Why Salt is a Problem
Increased salinity in water supplies in Arizona, and specifically Maricopa County, is an issue of growing concern. As people try to combat the natural water hardness of Arizona water supplies using conventional water softeners, increased discharge levels of salt are introduced into sewers, treatment plants and, at times, into groundwater aquifers through recharge. The increased salinity negatively impacts the environment and adds significant costs to our treatment processes.
The predominant residential method of combating hard water is water softening through ion exchange. Self-regenerating water softeners (SRWS) accomplish softening by employing resin to exchange sodium ions for the hardness ions present in source water. When the resin has exchanged all of its available sodium ions for hardness ions, a regeneration or flushing cycle is required to replace the lost sodium ions. The result is a waste stream of brine and hardness ions discharged to the sewer system. It’s through these repetitive discharges to the sewer system that SRWS add more salts to the wastewater stream.
Methods to Reduce Salinity
Scottsdale is unique among Arizona cities in our proactive work to reduce salinity in reclaimed water. Traditional wastewater treatment processes are not designed to address salinity, so elevated salinity concentrations in sewage translate into elevated salinity of reuse water – unless more expensive advanced water treatment is applied. The Advanced Water Treatment (AWT) facility at the Water Campus features a reverse osmosis system that reduces salinity in water used for golf course irrigation and indirect potable recharge. The technology is effective, but expensive.
The best way to reduce the costs of dealing with salinity is to reduce the salt at the source, before it is introduced into the waste stream. SRWS are estimated to increase the salinity of wastewater in Scottsdale by over 300 mg/l, which amounts to about 30 percent of the total salinity of the sewage discharged (the remaining salinity already exists in our CAP and SRP source water). A reduction of wastewater salinity by half this much, or 150 mg/l, could reduce the operating costs of the AWT by as much as $200,000 per year.
Scottsdale Unsalted Rebate Program
Water Resources has evaluated several strategies to reduce salinity caused by SRWS. To assess the viability of these strategies, including cost effectiveness and customer satisfaction, we developed a two-year pilot rebate program offering three specific rebates. Scottsdale’s City Council approved the program in March of this year by a 6 to 1 vote. The program is designed to reduce salinity entering the sewer system, while offering customers a range of options depending on their personal water quality preferences. The three approved rebate options available to Scottsdale sewer customers are as follows:
- Improved Efficiency Ion Exchange Water Softners: Rebates for customers who replace their less efficient, self-regenerating ion exchange water softeners with a new, more efficient ion exchange unit. This rebate allows the customer to continue to address hard water using a SRWS, but phases out less efficient units still in service.
- Portable Exchange Water Softners: Rebates for customers who remove their existing self-regenerating ion exchange water softener and subscribe to a portable exchange service, where the spent resin tanks are removed and replaced by a service provider who more efficiently regenerates the resin at their central facility. This rebate allows customers to soften their water through ion exchange, but the discharge to the sewer from the customers’ home is eliminated.
- Salt-based Water Softener Removal: Rebates for customers electing to disconnect and remove their existing self-regenerating ion exchange water softener. This rebate is for customers interested in discontinuing ion exchange water softening altogether.
The two-year rebate program officially kicked off on July 1 and as of Sept. 5, we have received over 60 applications. While we cannot recommend specific brands or companies, we do suggest that customers review a couple of websites: the Los Angeles County Sanitation District and the Arizona Water Quality Association. Both of these websites are great resources for learning about salinity and residential water treatment options. More information on this program and the rebate application are available on the Scottsdale Unsalted webpage.
From time to time, Water – Use It Wisely features guest bloggers who write about topics related to water and water conservation. The author of this blog post, Christopher Hassert, was appointed Water Resources Planning and Engineering Director for the City of Scottsdale in June 2008. As Planning and Engineering Director, he is responsible for planning and engineering of water, reclamation and reuse systems. He also acts as technical advisor performing policy level coordination, advisory, and administrative functions relating to capital projects in the Water Resources Division. Prior to joining the City of Scottsdale, Chris designed, inspected, and managed capital projects including, sewer collection systems, water/wastewater pump stations, water distribution systems, and wastewater treatment facility components. He is a professional engineer in the State of Arizona and has 22 years of civil engineering design and project management experience.