“BLEACH “ IN WATER TREAMTENT 325 
Others have claimed that it was impossible to make tea with such 
water. 
Advantages and Disadvantages of ‘‘ Bleach” in Water Treatment. 
These have been given as follows by Johnson (1910, i913): 
ADVANTAGES 
. Destruction of bacteria, especially intestinal forms. 
. Reliability of chemical and ease of application. 
. Absence of poisonous chemical compounds formed. 
. Cheap cost of chemical. 
. Rapid speed of reaction—no storage basins required. 
. Saves coagulating chemicals. 
. Allows much higher rate of filtration. 
. Reduces clogging of filters and lengthens the runs. 
COnIr Om oR WN eS 
DISADVANTAGES 
. Does not destroy all spore forms. 
. Does not get bacteria inside of suspended matter. 
. Does not remove turbidity. 
. Does not take color out or remove vegetable stain. 
. Inability to remove organic matter. 
. Leaves swampy tastes and odors. 
. Does not soften the water. Increases the hardness slightly. 
Bleach usually contains a little CaO which takes out some CO2. 
8. Care must be used to allow for reducible compounds such as 
nitrites or oxidizable iron. 
The quantity of “ hypo” to add to a water places the sanitarian 
between two fires—tastes in the filtered or final product and destruc- 
tion of the pathogenic bacteria. The absolute amount varies greatly. 
The bacteriological analysis together with turbidity determinations 
are probably the best indicators to tell whether the amount is sufficient. 
This must be determined for each separate water supply. Under 
ordinary conditions when added to the filtered water from 7-12 lbs. per 
million gallons is sufficient for disinfection. This will give from .28 
to .48 p.p.m. of available chlorine (based on 30 per cent bleach). Many 
factors influence the amount of bleach required by a water but tur- 
bidity is one of the most important especially when this is largely 
organic matter. The amount of bleach added to a water supply must, 
therefore, vary with the turbidity. Where storage basins are used, less 
“IO ot © be 
