1. Testing procedures As shown in Table 7,  take adequate amount of the filtrate and put it in 100 mL volumetric flask,  add 1.0 mL sulphuric acid solution (1 + 35) and 5.0m L potassium persulfate solution (40g/L),  use water to adjust the solution volume in the volumetric flask to about 25 mL, and put it on the adjustable electric furnace for slowly boiling for 15min until the solution is almost dried. Take out the flask and cool it by flowing water to room temperature water, and quantitatively transfer the solution to 50 ml volumetric flask.Add 2.0 mL ammonium molybdate solution (26 g/L), 3.0 mL ascorbic acid solution (20 g/L), dilute it with water to the scale, shake it well, place it  at room temperature for 10 min.At 710nm of spectrophotometer, use  10 mm cuvette to test the  absorbancy by means of the blank zero adjustment  without the test solution.
2. Calculation:
In the samples expressed in mg/L, total phosphorus (PO43 -) content is calculated according to the formula:
                       m1
        x1=                       mg/L
                       V1
where:
m1 - PO43  content expressed in ug obtained from the working curve,
V1- volume of the testing solution shifted, mL
c: Permissible difference:
Permissible difference the same with the inorganic phosphate
3. Measurement of total organic phosphorus: Total organic phosphorus = total phosphorus, total inorganic phosphorus  mg/L.（zjl）