- Select the disinfection method to use
Chlorination by the addition of chlorine to the water is the principal method of disinfec-
tion used today. To reduce the unpleasant effects that may result from using chlorine
alone, a mixture of chlorine and ammonia, known as chloramine, may be used. The am-
monia dosage is generally 0.25 ppm or less. Assume that the chloramine method is cho-
sen for this installation. - Select the method of taste and odor control
The methods used for taste and odor control are: (a) aeration, (b) activated carbon, (c)
prechlorination, and (d) chloramine. Aeration is popular for groundwaters containing hy-
drogen sulfide and odors caused by microscopic organisms.
Activated carbon absorbs impurities that cause tastes, odors, or color, generally, 10 to
20 Ib (4.5 to 9.1 kg) of activated carbon per million gallons of water is used, but larger
quantities—from 50 to 60 Ib (22.7 to 27.2 kg)—may be specified. In recent years, some
2000 municipal water systems have installed activated carbon devices for taste and odor
control.
Prechlorination and chloramine are also used in some installations for taste and odor
control. Of the two methods, chloramine appears more popular at present.
Based on the data given for this water-supply system, method b, c, or d would proba-
bly be suitable. Because method b has proven highly effective, it will be chosen tentative-
ly, pending later investigation of the economic factors.
Related Calculations. Use this general procedure to choose the treatment
method for all types of water-supply systems where the water will be used for human con-
sumption. Thus, the procedure is suitable for municipal, commercial, and industrial sys-
tems.
Hazardous wastes of many types endanger groundwater supplies. One of the most
common hazardous wastes is gasoline which comes from the estimated 120,000 leaking
underground gasoline-storage tanks. Major oil companies are replacing leaking tanks
with new noncorrosive tanks. But the soil and groundwater must still be cleaned to pre-
vent pollution of drinking-water supplies.
Other contaminants include oily sludges, organic (such as pesticides and dioxins), and
nonvolatile organic materials. These present especially challenging removal and disposal
problems for engineers, particularly in view of the stringent environmental requirements
of almost every community.
A variety of treatment and disposal methods are in the process of development and
application. For oily waste handling, one process combines water evaporation and sol-
vent extraction to break down a wide variety of hazardous waste and sludge from
industrial, petroleum-refinery, and municipal-sewage-treatment operations. This process
typically produces dry solids with less than 0.5 percent residual hydrocarbon content.
This meets EPA regulations for nonhazardous wastes with low heavy-metal contents.
Certain organics, such as pesticides and dioxins, are hydrophobic. Liquified propane
and butane are effective at separating hydrophobic organics from solid particles in tainted
sludges and soils. The second treatment method uses liquified propane to remove organ-
ics from contaminated soil. Removal efficiencies reported are: poly chlorinated biphenyls
(PCBs) 99.9 percent; polyaromatic hydrocarbons (PAHs) 99.5 percent; dioxins 97.4 per-
cent; total petroleum hydrocarbons 99.9 percent. Such treated solids meet EPA land-ban
regulations for solids disposal.
Nonvolatile organic materials at small sites can be removed by a mobile treatment sys-
tem using up to 14 solvents. Both hydrophobic and hydrophilic solvents are used; all are
nontoxic; several have Food and Drug Administration (FDA) approval as food additives.
Used at three different sites (at this writing) the process reduced PCB concentration from
500 to 1500 ppm to less than 100 ppm; at another site PCB concentration was reduced
singke
(singke)
#1