Delaware plant treats high-turbidity water
Originally constructed in 1917, then renovated in 1933, the Brandywine Water Treatment Plant in Wilmington, Del., required a retrofit into its mixed-media filter basins’ footprint in order to meet stringent drinking water standards and produce drinking water for approximately 200,000 New Castle County residents, including the city of Wilmington. Furthermore, the facility needed a robust system, as it had previously experienced significant turbidity occurrences due to heavy rainfall. As such, managers found that the plant’s conventional treatment, consisting of fixed-media filter beds, was not sufficient in preventing bacteriological breakthrough during elevated turbidity events.
To avoid the possibility of a bacteriological breakthrough or a violation of the U.S. Environmental Protection Agency (EPA)’s water surface treatment regulations, facility operators needed to find a treatment method that could adhere to EPA requirements, while delivering an efficient and higher-quality effluent—thus the plant upgrade.
To determine a suitable treatment method, the plant conducted a side-by-side pilot evaluation over a six-month period for which ferric chloride was used as the coagulant and actual flux rates were between 75 to 93 gal per sq ft, per day. A turbidity spike of 60 ntu, which lasted four days, was experienced during the pilot program. During that timeframe, the coagulant feed was discontinued, resulting in high transmembrane pressure (TMP), which caused excessive fouling of the membranes. Raw water from Brandywine Creek is coagulated with PAX-XL 19 aluminum chlorohydrate and settled in a sedimentation basin after pretreatment before reaching the membranes for filtration.
The membrane unit at the Brandywine Water Treatment Plant helped it increase capacity and meet stringent standards.
Following the pilot study, the city of Wilmington chose to upgrade its water treatment plant with a custom-built Aria FLEX filtration system from Pall Corp. that retrofits into the allotted footprint. The system offered the most effective treatment with minimal maintenance, as well as cost savings on water disinfection chemicals. It was the only unit capable of achieving a recovery rate of more than 98% of the original permeability. Additionally, it was compatible with the plant’s SCADA system, and effectively integrated with a quick turnaround time when placed back into service for minimal non-Pall, system-related downtime.
The system’s filters offered an advantage over the plant’s conventional system, as virus removal and chemicals were able to be delivered quickly, allowing the plant to more readily meet its disinfection regulations.
“The quality of water that the Pall racks produce is very good,” said George Flowers, water production supervisor at the Brandywine Water Treatment Plant. “This is a great system that is superb at removing impurities in water.”
While the plant’s conventional fixed-media filter beds were able to handle 100 APU, there was great risk associated with high-turbidity events. As bacteria were more prone to break through the filters, the plant needed to use excess amounts of chlorine to ensure that crypto giardia and other viruses were destabilized, in addition to conducting frequent backwashes, which produce higher volumes of wastewater. Occasionally, the plant would shut down during high turbidity events to avoid the possibility of an outbreak.
Since implementing Pall’s system, the plant has not been required to shut down when experiencing a high turbidity event, as the system is “equipped to handle higher raw water turbidity events in a more efficient and effective manner,” Flowers said.
A Simpler Process
The completed deployment of the Aria FLEX system allowed the plant to instantaneously reach a peak capacity of approximately 14 mgd. Overall, the water treatment process has been significantly simplified and improved since being put in place. The project resulted in the facility’s ability to increase its average capacity to 7 mgd, with peak instantaneous capacity of approximately 14 mgd. The plant upgraded from existing conventional treatment to a new system within its existing footprint.
Beyond the improved facility operations, the operator-friendly nature of the system was an asset to the plant. The previous method required an operator on-site at all times to maintain the water treatment and chemical levels. With the new system, facility operators can more readily manage other non-treatment-related operational tasks, while continuing to monitor and adjust water levels with ease as needed.
“Pall offers a virtual push-button system for the operator,” Flowers said. “Once the equipment is up and running, it is a pretty robust, virtually hands-off system that has dramatically simplified the water treatment process. The operator does not have to be as hands-on as [he or she] needed to be when we had the conventional system. There are no filter beds to measure and there is no need to check the clarity. The system automates everything and is easy to maintain.”
Pall’s Aria CARE customer service team were responsive, equipped and prepared throughout the installation process, and now provide continuous, remote monitoring to ensure the system is fully operational on an ongoing basis. Technicians worked with Brandywine plant operators to review the system’s practical and process operations, as well as shared best practices with the team. With the rental agreement, the team offer 24/7 phone support, and a technician can remotely troubleshoot any issues that may arise and quickly make necessary changes to the system.
Following its deployment, the customized membrane unit was able to fulfill the water quality needs of the Brandywine Water Treatment Plant, allowing it to meet more stringent drinking water standards of less than 0.03 ntu while delivering on the facility’s peak capacity needs. Not only does the plant no longer require a shutdown when experiencing high turbidity events, but it also is able to save time, resources and money due to the efficiency and quality of the new system.