Basic terms of reverse osmosis
Source: | Author:demihmain | Publish time: 2020-07-07 | 334 Views | Share:
what is ro system and ro membrane,we should start with these terms

Reverse osmosis membrane: a functional semi permeable membrane that allows solvent molecules to pass through but not solute molecules, is called reverse osmosis membrane.


Membrane element: the smallest unit of reverse osmosis membrane which can separate water inflow and water production is called membrane element by assembling reverse osmosis membrane with inlet channel grid, water producing channel material, water producing central pipe and stress resisting device with adhesives.


Membrane module: membrane components are installed in the pressure vessel shell to form membrane components.


Membrane device: a complete set of unit composed of membrane element, instrument, valve, high-pressure pump, security filter, local control panel and rack, which can be operated independently. Membrane device is used to realize reverse osmosis process.


Membrane system: a complete membrane water treatment process, which is designed for specific water source conditions and water production requirements, is controlled by pretreatment, dosing device, booster pump, water tank, membrane device and electrical instruments.

Section: the concentrated water of membrane module flows through the next group of membrane modules, which is called several sections.


Grade I: the water produced by membrane module is treated by the next group of membrane modules, and the water production after several times of membrane module treatment is called several stages.


Water production: water production refers to the water production capacity of reverse osmosis system, i.e. the amount of water passing through the membrane per unit time, usually expressed in t / h.


Recovery: refers to the percentage of feed water converted into produced water in membrane system.


Recovery rate = (produced water flow / inflow flow) × 100%


The recovery rate is related to the number and arrangement of membrane. Generally speaking, if the water flows through the membrane module composed of six membrane elements, the recovery rate of the first stage and the first stage is 50%, 75% and 87.5% respectively. The recovery of hydantoin membrane was 15%.


Desalination rate: desalination rate = (1-water conductivity / influent conductivity) × 100%


Conductivity: the ability of a solution to conduct current in numbers. It is often used to infer the total concentration of ions in water indirectly.


SDI: SDI (silt density index), also known as the sludge density index (fouling index), is an important index to characterize the inflow water quality of reverse osmosis. Different from turbidity, turbidity is to determine the content of particles and impurities in water by spectrophotometer or visual turbidimetric method, but it can not accurately measure some colloidal particles which are not sensitive to light. Turbidity is not necessarily proportional to SDI: that is, water with low turbidity may have a high SDI value. This is because there are quite a lot of pollutants that can pass through the water and can pollute the membrane, and these pollutants are often not detected when measuring the turbidity of raw water. Generally, SDI < 5 is required for the influent of reverse osmosis, and the maximum turbidity limit is 1ntu, which is generally controlled between 0.3-0.5ntu.


Redox potential: ORP is a parameter that characterizes the amount of oxidizing and reducing substances in water. The unit of redox potential is millivolt (MV). When the redox potential is positive, it means that there are oxidizing substances in the water body; when the redox potential is negative, it means that there are reducing substances in the water body. We often use ORP instrument instead of residual chlorine meter to reflect whether the residual chlorine in reverse osmosis inlet water is qualified. The specific value has different value for different systems and different situations. For RO membrane, there is no problem in partial reducing environment, because the protective liquid of membrane product itself is reducing solution. However, redox potential can not be a very small negative value, because it is easy to produce spoilage anaerobic bacteria and microorganisms. I think as long as the redox potential is lower than the background value, it is OK. (the background value of ORP is the ORP value of raw water without chlorine).

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