Tag Archives: Biogas

Anaerobic Digestion

What Is Sludge Thickening?

Posted on by Elliot Volpe
11
Nov

What Is Sludge Thickening?

Sludge thickening occurs when the liquids are removed from the sludge. This reduces the total sludge volume but the number of total solids that are suspended in the sludge is increased, often by 2-5x the amount. Depending on how much of the water is removed, the process is referred to as thickening or dewatering.

How Is Sludge Thickening Done?

There are 5 main methods of sludge thickening:

  • Gravity thickening
  • Centrifugal thickening
  • Flotation thickening
  • Gravity belt
  • Rotary drum

Gravity Thickening

Gravity thickening is done by using a tank or vessel that contains the sludge. Once the sludge enters the tank the heavier particles then sink to the bottom and the liquid stays at the top. There is a scraper that rotates at the bottom of the tank to allow the solids to stay in suspension. The sludge is then pumped out from the bottom of the tank with the liquid or effluent being pumped from the top of the tank to be further processed.

Credit: eddypump.com

Centrifugal Thickening

Centrifugal thickening works by introducing a centrifugal force upon the sludge. This actively encourages the heavy solids to move outwards, and the liquid effluent will be removed conveniently.

Credit: Sludge thickener & Centrifuge) | Download Scientific Diagram (researchgate.net)

Centrifugal techniques can be used in thickening and dewatering applications. However, there are some differences in the way they operate. These include:

  • Rotational speed
  • Throughput
  • Solids contents percentage of the product generated

When dewatering is wanted to be achieved the outcome will be a dry cake that can’t be moved by the use of pumping systems. Whereas thickened sludge will still be able to be pumped where needed.

Flotation Thickening

Flotation thickening is commonly referred to as dissolved air flotation (DAF). DAF works by injecting air into the water to reach saturation. This is then pumped at high pressure into waste-activated sludge. As the sludge then enters the vessel the solids float to the top and are removed and the effluent is removed from the bottom of the tank to be further treated.

Credit: Judd Water & Wastewater Consultants

Gravity Belt

Gravity belt thickening uses the same principle as gravity thickening, hence the name. However, a rotating belt is introduced into this method. The belt itself is porous which allows the excess water to pass through leaving the sludge sitting on the belt, which is then moved along by the felt and eventually drops off into the next part of the process. The excess water that has fallen through the belt drops into a sump and is then transferred for further treatment.

Credit: Judd Water & Wastewater Consultants

Rotary Drum

Rotary drum thickening works similarly to gravity belt thickening. A rotary drum uses a drum typically of 0.5-1.5m in length that is porous. Sludge is passed through the drum and the excess water falls through the holes in the drum into a sump to be further treated. The sludge continues to stay in the drum moving along continually until it reaches the end where it is then moved for further processing.

Credit: VIRIDIS Engineering 

What are the Benefits?

There are multiple benefits to the sludge thickening process. One of the main benefits is that sludge volume reduction brings down capital costs to treat high volumes of sludge and the further treatment steps that are needed. Sludge thickening is also beneficial from a process stability standpoint because of the reduction in mass of the sludge which means there are fewer heating requirements, smaller tank sizes needed, and less external input required.

 

Reference – Sludgeprocessing.com

Need help with your feedstock and sludge processing?

Get in touch to see how we can help

Contact Us
Anaerobic Digestion

What Are Biogas Blowers?

Posted on by Elliot Volpe
15
Sep

In the Anaerobic Digestion process biogas is produced which needs to be transferred from one place to another. The transfer of gas can be to the flare if it is excess gas, directly into a CHP unit or the national gird. This article explains how biogas can be moved from one part of the process to another.

What Are Biogas Blowers?

Gas blowers are often rotary, positive displacement machines that are used for the transportation of gases. Commonly, they are two or three lobe rotors. However, there are also centrifugal type blowers on the market. Biogas blowers can be used to supply, drive or extract biogas wherever needed in the process.

How Do They Work?

Positive displacement blowers have lobes inside that do not touch, meaning the gas is oil free. They rotate within the housing causing a pressure flow scenario. This means that the pressure varies to meet the systems requirements.

Centrifugal single stage blowers are constructed with spark proof aluminum casing and impellers. They do not require lubrication. Multi-stage blowers suck the gas into the inlet volute, from there every stage is linked to the first stage through a return channel. The main advantages of centrifugal type blowers are they are easy to install, low noise, minimal maintenance and no contamination.

References –

What is a Positive Displacement Blower? | Discover the Benefits of PD Blowers & Other Rotary Air Blower Solutions – Blocker and Wallace

Centrifugal Type Gas Blowers (ggepower.com)

Process Gas Rotary Blowers in Process Industry | HIBON

Need help with your feedstock processing?

Contact us to see how we can help

Contact Us
Anaerobic Digestion

Inflation Reduction Act – Green Energy Bill

Posted on by Elliot Volpe
26
Aug

The United States government have just passed the biggest climate bill in the history of the country, the Inflation Reduction Act (IRA). Whilst most see it as a major win for the climate and cutting greenhouse gas emissions, some companies aren’t so fond of the bill considering they will be the ones paying for it.

What is the Inflation Reduction Act?

The Inflation Reduction Act, or IRA as it’s commonly known, is a bill that aims to tackle important issues and rising inflation. The IRA 2022 bill has focused more on the reduction of contribution towards global warming and is a bid to be on track to meet the goals set out in the 2030 Paris agreement. With the United States being one of the highest emission countries, President Biden has pledged that the U.S will achieve net zero by 2050.

Where Is the Money Coming From?

The IRA 2022 is set to recover $749 billion. Of this amount, $369 billion will be focused on climate-related emissions reduction. These include Anaerobic digestion processes, biofuel production, wind, solar and biomass.

The US government is introducing a 15% minimum corporate tax on large corporations and a new 1% tax for companies purchasing their shares, which is set to take effect in 2023.

What Does The Inflation Reduction Act Mean for Biogas?

Tax credits that were once given to Anaerobic Digestion were commonly only one or two years in length. This led people in the industry to start guessing whether funding or incentives would be pulled from the industry and make it less viable for projects going forward. However, given the new Act that has been passed, project developers and land owners can now see these credits and incentives made near enough permanent for the next 10 years through eligibility provisions.

This means that on a project level, some developers can expect to see up to 50% investment tax credits (ITCs) or more of a qualifying project. This is compared to the usual 30% that they would have seen in past times.

There is also a big emphasis on carbon capture. This is shown by $100 billion being given to support federal, state and local projects to ensure carbon is captured directly from the air. Tax credits for industrial facilities and power plants will now increase from $50 per ton to $85. This incentive also aids the planning of a reduction in greenhouse gases (GHG).

The American Biogas Council’s View

The American Biogas Council are extremely please with the new bill being passed.

‘Before this bill, our industry had only benefitted from short one- to two-year extensions of a tax credit that served one sector of the biogas industry. While trying to attract investment to projects that take years to build and competing with other industries with long-term tax credits, this was not a long-term solution. For the first time, this bill gives developers and financiers certainty and a competitive edge that will fuel growth of the biogas and clean energy industries for years to come.’

One thing is for certain, the US government passing this IRA shows their intent on cutting emissions and funding alternative energy sources across America. This not only gives certainty to each industry but shows intent in pushing towards their goals of cutting green house gas emissions as per the Paris agreement.

For Anaerobic Digestion in particular, the US has 2,300 operational biogas systems. This is said to be only 15% of its potential. This means that with the backing of government, increased incentives, major improvements in knowledge and technology we can be certain that the future for the US Anaerobic Digestion industry certainly looks promising.

 

References – 

The IRA Revolutionizes AD Tax Credits | BioCycle

The US Inflation Reduction Act Explained | Earth.Org

Biogas industry applauds House passage of Inflation Reduction Act with ‘historic’ implications | Waste Dive

American Biogas Council Applauds Passage of Inflation Reduction Act and Historic Investment in Clean Energy – American Biogas Council

Need help with your feedstock processing?

Contact us to see how we can help

Contact Us
Anaerobic Digestion

2023 Separate Food Waste Plan

Posted on by Elliot Volpe
11
Aug

In the UK the government have put in place plans to see a separate food bin added in people’s homes dedicated to food waste. This bin would then be emptied and eventually end up at a local Anaerobic Digestion facility. The idea is to rescue food going to landfill and eventually de-composing and producing green house gases into the atmosphere.

What is Food Waste?

Food waste is quite simply the food that is not consumed or used by people, which is then commonly put into landfill. Many of us are guilty of buying food which then is forgotten, or we don’t get round to using in time. Once this is put into the waste bin, it then ends up going to landfill. Here the food is left to decompose. As it does this, the food decomposition process produces gases which pollute the atmosphere.

What are Green House Gases?

There are several gases that contribute directly to climate change. These are:

  • Carbon Dioxide (CO2)
  • Methane (CH4)
  • Nitrous Oxide (N20)
  • Hydrofluorocarbons (HFCs)
  • Perfluorocarbons (PFCs)
  • Sulphur Hexafluoride (SF6)
  • Nitrogen Trifluoride (NF3)

The main source of emissions is through Carbon Dioxide, which is emitted in the decomposition of food waste along with methane.

Effectively the gases we are producing are trapping the heat and energy from day to day use in the Earths atmosphere. This means that the planet is slowly warming up and global warming is becoming evermore a problem that needs to be dealt with.

Why Anaerobic Digestion?

Anaerobic Digestion is the perfect solution for dealing with food waste. Largely, this is due to the process being in an air tight tank, which means there are no green house gases emitted into the atmosphere.

The process takes the food waste, breaks it down and generates methane, which is a highly useful gas, as long as it isn’t emitted into the atmosphere. The Methane can then be injected back into the grid directly or it can be used to power CHP unit, which is effectively an engine. This then generates electricity that can be used to power the plant and any other operations or sold back to the grid.

The Negative to Separating Food Waste

The government are pushing this scheme as it challenges every household to really think about what they are throwing away unnecessarily. However, because of the introduction of another household waste bin it means there needs to be an extra service provided to collect the food waste from bins and this won’t be cheap.

 

References – https://www.bbcgoodfood.com/howto/guide/what-are-greenhouse-gases

Anaerobic Digestion

Biogas: Now More Than Ever

Posted on by Elliot Volpe
07
Jul

The future of biogas is extremely bright. This is largely due to business opportunities being exploited, developing infrastructure and the knowledge base to support rapid development. As a collective, the world has realised it needs to reduce its greenhouse gas emissions and find cleaner sources of energy.

Economic Impacts Fueling Biogas

Whilst many countries are putting in place plans to achieve net-zero by 2030, there are still many challenges that need to be addressed. There have been many dictating factors as to why biogas is becoming ever more important.

Whilst the COVID-19 pandemic seems somewhat behind us, we are still feeling the effects. None more so than the rate of inflation, with many people struggling due to the cost of living rising so sharply. Part of this is the cost of electricity and gas. Prices are continuing to rise with no sign of slowing down. In many places energy prices have more than doubled which makes for completely unsustainable living for people and families who were already struggling.

Another major factor is the Russian invasion of Ukraine. Whilst Russia supplied many countries with their gas, these countries have now cut ties with Russia and now they are forced to find other suppliers which are more expensive. This price increase is then being passed on to the consumer.

Knowledge Development

Many biogas project developers now have a vast knowledge base on carrying out successful projects with maximum profitability. This makes the proposition far more attractive for potential investors as they know their capital won’t be at as great a risk. This means there are more investors and growing knowledge bases, which means growth for the sector as a whole.

Biogas Market Growth

Th Biogas market is expected to see a 9.3% CAGR between now and 2028. The market was hit extremely hard during the COVID-19 pandemic and because of this we saw declines of -39.1% in 2020. However, the industry seems to be very much out of this phase with continuous growth predicted for many years to come.

Biogas Plant Market Size, Growth, Share | Global Report [2028] (fortunebusinessinsights.com)

Local Government Actions

With the demand for renewable energy increasing and the need for reduction in food waste, local governments in the UK have started to introduce schemes for households to separate food waste from all other waste by providing them with a dedicated food waste bin. This food waste will then be collected and taken to a centralised processing plant where it will be turned into energy. This new environmental bill is expected to lead to a reduction of 1.25 million tonnes of greenhouse gas per year.

Household food waste to be collected separately by 2023 and 50,000 city trees to be planted in Urban Tree Challenge Fund – Defra in the media (blog.gov.uk)

Improved Technology

Technology within the Biogas world is constantly improving. A key area this is true is the upgrading methods that have been developed. We are now seeing far more advanced techniques when it comes to extracting methane from the biogas. Because of this we are getting a better-quality biogas over a shorter period of time.

Also, other parts of the biogas process are improving, such as the CHP engines, feedstock processing equipment and the biological management of the process as a whole.

Conclusion

It is almost certain that AD will continue to grow at a significant rate due to the rising demand for cleaner energy. This aligns with government commitments and incentives and the technology suppliers making processes more efficient and providing education to the industry as a whole. For all aspects of the AD process, there has never been a better time to get involved in a movement towards a cleaner future.

Anaerobic Digestion

How Digestate Can Be Used

Posted on by Elliot Volpe
30
Jun

Once the feedstock has been digested in the digester we then get a residual. This residual is called digestate. The end product can be extremely good quality and useful for farmers to either pack and sell or spread it on their land. Spreading it on their land then means that it helps the crops grow. These crops are then either harvested and potentially put into the digester or are eaten by livestock whose waste feeds the digester. This makes it a circular economy.

What is Digestate?

Digestate is a residual outcome from the process of Anaerobic Digestion. It is extremely rich in nutrients and therefore a great fertiliser. The main nutrients in digestate are Nitrogen, Phosphorous and Potassium.

Different Types of Digestate

There are 3 common types of digestate:

Whole digestate – looks similar to livestock slurry and typically has less than 5% percent solids content

Liquid digestate – this is similar to whole digestate; however, the solids contents have been removed.

Fibre digestate – this is a compost like substance. Fibre digestate is the solids that were removed from the whole digestate.

Where Can It Be Used?

There can be many different uses for all types of digestate. Because the digestate has had the majority of toxins removed it makes for extremely good fertiliser. Liquid fertiliser is commonly spread on land to help crops grow. Fibre digestate can also be used as a compost/soil for personal use or it can be packaged and sold.

Regulations for Digestate

If the digestate is not to be considered as waste then it must meet the standards of the quality protocol and PAS110. These two standard ensure that the digestate that is being sold is fit for purpose and is non-toxic. These are two of the pillars that make up the biofertiliser scheme.

More on the benefits of Digestate

 

GP Biotec – What is Digestate?

BSI PAS 110: Producing Quality Anaerobic Digestate | WRAP

Need help with your feedstock processing?

Get in touch to see how we can help.

Contact Us
Anaerobic Digestion

Digester Mixing: How it’s Done

Posted on by Elliot Volpe
20
Jun

When feedstock is pumped into the digester it is important to ensure the solids remain in suspension. If this isn’t done it can lead to many process issues, with the result being poor biogas production. The most popular ways to do this is through digester mixing.

What is Digester Mixing?

In a digester, there are no moving parts. Therefore, solids will naturally settle and inhibit biogas production. Because of this digester mixing is commonly used. Digester mixing is when the medium inside the digester is mixed or stirred to ensure solids stay in suspension. This can be done through the use of mechanical mixing using propellers, or through the use of pumps or gas injection systems that keep recirculating the fluid.

Types of Digester Systems

Continuously Stirred (CSTR)

A continuously stirred digester is the most common in the AD world. As the name suggests the digester is continuously mixed. The liquid coming in displaces the liquid going out and this ensures the process stays balanced.

Plug Flow

A plug flow digester means that the contents are that much thicker that the solids continue to stay in suspension with little to no use of additional mixers. However, the liquid is displaced by incoming feedstock.

Different Methods of Digester Mixing?

Gas Injection

Gas injection systems can often be grouped into four common types:

  • Lances
  • Floor mounted diffusers
  • Draft tubes
  • Bubble guns

These systems are designed to introduce gas into the tank from different directions to allow the sludge to effectively move around and avoid causing the floating layer on the top of the fluid, as this is what inhibits the production of biogas.

Mechanical – Propeller

Propeller mixers are one of the most common types of mixers in an AD system. They’re efficient, easy to maintain and cost effective. They come in many variations. Such as wall/side mounted or even floor mounted. Due to their nature they are not removing or adding anything to the process but simply stirring everything round in the digester.

Mechanical – Pumping

Another way of digester mixing is to recirculate the fluid by means of pumping. This involves using a pump to draw the liquid out of the digester at a certain point and then pressurising it and pumping it back into the digester. The pressure that the fluid is being pumped back into is high enough to move the solids in the tank.

 

References

Different Types of Anaerobic Digester Mixing Systems (phsenesacinc.com)

Digester Mixing Fundamentals | BioCycle

Need help with your feedstock processing?

Get in touch to see how we can help.

Contact Us
Anaerobic Digestion

What is Gas Flaring?

Posted on by Elliot Volpe
04
May

Gas flaring is a common occurrence at many Anaerobic Digestion facilities. Being able to flare off gas is important for the process and also from a safety perspective. Failure to flare off gas correctly can lead to catastrophic consequences to the process and its hardware.

What is Gas Flaring?

Gas flaring is the process of burning off excess gas within a process. The gas is often not needed due to surplus or there may be a buildup of gas that could potentially become dangerous to the plant and people.

Why is Flaring Needed?

When the Anaerobic Digestion process has taken place and the biogas has been produced, it is then used in two ways. This is either through using the energy to power a CHP unit or through direct injection back into the grid. Often at times there is more energy produced by the process than is needed for the output. This then presents problems not only from a safety perspective but also an environmental point of view.

The two main options are:

  • Storage
  • Flaring

It is possible for biogas to be stored, usually in lagoons, whilst it is waiting to be used up. Commonly, it is only stored for a few hours before moving through to the desired end use. Biogas can be compressed but this is a more costly process and is usually used if there is an upgrading phase.

Alternatively, a flare can be used to allow the excess gas to be safely burned off in the event of excess gas or if the plant has failed and become potentially dangerous.

Different Types of Flare

Open Flares

When a process uses an open flare it often comprises of a burner with a windshield around it to protect the flame. Often controlled manually by means of a valve. The use of an open flare can be inefficient and difficult to achieve the correct mixture of gases for complete combustion. Many do not meet the efficiency demands and regulations that countries are putting in place and therefore are not a popular choice.

Enclosed Flares

Due to the design of the enclosed flare it promotes a uniform burn with the emissions being much lower than that of the open flare. There is much closer monitoring of emissions within an enclosed system and there is also better control over the combustion ratio too. Due to these reasons the enclosed flare is a popular choice for system designers.

Typical Flare Design

There a many common features that a flare must have to make it operational but also to ensure the safety of the plant and people. These include:

  • Knock out pot – the role of a knockout pot is to remove any condensed liquids or droplets from the flare gases
  • Flow control valve – a flow control valve is designed to ensure there is the correct amount of gas flow into the flare so that the burn takes place as designed
  • Gas booster/blower – a booster is used to pressurise the gas entering the flare in order to create better combustion
  • Failsafe valve – cuts off the flow of gas to the flare in the case of an emergency
  • Flame arrest – allows gases to pass through but prevents the transmission of a flame which reduces the risk of fire or explosion
  • Flame shroud – a shroud is used as a safety barrier round the flare and burner to avoid anyone coming into direct contact

 

Reference – Flaring_4-4.PDF (iea-biogas.net)

Need help with your feedstock processing requirements?

Contact us to see how we can help

Contact Us
Anaerobic Digestion

How to Maintain Biogas Quality

Posted on by Elliot Volpe
21
Apr

The biogas quality is one of the most important aspects of the process. Biogas is made up of Methane and CO2. However, the part we are most interested in is the Methane. This is what powers our CHP unit or can be injected back into the grid. This means in order for the process to be profitable we need the biogas quality to be sufficient.

What Can Affect Biogas Quality?

The biggest factor that affects biogas quality is the stress on the digester biology. There are many different ways the digester becomes stressed and can stop performing as it should. These include:

The most common stress on digester biology is the feeding of fresh feedstock into the digester. Fresh feedstock coming into the digester often causes spikes in the process. As the biology seeks to break down the feedstock it is working even harder to do so. This often means the biogas production drops as a result of this.

Another common reason for poor digester output is co-digestion of incorrect feedstocks. Some feedstocks complement each other well in aspects such as retention time and biologically stability. Others can work against one another and will produce a volatile mixture inside the digester.

How to Control Biogas Quality

Workout the correct HRT for the particular feedstock coming into the digester. HRT is the time needed for the feedstock to go through its biological breakdown to releasing methanogens. This value varies for each type of feedstock and also the volumetric size of the digester.

Another way to keep the issue under control is through the use of a multi tank system. This is where a receiving tank can be used to allow the feedstock to be fed in there, in the correct amounts. This can then be held in the reception tank and fed into the digester at a continuous rate and with stable biology.

The dry matter content can also be reduced in the feedstock. It is well known that the higher the value of dry matter content the less stable the process is. This is because of the requirements for efficient breakdown are much higher than that of manure. If liquid is added to the feedstock or co-digestion with manure takes place then the feedstock will breakdown in a more stable way. This means that the biogas quality will remain consistent and the process itself will not see as many peaks and troughs.

 

Reference – Roots Organics Ltd.

Need help with your feedstock processing?

Contact us to see how we can help

Contact Us
Anaerobic Digestion

Anaerobic Digester Design Considerations

Posted on by Elliot Volpe
13
Apr

There are vast amounts of variables in the Anaerobic Digestion process. Many variables can depend on site location and capacity, as well as the feedstock and its flow. However, it is essential to get the digester design correct for each individual site to operate correctly and be profitable.

More on Process Design

Anaerobic Digester Process Design

Temperature range

There are two main temperature ranges in AD. These are Mesophilic and Thermophilic. Dependent on the feedstock and what the process owner is actually trying to get out of the process will determine the temperature range the digester is operated at.

More on Digester Temperature

Desired Operating Range

If the process requires a higher temperature to break the feedstock down more efficiently and meet the requirements to enable the process to operate as it should, then this will be stated in the design process and worked around.

Digester Size & Design

The specification of a digester is done by assessing many different aspects of the process. One key consideration is the actual size of the land the process will be built upon. If the space isn’t physically big enough for the process that has been designed then it will not work. Another consideration is the amount of feedstock that is going to be processed by the digester and the retention time needed for the feedstock to be broken down properly.

Feedstock Types & Source

When designing the process and more specifically the digester, the feedstock type is a primary consideration. This is because it simply determines many other variables in the process. If the feedstock is a certain type and has characteristics when reacting in the digester then the levels of additives and other process optimisation techniques need to be determined based on the feedstock itself.

The source of feedstock relates to where it is coming from and how much of it is going to be in the digester. For example, if the feedstock is manure coming from cows off of a farm then we know exactly what the feedstock type is, which means we can get a good understanding of how it is going to act inside the digester. We also know roughly how much feedstock is going to be processed per day.

Feedstock Receiving Strategy & Feeding Plan

In addition to the actual feedstock being processed and where it is coming from we also have to take into consideration what we are going to do with that feedstock once we have obtained it. Is the feedstock going to be fed into the digester continuously for 24 hours of the day or will it be done in batches? We then have to determine if the feedstock coming in is going to be held in a storage vessel until it is ready for processing and ensuring the time between receiving the feedstock and actually processing it is monitored so we do not end up with a poor performing digester.

Pre or Post Pasteurisation

When the digester is being designed the pasteurisation aspect will need to be considered. Ensuring this stage is correct is essential. The digester or one of the digesters will need to be heated up to a certain temperature to kill off any pathogens in the feedstock. This is to ensure that the biological process is as stable as possible.

Need help with your feedstock processing?

Contact us to see how we can help

Contact Us