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u li INTERPRETATION OF RESULTS The numerical value attained in this test indicates the relative acidity or alkalinity of the liquor sample. A pH of 7.0 is neutral, but a pH in the range of 6.6 to 7.4 is normal. If the pH test indicates a value outside the normal range, immediately repeat test with another liquor sample and fresh test paper strip. If abnormality is confirmed, check all inputs to the system to find and eliminate dumping of strong acids or alkali. Extreme variations in pH will hinder the biological process which occurs in the sewage treatment system. The most fj common acids are muriatic (hydrochloric) or sulfuric. The most common alkali is sodium hydroxide. 15. CHLORINE CONTACT CHAMBER, TANK CONDITION: Look through hatch opening at surface of walls when chlorine contact chamber is empty. Visually observe ap- pearance of wails and record cleanliness according to the following code: r CLN: Clean DTY: Dirty 16. RELATIVE STABILITY, INFLUENT: From aeration chamber, take a sample of raw sewage from inlet line. Pour sample into a 60-m1 BOD bottle and test as follows: a. Fill the 60-ml BOD to overflowing, a! oiding aeration. b. Fill reagent dropper to upper mark (0.6 ml) of methylene blue solution from drop- per (stop at 0.2-m1 mark). Carefully withdraw dropper from liquor. Discard remainder of methylene blue solution before replacing in reagent bottle. c. Carefully insert ground-glass stopper in BOD bottle and invert several times to MIX. d. Add water to water-seai.cup formed around ground-glass stopper. e, Store BOD bottle in a suitable incubator at 20°C and observe sample daily until bluish color disappears. Determine relative stability from the table below, which is taken from APHA, 11th Edition: l 7 Time (days) 0.5 1.0 . 1.5 2:0 2.5 3.0 4.0 5.0 6.0 7.0 Rel Stab (%) 11 21 30 37 44 50 60 68 75 80 Time (days) 8.0 9.0 10 1.1 12 13 14 16 18 10 Rel Stab (%) 84 87 90 9�� 94 95 96 97 98 99 NOTE: The water seal on top of the glass stopper must be continually maintained during incubation, For incubation, a HACH Model 2150 incubator with refrigerator is satisfactory. If no incubator is available., the BOD bottle may be stored near constant temperature by placing it in a container of water which is kept in a room maintained F at approximately 70 7. In this case, the bottle should be immersed in water and shielded from light at all times. i f. Record numerical value .of relative stability from table above. E 17. RELATIVE STABILITY, EFFLUENT: From clarifier, take a sample of the clear super- natant, avoiding any floating solids. Pour this liquor sample into a 60-m1 BOD bottle and test as outlined in step 16 above. 11 18. OBSERVER: Record initials of person who collected data. F 7 'ts Y i t