Many countries are tightening their water quality legislation owing to the significant environmental challenges posed by excessive phosphorus in water bodies, says water treatment technology specialist Nordic Water products director Mattias Feldthusen.

Agricultural runoff and wastewater discharges can contribute to eutrophication, a process that leads to excessive algae growth which depletes oxygen levels in the water, resulting in hypoxic, or dead zones, where aquatic life cannot survive, Feldthusen explains.

“Phosphorus is often the limiting nutrient in freshwater ecosystems, meaning that controlling levels of this mineral can prevent or mitigate eutrophication,” he says.

Therefore, managing phosphorus levels in wastewater discharge is crucial for ensuring the sustainability of water resources.

Feldthusen notes that regulatory targets vary widely, from less than 8 mg/ℓ in South America to under 0.1 mg/ℓ in some European treatment plants.

“Most countries are aiming to reduce these levels even further,” he says, adding that this requires advanced treatment processes.

He highlights biological phosphorus removal (BPR), which leverages the natural ability of certain microorganisms to take up and store phosphorus, as an environment-friendly option.

“Known as enhanced BPR when used in wastewater treatment, it involves creating specific conditions that promote the growth of phosphorus-accumulating organisms.”

However, BPR is sensitive to operational conditions, which can dilute wastewater and temporarily reduce efficiency.

Chemical precipitation is another method, involving coagulants, such as ferric chloride or lime, which react with the phosphorus to form insoluble compounds that can be removed through sedimentation or filtration.

While this approach is effective, it increases sludge production and operational costs.

Other technologies being explored include membrane filtration and ion exchange and adsorption, which offer high removal efficiency, but introduce increased operational complexity and cost.

Feldthusen notes that most wastewater treatment plants already employ processes that remove up to 25% of total phosphate content, so chemical treatments are often required to achieve stricter compliance levels.

However, wastewater treatment plants are often constrained by space limitations and cannot install new equipment and processes. Therefore, innovative tertiary treatment solutions are increasingly necessary.

Feldthusen suggests lamella plate clarifiers, which can reduce phosphorus to less than 0.3 mg/ℓ, while disk filters achieve levels between 0.1 mg/ℓ and 0.15 mg/ℓ.

For even stricter requirements, Nordic Water’s DynaSand filter can reduce phosphorus levels to below 0.05 mg/ℓ, depending on coagulant dosages.