TM 5-813-8
=
CO 3 absent due to pH
pH 3.5
Bacterial count 50,000/100 milliliters (sulfide media, not a coliform test)
Silt density index 6.67 (Complete plugging in 2 minutes)
Turbidity 115 nephelometric turbidity unit (Total Suspended Solids 250 milligrams per liter)
Oil and grease 100 milligrams per liter
Use of these laboratory analyses with table 4-2 indicates that Rule 8 applies (see table A-2). Rule 8 states that
electrodialysis reversal should be investigated. The elevated bacterial count indicates the possible contamination of the
source with sewage effluent. This possible contamination should be investigated.
Assume that a bacteriological examination of a water sample indicated that the bacteria present are sulfur oxidizing
bacteria, responsible for the low pH of the sample. The bacterial count may not reflect the true level of bacteria in the
source, since aeration of the sample stimulates bacterial growth in the presence of the sulfide. Although no sewage
effluent contamination is detected, potential taste and odor problems with this water source are severe.
Use of table 4-3 results in three possible final process selections. Rule 7, Rule 8, and Rule 9 are all applicable for this
water source (see fig. A-4).
Rule 7 states that if water is below 1 nephelometric turbidity unit and has a silt density index above 4, specifications
for spiral-wound reverse osmosis processes should be prepared.
Rule 8 states that if water is clear and has a silt density index of less than 4, specifications for hollow fine-fiber
reverse osmosis processes should be prepared.
Rule 9 states that electrodialysis reversal specifications should be prepared. While no individual rule fits completely,
Rule 9 appears to be the most applicable. As this last example demonstrates, these tables are not intended to supplant
sound engineering judgment. They do not include all possible waters or conditions found in the continental United States.
Of the four water sources considered in this sample problem, the low salinity and turbidity of the 500-foot-deep well
would indicate that it would be the most economical water source for development. The other three sources should be
rejected. A drawing of a reverse osmosis system similar to that which would be used in treating such a well water is
shown in Figure A-7.
A-2. Sample source and process selection. A facility is planned for the California coast in an area not currently served
by an electric utility. Fresh surface water and groundwater do not exist or are unavailable in the area. The only water
source is sea water. The facility will have 3,000 permanent personnel. Natural gas is available. Use TM 5-813-1 to
determine daily water consumption. The calculation follows:
3,000 Persons x 150 gallons x 1.5 (Capacity)
day person
(Factor)
Daily water consumption = 675,000 gallons per day
The area is reasonably arid with a mean summer temperature greater than 59 degrees Fahrenheit and a mean winter
temperature greater than about 48 degrees Fahrenheit (see TM 5-813-1, figs. 2-5 and 2-7). Brine disposal at sea is
feasible. It is estimated that electricity would cost more than $.50/kilowatt hour if the facility could install a power
transmission line. A natural gas-powered internal combustion engine could produce power for approximately $.60/kilowatt
hour.
Summarize this data as shown below:
1-No fresh surface water or fresh ground water are available in the area.
2-The site is on the Pacific Ocean and sea water is available.
3-Solar energy is available.
4-Brine disposal at sea is feasible.
5-Power lines are remote. A natural gas supply is available for electricity generation by internal combustion
engine.
Use of table 4-1 with the above data indicates that Rule 4 will apply to a sea water source (see fig. A-8).
A-10
Previous Page
