Struvite Belt Press Removal Case Study
A wastewater treatment plant near Flagstaff, AZ was experiencing problems with keeping their belt aligned on the belt press. The belt press was in operation 4 days per week for 6 hours per day. The flow rate was 150 gallons per minute (gpm). Upon close inspection of the belt press system, the maintenance staff observed scale deposits on the rollers, pan and filtrate lines. Samples were taken for analysis. The lab report indicated that the scale deposits were composed of magnesium, ammonia and phosphate, which is struvite.
The plant acquired several products from different suppliers and ran a bench study to determine which product would dissolve the struvite and not damage the belt cloth
They took five (5) one gram samples of the struvite deposit and one inch squares of the belt cloth to soak in 100 ml for 24 hours. From these five tests, they found that Struvite Remover had the best performance. They ordered 5 gallons for additional testing on the belt press.
For the plant trial on the belt press, they make up a 50% solution of Struvite Remover and used a 3.5 gallon garden sprayer to deliver the dilution of product. Thirty minutes prior to shutting down the system they sprayed the 50% solution on the belt cloth, rollers and belt press pan. In the morning, they would run the rinse cycle for 10 minutes and start up the dewatering cycle.
After 5 operating days, the struvite deposits on the rollers had disappeared. Struvite scale on the belt press pan and wet areas started to disappear too! The overall operation of the belt press improved. They saw drier cake and used less polymer per dry ton. It looked liked the belt cloth was draining better, which meant the old polymer films were being removed too.
Upon completing the plant trial, they installed a small metering pump on a timer to feed Struvite Remover on the belt press at the end of the operating day. They no longer have a problem with the belt going out of alignment due to struvite deposits.