An important part of operating membrane systems is accurate data collection on a daily basis. The data will help predict normal maintenance schedules and will help determine the cause of any system upsets. Comprehensive data is very useful in determining when the membranes need to be chemically cleaned, or eventually replaced. It also alerts the operator to changes taking place such as fouling, leaking “O” rings etc.
The following description explains the typical data parameters listed on the Harn R/O Systems’ data sheets. At the end of each month the operator sends Harn R/O a copy of the completed data sheets for each plant that Harn R/O Systems has provided. Harn’s technical services department reviews and provides comments back to the plant operator. There is no charge for such service to Harn’s customers, and experienced eyes can detect trends indicating the need for cleaning, maintenance, or flow adjustment.
Description of Parameters to Monitor
Comments: Use one sheet for each train. Enter any additional information as might relate to the operation of the RO system (i.e., restocking day tanks, pre-filter changes, instrument calibration, which wells were operating, etc.).
Date: Enter the date of data collection – note: this should be done daily.
Cartridge Filter Inlet Pressure: Enter the well water pressure at the inlet to the main cartridge filter housing. If a low service boost pump is present then it would be same as low service boost pump discharge pressure.
Cartridge Filter Outlet Pressure: Enter the filtered water pressure at the outlet of the main cartridge filter housing.
Differential Pressure (dP): Enter the difference between the two preceding figures. Differential pressure should not exceed more then 10-15 psid. Read more on pretreatment here.
Silt Density Index (SDI): Enter the SDI of the feed water. This operation should be performed daily to assure that the feed water supply remains relatively free of particulate matter. Changes in the SDI can indicate that the raw water supply is changing or that the pretreatment process may need attention.
Hour Meter: An hour meter for the RO feed pump is usually located on the PLC control panel or in the MCC. The elapsed run time will determine pump/motor maintenance and help keep individual train operation even.
Feed Temperature: The temperature of the raw water supply affects the operation of the membrane system as well as the membrane pressure and permeate quantity. Generally, as the raw water temperature drops the permeate flow is reduced, unless additional membrane feed pressure is applied to the system to compensate. The temperature is usually displayed on the PLC control panel.
Feed Conductivity: Enter the feed conductivity in micromhos/cm. The feed conductivity may be displayed on the PLC control panel or on SCADA.
Permeate Conductivity: Enter the total permeate conductivity in micromho/cm. The total permeate conductivity may be displayed on the PLC control panel or on SCADA.
Rejection (%): Rejection is calculated from the feed water and permeate conductivities. Subtract the permeate conductivity from the feed water conductivity, and then divide that number by the feed water conductivity. To convert the resulting decimal to a percentage, multiply it by 100. The resulting number is the overall system rejection.
Feed Pressure: The feed pressure is the pressure at the membrane inlet of the first stage. This pressure is obtained by the selector valve and pressure indicator located on the RO skid panel or from a pressure transmitter reading on the PLC readout.
1st Stage Concentrate Pressure: The 1st stage concentrate pressure is the pressure as the concentrate exits the 1st stage vessels. This pressure is obtained by using the selector valve and pressure indicator on the R/O skid panel or from a pressure transmitter reading on the PLC readout.
2nd Stage Feed Pressure: The 2nd stage feed pressure is the pressure at the membrane inlet of the 2nd stage. This pressure is obtained by the selector valve and pressure indicator located on the RO skid panel.
Total Concentrate Pressure: The concentrate pressure is the pressure as the concentrate exits the vessels; prior to the concentrate control valve. This pressure is obtained by using the selector valve and pressure indicator on the R/O skid panel.
1st Stage Permeate Pressure: The 1st stage permeate pressure is obtained by using the pressure transmitter or the pressure indicator on the RO skid panel.
Total Permeate Pressure: The permeate pressure is obtained by using the pressure transmitter or the pressure indicator on the RO skid panel.
1st Stage Permeate Flow: The 1st stage permeate flow is indicated on the flow transmitter mounted to the RO skid panel.
Total Permeate Flow: The total permeate flow is indicated on the flow transmitter mounted to the RO skid panel.
Concentrate Flow: The concentrate flow is indicated on the flow transmitter mounted to the RO skid panel.
% Recovery: The recovery of the RO system is calculated by the total permeate flow divided by the feed flow. Learn more about percent recovery in the following blog post.
Feed Pump Speed: The Feed Pump VFD speed can be read from the MCC display.
There are some additional rows for recording other useful parameters such as scale inhibitor flor rate, 1st and 2nd stage permeate conductivities, concentrate valve position plus some readings that may need to be taken by hand sampling such as individual vessel flows or conductivities.
Notes should be made of dates of events such as chemical transfers, cartridge filter changes, system shut-downs etc.).
Maintain thorough and complete data sheets as the membrane manufacturer warranty requires all information be maintained especially during the membrane warranty period. The data collected can help determine the cause of system upsets and assess the need to clean the membrane elements. Cleaning elements when they are fouled can stretch out the time needed to buy new elements later.
Additionally; send all data to Harn R/O Systems on a monthly basis for review. This is a service provided with every membrane system we provide free of charge. We can also help you set up spreadsheets for data monitoring to automatically normalize and graph your data.