Have you got this knowledge about alkalinity in sewage treatment?
PH is an important factor affecting nitrification in sewage treatment. Some use solid sodium hydroxide, some use 30% liquid caustic soda, and some use sodium carbonate. What is the relationship between PH and pH? What is the difference between adjusting pH with sodium hydroxide and sodium carbonate? How to convert alkalinity in biochemical systems? Let's find out together.
1. The comparison of adjusting the pH of the nitrification system with sodium hydroxide and sodium carbonate
(1) The pH is adjusted with solid sodium hydroxide, and the local pH fluctuates greatly, which has a serious impact on the activity of microorganisms; the effect of 30% liquid alkali is relatively reduced.
(2) Use sodium carbonate to adjust the pH, the pH fluctuation is small, and a buffer pair can be formed at the same time to deal with the pH fluctuation.
(3) Nitration reaction requires nitrogen source, carbon source and other nutrients, and sodium carbonate can provide carbon source. Sodium hydroxide does not provide a carbon source.
(4) The advantage of sodium hydroxide to adjust pH is that the dosage is small and the relative cost is low.
(3) Definition and conversion of alkalinity
Alkalinity is the quantitative ability of an aqueous medium to react with hydroxide, which is quantitatively determined by titrating a certain volume of water samples to a certain pH with a strong acid standard solution. The measurement results are expressed in units of mg/L equivalent to the content of calcium carbonate. Its numerical value is related to the pH of the selected titration endpoint.
When the phenolphthalein indicator is used to titrate from red to colorless, the pH of the solution is 8.3, indicating that the hydroxide ions in the water have been neutralized, and the carbonates have been converted into bicarbonate. The titration result at this time is "phenolphthalein alkalinity" ".
Using methyl orange as an indicator, when the titration changes from yellow to orange-red, the endpoint pH is 4.4-4.5, indicating that the bicarbonate in the water has been neutralized, and the measured alkalinity is "methyl orange alkalinity" , also known as total alkalinity.
Conversion of alkalinity:
100mg/L calcium carbonate alkalinity = 106mg/L sodium carbonate alkalinity = 80mg/L sodium hydroxide alkalinity
The proportional coefficient of alkalinity and nitrification is 7.1, that is, 7.1 mg of alkalinity is consumed for every 1 mg of ammonia nitrogen oxidized to nitrate.
For example, if the water in the system is 1000m³, the ammonia nitrogen needs to be reduced from 110mg/L to 10mg/L.
The amount of ammonia nitrogen degraded in 1m³ wastewater is 100mg/L, and the alkalinity is 710mg/L.
Sodium hydroxide concentration conversion: 710*80/100=568mg/L.
1000m³ water needs to add 568mg/L*1000m³=568kg sodium hydroxide
