FILTRATION –
REVIEW CHECKLIST
Water Quality
Wastewater
Technical Water/Wastewater/#5.25, May 2001
Review and
Guidance
FACILITY NAME DATE
CONSULTING ENGINEER SITE INSPECTION (DATE & INSPECTOR)
PLANNING OR DESIGN PHASE
Influent
a) Flow rate (gpm)
average wet weather
peak hourly
b) Flow equalization will moderate filter
Influent quality and quantity
Filter Type
a) Pressure or gravity, up flow or down
flow. Gravity type preferred where
abnormal quantities of grease or similar
solids are expected.
b) Media (single, dual, and material)
c) Dimensions
d) Number and Surface Area (ft2) for each
unit (minimum 2 units)
wq-wwtp5-25
Minnesota Pollution Control Agency, 520 Lafayette Road North, St. Paul, Minnesota 55155-4194
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Water Quality – Wastewater Technical Review and Guidance Water/Wastewater/#5.25, May 2001
Hydraulics
a) Filtration Rate (gpm/ft2) based on total area with one unit
out of service
1) Maximum allowable is 5 gpm/ft2 (based on peak
hourly flow and all filters in service)
b) Total system head loss provided (ft)
c) Hydraulic & organic load of backwash water should be
considered
Media Type
a) Selection of media type or types will depend on specific
site conditions. For multi-media filters considerations
should be given to media compatibility.
b) Media specifications shall include effective size, depth,
and type(s).
c) Uniformity coefficient maximum is 1.7.
Backwash
a) Backwash source location (should be filtered water)
b) Water backwash rate; should expand each media layer a
minimum of 20% with a minimum backwash period of
10 minutes
c) Volume of water needed per backwash (gal)
d) Clear well volume (gal) and/or used backwash storage.
Min: 2 backwash volumes
e) Rate at which used backwash is returned to plant (max.
15% of average wet weather flow)
f) Size and number of backwash pumps; should be sized to
provide required rate to any filter with largest pump out of
service.
FILTRATION REVIEW CHECKLIST Page 2
Water Quality – Wastewater Technical Review and Guidance Water/Wastewater/#5.25, May 2001
g) Air scour rate, if provided (scfm/ft2) and equipment used
h) Surface spray rate (gpm)
i) Method for measuring and controlling backwash rate
j) Backwash initiation controlled by total head loss or
effluent turbidity or both.
k) Positive means for shutting flow off filter being
backwashed, and for controlling backwash rate.
l) Underdrain system for even distribution of backwash
water (without clogging from solids)
m) Graded gravel or other type of supporting media to aid in
distribution of backwash water and to prevent loss of
media.
Appurtenances
a) Washwater troughs
b) Surface wash equipment
c) Influent & effluent sampling points
d) Provisions for periodic chlorination of filter influent and
backwash water
Controls
a) Manual over-ride for automatic controls (including each
individual valve) essential to filter operation)
b) Manual controls
c) Controls should be enclosed and protected against high
humidity and/or weather conditions if outside.
d) Means of dewatering filter
e) Is influent fed to filters by gravity or pumps?
FILTRATION REVIEW CHECKLIST Page 3
Water Quality – Wastewater Technical Review and Guidance Water/Wastewater/#5.25, May 2001
Miscellaneous
a) Breakthrough turbidity
b) Filters should be housed
c) Ready and convenient access should be provided to all
components and the media surface without taking other
units out of service.
d) Pre-treatment (chemical coagulation, sedimentation, etc.)
should proceed filters if:
1) Effluent Suspended Solids limitations are less than 10
mg/l
2) Secondary effluent can fluctuate
3) Filters follow treatment with a significant amount of
algae
e) To prevent accidental dewatering of media, elevation of
clear well (or stilling box overflowing to clear well)
should be above the surface of the media.
FILTRATION REVIEW CHECKLIST Page 4
