ULTRAFILTRATION SYSTEM FOR
LATEX PAINT WASTEWATER TREATMENT
Audrey Chou Wykpisz, Process Engineer
DeSoto, Inc.
Chicago Heights, Illinois 60429
INTRODUCTION
Ultrafdtration is a pressure driven fdtration process in which a solution-suspension flows
past a membrane surface which is permeable to water and low-molecular-weight organics but
impermeable to suspended particles and large organic molecules. Ultrafdtration is used in
many industrial applications, especially in the food processing industry such as the concentration of cheese whey, sugar, apple juice and cranberry juice, and wastewater treatment
such as candy waste, coffee waste, pulp-mdl waste, electro paint recovery and synthetic
laundry waste [ 1-5].
DeSoto is a major manufacturer of consumer paints and industrial coatings with ten
manufacturing facdities, eight of which discharge process wastewater to publicly owned
treatment works. DeSoto realizes that the standard for the effluent of a latex plant may be
getting more restrictive and as such advanced wastewater treatment methods may be needed
in the future. A couple of years ago, an investigation was initiated and lab-scale studies were
done by using different modules. Finally, a Romicon ultrafiltration pdot system was chosen
for future testing at DeSoto's Chicago Heights Plant to determine the feasibdity of an ultrafiltration system for latex paint wastewater treatment.
OBJECTIVES
For a latex paint plant, the wastewater essentially comes from the washing of tanks,
floors and equipment. The characteristics of this wastestream are:
• Suspended Solids-10,000-50,000 mg/l
• Chemical Oxygen Demand-15,000-60,000 mg/l
• pH-6.5-8
Currently, wastewater is batch treated with a physical-chemical treatment, and is then
separated into supernatant and sludge. The supernatant is pumped into the biological lagoon
for aerobic treatment before discharge to a publicly owned treatment works, and the sludge
is mechanically removed for disposal.
During the busy season, approximately 18,000 gallons of wastewater per day are
generated, and during the slow season about 6,000 gallons per day.
The potential advantages of using an ultrafiltration system in the wastewater treatment
process are as foUows:
1. reuse up to 90% wastewater as raw material—reduce the cost;
2. eliminate the biological lagoon—recover the land; and
3. reduce the amount of sludge—cut the mechanical hauling and drumming expense.
The goals for this study are:
1. determine the flux rates achieveable on a day-to-day basis in an in-plant environment;
2. assess the tendency of the membranes toward reversible and irreversible fouling;
3. determine the best cleaning procedure to return membranes to the highest flux
rate between batches; and
4. determine what mechanical problems may be encountered with pumps, prefilters,
etc.
416