Exploration And Application Of The Cloud Point System In The Microbial Decolorization Of Triphenylmethane Dyes

Triphenylmethane dyes are chemical synthetic dyes, which are structurally stable,difficult degradation, intense carcinogenesis, tetratogenesis, and mutagenesis. It makes senseto study biodecolorization of these dyes for dye-treatment and human health. However, themicrobial decolorization of these dyes was restricted by substrate inhibition and producttoxicity, which makes the large-scale application difficult. Therefore, how to decolorize anddetoxicate these dyes simultaneously is an essential issue.Cloud point system is a two-phase system, which forms by adding nonionic surfactantinto aqueous solution above a certain temperature or additive concentration. One phase isCoacervate phase, or surfactant-rich phase, the other phase is water phase, or dilute phase.The phase separation temperature is cloud point.To achieve simultaneous decolorization and detoxification, the microbial decolorizationof triphenylmethane dyes was researched in the cloud point system. Aiming at the scientificproblems in microbial decolorization of these dyes, the study was performed as followed:microbial decolorization mechanism of triphenylmethane dyes by Aeromonas hydrophilaDN322p, participation mechanism of triphenylmethane dyes in the cloud point system, thebiocompatibility and detoxification ability of the cloud point system, and recovering ofsurfactant from coacervate phase. The basic results and conclusions are listed:1. A. hydrophila DN322p, an offspring of DN322re-isolated from a5yearslyophilization tube, was test for its decolorization capacity. Decolorization of crystal violetwas achieved within2.5h under shaking condition at30°C. Decolorization rate was up to98%(w/w) for50mg/L crystal violet. HPLC analysis of end product conformed crystal violetwas mainly converted into its leuco form. During the decolorization, dichloromethane extractof cell pellet exhibited obvious crystal violet and leuco crystal violet characteristicsabsorbance peaks at590nm and260nm separately by UV-Vis spectral analysis, whichindicated the strain had strong adsorption capacity on the two dyes. Results suggest the straindecolorizing crystal violet in a complex decolorization way combined adsorption andbiotransformation.2. A method for removing four triphenylmethane dyes from wastewater by cloud pointextraction with the nonionic surfactant Triton X-114(TX-114) was developed. Thetriphenylmethane dyes were crystal violet, ethyl violet, malachite green, and brilliant green. The cloud point of TX-114generally increased in the presence of any of the four dyes. In thecloud point system, these dyes were solubilized into a coacervate phase that left a color-freedilute phase. The extraction efficiency of the dyes increased with the temperature, TX-114concentration, and salt (NaCl and CaCl2) concentration. More than97%TX-114in the dilutephase was recovered by adjusting the volume ratio of dichloromethane to the dilute phase.The Langmuir-type adsorption isotherm was used to describe the dye solubilization. TheLangmuir constants m and n were calculated as functions of temperature. The results showedthat the solubilization of the triphenylmethane dyes in the cloud point system was related tothe partition coefficient (log P) and their molecular structures.3. The biological treatment of triphenylmethane dyes is an important issue. Mostmicrobes have limited practical application because they cannot completely detoxicate thesedyes. In this study, the extractive biodecolorization of triphenylmethane dyes by Aeromonashydrophila DN322p was carried out by introducing the cloud point system. The cloud pointsystem is composed of a mixture of nonionic surfactants (20g/L) Brij30and Tergitol TMN-3in equal proportions. After the decolorization of crystal violet, a higher wet cell weight wasobtained in the cloud point system than that of the control system. Based on the results ofthin-layer chromatography, the residual crystal violet and its decolorized product, leucocrystal violet, preferred to partition into the coacervate phase. Therefore, the detoxification ofthe dilute phase was achieved, which indicated that the dilute phase could be dischargedwithout causing dye pollution. The extractive biodecolorization of three othertriphenylmethane dyes was also examined in this system. The decolorization of malachitegreen and brilliant green was similar to that of crystal violet. Only ethyl violet achieved apoor decolorization rate because DN322p decolorized it via adsorption but did not convert itinto its leuco form. This study provides potential application of biological treatment intriphenylmethane dye wastewater.4. The Triton X-114was recovered by adding [BMIM]PF6into the coacervate phase ofcloud point system. The ternary phase diagram of Triton X-114/water/[BMIM]PF6at25°Cwas obtained and5points were chose as study subject in the two-phase region. We observedthe phase behavior of the system at room (25°C) and higher temperature (65°C). Aphenomenon of surfactant transfer was found between water phase and ionic liquid phase at65°C. An equal amounts of [BMIM]PF6was added into the coacervate phase, after the dilutephase was removed in the cloud point system of5dyes (anthraquinone dye–alizarin (AL),azo dyes–amaranth (AM) and methyl orange (MO), triphenylmethane dyes–crystal violet (CV) and malachite green (MG)). The AL was extracted into the ionic phase and thesurfactant remained in the water phase. So, the recovery of surfactant was succeeded. Then,the [BMIM]PF6was recovered from AL by adjusting pH value of the system.