Recovering valuable nutrients
Ammonia/Nitrogen Recovery
A DVO system can recover nutrients from digested waste to be used as fertilizer. When the nutrient recovery system is used, we remove ammonia/nitrogen through volatilization.
DVO’s Nitrogen Recovery process captures nitrogen ammonia that is otherwise lost, and places it in the form of a stable commercial fertilizer. This creates another revenue source (or operating cost offset) for the digester.
Solids Separation
When ammonia is separated it still leaves solids behind. These solids are then separated with both coarse- and fine-screen separation systems.
After nutrient recovery, solids settle extremely fast, and liquids at the top of a settling tank are exceptionally clean. Removing the solids takes out a large percentage of phosphorus and a smaller percentage of potassium fertilizer. This removal breaks the recycle buildup effect of P and K.
If this removal is still not enough, then we have had success (primarily with mixed substrate digesters that take in a lot of protein type material) with using dissolved air floatation (DAF) removal that does a very good removal percentage.
We have not found it necessary to utilize fresh water if we utilize some of the above steps to separate and settle/float the solids from the digested and ammonia removed liquids.
Poultry Litter Digestion
A DVO digester offers the unique ability to digest poultry manure on a belt-collection system where no bedding material is utilized. Our system:
- Works without outside waste material additions.
- Operates with little or no fresh water – egg wash water is sufficient.
- Utilizes scrubbed and recycled effluent liquid from the digester for dilution of the influent waste stream. Produces an economical, beneficial and stable nitrogen fertilizer from the odorous ammonia that is normally volatilized into the atmosphere.
- Significantly reduces odor from the poultry facility and its waste.
Project Example
A DVO system in operation at a 1.2-million-layer family farm in Ohio digests poultry litter, feathers, mortalities, and egg wash water.
The Situation
Anaerobic digestion of animal and organic wastes reduces odors and produces methane, which can then be converted into electricity, compressed natural gas or heat. This anaerobic digestion process has been proven on thousands of operations around the world, utilizing cattle, swine, and human wastes.
However, poultry manure was not able to be anaerobically digested at any commercial site because poultry do not have a urinary tract, and their waste is excreted at approximately 25% total solids. This number rises to 40-60% total solids when feathers are added along with the natural drying that occurs on collection belts in poultry houses. A fluid-based digester system is not effective in this situation without significant dilution of the waste with water to achieve 7-10% total solids. A reduction of this magnitude requires 5-8 times the volume of water, creating a subsequent water disposal problem after the digester.
The Solution
DVO developed a digester system that uses processed waste (digestate) after the digester, and after this digestate has gone through a solids separation system. The solids separation system reduces total solids content of the digestate, so this effluent water is suitable for dilution of the high-solids-content poultry manure. The practice of solids separation is well-proven on DVO digesters.
Continuous recycling of digester effluent liquids from a poultry digester does create an issue with accumulation of ammonium/ammonia in the liquid. Poultry waste is high in protein compounds, which biodegrade into amino acids and then into ammonium. Ammonium/ammonia can become toxic to methanogenic bacteria in the digester at levels above 3,500 ppm. The ammonia must be removed or the digester will become acidic and eventually fail. The patented DVO system uses a natural, non-chemical method to further process digester effluent and remove ammonium/ammonia. It also captures ammonia and converts it to a stable and marketable form – creating another revenue source (or operating cost offset) for the digester.
Poultry Flow-Chart*
The DVO poultry system is an efficient, continuous, low-maintenance system that requires minimal labor. It resolves issues surrounding poultry digestion and is an asset to the waste management of poultry facilities.
*NOTE: DVO may provide some, but not all, components depicted on this chart.