Online Analysis of Ortho- and Total Phosphate Phosphorous

The use of phosphrous for the treatment of waste water ensures that the environmental balance of water supplies is not disrupted by the presence of discharged effluent. It is therefore critical to monitor the presence of phosphorus compounds in wastewater.

Elemental phosphorus is highly reactive and can easily binds to oxygen present within the environment to form various types of phosphates including ortho-phosphates o-PO4, polyphosphates, and organic phosphates.

Phosphates in water sources can originate from a number of sources including minerals, detergents, agricultural runoff and other anthropogenic influents. To protect the environment and public health from the potential effects of phosphorous contaminants, federal environmental agencies have strict regulations regarding industrial phosphate emissions.

Total phosphate phosphorus (TP) is a plant nutrient that is found in particularly high concentrations in surface waters, however its presence can lead to eutrophication, or the over-fertilization of these water sources.

For biological sewage and wastewater treatment, the bioavailable o-phosphate phosphorus (o-PO4-P) promotes bacterial growth but can also be detrimental to rivers and lakes as an increase in nutrients can result in a growth that depletes oxygen supplies, kills fish and could even introduce harmful toxins, such as algae blooms and foams, to these affected areas. Phosphorus removal is therefore essential in wastewater treatment plants to ensure the environmental balance is not harmed by discharged effluent.

Toxic foam can form on the surface of natural waters containing high concentrations of phosphates. Inset: 2035 TP from Metrohm Process Analytics

Toxic foam can form on the surface of natural waters containing high concentrations of phosphates. Inset: 2035 TP from Metrohm Process Analytics.

Phosphorous Treatment of Wastewater

Most of the phosphorus components that are present in treated wastewater is bound to other filterable forms and removed as a precipitated sludge. Chemical treatment of coagulants such as calcium (Ca2+), aluminum (Al) and/or iron (Fe) can be costly and slow, which accounts for some of the reasons as to why biological treatment options have risen in popularity over the last decade.

In the wastewater treatment facility, it is important to know the concentration of o-PO4-P that is present within the influent stream in order to know the amount that is feeding the bacteria or the amount of reagents that will be needed for chemical treatment.

For environmental compliance monitoring purposes, treated effluent is monitored for the sum of all insoluble and dissolved phosphates present, which is a numerical value that is equivalent to the TP concentration. TP is not useful for identifying the origin of the phosphorus within a process, however it does provide useful information for the purposes of overall monitoring and wastewater compliance.

Monitoring Phosphorous Concentrations

The use of the Metrohm Process Analytics 2035 TP Analyzer provides users with the ability to monitor both the concentrations of o-PO4-P and TP in a continuous manner. It is important to note that for direct colorimetric applications, only o-PO4-P is measured in a sample.

Additionally, concentrations of TP can be determined by digesting the wastewater sample with heat, specified oxidizing agent and an acid prior to performing the photometric measurement on the freed o-PO4-P. To monitor the concentrations of both o-PO4-P and TP according to DIN EN ISO 6878:2004-09, a compact digestion cuvette photometer module is used.

Multiple sample streams can also be connected to the 2035 TP Analyzer to allow the user to have complete control over the efficiency of the phosphorus treatment process. The analyzer can send alarms for peak concentrations, saving bacteria or to notify the user if regulation limits have been reached.

This information has been sourced, reviewed and adapted from materials provided by Metrohm.

For more information on this source, please visit Metrohm.

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