Enhanced Biological Phosphorus Removal
Phosphorus is generally the limiting nutrient in biological growth, however, it can be found in high concentrations in dairy wastewater. If excess phosphorus is allowed to enter an inland or coastal waterway, a state of eutrophication can occur which is a dense growth of plant life that shields out natural light and depletes the water of oxygen. The lack of dissolved oxygen in the water results in in the die off of fish and other naturally present aquatic life.
Due to phosphorus being a limiting nutrient in biological growth, there is always residual phosphorus present in biologically treated wastewater. If phosphorus levels were allowed to get down to zero, it would cause massive microorganism die offs and biological treatment would be inhibited. Therefore, the excess phosphorus that remains after biological treatment must be specifically managed.
In recent years, the amount of phosphorus that can be discharged to local water bodies has been dramatically reduced for industrial wastewater producers, such as the dairy industry. Traditionally, phosphorus has been chemically precipitated and separated, generally via gravity settling. This process is carried out by using chemicals such as aluminum or iron salts to precipitate out the phosphorus. The precipitated solids must then be separated from the treated water stream. This can be accomplished in large settling tanks, sand filtration or with membrane filtration. The separated solids may be disposed in landfills or land applied, depending on region.
Enhanced Biological Phosphorus Removal (EBPR) is a relatively new approach to removing phosphorus from industrial wastewater. This process uses a supply of consistent high strength waste and return activated sludge from the aerobic process to feed a denitrification zone followed by staged fermentation zones to promote an environment which selects for phosphorous accumulating organisms (PAOs). PAO’s uptake ortho-phosphorus once they are added back to the aeration basin. Once the microorganisms uptake phosphorus, it is retained in the cell bodies as polyphosphate and eventually wasted with the waste sludge. Again, this relatively new approach is being successfully used by municipalities to meet strict phosphorus discharge limits and now by CFR for dairy wastewater.
In addition to EBPR, CFR has experience with other proven phosphorus removal techniques to integrate into an overall solution to achieve the final effluent limit and client’s goals.