Dairy Farm Digesters – Anaerobic Digestion Process For Manure

Anaerobic digestion and dairy farm digesters for waste management may appear to be an odd subject for this website. However, while this subject is still relatively unknown to most people, it will become a mainstream business for thousands of clever dairy farmers in the United States.

The reality is that many investors are on the lookout for sustainable firms to invest in to shield their children from the pain of climate change. Plus, it's worth noting that “green” firms are now performing exceptionally well on the stock market. Add to that the US government's objective of minimising food waste, which farm digesters can readily handle in their digesters as the last option. And then, all of a sudden, you have:

a lucrative sideline for farms and an investment opportunity for expert financiers willing to invest in bringing Dairy AD and food waste co-disposal to a new level.

Therefore, continue reading and keep in mind that you originally heard about it here!

The Anaerobic Digestion Process

Anaerobic digestion is a biochemical conversion process used to treat and reduce the bulk of organic wastes, including solids, such as organic sewage sludge or concentrated industrial biowaste. Bacteria degrade biodegradable material in the absence of oxygen. Anaerobic digestion is a process used in business and on a small scale at home to manage trash and generate fuel (i. e. Renewable Natural Gas).

Fermentation is a phrase that the majority of people are familiar with. Fermentation is a component of the process of anaerobic digestion. It is used industrially in the manufacturing of food and beverage products and the brewing of alcoholic drinks.

Background to Anaerobic Digestion in Dairy Farms

Anaerobic digestion has a variety of environmental and economic advantages. The critical element is that it creates renewable energy in the form of methane, a naturally occurring gas. As a result, the number of dairy farm anaerobic waste digesters has gradually grown in the United States during the last few years.

Previously, cow manure was deposited into a stagnant, smelly lagoon and left to dry before spreading on the fields. While it was resting, the emission of biogas (made naturally during anaerobic digestion) occurred spontaneously. This usually occurs before the manure slurry being spread on the fields. However, methane emissions contribute around 30 times as much heat as carbon dioxide. Therefore, if humanity wants to keep the planet's average temperature to 1.5 degrees, governments must address agricultural methane emissions through much-improved manure management.

In other words, naturally existing microorganisms convert slurry lagoons (which are found on all dairy farms without a biogas infrastructure) to methane gas. And, given the quantity of methane that contributes to global warming, this is extremely worrisome. This is because methane is a greenhouse gas that traps the sun's heat in our atmosphere 25 to 35 times more effectively than carbon dioxide.

The Dairy Farm Community Biogas Refinery Concept

A typical dairy waste-to-energy facility is comprised of many farms housing between 2,000 and 3,000 dairy cows. Methane is captured from dairy manure via anaerobic digestion and sent to a central conditioning facility via low-pressure collecting pipes. After treatment and contamination removal, the gas is sent to local consumers via the existing underground natural gas distribution network.

As previously stated, anaerobic digestion is when bacteria degrade organic matter in the absence of oxygen, resulting in the generation of biogas in four stages.

Milk Production's Carbon Footprint

Operating an anaerobic digestion process plant that utilises manure as a feedstock for biogas generation is one of the numerous actions that the agriculture industry must take to reduce the carbon footprint of milk production.

This technique removes a substantial amount of volatile solids (VS) from manure, therefore reducing the possibility of methane and carbon dioxide emissions during storage and later land application. The produced biogas can be utilised to generate electricity, refined further and used as low-emission automobile fuel, or even fed into the natural gas system.

In some parts of the United States, managing residual swine farm flows, such as slurry and hydrolyzate, is also a significant environmental problem.

It is important to seek innovative solutions to rivers and even aquifers caused by massive livestock activities. Additionally, it is desirable if they can be applied on-site, therefore minimising trash transfer. Co-digestion with anaerobic bacteria can be utilised as a long-term approach for controlling and valorizing these fluxes in dairy and swine farms. Installing a biodigester results in the generation of biogas for energy production and digested for agricultural usage.

What is a biogas system?

Anaerobic digestion is a natural biological process used in biogas systems to recycle organic waste by converting it to biogas, energy (the gas), and valuable soil products (liquids and solids). Following simple processing, biogas may be used to replace natural gas sustainably, while the digested materials—liquids and solids—can be turned into a variety of useful soil products, including:

a peat-moss substitute for horticultural compost, a liquid fertiliser, and even a fibre appropriate for use as animal bedding.

Biogas production from grass is also a well-established practical technology. Farmers with surplus grass that is not required for overwintering cattle might digest it to produce more biogas.

Today, many dairy producers in the United Kingdom have not only considered changing their business model but have already sold their herds!

Rather than milking cattle, they grow grass to feed directly to an anaerobic digestion unit and store silage for winter use. This makes sense in the wet regions of the United Kingdom and Ireland, where grass thrives. Producing the majority of other crops efficiently on their land is challenging for a variety of reasons:

Frequent late frosts, a chilly, wet, and windy climate, and an inability to rely on dry weather and sunshine to develop the crop and allow harvesting to occur.

While anaerobic digestion (AD) can help prevent significant volumes of methane, a potent greenhouse gas (GHG), from being released into the environment, it also helps protect farms' aquatic environment from contamination. It minimises nitrate buildup caused by high-intensity farming and produces natural fertiliser, which can considerably reduce purchased fertiliser.

When all of the climate benefits of AD are evaluated in conjunction with other emission reductions, the process becomes self-evident for Dairy Farm companies.

According to AD Company Brightmark, generating RNG (Renewable Natural Gas) from dairy manure can reduce GHG emissions by 400 per cent when replacing traditional vehicle fuels.

Dairy Manure Slurry the Ever Present Waste in Dairy Farming

Dairy manure is a frequent waste product in dairy production, and it offers a variety of challenges in terms of storage, management, and disposal. As previously stated, dairy manure generates foul odours, toxic ammonia, and greenhouse gases that contribute to global warming if manure management is not prioritised.

Never forget, though, that dairy manure digesters will always produce very little biogas per unit mass. When compared to the digestion of food waste, for example, it is extremely low. As a result, manure-based biogas production may be comparable in terms of cost per unit volume generated.

The practical use for waste control and the overall fit within the dairy company make a biogas system attractive to dairy farmers who co-digest food waste. Adding food waste to a digester balances it and improves its performance significantly, as food has the most energy of any feedstock. If there was ever a moment when a quart could be squeezed from a pint pot, it is when food waste is added to a manure digester!

Anaerobic digestion can also be configured so that it eliminates odours as it digests the manure. Additionally, by include food waste, the nutritional content of the digestate increases when applied to fields, resulting in a more beneficial soil amendment.

Arla, a renowned dairy cooperative in the United Kingdom, has turned cow manure into a type of “vehicle-friendly gasoline” in a large new operation in Buckinghamshire. Under Arla's idea, farmers will carry their cow manure to a new local anaerobic digestion (AD) facility. While there, it will be converted to pure biomethane and used as fuel. According to the firm, the pilot will eventually enable Arla to become the first dairy in the United Kingdom to use agricultural waste to generate biomethane to power its HGV distribution fleet.

How are Many US Anaerobic Digesters Working?

In the United States, anaerobic digestion systems for dairy farms are gaining popularity.

The EPA reported in July 2010 that 157 commercial digester plants were operating across the US. 22 of the 157 digesters were located in New York, making it the country's second most active digester state.

As a consequence of the increase in AD facilities, New York State now has more than 50 digesters, with more ones planned or under construction.

The Anaerobic Digester System

According to the US EPA, 52 manure-based AD systems produced RNG in the United States in March 2021.

These include pipeline injection projects as well as compressed natural gas (CNG) installations. Additionally, according to reports, 44 RNG initiatives are now under development (Source: EPA Agstar Livestock Anaerobic Digester Database). The EPA's RNG website includes a map of all landfill and anaerobic digester-based RNG projects in the United States.

The biogas digester is the system component that receives animal, human, and other organic wastes and allows them to decompose anaerobically, often as a slurry with water. The produced gas is collected in a storage container and then piped for further use as fuel. Variable volume storage (e.g., a flexible bag or floating drum) is more straightforward, less costly, and may be more energy-efficient than high-pressure cylinders, regulators, or compressors.

Anaerobic digestion requires constant monitoring and frequent modifications to equipment settings to work correctly. All commercial AD process facilities should conduct routine laboratory testing on the substrate (each digester's reactor tank). The experiments will examine the physical characteristics of the manure fed into the bioreactor tank, the substrate inside the tank (COD, per cent solids, ph, and other critical parameters), and the digestate output. All of these must be quantified and used to initiate corrective action immediately upon discovery of issues.

Through an overflow pipe, the effluent is sent into a covered manure pit. The organic content of the processed manure is reduced and stabilised, resulting in an almost odourless, homogenised liquid that repels rodents and flies.

During the AD process, only a tiny fraction of the manure is converted to biogas. Dairy cow excrement is made of around 85% water and 15% solids. Around 91% of these solids are volatile.

One digester at Penn State converts between 20% and 30% of volatile solids to biogas, typical for most biogas systems. This Penn State digester project aimed to promote environmentally friendly technology and zero waste concepts in animal agriculture. Additionally, the operator plans to mitigate adverse environmental impacts.

Dairy farms accounted for 203 of the estimated 248 biogas producers operating in the United States in 2017. (Source: U. S. Environmental Protection Agency [EPA], 2017 ).

The Importance of Biogas

In comparison to the global biogas capacity of 15 gw in 2015, the EU is the world leader in biogas energy production, with more than 10 gw installed and 17,400 biogas plants.

Using anaerobic digesters to collect methane and convert it to renewable energy is one of the recommended methods for the dairy sector to reduce its carbon footprint. Numerous initiatives around the country continue to spur the growth of biogas facilities.

In the United States and Europe, farm operations have shifted drastically: small farms are disappearing, while farm size and animal population on larger farms are increasing. Animals' growing spatial density has a variety of negative environmental implications. Anaerobic digestion is one technical solution for minimising the bulk of these impacts while simultaneously providing a source of regional energy.

The economic viability of using dairy-cow manure for any of the following:

on-farm production and use of biogas for electricity and heat generation, or conversion of biogas to biomethane, a natural gas substitute

This article evaluates.

With their four-chambered stomachs, cows have long been considered models of digestive ability, as anybody who has evaded cow pies in a field will confirm.

Each day, hundreds of pounds of faeces are produced by these grazing bovines and other animals. Concerns about animal waste management, energy conservation, and organic farming have revived interest in generating biogas from livestock manure. Two significant projects utilising clusters of anaerobic digesters have attracted the interest of dairy producers around the country.

When the building of the US biogas plants is complete, this network of dairy biogas plants will likely be the world's largest system of its kind.

BioGas Generation with Dairy Manure?

Anaerobic digesters are used to convert cow manure to biogas. Because biogas, like natural gas, is mostly composed of methane, it may be utilised to create electricity and power automobiles.

Renewable natural gas may be produced on animal farms using biogas recovery systems. Animal excrement is collected and fed to an anaerobic digester to stabilise and maximise methane output. The generated biogas may be converted to rng and used to fuel natural gas vehicles.

The capital investment required to construct a digester varies significantly depending on the design, size, and equipment utilised to generate biogas and/or separate manure fibre. Currently, the capital cost of a complete digester system is between $1,000 and $2,000 per cow, depending on herd size, with the cost of operating an engine-generator set at $0. 015 to $0. 02/kWh of energy output.

Anaerobic Digestion of Dairy Manure in the US

Dairy digesters are a sustainable technology that use cow faeces to generate methane, a renewable energy source and transportation fuel. Multiple environmental and social benefits accrue from the method. Additional information about dairy digesters is available on the USEPA's Agstar anaerobic digestion webpage.

It is quite uncommon for dairy farms to discharge a significant amount of milk from milking operations to manure digesters. Anaerobic digestion of animal dung has the capacity to inactivate enteric pathogens, reducing exposures to livestock and humans when digested materials are dispersed on land or used as bedding for animals.

Anaerobic Digestion of transport fuel or production of electricity?

Anaerobic digestion (AD) of animal faeces is a very effective method of converting undigested plant carbon to methane for use as a transportation fuel or power generation.

While AD is most commonly associated with dairy farming, it is also used to regulate manure and wastewater on swine and poultry farms. Anaerobic digestion systems can be classified as passive, low-rate, or high-rate. Due to the potential reduction of greenhouse gases (GHG) and the economic benefits of generating renewable energy from anaerobic digestion, Ad is a viable GHG emission mitigation technology for dairy and swine farms.

Energy-related expenditures can account for up to 29% of total farm operating expenses. The continuing increase in the real cost of energy-related farm inputs has significantly affected agricultural output costs. However, agriculture can replace some of the purchased energy in fossil fuels, commercial fertilisers, and field production of animal feed with bioenergy and organic fertiliser made from onsite renewable biomass such as animal manure to be economically and environmentally sustainable.

Anaerobic fermentation does not deplete nutrients. Anaerobic digestion of dairy manure on-farm is being used to generate power and eliminate odours. Acidogenic bacteria convert the majority of the organic content in manure to volatile fatty acids (VFAs), consumed by methanogenic bacteria, which produce methane, carbon dioxide, and a few other gases. While these microbial processes transform nitrogen, phosphorous, and potassium, they do not remove these nutrients.

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