Page 447 - Civil Engineering Formulas

STORMWATER, WASTEWATER, AND ENVIRONMENTAL PROTECTION 373

where R recirculation ratio Q /Q
r
Q recirculation flow
r
Q wastewater flow
The BOD loading for the first stage filter is calculated using
5
W (influent BOD , mg/L)(wastewater flow, Mgd)
5
\ (8.34 lb/Mgal/mg/L) (13.49)
The BOD loading for the second stage trickling filter is
5
W (1 E 1 )W (13.50)
loading to the second stage filter.
where W BOD 5
The NRC equation for a second stage trickling filter is
100
E 2 (13.51)
0.0561 W
1
1 E 1 BVF
The hydraulic loading to each filter is

(1 R)(Q)
Hydraulic loading (13.52)
(area)(1440 min/d)

DESIGN OF A RAPID-MIX BASIN
AND FLOCCULATION BASIN

The hydraulic retention time of typical rapid mix operations in wastewater
treatment range from 5 to 20 seconds. The required volume of the rapid-mix
basin, Fig. 13.6, is

Volume (V) (hydraulic retention time)(wastewater flow)

Polymer
addition

From To
secondary disinfection
treatment Rapid mix Flocculation Filtration
(coagulation)
FIGURE 13.6 Process flow for direct filtration. (Hicks—Handbook of Civil Engineering
Calculations, McGraw-Hill.)