Recycling Treated Municipal Wastewater for Industrial Water Use

Section 1: Introduction
Recycling Treated Municipal Wastewater for Industrial Water Use
The development of Minnesota’s Total Maximum Daily Load (TMDL) program will affect the discharge
allocations for many communities. For example, the Lake Pepin TMDL will affect nearly two-thirds of
the state. With a potential reduction requirement of one-half the phosphorus and solids loads to Lake
Pepin, and nonpoint source reduction practices still untested, it is likely that point source reductions will
be part of the solution. Wastewater recycling may be a cost-effective solution for some communities,
particularly when tertiary treatment processes are required to meet receiving stream discharge limits. If
these communities are also experiencing water supply limitations, the benefits of a wastewater recycling
option could be even more pronounced.
Wastewater Recycling Applications in Minnesota
Using recycled wastewater for irrigation has historically been practiced in Minnesota because surface
discharges are not possible in some areas and land application is used. Many of Minnesota’s rural pond
systems spray irrigate agricultural fields during the summer months when the ponds discharge. More
recent reuse applications involve cooling water for power generation, golf course irrigation in urban and
resort areas, and as toilet flush water for an institutional building. Table 1.3 provides a list of facilities that
Table 1.3. Wastewater Recycling Facilities in Minnesota
Facility Type of Reuse Flow, mgd
Hennepin County Public Works Toilet flush water 0.0056
Lake Allie Golf course irrigation 0.0056
Turtle Run South Golf course irrigation 0.0168
Izaty’s Golf and Yacht Club Golf course and alfalfa field irrigation 0.086
City of Nisswa Golf course irrigation and other uses 0.038
City of Montgomery Golf course irrigation and other uses 0.038
Shakopee Mdewakanton Sioux Community Wetland enhancement 0.96
City of Mankato Industrial – cooling water for power plant 6.2
are using treated, municipal wastewater effluent in Minnesota for uses other than agricultural irrigation.
The urban irrigation and toilet flush water systems used wastewater recycling because this was the
optimum practice for their wastewater discharge.
The Shakopee Mdewakanton Sioux Community (SMSC)’s 0.96 mgd WWTP is permitted to discharge to
one of two wetlands with downstream ponded areas that provide water for their golf course irrigation
system. State agencies are working with the SMSC to explore aquifer recharge to be used primarily in the
winter when irrigation is not needed.
The one industrial recycled wastewater application
in Minnesota was developed because of water
supply limitations. The Mankato Energy Center
(MEC) uses 6.2 mgd of treated wastewater from the
Mankato WWTP for its cooling water. Mankato
expanded their WWTP, shown in Figure 1.3, to
provide the water quality required for the cooling
towers. The MEC cooling water discharge is
returned to the plant as a permitted industrial user
and commingled with treated effluent prior to
dechlorination. The MEC uses an evaporative
cooling process with an average loss of 75%. The
MEC produces 365 megawatts with an ultimate
capacity of 630 megawatts.
Figure 1.3. Mankato Water Reclamation Facility
8 Metropolitan Council Environmental Services