CIVIL ENGINEERING FORMULAS

380 CHAPTER THIRTEEN

The average daily consumption of chlorine is

Cl 2 lb/d(average dosage, mg/L) (Mgd)(8.34) (13.77)

A typical chlorination flow diagram is shown in Fig. 13.8. This is a com-
pound loop system, which means the chlorine dosage is controlled through sig-
nals received from both effluent flow rate and chlorine residual.

SANITARY SEWER SYSTEM DESIGN

Compute the sanitary sewer system flow rate, SSfr, gal/day:

SSfr(city or town area, ac) (residential population/ac)

(gal/day of sewage per person) (13.78)

The residential population per acre (ac) can be determined from census data
or from data in engineering handbooks.
Convert SSfrfrom gal/day to cubic feet per second, cfs with

cfs1.55 (gpd/10^6 ) (13.79)

Size the main sewer, into which lateral sewers discharge, on the basis of
flowing full. This is the usual design procedure followed by experienced sani-
tary engineers.

Flow meter

Injector

Chlorine gas

Control signal

Chlorinator

Compressed

Control gas storage

signal

Chlorine residual

analyzer

Receiving water or reuse

Chlorine solution

Chlorine

contact

channel

Rotometer

Water

effluent

FIGURE 13.8 Compound-loop chlorination system flow diagram. (Hicks—Handbook of
Civil Engineering Calculation, McGraw-Hill.)