25    COAGULATION PRETREATMENT FOR ULTRAFILTRATION
OF PETROLEUM HYDROCARBON CONTAMINATED
WATERS
Jayadev Regula, Graduate Research Assistant
Beth Pascual, Graduate Research Assistant
Benin Tansel, Assistant Professor
Department of Civil and Environmental Engineering
Florida International University
University Park, Miami, Florida 33199
Robert Shalewitz, Project Engineer
U.S. Army Belvoir R D & E Center
Ft. Belvoir, Virginia 22060
INTRODUCTION
Asymmetric membranes, first developed in the late 1950s,1 traditionally are used in municipal water
treatment for desalination, removal of dissolved organic materials, softening, and liquid-solid separation.2 Other industrial applications of membrane technology include the food, chemical, and pharmaceutical industries. The implementation of stringent discharge limitations and regulations for industrial effluents, resource recovery and recycling of scarce compounds, usually not met by conventional
physical/chemical treatment processes, make membrane processes viable for industrial effluent treatment. Ultrafiltration (UF) as an industrial treatment process is found to be an effective treatment, in
both pilot and full scale operations, for the removal of oil, suspended solids, heavy metals and some
organics from pretreated industrial waste streams. UF, as a treatment process, is evaluated on the
basis of the flux rate, membrane characteristics, operating parameters, and fouling characteristics.
Membrane fouling causes a decrease in flux rates. This can be due to reversible fouling, caused by the
deposition of contaminants on the membrane surface (concentration polarization) and/or irreversible
fouling, caused by the deposition of macromolecules within the membrane structure pores.2'3,4 Coagulant addition before UF is a suggested means of reducing membrane fouling rate and improving the
removal of contaminants.5 Coagulant addition decreases the foulant's zeta potential to near zero. This
lessens foulant penetration into UF membranes by enhancing aggregation of compounds, to producing particles that are rejected at the membrane surface.
BACKGROUND: ULTRAFILTRATION
The ultrafiltration process utilizes hydrostatic pressure as the driving force for fractionating and
concentrating process contaminants from the liquid phase, based on the differences in molecular sizes
(similar to sieving process). The UF process separates molecules and particles with diameters varying
from the submicrometer range (i.e., below the resolution of an optical microscope) down to molecules
with a molecular weight in the range of 1,000 to 100,000 Daltons.4 The UF membranes generally
operate at hydraulic pressures between 25 and 150 psig.6 The separation of liquid-solid or liquid-liquid
mixtures by membrane processes is based on the differences in transport rates of the contaminants,
advective flow, and contaminant diffusion through the membrane interphase. The solute flux
through the membrane depends on the hydraulic gradient, concentration gradient, electro-chemical
potential differences, and the area of membrane.7 Important design parameters for a UF system
include system characteristics such as the hydrostatic pressure gradient and membrane characteristics,
like porosity, pore size, thickness and density of the membrane.3 The use of low operating pressures
minimizes energy costs and pumping equipment costs. The details of UF system design procedures
and design equations can be found in the literature.8,9,1°
Flux decline, caused by concentration polarization and irreversible fouling, affects UF performance.1 Organic and humic components in the waste streams can cause fouling of the membrane by
48th Purdue Industrial Waste Conference Proceedings, 1993 Lewis Publishers, Chelsea, Michigan 48118. Printed in
U.S.A.
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