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                    54 BC HOLSTEIN NEWS ❆ CHRISTMAS 2020
   Understanding Modern Biogas Production
Manure + MicrobesNutrients + Natural Gas!
Daniele Chiodini,
Chief Technical Officer, Andion Technologies, North America
While relatively new in BC, farm biogas technologies have been
in use for 20 years in Europe.
requirements where a response to either phosphate (P) or potash (K) is expected.
Digestate and nitrogen recovery technologies
Anaerobic digestion leads to several changes in the composition of the resulting digestate compared to the original feedstock, which are relevant for the plant availability of macro and micronutrients after field application. One of the most important processes is the ammonification of the different forms of nitrogen, which leads to a product which is much better suited for nutrient recovery technologies.
Farmers understand the anaerobic digestion process that takes place in a cow’s rumen. The production of biogas is similar – bacteria breaks down organic materials in an oxygen free environment, producing biogas and digestate (the by- product).
The resultant biogas is mostly methane and carbon dioxide in a ratio of 60%/40% and represents a renewable fuel that can be utilized for electricity generation or upgraded to pipeline quality and injected into the grid. Renewable energy is usually subsidised and provides additional revenue to the farm. The digestate (by- product) represents between 85% to 95% of the total mass of the incoming material.
From organic matter to biogas: how does it work?
Organic wastes used for biogas production include dairy, poultry and pig manures, food wastes, food processing wastes, fats/ oil/grease and crop residues. Some types of organic matter break down more easily than others. Generally, the more ‘digestible’ the organic matter is, the more biogas can be produced.
The digestion process can occur in a range of temperatures, typically between 40°C and 55°C and at various moisture levels, which determine both the conversion rate and composition of the effluent. Biogas is generated through four metabolic stages by different families of bacteria that grow naturally in oxygen free environments.
1.Hydrolysis: breaks down the complex organic matter like carbohydrates, fats and proteins into simple sugars, fatty acids and amino acids. (The nitrogen is held by the amino acids)
2. Acidogenesis: the products of the first phase are further decomposed into alcohols and volatile fatty acids
3. Acetogenesis: in this phase, alcohols and volatile fatty acids are converted againintohydrogen,carbondioxideand acetic acid
4. Methanogenesis: a family of archaea bacteria converts hydrogen and acetic acid into methane and carbon dioxide (biogas)
Digestate: a valuable organic fertilizer
The digestate is a stable, odorless and nutrient rich liquid and/or solid product
having great value in enriching soil structure and fertilizing plants. The digestate nutrient concentration will vary over time according to the incoming feedstock, the biogas plant and conditions at that time.
Digestate typically comes in three different forms:
the higher these values, the higher the ammonia in the digestate. Thus, controlling the pH and temperature variables makes ammonia-stripping the most efficient nitrogen-recovery technology with a removal efficiency of 75%-95% from the digestate!
After the ammonia stripping treatment of the digestate, two streams are produced:
1. Ammonium sulphate [(NH4)2SO4]: a clear liquid fertilizer with N-P-K values of 8-0-0 and 30% sulphur content
2. Digestate with 90% less ammonia load that can be used in agriculture with far less environmental concerns
Why should a farm build an anaerobic digestion system?
There are multiple benefits derived from manure management through an anerobic digestion system compared to traditional methods:
• Integration and diversification of farm revenue due to the sale of the renewable energy, savings in fertilizer cost, savings in animal bedding costs and revenue from tipping fees from off-farm materials,
• Local economic benefits due to local labour involved during construction, skilled labor to maintain the system and on-site nutrient recovery and utilization,
• Soil health conservation by reduction of nutrient run-off, pathogen destruction, reduction of synthetic fertilizer utilization
• Positive energy generation due to the efficiency of the process, the system is generating more energy than what is consumed to operate the facility
• Improved farm sustainability through a closed loop system from waste to resource, while reducing risks posed by traditional manure-management systems
• Community-friendly - thanks to odor reduction, creation of local job opportunities and legacy for future generations.
With 20 years experience in biogas generation successfully operating on dairies all over Europe, the payback estimates are typically 8-12 years. Data is being collected in BC to develop an accurate model to forecast operational conditions and payback estimates.
• •
Whole: typically, between 4-10% dry matter with a very similar appearance to livestock slurry
Liquid: watery fraction with 1-3% dry matter content, derived from a solid/ liquid separation process (screw press, decanter, belt press)
Solid: dewatered fraction with high fiber content and 25-35% dry matter
(Proteins, Polysaccharides, Fats/Oils)
(Sugars, amino acids, long chain fatty acids)
(Propionate, butyrate, etc.)
• Nitrogen: The anaerobic process is very efficient in converting organic nitrogen into ammonia nitrogen, thus 80% of the total nitrogen in feedstock is present as readily available nitrogen. This high level of availability means that digestate can be used as a direct replacement for commercial nitrogen fertilizer.
• Phosphate and potash: Digestate contains useful amounts of phosphate and potash, together with small quantities of other nutrients and trace elements to help maintain soil fertility. As a general rule, 50% of the phosphate and 80% of the potash will be available to the crop in the year of application. These values should be used to calculate crop nutrient
  H2 + CO2
Digestates typically contain:
Different technologies are currently available on the market for nutrient recovery like solid-liquid separation, ultrafiltration and reverse osmosis, drying, struvite, biological processes and ammonia stripping.
Among these technologies, a well suited one for nitrogen recovery from liquid digestate is ammonia stripping. The technology leverages the composition of the digestates and volatile nature of the ammonia gas, to recover the nitrogen in a highly concentrated liquid fertilizer called ammonium sulphate that can displace the use of synthetic fertilizers.
The critical process of converting volatile ammonia to a stable ammonium liquid is also affected by pH and temperature:
    Wishing you
a blessed Christmas, from all of us at Island Dairy Services Ltd. Your 100% locally owned and operated dairy service provider.

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