Grantee Research Project Results
Final Report: Sustainable Bio-Fertilizer from Anaerobically Digested Animal Manure
EPA Grant Number: SU836120Title: Sustainable Bio-Fertilizer from Anaerobically Digested Animal Manure
Investigators: Zhang, Ruihong
Institution: University of California - Davis
EPA Project Officer: Page, Angela
Phase: I
Project Period: September 1, 2015 through August 31, 2016
Project Amount: $14,965
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2015) RFA Text | Recipients Lists
Research Category: P3 Awards , Pollution Prevention/Sustainable Development , Sustainable and Healthy Communities , P3 Challenge Area - Chemical Safety
Objective:
The goal of this project is to design and demonstrate an integrated and efficient biological system capable of converting dairy manure digestate into organic biofertilizer products, both solid and liquid, that can provide nutrients to crops and also improve soil health. The biofertilizer products will be tested in vegetable crop fertility experiments. A life cycle assessment of production and application of our biofertilizer products will also be conducted and compared to synthetic fertilizers. This project requires the development of innovative and previously unexplored technologies to add value to a material currently viewed as a waste product. 3 The specific objectives of Phase I were to: 1. Research and demonstrate effective separation technologies for treatment of digestate to yield solids, nutrients, and water streams; 2. Design and produce novel, nutrient-rich, cost-effective and safe biofertilizer products and to evaluate their effectiveness on vegetable production; and 3. Conduct an economic analysis and environmental assessment for application in dairy manure digester systems and disseminate project results to dairy farmers and crop production consultants. The results benefit people, prosperity, and the planet by: 1. Contributing knowledge towards conservation of natural resources associated with energy and synthetic fertilizer production; 2. Promoting the prosperity of rural communities through job creation associated with a new technology, business development to market and sell the new products, and the introduction of a new profit stream for dairy farmers; 3. Reducing greenhouse gas emissions and water/air pollution while supporting sustainable agriculture by reducing the reliance on fossil fuel-based, synthetic fertilizers and promoting energy-efficient, low carbon, bio-based organic alternatives
Summary/Accomplishments (Outputs/Outcomes):
Our team acquired and characterized dairy manure digestate from an anaerobic digester located in Galt, CA. We found that the digestate contains many macro and micro nutrients essential for plant growth as well as beneficial microorganisms for soil. We studied the nutrient distribution among different size particle and liquid fractions. The results aided us in the design and optimization of separation methods to obtain the fractions with the most nitrogen, phosphorus, and potassium. We also compared dairy manure digestate with food waste digestate. We discovered different nutrient distribution profiles between the two types of digestate. For instance, more phosphorus and magnesium are contained in the finer solids of the dairy manure digestate than that of the food waste digestate. The distribution of nitrogen, calcium, potassium, and sodium, on the other hand, were similar between the two digestates. Based on results from our lab scale characterization and analysis, we designed, constructed, and demonstrated a small scale integrated system with treatment capacity of 300 gallons per day of raw digestate. The system produced solid and liquid fractions and consisted of a screw press and vibratory screen for coarse solid separation, followed by a membrane filtration unit for fine solid separation, and finally ambient air drying and a pellet mill for pelletization. The final pelletized products have a high packing density, useful for transportation, and exhibit slow release fertilizer properties. The nitrogen content of the pelletized products is close to 4%. Zeolite adsorption was investigated as a method for removing ammonia and other nutrients from the liquid fraction, followed by application of the nutrient rich zeolite as a potential soil amendment. However, we discovered that zeolite treatment resulted in an increase in the sodium content of the liquid above desired levels for irrigation water. Consequently, we also developed a novel strategy for reducing sodium desorption by pretreating the zeolite with calcium chloride prior to liquid treatment. 4 Our pelletized products were tested in a greenhouse trial growing Black Seeded Simpson lettuce. The growth period of lettuce is shorter than for tomatoes. Lettuce was investigated in lieu of tomatoes, as previously stated in the Phase I proposal because of the additional time needed for biofertilizer research. The production of lettuce in California is over two million tons annually; hence, its selection as a suitable substitute. The greenhouse trial showed that our pelletized products were able to meet the nutrients needs of lettuce. However, only half the yield was obtained as compared to the synthetic fertilizer treatment, possibly due to the lower bioavailability of nutrients in the pellets in the short lettuce growing period (Figure 1c). The organic nitrogen in the pellets needed more time to mineralize. Different strategies in processing and formulation of pellet production as well as in timing and amount of biofertilizer application need to be further investigated with different varieties of lettuce. Higher soil electrical conductivities were found with pelletized products than with synthetic fertilizer but the obtained values would not be considered problematic for healthy soil and plant growth. Lastly, an economic analysis showed the developed integrated system to have good potential for profitability when operated in large scale, with a payback period of less than 10 years for most of the scenarios investigated.
Conclusions:
All three objectives of Phase I were successfully met. For objective 1, we characterized two types of digestate, including a dairy manure digestate from a local California dairy. We also investigated multiple physical and chemical separation technologies, including screw press and vibratory screen separation, ultrafiltration, and ion exchange with zeolite. For objective 2, we successfully designed and demonstrated a small scale integrated system for production of solid and liquid biofertilizer products from digestate. The pelletized, solid products were then tested in a greenhouse study with lettuce, showing favorable growth trend and yields. The yield of lettuce fertilized with the pelletized products were not as high as that of lettuce treated with synthetic fertilizer. More research is required to optimize the products, solid and liquid, and to develop the best biofertilizer application rate and timing in order to achieve similar or better performance compared to synthetic fertilizers. Finally, for objective 3, economic models demonstrated excellent potential for profitability from the developed biofertilizer production system with short payback times.
Journal Articles:
No journal articles submitted with this report: View all 3 publications for this projectSupplemental Keywords:
Anaerobic digestion effluent, biofertilizer, dairy manure, digestate upgrading, nutrient recoveryRelevant Websites:
UC Davis EPA P3 Biofertilizer Team Exit
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.