Rapid and simple detection of ammonia nitrogen in coking plant wastewater (Financial incentive)

The dissolved ammonia is volatilized using the alkali expulsion method, and it can then be detected with an ammonia-sensitive electrode. HACH has an online version.

Could you explain the detailed testing methods?

Ammonia nitrogen (titrimetric method) (This method is equivalent to GB7478-87, etc.) 1. Pre-distillation of the water sample: 1) Take 50 ml of boric acid absorbent solution (concentration 2%) into a 500 ml conical flask； 2) Place the tip of the glass tube at the condensate outlet of the distillation apparatus at a certain depth below the surface of the boric acid absorption solution in the conical flask ； 3) Based on the estimated concentration of the water sample, take the corresponding volume of water sample from the table below, dilute it to 250 ml with ammonia-free water, and place it in a Kjeldahl flask ； Table of the relationship between ammonia nitrogen concentration and sampling volume. Limit concentrations of water samples (mg/L): 10, 25, 50, 125, 250, 500, 1250, 2500, 5000. Sampling volume (mL): 250, 100, 50, 20, 10, 5, 2, 1, 0.5. 4) Add bromothymol blue indicator (0.05%, pH 6.0–7.6) ； 5) Adjust the pH to around 7 using a sodium hydroxide solution (1 mol/L) or a hydrochloric acid solution (1 mol/L) (measure with a pH test strip) ； 6) Add 0.25 g of light magnesium oxide (the carbonates are removed by heating at 500°C) ； 7) Glass beads for adding ； 8) Immediately connect the Kjeldahl flask to the nitrogen ball and condenser ； 9) Pass cooling water ； 10) Heat and distill until nearly 200 ml of distillate is obtained (the liquid level in the conical flask approaches the 250 ml mark) ； 11) Remove the receiving bottle, adjust the volume to 250 ml with ammonia-free distilled water, and wait for titration ； 12) Stop heating and turn off the cooling water ； 13) For the blank, ammonia-free water is used in place of the water sample, and distillation is carried out using the same method as described above. 2 Distillate titration 1) Add 2 drops of mixed indicator to the distillate ； 2) Titrate with sulfuric acid solution (1/2H2SO4≈0.020 mol/L, to be calibrated) until the green color changes to light purple ； 3) Record the amount of sulfuric acid used ； 4) Titrate the blank using the same method. 3 Result Calculation: The titration results are substituted into the following formula to calculate the ammonia nitrogen concentration in the water sample: Ammonia nitrogen (N) = (A – B) × C × 14 × 1000 / V (mg/L), where A is the volume of sulfuric acid consumed during the titration of the water sample (mL) ； B—Volume of sulfuric acid consumed in the blank titration (mL) ； C—Concentration of sulfuric acid solution (mol/L); V—Volume of water sample taken (mL). 4 Precautions 1) Boiling over should be avoided during distillation, as this can lead to an increase in the temperature of the distillate and incomplete absorption of ammonia; it is advisable to control the heating intensity and continue distilling for about 30 minutes after boiling begins ； 2) The ammonia nitrogen concentration in water samples: generally, the maximum allowable concentration of residual ammonia is 6000 mg/l ； The maximum allowable concentration of ammonia vaporized wastewater is 2500 mg/l without the addition of alkali, and 40–800 mg/l with alkali added; it should normally be between 60–200 mg/l ； The limit concentrations for the oil removal tank, equalization tank, and emergency regulation tank are: 300 mg/l under normal conditions, and up to 800 mg/l in abnormal conditions ； At the beginning of operation, the limit concentration in the anoxic tank and aerobic tank is 80 mg/l; during the middle and later stages of operation as well as after normal operation, the limit concentration in the aerobic tank, secondary sedimentation tank, post-biological treatment tank, and flocculation sedimentation tank is 5 mg/l. 3) Mixed indicator: Mix methyl red solution (200 g of methyl red per 100 ml of 95% anhydrous ethanol) with methylene blue solution (100 g of methylene blue per 100 ml of 95% anhydrous ethanol) in a 2:1 ratio; it can be used for 1 month ； 4) Preparation of ammonia-free water by distillation: Add 0.1 ml of sulfuric acid per liter of distilled water, and redistill in a completely glass-made distiller. Discard the first 50 ml of distillate, and collect the remaining distillate in a glass bottle with a stopper and ground neck, storing it tightly sealed ； 5) Water sample storage: Water samples should be collected in polyethylene or glass bottles and analyzed as soon as possible; if necessary, sulfuric acid can be added to acidify the sample to pH