Phosphorus, Phosphate & Phosphonate

Blog | 19 June 2017

We are often asked about the difference between the 3Ps.  Here’s an insight into what they are and the differences between them:

Phosphorus P

The element Phosphorus – P is key to common forms of scale control and is traditionally present as phosphate or phosphonate groups. Often when testing waste water Total P will be determined, unfortunately this does not differentiate between P from phosphates and P from phosphonates.


Phosphates have conventionally been used in detergents to control scale. Both simple phosphates, like STPP (Sodium Tripolyphosphate), and complex phosphates, like TSPP (Tetrasodium Pyrophosphate) were used as builders in detergents to improve performance by chelating calcium and magnesium ions in hard water.  However, phosphates can cause serious ecological damage when disposed of into the watercourse.

Problems with Phosphate

The main problem with phosphate use is the potential to cause ecological damage in rivers and lakes via eutrophication. When phosphates are discharged into the watercourse, most commonly from detergents, fertilisers and sewage, they cause a spike in the nutrients required for plant growth.

Phosphate acts as a food source to plants and algae present in rivers and streams.  An increase in phosphate levels can lead to a surge in growth often resulting in algal blooms which blanket the surface of the water preventing sunlight penetrating to organisms below.  After the initial surge of plant growth, the lack of light for plants below the surface causes them to die.  As bacteria work to break down the dead plant matter they consume vast amounts oxygen resulting in severe oxygen depletion of the water in the area.  Depletion of oxygen levels in the water can cause the widespread death of animal and plant life, effectively creating a dead zone.

In light of this problem many industries have attempted to limit phosphate use and water companies have imposed strict limits on the levels that can be discharged.


Phosphonates are generally capable of offering the same level of scale control as phosphates but can be included in formulations at concentrations one order of magnitude lower than phosphates. As such much less P ends up being sent to drain after the rinsing process.

In sewage works using only primary treatment over 50% of phosphonates are removed from water to the sewage sludge, while those using secondary treatment remove 60 – 80%.

While phosphonates used in detergents are not readily biodegradable they do not bioaccumulate and cause no chronic or aquatic toxicity that negates the issue of ready biodegradability. Although not readily biodegradable, phosphonates are not immune to photodegradation, hydrolysis or biodegradation over time.

P - Free

Despite phosphonates being much safer than phosphates ecologically an entirely P – Free product would be even safer. So far this year Holchem have reduced phosphorus usage for scale control by 35%, with further reductions planned for later in the year. We are also able to offer a P-Free product in each product area.