Challenge

As the landlocked Budd Inlet Treatment Plant in downtown Olympia, Wash., neared capacity and faced marine discharge restrictions, four government partners started pondering alternatives for meeting future wastewater treatment needs. The LOTT Alliance, which is governed by a board of elected officials representing each of the partner jurisdictions – the cities of Lacey, Olympia and Tumwater, and Thurston County – developed a long-range plan with reclaimed water at its core. Strong public opinion influenced the alliance’s decision to start treating wastewater to a high enough quality that it could be put to beneficial use. The plan envisioned a system of three small satellite reclaimed water plants.

Solution

Construction on the first satellite, the 2-MGD Martin Way Reclaimed Water Plant, began in 2004, with the plant coming online in summer 2006. The facility used a core membrane bioreactor (MBR) from Siemens Water Technologies.

The facility generates reclaimed wastewater that meets Class A reclaimed water standards approved by the Washington State Departments of Health and Ecology. To limit operations and equipment requirements at  the reclamation plant, solids are returned to the sewer system for treatment at the main Budd Inlet Treatment Plant. Located on a major thoroughfare in Lacey, the facility had to fit into a small footprint, visually blend into the commercial and light industrial neighborhood and not generate odors.

In the MBR process, wastewater is screened before entering the tank where the biological treatment process takes place. Aeration within the aerobic reactor zone provides oxygen for the biological respiration and maintains solids in suspension. To retain the active biomass in the process, the MBR relies on submerged membranes rather than clarifiers, eliminating sludge settleability issues. This allows the biological process to operate at long sludge ages (typically 12 to 30 days) and increased mixed liquor suspended solids (MLSS) concentrations (typically 8,000-10,000 mg/l). High MLSS concentrations were beneficial to the process, fostering stable operation, complete nitrification, and reduced biosolids production, reducing biological volume requirements (and associated footprint) to only 20 to 30 percent of conventional biological processes.

 Further, the membrane tanks provided space-efficient solids separation and did not require a clarifier in the system. The submerged microfiltration membranes were located in a separated membrane tank and consisted of polymeric hollow fibers. These hollow fibers were bound together in modules, using a unique dual-potting system. By applying a low vacuum to the inside of the hollow fibers, the fully oxidized and nitrified water could be filtered through the membranes. Meanwhile, mixed liquor and air would be pumped continuously into each membrane module fiber bundle. The resulting cross-flow continuously would scour the membrane surface, preventing solids buildup.

Water utilities in Lacey and Olympia plan to purvey the alliance’s reclaimed water to endusers. The cities will be able to tap into the alliance’s main pipeline to get water for their own or customer uses.

Results

Eric Hielema, the alliance’s project manager for the Martin Way project says, “By using reclaimed water for these purposes, our citizens can help save hundreds of millions of gallons of drinking-quality water each year,” said Hielema. “The jurisdictions in Thurston County face many challenges supplying drinking water to their growing communities. These issues are the result of a lack of legal availability of water due to competing needs for regional water resources. The use of reclaimed water will ease some of the pressures on local water utilities.”

Due to the results of the MBR technology provided by Siemens,  the Martin Way plant will carry out their vision and already have  plans to construct other satellites in small increments, in order to allow for timely construction, to meet the region’s future wastewater treatment capacity needs.