OptaCell™ Plus Configured for Calcite Contactor Provides Flexible Operation While Stabilizing Aggressive Water

Craven County is located in the Eastern part of North Carolina at the mouth of the Neuse River. Their new water treatment plant was to include a reverse osmosis/nanofiltration (RO/NF) membrane system; however, the small membrane pore size removes many beneficial minerals, often resulting in a corrosive water. To stabilize the water before sending to distribution, Kurita America furnished a calcite contactor system in a horizontal pressure vessel configuration with fully isolated cells for flexible operation.

The RO/NF membrane process removes minerals associated with hardness and alkalinity, which affect the water’s pH and the overall molecular balance. Left alone, RO/NF membrane-treated waters could dissolve protective mineral deposits on the inside of pipes in the distribution system, releasing trace metals and other imbedded contaminants while exposing raw material to potential corrosion. This can impact aesthetic quality related to clarity, taste, and odor; and raise health concerns as contaminants, which accumulate slowly over many years in a distribution system, are released in a short amount of time, causing concentration spikes. A calcite contactor can be inserted after treatment to mitigate this, ensuring that a stable, balanced finished water enters the distribution system.

Calcite is a calcium carbonate media, crushed and sieved to a desired particle size. As water flows up through the media it dissolves the calcium carbonate solids until an equilibrium is met, in the process raising pH while adding both hardness and alkalinity back into the water. After treatment, the stabilized water will be less likely to cause corrosion concerns in the distribution system. As the calcite is consumed, it must be replaced periodically to sustain operation.

Kurita America provided two OptaCell™ Plus horizontal pressure vessels for calcite contactors. Generally configured for conventional media filtration, the units were customized to facilitate counter-flow operation with underdrain distribution and over-drain collection using stainless steel internals.  Further customization integrates each cell with a calcite conveyance system for ease of media replenishment. The OptaCell Plus offers the greatest in operator flexibility as each cell is completely isolated from the others and independently pressure tested, giving full redundancy that allows the addition of calcite to an individual cell without removing the others from service. Kurita America also provided a PLC control system to fully automate system operation and flush sequences.

Craven County unveiled their new water treatment facility in 2017. Kurita America’s calcite contactors provide an essential finishing process to protect the County’s potable water system and ensure a high level of quality.

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