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Separation

Dynamics

Paper Series

NC AWWA-WEA CONFERENCE

NOVEMBER 17, 2008

_______________________________________________________________________________

Separation Dynamics 611 South Woods Drive, Fountain Inn, SC 29644 U.S.A.

Phone: 864-862-2577 Toll Free: 877-WHY-DUMP Fax: 864-862-8185

Ultrafiltration for Oily Industrial Water

Mike PresleySeparation Dynamics, Fountain Inn, SC

Ivan A. Cooper

PE, WPC, Inc. Consulting Engineers, Charlotte, NC


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INTRODUCTION

Growing environmental concerns, an emphasis on quality and drive towards manufacturing efficiency

have made aqueous parts washing a recent subject of focus in the metal manufacturing industry.

There has also been a shift to aqueous parts washing by manufacturers replacing chlorinated solvent

washers and vapor degreasers. This shift has been mostly in response to EPA restrictions associated

with the manufacture and usage of chlorofluorocarbons (CFCs). With this increased activity in

aqueous parts washing, manufacturers must now address new environmental and economic

concerns.

Over the past several years, advances have been made in developing an industrial wastewater

reclaim system for a separation process for oily industrial wastewater which is extremely effective and

economical in recycling of aqueous parts washing solutions. This process is based on a cellulose

membrane technology that has major technical and commercial advantages over other approaches

that have been tried for this application. Manufactured membrane wall structure, material

hydrophilicity and wide operating parameters (pH and temperature) of this regenerated cellulose

membrane eliminate operation and maintenance problems traditionally associated with conventional

membranes.

This regenerated cellulose membrane is the core constituent of ultrafiltration systems designed to

continuously clean fluid in aqueous parts washers, oily wastewaters, floor cleanup water, and similar

industrial wastewaters. Results include dramatically improved parts washing performance, re-use of

valuable cleaning chemicals, minimized waste, and reduced labor. The unique cellulose membrane

allows these benefits to be realized without the operational difficulties traditionally associated with

conventional membranes. These systems are currently in operation in over 100 production facilities.

PARTS WASHER APPLICATION

Aqueous parts washing fluids generally consist of water and a cleaning additive (detergent)

maintained at concentrations between 2 and 10 percent. As parts are washed, cleaning fluid

becomes increasingly contaminated with metalworking lubricants, mill oils and other shop soils. This

results in reduced cleaning efficiency and requires operators to periodically discharge this fluid. In

this cyclical process, washer performance is continually changing, which either has a detrimentalaffect on cleaning efficiency, requires overcompensation by usage of elevated cleaner concentration

or shortened cleaning fluid work-life. Discharging of spent wash fluid generates an often sizeable

wastewater stream. This results in manufacturing downtime and additional labor and chemical

handling costs.

In a parts washing bath, oil and dirt particles are surrounded by surfactants in aqueous cleaners


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which enables soils to be lifted from part surfaces. This cleaning mechanism results in a stable oil-in-

water emulsion. Traditional oil removal methods such as coalescers, oil skimmers, and centrifuges

are mostly ineffective at removing emulsified oil. Distillers, flocculation chemicals, and encapsulation

equipment can help to minimize waste but can be expensive to operate and eliminate the ability to

reclaim cleaning chemistry.

One method for processing oil-in-water emulsions has been membrane filtration, specifically ultra-

and microfiltration membranes. These membranes are typically porous membranes having flow

through pores with pore sizes ranging from 0.01 10 m. (See Figure 1.) While conventional

ultrafiltration and microfiltration membranes have seen some success recycling these fluids, loss of

membrane flow rate, also known as fouling, has been a significant impediment to reliable operation.

In fact, an EPA Project Summary(1) which evaluates ultrafiltration to recover degreasing baths

discloses, One of the greatest limitations of ultrafiltration membranes are their tendency to foul. The

report goes on to say Fouling is mainly due to the accumulation of particles on the membranesurface and/or within the pores of the membrane itself. While this report concluded that ultrafiltration

was successful in this recycling application, clearly membrane fouling and maintaining permeate flow

is a major concern.

Figure 1 - Filtration Spectrum


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DIFFUSION SEPARATION TECHNOLOGY

Regenerated cellulose is an extremely hydrophilic polymer which is a highly desirable property for oily

water filtration applications.(2) Separation Dynamics Inc. (Fountain Inn, SC) manufactures and

markets an ultrafiltration system called EXTRAN, which is based on a patented hollow fiber

regenerated cellulose membrane. This cellulosic diffusion membrane was derived from technologyoriginally used by Johnson & Johnson (J & J) for hemodialysis, a process that mechanically filters

blood when kidneys no longer function normally.

Made from virgin cotton linters, this membrane has properties and structure different from

conventional membranes. The manufacturing process employed produces a diffusion membrane

which has a non-porous structure. (See Figure 2.) Due to the hydrophilic nature of cellulose, water

and water soluble components are highly soluble and will diffuse into and through the membrane wall.

Hydrocarbons (including emulsified metalworking lubricants) are rejected at the membrane surface.

Cellulose is practically impervious to most non-polar organic all solvents, temperature resistant to210F, and has an operating range of pH 4-12. These properties are highly desirable for aqueous

parts washing applications which are typically operated with alkaline cleaners at 120-160F.

These cellulose hollow fibers are bundled into a membrane module which contains thousands of

fibers, bundled together and encapsulated in a CPVC jacket. This module configuration is operated

in cross-flow mode. (See Figure 3.) Contaminated fluid is directed through the hollow fiber bores,

also called the lumens, and flows parallel to the (inside) membrane surface. Water and water-soluble

cleaning chemistry diffuse through the membrane wall. This clean fluid is the membrane Permeate

stream. Rejected oils and suspended solids are concentrated in the stream exiting the fiber lumens.

This fluid stream is known as the Retenate stream.

Development of alternative membrane technology using non-porous regenerated cellulose instead of

a pore sieving mechanism has been shown to significantly reduce membrane fouling and cleaning.

This is a key difference from conventional ultra- and microfiltration membranes that achieve

separations due to size exclusion based on a specific porous structure engineered into the membrane

surface. Typically, these pores become plugged as hydrocarbons adhere to the hydrophobic

membrane surface causing a loss of performance. As a result, these membranes require periodic

chemical cleaning and backflushing processes to maintain a suitable product flow rate.


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Figure 2. Scanning Electron Micrograph of Regenerated Cellulose Membrane

Figure 3 - Cross Flow Filtration Concept


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AUTOMATED MEMBRANE RECYCLING SYSTEM

Regenerated cellulose membrane modules are the core constituent of a system designed to clean

and recycle emulsified aqueous fluid in order to extend cleaning solution life. These membrane

systems separate free oil, emulsified oil and suspended particulate from wash fluid. A complete

recycling system is self-contained on a small skid containing a Feed Pump, Coalescing Tank,

Process Pump, Prefilter(s), membrane module(s) and automation control panel. (A typical process

flow diagram is shown in Figure 4a). Systems are available with a footprint of 2.5 x 4 or 4 x 5.

These systems are designed to achieve maximum benefit by operating 24 hours per day, 7 days per

week.

Filtration systems can be configured to operate either continuously (Figure 4a) or in batch mode

(Figure 4b). In either case, a Feed Pump automatically draws contaminated fluid to the Coalescing

Tank. A Process Pump continuously circulates fluid from Coalescing Tank, through a prefilter(typically a bag filter), through membrane module configured in a cross-flow filtration mode before

returning back to Coalescing Tank. The Permeate stream, consisting of clean water and water-

soluble cleaning chemistry, is plumbed to either original source tank (continuous operation) or a

separate clean fluid storage tank (batch operation).

Non-porous regenerated cellulose membranes are particularly effective in physically breaking

emulsions without chemical assistance. Rejected oil contamination and suspended particulates are

directed back to the Coalescing Tank. This tank is a stainless steel, V-bottom, heated vessel

designed to enhance concentration and removal of oil contamination separated from processsolution. The Coalescing Tank can be configured to automatically remove both light (specific gravity

< 1) AND/OR heavy (specific gravity > 1) soils. It is important to note that incorporation of a

membrane filtration system does not eliminate waste material. It does enable concentration and

removal of oil contamination to significantly reduce waste stream volume. In some cases, oil

contamination can be concentrated to a point that it has resale value as a waste oil product.

These systems continuously remove oils and particulate from process fluid, returning filtered solution

for re-use. Unlike conventional membrane filtration, a non-porous regenerated cellulose membrane

system is simple to operate and requires minimal maintenance. Chemical cleaning and backflushing

are not required to maintain permeate flow. Life cycle costs have been lower compared with

traditional units requiring maintenance cleaning, and there is often a significant cost savings with a

membrane cartridge replacement compared to a traditional membrane that requires cleaning costs

associated with operational labor, chemical, and backflushing waste disposal.


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Figure 4a. Diffusion Membrane System Continuous Operation

PERMEATE

Process

F

ilter

Process Pump

Feed Pump

Module

PARTS WASHER

WATER

CLEANING CHEMISTRY

OIL CONTAMINATION

MEMBRANE FILTRATION SYSTEM

CONT

AMINATED

FLUID

Figure 4b. Diffusion Membrane System

Batch Operation

FEED

TANK

Low LevelFloat

High LevelFloat

EXTRANTM

SYSTEMCONTAMINATED

FLUIDCLEAN WASH

FLUID

PERMEATE

TANK

PERMEATE


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CASE HISTORIES

Case History I

A major golf club manufacturer was regularly dumping water from a drawing process, floor scrubbers,

mop water and waste coolant. Before membrane filtration equipment installation, over 2,000 gallons

of wastewater were hauled each week at considerable cost. A goal was established to treat

wastewater to enable discharged to a POTW to eliminate hauling. A plan was implemented to

remove floating oil from wastewater tanks and an ultrafiltration unit was added to remove emulsified

oil and other suspended contaminants. Filtered water is now discharged to sewer and the facility

sells concentrated oil (which contains less than 1% water) to Safety-Kleen. Equipment installation

eliminated 100,000 gal/year of waste hauling with a resulting savings of $50,000/year and a six month

payback period.

Case History 2

A heat-treating operation at a major automotive bearing manufacturer in Georgia has a productionprocess that includes high temperature heat-treating, an oil quench, aqueous cleaning and then a

secondary heating step (tempering). The aqueous cleaning step is required to remove oil residue

after quenching prior to the final tempering step. This manufacturer had two aqueous cleaning baths

which were dumped and recharged weekly since insufficiently clean parts were susceptible to

staining and residual surface oil entering the tempering furnace would generate excessive smoke in

the plant. The manufacturer established a goal to eliminate part staining and smoke, while reducing

overall operating costs. An ultrafiltration system was installed to continuously remove emulsified oil

from wash water (both cleaning baths) to maintain constant cleaning effectiveness. Washing solution

is now recycled instead of being a weekly wastewater stream. This allowed cleaning chemistry to bereused, reduced water consumption, significantly reduced wastewater volume and eliminated smoke

generation. Waste hauling diminished by 86%, cleaner chemicals usage diminished by 87%, and

costs were reduced by 72%.

Case History 3

Schaefer Screw Products, Garden City, Ml, is a solid brass parts manufacturer. They operate a

screw machine products facility that manufactures a wide variety of brass pneumatic fittings, hydraulic

fittings and valve components for the automotive, consumer appliance and other markets. During the

manufacturing process, parts become coated with cutting oil and machine tramp oil. The final step

prior to quality assurance and packaging is passage through a Bowden parts washer which

incorporates a 300 gallon wash tank and a 300 gallon rinse tank, followed by a high temperature

dryer.

Schaefer Screw formerly relied on an organic solvent-based system to clean parts before delivery.


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Concerns about health hazards and environmental liability resulted in a change to an aqueous

cleaning system. When the tank contained fresh wash solution, the alkaline cleaner effectively

removed soils from the parts. But as more parts were cleaned, bath soil loading began to hinder the

cleaning process and multiple cleanings were required. In this cleaning process, the wash tank

received a net of approximately 0.75 gallons of oil per day. Without filtration, wash bath oil levels

increased continuously to a maximum of about 15% over a three month cycle.

As a result, many parts were rejected by quality assurance and re-washed - sometimes as many as

three washes were needed to pass inspection. To overcome the multiple washings from a soil-laden

parts cleaning operation, Schaefer Screw began to dispose of the wash and rinse baths more

frequently. More frequent process cleaning resulted in increased cost from escalated consumption of

both cleaner and deionized water.

High oil levels in the wash tank also caused the 300 gallon rinse tank to become unacceptablycontaminated. To overcome this, the rinse tank was dumped on a four day cycle. Due to heavy

metals and oil & grease content, the Detroit Sewer & Water District was pressuring Schaefer not to

discharge this wastewater and was threatening fines for non-compliance. Schaefer was required to

dispose of this wastewater through licensed industrial wastewater disposal facilities, which further

increased costs. Every three days, the company was paying for 600 gallons of dirty wash bath fluid

to be hauled.

An evaluation was performed comparing various technologies. Table 1 shows concepts evaluated

and positive and negative features of comparative technologies. A non-porous regenerated cellulosemembrane system was installed and operated 24 hours/day. This system filtered wash stage fluid at

a rate of 0.5 gpm. Figure 4 shows wash bath oil contamination loading as a function of operating time

before and after ultrafiltration system installation. With filtration, washer oil concentration stabilized at

less than 0.5%. This is more than 15 times cleaner than the average concentration of Schaefers

original washer cycle. Improvements in final product quality were quickly observed. Instead of

fluctuating over time, washing performance was consistent and quality inspection results were similar

to a freshly charged wash bath.

Bath life of both wash and rinse tanks has been extended to over a year. Make-up water is

periodically added to both tanks to compensate for evaporation. Economic benefits are realized by a

96% reduction in wastewater generation, a 71% reduction in detergent consumption and additional

savings in labor/downtime from rewashing and changing the bath. Annual comparisons are listed in

Table 2. Because of the ultrafiltration system, Schaefer capped their sewer connection and

cemented over floor drains. Discharge of washing fluid was no longer required.


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Table 1 - Comparative Technologies for Parts Washer Recycle

Technology Pro Con

Coalescing -Requires minimal capital investment

-Can extend bath life when using

compatible cleaning chemistry

-Breaks up mechanical emulsions

formed in the system

-Sensitivity to soil imbalances

introduced into the system

-Unable to split chemical emulsions

-Will not extend bath life indefinitely

-Cleaning agent chemistry becomes

unbalanced

Evaporation -Reduces generated waste -Does not recycle bath chemistry

-Expensive to operate

-Energy intensive

Porous membrane

(Nonceramic)

-Extends bath life

-Reduces wash bath changeovers

-Reduces cleaning agent costs

-Reduces generated wastes

-Selectively depletes components in

cleaning agent chemistry

-Requires harsh chemical cleaning (acid

washing)

-Flux rates do not stay constant

-May have trouble with wash baths

above 140 to 160 degrees F

-Difficulty with silicate and phosphate

based cleaners

-Membrane life reduced with pH under

3.5 or over 10.5

-May be adversely affected by solvents

Porous Membrane

(Ceramic)

-Extends bath life




-Impervious to most solvents

-Can work in baths up to 180 degrees F

-Selectively depletes components in


-Requires harsh chemical cleaning (acid

washing)

-Flux rates do not stay constant

-May have trouble with wash baths

above 140 to 160 degrees F

-Difficulty with silicate and phosphate

based cleaners

-Membrane life reduced with pH under

3.5 or over 10.5

Cellulosic Diffusion Membrane -Extends bath life




-Impervious to most solvents

-Can work in baths up to 180 degrees F

-Flux rates stay constant

-Compatible range of pH is 1.5 to 12.5

-Reduced pure water flux rate

compared to porous membrane

-Selectively deplete components in



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Figure 4. Wash Bath Oil Contamination for Schaefer Screw

Table 2 Oily Waste Recycle Comparison for Schaefer Screw Products

Before Recycling Diffusion Membrane

Waste Hauled 20,400 gals 800 gals

Detergent Usage 288 gals 84 gals

Maximum Oil Concentration 15% 1.5%

Case History 4

A leading Michigan producer of aluminum anti-lock brake components uses a 300 gallon Mann Gill

aqueous parts washer to remove metalworking lubricants and soils deposited during manufacturing.

These brake components are sent to a thermal deburring process after washing. Parts are then

shipped to be plated prior to delivery to the customer, a major automobile assembly plant.

Increased rejections by final product quality inspectors led to a search for the source of the problems.

A team of engineers from the manufacturer, electroplating company, and customer determined that

ash from thermal deburring was causing quality rejections. This ash resulted from insufficient cleaning

once oil contamination surpassed a critical level. Wash solution required low oil contamination levels,

which could be accomplished by either frequent dumping and replenishing, or by removing emulsified

oil by filtration.

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

0 14 28 42 56 70 84 98 112 126

Operating Time (days)

ContaminantConcentratio

n(%v

/v)

Untreated Wash Bath

Extran Treated Wash Tank (0.5 gpm)


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In order to maintain product quality, the wash bath was dumped twice per week while manufacturing

engineers sought an effective filtration solution. A non-porous regenerated cellulose membrane pilot

scale system was evaluated to filter the wash fluid. After 1.5 months of testing and onsite

development, the complete system began continuous 24 hours per day operation. The system

employed two membrane modules that filtered wash water at approximately 0.5 gpm. Permeate flow

rates were consistent throughout the trial period and a weekly cartridge filter replacement was

required.

During the trial, visual inspection of the wash bath showed both reduced oil contamination and parts

rejection by quality assurance inspectors. Wash bath life was extended from 2.5 days before filtration

to 2 months with ultrafiltration resulting in valuable cleaner savings and wastewater minimization.

DISCUSSION

As seen in the cases above, ultrafiltration with non-porous regenerated cellulose technology is able to

clean and recycle oil-in-water emulsions continuously. For aqueous parts washing applications, a

stabilized level of wash bath cleanliness can be engineered by proper sizing of an ultrafiltration

system. In terms of current wash bath operation, a given Day Cleanliness can be achieved:

)/(

)()(

daygalFLOWPERMEATE

galVOLUMEBATHWASHDAYSSCLEANLINESBATH (1)

Using this relationship between tank size, permeate flow rate and equivalent cleanliness level, an

ultrafiltration system can be sized/selected to provide washing performance relative to a specific day

of an existing process. For example, in the Schaefer Screw sample given above, an ultrafiltration

system sized at 0.5 gal/min (= 720 gal/day) maintained 300 gal wash bath at Day 0.42 Cleanliness.

CONCLUSION

Ultrafiltration systems that treat oil-in-water emulsions, and specifically aqueous parts washing fluid

using non-porous regenerated cellulose membranes can be effective in recycling aqueous fluids.

Manufactured membrane wall structure, material hydrophilicity and wide operating parameters (pH

and temperature) of this cellulose membrane eliminate operation and maintenance problems

traditionally associated with conventional membranes for these applications using a relatively

inexpensive membrane module replacement concept.

Implementing this recycling system allows manufacturers to maintain good product quality, minimize


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wastewater and re-use valuable cleaning chemistry. By maintaining extremely low oil contamination

levels in aqueous wash baths it may also be possible to reduce quantity and/or aggressiveness of

some cleaners.

REFERENCES

1. Gary D. Miller, Timothy C. Lindsey, AIisa G. Ocker, Michelle C. Miller, EPA Project Summary:

Evaluation of Ultrafiltration to Recover Aqueous Iron Phosphating /Degreasing Bath, September

1993.

2. Ultrafiltration and Microfiltration Handbook, M. Cheryan, CRC Press, 1998.

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