Recycling Treated Municipal Wastewater for Industrial Water Use

3.4 Storage and Transmission
Overview
Section 3: Recycled Wastewater System Components and Costs
Recycling Treated Municipal Wastewater for Industrial Water Use
An integral part of the planning, operation, and maintenance of recycled wastewater systems is the
transmission of the recycled wastewater to the customer. Transmission costs, both capital and O&M, are a
significant cost component of recycled wastewater projects. Transmission systems typically include onsite
storage, pump station(s), piping, off-site storage, diversion structures to off-site storage ponds, service
connections, and metering. Wastewater recycling regulations and guidelines generally include standards
for the design, installation, operation, and maintenance of the transmission systems. In addition, there are
very specific guidelines and requirements for any cross-connections to other systems, use of backflow
preventions devices and other plumbing features.
Storage
The conceptual recycled wastewater system, presented previously in Figure 3.1, provides for storage
facilities on the WWTP site to meet a range of storage volumes. The base recycled wastewater system
assumes that no storage is required, which is valid for a larger WWTP serving smaller industrial demands.
The cost curves developed for this study do not include storage requirements, but cost information was
developed to asses the impact of storage on system costs and is detailed in Section 5.5 of Appendix II-3.
For purposes of this study, it is assumed that where storage is needed, it is for diurnal, daily, or weekly
industrial demand patterns that the WWTP cannot meet with their continuous supply. Storage
requirements for industrial applications can vary widely. Some industries may have adequate storage to
meet peak hour requirements, but most would not have storage to handle significant volumes. Storage
would likely be needed with smaller WWTPs where the diurnal flows could drop below the required
demand of an industry or group of industries. Weekly demand patterns of industry could also change and
should be accounted for when establishing storage requirements.
This study does not consider any seasonal storage requirements for a reclaimed supply. Seasonal storage
would be required for WWTPs that incorporate reuse practices to reduce their discharges to waterways
and supply seasonal customers. These facilities would need to store and/or dampen peak flows to meet
NPDES limits during periods when the seasonal recycled wastewater customers do not use water.
Seasonal storage may also be required to meet a seasonal water demand, where peak demands cannot be
consistently matched by the WWTP flow. The majority of Minnesota’s industries have year-round water
demands. Some exceptions include: agricultural processing industries, which may depend on seasonal
crops; industries that use recycled wastewater for landscape irrigation; and some cooling water
applications. Seasonal storage facilities are common in recycled wastewater systems for irrigation
practices.
Recycled wastewater storage can also provide system reliability with a short-term supply if there is a
process disruption as well as additional contact time for chlorine disinfection.
Pumping
This study assumes a pump station is located on the WWTP site and is owned by the municipality. The
pump station is assumed to include standby and reliability features consistent with state water supply
requirements. The pump station is sized for peak flow and a residual pressure at the end of the pipe line of
40 psi, assuming delivery at the same elevation as the WWTP.
Transmission Pipelines
The majority of recycled wastewater transmission piping is polyvinyl chloride pipe (PVC) or ductile iron
pipe (DIP) meeting specific industry standards. For this study, the transmission system is assumed to be
all force main with the following characteristics: pipe with a diameter of 24 inches or less is PVC, DR 18,
Class 150 and greater than 24 inch diameter pipe is DIP, Class 51 with push-on joints. Pipelines are sized
to carry the peak hour demand of a given industry at a target velocity of 5 to 7 feet per second (fps).
Details assumed for the cost analysis are provided in Appendix II-3.
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