Method and principle of sewage treatment

M+x+xH-Re→M-M-Rex+xH+1

A-z+zOH-Re→A-Rez+zOH-1

The M+x cations in the above formula, the electric price number of x, the hydrogen ion exchange of H-Re on the cation resin of M+x cations, the anion of A-z, the electric price number of z, the OH- ions are released after the combination of A-z and anion exchange resin. H+ ions combine with OH- ions to form neutral water.

After the adsorption capacity of these resins is exhausted, they also need to be reduced, and cation exchange resins need strong acids to reduce; Anions, on the other hand, require a strong base to reduce. The adsorption capacity of cation exchange resin for various cations is different, and their strength and relative relationship are as follows:

Ba2+>Pb2+>Sr2+>Ca2+>Ni2+>Cd2+>CU2+>Co2+>Zn2+>Mg2+>Ag1+>Cs1+>K1+>NH41+>Na1+>H1+

The affinity strength of anion exchange resin with each anion is as follows:

S02-4+>I->NO3->NO2->Cl->HCO3->OH->F-

If the anion exchange resin is exhausted and not reduced, the weakest fluorine will gradually appear in the dialysis water, causing chondrosis, osteoporosis and other bone diseases. If the cation exchange resin is exhausted, hydrogen ions will also appear in the dialysis water, resulting in an increase in the acidity of the water, so whether the deion function is effective needs to be monitored from time to time. It is generally judged by the resistivity or conductivity of the water. The ion exchange resins used in deionization can also cause bacteria to multiply and cause bacteremia, which is worth noting.

Reverse osmosis

Reverse osmosis method can effectively remove inorganic matter, organic matter, bacteria, pyrogen and other particles dissolved in water, is the most important part of the treatment of dialysis water. To understand the principle of "reverse osmosis", we must first explain the concept of "osmosis". The so-called penetration refers to the separation of two different concentrations of solution with a semi-permeable membrane, in which the solute can not penetrate the semi-permeable membrane, then the water molecule with a lower concentration will pass through the semi-permeable membrane to reach the other side with a higher concentration, until the concentration on both sides is equal. Before the balance is reached, you can gradually apply pressure on the higher concentration side, then the aforementioned water molecule movement state will temporarily stop, at this time the required pressure is called "osmotic pressure", if the applied force is greater than osmotic pressure, then the water movement will go in the opposite direction. That is, from the high concentration side to the low concentration side, this phenomenon is called "reverse osmosis". The purification effect of reverse osmosis can reach the level of ions, and the exclusion rate of monovalentions can reach 90%-98%. divalent ions (divalent ions) can reach about 95% to 99% (to prevent the passage of substances with molecular weight greater than 200 Dalton).

The semi-permeable membrane materials commonly used in reverse osmosis water treatment are cellulosic, aromatic polyamides, polyimide or polyfuranes, etc., and its structural shape is spiral wound. hollow fiber type and tubular type, etc. The advantage of cellulose film in these materials is high chlorine resistance, but under alkaline conditions (pH ≥8.0) or in the presence of bacteria, the service life will be shortened. The disadvantage of polyamide is its poor tolerance to chlorine and chloramines.

If there is no pre-treatment before reverse osmosis, there is easy to accumulate dirt on the osmosis membrane, such as calcium, magnesium, iron plasma, resulting in the decline of reverse osmosis function; Some membranes (such as polyamide) are easily destroyed by chlorine and chloramines, so pre-treatment such as activated carbon and softener should be used before reverse osmosis membranes. Reverse osmosis although the price is higher, because the aperture of the general reverse osmosis membrane is about l0A below, it can exclude bacteria, viruses and pyrogen and even various dissolved ions, so it is best to prepare this step in the preparation of hemodialysis release water.

The debugging of reverse osmosis system is very important. We can grasp it from the following aspects:

Operating condition

Pre-operation preparation

Trial run

Separation process

The common processes in reverse osmosis membrane separation process design are as follows:

This method is that after the material liquid enters the membrane component, the concentrated liquid and the produced water are continuously drawn out, and the recovery rate of water in this way is not high, and the industrial application is less. The other form is a one-stage circulating process, which is to return a part of the concentrated water to the feed liquid tank, so that the concentration of the concentrated solution continues to increase, so the water production is large, but the water quality is reduced.

When reverse osmosis is used as a concentration process, when a concentration does not meet the requirements, this multi-step method can be used, which can reduce the volume of concentrated liquid and increase the concentration, and increase the water production accordingly.