How exactly does high salt wastewater treatment go about?

 With the rapid development of  economy, high salt wastewater emissions increase, making high salt wastewater treatment difficult to increase, how to choose high salt wastewater treatment process? What are the advantages and disadvantages of high salt wastewater treatment process? How to treat these high salt wastewater?
        High-salt wastewater is wastewater that contains organic matter and at least 3.5% (mass concentration) of total dissolved solids (TDS). This kind of wastewater comes from a wide range of sources, one type is chemical, pharmaceutical, petroleum, paper, dairy processing, food canning and many other industrial production processes, will discharge a large amount of wastewater, the water not only contains a lot of high concentrations of organic pollutants, accompanied by a large number of calcium, sodium, chlorine, sulfate and other ions. Another category is to make full use of water resources, some coastal cities directly use seawater as industrial production water or cooling water.

1. Dosing coagulation - air flotation, precipitation and traditional pretreatment process
       When the COD concentration of saline raw water is below 5000mg/L, and there is no requirement for the quality of crystallized salt, the traditional process is to put the saline raw water through the pre-treatment of “conditioning - dosing coagulation - air flotation, sedimentation”, and then enter the “evaporation concentration crystallization” process, and then enter the “evaporation concentration crystallization” process. “Evaporation, concentration, crystallization and desalination system”. The method of investment is small, low operating costs, but the crystallized salt quality is poor, difficult to sell.

2. Fenton or electric-Fenton catalytic oxidation pretreatment process
       Fenton reagent contains H2O2 and Fe2+, organic pollutants in wastewater has a strong oxidizing ability, and fast reaction speed, low investment, the effluent can be purified by precipitation to achieve the purpose of pretreatment.
       However, Fenton or electric - Fenton catalytic oxidation process requires specific reaction conditions: pH 2 - 4, and produce more iron sludge, the effluent will have color. When the saline raw water p H value is low, it is more economical to use, otherwise “add acid to reduce p H, add alkali to neutralize” process to increase the operating costs.COD concentration in 10000 mg/L or so is still good, such as too high, we need to multi-stage oxidation purification treatment, Fenton process has no advantage.

3. Double membrane pretreatment process
       First of all, the use of pore size in 20 - 2000Ao (10-6.5-10-4.5cm) semi-permeable membrane for ultrafiltration, can retain proteins, various types of enzymes, bacteria and other colloidal substances and macromolecules in the concentrate, while the water, solvents, small molecules and the formation of salt ions can be passed through the membrane into the permeate water.
       As the amount of water through the water is reduced, but the amount of salt remains unchanged, so the salt concentration in the permeate water increases. At this time and then use the pore size in 1 - 20Ao (10-7.5-10-6.5cm) semi-permeable membrane for reverse osmosis, inorganic salts, sugars, amino acids, BOD, COD, etc. are retained in the concentrate, only water and solvents into the permeate water, salt in the concentrate concentration increases further, sent to evaporation and crystallization of desalination.
       The advantage of the double membrane method of desalination is to significantly reduce the amount of water in the evaporation crystallization desalination, thus significantly reducing the operating costs and investment in the evaporation crystallization desalination. But pay attention to the following issues:
       Before ultrafiltration to adjust p H to neutral, hardness, SS purification, etc.;
       Raw water salt content in the 5000mg / L or less, otherwise the amount of water through the too low, the desalination rate is also reduced;
       As the membrane should be frequently washed, acid washing, alkali washing protection, the service life of the membrane is also limited, the operating cost is also relatively high;
       The biggest problem is the interception of the left behind higher pollution of the concentrate how to do? If you can extract valuable substances or a large number of biochemical wastewater dilution together with the treatment is good, otherwise, such as reuse will increase the accumulation of pollution; such as incineration, the investment and operating costs are extremely high;
       Salt content of more than 5000mg / L of wastewater can be directly desalted by evaporation and crystallization, and then the membrane method makes little sense, but be reminded that: desalination before evaporation and crystallization or to carry out effective pre-treatment.

4. Ozone/catalytic/coagulation composite pretreatment process
       Using ozone as a strong oxidizing agent and composite catalyst and coagulant, the full cross-linking synergistic reaction in a specific environment can make the ring chain and long chain in wastewater broken, and improve the biochemistry of wastewater.
       Creating suitable reaction conditions can also sufficiently oxidize dissolved organic pollutants in wastewater, destroy colloids, chromophores and odorophores in wastewater, and remove COD, BOD, SS, odor and some colors in wastewater, but not salt and more ammonia nitrogen.
       As ozone as a strong oxidizing agent and compound oxidizing nature of the catalyst and coagulant, so in the whole process of removing organic pollutants produced by the amount of mud is very small, and the reaction environment, the form and the process are much simpler than the Fenton process, can be multi-stage series operation, to ensure that the water to meet the expected indicators.
       Large amount of water and salt content of less than 5000mg / L of wastewater can be preferred double membrane method, concentration and then desalination;
       Salt raw water p H value of 2--4 salt raw water can be preferred Fenton process pretreatment; pH value of 5 or more of the high concentration of COD and salt content of more than 5000mg / L salt wastewater can be selected ozone / catalytic / coagulation composite pre-treatment process;
       Salt raw water with high color or high ammonia nitrogen, must be separate decolorization and deammonia treatment;

5. Evaporation crystallization desalination process
       For salt-containing solutions, due to its solubility, its crystallization from solution precipitation has two programs, the first is for the solubility with the temperature is not big, generally use the method of evaporation of solvents, and the second is the solubility with the temperature of the larger changes in the material system, the general use of the cooling solution method.
       Salt-containing wastewater is generally a mixture of many kinds of salt, due to the existence of the same ion effect, its solubility curve and the boiling point of the solution are different from a single system, generally its saturation solubility is lower than the saturation solubility of a single system, the boiling point is higher than the same concentration of a single system of boiling point. So to accurately grasp the solubility and boiling point of multi-component salt must be obtained through experimentation, which is the key to the design of evaporation desalination.
       For the design of evaporation desalination concentration endpoints, mainly depends on the subsequent separation equipment matching, selection of horizontal spiral discharge centrifuge, the evaporator solution should be about 10% solid, selection of two-stage piston push material centrifuge, the evaporator solution solid content of about 50%.
       The design of evaporation crystallizer is the key to the normal operation of the evaporation and desalination device, the design should consider the following factors: the generation of nuclei, supersaturation control, the elimination of short-circuit temperature difference, large particles of salt instant separation, forced circulation and flow rate, gas-liquid separation strength.