Reverse Osmosis Project Example of a Shanghai Equipment Manufacturing Enterprise
Reverse Osmosis Project Example of a Shanghai Equipment Manufacturing Enterprise
The service life of the reverse osmosis (RO) membrane elements in this system is 5 to 7 years.
The main reason for replacement is the aging of the ultrafiltration (UF) membrane elements, which cannot be effectively restored through chemical cleaning. Unqualified SDI (Silt Density Index) of the product water may lead to serious colloid blockage in the RO system, high operating pressure, and large inter-stage pressure differences. The system uses non-oxidizing biocides instead of oxidizing biocides (NaClO) to avoid oxidative damage to the membrane elements. The membrane elements have been in use since May 2019 and as of July 2024, after 5 years of use, the overall desalination rate still reaches above 97%, which is very ideal. The following is an example of the optimization of this reverse osmosis system and some related data.
Recent Operating Parameters of the Primary Reverse Osmosis System
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Primary Reverse Osmosis System Operation Monitoring Data |
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|
UF Membrane Model |
Water Temperature (℃) |
Inlet Conductivity (su/cm) |
Inlet(pH) |
Product Water Flow (t/h) |
Concentrate Flow (t/h) |
Product Water Conductivity (su/cm) |
Inlet Pressure (Bar) |
Inter-stage Pressure (Bar) |
Concentrate Pressure (Bar) |
Membrane Desalination Rate (%) |
|
|
22 |
231.9 |
6.2 |
59.9 |
18.5 |
6.4 |
10.9 |
10.1 |
8.7 |
97.3 |
|
|
22 |
231.9 |
6.2 |
63.1 |
19.4 |
6.7 |
9.3 |
8.5 |
8.0 |
97.1 |
|
|
22 |
231.9 |
6.2 |
44.3 |
17.8 |
6.5 |
11.4 |
11 |
10.7 |
97.2 |
|
|
22 |
231.9 |
6.2 |
54.6 |
18,1 |
6.4 |
10.3 |
10.4 |
8.6 |
97.1 |
Project Overview
The project has adopted a new process flow. In the pre-treatment stage of the water treatment system and before the RO feed water, non-oxidizing biocides are used for shock dosing. By precisely controlling the frequency and concentration of the shock dosing, microbial contamination in the pre-treatment and RO feed water is effectively controlled. Therefore, the possibility of chlorine leakage is directly avoided by not dosing NaClO in the pre-treatment, which also eliminates the need for a reducing agent in the RO feed water. As a result, the membrane elements maintain a good desalination rate throughout their entire service life.
Process Flow
1.Yangtze River Water Intake: The raw water (Yangtze River water) is first introduced into the treatment system.
2.Coagulation Sedimentation Tank: PAC (Polyaluminum Chloride) and non-oxidizing biocides are dosed in the coagulation sedimentation tank. The coagulation effect of PAC causes suspended solids and colloids in the water to form larger particles, which then settle naturally in the tank, removing most of the suspended impurities. Meanwhile, the non-oxidizing biocide kills microorganisms in the water, reducing the burden on subsequent treatment processes.
3.Sand Filter Tank: The sand filter tank further filters out suspended solids and organic impurities in the water.
4.Raw Water Tank and Raw Water Pump: The filtered water is collected in the raw water tank and then pressurized by the raw water pump and sent to the raw water heater.
5.Raw Water Heater: The raw water needs to be heated appropriately before entering the ultrafiltration device to meet the requirements of the subsequent treatment process.
6.Screen-type Self-cleaning Filter: This filter removes any residual small impurities in the water to protect the subsequent ultrafiltration device.
7.Ultrafiltration Device and Ultrafiltration Water Tank: The ultrafiltration device removes colloids, bacteria, viruses, and other small particles from the water, and the treated water is stored in the ultrafiltration water tank.
8.Security Filter and Reverse Osmosis Device: Before the ultrafiltration water enters the reverse osmosis device, it first passes through a security filter to remove large particle impurities and protect the reverse osmosis membrane. Subsequently, the water is pressurized by the primary and secondary high-pressure pumps and then undergoes deep desalination treatment through the primary and secondary reverse osmosis devices, removing most of the dissolved solids, organic matter, and bacteria from the water.
9.Fresh Water Tank and Fresh Water Pump: The fresh water is collected in the fresh water tank and then pressurized by the fresh water pump and sent to the EDI (Electrodeionization) device.
10.EDI Device and Deionized Water Tank: The fresh water passes through the EDI security filter and then enters the EDI device for further purification. The EDI device uses electrochemical reactions to remove the remaining ions from the water, producing almost ion-free deionized water. The deionized water is finally stored in the deionized water tank and then transported to the main plant by the deionized water pump.
Design of the Primary Reverse Osmosis System
1.RO Membrane Model: DA-HSRO-4040
2.High Treatment Capacity: The system is designed with an output capacity of 4×94t/h.
3.Optimized Membrane Ratio: A membrane ratio of 12:6 with a 6-core design is adopted.
4.High Recovery Rate: The recovery rate is 75%.
Suggestions for Chlorine Control
1.Chlorine is one of the main factors affecting the desalination rate of the membrane elements. Even a chlorine concentration of less than 0.1mg/L can cause slow oxidation of the membrane elements. Therefore, it is essential to ensure that the chlorine content in the RO feed water is 0mg/L.
2.Although not dosing NaClO in the pre-treatment can directly avoid the possibility of chlorine leakage, the process lacks a device to detect chlorine. Therefore, an online chlorine monitor can be installed to determine whether there is chlorine in the RO system feed water, avoiding oxidative damage to the membrane elements.
3.Activated carbon filters are very effective in removing residual chlorine. If used only for adsorbing chlorine, the service life of the activated carbon can be 3 to 5 years or even longer.