Renew Energy’s concept for advanced nutrient recovery is tailor-made to meet the requirements of each individual project. The recovery process offers many possibilities, and the final design will be based on water quality demands as well as fertilizer market opportunities and requirements.
In Renew Energy’s basic model, the degassed biomass is refined into clean process water, nitrogen rich fertilizer (ammonium sulfate), phosphor rich solid biofertilizer, and a potassium concentrate.
The nutrient recovery process consists of mechanical separation, ammonia stripping, and membrane filtration. One alternative is to exclude ammonia stripping and, instead, bind the ammonia in the concentrate by adding acid.
- Mechanical Separation: The degassed biomass is separated into two fractions: a fiber fraction (solid biofertilizer) containing the majority of the dry matter, and a thin liquid fraction (reject water) containing water soluble nutrients.
- Ammonia Stripping:The thin liquid fraction contains nutrients (ammonia-N, P, and K). After the anaerobic digestion, the liquid also contains carbon dioxide which has to be removed before ammonia can be released. Ammonia is absorbed in sulfuric acid and ammonia sulfate is produced as a well-known fertilizer concentrate.
- Membrane Filtration: The liquid from the ammonia stripping can be further treated by membrane filtration. Several different types of membrane filtration exist: micro, ultra, nano, and reverse osmosis. The common feature is that they can retain particles and salts over a certain size letting water and smaller particles pass through. The membrane filtration will create a concentrate stream and a permeate stream. The permeate stream from a reverse osmosis filtration can be used as clean process water.