Section Four
PROCESSES-H. SLUDGE CONDITIONING
54    OPTIMIZATION OF SLUDGE CONDITIONING FOR
RECESSED CHAMBER FILTER PRESS PERFORMANCE
Jitendra T. Shah, Senior Engineer
Nalco Chemical Company
Naperville, Illinois 60566
INTRODUCTION
Filter presses are becoming more popular devices for dewatering because of their ability to generate
higher cake solids than belt presses. Rising costs of landfilling and tougher environmental disposal
regulations are forcing waste generators to explore more efficient dewatering devices. Incineration of
sludge is more common on the East Coast where landfilling is expensive and scarce. Higher cake
solids produced in filter presses can be burned more economically in an incinerator.
The optimization of press performance is dependent on many variables such as throughput, maximum pressure, initial fill time, type of cloth, sludge feed solids and conditioning. Press performance
is measured by the amount of sludge dewatered, the dryness of the cake, cake release, and filtrate
quality. Waste plants that have low cake disposal costs or are capacity limited prefer higher throughput. However, plants that have high disposal costs or incinerate the dewatered sludge place more
emphasis on cake dryness. In most cases, there is usually a compromise between sludge processing
rates and final cake dryness.
The typical approach in improving filter press performance is to change one variable at a time. For
example, polymer dosage can be adjusted while the other variables are held constant. Optimal sludge
throughput or cake dryness is then achieved at a specific polymer dosage. The next step is to vary
other operational variables. This procedure usually fails to achieve optimization because it assumes
that one variable can be optimized independently of the others, which is frequently not the case.
Experimental design is a proven technique, the use of which is steadily growing in industry. The
benefits of this approach are many, including more information per experiment, an organized
approach toward collection and analysis of data, and the capability to see interaction among experimental variables.
Historically, experimental design has not been used extensively in industry because the design and
analyses have generally been too complex and time consuming for effective manual computation.
Within the last few years, computer software has been written that is more interactive. RS/Discover™
is an advanced software package developed to help in the design and analysis of industrial
experiments.1
A response-surface experimental design, generated with RS/Discover software, was performed on a
filter press used to dewater anaerobically digested sludge. The press was located at a medium sized
municipal wastewater treatment plant. Sludge was conditioned using a polymer fed prior to dewatering. Two variables, split-feed ratio and dosage, were evaluated.
OBJECTIVES
The objectives of the research were as follows:
1. To evaluate the effectiveness of polymers on sludge dewatering using a filter press.
2. To determine the optimum dosage and split-feed ratio to maximize cake solids.
3. Investigate filter press operating methods.
4. Evaluate filter cloths with varying porosities for filtrate quality.
44th Purdue Industrial Waste Conference Proceedings, © 1990 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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