Phosphorus Removal via Assimilation

When it comes to removing phosphorus from wastewater, there are a variety of ways it can be done. One method is to adjust the aeration and water movement through extended aeration systems and oxidation ditches. Another method is through assimilation and constructed wetlands.

Assimilation is the reduction of phosphorus in wastewater by incorporating the phosphorus, as an essential element in biomass, particularly through growth of photosynthetic organisms (plants, algae, and some bacteria, such as cyanobacteria). This is achieved through treatment ponds containing planktonic or attached algae, rooted plants, or even floating plants (e.g. water hyacinths, duckweed).

The use of constructed wetlands is another method that can be used to remove nutrients. First you must incorporate phosphorus into the biomass of plants planted in the wetland, and then you must remove and dispose of the biomass (harvesting the phosphorus). This biomass can be used for the production of biogas (methane) through the anaerobic digestion process.

The removal, disposal or reuse of the net biomass (either algae or other plants) is essential to the removal of the phosphorus from the water. If the plants are allowed to degrade in the water the phosphorus is added back to the wastewater and has to be assimilated again. The biomass produced may also be used in the production of methane/biogas for the production of heat or electrical energy to be used on site or sold back to the grid. The use of wastewater treatment plant effluent to grow beneficial algae to be used in the production of biofuels is being researched at universities and companies around the world.

Another method of disposal of the biomass is through composting. The material may be mixed with other biomass and allowed to compost and then be added back to the environment as an organic product.

The reuse of the nutrients in wastewater (nitrogen and phosphorus) may eventually be achieved with the evolution of current technologies. As these technologies improve, so will the percent of reuse and recovery of the valuable nutrients from our wastewater.


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