Carollo Engineers’ single-element reverse osmosis (RO) and nanofiltration (NF) pilot plant pro-vides a fast, cost-effective way to screen membranes and pretreatment chemicals. This pilot plant re-quires only one membrane element for each test, in comparison to the demonstration-scale pilot equipment which requires 21 membrane elements. For screening tests, where the results are not certain, the cost of the membranes and the rental fee for the two-stage demonstration-scale equipment is not justified. Cost-effective screening is accomplished with this pilot by using one membrane element, and simulated full-scale operational settings such as hydraulics and recovery.

Critical to the successful screening of membranes and pretreatment chemicals is an accurate simulation of the full-scale design conditions. Flux, recovery, and cross-flow velocities are important parameters in these evaluations and must represent full-scale conditions to provide an appropriate evalu-ation. The pilot plant is equipped with a program-mable logic controller (PLC) system capable of controlling feed water pH, permeate water flow (i.e., flux), and recovery. Full-scale cross flow conditions are created through concentrate stream recirculation, which provides adequate flow into and out of the membrane element. The system is also equipped with a data acquisition system that is accessible by remote telemetry. A low head feed water booster pump is provided, operating at approximately 5 gallons per minute (gpm) at 30 to 60 psi. As water flows through the pilot plant, pretreatment chemicals (i.e., acid and scale inhibitor) are added and the water is passed through cartridge filters. Cartridge filtered water is mixed with recycled concentrate water and the pressure is boosted using a high-pressure RO feed pump. Flows and pressures are metered at all critical locations. The permeate flow rate is controlled by metering permeate water flow rate and varying the speed of the high-pressure pump variable frequency drive (VFD). The recovery is controlled by metering concentrate flow rate and adjusting it with a control valve. A sample tap panel is provided to gather water from all points throughout the process. Manual flow measurements can be taken to verify electronic meter calibration.

Carollo has used this pilot plant to screen membranes and to develop initial design criteria in Florida, Kansas, Missouri, South Carolina, and Utah. It is sufficiently flexible in design to be housed in filter galleries, maintenance sheds, and temporary storage trailers. O&M manuals and standard operating procedures (SOP) are available. Data spreadsheets are also available to generate report-quality graphics.