Case Studies: Reclamation Program Saves Millions of Gallons of Water

Serving four communities and more than 78,000 people in the urban area surrounding Thurston County, WA, the LOTT Wastewater Alliance recently took the first step toward its 20-year wastewater resource management plan by selecting membrane bioreactor technology for its Hawks Prairie Reclaimed Water Satellite Treatment Plant.

One of the management plan's goals is to supply reclaimed wastewater where it is needed and reduce the load on the central regional plant. As part of the Alliance's 20-year plan, each of the three intended satellite plants will intercept existing regional sewer lines and extract municipal wastewater for local use.

The Hawks Prairie location, the first of the three plants, was selected because of its close proximity to several potential users of the reclaimed water. The location is also suitable for groundwater recharge basins where the water will filter through the ground to replenish groundwater supplies.

The water from the Hawks Prairie facility will be piped about three miles to a series of constructed wetlands storage ponds. From the pipeline and the ponds, water will be drawn for irrigation and for a variety of commercial or industrial processes. Water not distributed for direct use will circulate to the groundwater recharge infiltration basin.

The treatment plant will be constructed to blend into the surrounding commercial neighborhood and will be monitored and operated remotely through an extensive SCADA control system. The pond and recharge basin site will provide an attractive park-like setting in its commercial and light industrial neighborhood.

Water from the Hawks Prairie facility will meet Washington State's "Class A" reclaimed water standards. The "Class A" water has nearly unrestricted uses, including public contact, but is not considered suitable for human consumption. By meeting the standards, the LOTT communities will save hundreds of millions of gallons of drinking quality water each year.

MBR System Treats Resort Town's Seasonal Wastewater

Located at an elevation of approximately 3,500 feet in an extremely mountainous area, the Stevens Pass Wastewater Treatment Plant in Stevens Pass, WA, uses a MBR system to treat wastewater from the community and a major ski resort.

Besides the challenges of treating wastewater with temperatures that drop as low as 10°F in winter, the system will handle dramatically high fluctuations in flow during winter weekends — one-and-a-half to three times the weekday flow — and significant lows in the summer during the non-ski season. To accommodate the low flow periods, the facility is designed so that the membrane tanks will also operate as the process tankage. The independent operational control of the membrane system and biological process offer greater flexibility in meeting these challenging requirements.

By upgrading the facility, the design flow will be increased from 80,000 gpd to more than 200,000 gpd with the ability to provide nitrification and denitrification in the same volume of process tankage that was originally designed as a secondary treatment process. The facility will include new partitioned membrane tanks installed in existing basins to house the membranes and isolate them from the biological process tankage.