Study On The Techniques To Treat And Reuse The Chrome Tanning Wastewater

The discharge of chrome wastewater is big, which has caused serious environmental pollution, especially chromium, which is toxic, and can act as carcinogens, mutagrns, and teratogens. However, chromium is expensive. Thus, it is significant to develop a technique of simultaneous removal and recovery of chromium for environmental pollution and economic purpose.Currently, there are many methods available for the treatment of industrial wastewater containing chromium, which have their own advantages. However, none of them can achieve simultaneous removal and recovery of chromium efficiently from wastewater. The major objective of this work is to remove and recycle chromium effectively from wastewater using complex precipitation. It has achieved efficient removal of chromium by complex flocculants, and reused chrome sludge to preparate chrome tanning agents.In this study, it choose two alkaline agents including NaOH and CaO, three inorganic flocculants including FeSO4, Al2O3and MgO, and three organic flocculants including heavy metal ion capturing agent(Cr-BD), heavy metal ion precipitant(MT-1) and heavy metal ion removal agent(MT-2) to treat chrome tanning wastewater. The experiment results show that:1. The best pH value of NaOⅡ and CaO in treating chrome tanning wastewater is both8.5. There are some advantages to increase pH value with NaOH, such as the flocculation particles are larger, the settlement speed is quicker, the removal of total chrome is higher and the sediment quality is heavier, etc.2. In the experiments of treating one liter chrome tanning wastewater with three inorganic flocculants, the best quantity of FeSO4is700mg/L. while the removal of total chrome is higher than91%; the best quantity of Al2O3is800mg/L. while the removal of total chrome is higher than91%; the best quantity of MgO is700mg/L, while the removal of total chrome is higher than91%; and best effect of the three inorganic flocculants is MgO.3. The best pH value of the three organic flocculants in treating chrome tanning wastewater also is8.5. In the experiments of treating one liter chrome tanning wastewater with three organic flocculants. the best quantity of Cr-BD is800mg/L, while the removal of total chrome is close to98%:the best quantity of Al2O3is800mg/L. while the removal of total chrome is higher than97%; the best quantity of MgO is900mg/L. while the removal of total chrome is higher than97%; and best effect of the three inorganic flocculants is Cr-BD.4.In the experiments of treating chrome tanning wastewater with complex flocculants, the removal of total chrome in the best experiment is up to99.9%, with only1.27mg/L left which has met the national emission standards for chromium-containing wastewater. The ratio of Cr-BD, MT-1and MT-2is4.0.1.2and1.8.Reuse treated wastewater (that is neutral salt water) into tannery process and the influence of recycling time on wet blue are be studied in the paper. The experiment results show that:when the recycling time is no more than5, the Ts and chromium content of wet blue are normal and the wet blue has lots of advantages, such as its bone is tight, its particle is smooth, its square increased, et al. The concentrations of Cl-, total salt, SS and COD have a certain rule of change.In the paper, recycling the sludge to prepare chrome tanning agent is studied. The experiment results show that:comparing with industrial chrome power, the purpose of chrome tanning agent is not ideal. How to reused chrome sludge to prepare high quality chrome tanning agent should be further studied.