Membrane Pilot Testing at City of Tempe Water Treatment Plant
Carollo Conducts Membrane Pilot Testing at the City of Tempe Water Treatment Plant
Carollo Engineers, in partnership with the City of Tempe, is conducting a study to evaluate low pressure membrane filtration for treatment of Arizona’s Salt River Project canal water. In addition to providing an absolute barrier against pathogens such as Cryptosporidium and Giardia, microfiltration and ultrafiltration membranes are being used in combination with powdered activated carbon (PAC) to remove taste and odors. Two pilot units are being testedside by side, while a third pilot unit is being used to evaluate ceramic microfiltration membranes as an alternative for recovery of filter waste washwater. Hydraulic performance data alongwith physical and microbial water quality data developed from this study will be used to develop design criteria for full-scale implementation of membrane filtration.
For this study Carollo is developing the experimental plans, setting up the pilot units, and performing PAC testing. Carollo is also responsible for acquiring, interpreting and reporting all data. This task involves the use of an online data acquisition and master programmable logic controller system that allows remote monitoring and operations adjustment. Carollo is also in charge of pilot plant operations, including performing membrane chemical cleaning when required. The City of Tempe is assisting Carollo in setting up the units and providing daily maintenance and monitoring of the pilot plants. The City is also conducting water quality analyses.
Pilot Plant Process Description
Raw water is pumped from Tempe’s South Water TreatmentPlant bar screen area. Before entering the pilot area, PAC is added to the raw water feed line, ensuring that both units receive the same dose.
Microfiltration Pilot Plant Process Description
As shown in Figure 1, raw water for the Memcor microfiltration unit is fed to a 200-gallon storage tank. Raw water is then fed to the outside of the hollow membranefibers through the upper and lower headers of the membrane modules. The water is forced across the membrane producinga clean permeate which travels through the lumen of the fibers. Permeate flow is adjusted with a diaphragm valve providing back pressure. This unit utilizes an air backpulse backwash coupled with raw water scour. During backwash, high pressure air is vented through the membrane, causing a forceful outward release that loosens the cake of particles accumulated on the membrane’s outer surface. Raw water is rushed along the outside of the fibers, scouring away loosened particles. The membrane flux and the backwash frequency depend upon raw water quality and PAC dosage. These operating parameters are being optimized during the study.
Ultrafiltration Pilot Plant Process Description
The Aquasource ultrafiltration membrane pilot plant treats the same water source as the Memcor unit. Figure 2 illustrates a flow diagram of this unit. Downstream of the feed pump, a 200 µm prefilter retains the larger debris and prevents clogging of the hollow fiber lumen. Prefiltered raw water enters the concentrate loop and a recirculation pump.
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