Study On Resource Recovery And Harmless Treatment Of DMF Wastewater

Dimethylformamide(DMF)is widely used in leather industry,polyacrylonitrile fibre spinning and butadiene extraction craft as an important organic solvent. DMF wastewater only from leather industry is about one billion ton annual in China. DMF can pollute environment heavily because of its stable chemical property and bad biodegradation and is harmful to person's eyes and liver. DMF is confirmed as the potential substance that causes cancer in USA. 25mg/L is the highest concentration of DMF in water permitted by the Chinese government. Now the degradation is the major method for middle and low concentration DMF wastewater, which brings about resource waste. Under the direction of loop economics, DMF wastewater treatment using alkalization, Fenton reagent and photocatalytic oxidation was investigated respectively and try to carry out resource recovery from DMF wastewater and harmless disposition by photocatalysis in this paper. The effect of H₂O₂ dosage, Fe²⁺ dosage and DMF initial concentration on degradation rate of DMF was studied when Fenton reagent was used to degrade DMF wastewater. The results showed that degradation of CODcr was improved along with the increase of H₂O₂ dosage and DMF initial concentration decrease. The Fe²⁺ dosage existed optimal value(Fe²⁺/H₂O₂=40:1). But Fenton reagent was not suitable to industry application because of its high treatment costing. DMF was transformed to DMA when it was treated with alkali. DMA was absorbed by water or chlorhydric acid or recovered by condensation respectively when it was carried secretly from reaction system. The results showed that DMF was degraded completely when it reacted with NaOH at 60℃for 30 min. The absorbility was 95%, 81% and 100% when DMA was absorbed with water, condensation recovery and chlorhydric acid respectively. It was a better method that DMA was absorbed with water comparing the other two methods above. Photocatalytic technology is a new method of deeply degrading pollution of environment. But degradation of DMF wastewater with photocatalytic technology is reported rarely. It is the first time to particularly study the degradation of DMF wastewater with photocatalytic method. In this paper 0.05wt% DMF water solution was treated by photocatalytic degradation using P25 and TiO2 fiber as catalyst. The results showed that photocatalytic degradation rate of DMF can be improved with decrease of pH value, adding air and H2O2. Furthermore, experiments demonstrate the poor adsorption character of DMF on the surface of P25, which is the control step of photocatalytic degradation rate of DMF. Ozone can improve the photocatalytic degradation rate of DMF when P25 or TiO2 fiber was used as catalyst. Under the same reaction condition, photocatalytic degradation rate and speed of DMF in O3 system was almost 1.5 times and 2 times than that in air system. Through Hinsberg test secondary amine was proved as one of intermediates in the process of DMF photocatalytic degradation. Degradation speed of DMA in O3 system was higher than that in air system through the study of photocatalytic degradation of DMA when it was made as the representative sample of secondary amine. Hence we concluded that increasing degradation rate and speed of DMF was caused by fast degradation of secondary amine in the process of DMF photocatalytic degradation in O3 system. Different routes of industrial treatment were setup according to different initial concentration of DMF wastewater. Photocatalytic treatment using TiO2 fiber as catalyst was adopted directly for initial concentration of DMF wastewater ≤0.05wt% and the treatment costing is almost $5 per ton. Alkalization treatment in the first step and photocatalytic treatment in the second step was adopted for initial concentration of DMF wastewater≥0.3wt%. Take the wastewater of 8wt% for example, about $260 was gained when one ton wastewater was treatment. Photocatalytic treatment and alkalization combining photocatalytic treatment could be adopted for DMF initial concentration between 0.05wt% and 0.3wt%.