Study On The Technology Of Foam Separation For Desalination And Decolorization

Desalination and decolorazition, which are used to remove metal ions and acid ions and pigments from fermentation broths and wastewaters, are important operating units in the field of biochemical engineering. Until now, various strategies have been used for desalination and decolorization, including flocculence, ion-exchange, membrane separation, adsorptive method and chemical oxidation. However, it is not suitable for these methods to treat solutions of low concentrations of ion and pigment and these methods have high energy-consuming, complicated equipment, high investment, and even new environmental contamination. The integration of desalination and decolorization can simplify the separation process, lower cost and improve treatment efficiency. For solutions of low concentrations of ion and pigment, foam separation technique has achieved better recovery and enrichment and has high efficiency and low energy-consuming, thus attracting more attention. However, in the past studies, the integration of desalination and decolorization had not been achieved by foam separation due to the limit of surfactants. In this thesis, based on respective studies on desalination and decolorization by foam separation, a process of the integration of desalination and decolorization by foam separation was investigated to lower cost and optimize the process. An aqueous solution of copper sulfate(CuSO4), crystal violet and eosin Y was used as the study system with dodecyl benzene sulfonic acid (DBSA) and (1-Hexadecyl) trimethyl ammonium hydroxide (CTAOH) as collecting agents.In the process of removal of Cu²⁺ and crystal violet from the aqueous solution by foam separation, effects of pH, airflow rate, the concentration of surfactant (DBSA) and foam height (loading liquid volume) on removal performances were studied by single factor experiments. Based on the experiments mentioned above, orthogonal experimental design was used to optimize the operating parameters. The results showed that under the optimum conditions the removal percentage and enrichment ratio of Cu²⁺ were 98.5% and 4.5, and the removal percentage and enrichment ratio of crystal violet were 95.8% and 3.6. Compared to the use of lauryl sodium sulfate in the same process, metal ions such as Na+ could not be left in the residual solution by using DBSA. This will give significant implication to the development of new methods for desalination and decolorization.In the process of removal of slight CuSO4 and eosin Y from the aqueous solution by foam separation, DBSA and CTAOH were simultaneously used as collecting agents and the intergration of desalination and decolorization was achieved. Under the conditions of concentration of DBSA 0.23 g/L, concentration of CTAOH 0.096 g/L, pH 5/pH 6, airflow rate 150 mL/min and loading liquid volume 300 mL, a removal percentage of Cu²⁺, 97.2%, was obtained with an enrichment ratio of 10.8. Under the same conditions, the removal percentage and enrichment ratio of SO₄^2- were 91.2% and 7.4, and the removal percentage and enrichment ratio of eosin Y were 95.1% and 8.5. It is demonstrated that the successive addition of DBSA and CTAOH successfully realized the intergration of desalination and decolorization and did not introduce new ions during the foam separation process, by which the problem of ion residual was solved and better performances of desalination and decolorization were achieved.