Presentation on theme: "AD101 – Nutrient Transformations, Nutrient Management, and Benefits Pius Ndegwa Nutrient Management & Air Quality Specialist Biological Systems Engineering."— Presentation transcript:
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 Carbohydrate Protein Organic Matter Insoluble organic or inorganic compounds & Water
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) 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 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:
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°-41°C or at ambient temperatures between 20°- 45°C. 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:
AD101 – What Determines Choice of Design? Reactor schematic:
AD101 – Manure Collection and Handling System! 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% Source:
AD101 – Nutrient Transformations
SourceSpeciesCommentsReference 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 COD s N P Reduced by 71.4% Reduced by 79.9% Conserved 100% D.I. Massé, F. Croteau and L. Masse Cattle TKN NH 4 + TP Conserved 100% Increased by 70% Decreased by 30% P. R. Balasubramanian and R. Kasturi Bai
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.
AD101 – Nutrient Availability & Management
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.
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 (NH 4 + ) and ammonia (NH 3 )-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 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