Hydrology Tutorials

The quality will be determined by the planned use. Physical, chemical, and bacteriological testing of source waters is required to determine the level of treatment to supply the necessary water quality.

When the quantity withdrawn exceeds the recharge rate, quality inherently decreases; therefore, this must be considered during design.

a. Physical characteristics. The physical characteristics of the raw water source that must be evaluated are total suspended solids (TSS) and temperature. Turbidity and silt density index (SDI).

(1) Total suspended solids. The total suspended solids level of raw water sources must be evaluated to determine the level of pretreatment processes required. Raw water having low total suspended solids levels generally requires less pretreatment. The source with the lowest total suspended solids is preferred.

(2) Temperature. The temperature of the raw water source must be matched to the specific desalination process. In extreme cases, the water temperature may control the desalination process selection. A climatological survey must be made prior to finalization of process selection to determine the seasonal maximum and minimum water temperatures of the proposed water sources.

(3) Turbidity and silt density index. These two characteristics provide two different measures of the amount of fine particulate matter in the water.

Turbidity is measured in nephelometric turbidity units (a measure of the amount of light scattered by a known water sample thickness). Silt density index is a measure of the amount of 0.45-micron filter plugging caused by passing a sample of water through the filter for 15 minutes.

Turbidity must be determined for all desalination processes. Also, the silt density index must be determined for water being considered for reverse osmosis treatment.

b. Chemical constituents. The chemical constituents of the raw water must be determined to provide information for treatment selection.

c. Bacteriological quality. The bacteriological testing of the raw water must include a type of a coliform indicator organism count.

Procedures for filter membrane, most probable number fermentation tube, and standard plate count, coliform organism bacteriological testing techniques can be found in Standard Methods for the Examination of Water and Wastewater and TB Med 576.

Manufacturers' recommendations as to the media and procedures used to identify microbiological activity detrimental to the operation of a particular desalination system shall be followed.

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