First Commissioning of the RO System

It is key to ensure the long-term stable operation of the RO system by high-performance RO membrane elements, reasonable RO system design, and correct system operation and maintenance. The RO system is used and maintained by initial commissioning, daily use and maintenance, and system cleaning.

1. Inspection items before starting

● All pipelines, equipment, and connectors should meet the design pressure.

● The pretreatment equipment has been backwashed and rinsed thoroughly, ensuring that the effluent meets the design requirements, including SDI15<5, turbidity<1NTU, residual chlorine<0.1ppm, 0℃<temperature<45℃, pH=3～10, and no other oxidants (ORP<200).

● Check whether the status of all valves used in the system is appropriate, with the produced water discharge valve, concentrated water discharge valve, concentrated water pressure regulating valve, and flow bypass regulating valve of high-pressure pump fully opened.

● The chemicals and their concentrations in each dosing tank shall be accurate and reliable, and each chemical dosing device shall be set and operated correctly.

● All pipelines and equipment should meet the pH range of 2 to 12 (including during cleaning) specified by the design.

● All instruments shall be installed correctly and calibrated.

● Install high-pressure and low-pressure protection devices preventing back pressure and hydraulic shock and set them correctly.

● When using oxidants for sterilization during pretreatment, these oxidants shall be completely removed before entering the RO main unit.

● Check whether the automatic control electrical components of the RO system work properly.

2. Initial Startup Steps

1) Before starting the high-pressure pump, carefully check each item specified in "Inspection items before starting" to ensure that the pretreatment effluent meets the requirement of the RO feedwater.

2) Check all valves and ensure all positions are correct.

3) Fill the RO pressure vessel with qualified pretreatment effluent at low pressure and low flow rate and flush the membrane elements. At this time, the feedwater pressure should be controlled at around 30-60 psi, and the flow rate should be about 60-70% of the maximum feedwater flow rate of the corresponding membrane elements. Both the concentrated water and produced water should be completely discharged during flushing; antiscalants should not be added during flushing.

4) Pay close attention to whether there are any leakage points in the pipelines and connection components of the system, especially in the high-pressure parts.

5) It is recommended to flush membrane elements for the first time with qualified pretreatment effluent at low pressure for 15-25 minutes (soaking or overnight soaking is not advisable), and then flush at high pressure for 60-90 minutes (produced water flow rate should not be less than 50% of that designed for the system). Antiscalants should not be added during low-pressure flushing, but during high-pressure operation flushing. The produced and concentrated water should be discharged during the flushing process.

6) To prevent water hammer from impacting the membrane elements, the small-sized RO systems without electric slow-opening doors shall fill the pressure vessel (venting) with pretreatment water before starting the high-pressure pump; most of large-sized RO systems are started by electric slow-opening doors (electric butterfly valves) or the inverters.

7) Start the high-pressure pump. Slowly adjust the bypass control valve of the high-pressure pump to gradually increase the feedwater flow rate of the RO pressure vessel; at the same time, slowly close the concentrated water control valve to increase the pressure until the system recovery rate and produced water flow rate reach the design values. The pressurization process takes no less than 30-60 seconds, while the increase in feedwater flow rate takes no less than 20-30 seconds. Check whether the system operating pressure and membrane element pressure exceed the limit values.

8) Check whether the dosage of various drugs in the system is consistent with the design value.

9) Measure the conductivity of the feedwater, each pressure vessel, and the total produced water of the RO system. By comparing the produced water conductivity of each parallel pressure vessel, determine whether there are any leakage or other faults in the membrane elements, connectors, and sealing rings of the pressure vessels. Measure the pH value, conductivity, calcium hardness, and alkalinity of the concentrated water to calculate the LSI and S&DSI indexes thereof, and determine whether any CaCO3 scale is formed in the RO system under these operating conditions.

10) Allow the system to run continuously for 1-2 hours and record all operating data. After the system is put into normal operation, run continuously for 24-72 hours, then re-record all operating data and archive them.

11) Compare the design parameters based on the  operating and water quality analysis data, check whether the equipment runs normally and determine whether it meets the design requirements.

12) During the first week after commissioning, test the system performance regularly, and carefully record the operating parameters, ensuring normal operation of the equipment.

3. Determine the stability of the initial performance of membrane elements

It takes certain time for newly commissioned RO membrane elements to transition from initial performance to a stable state. Dry membrane elements can achieve stable performance after continuous operation for 2 days or longer.