Here we discuss the Anaerobic Digestion of Manure: The first section is a general informational article, followed by our original article where we explain their 2017 breakthrough in the throughput of manure-fed AD Plants described by the Ductor biogas company using chicken manure.
Anaerobic digestion (AD) of dairy manure provides several environmental and economic benefits, including the generation of renewable energy and the reduction of greenhouse gas emissions. But it is underused as a manure treatment alternative. Dairy manure is the largest single source of methane from livestock waste management in the United States.
Part 1 – The Basic Purposes of Anaerobic Digesters
Anaerobic digesters all serve the same basic purpose. They store manure in the lack of oxygen and provide the ideal environment for methane-forming microbes (methanogens) to develop. There are several distinct types of anaerobic digesters, each performing the same fundamental function in somewhat different ways.
Manure is the primary input if a digester is used to treat manure first and mainly. A word of warning is relevant to add here. Co-digestion may increase the quantity of nutrients in the effluent. So farmers contemplating co-digestion should first verify that they will still comply with their nutrient management plans after implementation.
Watch our video to see the work one company is doing for manure biogas:
Biomass-to-Energy Conversion by the AD Process
Previously, animal manure was collected and sold as fertiliser, or it was simply spread on agricultural land. Tighter environmental limits on smell and water pollution need some type of waste treatment to achieve them, which gives further incentives for biomass-to-energy conversion.
Anaerobic digestion is a unique treatment approach for animal manure management since it may provide positive advantages such as renewable energy, reduced water pollution, and reduced air pollutants. Anaerobic digestion of animal dung is gaining favour as a method of protecting the environment and efficiently recycling resources into farming systems.
Livestock Farmers Search for Ways to Develop AD
Livestock farmers interested in generating electricity from manure must first determine the quantity of biogas that their dung has the capacity to create. They may also want to know if additional material can be added to manure to increase the amount of biogas produced by the digester.
Anaerobic digestion may convert almost all organic matter (OM) to biogas. Some materials, however, produce more methane than others. Three metrics are important namely Volatile Solids (VS), Oxygen Demand (OD), and Biochemical Methane Prospective (BMP) These are monitored and the data collected is used to restrict the spectrum of methane-producing materials from potential to likely to probable.
Manure Management Requirements
Based on its size and location, each farm has distinct manure management requirements. Some dairy manure is managed as a solid, stored in mounds or stacks, dispersed daily, or left to lay on grazing pastures or ranges. These methane-reducing management strategies are widespread in smaller enterprises.
Larger enterprises, on the other hand, tend to handle manure in ways that have a larger potential for methane emissions. Flush collection systems gather and remove manure from barns and milking parlours using enormous amounts of water, whereas scrape collection systems remove manure from barns and alleys.
These systems transport manure to anaerobic lagoons, tanks, or clay ponds for long-term storage under anaerobic conditions, where the manure emits methane. Depending on the region and cropping method, some dairies store manure for up to a year or more before applying it to the field.
Methane Production Keeps it Simple
Methane production from manure is a simple process. When manure is sealed in an airtight container, it produces biogas, which is a combination of methane (CH4), carbon dioxide (CO2), and trace amounts of other gases. Because the process is so automated, anaerobic digestion was thought to be a prominent example of spontaneous production prior to Pasteur. The microbes that produce biogas were thought to spawn directly from dung.
To begin producing biogas, two components are required: organic waste and a seed colony of microbes. Manure, fortunately, includes both. Fresh manure contains 80 to 90%t organic matter, and most domestic animals expel living cultures of biogas generating organisms from their colons on a continual basis.
On-farm anaerobic digestion of dairy manure is utilised to generate electricity and reduce odours. During the digestive process, acidogenic bacteria convert much of the organic matter in manure to volatile fatty acids (VFAs), which are subsequently devoured by methanogenic bacteria to generate methane, carbon dioxide, and a few other gases.
These microbial activities change nitrogen, phosphorus, and potassium, but these nutrients are not eliminated. During the digestive process, some nutrients, such as sulphur, are transformed into other compounds; in this case, hydrogen sulphide gas is created.
The original 2017 article follows:
Part 2 – The Problem With Anaerobic Digestion of Manure
A new pre-treatment process development by Ductor™ raises new hope for super-efficient on-farm manure fed biogas plants.
Almost all organic materials such as manure are good feedstock materials for biogas production.
Farm manures, from dairy manure to chicken litter are available in abundance as feedstock. But, until now the AD Plants which process them have all suffered from a huge draw-back.
The reactors have to be very large because the fermentation process is very slow for these high Nitrogen (high-N) materials. So, biogas production is low compared with other lower N feeds.
This means that for on-farm manure anaerobic digestion to be economically viable, only very large farms that can provide economy of scale can benefit from these large AD plants.
The Need for a Breakthrough in Manure AD Plant Productivity
Until now the (high-N) reactors have had to be very large because the fermentation process is very slow for these high Nitrogen (high-N) materials.
A breakthrough in AD process technology is needed to raise the throughput rate. We know this is possible because every cow on the planet does it far more efficiently than any man-made biogas reactor!
The Ductor™ Approach which Resulted in AD Plant Productivity Doubled In Tests
High-N materials hamper biogas production by inhibiting the bacteria in charge of breaking down organic material.
So, Ductor's process designers said: “What if nitrogen could be separated from feedstock BEFORE biogas production?”
So, they embarked on a research and development project to find a way to do just that.
And, now this is possible, as a new approach to AD Plant process design using an additional fermentation stage to pre-treat feedstock. This new way has been developed in Finland by Ductor™.
This process is known as the Ductor™ fermentation technology, where feedstock is (currently) fermented for about five days to convert organic nitrogen into inorganic one, namely ammonia (NH3).
Ammonia is then processed out from slurry by stripping it out and storing it in liquid form, which can be used as a raw material for fertilizer production. According to Ductor's website in a trial the ratio of output fertiliser was 115 tons of ammonium sulphate, and 640 tons of solid organic material (fibrous digestate).
The Benefits of Ductor Fermentation Technology
This approach brings three clear benefits:
- Nitrogen is separated from bulk material, which now becomes a phosphorous fertilizer, and if potassium hydroxide is used as the pH controlling agent, a P & K fertilizer.
- Nitrogen no longer hampers the main biogas process, and thus a higher efficiency can be achieved.
- The removal of nitrogen allows new, high N feedstock materials such as poultry manure.
So, it really is possible to select new methods and approaches, and thus recycle the nutrients in a more efficient way.
A great benefit is that additional costs are more than compensated by the benefits brought in as side-effects such as improved biogas yield.
However, subject to ABP Regulations compliance, the separated fertiliser (ammonium sulphate) can become a premium value product sold off-farm as a renewable chemical fertiliser for income, while the fibrous digestate is returned to the farm fields to provide fertiliser for the farm itself.
Furthermore, it is understood that this process technology, which is very much still in its infancy, can be further developed for even better efficiency.
What Ductor Says About Their Fermentation Technology
“The biological method developed and patented by Ductor eliminates the nitrogen dilemma by turning problem waste into profitable recyclable goods. Fraunhofer UMSICHT has been supporting the development of Ductor™ technology for removing ammonia since 2013. “Here, the process principle and the results of the pilot plant in Helsinki were evaluated. From the results so far, it can be concluded that the technology will work,” says Joachim Krassowski, Group Manager of Energy Supply Systems at Fraunhofer UMSICHT. “The process development of DUCTOR, in my opinion, is very professional and has covered all the necessary steps, from laboratory tests to the development of a semi-industrial test facility, up to the first plant on an industrial scale which was erected in Tuorla.” December 2016
via Ductor.com Revolutionary Technology
“The Ductor® solution has a global market for the Anaerobic Digestion of Manure”
“Removing 60% of nitrogen – before biogas fermentation – is a ground-breaking innovation for the biogas industry. This is done by adding one fermentation step, prior to biogas fermentation, and a nitrogen stripping unit. This solution opens up a variety of new possibilities for improving the biogas economy and nutrient recycling. Ductor™’s technology has a global market, since the demand for solutions to improve the profitability of biogas production is tremendous everywhere.”
via Ductor.com Revolutionary Technology
Anaerobic Digestion of Manure Can Be a “Retro-fitting” Opportunity
At anaerobic-digestion.com we see this process as a retro-fitting opportunity for existing AD plants that are possibly struggling to make a good profit from their current biogas output. Biogas producing businesses in that position may wish to investigate the economic viability of ammonia removal by pre-treatment for their existing biogas plants.
About Ductor™ Corporation:
Ductor™ is a company with a unique portfolio of proprietary and patented technology to improve waste management, energy, and food production. Ductor™ has developed a unique fermentation system that removes more than 60 per cent of nitrogen from organic waste before biogas fermentation. Last year, Ductor™ was awarded a GCCA TOP 10 prize in Taipei.
Visit their website at: www.ductor.com
[Published July 2017. Updated December 2021.]