84    EVALUATION OF A SCREW PRESS FOR DEWATERING
STEEL INDUSTRY SLUDGES
Michael T. Unger, Associate Scientist
Laboratories for Environmental Research
Indiana University Northwest
Gary, Indiana 46408
BACKGROUND
The dewatering study was part of a research effort entitled, "Feasibility of Recycling Zinc Bearing
Dusts and Sludges Generated by the Northwest Indiana Steel Industry."
Results of that research suggest that more than 515,000 tons (2,000 pounds, dry weight basis) of wet
sludges are produced in northwest Indiana from blast furnace (BF), basic oxygen furnace (BOF),
electric furnace (EAF), and terminal treatment plant (TTP) sources with weighted average water
concentrations of 32.5, 32.1, 17.4, and 47.0%, respectively. This implies a total wet weight (for
sludges from northwest Indiana) of nearly 735,000 tons annually. These steel industry sludges must be
effectively dewatered before they can be easily or economically handled through reuse or disposal.
Most existing dewatering systems in the steel industry utilize conventional vacuum filters or centrifuges. However, limited data exist for newer dewatering technologies such as the screw press.
DESCRIPTION OF SCREW PRESS
Pilot work was done on various sludges generated by the northwest Indiana steel industry to
determine the dewatering capabilities of the Korean Hoilim Iron Works (HIW) screw press. The pilot
unit's screw measured 300 mm in diameter, was 2500 mm in length, and typically produced three dry
tons of sludge per day. A schematic of the screw press is shown in Figure 1.
The screw press has four main components: the driving gear, screw, strainer drum and effluent
basin. The wetted parts are made of stainless steel to minimize abrasion. A low screw rotation speed
(0.5 to 6 rpm) accounts for the small energy requirements of this dewatering system. This particular
unit was driven by a two horsepower (4.7 amp, 1.5 kilowatt) electric motor and the entire system was
mounted in a tractor trailer.
The positive displacement sludge pump was a variable speed Gorman Rupp pump with adjustments
from 0 to 100% stroke. The drive was a 0.5 horsepower (5.5 amp) electric motor and at 100% stroke
would pump approximately 20 gallons per minute.
The polymer pump was positive displacement with variable settings of 0 to 10. Maximum stroke
was equivalent to 20 gallons per hour.
The sludge tank, polymer tank, and flocculation tank had volumes of 350, 160, and 39 gallons,
respectively.
Adjustable operating parameters of the screw press include: strainer size (openings), screw rpm,
pressure plate position, and the type and dosage of conditioning polymers.
METHODOLOGY
Prior to the pilot testing, Calgon Corporation and/or Nalco Chemical did bench testing on the
sludges to be dewatered and determined the polymer type and approximate dosage to be used.
The first day in the field at a particular location was utilized to install the screw press. Services were
connected (electrical, water and steam), access to the sludge source was made, and the entire system
was checked out.
On the second day, trials began and operational parameters were recorded. The detention time
through the screw was typically 12 to 17 minutes; therefore, a trial was 30 to 60 minutes in duration
696