AdvantagesThe same efficiency of grit removal is
possible over a wide flow range.
Head loss through the grit chamber is
minimal,
By controlling the rate of aeration, a grit
of relatively low putrescible organic
content can be removed,
Preaeration may alleviate septic conditions
in the incoming wastewater to improve
performance of downstream treatment
units.
Aerated grit chambers can also be used
for chemical addition, mixing,
preaeration, and flocculation ahead of
primary treatment.
Disadvantages
Power consumption is higher than other
grit removal processes.
Additional labor is required for
maintenance and control of the aeration
system.
Significant quantities of potentially
harmful volatile organics and odors may
be released from wastewaters containing
these constituents.
Foaming problems may be created if
influent wastewater has surfactants
present.3) = (2.5)(4xl 0 6gal/day)(3min) = ^ 5 ft3 (?g 8 m3)
(7.48 gal/ft^3 )(24 h/d)(60min/h)- Determine the dimensions of the grit chamber
Width-depth ratio for aerated grit chambers range from 1:1 to 5:1. Depths range from 7 to
16 feet (2.1 to 4.87 m). Using a width-depth ratio of 1.2:1 and a depth of 8 feet (2.43 m),
the dimensions of the aerated grit chamber are:
Width = (1.2)(8 ft) = 9.6 ft (2.92 m)Length = (volume)/[(width)(depth)] = Q™9^ft) = 36.3 ft (11.1 m)Length-width ratios range from 3:1 to 5:1. As a check, length to width ratio for the aerat-
ed grit chamber sized above is: 36.3 ft/9.6 ft = 3.78:1 which is acceptable.
- Determine the air supply required
The air supply requirement for an aerated grit chamber ranges from 2.0 to 5.0 ft
3
/mm/'ft of
chamber length (0.185 to 0.46 m
3
/min-m). Using 5.0 fWmin/ft (0.46 mVmin-m) for de-
sign, the amount of air required is:
Air required (ftVmin) = (5.0 ft
3
/min/ft)(36.3 ft) = 182 fWmin (5.2 m
3
/min)- Estimate the quantity of grit expected
Grit quantities must be estimated to allow sizing of grit handling equipment such as grit
conveyors and grit dewatering equipment. Grit quantities from an aerated grit chamber
vary from 0.5 to 27 fWMgal (3.74 to 201.9 m
3
/L) of flow. Assume a value of 20 fWMgal
(149.5 m
3
/L). Therefore, the average quantity of grit expected is:
Volume of grit (ft
3
/d) = (20 ft
3
/Mgal)(4.0 Mgd) = 80 ft
3
/d (2.26 m
3
/d)Some advantages and disadvantages of the aerated grit chamber are listed below: