| Freezing method is a new wastewater treatment technology that achieves the concentration of contaminants and the recycle of water and useful material by physical transformation under freezing point. Due to its advantages of being non-selective to wastewater, having small corrosion to container and no pollution from external source, it has received extensive attention of both domestic and foreign scholars in recent years. This thesis studied the factors of treating dye intermediate wastewater by low-temperature crystallization, compared the treatment effects on tetrahydrofuran wastewater between progressive freezing treatment and suspension crystallization method, and designed a pilot plant to treat tetrahydrofuran wastewater.This thesis took four kinds of dye intermediate mother liquor as research objects, studied on the effects of temperature, pH and kinds of alkali on low temperature crystallization treatment. The results showed that the removal of chemical oxygen demands (COD) of simulated wastewater were all risen with temperature decreasing; at the pH range of 2 to 10, the organics precipitated temperatures were between -4℃ to 4℃ in each simulated wastewater, and the COD removal rate were all decreased; For amino G acid and K acid simulated wastewater, the higher acidity resulted in the smaller influence of temperature on COD removal rate, the lower temperature resulted in he smaller influence of acidity on COD removal rate; for G salt simulated wastewater, the effect of adding KOH to adjust pH was better. The effects of actual wastewater treatment were as follows, The G salt mother liquor was frozen for 12 hours at-12℃, the removal of COD was 55% while the main production was R salt. Then the pH of G salt filtering medium was adjusted to 7.0, and frozen 12 hours at-16℃, the removal of COD was raised to 62% while the main production was G salt. According to engineering calculation that the G salt mother liquor handling capacity of 10 m3/d, the static payback time was 0.48, the electric power of this technology was 8.41 kW; The removal of COD of β salt mother liquor achieved to 78.8% while recovery of (3 salt.Taking tetrahydrofuran wastewater as research object, this thesis studied on the effect of freezing temperature, adding ice crystals, stirring speed of freezing on progressive freezing treatment and suspension crystallization method. The results showed that both methods had relatively good removal efficiency in treating tetrahydrofuran wastewater, the highest COD removal rate was over 80%; For progressive freezing treatment, combined with energy consumption analysis, the optimal experimental conditions:freezing temperature was-4℃, temperature of adding ice crystals were-0.5℃～-1.0℃; For suspension crystallization method, the optimal experimental conditions:freezing temperature was-6℃, stirring speed was 300 r/min; Adding ice crystals could improve freezing process treatment effect significantly, the supercooling degree of wastewater should be paid attention to, otherwise it may cause deterioration of treatment effect; the effects of progressive freezing treatment and suspension crystallization method had little difference in conditions of lower ice formation rates or higher temperatures, when increased ice formation rate or decreased temperature, suspension crystallization method would be better. The electric power of this technology was 47.82 kWThe freezing pilot plant was based on freezing experiment that treating tetrahydrofuran wastewater in laboratory. the handling capacity was enlarged from 500 mL to 150 L, the optimal experimental conditions:freezing temperature was-2℃, stirring speeds were 100～ 200 r/min, the COD removal rate of two-stage freezing effluent was still over 95%, the electric power of this pilot plant was 1.3 kW. For the wastewater that quality varies obviously, this method could also have the same effect. |
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