Antimicrobial Resources for Disinfection of Potable Water Systems for Future Spacecraft

As human exploration adventures beyond low earth orbit, life support systems will require more innovation and research to become self-sustaining and durable. One major concern about future space travel is the ability to store and decontaminate water for consumption and hygiene. This project explores materials and technologies for possible use in future water systems without requiring point-of-use (POU) filtering or chemical additives such as iodine or silver that require multiple doses to remain effective. This experimentation tested the efficacy of a variety of antimicrobial materials against biofilm formation in a high shear CDC Biofilm Reactor (CBR) and some materials in a low shear Drip Flow Reactor (DFR) which(also utilizes ultra violet light emitting diodes (UVLEDs) as an antimicrobial resource. Most materials were tested in the CBR using the ASTM E 2562-07 1method involving the Pseudomonas aeruginosa and coupon samples that vary in their antimicrobial coatings and surface layer topographies. In a controlled environmental chamber (CEC), the CBR underwent a batch phase, continuous flow phase (CFP), and a harvest before analysis. The DFR portion of this experimentation was performed in order to assess the antimicrobial capabilities of ultraviolet-A LEDs (UV-A) in potable water systems. The ASTM E 2647-08 was modified in order to incorporate UV-A LEDs and to operate as a closed, re-circulating system. The modified DFR apparatus that was utilized contains 4 separate channels each of which contain 2 UV-A LEDs (1 chamber is masked off to serve as a control) and each channel is equipped with its own reservoir and peristaltic pump head. The 10 DFR runs discussed in this report include 4 initial experimental runs that contained blank microscope slides to test the UVA LEDs alone, 2 that incorporated solid silver coupons, 2 that utilized titanium dioxide (Ti02) coupons as a photocatalyst, and 2 runs that utilized silver coated acrylic slides. Both the CBR and DFR experiments were analyzed for microbial content via heterotrophic plate counts (HPC) and acridine orange direct counts (AODC). Ofthe materials used in the CBR, only two materials performed as anti~icrobials under high shear conditions (a reduction of 5 or more logs) showing a>7 log reduction in viable microbes

Elimination of micro-organisms in water treatment

Clean water supply and sanitation are regarded as major milestones in medical advances since the 19th century. Production and control of microbiologically safe drinking water has been an important challenge for the drinking water industry ever since. Based on recent progress in scientific literature the group of emerging waterborne pathogens has been changed and extended compared to well known pathogenic diseases in the early days (Cholera, Typhus). Epidemiological studies and outbreak reports have identified persistent protozoa Cryptosporidium and Giardia, but also bacteria such as Campylobacter and pathogenic E. coli and enteroviruses as waterborne pathogens. Quantitative Knowledge on dose-response for these pathogens enabled the introduction of a health based target in microbiological water quality control to minimize the risk of infection. In this thesis studies are presented aimed at quantifying the elimination of pathogenic micro-organisms in water treatment processes. Direct monitoring of these pathogens is not feasible. Monitoring of faecal indicator bacteria E. coli and spores of sulphite-reducing clostridia as process indicators susceptible and resistant to disinfectants in water treatment have been explored as an alternative method. The detection limit of the standard enumeration method for these bacteria was decreased for that reason. Additional methods were required for the water treatment processes slow sand filtration, surface water infiltration and UV disinfection and also for validation of the use of both bacteria as process indicators for elimination of pathogens. Elimination of multiple pre-cultured micro-organisms by disinfection and filtration processes is assessed in challenge tests and from literature studies at different scales. These data are compared with the elimination of indigenous organisms. On the basis of the results of these studies a generic methodology is proposed to assess the elimination capacity of the water treatment of a drinking water facility as input for the mandatory Quantitative Microbial Risk Analysis to evaluate the health based target for safe drinking water introduced in the revised legislation

Elimination of micro-organisms by water treatment processes : a review

The Dutch Drinking Water Decree prescribes that drinking water companies should demonstrate that their drinking water is microbiologically safe by performing a quantitative microbial risk assessment (QMRA). The required level of safety is a risk of infection of 10-4 per person per year. Such a QMRA requires knowledge about (i) the concentration of pathogens in source water and (ii) the efficacy of water treatment to eliminate these pathogens. Consequently, there is a need for a scientific database with the elimination capacity of all relevant processes used in drinking water treatment for viruses, bacteria and pathogenic protozoa. In the joint research program of the Dutch Drinking water Companies (BTO-programme) a project was defined to create such a database. An increasing amount of knowledge about the microbiological efficacy of drinking water treatment is published in the literature. This literature is collected and evaluated. Many publications describe experiments on the elimination of micro-organisms that are conducted in the laboratory under well-defined conditions with lab-strains of micro-organisms. Experience of Kiwa and of many others show that the efficacy of (well-controlled) full-scale treatment processes is usually lower than expected from a direct extrapolation of laboratory experiments. This can be due to several factors, such as the variability of the conditions in practice (feed water quality, temperature etc.), hydraulic differences between well-mixed laboratory vessel and a large flow-through reactor and the difference between micro-organisms in the laboratory and in the environment (survival state, attachment to particles etc.). This does not disqualify laboratory experiments. These provide a first impression of the efficacy of a process and in some cases data collection of full-scale conditions is not possible. Furthermore, for disinfection processes these studies are necessary to assess dose-response curves for selected pathogenic micro-organisms under standardised conditions. In addition laboratory experiments are needed to study the effect of conditions such as temperature, pH, turbidity etc. on the efficacy of a process. Combining these results with full-scale observations will optimise the process of risk assessment. The overall aim of this review was to produce a default value for the Microorganism Elimination or Inactivation Credit (MEC or MIC) of full-scale treatment processes and a description of the effect of water quality parameters and process control parameters on the elimination or inactivation capacity. The literature data are valued according to their representation of full-scale conditions. - For physical processes the calculated default value of MEC is weighted on the basis of the resemblance with full-scale conditions. - In the dose requirement table described for certain MIC values of a disinfection process, effects of microbial and process conditions on the dose-response curves assessed for spiked and pre-cultured organisms are included. Third edition in 2007 The report describes the state-of-the-art and will be updated periodically to incorporate the progress in research. In the last and second edition the literature on conventional treatment (coagulation and floc-removal plus rapid granular filtration) was evaluated and the chapters on coagulation and flocremoval, slow sand filtration and UV disinfection were updated. In the third edition a chapter on rapid granular filtration is added and the chapter on slow sand filtration was updated

Microbial elimination capacity of conventional water treatment for viruses, bacteria and protozoan (oo)cysts

In the process of Quantitative Microbial Risk Analysis prescribed by the Dutch Drinking Water Decree quantitative information about the elimination capacity of water treatment is necessary. Site specific data can be collected by monitoring the removal of surrogates like bacteriophages, indicator bacteria and spores. Spores of sulfite-reducing clostridia may serve as surrogate for persistent protozoan (oo)cysts. But this is not possible for all locations or processes. Alternative strategies are pilot plant studies or literature reviewing. In the current paper the latter has been explored for conventional treatment. A standard method was developed to evaluate quantitative data from literature and applied to establish the Microbial Elimination Capacity (MEC) of conventional treatment and the individual processes, coagulation/floc-removal and rapid granular filtration. With these results QMRA can be performed for sites with no or debatable quantitative data on micro-organism removal by site specific processes. Further studies are necessary to develop a standard method to include the observed variation of MEC in the calculation of the uncertainty level of the infection risk level assessed in the QMRA-process

Regrowth of bacteria on assimilable organic carbon in drinking water

Regrowth of bacteria on organic compounds in drinking water during distribution may result in a significant deterioration of water quality. The extend of regrowth as well as the nature of the involved bacteria depend on the concentration and types of organic compounds serving as sources of carbon and energy for growth. The concentration of these assimilable organic carbon (AOC) compounds in drinking water can be determined by growth measurements with pure cultures of selected bacteria. These organisms are added to water samples which have been heated at 60° C for 30 minutes to inactivate the bacteria which are originally present. Generally strain (P17) of the nutritionally versatile species Pseudomonas fluorescens is applied for AOC determination. The AOC concentration is calculted from the maximum colony count of this organism grown in the sample, using its yield value on acetate. A Spirillum species, strain NOX, is used for determining the concentration of carboxylic acids (including oxalate). The concentration of starch-like compounds is assessed by growth measurements with a Flavobacterium species strain S12, which is specialised in the utilization of maltose- and starch- like compounds. AOC concentrations of drinking water usually are only a small proportion of the total concentration of dissolved organic carbon. Biological processes during bank filtration, rapid san filtration, GAC filtration and slow sand filtration reduce the AOC concentration. Ozonation clearly increases the AOC concentration (mainly carboxylic acids). Observations in practical situations in the Netherlands revealed that regrowth is limited when AOC concentrations are below 10 µg of acetate-C eg/l. AOC release from plumbing materials should be prevented by application of materials which have been tested for growth-promoting properties

Inactivation credit of UV radiation for viruses, bacteria and protozoan (oo)cysts in water: a review

UV disinfection technology is of growing interest in the water industry since it was demonstrated that UV radiation is very effective against (oo)cysts of Cryptosporidium and Giardia, two pathogenic micro-organisms of major importance for the safety of drinking water. Quantitative Microbial Risk Assessment, the new concept for microbial safety of drinking water and wastewater, requires quantitative data of the inactivation or removal of pathogenic micro-organisms by water treatment processes. The objective of this study was to review the literature on UV disinfection and extract quantitative information about the relation between the inactivation of micro-organisms and the applied UV fluence. The quality of the available studies was evaluated and only high-quality studies were incorporated in the analysis of the inactivation kinetics. The results show that UV is effective against all waterborne pathogens. The inactivation of micro-organisms by UV could be described with first-order kinetics using fluence-inactivation data from laboratory studies in collimated beam tests. No inactivation at low fluences (offset) and/or no further increase of inactivation at higher fluences (tailing) was observed for some micro-organisms. Where observed, these were included in the description of the inactivation kinetics, even though the cause of tailing is still a matter of debate. The parameters that were used to describe inactivation are the inactivation rate constant k (cm2/mJ), the maximum inactivation demonstrated and (only for bacterial spores and Acanthamoeba) the offset value. These parameters were the basis for the calculation of the microbial inactivation credit (MIC=“log-credits”) that can be assigned to a certain UV fluence. The most UV-resistant organisms are viruses, specifically Adenoviruses, and bacterial spores. The protozoon Acanthamoeba is also highly UV resistant. Bacteria and (oo)cysts of Cryptosporidium and Giardia are more susceptible with a fluence requirement of <20 mJ/cm2 for an MIC of 3 log. Several studies have reported an increased UV resistance of environmental bacteria and bacterial spores, compared to lab-grown strains. This means that higher UV fluences are required to obtain the same level of inactivation. Hence, for bacteria and spores, a correction factor of 2 and 4 was included in the MIC calculation, respectively, whereas some wastewater studies suggest that a correction of a factor of 7 is needed under these conditions. For phages and viruses this phenomenon appears to be of little significance and for protozoan (oo)cysts this aspect needs further investigation. Correction of the required fluence for DNA repair is considered unnecessary under the conditions of drinking water practice (no photo-repair, dark repair insignificant, esp. at higher (60 mJ/cm2) fluences) and probably also wastewater practice (photo-repair limited by light absorption). To enable accurate assessment of the effective fluence in continuous flow UV systems in water treatment practice, biodosimetry is still essential, although the use of computational fluid dynamics (CFD) improves the description of reactor hydraulics and fluence distribution. For UV systems that are primarily dedicated to inactivate the more sensitive pathogens (Cryptosporidium, Giardia, pathogenic bacteria), additional model organisms are needed to serve as biodosimeter

Inactivation credit of UV-radiation for viruses, bacteria and protozoan (oo)cysts: a review (THESIS VERSION)

UV disinfection technology is of growing interest in the water industry since it was demonstrated that UV radiation is very effective against (oo)cysts of Cryptosporidium and Giardia, two pathogenic micro-organisms of major importance for the safety of drinking water. Quantitative Microbial Risk Assessment, the new concept for microbial safety of drinking water and waste water, requires quantitative data of the inactivation or removal of pathogenic micro-organisms by water treatment processes. The objective of this study was to review the literature on UV disinfection and extract quantitative information about the relation between the inactivation of micro-organisms and the applied UV fluence. The quality of the available studies was evaluated and only high-quality studies were incorporated in the analysis of the inactivation kinetics. The results show that UV is effective against all waterborne pathogens. The inactivation of micro-organisms by UV could be described with first-order kinetics using fluence-inactivation data from laboratory studies in collimated beam tests. No inactivation at low fluences (offset) and/or no further increase of inactivation at higher fluences (tailing) was observed for some micro-organisms. Where observed, these were included in the description of the inactivation kinetics, even though the cause of tailing is still a matter of debate. The parameters that were used to describe inactivation are the inactivation rate constant k (cm2/mJ), the maximum inactivation demonstrated and (only for bacterial spores and Acanthamoeba) the offset value. These parameters were the basis for the calculation of the Microbial Inactivation Credit (MIC = “log-credits”) that can be assigned to a certain UV fluence. The most UV resistant organisms are viruses, specifically Adenoviruses, and bacterial spores. The protozoon Acanthamoeba is also highly UV resistant. Bacteria and (oo)cysts of Cryptosporidium and Giardia are more susceptible with a fluence requirement of <20 mJ/cm2 for a MIC of 3 log. Several studies have reported an increased UV resistance of environmental bacteria and bacterial spores, compared to lab-grown strains. This means that higher UV fluences are required to obtain the same level of inactivation. Hence, for bacteria and spores, a correction factor of 2 and 4 was included in the MIC calculation, respectively, whereas some wastewater studies suggest that a correction of a factor of 7 is needed under these conditions. For phages and viruses this phenomenon appears to be of little significance and for protozoan (oo)cysts this aspect needs further investigation. Correction of the required fluence for DNA-repair is considered unnecessary under the conditions of drinking water practice (no fotorepair, dark repair insignificant, esp. at higher (60 mJ/cm2) fluences) and probably also wastewater practice (fotorepair limited by light absorption). To enable accurate assessment of the effective fluence in continuous flow UV systems in water treatment practice, biodosimetry is still essential, although the use of Computational Fluid Dynamics (CFD) improves the description of reactor hydraulics and fluence distribution. For UV systems that are primarily dedicated to inactivate the more sensitive pathogens (Cryptosporidium, Giardia and pathogenic bacteria), additional model organisms are needed to serve as biodosimeter

Inactivation credit of UV-radiation for viruses, bacteria and protozoan (oo)cysts: a review (AGGREGATION CH 6)

UV disinfection technology is of growing interest in the water industry since it was demonstrated that UV radiation is very effective against (oo)cysts of Cryptosporidium and Giardia, two pathogenic micro-organisms of major importance for the safety of drinking water. Quantitative Microbial Risk Assessment, the new concept for microbial safety of drinking water and waste water, requires quantitative data of the inactivation or removal of pathogenic micro-organisms by water treatment processes. The objective of this study was to review the literature on UV disinfection and extract quantitative information about the relation between the inactivation of micro-organisms and the applied UV fluence. The quality of the available studies was evaluated and only high-quality studies were incorporated in the analysis of the inactivation kinetics. The results show that UV is effective against all waterborne pathogens. The inactivation of micro-organisms by UV could be described with first-order kinetics using fluence-inactivation data from laboratory studies in collimated beam tests. No inactivation at low fluences (offset) and/or no further increase of inactivation at higher fluences (tailing) was observed for some micro-organisms. Where observed, these were included in the description of the inactivation kinetics, even though the cause of tailing is still a matter of debate. The parameters that were used to describe inactivation are the inactivation rate constant k (cm2/mJ), the maximum inactivation demonstrated and (only for bacterial spores and Acanthamoeba) the offset value. These parameters were the basis for the calculation of the Microbial Inactivation Credit (MIC = “log-credits”) that can be assigned to a certain UV fluence. The most UV resistant organisms are viruses, specifically Adenoviruses, and bacterial spores. The protozoon Acanthamoeba is also highly UV resistant. Bacteria and (oo)cysts of Cryptosporidium and Giardia are more susceptible with a fluence requirement of <20 mJ/cm2 for a MIC of 3 log. Several studies have reported an increased UV resistance of environmental bacteria and bacterial spores, compared to lab-grown strains. This means that higher UV fluences are required to obtain the same level of inactivation. Hence, for bacteria and spores, a correction factor of 2 and 4 was included in the MIC calculation, respectively, whereas some wastewater studies suggest that a correction of a factor of 7 is needed under these conditions. For phages and viruses this phenomenon appears to be of little significance and for protozoan (oo)cysts this aspect needs further investigation. Correction of the required fluence for DNA-repair is considered unnecessary under the conditions of drinking water practice (no fotorepair, dark repair insignificant, esp. at higher (60 mJ/cm2) fluences) and probably also wastewater practice (fotorepair limited by light absorption). To enable accurate assessment of the effective fluence in continuous flow UV systems in water treatment practice, biodosimetry is still essential, although the use of Computational Fluid Dynamics (CFD) improves the description of reactor hydraulics and fluence distribution. For UV systems that are primarily dedicated to inactivate the more sensitive pathogens (Cryptosporidium, Giardia and pathogenic bacteria), additional model organisms are needed to serve as biodosimeter