OF B IOFUEL S YNERGIES A S YSTEMATIC L ITERATURE R EVIEW

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A

S

YSTEMATIC

L

ITERATURE

R

EVIEW

OF

B

IOFUEL

S

YNERGIES

ISRN:

LIU-IEI-R--10/0092--SE

Written by:

Michael Martin and Jorge E. Fonseca A.

Linköping University

Environmental Technology and Management, Linköping University, SE-581 83 Linköping, Sweden

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A Systematic Literature Review of Biofuel Synergies

TABLE OF FIGURES

Figure 1: Report Methodology and Steps for finding Articles... 3

LIST OF TABLES

Table 1: Combination Word Search Results ... 5

Table 2: Articles saved in each folder in Refworks ... 6

Table 3: Categorization of Biofuel Synergy Articles... 6

Table 4: Final Listing/Categorization of Articles and Synergies... 7

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1 INTRODUCTION

Often biofuels are criticized in the media for their low production energy efficiency, environmental impacts and by using food for fuel production. An answer most critics rely on is stating how 2nd generation biofuels will solve all the problems the first generation biofuels possess[1]. However, 1st generation biofuels must “pave the way” for 2nd generation biofuels. They can do this by providing the infrastructure, technology and knowledge provided by the fuels.

In order to increase the efficiency of 1st generation biofuels, the theories of industrial symbiosis can be applied. Industrial symbiosis theories are designed to integrate production systems and other industries to improve energy efficiency and environmental performance[2,3]. By integrating biofuel production systems, the by-products of biofuels can be used in subsequent processes. By making use of by-products, excess heat, etc. the energy efficiency can be improved and allow for more benefits including economic and environmental performance[4].

Industrial symbiosis literature includes many examples of how industries can benefit from one another but does not include much literature on the integration of biofuels. Synergies do however exist as there are many by-products which are highly prized in other industries, e.g. glycerol and DDGS. The biofuels themselves can even be used in subsequent processes.

2 AIM

The aim of producing this literature study is to find relevant biofuel synergies1 within various fields from scientific literature. By searching for keywords and combining these with keywords related to biofuel synergies we can review the extent and knowledge of synergies between external industries with biofuels, between biofuel industries and the use of their by-products throughout various research fields.

The main research questions to be answered are:

 What do other research fields use biofuel by-products for?

 What are the current trends for the use of biofuels and their by-products?

 What substrates/by-products/wastes from other industries can be used for biofuel production?

 Which synergies exist in the literature beyond those presented in other phases of the research project?

 What are some potential uses for biofuels, their by-products and industrial wastes and utilities to integrate in symbiosis?

1_{Synergy is defined in this report as the relationship and cooperation between industrial activities by the shared}

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3 IDENTIFICATION OF RELEVANT ARTICLES

This report is based on an extensive systematic literature review of relevant literature for biofuel synergies, i.e. the handling of by-products between biofuel industries and external industries. The systematic literature review process was used due to its applicability in this context to allow for possible exclusion and inclusion of relevant articles based upon a clinical question, in this case finding biofuel synergies[5]. The literature review was carried out in a step-by-step manner in order to exclude non-relevant literature from the abundance literature on the subjects.

3.1 Searching for Keywords and Combinations of Keywords

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3.1.1 Step 1 – Gauging the number of relevant articles

The first step of the literature review was to review how many articles were available for the topics of biogas, bioethanol, biodiesel and thereafter biofuel and to provide a “pool” of articles for later analysis. The literature review was carried out using the Science Direct scientific database search engine (reference to science direct). No other search engines were used to find articles due to the time limits of the research project and extent of literature available from the Science Direct database. The searching criteria was limited to the following constraints:

 Dates: From: 2000 To: present 1998  Include: Journals and all books  Source: All sources

 Subject: All sciences

 Term within: Abstract, title and keywords

A search was conduced for articles concerning biogas, ethanol(bioethanol), biodiesel and biofuel articles. This led to a total of 1150, 20050(471), 1553 and 1699 number of articles for each topic respectively. A total of 24,452 articles were therefore available in the field. Based on the methodology of a systematic literature review, exclusion categories were thereafter applied, which are described in the following sections.

It was apparent that combination words were necessary to narrow the focus of the literature. Combination words were then used, to find relevant articles under each topic for biofuel synergies, i.e. relevant articles for all topics; biogas, bioethanol, biodiesel and biofuel.

Combination words to include with each topic keyword included:  Allocate;  Allocation;  by-product;  byproduct;  cooperation;  co-product;  coproduct;  exchange;  incorporate;  incorporation;  integrate;  integration;  symbiosis;  synergy;  synergies;  share;  sharing;  substitute;  substitution;  substrate;  residue;  and utility.

These combination words were chosen as they represent interaction between biofuels and external industries and could provide necessary literature for this study. Table 1 below shows a review of the number of articles found for each combination of search words.

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Table 1: Combination Word Search Results

Main Keywords Combination Words Biofuel

(1699) Biodiesel (1553) Ethanol (20050) Bioethanol (471) Biogas (1150) Symbiosis 1 0 4 1 Synergy 9 2 24 0 Cooperation 10 3 15 2 By-product 277 297 2293 135 Byproduct 57 90 266 38 Co-product 50 44 390 17 exchange 29 41 414 11 Share 42 12 68 16 sharing 0 0 22 1 substitute 49 77 93 26 substitution 34 20 222 20 allocation 21 4 22 4 Integrate 9 1 14 6 integration 57 16 116 18 Incorporate 7 3 27 3 incorporation 15 11 225 5 substrate 84 65 1265 170 residue 120 50 411 83 utility 13 3 99 5 Total Number: 884 739 5990 561

Upon finding the number of articles for each topic and combination word, further exclusion criteria were applied to produce relevant literature and narrow the number of articles for this study. As can be seen in Table 1, there are many articles provided for each topic; especially for ethanol. However, for some keyword+combination word searches, only a limited number of articles were returned. To finalize Step 1, some of the combination + keyword searches were disregarded from the previous listing of combination words. Those include the combination words, synergies, coproduct and allocate; which are not present in Table 1.

3.1.2 Step 2- Selecting Articles for further Analysis

Step 2 of the literature search was conducted in order to limit the number of articles and provide relevant articles for further in depth analysis in Steps 3 and 4. Following a review of the articles in each of these combination topic + keyword searches, many themes emerged for each respective biofuel topic. Many articles contained information about chemical experiments, second generation biofuels and hydrogen production which are beyond the scope of this study. The following exclusion criteria were thus applied in order to confine the literature to first generation biofuel production and interaction between biofuels and external industries for each respective biofuel topic.

Biodiesel

 Exclude 2nd_{Generation Biofuels i.e. Fischer-Tropsch and other synthetic diesel}

Biogas

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Ethanol

 Exclude 2nd_{Generation Biofuels i.e. cellulosic ethanol}

 Exclude articles about ethanol used for hydrogen fuel cells

Biofuel

 Exclude 2nd_{Generation Biofuels i.e. all second generation biofuel articles}

In some of the cases as shown above, there were over 1,000 articles for each topic and combined keyword respectively. After excluding the topics as aforementioned, the first 150 articles from the total listing in those cases where there were over 150 were reviewed and saved if relevant.

Articles that were considered relevant after the exclusion categories were saved in a referencing database, Refworks. Refworks was used due the ease of exporting citations and providing links back to the articles for subsequent steps. All articles were saved in a respective folder under that theme, i.e. there were 4 folders created which were labeled biofuel, biogas, ethanol and biodiesel. The number of articles contained in each folder are shown below in Table 2.

Table 2: Articles saved in each folder in Refworks

Biodiesel Biogas Bioethanol Biofuel Number of

Articles 54 145 49 106

3.1.3 Step 3 – Categorization of articles

The next step for limiting the number of articles and finding relevant articles was to categorize the articles in order to find if there were recurring themes. An in depth review of all abstracts was conduced from the articles reviewed in Step 2. These abstracts and articles were categorized based on their themes. During the process it was found that some of the articles were redundant or doubled in several folders and were therefore deleted before proceeding to the categorizing them. The categories for each folder can be seen in Table 3.

Table 3: Categorization of Biofuel Synergy Articles

Biodiesel Biogas Bioethanol Biofuel

 Glycerol (8)  Alcohol(2)  General(13)  Catalysts(8)  Algae(2)  Other(17)  Agricultural (52)  Animal (17)  Human & industrial (33)  Sustainability (43)  By-Products(13) o Industry(5) o Biomass(8)  Using By-Products(7)  General(12)  Advanced Processing(11)  Technology(15)  General(13)  Biofuel Integration (14)  Catalysts(6)  By-Products(11)  Cracking(3)  Raw Materials(31) o Biomass(13) o Industrial(18)  Other(2)

Total: 50 Total: 145 Total: 43 Total: 95

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3.1.4 Step 4 – Obtaining selected articles/synergies

A final listing of relevant articles was produced for Step 4 of the literature review. Once the articles were divided into categories the abstracts were reviewed for further relevance. Articles which contained information about integration of biofuel processes, making use of by-products and using residues and by-products of other industries for biofuel production were included in the final list.

Many articles were found to contain similar contents, i.e. from the categorized themes from Step 3. For example, many articles describe the use of biomass for biofuel production. Consequently, only a selected few in the case where many similar articles are present were selected for the final list. Thereafter, articles found under the biofuel heading have been split into their relevant categories. They contain synergies for the bioethanol, biogas and biodiesel categories and have therefore been added to each respective folder and list. The results of the final listing can be seen in Table 4 in the subsequent text.

4 RESULTS

Shown below in Tables 4 and 5 are the final listings for the synergy articles obtained from the said literature review. Table 4 consists of all synergies regarding biofuel synergies between external and biofuel industries, while Table 5 contains a collection of other interesting articles which contain many possible synergies and information about process optimization, state of the art processes and industry updates.

Table 4: Final Listing/Categorization of Articles and Synergies Bioethanol Articles

Synergies Present Article Title Type of Synergy

PaperEthanol Conversion of recycled paper sludge to ethanol by SHF and SSF using Pichia stipitis.

ExternalBiofuel

BreadEthanol Ethanol production from bread residues. ExternalBiofuel

WasteEthanol Feasibility of producing bio-ethanol from waste residues. A Canadian perspective.

DDGSFodder Feeding Corn Milling Byproducts to Feedlot Cattle BiofuelExternal

DDGSFood & Fodder Nutritional evaluation of four co-product feedstuffs from the motor fuel ethanol distillation industrustry in the Midwest USA.

BiofuelExternal

Heat and Steam  Ethanol Production

Integration of the bio-ethanol process in a network of facilities for heat and power production from renewable sources using process simulation.

ExternalBiofuel BiofuelBiofuel

Food wastes  Ethanol Diluted acid hydrolysis pretreatment of agri-food wastes for bioethanol production

Integration 

Production/Efficiency Analysis and decrease of the energy demand of bioethanol production by process integration

Separative reactors for integrated production of bioethanol and biodiesel.

Cheese Lactose Wastes

(Lactose)  Ethanol Fermentation of lactose to bioethanol by yeasts as part of integrated solutions for the valorization of cheese whey.

Ethanol  Biodiesel

Production Ethanolysis of used frying oil. Biodiesel preparation and characterization.

BiofuelBiofuel

Ethanol  Human Food and Pharmaceuticals

Separation of high-value products from ethanol extracts of corn by chromatography

BiofuelExternal Biodiesel Articles

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Glycerol  Biogas Anaerobic digestion of glycerol derived from biodiesel manufacturing

Glycerol  Vehicle Fuel Cleaner gasoline production by using glycerol as fuel extender.

Biofuel External

Algae  Biodiesel Biodiesel production from heterotrophic microalgal oil. ExternalBiofuel

Biodiesel By-Products 

Filters Activated carbons from waste biomass: An alternative use for biodiesel production solid residues.

Biodiesel  Cleaning

Agent Evaluation of biodiesel as bioremediation agent for the treatment of the shore affected by the heavy oil spill of the Prestige.

Solar Power  Biodiesel

Production Solar utility and renewability evaluation for biodiesel production process.

Glycerol  Hydrogen Steam reforming of biodiesel by-product to make renewable hydrogen.

Glycerol  Biogas Anaerobic fermentation of glycerol: a patch to economic viabilityfor the biofuels industry.

Glycerol  Feed Feeding value of glycerol as a replacement for corn grain in rations fed to lactating dairy cows.

Glycerol  Vehicle Fuel Glycerol based automotive fuels from future biorefineries. ExternalBiofuel BiofuelBiofuel GlycerolFilters and Microbiological Applications

Glycerol: A promising and abundant carbon source for industrial microbiology.

External/Oil Industries  Produce Biofuel from Veg. Oil

Production and characterization of the biofuels obtained by thermal cracking and thermal catalytic cracking of vegetable oils.

Algae  Biofuel Biofuel potential production from the orbetello lagoon macroalgae: A comparison with sunflower feedstock.

Algae  Biofuel Biofuels from microalgae-A review of technologies for production, processing and extractions of biofuels and co-products

Sewage Sludge 

Biodiesel A multicriteria approach to screening alternatives for converting sewage sludge to biodiesel.

Glycerol  Fuel Additive Conversion of biomass using glycerin to liquid fuel for blending gasoline as alternative engine fuel.

Algae  Biofuel Review on biofuel oil and gas production processes from microalgae.

ExternalBiofuel Biogas Articles

Synergies Present Article Title Category

Quinoa stalk,

totora and o-macrophytes + manure from llama, cow and sheep  Biogas

Anaerobic co-digestion of aquatic flora and quinoa with manures from Bolivian Altiplano.

Sugar beet and starch potato by-products  Biogas

Anaerobic digestion of by-products of sugar beet and starch potato processing.

Food waste  Biogas Anaerobic digestion of food waste: Comparing leachate exchange rates in sequential batch systems digesting food waste and biosolids.

Ryegrass Biogas

Digestate  Particleboard Anaerobic digestion of saline creeping wild ryegrass for biogas production and pretreatment of particleboard material.

ExternalBiofuel BiofuelExternal

Animal by-products 

Biogas Anaerobic digestion of slaughterhouse by-products. ExternalBiofuel Biogas digestate  Solid

Biofuel Applicability of biogas digestate as solid fuel. BiofuelExternal Biogas digestate  Food

for fish Aquacultural and socio-economic aspects of processing carps into some value-added products.

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Apple pulp  Biogas Biogas generation apple pulp ExternalBiofuel

Pineapple peels and rags.

 Biogas Ensilage of pineapple processing waste for methane generation.

Maize + Dairy cattle

manures  Biogas Biogas production from maize and dairy cattle manure—Influence of biomass composition on the methane yield.

Dairy industry  Biogas Comparison of the effectivities of two-phase and single-phase anaerobic sequencing batch reactors during dairy wastewater treatment.

Household biowaste 

Biogas Degradation of household biowaste in reactors. ExternalBiofuel Sludge from Pulp and

paper industy  Biogas Energy use and recovery strategies within wastewater treatment and handling at pulp and paper mills.

Municipal solid waste + agro-industrial by-products + Glycerol  Biogas

Enhanced methane and hydrogen production from municipal solid waste and agro-industrial by-products co-digested with crude glycerol.

Olive mill effluent and

olive cake  Biogas Enhancement of biogas production from olive mill effluent (OME) by co-digestion.

Agro-Industrial waste 

Biogas Enhancement of methane production from barley waste. ExternalBiofuel Silage, sugar beet tops and

oat straw +cow manure  Biogas

Laboratory investigations on co-digestion of energy crops and crop residues with cow manure for methane production: Effect of crop to manure ratio

Carbon Dioxide  Supplement for Plant Growth.

Landfill Biogas for heating Greenhouses and providing Carbon Dioxide Supplement for Plant Growth.

Animal waste  Biogas Manure's allure: Variation of the financial, environmental, and economic benefits from combined heat and power systems integrated with anaerobic digesters at hog farms across geographic and economic regions.

Oil cake  Biogas Oil cakes and their biotechnological applications – A review.

ExternalBiofuel BiofuelBiofuel

Organic municipal solid

waste  Biogas Substituting energy crops with organic fraction of municipal solid waste for biogas production at farm level: A full-scale plant study.

Soybean protein processing

wastewater  Biogas The performance and phase separated characteristics of an anaerobic baffled reactor treating soybean protein processing wastewater.

Biogas stillage Fertilizer Trace and nutrient elements in manure, dung and

compost samples in Austria

Microalgal biomas  Biogas

Carbon dioxide  Microalgal cultivation

Utilization of distillery stillage for energy generation and concurrent production of valuable microalgal biomass in the sequence: Biogas-cogeneration-microalgae-products.

BiofuelExternal External Biofuel

Agro wastes + Animal

wastes Biogas Wet explosion of wheat straw and codigestion with swine manure: Effect on the methane productivity.

External  Biofuel

Organic residues from the sugar and alcohol industry, urban solid and liquid wastes + Bovine and swine manure Biogas

Estimate of the electric energy generating potential for different sources of biogas in Brazil.

Stillage from the bioethanol process  Biogas.

Heat flow

Analysis and decrease of the energy demand of bioethanol-production by process integration.

Fermentation residues.  Biogas.

Heat flow

Evaluation of energy demand and the sustainability of different bioethanol production processes from sugar beet.

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Palm oil mill effluent 

Biogas. Life Cycle Assessment Of Hydrotreated Vegetable Oil From Rape, Oil Palm And Jatropha.

Biofuel production from different organic wastes. Energy flows between industries

Optimal location of lignocellulosic ethanol refineries with polygeneration in Sweden.

ExternalBiofuel Biofuel Biofuel

Agroindustial + Ethanol stillage  Biogas. Digestate  Fertilizers for biomass crops.

Stillage characterization and anaerobic treatment of ethanol stillage from conventional and cellulosic feedstocks.

BiofuelBiofuel BiofuelExternal

Table 5: Other interesting articles General Biofuel Articles

Synergies Present Article Title Type of Synergy

Review Competition between biofuels: Modelling technological learning and cost reductions over time.

Review Synergy analysis of collaboration with biofuel use for environmentally conscious energy systems.

Review

Review Progress in bioethanol processing. Review

Integration of systems for optimized energy efficiency

Integration water, energy and sanitation solution for stand-alone settlements.

ExternalBiofuel BiofuelExternal

Review Comparison of transesterification methods for production of biodiesel from vegetable oils and fats.

Review

A final listing of all synergies in Table 4 is available in Appendix E.

5 UNIQUE SYNERGIES FROM LITERATURE REVIEW

From the aforementioned synergies/articles the following lists have been produced to provide a summary of all unique synergies. When several synergies are of a similar theme, they have been summed into one type of unique synergy, although the feedstocks may be very different. For example, food industry synergies can be of many different types including fruits, vegetables, fats, dairy, etc.

5.1 Ethanol Synergies

 Ethanol DDGS for human food applications[6,7]  DDGS for animal feed[7,8]

 Integration with Extrusion technology for food/fodder production[8]  DDGS used as filler for bioplastics[8-10]

 Combustion of DDGS as a fuel source[10,11]  Corn Oil for biodiesel production[10]

 Fertilizer Production[10]  Construction materials[9,10]

 Bioethanol from food residues (bread, kitchen wastes, etc.)[12-15]  Paper sludge for ethanol production[13]

 Cheese whey lactose for ethanol production[16-18]  Ethanol DDGS and syrup for biogas production[10]

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5.2 Biogas Synergies

 Biomass Wastes as biogas source[19]  Biogas digestate used as solid fuel[20]  Digestate used as particle board fibers[21]  Household wastes as biogas source[22]  Food industry wastes as biogas source[23]

o Fruit industry wastes as biogas source[24] o Animal by-products as biogas source[25,26] o Dairy wastes as biogas source [27]

 Carbon dioxide from biogas upgrading for greenhouses/plant source[28]  Ethanol stillage as biogas source[11,29]

 Digestate used as fertilizer [30]

 Ethanol production heat used for biogas process[31,32]  Municipal solid wastes as biogas residue[33]

 Processing waste water for biogas production[34]  Oil cake as biogas source[35]

 Biogas digestate used as feed [36]

5.3 Biodiesel Synergies from Literature Review

 Biodiesel by-products used as carbon filters[37-39]  Glycerol to biogas production[40,41]

 Biodiesel used as remediation agent for treatment of oil spills[42]  Algae for biodiesel production[43,44]

 Glycerol added to gasoline as fuel extender[45]

 Biodiesel from waste oils (WVO, fish oil, animal tallow, etc.)[46-48]  Glycerol used to produce hydrogen [49-51]

 Glycerol used to produce ethanol, formate and hydrogen[52]  Biodiesel from sewage sludge[53,54]

 Glycerol as automotive fuel [45,55]  Glycerol used as animal feed[56]

6 ANALYSIS AND CONCLUSION

The literature review produced a large number of possible synergies to handle external and biofuel by-products. Among the 84 final synergy articles produced, biogas synergies seem to be a very popular option for the handling of industrial wastes and biomass. Algal biofuels were not as apparent as originally thought though some applications have been provided for the production of oil for biodiesel. Biodiesel synergies consisted primarily of the handling of waste oils for biodiesel production and the use of glycerol for a wide array of applications from vehicle fuel to filters. In the production of ethanol, the use of DDGS for various applications is very common and many possible synergies were produced. However, not many further applications for ethanol by-products have been uncovered though several articles deal with the use of different raw materials (which are industrial by-products) for the production of ethanol.

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Furthermore, there seems to be a large number of articles concerned with the production of hydrogen from the biofuels themselves, especially for the production of ethanol in various forms and thereafter utilizing the ethanol to produce hydrogen. Only one of these articles was highlighted for this literature review. Beyond hydrogen production, 2nd generation ethanol production was plentiful in the literature.

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PEIDONG, Z., YANLI, Y., YONGSHENG, T., XUTONG, Y., YONGKAI, Z., YONGHONG, Z. and LISHENG, W., 2009. Bioenergy industries development in China: Dilemma and solution. Renewable and Sustainable Energy Reviews, 13(9), 2571-2579.

DEMIRBAS, A., 2009. Biofuels securing the planet’s future energy needs. Energy

Conversion and Management, 50(9), 2239-2249.

DEMIRBAS, A., 2008. Biofuels sources, biofuel policy, biofuel economy and global biofuel projections. Energy Conversion and Management, 49(8), 2106-2116.

BÖRJESSON, P. and MATTIASSON, B., 2008. Biogas as a resource-efficient vehicle fuel. Trends in biotechnology, 26(1), 7-13.

GAUTAM, R., BARAL, S. and HERAT, S., 2009. Biogas as a sustainable energy source in Nepal: Present status and future challenges. Renewable and Sustainable Energy Reviews, 13(1), 248-252.

PRASERTSAN, S. and SAJJAKULNUKIT, B., 2006. Biomass and biogas energy in Thailand: Potential, opportunity and barriers. Renewable Energy, 31(5), 599-610.

KAYGUSUZ, K. and TÜRKER, M.F., 2002. Biomass energy potential in Turkey. Renewable

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MÜNSTER, M. and LUND, H., Comparing Waste-to-Energy technologies by applying energy system analysis. Waste Management, In Press, Corrected Proof.

ILLMER, P. and GSTRAUNTHALER, G., 2009. Effect of seasonal changes in quantities of biowaste on full scale anaerobic digester performance. Waste Management, 29(1), 162-167. NILSSON, L.J., PISAREK, M., BURIAK, J., ONISZK-POPŁAWSKA, A., BUĆKO, P., ERICSSON, K. and JAWORSKI, L., 2006. Energy policy and the role of bioenergy in Poland. Energy Policy, 34(15), 2263-2278.

BÖRJESSON, P. and BERGLUND, M., 2006. Environmental systems analysis of biogas systems—Part I: Fuel-cycle emissions. Biomass and Bioenergy, 30(5), 469-485.

BÖRJESSON, P. and BERGLUND, M., 2007. Environmental systems analysis of biogas systems—Part II: The environmental impact of replacing various reference systems. Biomass

and Bioenergy, 31(5), 326-344.

SALOMON, K.R. and SILVA LORA, E.E., 2009. Estimate of the electric energy generating potential for different sources of biogas in Brazil. Biomass and Bioenergy, 33(9), 1101-1107. NGUYEN, T.L.T., GHEEWALA, S.H. and GARIVAIT, S., 2007. Fossil energy savings and GHG mitigation potentials of ethanol as a gasoline substitute in Thailand. Energy

Policy, 35(10), 5195-5205.

Grinding matter for the UK's first biogas plant. 2008. World Pumps, 2008(496), 12-12.

RYAN, D., GADD, A., KAVANAGH, J. and BARTON, G.W., 2009. Integrated biorefinery wastewater design. Chemical Engineering Research and Design, 87(9), 1261-1268.

ODHIAMBO, J.O., MARTINSSON, E., SOREN, S., MBOYA, P. and ONYANGO, J., 2009. Integration water, energy and sanitation solution for stand-alone settlements. Desalination, 248(1-3), 570-577.

KLEEREBEZEM, R. and VAN LOOSDRECHT, M.C., 2007. Mixed culture biotechnology for bioenergy production. Current opinion in biotechnology, 18(3), 207-212.

MARTENS, W. and BÖHM, R., 2009. Overview of the ability of different treatment methods for liquid and solid manure to inactivate pathogens. Bioresource technology, 100(22), 5374-5378.

YU, L., YAOQIU, K., NINGSHENG, H., ZHIFENG, W. and LIANZHONG, X., 2008. Popularizing household-scale biogas digesters for rural sustainable energy development and greenhouse gas mitigation. Renewable Energy, 33(9), 2027-2035.

JURADO, F. and SAENZ, J.R., 2002. Possibilities for biomass-based power plant and wind system integration. Energy, 27(10), 955-966.

RAMACHANDRA, T.V., JOSHI, N.V. and SUBRAMANIAN, D.K., 2000. Present and prospective role of bioenergy in regional energy system. Renewable and Sustainable Energy

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WANG, Q., 2009. Prevention of Tibetan eco-environmental degradation caused by traditional use of biomass. Renewable and Sustainable Energy Reviews, 13(9), 2562-2570.

FENG, T., CHENG, S., MIN, Q. and LI, W., 2009. Productive use of bioenergy for rural household in ecological fragile area, Panam County, Tibet in China: The case of the residential biogas model. Renewable and Sustainable Energy Reviews, 13(8), 2070-2078. KATINAS, V. and MARKEVICIUS, A., 2006. Promotional policy and perspectives of usage renewable energy in Lithuania. Energy Policy, 34(7), 771-780.

MARKARD, J., STADELMANN, M. and TRUFFER, B., 2009. Prospective analysis of technological innovation systems: Identifying technological and organizational development options for biogas in Switzerland. Research Policy, 38(4), 655-667.

DEMIRBAS, M.F. and BALAT, M., 2006. Recent advances on the production and utilization trends of bio-fuels: A global perspective. Energy Conversion and Management, 47(15-16), 2371-2381.

BHATTACHARYA, S.C. and JANA, C., 2009. Renewable energy in India: Historical developments and prospects. Energy, 34(8), 981-991.

KATINAS, V. and SKEMA, R., 2001. Renewable energy policy in Lithuania. Energy

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SUZUKI, Y., KUBOTA, A., FURUKAWA, T., SUGAMOTO, K., ASANO, Y., TAKAHASHI, H., SEKITO, T., DOTE, Y. and SUGIMOTO, Y., 2009. Residual of 17β-estradiol in digestion liquid generated from a biogas plant using livestock waste. Journal of

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CHEN, B. and CHEN, G.Q., 2007. Resource analysis of the Chinese society 1980–2002 based on exergy—Part 2: Renewable energy sources and forest. Energy Policy, 35(4), 2051-2064.

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RAMACHANDRA, T.V. and SHRUTHI, B.V., 2007. Spatial mapping of renewable energy potential. Renewable and Sustainable Energy Reviews, 11(7), 1460-1480.

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MURPHY, J.D. and MCCARTHY, K., 2005. The optimal production of biogas for use as a transport fuel in Ireland. Renewable Energy, 30(14), 2111-2127.

FUJINO, J., MORITA, A., MATSUOKA, Y. and SAWAYAMA, S., 2005. Vision for utilization of livestock residue as bioenergy resource in Japan. Biomass and Bioenergy, 29(5), 367-374.

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APPENDIX B: BIODIESEL REFERENCES

Glycerine/Glycerol

Hayyan M, Mjalli FS, Hashim MA, AlNashef IM. A novel technique for separating glycerine from palm oil-based biodiesel using ionic liquids. Fuel Processing Technology

2010;91(1):116-20.

Siles López JÁ, Martín Santos,María de los Ángeles, Chica Pérez AF, Martín Martín A. Anaerobic digestion of glycerol derived from biodiesel manufacturing. Bioresource technology 2009;100(23):5609-15.

Frusteri F, Arena F, Bonura G, Cannilla C, Spadaro L, Di Blasi O. Catalytic etherification of glycerol by tert-butyl alcohol to produce oxygenated additives for diesel fuel. Applied Catalysis A: General 2009;367(1-2):77-83.

Kiatkittipong W, Suwanmanee S, Laosiripojana N, Praserthdam P, Assabumrungrat S. Cleaner gasoline production by using glycerol as fuel extender. Fuel Processing Technology;In Press, Corrected Proof.

Sánchez EA, D'Angelo MA, Comelli RA. Hydrogen production from glycerol on Ni/Al2O3 catalyst. International Journal of Hydrogen Energy;In Press, Corrected Proof.

Karinen RS, Krause AOI. New biocomponents from glycerol. Applied Catalysis A: General 2006;306:128-33.

Sun F, Chen H. Organosolv pretreatment by crude glycerol from oleochemicals industry for enzymatic hydrolysis of wheat straw. Bioresource technology 2008;99(13):5474-9.

Bonet J, Costa J, Sire R, Reneaume J, Pleşu AE, Pleşu V, Bozga G. Revalorization of glycerol: Comestible oil from biodiesel synthesis. Food and Bioproducts Processing 2009;87(3):171-8.

Alcohol

Encinar JM, González JF, Rodríguez-Reinares A. Ethanolysis of used frying oil. Biodiesel preparation and characterization. Fuel Processing Technology 2007;88(5):513-22.

Kiss AA. Separative reactors for integrated production of bioethanol and biodiesel. Computers & Chemical Engineering;In Press, Corrected Proof.

Gui MM, Lee KT, Bhatia S. Supercritical ethanol technology for the production of biodiesel: Process optimization studies. The Journal of Supercritical Fluids 2009;49(2):286-92.