Nutrient recovery systems and methods
Inventors
Zhao, Quanbao • Dvorak, Stephen W. • Chen, Shulin • Frear, Craig • VanLoo, Bryan J.
Assignees
Dvo Inc • Washington State University WSU • Andgar Corp
Publication Number
US-12209026-B2
Publication Date
2025-01-28
Expiration Date
2031-06-10
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Abstract
Methods, systems, and apparatuses for anaerobic digestion of waste fibrous material and the recovery of nutrients are provided. Methods, systems, and apparatuses disclosed herein provide mechanisms to release dissolved gases from anaerobic digester effluent. Methods, systems and apparatuses disclosed herein can recover one or more nutrients from anaerobic digested effluent using a range of temperatures, aeration rates, aeration times, pH ranges, and settling times.
Core Innovation
The invention provides methods, systems, and apparatuses for the anaerobic digestion of waste fibrous materials and the recovery of nutrients from the resulting effluent. This includes mechanisms to release dissolved gases from anaerobic digester effluent and enables the recovery of one or more nutrients, such as nitrogen and phosphorous, using a combination of heating, aeration, pH adjustment, variable settling times, and specifically controlled parameters such as the size and shape of aeration bubbles.
A key problem addressed is the lack of efficient, cost-effective technologies for recovering nutrients from anaerobic digester waste material, especially in agricultural settings. Traditional wastewater technologies are either not reliable or economical when applied to manure in farm environments. Consequently, existing anaerobic digesters do not recover sufficient nutrients, resulting in environmental threats from nutrient overloads on farms and wasted resources.
The disclosed methods and systems employ plug flow processes, customizable reactors, and integrated heat and aeration management to convert soluble ammonium to gaseous ammonia, which is captured and reacted with acid to form concentrated ammonium salts. The solutions allow for enhanced settling and separation of phosphorous-rich solids, flexibility in targeting specific nutrient removals, and the production of saleable products such as fibrous bio-fertilizers, peat, and Class A effluent that meets regulatory standards for pathogen control.
Claims Coverage
There is one independent claim, which encompasses six inventive features.
Heating and aerating anaerobic digester effluent to convert soluble ammonium to gaseous ammonia
The method comprises heating and aerating anaerobic digester effluent, which has been separated from waste fibrous material, in a plug flow aeration reactor. The reactor includes a gas headspace above the liquid level and below a ceiling to store gaseous ammonia, facilitating the conversion of soluble ammonium to gaseous ammonia.
Providing heated and aerated effluent to a settling chamber
After heating and aeration, the anaerobic digester effluent is transferred to a settling chamber, allowing for the separation and collection of nutrient-rich solids as part of the nutrient recovery process.
Sequential ammonia stripping with two stripping towers and acid reaction
Gaseous ammonia collected from the aeration reactor's headspace is directed to a first stripping tower, where it reacts with controlled amounts of acid. Unreacted gaseous ammonia is subsequently transferred from the first to a second stripping tower for further acid reaction, enhancing ammonium salt recovery.
Recovering ammonium salt produced from acid-ammonia reaction
The method recovers an ammonium salt that results from the reaction of acid with gaseous ammonia within the first and/or second stripping towers. This enables collection of a concentrated, saleable ammonium salt product.
Mixing biogas from an anaerobic digester with the effluent from the settling chamber
Biogas from the anaerobic digester is mixed with the effluent from the settling chamber, facilitating further treatment and aiding in pH adjustment or biogas purification.
Integration of upstream digestion of waste fibrous material
The method can further comprise an initial step of digesting waste fibrous material in an anaerobic digester prior to effluent heating and aeration, integrating the nutrient recovery process with standard anaerobic digestion operations.
The claim covers a multi-step process for nutrient recovery from anaerobic digester effluent, featuring integrated heating, aeration, sequential gaseous ammonia stripping with acid reaction in multiple towers, and downstream mixing with biogas, aimed at maximizing ammonium salt and nutrient solid recovery.
Stated Advantages
Enables high nutrient recovery rates from anaerobic digester effluent with ease of operation and reduced operating and capital costs.
Minimizes chemical addition and use of energy resources while recovering significant levels of nitrogen and phosphorous.
Produces organic separated solids and phosphorous-rich solids as valuable products such as bio-fertilizers.
System can be tailored and optimized to recover specific nutrients depending on farm requirements.
Optimizes operating parameters to handle various manure types with minimal energy and input requirements.
Animal waste solids do not need to be removed prior to anaerobic digestion or prior to operation of the nutrient recovery system.
Documented Applications
Processing manure and recovering nutrients in waste-processing systems on livestock farms, including dairies, cattle feedlots, and poultry farms.
Producing saleable bio-fertilizers such as fibrous solids, ammonium sulfate slurry, and phosphorous-rich organic solids from anaerobic digested effluent.
Producing Class A biosolids and Class A effluent that meet regulatory requirements for pathogen reduction for use as fertilizers or safe disposal.
Reducing nutrient loads, especially nitrogen and phosphorous, from commercial animal feeding operations to mitigate environmental threats and facilitate sustainable nutrient recycling.
Generating reclaim water from treated anaerobic digester effluent for reuse in agricultural processes, particularly in poultry manure digestion.
Use in zoos, animal parks, municipalities, and organizations caring for multiple animals for processing animal or human waste.
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