AD-A266 879

TE~kiNICAL REPORT 9207

REVERSE 0OSMOSIS WATER PURIFICATION UNIT:

EFFICACY OF CARTRIDGE FILTERS FOR REMOVAL OF BACTERIA AND

PROTOZOAN CYSTS WHEN RO ELEMENTS ARE BYPASSED

Stephen A. SchaubHelen T. HargettMark 0. SchmidtC

Ci)W. Dickinson Burrows EC

V- #;--AJUL 19 1993,

April 1993

U S ARMY BIOMEDICAL RESEARCH & DEVELOPMENT LABORATORY

Fort Detrick

FRdulck, MD 21702-5010

Approved for public release;

distribution unlimited.

U S ARMY MEDICAL RESEARCH & DEVELOPMENT COMMANDFod DetrlCkFodrwick, MID 21702-5012

NOTICE

Disclaimer

The findings in this report are not to be construed as an officialDepartment of the Army position unless so designated by other authorizeddocuments.

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Destroy this report when it is no longer needed. Do not return it to theoriginator.

Citations of commercial organizations or trade names in this report donot constitute an official Department of the Army endorsement or approval ofthe products or services of this organization.

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4. PERFORMING ORGANIZATION REPORT NUMBER(S) S MONITORING ORGANIZATION REPORT NUMBER(S)

Technical Report Number 9207

6a. NAME OF PERFORMING ORGANIZATION 6o. OFFICE SYMBOL 7a NAME OF MONITORING ORGANIZATIONU.S. Army Biomedical Research (if applicabl)•

and Development Laboratory ISGRD-UBG-O6c. ADDRESS (City, State, and ZIP Code) 7b ADDRESS (City, State, anid ZIP Code)Fort DetrickFrederick, MD 21702-5010

"a&. NAME OF FUNOING/ SPONSORING .b OFF'CE SYMBOL 9 PROCUREMENT INSTRUMENT IDENTIFICATION NUMBERORGANIZATION Naval Civil Engi- (if applicable)

neering Laboratory L66

Rc. ADDRESS (City, State, and ZIPCode) 10 SOLRCE 0; FUNDING NUMBERSPROGRAM PROJECT TASK WORK UNITPort Hueneme, CA 93043 ELEMENT NO NO NO ACCESSION NO.

11. TITLE (include Securrty Classficatron)

REVERSE OSMOSIS WATER PURIFICATION UNIT: EFFICACY OF CARTRIDGE FILTERS FOR REMOVAL OFBACTERIA AND PROTOZOAN CYSTS WHEN RO ELEMENTS ARE BYPASSED

12. PERSONAL AUTHOR(S)Stephen A. Schaub, Helen T. Hargett, Mark 0. Schmidt and W. Dickinson Burrows

13a. TYPE OF REPORT I3b. TIME COVERED 14. DATE OF REPORT (Yea,, Month, Day) 15 PAGE COUNTTechnical Report FROM Jan 88 TODec 88 93/04 29S16. SUPPLEMENTARY' NOTATION

1. COSATI CODES 18 SUBJECT TERMS (Continue on reverse if necessa•y and io•ntify by block number), FIELD GROUP SUB-GROUP Filtration Bacteria Cartridge filters

009Water Supply Protozoan cysts

19, ABSTRACT (Continue on reorso C nrcets.ry arnd tdentify by block numemr)

Two different filter combinations have been tested as candidate systems for bypassing thereverse osmosis membranes of the Army's ROWPU when treating fresh water: a spiral-woundcotton prefilter of 5.0 Vun nominal pore size combined with either a melt-blownpolypropylene depth filter or a pleated polypropylene filter of 3.0 um absolute pore size.• st organisms were Klebsiella terrigena, Cryptosporidium parvum oocysts, Rhodotorularubra, and 3.7 pm latex beads. Challenge waters were dechlorinated tap water and aworst-case water containing AC fine test dust and humic acid. The depth filter, testedseparately, achieved better than 99.9 percent reduction of C. parvum cocysts (the US1PAcriterion) at filtration rates of 1-2 •pm under all conditions. The pleated filter didnot achieve 99.9 percent reduction of C. parvum oocysts at a filtration rate of I gpm.None of the filter combinations tested was adequate for the removal of K. terrigena.

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TABLE OF CONTENTS

Page

PREFACE .............................................................. 1

INTRODUCTION ........................................................ 2

MATERIALS AND METHODS ................................................ 2

RESULTS AND DISCUSSION ............................................... 6

CONCLUSIONS .......................................................... 19

REFERENCES ........................................................... 21

DISTRIBUTION LIST .................................................... 25

APPENDICES

A. Performance of Prefilter: 150 mg/L Fine Test Dust Added ........ 22

B. Glossary of Terms ............................................... 24

TABLES

1. Prefilter Performance, AC Fine Test Dust Added ................... 82. Latex Bead Removal by Prefilter .................................. 123. Prefilter Microbial Removal: Run 1 .............................. 134. Prefilter Microbial Removal: Run 2 .............................. 145. Prefilter Microbial Removal: Run 3 .............................. 156. Final Filter Microbial Removal: Run 1 ........................... 177. Final Filter Microbial Removal: Run 2 ........................... 188. Final Filter Microbial Removal: Run 3 ........................... 20

FIGURES

I. ROWPU Bypass Filtration Test System P&ID ......................... 72. Prefilter Performance, 150 mg/L Fine Test Dust Added: Flow....... 93. Prefilter Performance, 150 mg/L Fine Test Dust Added: Head Loss. 104. Prefilter Performance, 150 rr-g/L Fine Test Dust Added: Product

Turbidity ............................... ...... ........... 11

mTIS RA&I

DTIC TAB

IJu:s tIf "I

7 ! I

PREFACE

This project was supported in part by the U.S. Naval Civil EngineeringLaboratory, Port Hueneme, CA. Project officer was James Lozier.

INTRODUCTION

The U.S. Air Force and Marine Corps have identified a requirement tobypass the reverse osmosis (RO) elements in the reverse osmosis waterpurification unit (ROWPU) for certain military applications. The RO membranecomponents of the ROWPU are provided as part of the treatment train so thatdrinking water can be produced from sea water, brackish water or chemicallycontaminated fresh water. Typically, the treatment of sea water yields 33gallons of product water for every 100 gallons of feed water, while treatmentof fresh water yields approximately twice as much. The Air Force and MarineCorps desire the capability to selectively bypass the RO elements whentreating fresh source waters that meet chemical criteria for field drinkingwater, thereby recovering 100 percent of the treated water as product. Anadditional advantage of bypassing the RO membrane would be that source watersknown to contain traces of chlorine or similarly corrosive chemicals could betreated without risk of damage to the RO membranes. This report describes aproject conducted at the U.S. Army Biomedical Research and DevelopmentLaboratory (USABRDL) to evaluate ROWPU-compatible cartridge filters in termsof their ability to remove infectious protozoan cysts known to be resistant tomilitary disinfection practices.

Tests were conducted using a 6-cartridge bench scale filtration apparatusconstructed for the Naval Civil ýngineering Laboratory (NCEL) by SeparationSystems Technology, Inc. (SSTI).' Two of six candidate cartridge filtersevaluated by SSTI for life cycle performance were selected by NCEL formicrobial tests at USABRDL.

MATERIALS AND METHODS

CHALLENGE MICROORGANISMS. Microbiological methods used in these studieswere in accord witih the Guide Standard and Protocol for TestingMicrobiological Water Purifiers.

Bacterial Preparation. Klebsiella terrigena (ATCC 33257) stock cultureswere grown for 24 hours at 360C in nutrient broth to obtain a stationary phaseculture. The culture was pelleted by centrifugation at 12,000 G, washed threetimes in sterile rhosphate buffered saline (PBS) at pH 7.0, and filteredthrough sterile Woatman #2 paper to remove cell clumpA. The stock bacterialsuspension was diluted in PBS to contain ca. 1.0 x 10 colony forming unitsper mL (cfu/mL) using a Klett-Sumnmerson photoelectric colorimeter (KlettManufacturing .o., Inc, NY). The K. terrigena suspension was quantified intriplicate by 1iltration of 1.0 mL volumes through 47 mm membrane filters(Type HAWG, 0.45 pm pore size, Millipore Corp., Bedford, MA). Each membranefilter was then placed on a 47 mm pad which contained 2.0 mL of m-Endo broth(Difco Laboratories, Detroit, MI) in a 50 x 9 mm snap-cap petri dish (Falcon1006, Becton Dickinson & Co., Lincoln Park, NJ). Plates were incubated at36 0 C for 24 hours, and the colonies displaying a green metallic sheen werecounted.

{2

Yeast Preparation. The morphological and size characteristics ofRhodotorula rubra (ATCC 36053) made the yeast suitable as a protozoan cystsimulant. The yeast cells were 3.5-4.5 pm in size with minimal budding (1.0percent); they were readily distinguishable frcm indigenous yeasts by theirpink color, and they could be quantified using membrane filtration techniques.Stock yeast cultures were prepared on YM agar (Difco) in 150-mm petri dishes.Each plate was inoculated with 1 x 10• yeast cells and grown at roomtemperature for 48 hours. Yeast cells from each plate were harvested andcollected in 100-mL sterile, distilled deionized water, pooled and c9untedusing a hemacytometer. These cells were further diluted tM 2 .0 x 10 /mL indistilled deionized water containing 0.01 percent Tween 20 [polyoxyethylene(20) sorbitan monolaurate (Aldrich, Milwaukee, WI), added to prevent clumping]and refrigerated. Yeast cells were determined to remain viable for at least10-14 days when stored at 40 C; however, fresh stocks were grown weekly for usein these studies.

Cyst Simulant Preparation. For testing, 3.7 pm latex AccubeadsTM (styrene

divigylbenzene copolymer, Fastek) were diluted to a final concentration of 2.0x 10 /mL in sterile distilled deionized water containing 50 Ag/mL of sodiumdodecyl sulfate. Numbers of beads were quantified by means of hemacytometerusing phase contrast microscopy.

Protozoan Oocyst Preparation. Infected calf feces (50 percent in 2.5percent potassium dichromate) containing Cryptosporidium parvum oocysts wereobtained from the University of Idaho and partially iurified for the filterchallenges using a modified method of Waldman et al. The calf fecessuspension was dispensed in 15-mL volumes into 50-ml. conical polypropylenýMcentrifuge tubes, and a volume of 25 mL of PBS (pH 7) containing Tween 20(0.05 percent), penicillin (100 units/mL) and streptomycin (100 Ag/mL) wasadded to each tube. The tubes were mixed well (vortexed) and centrifuged at750 G for 10 minutes; 30-mL volumes of the supernatants were discarded, andthe pellets were resispended in 25 mL of PBS. After the contents of the tubeswere vortexed, all tubes were refrigerated overnight at 40 C. Next, each ofthe tubes was again mixed, sonicated for one minute and centrifuged at 750 G.A 25 mL volume of the supernatant was disc9rded from each tube and replacedwith PBS containing 0.05 percent Tween 20"H but without antibiotics. Thecontents of each tube were again vortexed. Ten mL of anhydrous ether wasadded to each tube and mixed with the suspension for one minute. The tubeswere then centrifuged at 500 G for IMminutes, and the top three layers(ether, debris plug and PBS-Tween 20 ) were removed and Ti carded. Thepellets were resuspended in a final wash of PBS-Tween 20 " (0.01 percent) andcentrifuged at 750 G. All supernatants were discarded, and the pelletsTMcontaining the cysts were resuspended in PBS with 0.01 percent Tween 20 "M andpooled. A sample of the oocyst suspension was diluted to 1:20 and 1:30, andthe oocysts were counted in a hemacytometer using phase contrast microscopy.No morphological changes were observed in the oocysts which would indicatedegradation had occurred by this purification process; the oocysts werespherical and measured 4.0-4.5 pm in size. The final stock suspensioncontained 5.42 x 10 oocysts/L. Phase-contrast microscopic examination of thecysts showed no morphological changes or losses due to excystation afterstorage at 5°C for 7 days. The partially purified oocyst suspension wasdetermined, by fecal coliform analysis, to be free of interfering bacterialcontaminants and, by microscopic examination, to be free of fecal debris andyeasts. 3

QUANTIFICATION OF CHALLENGE MICROORGANISMS AND SIMULANTS

Bacteria and Yeast Analyses. Test and control water samples containing K.terrigena were diluted in PBS and assayed on membrane filters in triplicate asdescribed above using m-Endo broth. Colonies having a green metallic sheenwere counted after 24 hours incubation at 360C. R. rubra yeast samples inwater were serially diluted in sterile distilled deionized water andquantified using the membrane filter method described above with YM broth atpH 3.3. The pink yeast colonies were enumerated after incubation at 360 C for24 hours.

Oocysts and Bead Analysis. After challenge water samples were collectedfrom each sampling point, final concentrations of 0.1 percent Tween 20 and1.0 percent newborn calf serum were added to each sample to prevent adsorptionof the oocyst and bead materials to the glass collection flasks. Each samplewas filtered through a 47-mm, 1.0 um-pore size, polycarbonate membrane filter(Nuclepore Corp., Pleasanton, CA) followed by a Vash of 100 mL of distilleddeionized water containing 0.1 percent Tween 20." The membrane filter wastransferred to a 60-mm plastic petri dish and was~gd with 5.0 mL of distilleddeionized water containing 0.01 percent Tween 20." The wash was collected,transferred to a 50-mL polypropylene centrifuge tube and saved. The membranewas cut into eight pieces with a sterile scalpel and placed in a separate 50mL centrifuge tube. Wash solution (10 mL) was used to rinse the petri dish,and that rinse was collected and used to wash the filter pieces in the secondcentrifuge tube. After the material in the tube was thoroughly mixed on avortex mixer, the wash material was collected and pooled with the wash in thefirst tube; this step was repeated twice. The membrane was given a final10-mL wash with vigorous mixing for one minute. The tube containing all thewash material was centrifuged at 1200 G for 10 minutes at 40 C. Thesupernatant was pipeted off and discarded, leaving a volume of 0.8-1.0 mLwhich was used to resuspend the pellet.

For quantification, a volume of 200 uL of a concentrated bead-oocystsuspension was pipeted into duplicate 4-mL polypropylene tubes. A volume of100 pL of 2 percent malachite green was added to each tube and allowed tostand for 20 minutes at room temperature. A volume of 100 uL of 1 percentsulfuric acid was added to each tube just prior to counting. The tubes werevortexed and sonicated briefly to fully disperse the cycts and beads. Acoverslip was placed on the hemacytometer, and the chamber was filled withsample using a pasteur pipet. The filled chamber was allowed to settle for aminimum of 2 minutes (beads settle slower than oocysts). For each sample tubeone chamber of 5 squares was counted, unless the average of each squarecontained 1 or less; then two chambers or 10 squares were counted. Counts ofduplicate sample tubes were averaged. If no beads were found in the dilutedsamples they were again cuunted using undiluted sample material. Beadsappeared as well-defined, cilor-free opaque shiny spheres. A minimumdetection level of 1.0 x 10 was established for counting the beads andoocysts using the hemacytometer under phase contrast microscopic conditions.

S• • • • i i • i • i i i :Zl I •I I I • I I • I : I: •4

CHALLENGE WATER CHARACTERISTICS

General Challenge Water. Tapwater was collected in large fiber glass testtanks, and sodium thiosulfate (10 mg/L) was added to neutralize residualchlorine. The water was also stored overnight before testing to assurecomplete dechlorination..

Worst-Case Challenge Water. Tapwater was collected in large fiber glasstest tanks and sodium thiosulfate (10 mg/L) was added to neutralize residualchlorine. Worst-case challenge water was prepared according to the GuideStandard and Protocol, Section 3.3.3, Test Water #3 (Challenge Test2Water/Ceramic Candle or Units With or Without Silver Impregnation). 2

(1) Turbidity: A turbidity of 30 nephelometric turbidity units (NTU) wasobtained using 150 mg/L of AC fine test dust (A.C. Spark Plug Div., GeneralMotors Corp., Flint, MI) for the challenge water as measured in a Model 2100ATurbidimeter (Hach Chemical Co., Ames IA). The test dust particle sizedistribution was follows:

Micrometers Percent less than

5.5 38+311 54 + 322 71 + 344 89 ± 3

176 100

(2) Total organic carbon (TOC): Humic acid, sodium salt (Cat. No.H1,675-2, Aldrich Chemical Co., Milwaukee, WI) was incorporated at 10 mg/L oftest water.

(3) Temperature: Test water temperatures were ambient (ca. 200 C).

(4) Total dissolved solids (TUS): Sea salts (Cat. No. S-9883, SigmaChemical Co., St. Louis, MO) were added at a concentration of 1500 mg/L oftest water.

TEST FILTERS. Cotton prefilters used in these studies were 20-inch,spiral wound, 5.0-pm nominal pore size (DW 5-01-20-1, Delta Pure FiltrationCorp., Ashland, VA, or the equivalent); six were placed in parallel in apressure housing similar to that used on the 600-gph ROWPU. Single 10-inchprefilters of the same composition were used for preliminary studies. Two10-inch cartridge filters, both rated at 3 pm pore size absolute, wereevaluated for the RO bypass study. The Pall Profile (MCY1001Y030, sincediscontinued and replaced by RMIFO3OH21, Pall Corp.,REast Hills, NY) is amelt-blown polypropylene depth filter; the Nuclepore polypropylene pleatedfilter (QMC-P-10"-0.S) has about 6.0 ft' effective filter area.

TEST STAND. Preliminary and prefilter studies were performed iising a 10inch filter cartridge holder connected to a feed supply tank and a collectiontank. Pressures and flow rates were monitored and controlled by valvesconnected to pressure gauges installed immediately before the filter cartridgeinlet and after the filter cartridge outlet. For studies simulating bypass ofthe ROWPU RD elements, the following system was provided by NCEL:

5

The test stand was 72 inches long and 36 inchis wide, with a front panelheight of 54 inches (Figure 1). The system was mounted on 8-inchsemi-pneumatic wheels and was designed to accommodate six 10-inch cartridgefilters. A 208-V single-phase centrifugal pump, protected by a 20-meshstrainer, provided feedwater at a maximum pressure of 90 psig. Feedwaterpressure was r :gilated by a 0.5-inch PVC regulating valve prior to passingthrough the prefilter pressure housing described above. Filtered feedwater atapproximately 13 gpm was reduced to a maximum of 80 psig and 12 gpm by aregulating valve at the system exit. Feedwater flow through each cartridgewas maintained at 1.0-2.0 gpm by flow control valves. Instrumentation wasprovided to measure feedwater temperature, pressure, flow rate, cumulativefeedwater flow, differential pressure across ttie prefilters and each cartridgefilter, and flow rate through each filter. Differential pressure measurementacross each cartridge was accomplished using a 7-round valve to allowswitching from one position to another; a single differential pressure gaugewas used with one of the valve positions connected to the feed manifold.Sampling valves allowed the collection of both raw and prefiltered feedwaterduring system operation.

RESULTS AND DISCUSSION

Preliminary Filter Characterization

Two tests were run initially with the standard 5.0-nm ROWPU prefilters toestablish changes in pressure and flow rates over time using AC test dustccncentratiois of 250 mg/L, corresponding to 57 NTU, and 50 mg/L in order todetermine loading effects on the filters (Table 1). Initial flow rates wereabout I gpm. As would be expected, filter life, as measured by pressuredifferenti3l elevation and associated flow rate reduction, was much longer atthe lower turbidity loading (50 mN/L).

The initial tests were followed by a series of four tests onrepresentative prefilters using 150 mg/L (30 NTU) of AC test dust, the levelof challenge recommended in the Guide Standard and Protocol. 2 Prefilterefficiencies varied greatly with respect to pressure change (head loss) andflow rate for the four cartridges tested (Figures 2-4, Appendix Tables A1-A4).All runs were discontinued when the pressure differential reacred about 20psig, the typical cutoff for changing ROWPU prefilters in the field. Threefilter runs continued to produce water at an acceptable rate for 360 or 390minutes; in Run 2 the filter plugged after 120 minutes. The four filterstested generally provided product water with residual turbidity less than INTU, although the initial time required to achieve this turbidity level variedwith increased head loss.

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TABLE 1. PREFILTERa PERFORMANCE, AC FINE TEST UU AOODDED

Time, min 250 mg/L AC test dust ýOnqL AC test dustFlow Head loss Product turbidit. F-o- Haýd loss

gpm psi NTU psi

0 0.90 2 24 230 0.71 4 4.5 260 0.63 14 1.2 ',0 390 0.48 24 0.94 '.90 3

120 0.34 28 0.55 0.90 3.5150 0.26 31 0.56 0.90 4180 0.87 5210 0.82 10240 0.77 13270 0.66 16300 0.61 19330 0.58 22360 0.50 24390 0.48 26420 0.45 27

a. Spiral wound cotton, 10 inch.

Another preliminary test to determine the cyst removal capability of theROýPU prefilters was carried out by addition of latex bead simulant (2.0 X10 I/L) and AC test dust (150 mg/L, 30 NTU) to 450 gallons of feed wa.er.Samples were taken from the feed tank after 30 minutes and at thE end of therun to detect any loss of beads due to electrostatic attraction to the tank orplumbing; no loss occurred. Filtered water samples were collected after 30,75, 120, and 210 minutes, the last being the point in time where the filterclogged after passage of about 200 gal. Results are shown in Table 2. Latexbead removal improved to >99 percent as the filters became loaded with thetest dust, while pressure differential increased and flow rate decreased.

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TABLE 2. LATEX BEAD REMOVAL BY PREFILTERa

Latex BeadTime, min Pressur.e, psi Flow Rate Challenge Sample % Total

Inlet Outlet gpm in-culum recovery/L removal

0 34 32 0.92 b15 35 32 0.92 b30 35 33 0.90 1.82 X 106 1.51 X 105 91.760 35 32 0.90 b75 34 31 0.90 1.82 X 106 1.36 X 105 92.590 35 28 0.90 b

120 34 25 0.87 1.82 X 106 8.80 X 103 99.5135 34 20 0.82 b150 34 17 0.77 b165 34 15 0.71 b180 34 12 0.61 b195 34 10 0.56 b210 34 7 0.50 1.82 X 106 6.78 X 10 99.6

a. Spiral wound cotton, 10 inch.b. Not sampled.

ROWPU Prefilter Microbial Tests

Tests of the 5.0 pm prefilter were performed using the Guide Standard andProtocol general challenge wa er,2 with the addition qf AC fine test dust (150mg/L), K. terrigena (1.0 X 10 I/L), R. rubra (1.0 X IO'/L), and 3.7-sm latexbeads (1.0 X 10 /L). C. parvyum oocysts used in the challenge were dilutedinto 600 ml sterile water containing red food coloring (105TL), with orwithout newborn calf oerum (6.0 mL) and 10 percent Tween 20 (6.0 mL). Theoocysts (ca. 2.0 X 10 /L) were placed in a stirred flask connected to thechallenge water inlet line to the prefilter at the start of the. test run; justprior to each sample collection, the cysts were injected into the feedline ata rate of 50 mL/minute with a peristaltic pump. In the first run (Table 3),the filtered samples were collected after a 1-minute injection of cysts. A32.4 percent loss of cysts in the challenge inoculum was attributed to surfaceadsorption. To reduce the loss in the second run (Table 4), the flask andftqglines were coated with I percent newborn calf serum and 0.1 percent Tween20, , prior to addition of the cyst suspension. The cyst loss was furtherreduced in the third run (Table 5) when samples were collected after a3-minute injection of cysts. Since the injection rate of cysts into thefeedline remained constant throughout each run, the numbers of cysts in thechallenge inoculum increased as the flow rate decreased. Oocyst and oocystsimulant removals increased as did turbidity removal as the filters cloggedand pressure built up across the cartridge. There was significant variationamong prefilters as determined by the amount of water filtered before cloggingoccurred. Comparison of oocyst vs simulant at each sampling time for the 3runs indicated good agreement with respect to removal efficiency. Removal of

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Final Filter Incorporation Study

In these tests, the 3.0-pm filters described above were incorporatedin-line after the 5.0-pm prefilters so that the complete bypass app oach couldbe evaluated. Again, the Guide Standard and Protocol was followed. Virusremoval capabilities were not evaluated during this study because of theextreme difference in size of the virus versus the filter pore size (ca. 0.02pim vs 3.0 pm) and a!.k of active charges on the filtzr material to effectvirus adsorption. The candidate systems each received the microbial challengein tap water for the first 5 days of operation, followed by up to 5 days (orto the point where irreversible clogging of the filters occurred) in which thefilters received the worst-case water containing AC dust, humic acids and highTDS at pH 7.7 or 9.0. The 48-hour stagnation test specified in the GuideStandard and Protocol was not performed, since the proposed ROWPU bypasssystem is intended for uninterrupted service.

Challenge organisms were K. terrigena bacteria, C. parvum protozoan cysts,and 3.7 pm latex beads- challenge levels were those stated in the GuideStandard and Protocol.2 The challenge bacteria and latex beads were added tothe challenge water reservoir tank and maintained throughout the study.Sample ports were located in the test stand just prior to the 5.0-pmprefilters, after the prefilters, and in the product water reservoir followingeach 3.0-pm filter. C. parvum oocysts were added through an injection port tothe water feedline just after the prefilters. (Note that C. parvum was usedas a challenge only to the final filters in order to minimize handling of thepathogenic and chlorine-resistant cysts.) The cysts were introduced andsampled using a pulse chase approach in which the cysts were injected for aperiod just long enough to maintain yug flow characteristics of the cysts inthe system. Calf serum and Tween 20 were added as before to preventadsorption of oocysts to the surfaces of the stock container and tubing, andred food colorirg was added to provide a visual indication that a steady statein the pulse chase oocyst challenge had occurred before sampling. Sampleswere taken after red dye had gone completely through the system for ca. 2minutes. The cyst samples were taken at the sample collection ports in frontof and after the final polishing filters.

The test system was initially operated at a constant flow of 3 gpm so thateach final filter cartridge saw a flow rate of 1 gpm for both thedechlorinated tap water and the worst-case water. In this mode approximately750 gal of challenge water was passed through the test system each operationalday f250 gal/candidate filter). Daily runs were continued until thedifferential water pressures from the final polishing filters exceeded 20 psi,which occurred after 1-2 days of operation in worst-case water. Testoperations were then concluded with final microbiological sampling. Theresults are summarized in Tables 6 and 7. These tables show the levels ofeach organism (averaged over three filters of each type) at each of the threesampling points and the total percent removals for the complete filtrationsystem.

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118

=7717

From Table 6 it is evident that 90-98 percent re.,ioval of K. terrigenabacteria was achieved in the total bypass system using polypropylene depthfilters, well below the U.S. Environmental Protection Agency (USEPA) criterionof 99.9999 percent removal. On the other hand, removal of latex beadsgenerally exceeded 99.99 percent (except for day 6), well above the USEPAcriterion of 99.9 percent removal. The final filters alone removed C. parvumcysts with greater than 99.9 percent efficiency throughout the tests. Noimportant loss of filterability was observed for either cysts or beads inworst-case water vs the dechlorinated tap water. Bacterial removals forpleated polypropylene filters were comparable with those for the polypropylenedepth filters, but the pleated filters were much less effective in removal ofbeads and cysts and did not consistently meet USEPA criteria for any challenge(Table 7).

A separate test was conducted to evaluate the polypropylene depth filtersat a flow rate of 2 gpm (Table 8). For this study two filters were used inparallel instead of three; the prefilter system was maintained as before.Sampling for cysts and beads in the dechlorinated tap water challenge wasperformed after throughputs of 200 gal and 1200 gal per filter. Theworst-case water challenge was sampled only after differe tial pressureexceeded 25 psi (a value concurred in by the manufacturer ). Bacterialremovals were not evaluated. The only other significant departure from theprotocol was that daily filtration was not discontinued after 250 gal ofwater, but was continued throughout the day. The higher flow rate did notadversely affect the filtration of cysts or their simulants in either thedechlorinated tap water or, upon clogging, in the worst-case water. Acomparison of Table 8 with Table 6 indicates that total removal percentageswere similar. During this run the flow rate was dropped to 1 gpm/filter for ashort period of time to directly compare bead removals for the same filter atthe different flow rates; the removal efficiencies were comparable.Worst-case water also had no significant impact on the efficiency of removalof the cyst size particles, and a test performed on a separate set ofpolypropylene depth filters at pH 9 in worst-case water demonstrated removalefficiencies for cysts and beads essentially identical to those observed at pH7.7 (Table 8).

CONCLUSIONS

Two different filter combinations have been tested as candidate systemsfor bypassing the reverse osmosis membranes of the Army's ROWPU when treatingfresh water, namely, a spiral-wound cotton prefilter of 5.0-Am nominal poresize combined with a melt-blown polypropylene depth filter of 3.0-pm absolutepore size and the same prefilter combined with a pleated polypropylene filterof 3.0-pum absolute pore size. Test organisms were Klebsiella terrigena (arepresentative enteric bacterium), Cryptosporidium parvum (an entericprotozoan pathogen) oocysts, Rhodotorula rubra (a yeast, used to testprefilters only) and 3.7-pm latex beads; challenge waters were dechlorinatedtap water and a worst-case water containing AC fine test dust and humic acid.Physical removal of C. parvum oocysts appeared to correlate well with removalof R. rubra and latex beads.

19

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Neither the prefilters nor the reverse osmosis bypass filters wereadequate for the removal of K. terrigena; the 3.0-micron filters at best couldreduce the bacterial challenge by no more than 2 orders of magnitude. (Asanticipated, improved reductions for all microbial challenges were achievedwith time in worst-case water, corresponding to reduction in average pore sizeof the filter material through particle entrapment.)

The polypropylene depth filter, tested separately, achieved better than99.9 percent reduction of C. parvum oocysts (the USEPA criterion) atfiltration rates of 1-2 gpm, whether challenged with dechlorinated tap wateror worst-case water (pH 7.7-9.0). Latex bead removal for the complete systemgenerally exceeded 99.99 percent. The pleated polypropylene final filter, onthe other hand, did not achieve 99.9 percent reduction of C. parvum oocysts ata filtration rate of I gpm in either challenje water, and removal of latexbeads for the complete system was irregular and inconsistent with the putativeabsolute pore size.

The data from this study would support the use of filtration of drinkingwater for the removal of protozoan cysts even down to the size range of C.parvum oocysts of ca. 4-pm diameter. Based upon the analysis of the completereverse osmosis bypass system data, it is concluded that a system usingpolypropylene depth filters of 3.0-pm absolute pore size would be capable ofproviding adequate removal of the cyst challenges throughout their effectiveuse life. Although this system appears to be a suitable candidate for the RObypass of Air Force and Marine Corps ROWPUs, pre- or post-disinfection (atnormal field military concentrations) would still be required to removeresidual bacteria and enteric viruses from the prodL-ct water.

REFERENCES

1. Milstead, C.E. 1988. Development, testing, and evaluation of a RO bypassfiltration system for the 1200 gph ROWPU. Final Report P.O. # 0191-J358-1,Separation Systems Technology, Inc., San Diego, CA.

2. Guide Standard and Protorol for Testing Microbiological Water Purifiers,Report of Task Force, U.S. Ervronmental Protection Agency, Criteria andStandards Division, Office oi 'inking Water, Washington, DC 20460, April1987.

3. Waldman, E., S. Tzipori and J.R.L. Forsyth. 1986. Separation ofCryptosporidium species oocysts from feces by using a Percoll discontinuousdensity gradient. J. Clinical Microbiology, 23(l), 199-200.

4. Pall Corporation, personal communication.

21

APPENDIX A

PERFORMANCE OF PREFILTER: 150 MG/L AC FINE TEST DUST ADDED

TABLE Al. RUN NO. I

Time Flow Inlet pressure Outlet pressure Product turbiditymin gpm psig psig NTU

0 0.85 34 32 1630 0.82 34 32 1660 0.82 34 32 1290 0.71 34 30 4.8

120 0.74 34 29 1.4150 0.69 34 25 0.64180 0.66 34 23 0.55210 0.61 34 20 0.55240 0.56 34 17 0.65300 0.53 34 14 0.60330 0.48 34 11 0.67360 0.45 34 9 0.60

TABLE A2. RUN NO. 2

Time Flow Inlet pressure Outlet pressure Product turbiditymin gpm psig psig NTU

0 0.90 34 32 2330 0.87 34 30 8.460 0.79 34 25 2.090 0.63 34 17 1.0

120 0.53 34 12 0.62

22

TABLE A3. RUN NO. 3

Titre Flow Inlet pressure Outlet pressure Product turbiditymin gpm psig psig NTU

0 0.85 34 32 2630 0.82 34 32 2160 0.77 34 31 2090 0.77 34 31 20

120 0.74 34 31 18150 0.74 34 30 16180 0.74 34 29 11210 0.66 34 27 6.5240 0.63 34 24 2.2270 0.61 34 22 1.0300 0.58 34 20 0.57330 0.53 34 18 0.40360 0.50 34 16 0.45390 0.50 34 14 0.35

TABLE A4. RUN NO. 4

Time Flow Inlet pressure Outlet pressure Product turbiditymin gpm psig psig NTU

0 0.85 35 33 1830 0.69 35 33 1860 0.69 ^5 13 1690 0.66 35 33 15

120 0.63 35 32 15150 0.63 35 32 15180 0.63 35 32 15210 0.63 35 32 11240 0.63 35 31 7270 0.59 35 30 6.9300 0.58 35 28 4.3330 0.58 35 26 2.0360 0.56 35 24 1.4390 0.56 35 23 0.4

23

APPENDIX B

GLOSSARY OF TERMS

cfu colony forming unitsgal gallon(s)gph gallons per hourgpm gallons per minuteNCEL Naval Civil Engineering LaboratoryNTU nephelometric turbidity unitsP&ID process and instrumentation diagramPBS phosphate buffered salinepsi pounds per square inchpsig pounds per square inch (gauge)PVC polyvinyl chlorideRO reverse osmosisROWPU reverse osmosis water purification unitSSTI Separation Systems Technology, Inc.TDS total dissolved solidsTOC total organic carbonUSABRDL U.S. Army Biomedical Research and Development LaboratoryUSEPA U.S. Environmental Protection Agency

24

DISTRIBUTION LIST

No. ofCoples

4 CommanderU.S. Army Medical Research and Development CommandATTN: SGRD-RMI-SFort DetrickFrederick, MD 21701-5012

2 Defense Technical Information CenterATTN: DTIC-FDACCameron StationAlexandria, VA 22304-6145

3 CommandantU.S. Army Medical Department Center and SchoolATTN: HSMC-FCFort Sam Houston, TX 78234-6100

2 CommanderU.S. Army Biomedical Research and Development LaboratoryAFrTN: SGRD-UBZ-ILFort DetrickFrederick, MD 21702-5010

1 HQDA (SGPS-PSP)5109 Leesburg PikeFalls Church, VA 22041-3258

1 HQDA (DALO-TSE-W)The Pentagon, Room ID600Washington, DC 20310-0561

1 CommanderU.S. Army Environmental Hygiene AgencyATTN: HSHB-ME-WRAberdeen Proving Ground, MD 21010-5422

1 CommanderU.S. Army Natick Research, Development and Engineering CenterATTN: STRNC-WEBNatick, MA 01760-5018

I CommanderU.S. Army Belvoir Research, Development and Engineering CenterFuel and Water Supply DivisionATTN: STRBE-FSEFort Belvoir, VA 22060-5606

25

CommanderU.S. Army Special Warfare Center and SchoolATTN: ATSU-CD-ML-MFort Bragg, NC 28307-5000

CommanderU.S. Army Quartermaster Center and SchoolATTN: ATSM-CDMFort Lee, VA 23801-5000

CommanderU.S. Naval Civil Engineering LaboratoryCode L-66Port Hueneme, CA 93046

CommanderU.S. Air Force Engineering and Services CenterATTN: DEOPTyndall Air Force Base, FL 32403-6001

26