Biofuels and Biotechnology Flashcards
Define bioenergy and give exmaples
Any form of energy derived from biological material
- Heat
- electricity
- Liquid transportation fuels and biogas
Define biofuel
Generally refers to liquid transportation fuels and biogas. Strict definition also includes solid biomass for combustion
Give 5 current major biofuels
Bioethanol (Yeast - Saccharomyces) Biobutanol (Bacteria - Clostridium) Biodiesel (Plants, algae, bacteria) Biohydrogen (algae, bacteria) Anaerobic digestion (bacteria and archaea)
Describe current bioethanol usage
- Brazil and USA use bioethanol/gasoline blends in most cars (e.g. E10 (10% ethanol))
- E85 blend used in flex-fuel vehicles (FFV). 40 million FFV globally (20 mil in Brazil, 15 mil in US)
- In US mid-west, 10% ‘gas’ is bioethanol
Describe 1st gen bioethanol production
- 2.5 billion gallons made annually in US (predominantly in Iowa, Illinois, Wisconsin and Nebraska)
- Grains of corn used (65-70% starch). Corn ground up to ‘meal’ and cooked to breakdown starch to glucose. Yeast added in fermentation (48 hrs). Ethanol is distilled off and further cleaned. Spent grains processed for animal feed/syrup
- In Brazil process is the same but with sugar cane instead of corn
Describe biobutanol, how it is made, and give benefits
- A 4 carbon straight chain alcohol which is normally made from oil (synthetic butanol) but can be made biologically by Clostridium bacteria using ABE fermentation under anaerobic conditions.
- Currently made using starch. In 2012 the first cellulosic n-butanol was made from residual corn waste
- Biobutanol is a very versatile transportation fuel: Can be used in normal cars and other vehicles (drop-in fuel), and can be pumped around better than ethanol as less corrosive and less volatile. Butanol also used in chemical industry, and so can be sold for more than biofuel
Describe biodiesel, how it is made and give benefits
- Biodiesel is a mixture of fatty acid esters which are made from triacylglycerols (TAGs) from biological sources.
- Most common to react a TAG with methanol to get a fatty acid methyl ester in a transesterification reaction.
- Considered renewable as primary feedstock is vegetable oil or animal fat. Also low contribution to global warming as CO2 used to make fats were taken from the air, and it emits lower emission when combusted.
Plants as TAG producers
- Plants use TAG as major storage lipids in seeds
- Vegetable oil is currently the most widely used source of TAGs for biodiesel
- Best plants for TAGs are Rapeseed oil, Sunflower seed oil, Soybean oil, Palm oil
- In UK, 400,000 hectares oilseed rape grown annually (also a break crop for wheat)
Microalga as TAG producers
- Unicellular photosynthetic eukaryotes
- Many microalaga accumulate TAGs in response to stress and N-limitation (Trade-off as stress and limited N will reduce overall yield). Chlorella vulgaris can have 70% of dry mass as TAGs. Chlamydomonas reinhardtii being engineered (competing pathways to TAG removed)
Describe a non-photosynthetic TAG producer
- Actinomycetales bacteria have uniquely developed a storage lipid cycle that leads to accumulation of TAGs
- In the bacteria, TAGS function as cellular fuel (beta-oxidation), form components of the plasma membrane, and substrates for the enzymatic production of extracellular lipids
- Rhodococcus grown with gluconate as carbon source can accumulate up 76% of cell dry weight in TAGs
Describe hydrogen as a fuel and how it is currently made
- Engine combustible
- Highest mass to energy ratio of any chemical (rocket propellant)
- Carbon free and main source is water
- Currently made via steam reformation of natural gas (needs high temperature and catalysts)
- Can also be made by water splitting using electrolysis (high electricity cost)
Biological manufacture of hydrogen
- Biophotolysis was discovered to occur in alage during photosynthesis if limited for sulphur (low and variable production levels)
- Bacteria can build H2 aspart of their normal fermentative metabolism. Can yield 4H2 per glucose. Uses hydrogenase enzymes (O2 sensitive and easily damaged)
- Hydrogenases can also work in vitro, therefore development of oxygen-tolerant hydrogenases may be the future
Describe anaerobic digestion and how it can be used to make biofuel
AD is microbial digestion of organic waste to methane containing biogas, CO2, and an N rich digestate that can be used as fertiliser
- Flexible in terms of feedstocks and is the UK governments preferred means of disposing of food waste
How has the green revolution influenced yields
Maize in US - yield up 6 fold, 20% decrease in harvested area
700% yield increase in 50 years
Give problems associated with biofuels as a business
- Competing with fossil fuels (easy to remove)
- High volume, low value business (investments only worthwhile at ~1m tonnes of biomass per year e.g. sugar cane ethanol was suppoerted by the brazilian government for 30 years before it became competitive)
- Lignocellulose a challanging substrate (70% polysaccharide, but only 40% of that easily removable hexose sugar) - cost efficiency of removal
Describe the cost challenge associated with bioethanol
- EU mandates that by 2020, 20% of all liquid tranportation should be biofuel, but only 5 % of this can come from food commodities (1st gen)
- Making bioethanol from lignocellulose is a 4 step process, with first 2 steps amount to 1/3 cost
- 2g sugar = 1g ethanol + 1g CO2
- Prices of feedstocks (sugar/mollases/wheat/straw) vs. cost of processing + amount feedstock required per 1g ethanol leaves very fine profit margin
Describe the problems with using lignocellulose to make biofuels
- Only a portion of the feedstock potentially fermentable
- Need to generate value from the rest of the feedstock
- Requires a lot of energy to get sugars out
- Feedstock has low density, causing logistical challenges
Give ways to add value to the waste products of lignocellulosic biofuel production
- Use nutrients from anaerobic digestion/microwave conversion of lignin as fertilisers
- Biogas can be produced from anaerobic digestion/microwave conversion
- Spent fermentation broth can be watered down and added to feedstock conversion
- Other products such as high value and platform chemicals, and animal feed can also be produced
Describe pretreatment and state why it is required when making lingocellulosic bioethanol
- Breakdown of physical structure of the feedstock to allow increased digestibility and biofuel prodution
Required:
- To allow enzymatic saccharification
- Open up structure to give access
- Break up lignin network
- Remove/avoids inhibitors of saccharification
- Sterilises feedstock
Give pros and cons of pretreatment
Pro: 70% increase in enzymatic hydrolysis after pretreatment
Con: 30% of processing cost, High energy and specialist equipment required
Give types of pretreatment
Physical: Particle size reduction, Hydrothermolysis, steam explosion
Chemical: Acid, base, AFEX (ammonia fibre expanision)
Biolgical: treatments such as lignin degrading fungi suggested (logistics problems as dwell times are long)
Describe how to improve feedstocks for processing
- Increase digestibility
- Lower energy/chemical input
- Lower enzyme laoding
- Decrease in inhibitor production
- Improve the amount of available sugars and type of sugars
What is the role of lignin?
Increases wall rigidity and renders network insoluble and resistant to degradation
- 3 types, all formed from phenylalanine
- H,G and S types
Describe studies attempting to make more digestible plants
Chen and Dixon, 2007 - Made hct mutants of alfalfa which are high degestible, but dwarfed
Van Acker et al, 2013 - Selected KO mutants in arabidopsis for analysis of biomass digestibility and lignin content
- Some mutants there was no effect, others showed cellulose conversion of 77.9% without pretreatment (88.3% with)
Give basic information about fermentation
- Second energy supply route that functions in the absence of an alternative electron receptor
- Glucose converted to pyruvate mainly through glycolysis pathway (makes 2ATP + 2NADH)
- E.coli undergoes mixed acid fermentatio (produces mix of acetate, ethanol, succinate, CO2 and H2)
Give the organims which can make each type of biofuel
Ethanol: S.cerevisieae, Z.mobilis, E.coli (bioengineered)
Butanol: Clostridium species (ABE fermentation)
Hydrogen: E.coli (manipulation of mixed acid fermetation)
Describe ethanol formation in yeats and z.mobilis
Yeast: S.cerevisieae ferments glucose into ethanol through EMP pathway (1 mol glucosu = 2 mol ethanol)
Z.mobilis:
- homo-ethanol fermentation (produces higher ethanol yield than yeast)
- Uses Entner-dondoroff pathway for glycolysis (produces less ATP, thefore must convert more glucose to ethanol)
Describe ABE fermentation
- Developed by PAsteur
- Named for acetone, butanol, ethanol products (ratio manipulated by strain/conditions)
- Carried out by Clostridium species
Two step process:
1) Acidogenicphase, duringthegrowthphaseinanaerobicconditions,
producesaceticandbutyricacids(likenormalfermentation). Resultsintheacidificationofthegrowthmedium.
2) Oncemostofthecarbonintheenvironmenthasbeenconsumed
and growthratedrops,secondphasewhereenergy&reducing
potential
can beproducedbythereuptake ofacids. Acids converted to neutral products, namely acetone and butanol
Describe the process of biohydrogen fermentation
- E.coli mixed acid fermentation product
- Created by the formate-hydrogen-lyase (FHL) enzyme
- E.coli engineered to increase FHL activity and decrease competing pathways
Describe the FHL complex
- Membrane bound complex
- Regulatory mutants in hycA and fhlA can increase levels over WT, but other stages limit higher production levels
- Requires metal co-factors (Fe-S clusters, Mb co-factors) and 21st amino acid selenocysteine (requires dedicated apparatus to insert and is the rate limiting stage for increasing Fdh-H (subunit) activity
Describe how to overcome carbon loss in EMP pathway
- when glucose converted to pyruvate by EMP or ED pathway, a carbon molecule is lost during conversion to AcetylCoA (directly to CO2 or from breakdown of formate)
- Potential for enzymes in the pentose phosphate pathway to rearange sugars to make 4+2 from 6 instead of 3+3
Describe the components of lignocelllulose
Cellulose: linear polymer of B-(1-4)-linked glucose organised in regular crystalline arrangement forming linear, insoluble microfibrils
Hemicellulose: More complex polysaccharides often rich in pentose sugars such as xylose and arabinose + a variety of other modifications that allow them to attach to cellulose and lignin
Lignin: highly irregular network of cross-linked phenylpropanoid type molecules
