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HJ 828-2017: Water quality -- Determination of the chemical oxygen demand -- Dichromate method
HJ 828-2017
NATIONAL ENVIRONMENTAL PROTECTION STANDARD
OF THE PEOPLE’S REPUBLIC OF CHINA
Replacing GB 11914-89
Water quality - Determination of the chemical oxygen
demand - Dichromate method
ISSUED ON: MARCH 30, 2017
IMPLEMENTED ON: MAY 01, 2017
Issued by: Ministry of Environmental Protection
Table of Contents
Foreword ... 3 
1 Scope ... 5 
2 Normative references ... 5 
3 Terms and definitions ... 5 
4 Principle of the method ... 6 
5 Interference and elimination ... 6 
6 Reagents and materials ... 6 
7 Instruments and apparatuses ... 9 
8 Sample ... 9 
9 Analysis steps ... 9 
10 Result calculation and expression ... 11 
11 Precision and accuracy ... 11 
12 Quality assurance and quality control ... 12 
13 Waste disposal ... 12 
14 Matters needing attention ... 13 
Appendix A (Informative) Rough determination method of chloride ion content
... 14 
Water quality - Determination of the chemical oxygen
demand - Dichromate method
WARNING: The reagent, mercuric sulfate, that is used in this method is
highly toxic, and laboratory personnel shall avoid direct contact with it.
Sample preparation shall be performed in a fume hood.
1 Scope
This Standard specifies the dichromate method for determining chemical
oxygen demand in water.
This Standard applies to the determination of chemical oxygen demand in
surface water, domestic sewage and industrial wastewater. This Standard does
not apply to the determination of chemical oxygen demand in water, of which
the chloride concentration is greater than 1000 mg/L (after dilution).
When the sampling volume is 10.0 ml, the detection-limit of this method is 4
mg/L, and the lower limit of determination is 16 mg/L. The upper limit of
determination of undiluted water samples is 700 mg/L; when the limit is
exceeded, the determination shall be made after dilution.
2 Normative references
This Standard refers to the terms of the following documents. For undated
references, the valid edition applies to this Standard.
GB 11896, Water quality - Determination of chloride - Silver nitrate titration
method
GB 17378.4, The specification for marine monitoring - Part 4: Seawater
analysis
HJ 506, Water quality - Determination of dissolved oxygen - Electrochemical
probe method
HJ/T 91, Technical specifications requirements for monitoring of surface
water and waste water
3 Terms and definitions
The following terms and definitions are applicable to this Standard.
6.1 Sulfuric acid (H2SO4), ρ = 1.84 g/ml, guaranteed reagent.
6.2 Potassium dichromate (K2Cr2O7): primary reagent; take an appropriate
amount of potassium dichromate and dry in a 105°C oven to constant weight.
6.3 Silver sulfate (Ag2SO4).
6.4 Mercury sulfate (HgSO4).
6.5 Ammonium ferrous sulfate ([(NH4)2Fe(SO4)2·6H2O]).
6.6 Potassium hydrogen phthalate (KC8H5O4).
6.7 Ferrous sulfate heptahydrate (FeSO4·7H2O).
6.8 Sulfuric acid solution: 1+9 (V/V).
6.9 Potassium dichromate standard solution
6.9.1 Potassium dichromate standard solution c ( K2CR2O7) = 0.250 mol/L.
Accurately weigh 12.258 g of potassium dichromate (6.2); dissolve it in water;
fix-volume to 1000 ml.
6.9.2 Potassium dichromate standard solution c ( K2CR2O7) = 0.0250 mol/L.
Dilute the potassium dichromate standard solution (6.9.1) 10 times.
6.10 Silver sulfate-sulfuric acid solution.
Weigh 10 g of silver sulfate (6.3); add it to 1 L of sulfuric acid (6.1); leave it for
1 ~ 2 day(s) to dissolve it; shake it well; shake carefully before use.
6.11 Mercury sulfate solution, ρ = 100 g/L.
Weigh 10 g of mercury sulfate (6.4); dissolve in 100 ml of sulfuric acid solution
(6.8); mix it well.
6.12 Ammonium ferrous sulfate standard solution
6.12.1 Ammonium ferrous sulfate standard solution, c[(NH4)2Fe(SO4)2·6H2O] ≈
0.05 mol/L.
Weigh 19.5 g of ammonium ferrous sulfate (6.5) to dissolve in water; add 10 ml
of sulfuric acid (6.1); dilute to 1000 ml after the solution is cooled.
7 Instruments and apparatuses
7.1 Reflux device: All-glass reflux device for 250 ml conical flask with grinding
mouth. Water-cooled or air-cooled all-glass reflux device can be selected. Other
equivalent condensation reflux devices are also applicable.
7.2 Heating device: electric furnace or other equivalent digestion device.
7.3 Analytical balance: sensitivity of 0.0001 g.
7.4 Acid burette: 25 ml or 50 ml.
7.5 Instruments and apparatuses that are commonly used in general
laboratories.
8 Sample
Collect and store water samples in accordance with the relevant regulations of
HJ/T 91. The volume of the collected water sample shall not be less than 100
ml.
The collected water samples shall be placed in glass bottles and analyzed as
soon as possible. If it cannot be analyzed immediately, sulfuric acid (6.1) shall
be added until pH < 2; store it at 4°C for less than 5 days.
9 Analysis steps
9.1 Samples of CODCr concentration ≤ 50 mg/L
9.1.1 Sample determination
Take 10.0 ml of water sample into the conical flask; add 5.00 ml of mercury
sulfate solution (6.11), potassium dichromate standard solution (6.9.2) and
several explosive boiling-proof glass beads (6.15) in order; shake well. Add
mercury sulfate solution (6.11) at a mass ratio of m[HgSO4]:m[Cl-] ≥20: 1; the
maximum addition is 2 ml.
Connect the conical flask to the lower end of the condenser of the reflux device
(7.1); slowly add 15 ml of silver sulfate-sulfuric acid solution (6.10) from the
upper end of the condenser to prevent the escape of low-boiling organics; rotate
the conical flask to mix evenly. Since the solution begins to boil, maintain a
slight boiling reflux for 2 h. In the case of a water-cooled device, condensate
shall be introduced before adding the silver sulfate-sulfuric acid solution (6.10).
mg/L, 7 mg/L, 9 mg/L, and 19 mg/L, respectively; the reproducibility limits R are
6 mg/L, 8 mg/L, 13 mg/L, and 47 mg/L, respectively.
Seven laboratories measure actual water samples, of which the chemical
oxygen demand concentration is 16 mg/L~3.65×104 mg/L, in a variety of
industries, including surface water, domestic sewage, sewage treatment plant
wastewater, pharmaceutical wastewater, textile wastewater, printing and dyeing
wastewater, papermaking wastewater, pesticide-containing wastewater and
smelting wastewater. The obtained results: the relative standard deviation of
the samples whose chemical oxygen demand concentration is 16 mg/L ~ 95
mg/L is 1.3%~11%; the relative standard deviation of the samples whose
chemical oxygen demand concentration is 108 mg/L ~ 250 mg/L is 0.4%~6.2%;
the relative standard deviation of the samples whose chemical oxygen demand
concentration is 340 mg/L~3.65×104 mg/L is 0.3%~5.1%.
11.2 Accuracy
Seven laboratories measure the certified standard samples, of which the
chemical oxygen demand concentrations are 28.9±2 mg/L, 74.2±4.9 mg/L, and
208±10 mg/L; the relative errors are -2.8%~1.6%, -5.8%~3.5% and -
0.9%~2.4%, respectively. The final relative errors are 0.43%±4.2%,
0.14%±5.8%, and 1.2%±2.2%.
12 Quality assurance and quality control
12.1 Blank test
For each batch of samples, at least perform two blank tests.
12.2 Precision control
Each batch of samples shall have 10% of parallel samples. If the number of
samples is less than 10, make at least one parallel sample. The relative
deviation of parallel samples does not exceed ±10%.
12.3 Accuracy control
During the determination of each batch of s...