Three Biological Approaches to Reducing Total Phosphorus in Water

Excessive total phosphorus in water bodies is a primary driver of eutrophication, leading to harmful algal blooms, oxygen depletion, and ecosystem degradation. Compared to chemical precipitation and physical adsorption, biological phosphorus removal offers distinct advantages: lower operational costs, minimal chemical sludge production, and greater environmental compatibility. Currently, Three  major categories of biological methods are widely employed to reduce total phosphorus concentrations in water.

1.  Polyphosphate-Accumulating Organisms

EBPR is the most extensively applied biological phosphorus removal technology in wastewater treatment. The process relies on polyphosphate-accumulating organisms (PAOs)—specialized bacteria capable of storing excessive amounts of intracellular polyphosphate. The fundamental mechanism involves alternating anaerobic and aerobic conditions. Under anaerobic conditions, PAOs release stored phosphate from their cells while taking up volatile fatty acids and converting them into intracellular carbon storage polymers such as poly-β-hydroxybutyrate (PHB). 

When transferred to aerobic conditions, PAOs degrade these stored polymers to generate energy and uptake dissolved orthophosphate from the water in quantities far exceeding their immediate metabolic needs, storing it as polyphosphate within their cells. By wasting phosphorus-rich sludge, phosphorus is permanently removed from the system. Common EBPR configurations include anaerobic–oxic (A/O), anaerobic–anoxic–oxic (A²/O), sequencing batch reactors (SBR), and oxidation ditch processes.

2. Denitrifying Phosphorus Removal

Denitrifying phosphorus removal represents a significant advancement over traditional EBPR. This approach employs denitrifying polyphosphate-accumulating organisms (DPAOs)—microorganisms capable of using nitrate (NO₃⁻) or nitrite (NO₂⁻) as electron acceptors under anoxic conditions to simultaneously uptake phosphorus and denitrify nitrogen. DPAOs exhibit a "dual-function" metabolic characteristic: they release phosphate under anaerobic conditions while storing organic substrates, and subsequently take up excess phosphate under anoxic conditions using nitrate as the electron acceptor. 

By combining nitrogen and phosphorus removal into a single anoxic phase, this approach can save approximately 30% of organic carbon demand and reduce excess sludge production compared to conventional processes. It is particularly advantageous for treating wastewater with low carbon-to-nitrogen ratios.

3. Constructed Wetland Ecological Restoration

Constructed wetlands achieve phosphorus removal through the synergistic action of plants, microorganisms, and substrates. Plant uptake is a significant pathway: aquatic macrophytes absorb orthophosphate directly from water and sediment for growth. Root systems excrete organic compounds that provide carbon sources for rhizosphere microorganisms, promoting the growth and metabolism of PAOs and other functional bacterial communities. 

Additionally, the alternating anaerobic and aerobic zones within wetland systems can support enhanced biological phosphorus removal. This approach is low-cost, environmentally sustainable, and particularly suitable for treating diffuse pollution sources and rural domestic sewage.