Recycling Treated Municipal Wastewater for Industrial Water Use

TM3: Recycled Wastewater System Components and Costs
Recycling Treated Municipal Wastewater for Industrial Water Use
dissolved salts. The sedimentation process would be followed by filtration and
disinfection. Another alternative is a microfiltration process followed by membrane
softening, which could also serve industries that need nearly complete removal of
dissolved salts, as with boiler feed water. Removal of dissolved salts can also be
handled with an ion exchange unit process after a softening/filtration process.
A secondary membrane WWTP (membrane bioreactor) would be an option for a new
or expanding WWTP that expects a significant reclaimed water use. Disinfection
requirements would be less and the majority of other constituents are markedly lower
than with conventional secondary treatment. Trace constituent removal can also be
achieved with carbon adsoprtion and advanced oxidation processes, as discussed in
subsequent sections.
If Minnesota continues to adhere to the Title 22 California Water Recycling Criteria
and the reuse application requires a recycled tertiary water (for potential human
contact uses such as recycle water in cooling towers), most existing WWTPs would
need to add a filtration process to supply reclaimed water. The requirement for a
chemical addition/flocculation/ sedimentation process will be site-specific and in
some cases will depend on the types and size of particles in the secondary effluent
and effectiveness of the disinfection process. Some facilities may include the chemical
addition process system to meet phosphorus removal goals for both the NPDES
permit and specific reclaimed water requirements for the industry served. The
treatment technologies approved to meet the Title 22 criteria are listed in Appendix A,
Exhibit 2.
The following subsections provide an introduction to unit processes to remove
specific categorical constituents. The technologies presented are principally for
applications onsite at WWTPs. However, the processes could be used alone or in
combination with treatment facilities on the industrial site, particularly where a single
user has a unique water quality. Package systems (multiple process units) supplied by
manufacturers, applicable to industries with smaller demands and/or to target
specific constituents, are not identified in this study. Some proprietary processes are
identified for specific unit processes to present the variety of technologies available.
3.2.2 Enhanced Suspended and Dissolved Solids Removal (Chemical
Addition/Softening)
With hard, high salt waters common in Minnesota, treatment may be required to
lower hardness and dissolved solids in the reclaimed supply to an industry.
Traditional chemical addition/coagulation/flocculation/sedimentation processes can
be used to reduce dissolved solids, as well as remove suspended solids in the effluent.
In addition, a coagulation process may be required to meet the Title 22 regulations for
process requirements.
If the industrial water demand uses the majority of the municipal effluent generated,
it may be cost-effective to locate the treatment process at the WWTP. Additional
benefits can also be realized by the municipality if the planning for a reclaimed
supply coincides with expansion and/or improvements planning to meet new
Craddock Consulting Engineers 9
In Association with CDM & James Crook
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