Solution Strengths, Weaknesses and Critical Indicators
- Use heat to produce either manure with less water or dried manure solids
- Reduce water in manure using a series of evaporators or recompressed process generated steam to evaporate water from liquid slurries—energy is supplied either by purchased fuel and/or waste heat from other processes
- Systems that dry separated solids use either a belt or drum to evaporate water from separated solids—energy is supplied either by purchased fuel, electricity and/or waste heat from other processes
- Compounds are released as the water is driven off (i.e. ammonia, hydrogen sulfide), this often requires additional treatment such as condensation of the water and/or scrubbing of the chemicals
- Requires purchased energy and costs are a significant concern leading to a trade-off between input costs and gains in liquid concentration and transportation/market of by-products
- Proven technology for nitrogen recovery, phosphorous recovery, storage reduction, GHG reduction, odor control and pathogen reduction
- Evaporator technology is designed to concentrate liquid manure to reduce volume.
- Evaporative systems typically use multi-stage thermal and/or electrical inputs under vacuum to distill and then condense ‘clean water’ from manure liquids with residual manure remaining as a concentrate.
- Evaporative systems are an option for volume reduction with most of the nutrients captured in the residual concentrate stream.
Economic/Return on Investment Considerations
- Presently no evaporative systems are in operation on U.S. dairies. There are some commercial evaporative technologies operating on dairies in Europe.
- Capital and operating costs are high, due to system complexity and large energy input requirements.
- In Europe, commercial applications almost exclusively treat anaerobically digested manure so waste heat from the power generators can be utilized to help offset the high energy requirements needed to evaporate water from manure liquids.
- Currently, there is a lack of technical data, economic studies, and operational experience for evaporative technology of dairy manure.
- Industry confidence in Europe is high regarding the commercial potential of evaporative technologies to process cow manure.
- Evaporative technologies are commercially available in Europe to process dairy manure due in-part to increased regulatory requirements for storage and application of cow manure.
- A new evaporative technology is being designed to treat dairy wastewater in the U.S. If successful, this new and innovative dairy approach would use available electricity from the grid to operate a mechanical vapor recompression type system to produce dried manure solids, clean water and aqueous ammonia.
- Evaporative technology is a commercially available technology in Europe.
- Evaporative technology is being tested at scale with a partner dairy in the U.S. to demonstrate its effectiveness for the U.S. dairy industry.
- Primary Benefits
- Evaporative technologies reduce moisture in manure liquids resulting in a volume reduction of approximately 40-75%, and total solid content in the concentrate stream of 10-15%.
- Pilot scale studies show potential for much larger volume reduction, even on the order of 90% when combining evaporative systems with dryers, while potentially reducing energy inputs via mechanical vapor compression.
- Nearly all (95%+) of the phosphorus, nitrogen, and potassium in the manure liquid can be partitioned with the concentrated products.
- Evaporative technologies can be designed to control ammonia and volatile organic emissions during treatment, with pH control and companion use of strippers/membrane systems as options.
- Due to the high operating temperature, pathogen treatment is extensive (>67%+) leading to both concentrate and condensate with pasteurization level reductions.
- The concentrate product provides for off-farm valued-added sales of fertilizer or on-farm use with reduced, storage, handling and application costs.
- Evaporation systems can significantly reduce odor by capturing ammonia as well as volatile organics in the condensate stream while also significantly reducing greenhouse gas emissions due to reduction of stored liquid under anaerobic conditions.
- Waste heat from the dairy can be used to lower energy costs for evaporator and dryer.
How it works?
- Evaporative technologies use heat to drive off the water in the manure or digestate.
- The systems often include a series of evaporators to sequentially evaporate water from liquid slurries or by recompressing process generated steam to drive water evaporation.
- Energy is supplied either by purchased fuel and/or waste heat from other processes.
Pretreatment and/or Post-treatment Required
- Evaporation technologies require coarse solid separation pretreatment to remove bulk solids.
- A liquid concentrate that can be pumped is generally the desired product (from evaporation) and can serve as input for additional processing.
- Evaporation is itself a pre-treatment process for clean water and nutrient separation technologies.
- Evaporative technologies have not been utilized for processing dairy manure in the U.S. either pilot or large scale which is a knowledge gap that requires more investigation to assess technical suitability, product quality, and economics.
- The requirement for purchased energy is a significant concern leading to consideration between input costs and benefits gained through the production of more nutrient dense co-products.
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