TM 5-814-9
(d)
Asphalt. Asphalt also can be used as a
involved in removing suspended solids by filtration
basin liner. However, it should he
are complex. Some straining occurs at the filter
noted that petroleum-based products,
surface; however, most solids removal in granular
solvents, lubricants, and other fluids
filters of the type used at CVWFs occurs within the
used in vehicle operations and
pore space of the filter media particles and by
cleaning can degrade an asphalt liner.
absorption of impurities onto the filter media sur-
These products destroy the binder
faces. Additional straining between media particles
material in the asphalt and cause the
in the filter also contributes to overall solids
liner to fail. The designer should he
removal. Although the primary purpose of the filters
aware of this potential problem before
is to remove suspended solids and provide a
using asphalt as a liner.
polishing step prior to recycling, they also are
Sediment removal. The equalization basin de-
(6)
and algal populations through a combination of
sign should include means for dewatering and
physical and biological processes without the ad-
gaining access to the basin. Basins should be
dition of chemicals. The effluent quality from
designed for infrequent sediment removal in
filtration is such that any discharge or reuse is
the range of from 10 to 20 years based on
environmentally safe and will cause no increased
estimated solids carryover from the sediment
pump wear. Adequate product water is achieved
basin. Sediment storage should he from 1 to 2
with minimal O&M costs and personnel. This type
feet (0.3 to 0.6 meters). In selecting the liner,
sand filter does not require backwashing.
designers should consider the method and
Configuration The surface of an intermittent
equipment the facility will use to remove sedi-
(1)
ment. The liner used should sustain the least
sand filter may he divided into two, three, or
damage to its bottom and side walls during
four cells. The cells may share a common
cleanout. A ramp with a slope of 1 to 6 (17
underdrain collection system, but will have
percent) may have to be constructed to allow
separate distribution systems. Each cell
cleaning equipment access to the basin.
should be physically separated by surface
partitions to prevent wastewater from spilling
b.
Dosing tank (optional). A dosing tank or device is
over from one cell to another. At the
a storage structure or component located after the
designers option, the partitions may also
equalization basin and before the filters. The pur-
completely separate the 36-inch (0.9 meter)
pose of the dosing tank is to discharge settled water
sand layer between cells; a minimum of 12-
to the intermittent sand filters at the desired dosing
inch (0.3 meter) penetration is recommended.
rate and frequency. The first choice for delivering
Siting. Intermittent sand filters can require
Influent to the filter surface is by gravity flow;
(2)
however, if this design is not possible, automatic
large areas. Therefore, the most desirable
operation is an important alternative. Automated
topographic and location criteria would in-
delivery is done using flow-activated valves, dosing
clude a level site that is free of trees, woody
siphons, timer-controlled valves, or pumps. It is
vegetation, and rock; a deep groundwater
suggested that a dosing siphon or electronically
table; good natural drainage away from the
triggered valve he provided in the dosing basin in
filters; and proximity to the main pump
conjunction with the distribution piping. The most
station and water supply basin. Open filters
economical dosing siphon in sewage systems is the
should he located away from or protected
type with proper bypass pipes and valves; however,
against windblown dust from unpaved tank
electronic float-actuated valves with manual over-
trails. Site conditions may require windbreaks
ride mechanisms are also effective. Both
such as fences, trees, or shrubs to prevent
approaches require a minimum elevation
wind erosion of the filter media and/or
differential between equalization basin water level
prevent dust from settling on the filter surface.
and filter surface. Water flows by gravity from the
It is desirable that the site be high enough
equalization basin to the filter pump wet well and
above the maximum water elevation in the
then is pumped to the filters via a filter valve
water supply basin to allow for gravity flow
control box or valve house.
into the water supply basin.
c.
Intermittent sand filters. Intermittent sand filters
Sizing. The size of these filters and their
(3)
provide an economical, effective method of treating
pumping system is determined by three fac-
water prior to reuse at the wash facility. Filters
tors: daily dosing rate, dosing frequency, and
provide a final polishing step by further reducing
dosing rate.
residual BOD5 and suspended solids that maybe in
(a)
Daily dosing rate. This rate is the
the water. This step renders the water suitable to be
maximum wastewater volume per day
pumped and reused for washing. The mechanisms
6-16
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