Recycling Treated Municipal Wastewater for Industrial Water Use

TM3: Recycled Wastewater System Components and Costs
Recycling Treated Municipal Wastewater for Industrial Water Use
In addition to the specific constituent limits established by the Title 22 criteria, which
are only for total coliform, there are also best practices that must be employed for
specific uses. Title 22 defines the water quality/treatment technology criteria applied
to reclaimed water for industrial uses under two general categories:
Disinfected secondary-23 recycled water (secondary-23 recycled water)
Disinfected tertiary recycled water (tertiary recycled water)
Secondary-23 recycled water is wastewater processed through a secondary treatment
system that is disinfected to meet a total coliform limit of 23/100 ml, based on a
running 7-day median, and does not exceed 240/100 ml total coliforms in any 30-day
period. There are no specific treatment requirements following secondary treatment
or for disinfection practices. Any technologies employed must be on the Title 22
approved list or demonstrated to be effective as defined in the regulations. Appendix
A, Exhibit 2 contains the list of approved technologies.
Tertiary recycled water must meet a total coliform limit of 2.2/100 ml, based on a
running 7-day median, and cannot exceed 23/100 ml total coliforms in any 30-day
period. The secondary treatment system effluent must be filtered using any Title 22
approved filtration technology. Disinfection by chlorination requires a 90-minute
contact time, based on peak dry weather design flow, with a dose that provides a CT
(the product of total chlorine residual and modal contact time measured at the same
point) value of not less than 450 mg-min/l at all times. Other disinfection processes,
when combined with the filtration process, must demonstrate inactivation and/or
removal of 99.999 percent of the plaque-forming units of F-specific bacteriophage
MS2, or polio virus in the wastewater. A virus that is at least as resistant to
disinfection as polio virus may be used for purposes of the demonstration. In
addition, if the tertiary recycled water is used as cooling water in a process with
cooling towers or other equipment that produces a mist, a drift eliminator and use of
chlorine or a biocide to control Legionella and other microorganisms are required.
3.1.2 User-Specific Requirements
The total coliform limits imposed by the Title 22 regulations are the regulatory criteria
assumed for all Minnesota industrial reclaimed water uses. The other water quality
criteria that will drive the treatment process selection will vary with the specific use of
the water. These use-specific criteria do not need to meet a regulatory permit limit,
but would likely be listed as site-specific water quality standards in a user agreement.
Generalized water quality limits for various industrial uses are provided in Table 2.
While this is a limited list, it is the mid-range of quality expected for use by each
industry group listed. Industries such as sand and gravel washing operations would
have less stringent criteria, while electronics production typically requires much more
stringent criteria.
6 Craddock Consulting Engineers
In Association with CDM & James Crook
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