The use of bio-based fuels for vehicles can provide a new market and greater incentive to decentralised production of ethanol and biogas from biomass and wastes, thereby integrating the use of wastes and biomass with biofuel production for the transport sector. Biofuels provide an alternative to fossil fuel dependency and emits less pollutants; for example a bus using biogas will produce 1.2 tonnes less nitrogen oxides and 30 tonnes less carbon dioxide per year. Sweden plans to replace 15% of the fossil fuel consumption in the transport sector with alternative fuels by 2010. This will be achieved through a number of measures, such as low blending of ethanol in petroleum, introducing flexible fuel vehicles, and using biogas and ethanol by fleets of buses and lorries. To support this strategy, a number of other economic control measures will be introduced. 

In 1991 the Swedish Transport & Communications Research Board launched a programme to demonstrate the use of biogas and ethanol as bio-based fuels for buses, lorries and cars. Results showed that ethanol and biogas are viable alternative fuel options although they cannot yet compete with fossil fuels in today's market. Another objective of the programme was to gain experience and to provide information to various interested parties (politicians, distributors, vehicle operators, etc) on future investments in biofuels. 

This paper provides information on projects in different cities in Sweden on the use of ethanol and biogas by transport vehicles and presents a scenario for discussion on how an integrated system could be developed to use agricultural wastes and sewage to generate ethanol and biogas as alternative fuels for the transport sector, and how nutrients from the effluents can be recycled to agriculture and forestry. 

A number of global events during the past 3 decades have increased concerns on environment impacts of the use of fossil fuels and the energy security. First, was the oil crisis in the 70's, then the poor air quality in cities of the 80's, global warming in the 90's. These gave many countries the desire to reduce their dependence on oil imports and led them to do extensive research on how to reduce fossil fuel consumption and particularly in transportation. The concern on the need to reduce the emissions of greenhouse gases has strengthen this desire. The use of more efficient engines in cars now enable them to travel 30 % more distance with the same volume of fuel. The development of alternative fuels such as biofuels can also play a major role in decreasing the dependency on oil and oil imports but more importantly to reduce harmful emissions. 

Ethanol has been regarded as one popular option in the future as it can be produced locally by alcoholic microbial fermentations of sugars that may be derived from starch or cellulosic plant materials. Another bio-fuel of growing importance is biogas and this can be produced from solid wastes, sewage, agro-industrial wastewaters, etc. by microbes during methanogenic anaerobic fermentation. Biogas production has an additional advantage in that it does not compete with human food demands for grain or starch as ethanol production does. Other types of biofuels such as methyl esters may be mixed with standard petrol (gasoline) or diesel. Methyl esters are derived from vegetable oils such as rapeseed oil, sunflower oil, palm oil or soybean oil, and this is mixed with standard diesel to give "bio-diesel". 
 
An very important and unique feature about  biofuels is that they can be produced locally with local resources and technology. Municipals and industries pay to dispose or treat the organic wastes they generate but since these can be converted to biogas, it is possible to reduce costs or income from the production of biofuels. Biofuels also emit less pollutants than fossil fuels and therefore their popular use would reduce air pollution and carbon dioxide emissions. However the price of biofuels cannot compete with petroleum prices yet unless more efficient technology is used to produce these fuels and/or changes and creation of  government policies, taxes and tariffs are done to favour the production and use of biofuels. 
 
In Sweden, a large source of diesel emissions in urban areas comes from transportation vehicles like taxis, buses and lorries that are used for public transportations including transport of consumer goods and garbage. 61 % of CO2 emissions come from road traffic and 91 % of the CO2 produced by the transport sector is from diesel and petrol fuel; the remaining 9 % from aviation fuel. The Swedish Transport and Communications Research Board (KFB) (http://www.kfb.se) is the primary body responsible to develop and field test engine-grade ethanol and biogas on a large scale for transportation vehicles. KFB's biofuel programme started in 1991  to develop, test and evaluate equipment and systems using fuels (engine-grade alcohols and biogas) from renewable resources with other partners from both the private and public sectors. As for the potential use of alternative fuels (Table 1)  biogas is the only fuel that has both short and long term potentials. Etahnol from sugar- and starch containing plants has a short term potential but must give way to competition by human food demands in the future and swicth to cellulose as its renewable raw material.  Reformulation of petrol and diesel and the use of natural gas are needed to conserve fossil fuel resources. 

Sweden plans to replace 15% of the fossil fuel consumption in the transport sector with alternative fuels by 2010. This will be achieved through a number of measures, such as low blending of ethanol in petroleum, introducing flexible fuel vehicles, and using fleets of neat ethanol and biogas buses and lorries. To support this strategy, a number of other economic control measures will also be introduced. 

BIOGAS 
 
 

Biogas is an environmentally friendly biofuel and is mainly used in stationary facilities. It  has a great potential as a biofuel for vehicles. There are different scales in the technology available to enhance methane production and to recover the biogas. To use it  in vehicles, it must be purified to 96-100 methane by removing or separating carbon dioxide, moisture, hydrogen sulphide and other corrosive components in the gas. The purified gas is then compressed to a pressure of 200-250 bars for use in the vehicle. Approximately 50 buses, 2 lorries and 50 dual-fuel vehicles were used for the KFB experiment in four locations in Sweden. 
 

In the city of Trollhattan, the demonstration project started with two Volvo lorries which were used for municipal refuse collection. It now runs a fleet of 15 buses. Biogas is piped from a sewage treament plant. The potential of biogas production using wastes that are normally landfilled from a fish processing plant and an animal feed plant has been identified. 
 
 

A gas processing installation has been commissioned at the sewage works in the city of Uppsala in 1996 for its pilot demonstration project for 20 buses, six cars and a refuse truck (Figure 4) . Stockholm city produces a large quantity of biogas and has 60 vehicles in its pilot project. 

The use of biogas is constrained by the size of the gas tank in the vehicle. A car can hold enough biogas for 150-200 kilometers. The major work in the future has been identified to be large scale gas production and processing of the gas and developing filling and distribution systems.  Gas tanks in vehicles can be filled using high-speed filling or slow speed filling. High speed filling will take 10-15 minutes for a bus and 3-4 minutes for a car. Gas from a high pressure storage faciltiy at 250-300  bars is injected into a vehicle tank which holds the gas at 50-100 bars. Slow filling uses a compressor to fill the gas direcly into a vehicle tank. This method is useful if vehicles can be taken off the streets for several hours daily, e.g. buses that operate only during the day. 

About 1.5 TWh of energy is produced as biogas in over 200 biogas installations in Sweden. If cities with more than 20,000 inhabitants sent their organic wastes to biogas installations, then it is estimated that 55 cities can produce more than 20 TWh. The practical potential is however about 6-8 TWh (Lindberg, A. 1997) due to financial constraints in investments for production and gas distribution facilities. 

Ethanol 

Ethanol can be used as pure form in otto engines and diesel engines or blended into petrol or diesel fuel. It has been used as alternative vehicle fuel  in times of war or economic depressison so it is not a new practice. Ethanol is a suitable fuel due to its high octane count which permits controlled ignition at high pressure using the spark in the engine. When ethanol is used in diesel engines, the cetane count needs to be increased from 5 to 47; this is done with an additive which serves as an ignition improver. Blending small amounts of ethanol can be used to quickly introduce its use on a large scale. In Sweden, there are currently about 300 ethanol buses, 7 lorries and about 100 flexible fuel vehicles running on ethanol since 1997. This has been due to the successful demonstration project in the capital city of Sweden, Stockholm. Thirty two city buses  were converted to solely use ethanol to determine whether it was possible to achieve appreciable improvements in the gas emissions values when compared to buses run on diesel. The project generated very impressive results and Stockholm's public transport "Stockholm Transport" (SL) has now decided to phase out all their diesel buses in favour of ethanol and hydrid buses as ethanol buses generate far less nitorgen oxides and particulates than diesel buses. There are currently about 130 Scania made ethanol buses on the streets of Stockholm and the long term goal is to have about 300 ethanol buses in the city by the year 2000.  Over the past 5 years, smaller projects using ethanol powered vehicles in other Swedish cities were also demonstrated. 

It costs SEK 95,000 per year (or about 1,000 US$ per month) more to run an ethanol bus than a diesel bus. This extra cost is almost entirely due to the cost of ethanol. To promote a shift from a fossil-based tarnsport system to a bio-fuel based one, the exisitng system needs to be changed. Extra CO2 taxes and other environmental taxes are necessary as a strategy to favour a sustainable tarnsport system. The Swedish Government therefore will plan to pass a new resolution on traffic policy this year in order to favour implementation of strategies for alternative fuels. the strategy aims at reaching a level of approximately 15 % replacement of fossil fuels by the year 2010 using a number of measures; such as low blending of ethanol in petrol, introducing flexible fuel vehicles, and using fleets of solely ethanol buses and lorries. Seven solely ethanol fueled lorries in a test period of a total of  90,000 kilometers showed that the conversion of 7 litre diesel engines performed very well in day-to-day work. These lorries were used in various cities and for a variety of purposes. 
 

Ethanol can be produced by microbial fermentation or by gasification. This paper will concentrate on fermentation. Biobased production of engine ethanol may use the following raw materials: (a) sugar-containing agricultural products: This is an attractive raw material source especially for sub-tropical countries for growing sugar cane and beet root. (b) starch-containing raw materials: most beverage spirits in Sweden are produced from hydrolysed starch from grains and potatoes. These materials have a higher food-value and  generate a lower income return if used for ethanol production (c) pulp, and hemi-cellulose raw materials and wastes: Ethanol production from these materials are ideal but they require more complex process since separation of hemicellulose and lignin is required to expose the cellulose for hydrolysis before fermentation. One tonne of softwood can theoretically produce 440 liters of ethanol. Traditional methods use yeasts through hexose fermentation. There has been intensive research to achieve higher conversion efficiency, e.g. by genetic manipulation so that yeasts will also use pentoses, by reducing the number of by-products from yeasts or biomass growth. New methods for ethanol recovery using molecular-membrane technique, extraction and various other combinations of distillation will also reduce production cost. 
 
 

Prospects of the Future 

The Swedish demonstration programme for promoting use of ethanol and biogas as motor fuels has shown that there are technology available for starting switching from use of petrol and diesel to renewable sources like ethanol and biogas. The new technology developed and tested in Swedish cities are good examples on ecocycle technology which is providing solutions not only for the transport sector but also for waste management, agriculture and forestry. Hence, the examples given are so-called win-win solutions. The programme has also resulted in an increasing interest of using this new technology among a large group of actors as oil companies, manufacturers of vehicles, municipalities, bus and trucking companies etc.  However, the major barrier for getting a wider acceptance of the new technology is still the cost. In order to overcome this problem, there is a need to further develop cost-effective solutions at the same time as all measures has to be taken politically to start internalising the environmental costs in all fuel prices. 

In Sweden the introduction of new projects of using ethanol and biogas are spreading among our cities supported by central and local governments as well as by private companies and individuals. On a global scale there are a number of outreach activities started in order to involve stakeholders in other countries. By involving local actors in many cities world-wide in a coordinated  procurement process there are possibilities to develop a strong actor who can push the oil and car industry to provide them with the new and sustainable technology. 
 

References 

Johansson, B. 1996. Energy balances. Possibilities for replacing petrol and diesel with fuel from Swedish biofuels. KFB Note 1996:22 
KFB, SIKA, NUTEK. 1996. Background material for assessing the introduction of alternative fuels. Report compiled at the request of the Communications Committee (KomKom). KFB Information 1996:13 
Lindberg, A. 1996. Biogas plants in Sweden. KFB Report. 1996:21. (VA Research Report 97:A) 
Månsson, T. 1997. Bio-based fuels fro buses, lorries and cars. CADDET Newsletter. no 3. Sept.1997.pages 7-9. 
Månsson, T. 1998. Clean vehicles with biofuels - A state of the Art Report. KFB Report 1998:18 
Zacchi,G. 1996. Ethanol from lignocellulose. Working report. May 1996.