Membranes Offer Water Plant Flexibility
Submerged membrane system doubles Kennewick plant’s capacity
In 1979, a water filtration plant was built for the city of Kennewick (Wash.) to treat its Columbia River source.
The 7.5 mgd plant was designed to augment the primary drinking water sources—two Ranney Collector Wells. By 2002, it was necessary for the southeastern Washington plant to expand to 15 mgd.
The city wanted to be able to operate the plant year-round and rely less on the wells. The treated water also had to meet both current and anticipated Safe Drinking Water Act regulations.
Following a thorough analysis and recommendation, the city decided to use submerged membranes in lieu of the existing granular media filtration process.
USFilter was chosen as the membrane supplier based on pilot testing, bids on equipment capital costs and on lifecycle costs.
An aggressive schedule allowed the plant to be brought online by 2005. Because of a limited construction window, the design and construction of this project was split into two phases.
A quick turnaround was key to the installation’s success. Converting the city of Kennewick’s water treatment plant from conventional filtration to membrane filtration involved an aggressive project schedule. Construction began in August 2004 and the plant was online by April 2005.
Specific tasks included:
• Increasing the pretreatment capacity from 7.5 to 15 mgd with a parallel
• Eliminating ozone using powdered activated carbon and potassium per- manganate for taste and odor control;
• Installing submerged membranes in the existing filter basins;
• Using the water washwater reclama- tion building to house the ancillary
membrane equipment and the wash- water plate settler; and
• Switching disinfection from chlorine gas to bulk sodium hypochlorite.
The Memcor CMF-S system offered significant cost savings for the conversion because no new buildings were needed. It provided the greatest flexibility to meet future regulations. It could be easily automated, and it had the shortest construction time. The plant was able to double water treatment capacity in the same footprint. The submerged membrane system’s thoughtful design allows the plant to expand capacity to 20 mgd by summer 2007.