May 2007, Vol. 19, No.5

Problem Solvers

Lower Nitrates, Low Maintenance

Problem:

Increased nitrates and perchlorate contamination in well water.


Solution:

Service ion-exchange vessels remove contaminants.

The City of Porterville in the agriculturally rich Central Valley of California has a well system owned and operated by California Water Services Co. (San Jose, Calif.). This stand-alone system supplies water to approximately 44 customers. The ongoing use of fertilizers in the area, as well as unregulated septic systems, contributed to an increase of nitrates in the water. Also, an unidentified plume of perchlorate contamination was found in the well water.


The nitrate concentrations had been steadily increasing, and through continuous monitoring, California Water Services determined that the nitrate concentration exceeded their in-house standards for California Department of Health Services (DHS) compliance during winter 2003, and the well was taken out of service. California Water Services had to provide bottled drinking water to residents, while some water was pumped to residents for nonpotable use

Searching for Solutions

California Water Services looked for options to provide water to its customers, but its efforts were hampered by the area’s lava-rock-based geology, which is not conducive to drilling a new well. The company needed a system that could be installed to keep the contaminated wells in service while meeting the DHS requirements for nitrates and perchlorate in the finished water. The system had to be very low-maintenance, reliable, and not produce any onsite wastes that would require disposal. California Water Services also reviewed onsite regenerable systems but removed them from consideration, since it had no means to dispose of onsite-generated wastewater.

California Water Services asked Siemens Water Technologies (Warrendale, Pa.) to design and build a system to remove the nitrates and perchlorate. The final design used two separate service ion-exchange systems.

Service ion-exchange technology consists of vessels containing ion-exchange resins that treat the water. When the resins in the vessels are no longer able to remove contaminants (have reached their capacity limit), a service technician removes the resins by slurrying them from the vessel and transports them offsite for regeneration or disposal. Fresh resins are slurried into the vessel, making the system operate continuously.

Two vessels were installed at the contaminated well site to remove perchlorate, each containing perchlorate-selective resin. The water was pretreated before it was fed to the nitrate system to prevent perchlorate buildup on the nitrate resin.

Two vessels also were installed to remove nitrate. Each of these vessels contained nitrate-selective anion exchange resin.

In both the perchlorate and nitrate removal systems, the first vessel removes the bulk of the contaminant while the second vessel continuously “polishes” the water to meet final effluent quality guidelines.

Benefits of Service Ion Exchange


With service ion exchange, the utility does not have to worry about resin regeneration and disposal. The vendor exchanges the perchlorate resins approximately once every 6 months and the nitrate resins about once every 3 months. The vendor also takes the spent perchlorate resins to an incinerator for disposal and returns the spent nitrate resins to its offsite regeneration plant, where they are regenerated, disinfected, and held for the next exchange.


According to Nelson Lui, project engineer for California Water Services, the system operates with little or no maintenance and contains one continuous nitrate monitor to monitor the nitrate effluent water quality.


These low-maintenance requirements make the ion-exchange system cost-effective for the plant. California Water Services spends only about 6 hours per week for overview of the system, which frees its technicians for other work. The system is leased from Siemens Water Technologies, so the only capital costs were for installing the system and leveling ground work, which included a concrete pad, piping, and a small amount of electrical work for $90,000

For more information, contact Lui at (408) 367-8330 or nlui@calwater.com; Tim Peschman, remediation product manager at Siemens Water Technologies, at timothy.peschman@siemens.com or (651) 638-1325; or Doug Gillen, director of environmental products at Siemens, at douglas.gillen@siemens.com or (415) 613-7597.