Archive for February, 2012
Copper fouling in a water softener in Utah
One of Intermountain Soft Water’s Utah soft water service technicians sent me this photo today:
The photo shows the rear view of an Imperial 2.x series water softener with its solenoid back-cap removed. The flow path of this control valve is such that the backwash port is at the bottom, and soft water flows through the top port for time brine refill.
The softener is 5 years old and the homeowner has been neglecting to maintain his Pur-Gard fluid level. It is evident that there are low levels of copper in his influent water supply. The low levels of copper have been retained within the softening resin and then discharged as a concentrate during the regeneration process. The milky blue color in this picture is from copper sulfate which forms during the regeneration process.
Copper can come from a variety of sources, not just from the city supply. This particular city’s Consumer Confidence Report indicates negligible levels of copper at the plant, so evidently the elevated copper is a localized issue.
Ionic copper levels can increase due to localized corrosion from dissolved CO2 gas, electrolysis, and even microbially induced corrosion.
Water softeners are primarily designed to remove calcium and magnesium ions from water. All cation resins are attracted to metallic ions, but very few resins are able to release them properly and uniformly during a regeneration.
Resin cleaners like Pur-Gard assist the resin in purging metallic ions from it’s structured matrix. As a side benefit, Pur-Gard will hold the metals in suspension through the use of EDTA, an effective chelating agent.
By not keeping their Pur-Gard reservoir consistently full, the resin was unable to effective purge heavy metals from its matrix. Metallic fouling will cause a decrease in the overall effective capacity of the resin. This capacity decrease results in the softener being unable to maintain a continuous supply of soft water.
The homeowner noticed evidence of hard water bleed-through with hard water spotting, poor laundry results, and soap scum. Being enterprising, he adjusted the efficiency setting on his Evertech controller and causes the system to use more salt to clean itself. This was a temporary solution to the symptoms, but did not actually address the underlying problem.
High concentrations of salt brine can induce osmotic shock to resin and accelerate natural attrition. Accelerated attrition induces premature physical failure and the resin will begin to crack and fracture. Cracking and fracturing result in a net pressure drop across the resin bed which diminishes the systems overall ability to properly clean itself and causes a greater deltaP (Pressure differential) during service.
The solution to this problem was a complete cleaning and disinfection as well as augmenting the resin with Hydrolyte 525-2, designed specifically to accommodate metallic ions in water with a minimum of physical attrition.
Dealing with Organic Fouling on Anion Resin
Brine cleaning is an effective treatment for removing organic contaminants on strong and weak base anion resins in demineralizers, organic traps and Dealkalizer units. When working with elevated levels of organics in the feed water, it is smart to perform regular brine treatments as part of your planned preventative maintenance program.
The following cleaning procedure is quite effective:
- Run resin column to the exhaustion point at 25% of your normal service flow rate.
- Backwash at the regular DLFC (Backwash Flow Control) rate for 10-20 minutes. An air-sparging will be helpful – plan on a minimum of 4 Bed Volumes.
- Drain the bed completely.
- Pump 2 bed volumes (13 gal/cu.ft) of a warm 10% NaCl or 1% NaOH solution into the mineral tank.
- Drain to bed level over 1 hour and allow the regenerant solution to soak for a further 3-16 hours. (An alkaline brine solution warmed up to approximately 120°F (50°C) for type I and weak base anions or 105°F (40°C) for type II.
- Displace with 2-3 bed volumes water (15-20 gal/cu.ft) over 20-30 minutes.
- Rinse out with 3-5 bed volumes DI water fast rinse (20-40 gal/cu.ft).
- Regenerate the system twice (same regenerant concentration).
- Rinse and return the system to service.
- Run 80% of the standard run-cycle to drain.
- Regenerate the system.
Obviously, soft/softened water is the ideal for operation anion systems and ESPECIALLY for regeneration and remediation procedures like this.