The North Clackamas County Water Commission (NCCWC) owns and operates a 10-mgd slow-sand filtration plant in Oregon City, Ore., that treats water from the Clackamas River. The commission is made up of the Sunrise Water Authority, Oak Lodge Water District and the city of Gladstone.
The commission’s existing slow-sand plant operated well under most water quality conditions, including algae blooms and seasonal taste and odor events. However, when turbidity levels reached 10 NTU, the plant was shut down and the cmmission was required to purchase additional supply from a neighboring agency to meet demands. Turbidity events would result in plant shutdowns ranging from 15 to 30 days a year.
A need for more
In 2004, the rapidly growing Sunrise Water Authority undertook a 10 mgd expansion to the existing slow-sand plant. In cooperation with their consultant, MWH, the SWA chose Memcor submerged membrane filtration for the plant expansion.
“Membrane technology was the perfect complement to the existing slow-sand filter plant,” said Kathryn Mallon, vice president at MWH. “Like the slow-sand plant, the membrane plant can easily be operated unattended, reducing the overall staffing needs. Further, the membrane plant performs extremely well during water quality conditions that challenge the slow-sand plant. Having the flexibility of operating two different types of filtration systems allows the Commission to optimize their operating costs and treated water quality based on the raw water conditions.”
In addition to the treatment challenges, SWA also needed additional supply in less than two years to meet increasing system demands.
The Memcor CS submerged membrane system was selected by the Sunrise Water Authority as the most cost-effective solution to meet its water quality needs. The submerged system enabled the SWA to:
- Easily handle turbidity spikes from fluctuating river water without losing capacity;
- Employ PAC in the feed to address taste and odor; and
- Utilize ACH for assistance in the reduction of TOC and algae.
The new state-of-the-art facility was able to meet SWA’s objectives in a compact footprint that easily fit within the confines of the existing plant site.
In comparison to the previous slow-sand filtration facility, the Memcor membranes were able to effectively and efficiently provide exceptional water quality on a consistent basis, despite changing feed water conditions. During the summer and early fall months when TOC or algae was prevalent in the river, constant chemical addition was replaced with seasonal chemical dosing, thus reducing annual operating costs.
Unlike conventional filters, Memcor membranes provide a physical barrier that is capable of eliminating solids, viruses, bacteria, and protozoa, such as Giardia and Cryptosporidium, down to 0.04 microns from the water. This reduces the quantity of chemicals that need to be used in the treatment process.
The NCCWC facility now boasts a 10-mgd capacity, low-pressure membrane water treatment plant housed in a 13,000 sq-ft building. The filtration building includes all of the ancillary facilities to the membrane operation, as well as a new control room, maintenance area and chemical feed facilities. The new treatment process is simplified and makes more financial sense for the Sunrise Water Authority. The facility is fully automated with SCADA technology, eliminating the need for 24-hour monitoring, which significantly cut labor costs.
“The project was fast-tracked,” Schacht said. “We received the products we needed in a very timely manner. They exceeded our expectations.”