Transcript 1st Annual Review

AD101 – Nutrient Transformations, Nutrient
Management, and Benefits
Pius Ndegwa
Nutrient Management & Air Quality Specialist
Biological Systems Engineering
Washington State University
AD101 – Overview
1. Anaerobic Digestion Process
2. Types of AD Systems
3. Nutrient Transformations
4. Nutrient Availability & Management
5. Benefits
AD101 – Anaerobic Digestion Process
Organic Matter
Protein
Insoluble
organic or
inorganic
compounds
& Water
Carbohydrate
AD101 – Desirable AD Conditions
1.
Anaerobic bacteria break down or "digest" organic material in the
absence of oxygen and produce "biogas" as a waste product
2. Temperature. Anaerobic bacteria communities can endure temperatures
ranging from below freezing to above 135°F (57°C), but they thrive best at
temperatures of about 98°F (37°C) (mesophilic) and 130°F (54°C)
(thermophilic)
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For AD operated in the thermophilic range, digestion and biogas production is
faster than in the mesophilic range. However, the process is highly sensitive to
disturbances, such as changes in feed materials or temperature.
On the other hand, the AD operated in the mesophilic range must be larger (to
accommodate a longer period of digestion within the reactor) but the process is less
sensitive to upset or change in operating regimen.
AD101 – Desirable AD Conditions
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The AD pH. In most cases, the pH is self-regulating but bicarbonates are
sometimes used to maintain consistent pH. Optimal pH range is between 6.8 to
8.5, i.e. slightly alkaline.
Acid forming bacteria grow much faster than methane forming bacteria. This can
reduce pH to unfavorable pH for methane forming bacteria thus inhibiting the
activity of methanogens. This is referred to souring and may result in failure of
the AD.
Reactor schematic: http://www.makingenergy.com/
AD101 – Types of AD Systems
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Classification:
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Based on: Operational temperature or Design
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Operational Temperature:
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Low temperature digestion, commonly referred to mesophilic
digestion (mediated by mesophile bacteria) occurs optimally
between 37°-41°C or at ambient temperatures between 20°45°C.
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High temperature digestion referred to thermophilic digestion
(mediated by thermophile bacteria) takes place optimally at
between 50°-52° and up elevated temperatures up to 70°C.
AD101 – Types of AD Systems
Designs Classification
Reactor schematic: http://www.makingenergy.com/
AD101 – What Determines Choice of Design?
http://www.rcminternationalllc.com
http://www.rcminternationalllc.com
Reactor schematic: http://www.makingenergy.com/
http://www.cadyinc.com
AD101 – Manure Collection and Handling System!
Source: http://www.makingenergy.com
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Source: http://www.menschmfg.com
The plug flow digester is best suited for handling manure with a solids
content of 11% to 13%
A complete mix digester operates best with a solids content of 3% to 10%
Lagoon typically operates on very dilute waste streams of approximately 3%
AD101 – Nutrient Transformations
AD101 – Nutrient Transformations
Source
Poultry
Species
Comments
TKN
Conserved 100%
Organic - N Reduced by 53%
NH4+
79.6% of TKN
Reference
J. A. Field, R. B. Reneau, Jr. , W.
Kroontje and J. S. Caldwell
Swine
TS
CODs
N
P
Reduced by 71.4% D.I. Massé, F. Croteau and L.
Reduced by 79.9%
Masse
Conserved 100%
Conserved 100%
Cattle
TKN
NH4+
TP
Conserved 100% P. R. Balasubramanian and R.
Increased by 70%
Kasturi Bai
Decreased by 30%
AD101 – Nutrient Transformations
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The process of AD bio-converts organic nutrients into inorganic
nutrients
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Organic-Nitrogen (proteins) converts into ammonium-Nitrogen and biogas
Organic-Phosphorus (lipids) is converted to Ortho-Phosphorus and biogas
Both Ammonium-N and Ortho-P are both plant available, i.e. AD results in
more bio-available plant nutrients.
Implication: Application timing is an issue and should be carefully planned.
Total Quantities: Total amounts of vital nutrients entering the AD
process remains the same, i.e. nutrient are conserved during the AD
process.
Potassium (K): Does not undergo any transformations during AD
of manure.
AD101 – Nutrient Availability & Management
AD101 – Nutrient Contents in AD Effluents
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The actual nutrient value of AD effluent depends two factors:
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The nutrient value of the raw manure, which in turn depends on diet,
species of animal, method of collection, and storage of manure.
The extent or completeness of digestion process.
Chemical analysis or an equivalent analysis of each effluent
should be obtained before applying manure to a field.
AD101 – Nutrient Availability and Management
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In general, availabilities (to plants) of N and P are increased
during anaerobic digestion via mineralization of respective
organic components.
However, there can be considerable loss of N from the more
volatile ammonium (NH4+) and ammonia (NH3)-N species that
could reduce eventual N availability depending effluent storage.
P and K on the other hand are not subject to volatilization loss!
In lagoon storage of the effluent, significant P could settle with
the sludge and thus reduce it availability in the lagoon liquid.
Bottom Line: Chemical analyses is essential for proper nutrient
management of the digester effluents.
Recap: AD Pros and Cons
• Pros
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Produces usable products: Biogas & nutrient-rich effluent
Reduce solids or biomass (compared to Aerobic process)
Reduces odors
Reduces emissions of greenhouse gases
Converts N and P to more plant available forms
• Cons
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Expensive to install
Requires additional resources to operate and maintain
By itself, does NOT address excess nutrient problem
Could result in excessive ammonia emissions
Thank You!
Questions?