Linden Laboratory Civil, Environmental and Architectural Engineering University of Colorado, Boulder. November 9,

Transcription

1 Laboratory MS- 2 Coliphage Testing of the SteriPEN Adventurer Opti against the US EPA Guide Standard and Protocol for Testing Microbiological Water Purifiers Linden Laboratory Civil, Environmental and Architectural Engineering University of Colorado, Boulder November 9, 2015 Karl.linden@colorado.edu 1

2 Introduction The SteriPEN Adventurer Opti, a handheld water purification device that uses ultraviolet (UV) light to disinfect water, was challenge tested with MS- 2 coliphage in the laboratory. The SteriPEN uses a low pressure UV bulb which emits light at 254 nm. The UV light is absorbed by an organism s DNA, inactivating the organism from further replication (1). The SteriPEN is marketed as a portable water treatment device to be used in the outdoor and backpacking space whereby one liter of water can be batch treated in a one liter container by swirling the SteriPEN in the source water. The device includes a simple button which is pushed once to trigger a 90 second treatment time of one liter of water or twice to trigger a 45 (48) second treatment time of half a liter of water. Additionally, the device includes a sensor that only allows the UV light to become illuminated when the device is submerged in water. Test Organism The challenge organism was the MS- 2 coliphage. MS- 2 was chosen because it is a commonly used indicator organism in UV validation testing. MS- 2 has the advantage of being easily propagated at high concentrations and thus can demonstrate high log reductions (2). Methods The SteriPEN was tested in two test waters, a general test water and a challenge test water which met the United States Environmental Protection Agency s Guide Standard and Protocol for Testing Microbiological Purifiers (3) (see Table A1 in Appendix). The general test water was dechlorinated, activated carbon treated tap water. The challenge water was this same general test water but augmented to meet the guidelines of the EPA protocol. Specifically, EPA Test Water #1 and EPA Test Water #4 were used. The characteristics of both waters as tested are shown in Table 1 below. Temperature and ph was measured using an Orion 8157BNUMD probe attached to a ThermoScientific Orion Star A211; ph adjustment was not necessary. TOC, adjusted using glucose, was measured using a Shimadzu TOC Analyzer. Turbidity and UV absorption was adjusted by addition of Kaolin clay. Turbidity was measured with a Hach 2100N Turbidimeter and UV absorption (1 cm cuvette) was measured with a Cary 100 Spectrophotometer. TDS was adjusted through the addition of NaCl (lab grade) and measured gravimetrically. Photos of the test waters in the exposure vessels are presented in Figure 1. 2

3 Table 1. Actual Test Water Characteristics. Parameter General Test Water Chlorine Residual (ppm) None (<0.05) ph 7.18 Total Organic Carbon (mg/l) 0.23 (<1.0) Turbidity (NTU) 0.20 (<0.5) o Temperature ( C) 22 Total Dissolved Solids (mg/l) 100 UV Absorbance (1/cm) UV Transmittance (%) 99.9 Note: requirements for test waters water quality are in Table A1. (3) Challenge Test Water None (<0.05) Figure 1. General test water (left) and challenge test water (right) MS- 2 coliphage was acquired from GAP EnviroMicrobial Services Ltd. at a stock concentration of approximately 1012 PFU/mL. The UV dose response curve for this MS2 stock is presented in the Appendix in Figure A1. A batch of approximately ten liters of both the general water and challenge water were spiked with approximately ten ml of the MS- 2 to obtain a starting concentration around 109 PFU/mL. 3

4 Three SteriPENs were then tested three times in each water, whereby one liter of water was transferred to a 1000 ml Pyrex beaker and the SteriPEN was used to treat the water. The UV dose was administered by placing the device in the water and pushing the button once to illuminate the UV light. The water was then continuously stirred with the device at a moderate speed for the duration of the test. The general water was treated with one 90- second dose and the challenge water was treated with two- 90 second doses. 50 ml samples of each control and treated sample were then enumerated to determine the MS- 2 coliphage concentration using methods following EPA method 1602 and Standard methods 9224E (4). Each sample was plated in duplicate and plaques counted to determine MS- 2 concentration. Results Tables 2 and 3 summarize MS- 2 coliphage results of the general test water treated for one- 90 second dose and the challenge water tested for two- 90 second doses. Table 2. General test water MS- 2 coliphage results. Control (PFU/mL) Treated General Water Log Reduction (PFU/mL) SteriPEN #1 1.04x x SteriPEN #2 1.12x x SteriPEN #3 9.65x x Average 3.13 Table 3. Challenge test water MS- 2 coliphage results. Control (PFU/mL) Treated Challenge Water Log Reduction (PFU/mL) SteriPEN #1 1.09x x SteriPEN #2 1.29x x SteriPEN #3 1.16x x Average 5.77 The treated values are an average of triplicate individual experiments, while the control values are three individual measurements, corresponding to each experiment, taken over the course of the testing from each batch of water. These data are also plotted in Figure 2. 4

5 Log Reduction General Water (90 Seconds) 5.77 Challenge Water (180 seconds) Figure 2. MS- 2 Coliphage Log Reduction for General and Challenge Test Waters. Conclusion The SteriPEN achieved a 3.13 log reduction (99.926%) of the general test water with a single 90- second dose and a 5.77 log reduction ( %) of the challenge test water with two 90- second doses. Providing two doses of the SteriPEN to the challenge water proved effective in MS- 2 inactivation, even with the decreased water quality. Comparable results were demonstrated in a similar study whereby a log reduction of was measured with the general test water and a log reduction of was measured with the challenge test water (5). The sensitivity of the MS2 used in this testing was determined in a separate set of experiments. Based on these results the general test water was exposed to an approximate UV dose of 68 mj/cm 2 and the challenge test water was exposed to a dose of about 155 mj/cm 2. The testing conducted on both general test water and challenge test water indicates that SteriPEN meets the requirements set forth by the U.S. Environmental Protection Agency (EPA) and is adequate for the inactivation of bacterial, viral, and protozoan pathogens in drinking water. The EPA Guide Standard and Protocol for Testing Microbiological Water Purifiers (3) requires a minimum 6- log reduction/inactivation of bacteria, 4- log reduction/inactivation of viruses (rotavirus and poliovirus), and 3- log reduction/inactivation of protozoan (Giardia) cysts. Based on well established data in the peer reviewed literature (6) the inactivation of MS2 coliphage at the levels reported herein for both testing scenarios meet and exceed 5

6 all the requirements set forth in the EPA Guide Standard and Protocol for Testing Microbiological Water Purifiers. References 1. Ultraviolet Light Disinfection Technology in Drinking Water Application An Overview. United States Environmental Protection Agency, Office of Water. EPA 811- R September, Ultraviolet Disinfection Guidance Manual. United States Environmental Protection Agency, Office of Water, Washington, DC., USEPA - Task Force Report. Guide Standard and Protocol for Testing Microbiological Water Purifiers. United States Environmental Protection Agency, Registration Division, Office of Pesticide Programs and Criteria and Standards Division, Office of Drinking Water, Washington, DC., Method 1602: Male- Specific (F+) and Somatic Coliphage in Water by Single Agar Layer (SAL) Procedure. United States Environmental Protection Agency EPA 821- R , Testing of SteriPEN, a Portable Ultraviolet Light Water Purifier, Using MS- 2 Coliphage. A&L Laboratory Inc., Report to Hydro- Photon Inc., Hijnen, W., Beerendonk, E., and Medema, G. Inactivation Credit of UV Radiation for Viruses, Bacteria, and Protozoan Cysts in Water. Water Research, 40,

7 Appendix Table A1. Required physical and chemical characteristics of test waters 7.0 MS2.LP.UV.dose.response. curve Log.Inactivation. (Log.Co/C) UV.Dose.(mJ/cm2) Figure A1. UV dose response curve for the MS2 coliphage stock used in this study. 7