Metro - ECCV Zero Liquid Discharge Pilot Study_Application

• Basin Roundtable: Metro
• Applicant: East Cherry Creek Valley Water and Sanitation District
• Description: Zero Liquid Discharge Pilot Study
• Account Source: Basin & Statewide
• Board Meeting Date: 9/19/2007
• Contract/PO #: 150412
• WSRF - Doc Type: Grant Application

the water is unusable and has to be disposed of. This waste stream, termed the
concentrate or brine, contains the contaminants and TDS rejected by the membrane.
Because the brine contains an increased concentration of contaminants and TDS in a
relatively large volume of water, its disposal can be problematic. Concentrate disposal
typically is the greatest technical challenge when considering high pressure membrane
treatment.

For high-pressure membranes, the concentration of contaminants or TDS in the brine
stream increases dramatically as recovery increases. Figure 4.3 illustrates the
relationship of TDS in the brine to recovery assuming an untreated water TDS of 1,000
milligrams per liter (mg/L). In this example, a membrane system operating at a relatively
low recovery of 80% will produce a brine stream with a TDS of 5,000 mg/L, a 5-fold
increase over the raw water. Increasing the recovery from 80% to 90% will produce a
brine stream with a TDS of 10,000 mg/L, a 10-fold increase over the raw water.

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Recovery (Percent)

Figure 4.3. Relationship between TDS in the Concentrate and Recovery Assuming
an Untreated Water TDS of 1,000 mg/L.

4.3 Membrane Treatment Design Considerations

For brackish water treatment, a split stream process is used. Since the membranes
remove nearly all the TDS, the membrane treated water quality far exceeds drinking
water requirements for TDS and many other contaminants (secondary maximum
contaminant level (SMCL) for TDS = 500 mg/L). High-pressure membranes treat one
leg of the process stream while the second leg of the process stream bypasses the
membranes. The by-passed and membrane treated water is blended downstream of the
10