Biological Approaches to Excess Phosphate Removal

Excessive phosphate in water bodies is a primary driver of eutrophication, leading to algal blooms, oxygen depletion, and loss of aquatic biodiversity. While chemical precipitation and physical filtration are effective, they often incur high costs and generate secondary waste. 

Biological phosphate removal offers a sustainable, low‑energy alternative by harnessing the natural metabolic processes of microorganisms and plants. These approaches not only reduce phosphate concentrations but also integrate well with ecological treatment systems. The main biological strategies include enhanced biological phosphorus removal, algal uptake, and constructed wetlands.

Enhanced Biological Phosphorus Removal 

EBPR is a well‑established process used in wastewater treatment plants. It relies on a cycling of aerobic and anaerobic conditions to select for polyphosphate‑accumulating organisms. Under anaerobic conditions, these microorganisms take up volatile fatty acids and release phosphate into the water. Under aerobic conditions, they uptake phosphate far in excess of their metabolic needs, storing it as polyphosphate granules within their cells. 

By wasting sludge rich in polyphosphate, the net phosphate concentration in the treated water is significantly reduced. The efficiency of EBPR depends on the availability of suitable carbon sources, such as acetate or propionate, and careful control of dissolved oxygen and sludge retention time. When properly managed, EBPR can achieve phosphate removal rates exceeding 90 % without chemical addition, making it a cost‑effective option for municipal and industrial wastewater.

Algal and Macrophyte Uptake

Microalgae and aquatic plants assimilate phosphate directly from the water as a nutrient for growth. In treatment ponds or photo‑bioreactors, algae rapidly take up phosphate along with nitrogen, converting dissolved nutrients into algal biomass. The biomass can then be harvested, removing phosphorus from the system permanently. 

This approach is particularly attractive because it simultaneously produces biomass that can be used for bioenergy or fertiliser. However, performance is sensitive to temperature, light, and hydraulic retention time. Larger aquatic plants, such as water hyacinth or duckweed, also uptake phosphate and can be used in floating treatment wetlands. Regular harvesting is essential to prevent the plants from dying and releasing phosphorus back into the water.

Constructed Wetlands

Constructed wetlands are engineered systems that mimic natural marshlands. They combine physical filtration, chemical adsorption, and biological uptake. Phosphate is removed through plant uptake, microbial assimilation, and storage in wetland soils. 

The design typically consists of a shallow basin planted with emergent macrophytes, through which water flows slowly. The plants provide surface area for biofilm growth, and the associated microorganisms contribute to phosphorus cycling. While phosphate removal in wetlands is often slower and less complete than in EBPR, the systems are low in energy consumption and provide additional benefits such as habitat creation and flood attenuation.