Total Nitrogen And Total Phosphorous Monitoring In Waste Water Treatment Plants

Nutrient pollution in waste water is an increasingly challenging environmental issue. Nutrient pollution impacts natural water sources resulting in serious environmental and human health issues, and impacts the overall situation of water availability and handling.

Nitrogen and phosphorus are nutrients that are a natural part of the ecosystem. However, excess of these elements being released into water by a range of human activities can adversely affect aquatic life.

The presence of too much nitrogen and phosphorus accelerates the growth of algae to a pace that ecosystems cannot handle. Significant increase in algae growth, also known as algal bloom, harms water quality, and decreases the quantity of oxygen in water. This reduction in oxygen makes it difficult for aquatic life to survive, leading to the death of fish in large numbers, and also making the water “dead”. Algal blooms also produce elevated toxins and encourage bacterial growth, making water unfit for consumption. Humans who come into contact with this polluted water either by direct consumption or by consuming tainted fish or shellfish are likely to fall sick.

It therefore becomes imperative for water and waste water treatment plants to deal with excess nutrient removal, so that overall environmental balance is maintained when waste water is discharged.

As the control of nutrients is inevitable, so also is the need of online monitoring of parameters likes total nitrogen and total phosphorus.

Total nitrogen includes organic nitrogen, ammonia (NH3), nitrate (NO3) and nitrite (NO2).

Monitoring Method

While there are certain direct as well as co-relative type methods used to determine the Total Nitrogen (TN) and Total Phosphorus (TP) in water, the most appropriate would be including a persulfate digestion followed by colorimetry. The persulfate method determines the total nitrogen content by oxidising all forms of nitrogen to nitrate. Alkaline oxidation occurs at higher temperatures (about 100 – 110°C). A reducing agent (viz. sodium metabisulfite or hydrazine sulphate, etc.) is added after the digestion to eliminate halogen oxide interferences. The nitrate concentration is determined once the conversion of N (nitrogen) to NO3 (nitrate) has occurred. Nitrate (NO3) then reacts with chromotropic acid under strongly acidic conditions to form a colour complex with an absorbance maximum at 550-580 nm. This absorbance is directly proportional to the concentration of the Total Nitrogen (TN) in water based on Beer Lambert Law.

Similarly Total Phosphorus is the sum of organic and inorganic phosphorus compounds in water.

Today, analytical solution providers offer true real time or online analysis solutions for measurement of TN and TP in waste water applications. The analysers are available in rugged designs that can measure using chemical methods, yet with negligible human intervention and less down time. They can be hooked with local software or can be connected through a modem to transmit data remotely to a central server or data monitoring station of a plant as well as pollution board authorities.

Analysers with appropriate features like auto dosing of chemicals and oxidation modules, cleaning, auto validation or calibration offer a comprehensive and real time monitoring solution for crucial parameters like TN and TP for water and waste water applications.

Based on the analysis, the appropriative corrective action for treatment can be adopted. This will help municipal and industrial treatment plants to operate more efficiently, reduce the cost of chemicals and biological cultures and result in better treatment of water.

The above described method can be considered as the true representation of process parameters rather than any corelative type of analysis. The concentration of such parameters is so dynamic in the process, that the corelative methods may not be accurate or truly representative of the process situation.