Algae Biomass Methane Digester for Renewable Electricity

8/14/2019 Algae Biomass Methane Digester for Renewable Electricity

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Algal Production for Biogas Electricity

Methane and power produced in anaerobic digestion facilities can be utilized to replaceenergy derived from fossil fuels, and hence reduce emissions of greenhouse gasses.This is due to the fact that the carbon in biodegradable material such as algae is part ofa carbon cycle. The carbon released into the atmosphere from the combustion of biogashas been removed by plants in order for them to grow in the recent past. This can haveoccurred within the last decade, but more typically within the last growing season. If theplants are re-grown, taking the carbon out of the atmosphere once more, the system willbe carbon neutral. This contrasts to carbon in fossil fuels that has been sequestered in

the earth for many millions of years, the combustion of which increases the overalllevels of carbon dioxide in the atmosphere.

Biogas plants consist of two components: a digester (or fermentation tank) and a gasholder. The digester is a cube-shaped or cylindrical waterproof container with an inletinto which the fermentable mixture is introduced in the form of a liquid slurry. The gasholder is normally an airproof steel container that, by floating like a ball on thefermentation mix, cuts off air to the digester (anaerobiosis) and collects the gasgenerated. In one of the most widely used designs (Figure 2), the gas holder isequipped with a gas outlet, while the digester is provided with an overflow pipe to leadthe sludge out into a drainage pit.

The average cost of a digester is nearly $1.5 million, and it takes about six years to earnback that original investment without any grants.

Creation of biogasBiogas is a product of the metabolism of methane bacteria and is created when thebacteria degrade a mass of organic material. The methane bacteria can only work andreproduce if the substrate is sufficiently bloated with water (at least 50 %). In contrast toaerobic bacteria, yeasts and fungi they cannot exist in a solid phase.

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Exclusion of airThese micro-organisms are strongly anaerobic. If the substrate still contains oxygen, asfor example is the case with liquid manure, then aerobic bacteria must use this up first.This happens during the first phase of the biogas process. Low quantities of oxygen,

such as occur through the deliberate aeration of air in order to desulphurise thematerial, do not cause any harm.

TemperatureThe working range of the methane bacteria lies between 0 and 70C. At highertemperatures they are killed off, with the exception of a few strains which can survive intemperatures up to 90C. The speed of the decomposition process is heavily dependenton temperature. The following applies: the higher the temperature, decompositionoccurs more quickly, the production of gas is higher, the decomposition time is shorterand the content of methane in the biogas is lower.Practical experience has shown that there are typical temperature ranges in whichparticular strains of bacteria feel quite comfortable:

mesophile strains at temperatures of 25-35Cthermophile strains at temperatures above 45CThe higher the temperature, the more sensitive the bacteria are to temperaturevariations, especially when these occur for a short time and the temperature drops.Whilst in the mesophile range daily variations of from 2 to 3C about the medium canstill be supported, for the thermophile range these variations should not be more than1C. Over longer periods of time (around 1 month) the bacteria become accustomed tonew temperature ranges.The pH value The pH value should be in the weakly alkaline range of about 7.5. Forliquid manure and dung this range usually occurs naturally during the second phase ofthe decomposition process, as a result of the creation of ammonium. For more acidic

substrates such as slop, whey and silage it may be necessary to add lime in order toincrease the pH value.

Supply of nutrientsMethane bacteria cannot break down fats, protein, carbohydrate (starch, sugar) andcellulose in pure form. In fact they need soluble nitrogen compounds, minerals andtrace elements to break down the cellular mass of these materials. Sufficient quantitiesof these substances are present in dung and liquid manure. But Algae Biomass andgrass too (in fresh and preserved form) as also marc, slop and whey contain sufficienttotal nutrients and can in principle be broken down alone. In practice however it isrecommended that dung and liquid manure are used as a stable basic substrate and

additional amounts of the materials referred to are added, so as to avoid segregationand to achieve a good buffering of acids and lyes.

Stages



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The key process stages of anaerobic digestion there are four key biological andchemical stages of anaerobic digestion:

1. Hydrolysis

2. Acidogenesis

3. Acetogenesis

4. MethanogenesisIn most cases biomass is made up of large organic polymers. In order for the bacteria inanaerobic digesters to access the energy potential of the material, these chains mustfirst be broken down into their smaller constituent parts. These constituent parts ormonomers such as sugars are readily available by other bacteria. The process ofbreaking these chains and dissolving the smaller molecules into solution is calledhydrolysis. Therefore hydrolysis of these high molecular weight polymeric componentsis the necessary first step in anaerobic digestion. Through hydrolysis the complexorganic molecules are broken down into simple sugars amino acids, and fatty acids.

Acetate and hydrogen produced in the first stages can be used directly bymethanogens. Other molecules such as volatile fatty acids (VFAs) with a chain length

that is greater than acetate must first be catabolised into compounds that can be directlyutilized by methanogens.

Digestate is the solid remnants of the original input material to the digesters that themicrobes cannot use. It also consists of the mineralized remains of the dead bacteriafrom within the digesters. Digestate can come in three forms; fibrous, liquor or a sludge-based combination of the two fractions. In two-stage systems the different forms ofdigestate come from different digestion tanks. In single stage digestion systems the twofractions will be combined and if desired separated by further processing.

Digestate liquor can be used as a fertilizersupplying vital nutrients to soils. The solid,fibrous component of digestate can be used as a soil conditioner. The liquor can beused as a substitute for chemical fertilizers which require large amounts of energy to

produce and transport. The use of manufactured fertilizers is therefore more carbonintensive than the use of anaerobic digestate fertilizer. This solid digestate can be usedto boost the organic content of soils. There are some countries, such as Turkey wherethere are many organically depleted soils, and here the markets for the digestate can be

just as important as the biogas.

In countries that collect household waste, the utilization of local anaerobic digestionfacilities can help to reduce the amount of waste that requires transportation to

http://en.wikipedia.org/wiki/Hydrolysishttp://en.wikipedia.org/wiki/Acidogenesishttp://en.wikipedia.org/wiki/Acetogenesishttp://en.wikipedia.org/wiki/Methanogenesismailto:[email protected]://en.wikipedia.org/wiki/File:Stages_of_anaerobic_digestion.JPGhttp://en.wikipedia.org/wiki/Hydrolysishttp://en.wikipedia.org/wiki/Acidogenesishttp://en.wikipedia.org/wiki/Acetogenesishttp://en.wikipedia.org/wiki/Methanogenesismailto:[email protected]


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centralized landfill sites or incineration facilities. This reduced burden on transportationhas and will reduce carbon emissions from the collection vehicles. If localized anaerobicdigestion facilities are embedded within an electrical distribution network, they can helpreduce the electrical losses that are associated with transporting electricity over anational grid.

The second by-product (acidogenic digestate) is a stable organic material comprisedlargely of lignin and cellulose, but also of a variety of mineral components in a matrix ofdead bacterial cells; some plastic may be present. The material resembles domesticcompost and can be used as compost or to make low grade building products such asfibreboard.

The third by-product is a liquid (methanogenic digestate) that is rich in nutrients andcan be used as a fertilizer dependent on the quality of the material being digested.Levels of potentially toxic elements (PTEs) should be chemically assessed. This will be

dependent upon the quality of the original feedstock. In the case of most clean andsource-separated biodegradable waste streams the levels of PTEs will be low. In thecase of wastes originating from industry the levels of PTEs may be higher and will needto be taken into consideration when determining a suitable end use for the material.

Digestate typically contains elements such as lignin that cannot be broken down by theanaerobic microorganisms. Also the digestate may contain ammonia that is phytotoxicand will hamper the growth of plants if it is used as a soil improving material. For thesetwo reasons a maturation or composting stage may be employed after digestion. Ligninand other materials are available for degradation by aerobic microorganisms such asfungi helping reduce the overall volume of the material for transport. During thismaturation the ammonia will be broken down into nitrates, improving the fertility of the

material and making it more suitable as a soil improver. Large composting stages aretypically used by dry anaerobic digestion technologies.

Wastewater

The final output from anaerobic digestion systems is water.

Algae Biomass Production for Biogas

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Algae as Biogas resource. Algae as electricity is another resource derived from algalbiomass.

This is not Rocket Science (heres the layman's explanation)

Algae is a single cell organism

Algae feeds on the Hydrogen from the H2O and the Carbon from the CO2 and

through the process of photosynthesis produces Hydrocarbon Chains and releases

Oxygen. Most strains of the Green and Green-Blue Algae can double their mass

every 24hour growing cycle. Different strains of Algae produce Algae Oil with slightly

different hydrocarbon chains

Microalgae have much faster growth-rates than terrestrial crops. The per unit areayield of oil from algae is estimated to be from between 2,000 to 20,000 gallons per

acre, per year(4.6 to 18.4 l/m2 per year); this is 7 to 30 times greater than the next

best crop, Chinese tallow (699 gallons).

Studies show that algae can produce up to 60% of their biomass in the form of oil.

Because the cells grow in aqueous suspension where they have more efficient



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access to water, CO2 and dissolved nutrients, microalgae are capable of producing

large amounts of biomass and usable oil in either high rate algal ponds or

photobioreactors. This oil can then be turned into biodiesel which could be sold for

use in automobiles. The biomass (algae cake) can be used for biogas production

into methane to generate electricity. The more efficient this process becomes the

larger the profit that is turned by the company. Regional production of microalgaeand processing into biofuels will provide economic benefits to rural communities.

Biobutanol

Butanol can be made from algae using only a solar powered biorefinery. This fuel

has an energy density similar to gasoline, and greater than that of either ethanol or

methanol. In most gasoline engines, butanol can be used in place of gasoline with

no modifications. In several tests, butanol consumption is similar to that of gasoline,

and when blended with gasoline, provides better performance and corrosion

resistance than that of ethanol.

The green waste left over from the algae oil extraction can be used to produce

butanol.

Biogasoline

Jet Fuel is being made from algae oil currently.

Flare Test-Establish that fuel combusts, not explodes.

Can Combustor Test-Fuel is compatible with basic jet technology.



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Algae seems to hold the most promise to meet many needs to include methane

gas production for electricity.

Algae Desirable Characteristics:

Easy to grow

Grow anywhere

High yield per acre

Not used for Human or Animal Consumption

Environmentally friendly



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Algae remove massive amounts of CO2 (Carbon dioxide) from the air. Algae farms are

glutton eaters of CO2 gas providing a means for recycling waste carbon dioxide from

fossil fuel combustion. It is possible to sequester as much as one billion tons of CO2 per

year from algae farms. The United States has one energy plant that produces 25.3

million tons of CO2 by itself. This technology has attracted companies that need

inexpensive CO2 sequestration solutions & renewable energy solutions.

The combination of algae production & methane biogas is a green way to create

endless renewable clean energy for many cities and industries.


Algae Biomass Methane Digester for Renewable Electricity

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