USE OF UV RADIATION AS AN ALTERNATIVE TO CHLORINE GAS FOR WASTEWATER DISINFECTION.

By Arif Jaffer , Jasem Al-Muaili and Mohammed Al-Moniee

Jaffer is an engineering specialist in the Lab Research and Development Center. He holds a bachelor’s degree in chemical engineering from Oklahoma State University and presented numerous papers at professional international conferences. Al-Muaili is a chemist in Lab Research and Development Center. He holds a bachelor’s degree in chemistry from King Saud University, Riyadh. Al-Moniee is a chemist in Lab Research and Development Center. He holds a bachelor’s degree in chemistry from the University of Toledo, Ohio, USA

ABSTRACT

The current practice of using chlorine gas for the disinfection of effluents at Saudi Aramco Wastewater Treatment plants possesses several safety and environmental concerns. In an effort to eliminate these concerns, Saudi Aramco Engineering Standard has been revised to discourage the use of chlorine gas in wastewater facilities and to consider other alternatives.

This pilot plant study aims to investigate whether the use of Ultra-violet radiation (UV) is an acceptable alternative to chlorine gas or sodium hypochlorite disinfection systems. Sodium hypochlorite systems are safer than chlorine gas but they are less cost effective to install and operate. This paper evaluates UV disinfection process to determine whether it is a viable option for Saudi Aramco wastewater plants. It also evaluates options for controlling the scaling that is expected with high TDS local wastewater and determines the cost effectiveness of this type of disinfection method. The study also attempts to identify and solve other operating problems that are identified during the on-site pilot plant test.

1 · Determine the cleaning frequency for the INTRODUCTION quartz sleeves (Fouling rate). The water industry has relied heavily on the use of chlorine gas to disinfect wastewater treatment plants. Chlorine gas is a very effective The Disinfection Chemistry disinfectant and capable of killing most of the Disinfection in wastewater is a process to pathogens present in water. New environmental inactivate waterborne pathogenic (disease- regulations have arisen that limit the use of producing) bacteria and other harmful chlorination as a major disinfectant process. microorganisms that may be present in the water Toxicity and safety concerns, as well as the (Blatchley et al., 1997,p.1581). The two main requirements for dechlorination are among the disinfection processes are chlorination and UV major limitations of chlorine gas. Because of irradiation. The following is a brief description current regulations, extensive research has been of each process. going on to evaluate alternatives to chlorine gas: Ozonation, UV irradiation, Chlorination chlorination/dechlorination and sodium In the United States and most other countries hypochlorite. worldwide, the use of chlorine and its compounds is a standard disinfection process Currently, the Rahima Sewage Treatment Plant (Isaac, 1996a, p. 47), as a result of its being uses chlorine gas to disinfect wastewater effective, inexpensive and very reliable. treatment effluent. This presents a potential risk Chlorine is the basis of comparison of the to the community. Also, discharging chlorine to effectiveness of other disinfectants. Chlorine is the Tarut bay may harm the marine environment. abundant and can be produced by the electrolysis These two concerns have led to the investigation of aqueous solutions of alkali metal chloride of ultra-violet radiation as an acceptable such as sodium chloride, in the following alternative to chlorine gas. reaction (Austin, 1984, p. 232) : Based upon earlier findings, Engineering Services in cooperation with Community NaCl(aq) + H2O(l) NaOH(aq) + Services initiated a pilot plant study at the 1/2H2(g) + 1/2Cl2(g). Rahima Sewage Treatment Plant. The objectives of the pilot plant study were as follows: Chlorine dissociates in water in the following · Determine the efficiency of UV as a method reaction (Isaac, 1996a, p. 47): of disinfection; + - · Determine the UV dose required to achieve Cl2 + H2O HOCl + H + Cl . the target disinfection level; and Although chlorine gas is effective as a disinfectant, restrictive environmental regulations discourage its use. The new

2 regulation covers, among other things, the Due to the simplicity and effectiveness of the allowable disposal limits, the safety of personnel, technology, the number of UV units in operation and the toxicity of chlorine gas. As a result, the has increased rapidly. According to Lau wastewater purification industry decided to (1997,p. 66), "the number of UV disinfection investigate other technologies such as ozonation systems in operation grew from approximately and UV irradiation. 50 in 1985 to 500 by 1990, and to more than UV Irradiation 1500 by 1995." UV rays are present naturally in sunlight and are UV TECHNOLOGY known to be germicidal. UV can be emitted Improvements in UV Technology artificially by a variety of arcs and incandescent The technology of UV irradiation has been lamps. The UV rays fall between 100 improving since it started commercially in the nanometers (nm) and 400 nm with the ideal mid 1980s. The introduction of MP (medium bactericidal level at 254 nm. pressure) along with high intensity lamps made UV is a physical process where the organism's UV very attractive. Tchobanoglous (Valenti, DNA is altered so that the cells are no longer 1997, p. 83), says that "now, one lamp can do the reproduced. UV does not kill organisms, as work of 20." Studies have also revealed that UV chlorine does, but it prevents their production. irradiation is complying with fecal The water to be disinfected is passed through an coliform limitation on a consistent basis

Figure 1. Ultraviolet radiation spectrum (Adapted from Ultraviolet…, 1998) irradiation chamber. Most of the (Blatchley, 1993, p.353). Microorganisms, such as bacteria, yeast's, and Advantages of UV Technology over viruses are inactivated within seconds of being Chlorine Gas Disinfection exposed to the UV light.

3 The use of UV irradiation technology to disinfect effectiveness with traditional wastewater has increased tremendously during chlorination/dechlorination systems for treating the last 10 years (Loge et al., 1996a, p. 1078). wastewater effluent" (Study Finds…,1998, p. "Ultraviolet (UV) disinfection compares 24). Table 1 summarizes the advantages that UV favorably in terms of efficiency and cost- radiation offers over chlorination.

Table 1. Comparison between UV Technology and Chlorine Gas Disinfection

UV Technology Chlorine Disinfection · Physical process · Chemical process · Environmently acceptable · Toxic, needs dechlorination process · Treatment time 0-30 seconds · Treatment time 0-30 minutes · No safety hazardous ( flammability, and · safety hazardous ( flammability, and explosion) explosion) · Easy to handle and operate · Difficult to handle and operate · None-corrosive · Corrosive

DEFICIENCY OF CHLORINE GAS DISINFECTION Background Transportation of Gas Cylinders Even though the discovery of UV irradiation was Chlorination in wastewater is accomplished made as early as the 1900's, it was through the injection of chlorine gas. Chlorine not until the mid-1980's that this technology was gas is shipped and transported in cylinders. Each used commercially (Linden, 1998, p. 58). The chlorination plant is equipped with storage research of UV technology has progressed in facilities and tools to handle the gas. UV response to the need for an alternative to chlorine irradiation does not involve any chemicals to be gas. The several factors that attributed to shift added to water. George Tchobanoglous (Valenti, researchers and scientists to UV irradiation are 1997, p. 83), described below.

Professor Emeritus of civil and environmental engineering at the , Davis says, "the main advantage UV has over standard disinfection techniques is that the light-

4 based system eliminates the transport and use of 3000 pounds of gas escaped, forming a chlorine chlorine." The transporting and storing of cloud that was five miles long, one mile wide, chlorine gas is not only expensive, but also very and 30 ft. thick, forcing the evacuation of 4000 dangerous because the risk of a gas leak can people" (Voutchkov, 1995, p. 40). never be eliminated. The operation of UV irradiation is far safer than chlorination and requires the least safety Requirement to Dechlorination precautions. The new environmental regulations require for any sewage treatment plants that use chlorine gas CLASSIFICATION OF UV to dechlorinate the water before dumping it into DISINFECTION SYSTEMS a reservoir (Voutchkov, 1995, p.40). If the The two principles of UV disinfection systems reservoir contains marine life, the process of are continuous-wave, low-pressure mercury dechlorination is necessary (Isaac, 1996b, p. 69). vapor lamps (LP) and continuous-wave, medium The process of dechlorination is accomplished pressure mercury vapor lamps (MP) (Hunter, by the addition of other chemicals such as sulfur 1998,p. 41). The LP system is characterized by dioxide. The addition of such a facility is very being monochromatic, and its output is at the expensive and adds about 30% to the cost of peak germicidal range of 253.7 nm (Linden, chlorination (Cairns, 1992, p. 1.). It is believed 1998,p. 58). On the other hand, the MP system that the cost of UV irradiation will be equivalent produces polychromatic output at a range of 220 or even less expensive if the dechlorination to 300 nm and reaches near-infrared (Hunter, process is added. 1998, p. 41). The LP system is used for low to Increased Cost Due to the medium wastewater flows up to 38 million Uniform Fire Code gallons per day (MGD). The application of the MP system is becoming more common Chlorination facilities are required to be especially for high wastewater flows (Linden, equipped with special scrubbers and fire 1998, p. 58). Table 2 summarizes the key differences between LP and MP UV systems. extinguishers, which are extremely costly in case of fire or chlorine gas leaks. "One of the more recent accidents occurred at a water treatment plant in Morristown, Tennessee. Approximately

5 Table 2. Comparison between LP and MP UV System

LP System MP System · Mono chromatic output at 253.7 nm · Polychromatic output at 220-300 nm · About 85% of existing UV system · About 15% of existing UV system · Typical for small to medium flows up · Typical for higher flows to 10 mgd · Hydraulic residence time is 10 to 20 · Hydraulic residence time is 0.5 to 3 seconds seconds seconds under turbulent flow conditions installed UV irradiation units. Existing plants In general, the use of UV systems to treat sewage that either replaced their chlorination system or water has become very popular over the last upgraded their facilities to include UV are not decade. For example, in 1987, the total treated reported in Figure 2. wastewater effluent with newly installed UV equipment was about 250 million gallons per day Within the UV technology, the use of MP has (mgd) compared to 1500 mgd in 1996. The also increased during the last five years. The increase in popularity trend is illustrated in number of MP systems has increased from a

2000 7440 medium pressure systems low pressure systems total UV systems 1500

1000 Millions of gallons per day 500

0 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 Total Year Figure 2. Municipal Wastewater Effluent treated with Newly Installed UV disinfection Facilities, 1987-96 (Adapted from Linden, 1998, p. 58)

Figure 2 which shows the total effluent treated couple of plants in 1993 to almost forty-five with new UV facility for the years from 1987 to systems in the year 1996. The sudden increase is 1996. Over a period of ten years, 7440 mgd of wastewater has been disinfected with newly

6 attributed to results which demonstrate that MP concentrations between 0 and 250 mg/L, units are more effective than LP units in treating decreasing the overall available UV radiation for low quality effluents (Blatchley III, 1994, p. disinfection" (Linden et al., 1998, p. 221). 363). Figure 3 shows the number of UV It is very important to stop the operation of the disinfection systems installed of both LP and MP UV unit from time to time to clean the lamps during the years 1990 to 1996. Extensive (Acher et al., 1997, p. 1403). UV dose is a

low pressure systems medium pressure systems

160

140

120

100

80 instaled 60

40

Number of UV disinfectin systems 20

0 1990 1991 1992 1993 1994 1995 1996 Year Figure 3. Newly Installed UV Disinfection Facilities, 1990-96 (Adapted from Linden, 1998, p. 58) function of intensity and time and is calculated Improvement has been achieved in MP using the following equation: technology, and as a result, many new plants will select MP units over the LP. Of course, design D = I X t consideration will dictate the final assessment. where LIMITATIONS OF UV IRRADIATION D is UV dose, measured in mW.s/cm2, Background I is average intensity of UV light in mW/ cm2, Even though UV is a very attractive alternative t is residence or exposure time in seconds (s). to chlorination, it has some limitations such as (Loge et al., 1996a, p. 1078) Appendix A shows the potential of lamp fouling, lack of residual the relative sensitivity of various microbes. effect, inability to inactivate certain protozoa Finding the required optimum dose is a very pathogens, and safety issues related to exposure complex process and depends on a variety of to UV irradiation. The following is a brief factors such as water quality and flow rates. description of each item. Appendix B illustrates a numerical example that Potential of Lamp Fouling: Most wastewater details the steps considered in the design of an contains particulate species that may cause UV disinfection system. The assumption used in fouling of the UV system. Appendix B is shown in Appendix C. "Particulate in wastewater absorbed and scattered UV light at suspended solids

7 Fouling of the system will dramatically affect the 1997, p.16) as shown in Figure 4. Generally, intensity better water of UV 100 quality in lamps, 90 terms of which in 80 turbidity, turn will 70 color, and affect the 60 total overall suspended 50 performa solids, % Lamp Fouling 40 nce of indicated 30 the plant. higher 20 Many intensity and 10 scientists consequently 0 have 0 20 40 60 80 100 120 140 160 180 200 a higher UV Elapsed Time After Lamp Cleaning, Days studied dose for the the potential of UV lamp same flow. Each plant has to correlate its own data since the quality of water varies from place to place and from time to time. The main concept is consistent. Fouling will occur and a lamp cleaning protocol has to be established and performed. The intensity is also related to the number of UV lamps required in a specific plant. As the intensity increases, the number of lamps exponentially decreases. For example, 65% intensity requires half the number of lamps with 50% intensity (Mann et al., 1992, p. 80).

Figure 4. Percent Lamp Fouling as a Function of Elapsed Time after Lamp Cleaning (Fouling Curve) (Data adapted from Oppenheimer et al., 1997, p. 17) fouling and several experiments have been conducted to determine the relationship between lamp fouling and quality of water. In one experiment, the lamp fouling was correlated with the elapsed time in days (Oppenheimer et al.,

8 Safety Issues Related to Exposure to UV Irradiation In terms of safety, the only shortcoming of UV Technology is over exposure to the radiation. "Over exposure to UV radiation can affect No Residual Effect Disinfectant unprotected skin. The short-term effect from Unlike chlorine gas, UV produces no residual moderate exposure reddens the skin. Excessive effect within the effluent (Lau, 1997, p. 65). exposure may cause blistering or bleeding. The Having residual can be both beneficial and eyes are at most risk from UV radiation". (Mann harmful at the same time. Residual disinfectant et al., 1992, p. 81). Generally, the safety issues assures that no harmful microorganisms are related to UV are least important compared to present in the water. However, in the case of chlorination. chlorination, the residual chlorine could react with the organic contaminants in the wastewater OPERATIONAL PROCEDURES and form toxic compounds. The manufacturers The operational procedures used in pilot testing of UV irradiation design their units to treat the the Trojan UV disinfection system are presented worst case scenario and worst possible water and discussed as follows: quality to ensure a complete disinfection and Operations eliminate the requirements of residuals. It is During the entire testing period (August 29,1998 very important that the UV manufacturers - December 20,1998), the system was operated provide their own UV dose calculation since it is 24 hours a day with periodic grab sampling. impossible to directly measure the dose During Phase 1, the quartz tubes were wiped (Moreland et al., 1998, p. 47). cleaned Saturday through Wednesday every Limitation Against Certain Types of Protozoa week. A 5% solution of "Lime-A-Way", a Pathogen detergent containing phosphoric and nitric acid Certain types of microorganisms in wastewater was applied with a soft cloth to remove any are not inactivated by UV irradiation. The accumulated solids and scale buildup. During mechanism is not fully understood, and many Phase 2 (October 18- December 20) no cleaning scientists and UV equipment manufacturers are was performed. investigating this subject. In general, these Wastewater temperature, UV intensity (measured microorganisms are not common in wastewater by probes), and lamp age were recorded at the and therefore are not a potential hazard to most time of sampling. Transmittance and flow rates of the wastewater facilities. In drinking water were recorded on site daily. applications, this issue requires careful Sample Collection assessment. Secondary wastewater samples were collected from the inlet and outlet of the UV pilot plant on a regular basis. Samples were collected in amber

9 polyethylene bottles to eliminate effects of light and buffered (Method 9050) according to during transport and processing. Samples were Standard Methods, 17th Edition. also collected after chlorination to compare the results with UV. Particle Size Analysis Laboratory Processing Particle size distribution measurements were Samples for microbiological tests were made to characterize the solids in the secondary immediately placed in an ice chest, and upon effluent. A Coulter Counter Multisizer 11 with return to the laboratory, they were placed in a apertures of 30, 100, and 200 mm was used to refrigerator to halt any biological activity. The measure the particles present in the wastewater. maximum elapsed time between sampling and Details of the particle size analysis procedure can refrigeration was 60 minutes. be found elsewhere (Darby,1988). The influent and effluent samples were analyzed Determination of UV Dose for various water quality parameters. A Hach UV dose was calculated using equation below Model 2100 turbidimeter was used to measure D= I*T turbidity. Total suspended solids were measured Where D= UV dose, W-s/sq.cm. according to Standard Methods, 17th Edition I= intensity of the germicidal UV energy, (Method 2540D). Percent transmittance was W/sq.cm. measured at 253.7 nm with a Perkin-Elmer t= exposure time, sec. model Lambda 4B UV/VIS spectrophotometer. Experimental Design and Organism Testing The size of the total bacterial population was Procedure determined by Heterotrophic Plate Count The experimental work conducted in this study (Method 9215). Neat and diluted samples were involved a UV 3000 pilot plant testing at the spread-plated in duplicate on R2A agar. Agar Rahima Sewage Treatment Plant. The UV3000 plates were incubated at 37 degrees C until no system featured low-pressure ultra violet (UV) further increases in colony numbers were lamps arranged horizontally in a stainless steel observed (normally 5-7 days). A low power- channel. The specific model tested was dissecting microscope was used to count the UV3150K-PTP. It contained two banks of 3 numerous microcolonies that appeared on the modules each, and each module held 2 UV plates. lamps. The banks were installed in series. The The multiple-tube fermentation technique was effluent was pumped at a measured flow rate used to enumerate fecal and E.coli to according through the channel. The UV dose applied was a Standard Methods, 17th Edition (Method 9221). product of reactor intensity and exposure time. A minimum of 3 dilutions was used for each Exposure time is a function of the flow rate past sample with 5 tubes per dilution. All glassware the UV lamps. Reactor intensity is a function of and sample bottles were autoclaved prior to use. lamp age, effluent transmittance and sleeve Dilution water was autoclaved (Method 9020)

10 fouling. Photographs of the UV system are · Phase 2- Determine the sleeve cleaning shown in the Appendix. frequency, approximately 8 weeks Experimental Design Phase 1. Disinfection Efficiency The UV disinfection study was conducted in two The objective of this phase was to determine the phases and the objectives were as follows: target dose to be applied. By varying the flow · Demonstrate the efficiency of UV as a rate through the pilot unit, the effective dose method of disinfection delivered was varied and this was plotted against · Determine the UV dose required achieving bacteriological counts coming out of the unit. In the target disinfection level for Rahima order to determine the flows, at which the pilot secondary wastewater. plant should be operated, the disinfection · Determine the cleaning frequency required standards were defined. The standard defined for the quartz sleeves. (Fouling rate) was that fecal and E.coli should be less than 200 Preliminary Phase MPN per 100 ML of sample. Transmittance and During the preliminary phase of the study, many Total Suspended Solids levels were determined. meetings were held between the supplier, The flow never exceeded 100GPM as that would proponent, EPD and LR&DC to discuss the have short-circuited the effluent over the top experimental procedures. In addition, operating sleeves since the water layer was greater than 1 inch. The following steps were implemented characteristics of the UV disinfection system during phase 1 of the test. were evaluated. Fecal and E.coli were selected as the indicator organism to test the performance of the UV · The unit was operated with both banks and disinfection system. at the following flow rates : 50,60, 75 and 100 GPM and with samples taken at each Test Procedure flow rate. The UV pilot plant was located near the final · Prior to daily sampling the sleeves were effluent channel. A submersible pump was cleaned using a mild inorganic acid. placed in the basin upstream of the present · The pump always started before the lamps chlorination injection system. Effluent was were turned on. pumped through the UV pilot plant at selected flow rates to provide a range of UV doses. · The unit operated on a continuous basis i.e. 24 hours a day, hence there was no need to Installing a flow meter at the discharge side of wait for the lamps to warm up before taking the pilot controlled the flow rate and the flow a sample. Samples were taken from the rates were monitored through the monitoring inlet/outlet of the UV unit and from the screen. channel after chlorination. The study was divided into two phases: · The data collected was used to determine the · Phase 1- Determine the disinfection UV dose required for the plant effluent to efficiency, duration approximately 6 weeks. achieve a target level of disinfection.

11 · All the results and graphs are included in the · All parameters were recorded and are Appendix included in the Appendix. · The data collected shows 57mWs/cm2 is the · The test ended after 8 weeks (October 18- target dose for the Rahima secondary December 20,1998) of operation and still the wastewater plant effluent. disinfection limit did not exceed 200 MPN Phase 2. Fouling test/Cleaning per 100 ML of sample. The fecal and E.coli Frequency numbers were mostly below 2 MPN per 100 ML sample. Fouling or coating on the lamp sleeves · The UV dose at the end of the test was 21.5 effectively blocks and decreases the UV intensity mWsec/sq.cm. available for disinfection. Upstream processes · The fine milky film (CaCO ) observed on and the presence of hardness and iron present in 3 the sleeves was analyzed in the laboratory the influent determined the amount and rate of and the results are included in the Appendix. fouling. The fouling rate is site specific, and therefore, it was important that we incorporate · The fecal and E.coli data are graphed versus this phase to our test protocol. time in days. The effluent was pumped continuously through CONCLUSION the pilot plant for 8 weeks and microbiological Evaluation of alternatives to chlorination tests were conducted twice a week and the fecal revealed that UV radiation is the most viable and E.coli. Levels were below the agreed range option for wastewater treatment disinfection. In of 200. The intensity level had decreased from many applications, UV radiation is more 7.6 mW/sq.cm2 to 2.8 mW/sq.cm2. After the effective and less expensive than chlorination. cleaning on December 20,1998 the intensity The use of UV technology will eliminate the reading came back to 7.2 mW/sq.cm2. A slight safety hazards and toxicity concerns created by decrease in intensity was expected due to the age chlorination, as well as the requirement of of the bulbs (approximately 3000 hours). The adding a new dechlorination facility. Finally, the following actions were taken during the second implementation and operation of UV radiation is phase of the test: simple and requires few operators and low maintenance as compared to a chlorination · Only one bank was operated at 100 GPM facility. and the sleeves were cleaned at the Since the characteristics of wastewater vary from beginning of the test on October 18, 1998. place to place and from time to time, it is · The pilot plant was operated continuously extremely important to run a pilot plant until the end of the test. evaluation study prior to applying UV · Twice a week, grab samples were taken technology. Based on the pilot plant data, UV from the UV influent and effluent for UVT, technology is recommended as the alternative to TSS, Intensity, Particle size count, influent chlorine gas or sodium hypochlorite at Saudi and effluent coliform counts. Aramco wastewater treatment plants that do not

12 need to maintain a chlorine residual in their effluent. This technology has the potential to provide safer, more effective disinfection at a lower cost than is possible through the use of alternate disinfection methods.

ACKNOWLEDGMENTS

The authors wish to thank the Saudi Arabian Ministry of Petroleum and Mineral Resources and the Saudi Arabian Oil Company (Saudi Aramco) for granting their permission to publish this paper.

This study was made possible by a joint effort between Lab R&D Center and Environmental Protection Department for the Community Services (Ras Tanura Community Services Department and Dhahran Utilities Department). The authors acknowledge the assistance and efforts contributed in carrying out this study by many personnel and units in both departments.

13 BIBLIOGRAPHY Disinfection", Trojan Technology, Inc., Ontario, Canada, September 1992. 1. Austin, George T., 1984, Sherve's Chemical Process Industries. McGraw-Hill Book 8. Farrell, Ann, Craig, Doug, and Putnam, company: New York, New York. Lynne, "UV Disinfection Meets Strict California Standards", Public Works, 2. Acher, A., Fisher, E., Turnheim, Roni, and October 1994. Manor, Y., "Ecologically Friendly Wastewater Disinfection Techniques", 9. Hunter, Gary L., O'Brien, Walter J., Hulsey, Water Research, Vol. 31, No. 6, 1997. Robert A., Carns, Keith E., and Ehrhard Ray, "Emerging Disinfection Technologies", 3. Blatchley III, Ernest R., "Disinfection and Water Environment and Technology, June Antimicrobial Processes", Water 1998. Environment Research, June 1994. 10. Isaac, Russell A., "Disinfection Chemistry", 4. "Disinfection and Antimicrobial Processes", Water Environment & Technology, Water Environment Research, June 1993. September 1996a. 5. Blatchley III, Ernest R., Bastian, Chad, Duggirala, Ravi K., Alleman, James, E., 11. "Disinfection Dialogue", Water Moore, Mark, and Schuerch, Peter, Environment and Technology, May 1996b. "Ultraviolet Irradiation and Chlorination/Dechlorination for Municipal 12. Lau, Peter J., "Applying Disinfection Wastewater Disinfection: Assessment of Alternative to Wastewater Treatment", Performance Limitations", Water Pollution Engineering, September 1997. Environment Research, Vol. 68, No. 2, 1996. 13. Linden, Karl G., “UV Acceptance”, Civil Engineering, March 1998. 6. Blatchley III, Ernest R., Bruce A. Hunt, Ravikrishana Duggirala, John E. Thompson, 14. Linden, Karl G. and Darby, Jeannie, L., Jiangong Zhao, Tawfic Halaby, Ronald L. "Ultraviolet Disinfection of Marginal Cowger, Christopher M. Straub and James Effluents: Determining Ultraviolet E. Alleman, "Effect of Disinfectants on Absorbance and Subsequent Estimation of Wastewater Effluent Toxicity", Water Ultraviolet Intensity", Water Environment Research, Vol. 31, No. 7, 1997. Research, Vol. 70, No. 2, 1998.

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15 APPENDICES

Appendix A. Comparative Sensitivity of Microbes to UV Disinfection (Adapted from Cairns, 1996, p. 16)

Microbe Dose (mW s/cm2) For 90% Reduction in Counts Bacteria Bacillus anthracis 4.5 Bacillus anthracis spores 54.5 Bacillus subtilus spores 12.0 Clostridium tetani 12.0 Corynebacterium diptheriae 3.4 Escherichia coli 3.2 Legionella pneumophila 1.0 Micrococcus radiodurans 20.5 Mycobacterium tuberculosis 6.0 Pseudomonas aeruginosa 5.5 Salmonella enteritidis 4.0 Salmonella paratyphi 3.2 Salmonella typhi 2.1 Salmonella typhimurium 8.0 Shigella dysenteriae 2.2 Staphlococcus aureus 5.0 Streptococcus faecalis 4.4 Streptococcus pyogenes 2.2 Vibrio comma 6.5 Viruses F-specific Bacteriophage 6.9 Influenza Virus 3.6 Poliovirus 7.5 Rotavirus (Reovirus) 11.3 Yeasts Saccharomyces cerevisiae 7.3 Moulds Penicillium requeforti 14.5 Aspergillus niger 180 Protozoa various 60-200

16 17 18 Appendix C. Assumption Used in the Design of UV Disinfection Systems (Loge, et al., 1996, p. 912)

19