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Fair is the marigold, for pottage meet. Gay. (2.) MARIGold. See CALENDula, N° 1. is given under the articles BLEACH in G, CHEMistry, ColousMA KING, &c., He made the experiment by mixing 10 lb. of flints with 2 lb, of sea salt; but obtained only a mass of the colour of litharge, and the fumes were not perceptibly acid. They are boiling the water and adding chlorine (household bleach, such quantity of bleach and water mixture to meet the desired emergency in water ( at altitudes above feet above sea level, boil for three to five minutes longer). When boiling is not practical, chemical disinfection should be used. The evaluations in this report are not exhaustive literature reviews but, rather, are .. In halogen-disinfected waters, naturally occurring bacteria can be from one to two .. of any chlorine species, the test medium must meet certain exacting criteria. .. At saturation in water at 20°C, a 2% weight mixture of ozone and oxygen.
Tertiary treatment filters the water to remove whatever solids remain, disinfects it with chlorine, and removes the salt.
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For Indirect Potable Reuse IPR —recycled water that eventually becomes drinking water—tertiary-treated water undergoes advanced water technology, then spends time in groundwater or surface water, such as a reservoir, before being sent to drinking water supplies. Advanced water technology first involves microfiltration that strains out any remaining solids. The water is then disinfected by ultra violet light UV or ozone and hydrogen peroxide.
Finally it is added to groundwater or surface water reservoirs where it stays for an average of 6 months to be further purified by natural processes. This is done mainly to assuage public anxiety about drinking recycled water. Once drawn from the groundwater or reservoir, the recycled water goes through the standard water purification process all drinking water undergoes to meet U. Environmental Protection Agency standards. During this time, its Advanced Water Purification Facility is producing 1 million gallons of purified water each day, though no water is being sent to the reservoir.
IPR is more economical for San Diego than recycling more sewage for irrigation would be because recycled irrigation water must be conveyed through special purple pipes to separate it from potable water; expanding the purple pipe infrastructure would cost more than IPR.
Recycled water is also less expensive than desalinating seawater. After advanced water treatment, half the recycled water is injected into the aquifer to create a barrier against saltwater intrusion. The other half goes to a percolation pond for further filtration by the soils, and then after about 6 months, ends up in drinking water well intakes.
Singaporewith no natural aquifers and a small landmass, has struggled to provide a sustainable water supply for its residents for decades. Jerry Wong Init opened the first plants to produce NEWater, recycled drinking water purified by advanced membrane techniques including microfiltration, reverse osmosis and UV disinfection. After treatment, the water is added to the reservoirs.
NEWater, which has passed more than 65, scientific tests and surpasses World Health Organization drinking water standards, is clean enough to be used for the electronics industry and to be bottled as drinking water.
It is expected to produce 2. Namibia, the most arid country in southern Africa, has been drinking recycled water since The transmission of diseases such as typhoid and paratyphoid fevers, cholera, salmonellosis, and shigellosis can be controlled with treatments that substantially reduce the total number of viable microorganisms in the water.
While the concentration of organisms in drinking water after effective disinfection may be exceedingly small, sterilization i. Sterilization is not only impractical, it cannot be maintained in the distribution system. Assessment of the reduction in microbes that is sufficient to protect against the transmission of pathogens in water is discussed below.
Chlorination is the most widely used method for disinfecting water supplies in the United States. The near universal adoption of this method can be attributed to its convenience and to its highly satisfactory performance as a disinfectant, which has been established by decades of use.
It has been so successful that freedom from epidemics of waterborne diseases is now virtually taken for granted. As stated in Drinking Water and Health National Academy of Sciences,"chlorination is the standard of disinfection against which others are compared. The method of choice for disinfecting water for human consumption depends on a variety of factors Symons et al.
Economic factors will also play a part in the final decision; however, this study is confined to a discussion of the five factors listed above as they apply to various disinfectants. The propensity of various disinfection methods to produce by-products having effects on health other than those relating to the control of infectious diseases and the possibility of eliminating or avoiding these undesirable by-products are also important factors to be weighed when making the final decisions about overall suitability of methods to disinfect drinking water.
The subcommittee has not attempted to deal with these problems since the chemistry of disinfectants in water and the toxicology of expected by-products have been studied by other subcommittees of the Safe Drinking Water Committee, whose reports appear in Chapter III of this volume Chemistry and Chapter IV Toxicity of Drinking Water and Health, Vol. Organization of the Study The general considerations noted in the immediately following material should be borne in mind when considering each method of disinfection.
Available information on the obvious major candidates for drinking water disinfection—chlorine, ozone, chlorine dioxide, iodine, and bromine—is then evaluated for each method individually in the following sections. Other less obvious possibilities are also examined to see if they have been overlooked unjustly in previous studies or if it might be profitable to conduct further experimentation on them.
Disinfection by chloramines is dealt with in parallel with that effected by chlorine because of the close relationship the former has to chlorine disinfection under conditions that might normally be encountered in drinking water treatment.
The evaluations in this report are not exhaustive literature reviews but, rather, are selections of the studies that, in the judgment of the committee, provide the most accurate and relevant information on the biocidal activities of each method of disinfection. The analytical methods that are described in this report are those that are most likely to be used by persons involved in disinfection research or water treatment.
A review of all existing analytical methods, some of which may be more sophisticated than those described below, would be impractical within the constraints of time and space available and is not within the scope of this document. The conclusions of the study are then recorded on the basis of this evidence. General Aspects of Disinfection In any comparison of disinfection methods, certain considerations should be discussed at the outset since they are relevant to most, if not all, methods.
The quality of the raw water i. Equally applicable to all methods are appropriate standards for verifying the adequacy of disinfection, differences in response to disinfectants between organisms that were obtained directly from the field and those that have been acclimated to laboratory culture, and the maintenance of potability from treatment plant to the consumer's tap.
The use of chlorination as presented in examples in the following pages does not imply that it is necessarily the method of choice. Rather, this method has been studied more thoroughly than other methods.
Raw Water Quality In addition to potential pathogens, raw water may contain contaminants that may interfere with the disinfection process or may be undesirable in the finished product. These contaminants include inorganic and organic molecules, particulates, and other organisms, e. Variations among these contaminants arise from differences in regional geochemistry and between ground- and surface-water sources.
Disinfectant Demand Many inorganic and organic molecules that occur in raw water exert a "demand," i. Therefore, higher "demand" waters require a greater dose to achieve a specific concentration of the active species of disinfectant. This demand must be satisfied to ensure adequate biocidal treatment. Ferrous ions, nitrites, hydrogen sulfide, and various organic molecules exert a demand for oxidizing disinfectants such as chlorine.
The bulk of the nonparticulate organic material in raw water occurs as naturally derived humic substances, i. The structure of these molecules is not yet fully understood. However, they are known to be polymeric and to contain aromatic rings and carboxyl, phenolic, alcoholic hydroxyl, and methoxyl functional groups. Water, particularly surface waters, may also contain synthetic organic molecules whose demand for disinfectant will be determined by their structure. Ammonia and amines in raw water will react with chlorine to yield chloramines that do have some biocidal activity, unlike most products of these side reactions.
If chlorination progresses to the breakpoint, i. This phenomenon is discussed more fully below. The nature of the demand reactions varies with the composition of the water and the disinfectant. Removal of the demand substances leaves a water with a lower requirement for a disinfectant to achieve an equivalent degree of protection against transmission of a waterborne disease. Physical and Chemical Treatments Various treatments applied to raw water to remedy undesirable characteristics, e.
Microorganisms may be physically removed or the disinfectant demand of the water altered. Presedimentation to remove suspended matter, coagulation with alum or other agents, and filtration reduce the organic material in the raw water and, thus, the disinfectant demand.
Removal of ferrous iron similarly reduces the demand for oxidizing disinfectants as will aeration, which eliminates hydrogen sulfide. Prechlorination to a free chlorine residual is practiced early in the treatment sequence as one method to alter taste- and odor-producing compounds, to suppress growth of organisms in the treatment plant, to remove iron and manganese, and to reduce the interference of organic compounds in the coagulation process.
The necessity for these treatments or others is determined by the characteristics of the raw water. The selection of one of the various methods to achieve a particular result will be based upon cost-effectiveness in the particular situation.
When chlorination is used, the application or point of application in the treatment sequence of some of the above-mentioned procedures can affect the undesirable THM content of the finished water. Reduction of precursors in raw water by coagulation and settling prior to chlorination reduces final THM production Hoehn et al. The available information on these variations is limited, and a universally applicable procedure cannot be recommended in view of the diverse treatments required for different raw waters.
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Particulates and Aggregates To inactivate organisms in water, the active chemical species must be able to reach the reactive site within the organism or on its surface.
Inactivation will not result if this cannot occur. Microorganisms may acquire physical protection in water as a result of their being adsorbed to the enormous surfaces provided by clays, silt, and organic matter or to the surfaces of solids created during water treatment, e. Viruses, bacteria, and protozoan cysts may be adsorbed to these surfaces.
Such particles, with the adsorbed microorganisms, may aggregate to form clumps, affording additional protection. Organisms themselves may also aggregate or clump together so that organisms that are on the interior of the clump are shielded from the disinfectant and are not inactivated. Organisms may also be physically embedded within particles of fecal material, within larger organisms such as nematodes, or, in the case of viruses, within human body cells that have been discharged in fecal material.
To disinfect water adequately, the water must have been pretreated, when necessary, to reduce the concentration of solid materials to an acceptably low level. The primary drinking water turbidity standard of 1 nephelometric turbidity unit NTU is an attempt to assure that the concentration of particulates is compatible with current disinfection techniques.
Where it is possible to obtain lower turbidities, this is desirable.
Disinfection studies in which the complications of adsorbed organisms, aggregation, or embedment were thought to occur were excluded from this study. The conclusions in this report should not be extrapolated to such situations as the disinfection of turbid or colored waters.
The Importance of Residuals Water supplies are disinfected through the addition or dosage of a chemical or physical agent. With a chemical agent, such as a halogen, a given dosage should theoretically impart a predetermined concentration residual of the active agent in the water. From a practical point of view, most natural waters exert a "demand" for the disinfectant, as discussed above, so that the residual in the water is less than the calculated amount based on the dosage.
The decrease in residual, which is caused by the demand, is rapid in most cases, but it may be prolonged until the residual eventually disappears. In addition, the chemical agent may decompose spontaneously, thereby yielding substances having little or no disinfection ability and exerting no measurable residual.
For example, ozone not only reacts with substances in water that exert a demand, but it also decomposes rapidly. To achieve microbial inactivation with a chemical agent, a residual must be present for a specific time. Thus, the nature and level of the residual, together with time of exposure, are important in achieving disinfection or microbial inactivation.
Residual measurements are important and useful in controlling the disinfection process. By knowing the residual-time relationship that is required to inactivate pathogenic or infectious agents, one can adjust the dosage of the disinfecting agent to achieve the residual that is required for effective disinfection with a given contact time. Following disinfection of a water supply at a treatment plant, the water is distributed to the consumers.
A persistent residual is important for continued protection of the water supply against subsequent contamination in the distribution system. Accidental or mechanical failures in the distribution system may result in the introduction of infectious agents into the water supply.
In the presence of a residual, disinfection will continue and, as a result, offer continued protection to the users. Physical agents such as radiation may provide effective disinfection during application, but they do not impart any persistent residual to the water. The dosage of a chemical agent that is used to effect microbial inactivation should not be so great that it imparts a health hazard to the water consumer.
Sodium hypochlorite as a disinfectant
From another point of view, the aesthetic quality of the finished water should not be impaired by the dosage of the chemical agent or the residual that is required for effective disinfection. These qualities might include discoloration of water from potassium permanganate KMnO4 or iodine or problems of taste and odor from excessive chlorine.
Application of the Disinfectant Optimum inactivation occurs when the disinfectant is distributed uniformly throughout the water. To disperse the chemical disinfectant when it is added to the water, it must be mixed effectively to assure that all of the water, however small the volume, receives its proportionate share of the chemical.
Additions of a disinfectant at points in a flowing water stream, e. In such cases, mechanical mixing devices are needed to disperse the disinfectant throughout the water. Disinfection by radiation treatment also requires good mixing to bring all of the water within the effective radiation distance. Microbiological Considerations 1 Comparison of the biocidal efficacy of disinfectants is complicated by the need to control many variables, a need not realized in some early studies.
Halogens in particular are significantly affected by the composition of the test menstruum and its pH, temperature, and halogen demand. For very low concentrations of halogen to be present over a testing period, halogen demand must be carefully eliminated. Different disinfectants may have different biocidal potential.
In earlier work, analytical difficulties may have precluded defining exactly the species present, but new techniques allow the species to be defined for most disinfectants. Information on the species of disinfectant actually in the test system should be included in future reports on disinfection studies. Investigators studying efficacy have usually adopted one of two extremes. Some have conducted carefully designed laboratory experiments with controls for as many variables as possible.
Certain of these investigators have reduced the temperature to slow the inactivation reactions. Although these experiments yield good basic information and can be used to determine which variables are important, they often have little quantitative relationship to field situations. The other extreme, a field study or reconstruction of field conditions, is difficult to control. Moreover, their results are often not repeatable. In addition to the variables noted above, prereaction of chemicals in the test system, the culture history of the organism being used, and the ''cleanup" procedures applied to it may also affect the observed results.
Despite these problems, there have been some attempts to standardize efficacy testing. Model Systems and Indicator Organisms A major factor that influences the evaluation of the efficacy of a particular disinfectant is the test microorganism. There is a wide variation in susceptibility, not only among bacteria, viruses, and protozoa cyst stagebut also among genera, species, and strains of the microorganism.
It is impractical to obtain information on the inactivation by each disinfectant for each species and strain of pathogenic microorganism of importance in water. In addition, interpretation of the data would be confounded by the condition and source of the test microorganism e. The overwhelming majority of the literature on water disinfection concerns the inactivation of model microorganisms rather than the pathogens.
These disinfectant model microorganisms have generally been nonpathogenic microorganisms that are as similar as possible to the pathogen and behave in a similar manner when exposed to the disinfectant. The disinfectant model systems are simpler, less fastidious, technically more workable systems that provide a way to obtain basic information concerning fundamental parameters and reactions.
The information gained with the model systems can then be used to design key experiments in the more difficult systems. The disinfection model microorganism should be clearly distinguished from the indicator organism.
The indicator microorganism, as defined in Drinking Water and Health National Academy of Sciences,is a "microorganism whose presence is evidence that pollution associated with fecal contamination from man or other warm-blooded animals has occurred.
The indicator should always be present when fecal material is present and absent in clean, uncontaminated water. The indicator should die away in the natural aquatic environment and respond to treatment processes in a manner that is similar to that of the pathogens of interest. The indicator should be more numerous than the pathogens. The indicator should be easy to isolate, identify, and enumerate.
Only a restrictive application of the second criterion is necessary for a disinfection model. The response of the test microorganism to the disinfectant must be similar to that of the pathogen that it is intended to simulate.
The disinfection model is not meant to function as an indicator microorganism.Fresh Water Meets Sea Water – Boundary Explained
During the latter part of the nineteenth century, investigators recognized the presence of a group of bacteria that occured in large numbers in feces and wastewater. The most significant member of this group currently called the coliform group is Escherichia coli. Since the late nineteenth century, this coliform group has served as an indicator of the degree of fecal contamination of water, and E.
Butterfield and co-workers Butterfield and Wattie, ; Butterfield et al. At pH values above 8. At pH values of 6. Only slight differences between the two genera were found when chloramines were used as the disinfectant.
The bactericidal activity of chloramine was noticably less than that of free chlorine. Bacteria of the coliform group, especially E. The bacterial viruses of E. At present, the data to justify the bacterial viruses as indicators for enteric viruses are limited and inconsistent.
However, there is a growing body of knowledge on the utilization of bacterial viruses as disinfection models. Hsu and Hsu et al. They showed that inactivation of both the f2 virus and poliovirus 1 were inhibited by increasing concentrations of iodide ion and that both f2 RNA and poliovirus 1 RNA were resistant to iodination. They found enteric viruses to be most resistant to free chlorine followed by RNA phages, E. The f2 virus was shown to be more resistant to this form of chlorine than poliovirus 1 and T2 coliphage.
Both viruses were treated together in the same reaction flask, thereby eliminating any inherent differences due to virus preparations and replicate systems. In wastewater effluent at pH 6. The f2 virus appears to be more sensitive to free chlorine but more resistant to combined chlorine than poliovirus 1 is. They observed that the yeast was more resistant to free chlorine than were poliovirus 1 and the enteric bacteria under all conditions tested.
The acid-fast bacilli were most resistant. There is no generally accepted disinfection model for protozoan cysts. In disinfection studies for protozoan diseases, investigators have used the pathogen or its cysts. Work with such systems is, however, generally difficult.
The use of disinfection models provides useful information that is helpful to the comparison of the relative efficiencies of various disinfectants in the laboratory and in controlled field investigations.
While not as widely accepted, the bacterial viruses of E. The difficulty of available methods has limited the number of disinfection studies with protozoan cysts. Laboratory Cultures versus "Naturally Occurring" Organisms The resistance or sensitivity to disinfectants of some bacteria e. This is true in spite of the fact that standardized procedures govern the conditions under which cells are grown, harvested, washed, etc. Examples of such differences range from Gram-negative bacteria and their comparative resistance to disinfectants in general Carson et al.
Disinfectants Sodium hypochlorite
Presumably, the mechanisms creating this phenomenon among these three groups vary widely. The comparative resistance to disinfectants among Gram-negative bacteria varies greatly.
A good example of this is the study of Favero and Drake They first applied the term "naturally occurring" to certain Gram-negative bacteria with the potential for rapid growth in water.
They observed that Pseudomonas alcaligenes, a common bacterial contaminant in iodinated swimming pools, could grow well in swimming pool waters that had been sterilized by membrane filters and rendered free of iodine or chlorine. Starting with contaminated swimming pool water that contained a variety of bacteria, they isolated a pure culture of P. Since these cells had been isolated in pure culture without exposure to conventional laboratory culture media, they were referred to as "naturally occurring" P.
Subsequent tests showed that these naturally occurring cells were significantly more resistant to free iodine than were cells of the same organism that had been subcultured one time on trypticase soy agar. In fact, standard disinfectant tests using the cells that had been subcultured on an enriched laboratory medium suggested that P. This was obviously an erroneous assumption.
The discovery that naturally occurring cells were extremely resistant to iodine explained the relatively high concentrations of P. Subsequently, Favero et al. Naturally occurring cells that were grown in distilled water reacted quite differently to chemical and physical stresses than did cells grown on standard laboratory culture media.
For example, naturally occurring cells of P. In halogen-disinfected waters, naturally occurring bacteria can be from one to two orders of magnitude more resistant to the disinfectant than cells of the same organism that had been subcultured on conventional laboratory culture media. Since standard disinfectant testing necessarily employs subcultured and washed bacterial cells, a false sense of confidence may be created if these data are used as an absolute criterion for the dilution of a disinfectant.
These results could explain the frequent discrepancies between tests that are performed under laboratory conditions and those that are performed under field conditions. If bacteria could be used in their naturally occurring state, one might explore the possibility of bridging the gaps between laboratory and field conditions by using this experimental system.
The ability of some Gram-negative bacteria to grow in water makes it possible to produce and control large numbers of cells for such studies.