United States
Environmental Protection
Agency
Municipal Environmental Research _
Laboratory
Cincinnati OH 45268
i
Research and Development
EPA-600/S2-82-031 August 1982
Project Summary
Top-Feed Vacuum Filtration of
Waste-Activated Sludge
Donald J. Carr, Joseph E. Milanowski, Mahendra K. Gupta, and John H. Moser
The objectives of the project were to
evaluate the effectiveness of a top-
feed vacuum filter on a prototype
basis and tocompare the performance
and cost-benefit relationship of a top-
feed vacuum filter with a conventional
bottom-feed vacuum filter. This proj-
ect evolved out of earlier work done
under EPA Grant No. WPRD 71-01-
68, which studied the performance of
a pilot-scale top-feed vacuum fiJter.
The results from this study indicated
that a top-feed vacuum filter would
increase the sludge dewatering
capacity of each filter, produce a drier
sludge cake, and use less ferric chlo-
ride than a conventional bottom-feed
vacuum filter. A significant drawback
of the pilot-scale study was that no
statistically valid comparison could be
made between the pilot-scale top-
feed vacuum filter and a full-scale
conventional botton-feed vacuum fil-
ter. Thus, an evaluation of two full-
scale units, operating on a
side-by-side basis, was undertaken.
This Project Summary was devel-
oped by EPA's Municipal Environ-
mental Research Laboratory,
Cincinnati. OH, to announce key find-
ings of the research project that is
fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
A full-scale evaluation was per-
formed at the Jones Island Wastewater
Treatment Plant of the Milwaukee (Wis-
consin) Metropolitan Sewerage District
to determine the effectiveness of a top-
feed vacuum filter and to compare its
performance and cost-benefit relation-
ship with a conventional bottom-feed
vacuum filter. As part of this project,
two 12-ft-diameter (3.7-m) by 16-ft-
long (4.9-m) vacuum filters were pur-
chased and installed in the Filter
Building at the Jones Island Plant. The
filters and support equipment were
identical, except for the method of
sludge pickup.
Testing was performed around the
clock for approximately 9 months dur-
ing two time periods (from June to Sep-
tember 1979 and from February to
August 1980). Shutdown was limited to
maintenance work and routine filter
washing. All tests were performed only
on thickened waste-activated sludge
since the Jones Island Plant had no
primary treatment at the time. The
thickened waste-activated sludge had a
feed concentration of approximately
18,000 mg/L. Before filtration, the
sludge was conditioned with ferric chlo-
ride, reducing the pH to between 3 and
4.
Results and Conclusions
The top-feed filter was found to be
more efficient when forming a filter
cake because of its basic design config-
uration (resulting in a longer drying
time even at similar cycle times). At
equivalent solids loading rates of
approximately 1.5 Ib/hr/ft2 (7.34
kg/hr/m2), a 3-minute, 40-second
cycle time produced the optimum cake
> US.GOVERNMENTPRINTINQ OFFICE 1982-559-017/0754
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solids (15.0 percent) for the top-feed fil-
ter, which was significantly (based on
statistical analysis) drier than the
bottom-feed filter (14.4 percent).
Further increase in cycle time to 4 min-
utes did not produce any significant
increase in cake solids from the top-
feed filter, but did produce an increase
for the bottom-feed filter, with the
resultant cake solids comparable to the
top-feed filter.
Chemical conditioning studies using
similar flocculation facilities located
adjacent to each experimental filter
indicated that there is no significant dif-
ference between the chemical dosages
required to operate the top-feed filter
and the bottom-feed filter at optimum
levels. Dewaterability appears to be a
function of the sludge itself and is not
influenced by the filter design. Local
sludge conditioning (ferric chloride con-
ditioning done adjacent to experimental
filters) produced drier filter cakes at
higher solids yields for both filters than
centralized sludge conditioning done
remotely. Shear forces in sludge distri-
bution lines appear to have adverse
effects on floe particle structure. When
such sludge is filtered, the sheared floe
particles reduce filter cake porosity by
filling in the voids between the larger
floe particles.
Critical to the routine operation of
vacuum filters of the top-feed design is
a hopper seal that is effective and has a
long life. Whereas considerable pro-
gress was made during the course of
the project, more work needs to be
devoted to developing a seal and wear
sheet having better sealing properties
and a longer life.
Analysis of the unique operating and
maintenance and capital costs perti-
nent to the individual experimental fil-
ters show the top-feed filter capital
costs to be significantly lower than the
bottom-feed filter ($15,350 vs. $22,400
per filter), whereas the operating costs
are significantly higher ($1,120 vs.
$ 154 per filter per year). A cost compar-
ison of the operating and amortized cap-
ital costs indicates there is no
significant difference between the top-
feed filter and bottom-feed filter costs
($2,682 vs. $2,434 per filter per year,
respectively).
These values are based on an analy-
sis of the operating and capital costs
that are unique to each filter. Any oper-
ating cost common to both filters such
as the cost of the filter drum were not
included in the cost analysis. All costs
have been adjusted to mid-1980 dol-
lars. The net costs are amortized on a
20-year basis at an 8-percent interest
rate.
The full report was submitted in ful-
fillment of Grant No. S800969 by Rex-
nord, Inc., under sponsorship of the U.S.
Environmental Protection Agency.
Donald J. Can, Joseph E. Milanowski, and Mahendra K. Gupta are with
Rexnord. Inc., Milwaukee, Wf 53214; John H. Moser is with Milwaukee
Metropolitan Sewerage District, Milwaukee. Wl 53202.
Roland V. Villiers is the EPA Project Officer (see below).
The complete report, entitled "Top-Feed Vacuum Filtration of Waste-Activated
Sludge," (Order No. PB 82-227 687; Cost $13.50, subject to change) will be
available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
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