biomass to liquid fuel must be lower than the current gasoline prices (Wayman and Parekh, 1990; Subramanian et al., 2005). It seems how-ever; now much more ttainable because of increasing efforts of researchers working towards improvisation in the efficiency of biomass conversion technologies (Vertes et al., 2006).

However there is still huge scope to bring down the cost of biomass-to-ethanol conversion. The cost of feedstock and cellulolytic enzymes are two important parameters for low cost ethanol production. Biomass feedstock cost represents around 40% of the ethanol production cost (Hamelinck et al., 2005). An analysis of the potential of bioethanol in short and long term (2030) in terms of performance, key technologies and economic aspects such as cost per kilometer driven has been conducted recently by Hamelinck and Faaij (2006). In this analysis, the production cost of bioethanol was found to be within the range of 16-22 _/GJHHV (Euro/Giga Joules High Heating Value) at present and down to 13 _/GJHHV in future (2030). The feedstock cost is major parameter influencing the ethanol production cost at a rate of 2-3 _/GJ fuel. Employing integrated approaches using the larger industrial facilities by integrated action plan along with cheap feedstock and potent cellulases could make the process more economically viable (Sun and Cheng, 2002; Dien et al., 2006)

Securing long supply of energy sources requires not only that existing fuel resources be utilized as economically as possible along with their diversification uses. Keeping this point of view, bioethanol is identified and portrayed as the entity for ensuring energy security in future fuel interests and global requirements.

The choice of feedstock for ethanol production depends upon its availability and the ongoing uses. For example, agroresidues such as wheat straw, sorghum and barley straw are not preferable for bioethanol production due to their use as animal fodder. On the contrary,  groresidues like sugarcane bagasse, rice straw, rice bran, groundnut shell, corn stover, Brassica carniata stalks and soyabean  stalks etc can be used directly because these sources are not preferably used as fodder for livestock. Some dedicated energy sources like damaged rice and sorghum grains (Suresh et al., 1999), sunflower stalks and hulls (Sharma et al., 2000), Eicchornia crassipies (Nigam,  2003), P. brava (Sanchez et al., 2004), alfalfa fibers (Sreenath et al., 2001), residual starch and crushed wheat grains (Davis et al., 2006), agro waste (Campo et al., 2006) and Saccharum spontaneum (Gupta, 2006) are more feasible sources for bioethanol production. Also, organic waste and municipal solid waste (MSW), which contain significant amount of cellulose could be cost economic friendly and solve the problem of solid waste storage and management.

In India, Department of Biotechnology, Govt. of India funded a nationwide research project towards the use of selective weeds like Lantana camara, Prosopis juliflora and fruit or vegetable waste into ethanol conversion due Chandel et al. 025 to their vast abundance, low cost and rich in fermentable carbohydrates.

An important factor for reducing the cost of bioethanol production is to use larger industrial facilities rather than smaller ones. Ward and Singh (2002) also suggested the integrated approach (Process engineering, fermentation and enzyme and metabolic engineering) could improve the ethanol production economics. By increasing the plant size, the investment per unit output of product falls off, a ten-fold increase in size reducing the unit cost to less than one-half and thereby reducing unit capital cost charges and conversion cost reducing profitability (Wayman and Parekh, 1990; Henke et al., 2006).

To further improve the economy of ethanol production, energy integration of the ethanol production, to already existing plants such as pulp and paper plants is necessary. O’ O’Boyle et al. (1991) reported that the cost of producing ethanol from pine with a diluted acid hydrolysate process, was estimated to be 3.22 SEK L-1 in a stand alone plant in comparison to 2.54 SEK L-1 with an integrated plant. They projected that the cost of bioethanol can be reduced from US$ 1.22 per liter to about US $ 0.31 per liter on the basis of continuous improvement in pretreatment of biomass, enzyme application and fermentation.
Aristidou and Penttila (2000) reported that the total cost of ethanol will be dropped from more than $1.0 per litre to ~ $0.3-0.5 per litre, with a projected cost of less than $0.25 per litre in the near future.

Wilke et al. (1981) has made the first effort to analyse the cost of the conversion of biomass to ethanol process based on a SHF operation and concluded that neat ethanol could compete with gasoline at the oil prices at $20 to $30 per barrel. Foody (1988) has emphasized the importance of improvement in cost effective cellulases production and outlined the potential for bringing down the price of bioethanol from 25-55 cents to 10-28 cents per liter. Subsequently, Wright (1988) and Hinman et al. (1992) evaluated the benefits of SSF process over to SHF technology and reported the cost based on economic evaluation of bioethanol keeping view the SSF mode of operation. Wooly et al. (1999) explained the further economic analysis of bioethanol ($ 0.78 per gallon) and suggested a projected cost of as low as $ 0.20 per liter by 2015 if enzymatic processing and biomass improvement targets are met. The projected cost of ethanol production from cellulosic biomass as per the earlier estimates ($4.63/gallon in 1980) has been reduced by almost a factor of four ($1.22/gallon) over the last 20 years (Wyman, 1999; Wyman, 2001).

However, Kadam et al. (2000) reported that ethanol production cost can be achieved at $ 1.20 per liter by using two-stage dilute acid hydrolysis process. Krishnan et al. (2000) worked out on economics of ethanol production from dry-milled corn starch in fluidized–bed reactors using immobilized Z. mobilis cells. They analysed the cost of ethanol for 15 million gal/year production plant 026 Biotechnol. Mol. Biol. Rev. using Aspen Plus (Aspen Technology, Cambridge; MA) process simulation software and concluded that the operating cost savings of ethanol production in the range of 1.1 - 3.1 cents/gallon. Kwaiatkowski and Co-workers (2006) developed a model for cost evaluation of ethanol production from 40 million gal/year ethanol producing facility using corn dry-grind process technology. The model was developed using Super Pro Designer R  software and data collected from ethanol producers, technology suppliers, equipment manufactures and engineers working in the different industries. The cost of ethanol was found to be increased from US$ 0.235/L to US$ 0.365/L as the price of corn increased from US$ 0.071 to US$ 0.125 /kg.

The bioconversion of pentosans and hexosans from lignocellulosic biomass to ethanol need to be achieved with the maximum efficiencies in terms of higher yield and improved productivity to make the biomass-to-ethanol process economical. The economics of the ethanol process is determined by the cost of sugar. The average biomass cost amounts to ~$0.06 per kg of sugar, or a contribution to the feedstock costs for ethanol production of as low as $0.10 per liter (Aristidou and Penttila, 2000). Wingren et al. (2003) evaluated the SHF and SSF economic using cellulase enzymes in both configurations with SSF being less expensive by about 10%; and estimated the ethanol production cost of 0.56 – 0.67 $/L.

Later, Wingren et al., 2004 studied the effect of reduction in yeast and enzyme concentration in SSF process and concluded final ethanol production cost 4.80 SEK/L (2.34 US$/gal). According to the National Renewable Energy Laboratory (NREL, Colarado, USA) estimations, ethanol production cost of 20 cents per litre is possible in another 15 years from lignocellulose biomass employing designer cellulases and SSCF (simultaneous saccharification and co-fermentation) process (Ghose and Ghose, 2003). However, in both the process, the use of cellulase makes the process cost effective (Mielenz, 2001; Alzate et al., 2005; Gray et al., 2006). According to the analysis of US DOE (US Department of energy), if the enzyme cost can be brought for less than 10 cents per gallon of ethanol the cost of making ethanol could drop as low as 75 cents / gallon (Griffith and Atlas, 2005). Apart from focusing the economics of cellulase production cost, several studies are being carried out to improve the ethanol production by improving acid hydrolysis process. Luong and Tseng (1984) evaluated the technoeconomics of ethanol production under continuous culture using immobilized cells of Z. mobilis using plug-flow reactor. They found this technology economically attractive and finally concluded that at least 4 cents/gal of ethanol could be saved using immobilized cells rather than the conventional batch system. They further suggested that by switching from batch to immobilized processing; the fixed capital investment is substantially reduced, thus increasing the profitability of ethanol production by fermentation. Von Sivers et al. (1994) analysed the cost economics of ethanol production (48 cents/gallon) from detoxified willow hemicellulosic hydrolysate using recombinant E. coli K011. Zacchi and Axelsson (1989) suggested preconcentrating dilute sugar solution using reverse osmosis is economically feasible to getting high ethanol concentration in fermented broth. Cysewki and Wilke (1976) described cell recycle and vacuum fermentation processes for continuous ethanol production on a production capacity of 78,000 gal ethanol / day employing molasses as the fermentation substrate and estimated ethanol production cost 82.3 and 80.6 cent/gal, for the cell recycle and vacuum processes, respectively.

More recently Zhang (2006) analyzed the cost economics of ethanol production from a small-size lignocelluloses refinery with a capacity of 100 tones per day producing approximately 3 million gallons of ethanol plus coproducts. He estimated the cost of ethanol production ~$1.00-1.20 per gallon.

The distillation cost of per unit amount of ethanol produced is substantially higher at low ethanol concentrations, the researchers have dealt with the idea of concentrating sugar solutions prior to fermentation (Cyweski et al., 1976; Oh et al., 2000; Iraj et al., 2002). Ethanol distillation cost can be further improved by using membrane distillation process. It has the lowest operational cost, flexible, simple to use and is easy to maintain. It is most efficient and cost effective option among the available distillation processes (Gonsalves, 2006).

Ethanol and Environment
Ethanol represents closed carbon dioxide cycle because after burning of ethanol, the released carbon dioxide is recycled back into plant material because plants use CO2 to synthesize cellulose during photosynthesis cycle (Wyman, 1999; Chandel et al., 2006a). Ethanol production process only uses energy from renewable energy sources; no net carbon dioxide is added to the atmosphere, making ethanol an environmentally beneficial energy source (Figure 5). In addition, the toxicity of the exhaust emissions from ethanol is lower than that of petroleum sources (Wyman and Hinman, 1990). Ethanol derived from biomass is the only liquid transportation fuel that does not contribute to the green house gas effect (Foody, 1988).

As energy demand increases the global supply of fossil fuels cause harm to human health and contributes to the green house gas (GHG) emission. Hahn-Hagerdal (2006) alarmed to the society by seeing the security of oil supply and the negative impact of the fossil fuel on the environment, particularly on GHG emissions. The reduction of GHG pollution is the main advantage of utilizing biomass conversion into ethanol (Demirbas, 2007). Ethanol contains 35% oxygen that helps complete combustion of fuel and thus reduces particulate emission that pose health hazard to living beings. A study conducted by Bang-Quan et al. (2003) on the ethanol blended diesel (E10 and E30) Chandel et al. 027

Figure 5. Ethanol represents closed CO2 cycle.

combustion at different loads found that addition of ethanol to diesel fuel simultaneously decreases cetane number, high heating value, aromatics fractions and kinematic viscosity of ethanol blended diesel fuels and changes distillation temperatures. These factors lead to the complete burning of ethanol and less emissions. With its ability to reduce ozone precursors by 20 - 30%, bioethanol can play a significant role in reducing the harmful gasses in metro cities worldwide. Ethanol blended diesel (E-15) causes the 41% reduction in particulate matter and 5% NOx emission (Subramanian et al., 2005; Chandel et al., 2006a). One of the disadvantage in using ethanol as fuel is that aldehyde predominantly acetaldehydes emissions are higher than those of gasoline. However acetaldehydes emissions generate less adverse health effects in comparison to formaldehydes emitted from gasoline engines (Gonsalves, 2006).

Environmental impact of bioethanol production technologies and their life-cycle assessment (LCA)
Life-cycle assessment (LCA) is a conceptual framework and methodology for the assessment of environmental impacts of product systems on a cradle-to-grave basis (Graedel, 1999; Tan et al., 2002). Analysis of a system under LCA encompasses the extraction of raw materials and energy resources from the environment, the conversion of these resources into the desired products, the utilization of the product by the consumer, and finally the disposal, reuse, or recycle of the product after its service life (Tan et al., 2002). The LCA approach is an effective way to introduce environmental considerations in process and product design or selection (Azapagic, 1999). Based on life cycle assessment (LCA) studies, ethanol production technologies can be compared. Energy production and utilization cycles based on cellulosic biomass have near-zero green house gas emissions on a life cycle basis (Lynd et al., 1991). Biomass utilization into ethanol production offer environmental benefits in terms of nonrenewable energy consumption and global warming impact. Kim and Dale (2005) studied LCA emphasizing corn and soyabean production and their utilization into bioethanol and biodiesel production and concluded that both the biofuels have environmental benefits in terms of nonrenewable energy consumption and global warming impact. However biomass utilization into ethanol also tends to increase acidification and eutrophication, primarily because large nitrogen, phosphorus are released after cultivation of crops. Lechon et al. (2005) studied the LCA of ethanol production from wheat and barley grain and found that barley is a better option than wheat in terms of fulfillment of the green house gas emissions.

Figure 6. Coordinated action for improvement of biomass to ethanol and its long term benefits.

In an extensive study by Kadam (2000), LCA of acid and enzymatic hydrolysis was compared. All environmental flows were examined from the product life cycle, its production and extraction from raw materials through intermediate conversion process, transportation, distribution and use. Dilute acid process was found better than the enzyme process in terms of greenhouse gas potential, natural resource depletion, acidification potential and eutrophication potential (Kadam, 2002). The reason is dilute acid process sends a much higher proportion of biomass to the boiler for electricity production, which in turn offsets large amounts of emissions (Kadam, 2000). Conversely the concentrated acid process is a net consumer of energy in terms of high acid load and reaction temperature, results in very high values for green house gas (GHG) effect and other impact parameters (Kadam, 1999). Kemppainen and Shonnard (2005) compared the energy consumption and environmental impact for ethanol production using timber wood and recycled news print. The news print conversion into ethanol has a slightly lower overall composite environmental index compared to the timber process. However ethanol production from timber takes less energy, electricity and produces fewer emissions.

A study conducted by Hu et al. (2004) revealed that the E-85 fueled vehicle is better vehicle than the gasoline fueled car by balancing of all the 3E”s the energy, environmental and economic aspects. E-85 fuelled FFV (fossil fuelled vehicle) is about 15% higher efficient when compared to gasoline fuelled car. It also lowers the pollutant emission viz. particulate matter, CO2, CO, NOx emission than gasoline fuelled car. E-85 fuelled vehicle is higher in total energy consumption and a good combined energy indicator. This was also in agreement with the recent life cycle-based (well to wheel) studies of fuel / propulsion alternatives for light–duty vehicles with a focus on lignocelluloses derived fuel ethanol by reducing 86% lower life cycle green house gas emissions as compared to the gasoline (Fleming et al., 2006).

Tonan et al. (2006) has discussed the integrated assessment of energy conversion processes by evaluating the thermodynamic, economic and environmental parameters and found that water and air emissions of the plant producing ethanol are relatively low. The tansformity of ethanol (1.32 x 105 seJ/J) is quite high if compared to that of fossil fuel (5.4 x 104 seJ/J). This is even when bioethanol production is driven by a large amount of nonrenewable inputs (fertilizer, fuel, machinery).

Conclusion
In spite of laboratory based bioethanol success stories, the production of fuel ethanol at plant scale still remains a challenging issue. A positive solution to this issue could bring economic advantage not only for fuel and power industry, but also benefit the environmental rehabilitation and balance issues and cause. Worldwide, there is only one company, Iogen Corporation, Canada (http://www.iogen.ca), produce bio-ethanol at commercial scale using wheat straw and corn stover. In India, despite plentiful availability of biomass, there is no commercial ethanol production plant from lingocelluloses. The key to the establishment of a commercial bioethanol production facility and the reduction in capital thereof, resulting in lessening of operating costs from each of the units of operations will be an achievement par standards of excellence and utility! Industry attention, not just the accolades is required for searching the answers to the fast paced fuel drain phenomena threatening to takeover into as a major crisis or even worse an economic depression by the end of 21st century! For a flourishing bioethanol industry, government support is critical in correcting tax anomalies, exemption from excise and sales tax, deregulation of feedstock and its pricing and encouraging pilot projects and R&D work on bioethanol. Advances in pretreatment by acid catalyzed hemicellulose hydrolysis or employing an integrated approach in the form of consolidated bioprocessing with application of novel, tailored cocktails of enzymes for the cellulose breakdown coupled with the recent development of genetically engineered microorganism those ferment all possible sugars in biomass to ethanol at high productivity are the major key factors to make bioethanol program successful at commercial scale (Figure 6). The other important aspect by deploying the bioethanol option is its benefit to the environment. Ethanol is one of the best tools to fight vehicular pollution; its clean burning reduces the harmful gasses and particulate emissions that pose health hazard. The implementation of bioethanol policy can be helpful in improving in envi-ronment and rural economic development with sustainable agricultural practices and enhancement of biomass feedstock conscious usage towards the bioethanol industry will bring up the new age farmer into the limelight and horizon of activities and threshold of business to become renewed with options to deal better in life! A better farmer will ultimately usher in a better livelihood for one and all!

ACKNOWLEDGEMENT
We gratefully acknowledge the financial support from Universiti Malaysia Sabah,Kotakinabalu, Malaysia. Chandel et al. 029
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