Large and small communities alike rely on USFilter membrane filtration systems to handle challenging water issues. Innovative and highly adaptable membrane technologies are discussed in the following case studies.
One example is Carmichael, Calif., where the water district uses a MEMCOR® CMF (continuous microfiltration) system to treat backwash thereby maximizing recovery and minimizing waste disposal.
A second case study profiles Oconee County, Ga., where a MemJet™ MBR (membrane bioreactor) system plays an integral role in the expansion of its wastewater plant.
Strict California standards
The Carmichael (Calif.) Water District, a publicly owned and operated agency serving approximately 39,000 residents in suburban Sacramento County, Calif., was under a state mandate to enhance its treatment of the American River water.
Carmichael is entitled to water from the American River, with supplemental water from groundwater wells. With about 75% of its water coming from the river, the district needed to find a treatment method that provided a high level of public health protection, but still ensured the environmental well being of the nearby American River watershed. It was also necessary to gain community approval of the proposed method.
With the assistance of local design engineer Montgomery Watson Harza and input from a community advisor group, the district evaluated many conventional and non-conventional filtration methods, and ultimately selected membrane technology for installation at its Bajamont Way Water Treatment Plant (WTP).
The decision was based on several factors:
- A successful pilot study of MEMCOR® CMF technology;
- MEMCOR® membrane integrity testing capabilities;
- Competitive equipment costs from USFilter; and
- The company’s full-scale plant experience.
An effective solution
Source water from the American River is collected in manmade Ranney wells and the raw water flows through pipes tunneled beneath the American River. It is then conveyed by gravity to the membrane treatment plant and enters the membrane system through the feed manifold. The MEMCOR® CMF system resides within a single-story residential style structure designed to blend with the surrounding community. The building is located on a 1.6-acre site where the district’s maintenance facility once stood.
The system has 12 microfiltration skids—each containing 90 modules—for primary filtration. The facility’s average flow is 9 MGD with peak capacity of 17 MGD. To maintain a constant product water flow rate, the system’s design allows for 11 skids to be online and one unit to remain on standby for offline chemical cleaning.
Backwash water is treated by a second-stage microfiltration system consisting of two skids with 96 membrane modules in all. This stage recovers and treats up to 90% of the backwash water, equal to about 600,000 GPD. The plant is able to process more than 99% of its water supply into potable water.
In compliance with California Depart-ment of Health Services regulations, filtrate water from the secondary stage is sent back to the head of the plant.
In late 2002, a third stage consisting of two additional CMF skids with six modules each was installed to treat the backwash waste from the secondary stage, increasing the overall plant recovery to 99.96%.
Positive results
Installation of the MEMCOR® CMF system at the Bajamont Way WTP dramatically improved water quality. The plant consistently delivers water with turbidity of less than 0.05 NTU and its automated and highly sensitive integrity test system allows operators to directly verify over 4-log reduction of pathogenic organisms easily meeting existing and future drinking water regulations for removal.
In addition to improving water quality, Carmichael’s CMF system has minimized waste disposal due to the backwash recovery system. This protects the biological, aesthetic and environmental qualities of the American River.
Since installing the system, the district has reduced its sediment flushing program by 80%. Operating and labor costs are also minimized with the CMF system’s membrane integrity monitoring and minimum mechanical maintenance.
System integral to plant expansion
The Calls Creek wastewater facility serves the city of Watkinsville, Ga., and outlying areas of Oconee County, which has a longstanding policy restricting the use of treated wastewater for residential applications in order to preserve water to accommodate commercial business.
The previous wastewater treatment facility utilized a USFilter Envirex Orbal™ biological process. This system consists of a three-channel looped reactor activated sludge process. USFilter performed a pilot study incorporating the MemJet™ MBR system into the biological plant loop of the facility in a three-stage process.
Providing a solution
As a result of pilot testing, USFilter installed a 1 mgd MemJet™ MBR system to accomplish a superior level of biological treatment as well as increase capacity of the UV system through improved transmissivity. The facility also gained two ultra-fine screens that have a nominal opening of 250 microns and screen 100% of the forward flow plus the recycle flow between the Orbal system and the membrane system. In addition to the ultra-fine screening, USFilter incorporated an inert removal sidestream from the sump of the screen system.
The final component of the biological treatment process is an Ultrair digester added to enhance biological reduction of waste sludge. The Ultrair process removes trash and inert matter from the mixed liquor enhancing the membrane bioreactor performance.
With the expansion, Calls Creek’s current wastewater treatment capacity will increase from 400,000 gpd to over 670,000 gpd. The plant can easily be expanded to 1 mgd with the addition of a single membrane tank to accommodate commercial growth and provide service to unincorporated areas for future use.
By installing the screening and the inerts removal system, along with the Ultrair Bioreactor, biosolids will be reduced by more than half, minimizing the total amount of sludge removed from the facility.
