Dissolved wastewater phosphate can be difficult to filter and often escapes filtration and enters water or soil. It reacts with various elements present in water and soil to form compounds that affect aquatic organisms. Hence it is necessary to understand how Phosphate reacts and what are the compounds formed. In this article I discuss some of the reactions in order to find out whether it needs to be treated.

Phosphate In Wastewater

Wastewater Phosphate testing usually relies on the Molybdophosphoric acid found in samples of wastewater being tested for the presence of phosphate in wastewater. The method used here is the Vandate method. It is a calorimetric method that is best suited for Phosphorous detection and is used in laboratories. This is applied if the Phosphorous content is in the range of 1 to 10 mg/l. Wastewater contaminated by industrial effluents contains several dissolved chemicals. One of these effluents may be Stannous Chloride. If this is found in wastewater then it can reduce the Molybdophosphoric acid into Molybdenum. During laboratory analysis this testing yields a residue of Molybdenum that is richly colored in blue. Here’s the chemical reaction:

PO4 + I2(NH)2MoO4 + 24H2O -> (NH4) 3PO4.12MoO3 + 2INH4 + 12H2O

(Ammonium phospho molybdate)

As you can clearly see from the chemical reaction above, the wastewater phosphate (PO4) can react with Ammonium Molybdate (I2(NH)2MoO4), which can exist in wastewater to form Ammonium Phosphomolybdate ((NH4)3PO4.12MoO3). Under laboratory testing this Phosphomolybdate is obtained as a yellow precipitate. It is more commonly called as the Ammonium Molybdate Phosphomolybdic Acid or the Ammonium Phospho-molybdate. The IHH4 acts as an inhibitor during this reaction process. Some residual water is also obtained as a result of this reaction along with the precipitate.

Due to the complex composition of the wastewater and in the presence of various substances, certain other residue can also be formed as a result of the reaction of the phosphate in wastewater. One such compound that gets formed is Ammonium Phosphate ((NH4)3PO4.12MoO3). It does not occur alone and is formed along with Tin (Stannous). Here’s the reaction:

(NH4)3PO4.12MoO3 + Sn4 is molybdenum blue + Sn4

The 12MoO3 in the above reaction is Molybdenum Trioxide. Tin is also obtained which is represented here as Sn4. It is colored in molybdenum blue. These are some of the reactions that can take place in wastewater. Hence it is necessary to completely understand the nature and properties of various chemicals found in wastewater to be able to treat it effectively.

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