(a) Phosphorus
removal.
(i) Equipment requirements.
(A) Flash mixing. Chemical addition points
shall be at points of high turbulence, such as Parshall flumes, hydraulic
jumps, or separate mixing basins.
(B) Flocculation. Inlet and outlet design
shall prevent short circuiting and turbulent destruction of floc. Minimum
detention time shall be 20 minutes at the average design flow rate.
The velocity of flocculated water to settling basins shall
be 0.5 to 1.5 fps (0.15 to 0.46 mps). Changes in direction shall be with long
radius elbows or curved channels.
(C) Chemical feed equipment. Storage shall be
provided for at least 14 days of chemical supply. Liquid chemical storage tanks
shall have a liquid level indicator, an overflow, and a receiving basin capable
of holding 110 percent of the stored volume, or a drain capable of receiving
accidental spills or overflows. Liquid chemical storage shall be provided with
heat.
(b)
Ammonia nitrogen reduction.
(i) Activated
sludge. Ammonia nitrogen removal by activated sludge processes shall be
designed with sludge retention time of at least 15 days and shall provide at
least 16 hours of hydraulic detention time. Aeration requirements are described
in Section 15.
(ii) Attached
growth. Rock media trickling filters shall not be used for ammonia reduction.
Fabricated media trickling filters used for ammonia shall be designed using a
BOD loading of less than 14 lb/1000 cu ft (224 kg/1,000
m3) of media. Rotating biological contactors used
for ammonia reduction shall be designed with hydraulic loadings less than 1.0
gpd/sq ft (40.7 L/m2/d) of media surface area. At
least four stages shall be provided for ammonia nitrogen removal.
(iii) Lagoons. The design of facultative
lagoons for ammonia removal shall provide a minimum detention of 180 days.
Aerated lagoon systems may be designed for 160 days.
(c) Solids reduction.
(i) Filtration.
(A) Filtration rate. The maximum hydraulic
loading for 24 inch (61 cm) or deeper media is 5 gpm/sq ft (292.5
m3/m2/d) of filter area.
Filtration rates for shallower media shall be limited to 3 gpm/sq ft (175
m3/m2d).
(B) Backwash requirements. Provide a minimum
backwash rate of 20 gpm per square foot (1170
m
3/m
2/d) of filter bed
for 24 inch (61 cm) or deeper media and 12 gpm/square foot (702
m
3/m
2/d) for shallower
media; supply shall be filtered water. A rate of flow regulator on the main
backwash line shall be provided. The total backwash water storage capacity
shall be adequate for twenty 20 minutes of continuous backwash.
Air scour or surface wash facilities are required. All
surface wash devices shall be provided with a minimum flow rate of 0.5 gpm per
sq ft (29.3 m3/m²d) water pressures of 50 psi
(3.52 kg/cm2) or greater and use filtered
water.
(C) Backwash waste
handling and treatment. Waste filter backwash shall be collected in a surge
tank and recycled to the treatment plant at a rate not to exceed ten percent of
the average plant design flow rate. Waste backwash water may be returned to any
point upstream of the biological treatment units.
(D) Number of units. At least two units shall
be provided. With one filter out of service, the remaining filters shall be
capable of passing the maximum day design flow rate.
(E) Controls. Controls should be provided to
remove a filter from service, backwash the filter, and return it to service.
Where the control is automatic, there shall also be a means of manually
overriding the operating equipment, including each valve essential to filter
operation.
In addition, the following shall be provided:
(I) Sampling tap on filter influent and
effluent.
(II) Indicating and
recording loss of head gauge.
(III)
Flow rate indicating and control.
(IV) Means for feeding polymer as a filter
aid at a controlled rate to filter influent water when chemically coagulated
effluent is being filtered.
(ii) Microscreens.
(A) Pilot testing. Pilot plant testing on the
fluid to be screened or data from other similar applications to demonstrate the
suitability of the proposed filter fabric, fabric life, proposed loading rates,
and other design criteria shall be provided.
(B) Loading rates. Flow equalization
facilities shall be included in the design to moderate influent quality and
flow variations.
The screening rate shall be selected to be compatible with
available pilot plant test results and selected screen aperture, but shall not
exceed 1.5 gpm/sq ft (87.8
m3/m2/d) for lagoon
effluent or 5 gpm/sq ft (292.5
m3/m2/d) for activated
sludge or attached growth effluents based on the maximum hydraulic flow rate
applied to the units. The screening rate shall not exceed 0.75 lb/sq ft/day
(3.7 kg/ m2/day). The effective screen area shall be
considered the submerged screen surface area less the area of screen blocked by
structural supports and fasteners.
(C) Backwash requirements. The backwash water
shall be at least eight gpm/ linear foot (99 Lpm/m) of screen length at 60 psi
(4.2 kg/cm2), obtained from microscreened
effluent.
(D) Controls. Each
microscreen unit shall be provided with automatic drum speed controls with
provisions for manual override.
(d) Rapid infiltration.
(i) Wastewater preapplication requirements.
Rapid infiltration shall be preceded by settling or fine screening having 0.6
inch (15.2 mm) or smaller openings.
(ii) Hydraulic loading rates.
(A) Permeability. Hydraulic capacity of the
rapid infiltration site shall be based upon soil permeability, basin
infiltration tests, or cylinder infiltrometer tests. Design loading rates based
on these tests shall be as follows:
Field Measurement |
Annual Loading Rate
|
Basin infiltration test |
10% of minimum
measure rate |
Cylinder infiltrometer |
2% of minimum
measured rate |
Permeability |
5% of conductivity of most
restricting soil layer |
(B)
Precipitation. The total hydraulic load to the rapid infiltration basins
includes precipitation. The one in ten year precipitation event should be used
as the basis for design.
(C) Cold
weather conditions. The design must recognize that drying rates, oxidation
rates, nitrification and denitrification rates all decrease in cold weather.
Cold weather loading rates shall be used to determined land requirements or
cold weather storage shall be used. Provisions should be made to mow and disc
basin surfaces in the fall to prevent ice from freezing the vegetation near the
soil surface. Snow fences can be used to keep snow cover on the rapid
infiltration basins to insulate the applied wastewater and soil.
(iii) Land requirements.
(A) Storage. A minimum of fourteen (14) days
of storage shall be provided. Where applied sewage will be less than 4° C,
160 days of effluent storage shall be provided.
(B) Location. Rapid infiltration basins shall
be located more than 500 feet (152 m) from existing habitation.
(iv) Basin size. Individual basin
size shall not be greater than five (5) acres (2.0 ha). Basin sizing should be
based upon a maximum water depth of twelve (12) inches (30.5 cm) in the rapid
infiltration basins.
(v) Subsurface
drainage. The capillary fringe above the groundwater mound shall not be closer
than two (2) feet (0.6 m) to the bottom of the infiltration basin. The distance
to groundwater shall be at least five (5) feet (1.5 m) below the soil surface
within two (2) days following wastewater application.
(vi) Groundwater monitoring. Refer to Chapter
3, Section 15, of the regulations.
(e) Intermittent sand filters.
(i) Wastewater preapplications treatment
requirements. Intermittent sand filters shall be preceded by settling or fine
screens having 0.06 inch (1.5 mm) or smaller openings.
(ii) Hydraulic loading rates. The maximum
application rates shall be limited to:
|
Maximum Application Rate |
Source |
gallons/acre/day |
(m3/ha/d) |
Primary Effluent |
130,000 |
(1216)
|
Secondary Effluent |
400,000 |
(3742) |
Lagoon Effluent |
300,000 |
(2806)
|
(iii) Media. The minimum sand depth shall be
twenty-four (24) inches (0.6 m). The sand must be free of cementing materials
and clay or loam. The sand should have an effective size of not less than 0.2
mm and not greater than 0.5 mm, and a uniformity coefficient of less than 5.
Clean graded gravel shall be placed around the under drains
and to a depth of at least twelve (12) inches (0.3 m) over the top of the
underdrains.
(iv)
Underdrains. All intermittent sand filters shall be provided with underdrains.
Underdrains shall be at least four (4) inches (10.2 cm) in diameter. The
under-drain pipe shall have a minimum slope of 5 feet per 1,000 feet (5 m/1,000
m).
The groundwater shall be at least two (2) feet (0.6 m)
below the bottom of the underdrain pipe.
(v) Number of units. Three (3) or more
filters shall be provided.
(vi)
Dosing.
(A) In each dosage of an intermittent
filter, the hydraulic capacity shall permit covering the bed to a depth of two
(2) inches (5 cm), within twenty (20) minutes or less.