What Happens When Phosphorus Removal Fails?

What Happens When Phosphorus Removal Fails?

As society becomes more environmentally conscious, regulations tighten. A recent example is a trend toward limiting phosphorus levels in WWTP (Wastewater Treatment Plant) discharges. Phosphorus can promote the growth of undesirable plant material in environmental waters. As plant operators strive to meet these regulations, they introduce processes that can be subject to negative effects of certain environmental conditions and other factors. In this article, we’ll discuss: The reasons for removing phosphorus from wastewater, The strategies used to remove it, How those processes can be affected by conditions, and What can happen if the processes lose some of their effectiveness. We’ll also discuss Transcend Water’s role in efficiently designing phosphorus removal processes and how they support the wastewater treatment industry.

Why Remove Phosphorus from WWTP Discharges?

Phosphorus is an essential component of fertilizers. As such, one might think there’s nothing wrong with having it in environmental waters, but its fertilizing properties are precisely the reason. When excessive plant material grows in ponds, lakes and rivers, it can make the water cloudy and develop algae blooms that limit sunlight penetration and lower the oxygen content of the water, making it less desirable for marine animal life.

In some rural communities in the UK and elsewhere, WWTP discharges and agricultural run-off have been identified as significant sources of phosphorus in lakes and rivers, so authorities are tightening regulations on phosphorus from WWTPs.

How is Phosphorus Removed from Wastewater?

Phosphorus removal processes in larger-scale plants have been common for some years. In smaller plants, though, several factors make the implementation of such processes more difficult:

  • The experience level for adapting large-plant processes to small plants is limited.
  • Feedwater flows may vary more widely in smaller plants.
  • Some small WWTPs are in difficult-to-access locations.
  • Management and monitoring programs may be less robust.

There are several methods for phosphorus removal, and they fall into two major categories, chemical and biological. The chemical processes use materials that combine with dissolved phosphorus and can be precipitated out of the water. Biological processes introduce phosphorus accumulating organisms (PAOs), which derive energy from an external carbon source and certain energy-releasing chemical reactions.

Factors Affecting Phosphorus Removal

Several factors can affect the performance of biological phosphorus removal:

  • Temperature of the feedwater
  • The source of the carbon used as a PAO energy source
  • Dissolved oxygen level
  • Hydraulic retention time
  • Concentration of volatile fatty acids (VFAs) in the feedwater
  • pH of the feedwater

The first two factors are the most important. In areas with heavy rain and particularly, heavy snowfall, significant dilution and cooling of feedwater can be a major factor reducing the efficiency of EBPR (Enhanced Biological Phosphate Removal) systems.

Acetate and sodium citrate are two of the most used carbon sources for PAOs. The PAOs consume the carbon in anaerobic conditions and then use the carbon during aerobic conditions for energy to consume phosphorus.

In wastewater management systems treating municipal waste, higher concentrations of VFAs from food processing tend to be present during the week and lower on weekends. The phosphorus removal performance increases when the feedwater contains less VFAs.

High dissolved oxygen levels result in rapid deterioration of the phosphate removal process.

When Phosphorus Removal Deteriorates…

Allowing phosphorus levels to rise in bodies of water can result in the water’s eutrophication (a build-up of nutrients), encouraging excessive plant growth. This can make the water murky (see the image above), limiting sunlight penetration and dissolved oxygen levels. While some plant life provides nutrition for marine animals, excessive levels become unhealthy and discourage marine animal life.

Transcend Water has developed the Transcend Design Generator to take the pain out of wastewater treatment plant design. This unique tool can generate a preliminary plant design in as little as 8 hours instead of the grueling weeks or months required for manual design calculations. A recent addition to the Design Generator is biological phosphorus removal as one of the process options. Visit Transcend’s website to learn more and discuss your wastewater treatment needs with their experts.

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