The purpose of this experiment is to analyze the P content in a wastewater sample and to test the efficiency of 2 different methods for P removal from wastewater.
To analyze the P content in a wastewater sample, standard P solution is made and calibration curve is generated and phosphate concentration in wastewater is determined by using calibration curve that is generated. To determine the concentration of P, vanadomolybdophosphoric acid spectrophotometric method is used. The predominating form of phosphate is dependent on pH.
H₃PO₄ ⇌ H₂PO₄⁻ + H⁺ pKₐ=2.12
H₂PO₄⁻ ⇌ HPO₄²⁻ + H⁺ pKₐ=7.25
HPO₄²⁻ ⇌ PO₄³⁻ + H⁺ pKₐ=12.7
This method is under the acidic condition and ammonium molybdate is reacted with phosphate, then, the product reacts
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By adding theoretical dose of alum which was 6.55mg of alum, 4.9% of phosphate was removed. However, by adding pragmatic dose of alum which was 20mg of alum, 86% of phosphate was removed. This was because that the equilibrium the equation,
Al³⁺ + HₐPO₄³⁻ ͣ ⇌ AlPO₄ + aH⁺ showed that when excess Al³⁺ was added, then the reaction went forward which would make more products of AlPO₄ + aH⁺. Therefore, by adding pragmatic dose of alum of 200mg/L produced more precipitate of AlPO₄ which was the way of removing phosphorus so this was more effective than by adding theoretical dose of alum.
Answers
2 main hazards were acidified vanadate-molybdate reagent and sodium hydroxide. Especially for handling the acidified vanadate-molybdate reagent, the gloves and safety glasses must be worn and it has to be used in fume hood. For NaOH, must be careful when handling so that it does not spill. If there is a spillage, contaminated clothes should be removed, and rinse eyes, skin, clothes and equipment with lots of water and also must report supervisor.
H₂PO₄⁻, HPO₄²⁻ present in pH of 7.25.
M(H₂PO₄⁻) = 97g/mol
0.1/ 97 = 1.03x10⁻³mol/L
1.03x10⁻³ x 31 = 0.0319 =
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When pH is high which means more OH⁻, then aluminum ions will react with hydroxide ions to form aluminum hydroxide. Phosphate ions are acting as a natural buffer.
If the equipment is not washed with acid, it would cause an error. This is because the phosphorus analyzing is dealing with low concentration of phosphorus and it is easily contaminated by detergent and other chemicals and it has to be washed by using an acid and also it has to be rinsed with distilled water once it is rinsed with acid. Also refer to section 4 (discussion).
Calcium phosphate is found in teeth and bones.
Alum is used for the sedimentation tank in water treatment places because alum addition leads to flocculate the charged colloidal particles.
For alum-precipitation, the aluminum phosphate from the wastewater would have bacteria and viruses. When phosphate from wastewater is used, the main problem is that there will be microbiological hazards so the plants and animals can be contaminated from that alum-precipitation.
One person generates 150L of wastewater, 500 habitants in Rongotea and each 1L; it needs 200mg of