(1) preprocessing

 

The efficiency and life of reverse osmosis system are closely related to the pretreatment effect of raw water. Pretreatment can effectively reduce the fouling, scaling and damage risk of the influent, prolong the service life of the membrane and reduce the operation cost.

 

(2) the pH value of the influent

 

The pH value also has a great influence on the performance of the membrane system. The landfill leachate needs to turn the pH value into acidity before entering the DTRO. On the one hand, it can prevent the insoluble inorganic salts from scaling. On the other hand, the free ammonia in the leachate and the added acid can form the two valence ammonia salt, and the retention of the DTRO like polyvalent ions is very high. It can improve the removal rate of ammonia nitrogen which is the most difficult to remove.

 

The change of the pH value of the influent will affect the permeability of the reverse osmosis membrane. With the increasing of the pH value, the flow flow is inversely proportional to the pH value. The higher the pH value, the smaller the flow flow, but the inflection point after the pH value is greater than 7, and then the pH value continues to rise and the flow flow increases. Therefore, the pH value of the influent is acidic or alkaline, which is conducive to increasing the water production flux.

 

The water quality of landfill leachate itself is very complex and has high salt content. With the operation of the system, the insoluble salts are easily accumulated at the end of the system and eventually make the scale of the diaphragm affect the permeability. Therefore, the pH value of the reverse osmosis water treatment should be controlled to be acidic. At the same time, the pH value range of the influent can be controlled to about 6 when considering the reduction of alkali addition.

 

(3) the operating pressure of the system

 

Reverse osmosis system operation pressure is the most important factor affecting the operation cost of reverse osmosis technology, and has a very important impact on the normal use of reverse osmosis membrane. Because of the characteristics of leachate, higher pressure is favorable for the interception of pollutants. But higher pressure is also more likely to cause blockage and pollution of membrane modules. There is a linear relationship between the flux and the operating pressure of the membrane system. At the same time, the desalination rate of membrane system increases with the increase of influent pressure.

 

(4) the recovery rate of the system

 

The recovery rate is an important index of reverse osmosis, which is defined as the volume of liquid through the volume divided by the volume of the original solution. The leachate with conductivity of 20000 s/cm was used as the research object to control the influent pressure of 4.0MPa. The reflux pump regulates the control valve at the same time, so as to synchronize the flow of water with the water output of the liquid, so that the recovery rate of the membrane module is changed, and the recovery rate of the system is inversely proportional to the flux through the liquid. This is because the reverse osmosis process is a process of applying pressure at the inlet end to reverse the natural infiltration of dilute solution into concentrated solution.

 

The desalination rate of the membrane component is proportional to the permeation flux, which is due to the relatively high salt concentration in the inlet side, and the relatively low desalination rate of the larger flux and the lower permeation flux.

 

(5) influence of water inlet temperature

 

The effect of temperature on the performance of the membrane is very serious. With the increase of temperature, the viscosity of water gradually decreases and the water production flux gradually increases.  In the design of the membrane system, the influence factors of the temperature on the film interception should be fully considered. Through the correction system provided by the diaphragm manufacturers and other ways, the standardization of the operating parameters is beneficial to the accurate control of the operating condition of the system.

 

With the increase of temperature, the desalination rate of membrane decreases, the color of permeation liquid increases and the water quality becomes worse. This is because with the increase of temperature, the diffusion rate of the salt through the diaphragm will increase gradually, which is greater than the rate of water passing through the diaphragm, which shows the decrease of the desalination efficiency of the diaphragm.