White Plains Microfiltration Plant Upgrade - Changing Membrane Material and Overcoming Challenges

Authors:

  • Anni Luck, Troy Walker - Hazen and Sawyer
  • Joseph J. Nicoletti, Jr., Brian Murphy - City of White Plains

The City of White Plains purchases over 90% of its water supply (average demand of 8 mgd) from New York City (NYC). Consumption of water by White Plains in excess of the current NYC per capita usage is assessed at a surcharge. Therefore, to avoid the excess usage surcharge, the City installed two microfiltration (MF) membrane units at its Orchard Street Pumping Station in 1999 to treat water from its two nearby reservoirs. At the time of its installation, this facility was one of the first MF systems piloted and fully commissioned in the Northeast. The MF units were operated only during the summer months (mid-May through mid-September) to meet the higher water demands experienced during these months by supplementing the water purchased from NYC.

Due to unforeseen changes in source water quality, these MF units are currently out of service. Iron fouling in the interstices between the polypropylene (PP) membrane fibers within the modules has resulted in poor production performance, fiber breakage, and a poor response to fiber cleaning. As identified through an autopsy on a sample module, iron from the feed water appears to have deposited in between the membrane fibers and expanded the fiber bundle onto the supporting mesh, leading to compression and breakage of the outer fibers in contact with the mesh.

After reviewing alternatives, including purchasing new systems from another membrane vendor, the City decided to replace the membrane modules within the existing MF skids. The retrofit will consist of replacing the existing PP fiber membrane modules with new polyvinylidene fluoride (PVDF) membrane fiber modules, providing provisions for iron and manganese pretreatment, modifying the backwash method to incorporate a new low-pressure combined air/water backwash procedure, and physical modifications to the MF skids to accommodate the new system upgrades. The MF plant upgrade maximizes re-use of existing equipment where appropriate while incorporating the latest membrane technology and improving operational ease.

This paper provides an overview of the drivers for the project while elaborating on:

1) BENEFITS (pretreatment flexibility offered by the oxidant-tolerant PVDF fibers, energy savings from the new low-pressure backwash system, cost savings from maximizing re-use of existing infrastructure and use of lower cost MF cleaning chemicals, etc.);

2) CHALLENGES (designing within existing space constraints, minimizing impact to existing processes, integrating upgrades around existing equipment, etc.);

3) LESSONS LEARNED (providing operational flexibility to account for potential future water quality fluctuations, sample case study of cost-effective upgrade through re-use of existing MF skid with membrane material change-out, etc.)

For more information, please contact the author at aluck@hazenandsawyer.com.

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