Page 5: Canadian Guidelines for Domestic Reclaimed Water for Use in Toilet and Urinal Flushing
Table 1 recommends levels for several reclaimed water quality parameters. Within an overall management framework, the guideline values in Table 1 are intended to enhance treatment reliability and disinfection effectiveness, thus protecting public health. These guideline values could be used to ensure water quality conditions upon start-up of a reclaimed water system, for periodic verification of the system and as a safety precaution if operational parameters are not met.
| Parameter | Units | Water quality parameters
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|---|---|---|---|
| Median | Maximum | ||
Table 1 Footnotes
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| BOD5 | mg/L | = 10 | = 20 |
| TSSTable 1 Footnote b | mg/L | ≤ 10 | ≤ 20 |
| TurbidityTable 1 Footnote b | NTU | = 2 | = 5 |
| Escherichia coliTable 1 Footnote c | CFU/100 mL | Not detected | = 200 |
| Thermotolerant coliformsTable 1 Footnote c | CFU/100 mL | Not detected | = 200 |
| Total chlorine residualTable 1 Footnote d | mg/L | ≥ 0.5 | |
All domestic reclaimed water used for toilet and urinal flushing should be disinfected. Primary disinfection may be accomplished by any chemical, physical or biological means that results in the destruction, inactivation or removal of microorganisms. Chlorination should be used at least as a secondary means of disinfection to maintain chlorine residual within the storage system (if applicable) and the distribution/plumbing system. Box 1 provides the rationale for selecting these parameters. A management program, including treatment technologies in place, should consistently achieve the reclaimed water quality criteria shown in Table 1.
| Parameter | Rationale for selection |
|---|---|
| Biochemical oxygen demand (five-day) (BOD5) | Excessive five-day biochemical oxygen demand (BOD5) can lead to aesthetic and nuisance problems (odour and colour problems). Organics can be broken down by microorganisms, causing a decrease in oxygen content of the water, and can adversely affect disinfection processes. Maintaining BOD5 at the levels recommended in Table 1 will help ensure that aerobic conditions are maintained in the system. |
| Total suspended solids (TSS) |
Total suspended solids (TSS) are monitored for both health and aesthetic reasons. Organic contaminants and heavy metals are adsorbed on particulates, and this suspended matter can shield microorganisms from disinfectants and can lead to odour problems. Maintaining levels at or below those noted in Table 1 will help disinfection efficiency; it is recommended that either TSS or turbidity be monitored. |
| Turbidity | Turbidity is monitored for both health and aesthetic reasons. Turbidity can be organic in nature and may contain toxins or harbour pathogens. Excessive turbidity can lead to odour problems and will interfere with disinfection. It is a useful parameter for monitoring the performance of the treatment unit or facility. Maintaining levels at or below those noted in Table 1 will help disinfection efficiency; it is recommended that either TSS or turbidity be monitored. |
| Escherichia coli | In systems reclaiming domestic wastewater, the presence of E. coli in water leaving the treatment unit can be used to assess disinfection adequacy. A well-designed and welloperated treatment system should be capable of consistently reducing E. coli to undetectable levels. Therefore, the guideline for E. coli in domestic reclaimed water systems is none detectable per 100 mL. However, as even the most sophisticated treatment system cannot provide water that is absolutely free of disease-causing microorganisms all the time, a maximum concentration of 200 CFU/100 mL is acceptable under the conditions outlined in Section 2.1. For systems reclaiming only greywater, it is recommended that thermotolerant coliform values be utilized instead of E. coli. |
| Thermotolerant coliforms |
The presence of thermotolerant coliforms in domestic reclaimed water leaving the treatment unit can be used to assess disinfection adequacy in systems reclaiming wastewater or greywater. Some greywater systems have been shown to have high levels of thermotolerant coliforms in the absence of E. coli. A well-designed and well-operated treatment system should be capable of consistently reducing thermotolerant coliforms to undetectable levels. Therefore, the guideline for thermotolerant coliforms in domestic reclaimed water systems is none detectable per 100 mL. However, as even the most sophisticated treatment system cannot provide water that is absolutely free of diseasecausing microorganisms all the time, a maximum concentration of 200 CFU/100 mL is acceptable under the conditions outlined in Section 2.1. |
| Total chlorine residual |
Disinfection is essential to this process, and a chlorine residual must be present in the domestic reclaimed water storage system and distribution system piping. The total chlorine residual is a measure of all chemical species containing chlorine in an oxidized state. It is usually the sum of the free and combined chlorine concentrations present in water. A minimum measurable total chlorine residual of 0.5 mg/L is an indication that the level of disinfection is adequate (e.g., exceeds the chlorine demand) and may control bacterial regrowth in the reservoir or storage tank. Monitoring chlorine residual is also a simple, quick and inexpensive measure for providing information on microbiological water quality. |
Reclaimed water treatment systems have different monitoring requirements for systems during the start-up period and for ongoing verification monitoring of established systems. Systems at start-up require a more intensive sampling regime to verify that the treatment system is performing adequately. During the first 30-day period of operation (i.e., start-up), a minimum of five samples should be collected and tested for all of the guideline water quality parameters listed in Table 1. Some parameters, such as chlorine residual, may be tested more frequently. The samples should be collected at regular intervals during the 30-day period. The median of five samples should meet the values outlined in Table 1. The maximum limit for any parameter should not be exceeded. This monitoring frequency needs to be continued until the system is shown to meet all of the guideline values in Table 1.
When a 30-day sampling period shows that the treated domestic reclaimed water meets the guideline values for all the parameters, the monitoring frequency can be reduced for some parameters. Monitoring frequencies for residual chlorine and for turbidity or TSS (where possible) should be maintained, whereas frequencies for E. coli or thermotolerant coliforms and BOD5 can be reduced to semi-annual or annual monitoring (depending on the jurisdiction) to verify that the system is still working effectively. During semi-annual or annual monitoring, a minimum of two samples should be taken for each parameter being analysed. These samples should be collected at least an hour apart to provide a better estimate of the water quality being produced. The results from these samples should meet the median values outlined in Table 1, without exceeding the maximum value. If only two samples have been collected (and therefore a median cannot be determined), as long as one sample is less than or equal to the median value and all samples are less than the maximum value, the water quality is still considered to meet the guideline for that parameter. If both samples exceed the median or any sample exceeds the maximum, follow-up samples should be collected to confirm the exceedance.
Confirmation of an exceedance of any guideline parameter should result in the system returning to monitoring as outlined for systems during the 30-day start-up monitoring period and an investigation into the cause of the exceedance. If the guideline median values are exceeded, but all samples are less than the maximum values, the system can continue to be used during the investigation of the water quality. If the maximum values have been exceeded for any parameter, the system should be bypassed until the problem has been shown to be corrected and the water quality returns to meeting the guideline values.
To complement the guideline values, jurisdictions can calculate health-based treatment goals to achieve a health target (see Section 4.5). Potential sources of domestic reclaimed water considered in these guidelines include domestic wastewater and greywater. The source of the water to be reclaimed may have an impact on the treatment goals required to achieve the guideline values in Table 1. The risk assessment (outlined in Section 4.0 and Appendix B) provides an example of treatment goals as log removal requirements for treating domestic reclaimed water derived from wastewater. An important variable for calculating removal/inactivation requirements is the initial pathogen concentrations. Appendix B uses default values for pathogen concentrations in wastewater. System-specific data on pathogen concentrations can be gathered and used as an alternative to the default values.
There are limited published data currently available on pathogen concentrations in greywater sources; therefore, default values for greywater have not been included. In the absence of default values for greywater, the wastewater default values can be used. However, site-specific data may be particularly useful for greywater systems, as they would be expected to have lower inputs of faecal matter than wastewater, and thus lower concentrations of enteric pathogens. Although the faecal inputs are expected to be lower, the concentrations of microbiological and chemical hazards in greywater can vary over a wide range (see Tables 3 and 5 in Part II). It is hoped that over the longer term, sufficient data on pathogen concentrations in greywater will become available, making it possible to calculate removal/inactivation requirements specific to greywater.
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