The Cincinnati Zoo uses an ultrafiltration system (UF) to treat stormwater. The reclaimed water is collected from 14 acres of the park, including parking lots, animal exhibit yards, rooftop drains, and walking path storm drains. Those sources are combined and routed through a straining basin to a 300,000-gallon retention tank system. From there, the water is pumped from a wet well to the UF system, producing irrigation water and make-up water for various animal exhibits. These include underwater viewing of polar bears and sea lions, as well as moats for lions, cheetahs, and African wild dogs.
The UF stormwater recovery system was showing a drastic deterioration in product flow. A contracted service company performed an extensive cleaning. They first circulated a competitor’s acid cleaner at a pH of 1.6 for two hours, followed by an alkaline cleaning at pH 12.8. The high pH cleaner was circulated for about 1.5 hours at 96°F, followed by an overnight soak.
The next morning, the system was cleaned for a few more hours with a fresh alkaline solution at pH 12.4. The system was finally cleaned with a second acid solution for an additional hour. The transmembrane pressure (TMP) and flow did not recover to design values. Within a few days, the product flow started to decrease again until the UF system’s operation had to be completely halted.
The Cincinnati Zoo operations team requested Alkema Solutions’ assistance in finding an optimum procedure to clean their UF elements. A cleaning study was performed in our laboratory and it was determined that a 2 percent solution of AWC UF-428, an alkaline, chlorinated cleaner, should be applied. The most effective cleaning protocol consisted of alternating forward and reverse circulations with soaking for a total of 6 hours.
These recommendations were implemented in cleaning the remaining modules. As a result, the UF system’s performance was recovered with a 20-fold increase in flux and an 87 percent decrease in TMP. These positive results enabled the Cincinnati Zoo to resume operation of the UF system at optimum performance, thereby enabling them to handle the stormwater runoff.