Chinese Quality Standard for Surface Water Sources A part of typical water quality standard limited value(Unit:mg/L) Pollutants Class I ClassⅡ ClassⅢ Class IV Class V Dissolved oxygen ≥ 7.5 6 5 3 2 Permanganate index≤ 2 4 6 10 15 COD ≤ 15 15 20 30 40 BODs ≤ 3 3 4 6 10 NH3-N ≤ 0.015 0.5 1.0 1.5 2.0 Total P ≤ 0.02 0.1 0.2 0.3 0.4 Total N ≤ 0.2 0.5 1.0 1.5 2.0 Arsenic ≤ 0.05 0.05 0.05 0.1 0.1 Hg ≤ 0.00005 0.00005 0.000 0.001 0.001 Cd ≤ a001 0.005 005 0.005 0.01 9 Chinese Quality Standard for Surface Water Sources A part of typical water quality standard limited value (Unit：mg/L) Pollutants ClassⅠ ClassⅡ Class Ⅲ Class Ⅳ Class Ⅴ Dissolved oxygen ≥ 7.5 6 5 3 2 Permanganate index ≤ 2 4 6 10 15 COD ≤ 15 15 20 30 40 BOD5 ≤ 3 3 4 6 10 NH3-N ≤ 0.015 0.5 1.0 1.5 2.0 Total P ≤ 0.02 0.1 0.2 0.3 0.4 Total N ≤ 0.2 0.5 1.0 1.5 2.0 Arsenic ≤ 0.05 0.05 0.05 0.1 0.1 Hg ≤ 0.00005 0.00005 0.0001 0.001 0.001 Cd ≤ 0.001 0.005 0.005 0.005 0.01 9