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The Amazing Realities of the Humble Anaerobic Digester
For a biogas digester to produce gas, it just requires seeding with methane-producing bacteria. This isn't hard because these exist all around us.
Biogas is generated by the breaking down of natural, biodegradable waste or product (also called biomass) such as veggies, leaves, grass, weeds, remaining food scraps as well as such.
It's called a digester because natural product is consumed as well as digested by bacteria to generate biogas.
Organic feedstocks are very flexible, varying from farm manures and also crops, to sewage sludge and also event catering wastes and also food wastes (consisting of raw and also cooked food, consisting of meat items).
The REA has been involved in campaigning for the manufacturing of biogas in the UK considering that 2001 as well as formed the Biogas Sector Group in 2004.
Every tonne of food waste reused by anaerobic food digestion as an option to garbage dumping that material avoids in between 0.5 and 1.0 tonne of CARBON DIOXIDE going into the environment, one of the numerous benefits of anaerobic food digestion.
What Can Go Into a Digester?
Anything natural can be fed to the digester supplied it's naturally degradable and also has very percentages of cellulose. Other common natural products made use of in biogas digesters consist of sewer, glycerin, algae and also lawns. After the methane-producing microorganisms is presented, the microorganisms will reproduce and the procedure continues definitely, and there is no risk that the bacteria will certainly die.
Diversified farming nowadays is everything about sustainable renewable energy, from discussing green energy resources, to products, services, and innovation advancements in this field.
A typical anaerobic digestion plant (digester) creates as much as 1,900 m3/hr of enriched biomethane by cleansing.
Also, many are updating the methane-rich biogas created from the anaerobic food digestion of waste.
Like natural gas, biogas is made use of as a gas to create electricity to power farm equipment, for lights applications, in gas stoves for food preparation, and also for transport.
Not Just a Large Tank with a Glossy Plastic Dome Over It!
A biogas digester (also known as a biogas plant) is a large tank where inside biogas is created with the decomposition/breakdown of raw material through a process called anaerobic food waste digestion.
Biogas can additionally be cleaned as well as upgraded to create pressed natural gas (CNG) or liquefied natural gas (LNG).
CNG as well as LNG can be utilized to fuel vehicles and also cars and trucks. All anaerobic food digestion systems stick to the same basic concepts whether the feedstock is food waste, pet manures or wastewater sludge. The systems may have some differences in style but the procedure is generally the very same.
A Proportion of Carbon Dioxide - Always Found in Raw Biogas - Needs Removing from the Gas
A percentage of CO2 is always found in biogas when it is formed. It has to be removed during upgrading as there is none in natural gas LNG.
After removing the CO2 (as well as various other trace gases using a variety of methods in a procedure referred to as upgrading) the continuing to be methane is known as Renewable Gas or Biomethane.
The Coevorden (BEC) bio-digester, which provided the very first cubic meters of eco-friendly gas to Gasunie's nationwide gas network, is an example of an upgraded biogas supply.
One cubic metre of biogas at 60% methane material converts to 6.7 kWh energy.
After the gas is gotten rid of the slurry will certainly flow back right into the container it remained in at first.
Biogas is extensively made use of in homes around the world, particularly in nations where this modern technology has been extensively readily available and made use of.
As an example, in Europe companies such as ENER-G deal small CHP (4kWe to over 10MWe) from biogas, with around 170MWe currently set up.
Natural Fertilizer Output Enhances Soil Quality
The digester upgrades the biogas to biomethane (~ 98%; 1.5% nitrogen). The gas to grid plant at Bristol Sewage Treatment Works was the initial and largest of its kind.
The upgrading method prevents biomass transportation problems, in contrast with present biorefineries, while effectively valorizing decentralized biomass feedstocks such as agricultural waste or energy plants.
City of Oslo Digester Plant
Another example is the biogas digester plant which is operated behalf of EGE (Waste-to-Energy Agency) and the City of Oslo. Sweden is a globe leader in upgrading and use biomethane for transportation, and has lots of 'biogas lorries', including private cars, buses, as well as even a biogas train and a biogas powered exploring automobile group.
Gas is commonly used as a transportation fuel in lots of European nations, especially Italy, which flaunts 650,000 gas powered lorries.
A recently funded research study program on fuel will assess the opportunity of making use of biogas as a fuel for compression ignition engines of non-road cars as well as tractor makers of plant utilized in agriculture.
Gas Injected to the Natural Gas Grid
Biomethane made from biogas is slightly lower in calorific value than natural gas. To supply all users fairly it needs to be supplemented with a higher calorific gas. Propane from cylinders is the usual solution.
However, some biogas plant operators are finding ways to avoid this unwanted use of a fossil derived fuel by improving the calorific value their digester supplies.
This enriches the gas to natural gas quality and calorific worth.
After enrichment the biogas generated from the digesters then enters the gas to grid plant.
Sewage Treatment Sludge from Wastewater Treatment (Sewage Works)
Sewer sludge as well as food waste is dealt with and pumped right into a collection of anaerobic digesters.
Sewage Works biogas from sludge provides the nationwide grid with sufficient gas to provide thousands of regional residences and also guarantee the sewer treatment works is energy self-sufficient.
This freely generated biomethane can, of course, after that be infused into the gas grid.
Update on the State of Anaerobic Digestion in the UK with the Latest Number of Operational Plants
Anaerobic digestion (AD) mostly uses existing waste feedstocks, at times partly with purpose-grown crops, helping to reduce carbon emissions from waste, energy use, agriculture, and any business with access to organic waste:
1.Waste: by converting it into less harmful forms, including reducing odors when spread on land
2.Heating: by providing hot water for heating buildings, drying crops etc
3.Electricity use: by providing renewable biogas for electricity generation
4.Agriculture: by providing biogas for use as fuel for farm machinery.
5.Any business: which creates waste organic material (biomass) or has access to it.
That’s why Anaerobic Digestion (AD) is a key part of a low-carbon emissions future, in a circular economy that turns wastes into renewable resources.
Anaerobic Digestion's in the Production of Low-carbon Methane
AD has a potentially important role to play in the production of low-carbon methane.
When biogas is upgraded (purified) the “biomethane” output could meet 30% of the UK’s domestic gas demand.
At the same time this would abate 50 million tonnes of Carbon dioxide-equivalent over the next 25 years, as well as helping to provide energy and food security.
In the past 10 years, the AD industry has grown from a capacity of 170 megawatts electrical-equivalent (MWe-e) in to 899 MWe-e today.
There are 648 AD plants across the country, producing renewable energy and natural fertilizer.
AD Growth is Mostly in Biomethane Production
AD growth is currently most notable in biomethane, where around 30 new facilities are due to connect to the gas grid within the next couple of years, on the back of a tariff incentive under the UK government's Renewable Heat Incentive.
These new facilities should add enough additional capacity to power almost 200,000 homes each year.
Production of biomethane as a transport fuel is also being facilitated by the Renewable Transport Fuel Obligation.
AD Facilities Growth in Recycling Inedible Food Waste
In addition. the number of AD facilities recycling inedible food waste is likely to grow over the next decade as more local authorities in England introduce separate food waste collections in the wake of legislation proposed in the Resources and Waste Strategy (published in Autumn 2018).
AOBA estimates that the amount of food waste diverted from landfill as a result could lead to 80 new food-waste AD facilities.
This would increase UK biogas industry Capacity by 187MWe-e (the equivalent of Fellside Power Station), reducing CHG by emissions by 1.5 million tonnes of CO2 equivalent - or 2.4 per cent.
Many unfortunate UK owners of diesel powered cars feel they have been duped into buying them by false "green" promises about diesel vehicles. They think that although they never sought to contribute to city air pollution, they are trapped into continuing to run their polluting vehicles. At least, they do resolve themselves not to take action until they trade in their current vehicle, often not until several years time. It has been commonly accepted that if you own a diesel vehicle, not by your own preference, but having been encouraged to own a diesel by the government. You are left with no alternative but continue.
Via Wikipedia - Donald Trung Quoc Don (Chữ Hán: 徵國單) - CC BY-SA 4.0
But, the fact is that you don't have to continue! You do have an alternative to using it, as is.
You don't need to feel vaguely uncomfortable every day "doing the school run", knowing now what we do, about the health dangers to children from tiny "particulates" in your car's exhaust, for example
Running a polluting diesel is easy to put-right, and it need not cost you in the long term. It could even save you money.
As explained in our press release below, most diesel engines can be converted to run on liquid natural gas (LNG).
Having done that, owners would preferably run them on carbon neutral bio-LNG from anaerobic digestion. But, supplies aren't universally available, whereas LNG is.
LNG conversion, essentially by adding gas storage cylinders to your vehicle, costs a couple of thousand pounds. But, you’ll soon recover that at the pump in cheaper fuel, over 12-18 months (c.10,000 miles).
This was just one of the topics featured during the recent ADBA "Global outlook for biomethane and infrastructure development" event co-located with the World Biogas Summit earlier this month.
Anaerobic Digestion and Bioresources Association - PRESS RELEASE (July 2019):
Birmingham biogas trade event to show the way on Bio-LNG
Bristol City Mayor Martin Rees announced on Thursday last week [20 June 2019] a consultation on proposals to ban diesel cars from the city to tackle air pollution, which is now a bigger killer than tobacco and three times larger than Aids, tuberculosis and malaria combined.
The UK government has said it will ban the sale of diesel cars from 2040. It would seem that if you own a diesel, having been encouraged to own a diesel by the government, you have been left in a no-win situation. Not so. Most diesel engines can be converted to run on liquid natural gas (LNG) – preferably carbon neutral bio-LNG from anaerobic digestion. It will cost a couple of thousand pounds but you’ll soon recover that at the pump over 12-18 months (c.10,000 miles).
There are over 20m LNG cars in the global fleet and, for HGVs, Bio-LNG is rapidly gaining traction as fuel – as it reduces CO2 emissions by over 85%, NOx emissions by 50-70%, and almost zero particulate matter. It has been found that fleet operators who switch to renewable natural gas (biomethane) more than exceed what is required under the benchmark minimum standard for emissions. Fuel savings are notable too. With costs that are typically 33% less – and in some instances, as much as 50% less – operators can see that biogas makes commercial sense. It means that the filling-station infrastructure is emerging too.
The shift makes economic sense. London and Norwich have been taking the lead on the introduction of what are known either as Low Emissions Zones or Clean Air Zones with another 30 cities and local authorities across the UK set to introduce similar measures.
Under these schemes buses and HGVs failing to meet minimum standards face charges for entering the zones of £200 a day. Such zones are commonplace in cities across mainland Europe.
Meanwhile biomethane as fuel for transport has been boosted by an EU directive requiring Member states to ensure a sufficient number of publicly accessible refuelling points to allow the circulation of CNG vehicles both in urban and sub-urban areas and on the TeN-T core network, ideally every 150 km, to be built by end-2025.
Furthermore, the government’s Renewable Fuel Transport Obligation has increased the biofuels volume target, including biomethane, from the current 4.75% to 9.75% in 2020, and 12.4% in 2032.
The future of Bio-LNG will be a key theme at both UK AD and World Biogas Expo 2019 and its co-located thought-leadership forum World Biogas Summit on 3rd-4th July in Birmingham.
CNHi Industrial will display its IVECO Stralis Natural Power truck and latest FPT Industrial Natural Gas engines, whilst New Holland will showcase the innovative Methane-Powered Concept Tractor, combining visionary design with advanced and sustainable biomethane combustion, a key element in the Energy Independent Farm™ concept, which sees farmers producing fuel from waste products.
- Press Release Ends -
Other top topics during the 2019 Biogas Summit earlier this month were:
UK Cities ramp up the fight against air pollution
Bio-LNG gains traction as a solution to reduce carbon emissions from vehicles
Prototype tractor and other vehicles on display at UK AD and World Biogas Expo
Why not make biogas from straw! New extrusion process it possible that a good feedstock can be created through the far more rapid development of anaerobic digestion of straw.
Research Sources for the Bioextrusion Process
The Bioextruder can create totally new feedstock options such as straw and desiccated grasses, or increase the biogas yield of traditional substrates such as maize or grass silage.
Depending on the solution required Rika Biogas Technologies can also specify equipment that can increase yields, speed up digestion and remove extraneous materials. These items normally sit in line with the extruder to produce a fully integrated feeding and feedstock processing solution that ultimately reduces your running costs. www.bioextruder.co.uk
Bioextrusion was Originated by LEHMANN
The Process of "Bioextrusion research and development was begun by LEHMANN®"
[Bioextrusion] leads to the formation of new bacteria stains and an improved C/N-ratio, because celluloses and hemicelluloses is decomposed and liberated from the embedding lignin layer. The 5- and 6-times sugar is faster available. Low-molecular and fast transforming substances like alcohol and other compounds develop.
The Fraunhofer institute IKTS in Dresden and LEHMANN Maschinenbau GmbH Jocketa have investigated to to what extent these difficult substrates are suitable for biogas production. via www.lehmann-maschinenbau.de
New insights into the impact of bioextrusion on biomass deconstruction using carbohydrate-binding modules
Lignocellulosic biomass is a sustainable source of renewable substrate to produce low carbon footprint energy and materials. Biomass conversion is usually performed in two steps: a biomass pretreatment for improving cellulose accessibility followed by enzymatic hydrolysis of cellulose. In this study we investigated the efficiency of a bioextrusion pretreatment (extrusion in the presence of cellulase enzyme) for production of reducing sugars from corn crop agricultural residues. Our results demonstrate that bioextrusion increased the reducing sugar conversion yield by at least 94% at high solid/liquid ratio (14%–40%). via www.sciencedirect.com
During the process the substrate is decomposed into its cell structure by a double-screw extruder with pressure with that high temperature and resulting of alternating load and multiple pressure/relaxation cycles in the machine. The biogas yield increases due to a better biochemical-availability and a strong enhanced surface area. The fiber is ideal culture medium of metabolizing bacteria.
This leads to the formation of new bacteria stains and an improved C/N-ratio, because celluloses and hemicelluloses is decomposed and liberated from the embedding lignin layer. The 5- and 6-times sugar is faster available. Low-molecular and fast transforming substances like alcohol and other compounds develop.
The sustainability and efficiency of biogas production is primarily determined by the substrate costs. It is necessary to exploit new substrates and to increase the energetic utilization ratio of the used substrates. Till now, highly lignocellulosic substrates or residues like straw or landscaping residue materials as "not or limited usable for biogas production".
The transcription text of the video: "Let's Make Biogas from Straw" follows:
Let's Make Biogas from Straw Not Field Crops.
Around 30 million tonnes of cereal straw are produced in Germany annually.
It has been estimated that 8 to 13 million tonnes of this could be used sustainably for different energetic paths of utilization.
Large quantities of straw are also produced in the UK, and throughout temperate climate regions globally.
Straw is one of the agricultural residues with the largest untapped potential for use as a biomass feed for biogas.
But, so far here has been only limited use of the energy in straw and what has been used has been based on thermal recovery, such as by pelletizing straw for domestic heating.
The disadvantages of this are the extremely large storage capacity needed for the dry material, as well as the high CO2 emissions from transport and processing.
In contrast, the use of straw in anaerobic digestion seems sensible.
The nutrients and organic matter, which was not converted into biogas in the fermentation process, are available again as a high quality digestate after fermentation, with the resulting digestate available to sustain this as a cycle by, its use as a crop fertilizer.
But there is a problem with this. Straw has a very high content of lignocelluloses and a low portion of readily fermentable materials.
During the fermentation process this causes very long digestion times and a low biogas yield.
Also, straw tends to float in the digester, even after being shredded.
Unwanted floating layers can then easily become a mixing problem, again reducing biogas production.
While some digester mixers might be able to cope, the mixing energy used reduces the remaining energy which can be sold.
A Solution to Low Straw Biogas Yields
One German company has devised a solution which they call Bioextrusion®.
The treatment (extrusion) of the straw has 3 beneficial effects:
1 - It reduces the particle size (fibre length) for reduced viscosity and easier mixing.
2 - The lignocellulosic structure is partially destroyed and,
3 - At the same time, the absorptive capacity of the straw increases, and the floating behavior of straw fibers inside the fermenter is much reduced.
After Bioextrusion® the straw is described as spreading almost perfectly in the operating volume of the fermenter.
Straw substrate which is modified by Bioextrusion® is then suitable for wet-fermentation in the standard CSTR process.
On arable farms Bioextrusion® may also be used to raise biogas output from other crop residues such as maize.
Ultrasound Disintegration means the breakdown of biogenic sludge into minute particles by external forces.
The resulting increase in surface area causes an acceleration of the organic breakdown process, and thereby results in an increased biogas yield.
For the full article we wrote on this subject visit: https://anaerobic-digestion.com/how-ultrasonic-disintegration-of-sewage-sludge/
In addition, the release of exo-enzymes from the external cell layer increases the enzyme activity in the digester.
In ultrasonic disintegration, the electrical oscillations created by a generator are transformed by a converter (sonic transducer) into mechanical vibrations.
These vibrations are transferred into the surrounding medium by means of a device known as a sonotrode.
Following the rhythm of the ultrasonic frequency, they cause high alternating positive and negative pressure phases, depending on whether the oscillator is expanding or contracting at the time.
During the negative pressure phase, microscopical cavities are formed in the liquid exposed to the ultrasonics; these then collapse in the subsequent positive pressure phase. This process is known as cavitation.
From the implosion, which releases high pressures and temperatures, strong impact and shear forces occur in the area immediately around the cavities, and these cause the surrounding micro-organisms to disintegrate.
Wet Process Biodigesters Explained with Pros and Cons
We went back to basics to explain how biodigesters work and their benefits and problems in this video and in the article below. We hope you find it a useful combination of video presentation and reading material.
Biodigesters use the decomposition of organic matter in anaerobic conditions to facilitate the extraction of the resulting biogas for use as energy.
The biodigester has an entrance for the organic material, a space for its decomposition, an outlet with control valve for the gas (biogas), and an outlet for the material already processed (digestate).
Necessary conditions for biodigestion
Temperature is very important for the production of biogas, since the microorganisms that carry out biodigestion reduce their activity outside these temperatures.
The temperature in the digestive chamber must be between 20º C and 60º C. To optimize the production time it is desirable to maintain a temperature between 30º C and 35º C.
The level of acidity determines how the fermentation of the organic material unfolds.
The pH of the material must have a value between 6.5 and 7.5.
Being outside this neutral range, organic matter runs the risk of rotting, as the relative activity of the wrong microorganisms increases. This usually produces a very unpleasant odor.
The container must be perfectly sealed to prevent oxygen from entering and thus have an adequate airtight seal.
The most commonly used materials to produce biogas are manure, from cows, horses, pigs and human sources.
However, almost all organic materials can also be used.
To achieve efficient decomposition, the organic matter must be in digestible sizes, because as ageneral rule, the faster the production of biogas the smaller the particle size.
The organic matter fed into the biogas plant must at all times have a balance of carbon and nitrogen.
Structure of a biodigester
There are many variations in the design of the biodigester.
Some elements that are commonly incorporated are:
Fermentation Chamber: The space where biomass is stored during the decomposition process.
Gas storage chamber: The space where the biogas accumulates before being extracted.
Loading point for adjusting the particle size and a funnel for adjustment of the water content: This is the entrance where the biomass is added to the digester tank (biodigester).
Pile of discharge: The output, serves to remove waste that are spent and are no longer useful for biogas, but can be used as fertilizer (digestate).
Agitator: Displace the residues that are in the bottom up of the biodigester to take advantage of all the biomass.
Gas pipe: The output of biogas. It can be connected directly to a stove or it can be transported by means of the same pipe to its place of use.
Advantages of Biodigesters
The anaerobic digestion process or fermentation process which takes place in all biodigesters, is a renewable and sustainable energy source. Taking advantage of the natural production of biogas reduces the need to use non-renewable energy. This in turn helps reduce climate change, by minimizing the output of greenhouse gases.
It is possible to use secondary products as fertilizer or fertilizer. It avoids the use of local firewood, thus reducing the pressure on forest resources. Encourages sustainable development. Redirect and take advantage of the greenhouse gases produced by landfills and industrial farms, which reduces the carbon footprint of these establishments and decreases their contribution to climate change.
It can help governments comply with national and international responsibilities to reduce the emission of carbon into earth's atmosphere.
It prevents the contamination of aquifers.
Creates specialized jobs.
Creates the possibility of farmers and many other businesses that end-up creating a lot of organic waste matter (biomass) developing a cutting-edge and sustainable "green" project.
Disadvantages, risks and special considerations
Ideally, the location should be close to where the biomass is collected.
The temperature of the digestion chamber must be maintained between 20º C and 60º C; Creating such temperatures may limit its use in cold places.
Biogas contains a byproduct called hydrogen sulfate, which is a corrosive and toxic gas for humans.
As with any other combustible gas, there is a risk of explosion or fire due to malfunction, maintenance or safety.
Biogas contains varying amounts of a byproduct called hydrogen sulfide, which is a corrosive and toxic gas at even very low concentrations for humans.
As with any other combustible gas, there is a risk of explosion or fire due to malfunction, maintenance or safety.