AD101

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AD101 Nutrient Transformations, Nutrient
Management, and Benefits

• Pius Ndegwa
• Nutrient Management Air Quality Specialist
• Biological Systems Engineering
• Washington State University

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AD101 Overview

1. Anaerobic Digestion Process
2. Types of AD Systems
3. Nutrient Transformations
4. Nutrient Availability Management
5. Benefits

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AD101 Anaerobic Digestion Process
Organic Matter
Protein
Insoluble organic or inorganic compounds Water
Carbohydrate
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AD101 Desirable AD Conditions

• Anaerobic bacteria break down or "digest" organic
  material in the absence of oxygen and produce
  "biogas" as a waste product
• Temperature. Anaerobic bacteria communities can
  endure temperatures ranging from below freezing
  to above 135F (57C), but they thrive best at
  temperatures of about 98F (37C) (mesophilic)
  and 130F (54C) (thermophilic)
• 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.

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AD101 Desirable AD Conditions

• 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/
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AD101 Types of AD Systems

• Classification
• Based on Operational temperature or Design
• Operational Temperature
• Low temperature digestion, commonly referred to
  mesophilic digestion (mediated by mesophile
  bacteria) occurs optimally between 37-41C or at
  ambient temperatures between 20-45C.
• High temperature digestion referred to
  thermophilic digestion (mediated by thermophile
  bacteria) takes place optimally at between
  50-52 and up elevated temperatures up to 70C.

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AD101 Types of AD Systems

• Designs Classification

Reactor schematic http//www.makingenergy.com/
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AD101 What Determines Choice of Design?
http//www.rcminternationalllc.com
http//www.rcminternationalllc.com
http//www.cadyinc.com
Reactor schematic http//www.makingenergy.com/
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AD101 Manure Collection and Handling System!
Source http//www.menschmfg.com
Source http//www.makingenergy.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

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AD101 Nutrient Transformations

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AD101 Nutrient Transformations

Source Species Comments Reference
Poultry TKN Organic - N NH4 Conserved 100 Reduced by 53 79.6 of TKN J. A. Field, R. B. Reneau, Jr. , W. Kroontje and J. S. Caldwell
Swine TS CODs N P Reduced by 71.4 Reduced by 79.9 Conserved 100 Conserved 100 D.I. Massé, F. Croteau and L. Masse
Cattle TKN NH4 TP Conserved 100 Increased by 70 Decreased by 30 P. R. Balasubramanian and R. Kasturi Bai

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AD101 Nutrient Transformations

• The process of AD bio-converts organic nutrients
  into inorganic nutrients
• 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.

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AD101 Nutrient Availability Management
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AD101 Nutrient Contents in AD Effluents

• The actual nutrient value of AD effluent depends
  two factors
• 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.

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AD101 Nutrient Availability and Management

• 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.

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Recap AD Pros and Cons

• Pros
• 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
• Expensive to install
• Requires additional resources to operate and
  maintain
• By itself, does NOT address excess nutrient
  problem
• Could result in excessive ammonia emissions

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Thank You!Questions?