Ultrafiltration for Oily Industrial Water

8/10/2019 Ultrafiltration for Oily Industrial Water

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Ultrafiltration for Oily Industrial Water

ULTRAFILTRATION FOR OILY INDUSTRIAL WATER

Mike Pressley, Separation Dynamics, Fountain Inn, SC*

611 South Woods Dr., Fountain Inn, SC 29644

Tel 864-884-7730

[email protected]

Ivan A. Cooper, PE, WPC, Inc. Consulting Engineers, Charlotte, NC

ABSTRACT

Oily industrial wastewater discharges are a prime candidate for water minimization and chemical recycle

and reuse. An ultrafiltration membrane system can continuously remove emulsified metalworking fluids

and suspended solids from parts washing solutions, enabling reuse of water and detergents. System

design can be structured to minimize waste hauling by removing oil and suspended solids from these

spent metalworking fluids. Overall results can be a substantial reduction in wastewater volume, recycling

of valuable cleaning chemicals and more sustainable manufacturing.

A commercial, regenerated cellulose-based ultrafiltration membrane system has been developed to

successfully to remove emulsified oil from water without requiring regular membrane cleaning.

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.

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

and potentially recycle emulsified aqueous fluids such as aqueous parts washers, floor scrubber and mop

water, and similar industrial wastewaters.. This membrane technology allows for more practical use of

ultrafiltration in oily metalworking plant applications, where traditional ultrafiltration would typically require

intensive maintenance and membrane cleaning regimens. Several case studies are presented that

identify cost saving approaches for water use reduction and process fluid reuse with non-porous

regenerated cellulose ultrafiltration membrane systems.


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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 operationand 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 detrimental affect 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 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


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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 is their tendency to foul. The report goes on to say Fouling is

mainly due to the accumulation of particles on the membrane surface 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 a

ultrafiltration system called EXTRAN, which is based on a patented hollow fiber regenerated cellulose

membrane. This cellulosic diffusion membrane was derived from technology originally 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 to 210

F, and has anoperating 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 toCoalescing 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 process solution. 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. Diffus ion Membrane System Batch Operation

FEED

TANK

Low Level

Float

High LevelFloat

EXTRANTM

SYSTEMCONTAMINATED

FLUIDCLEAN WASH

FLUID

PERMEATE

TANK

PERMEATE


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CASE HISTORIES

Case Histo ry 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 be reused, reduced waterconsumption, 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.

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


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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 unacceptably

contaminated. 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 thiswastewater 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 cellulose

membrane 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 lessthan 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%

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)

Contamin

antConcentration(%v

/v

)

Untreated Wash Bath

Extran Tr eated Wash Tank (0.5 gpm)


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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.

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 partsrejection 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


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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

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 somecleaners.

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.

Documents

Ultrafiltration for Oily Industrial Water