A Novel Approach For Methylene Blue Removal By Calcium Dodecyl Sulfate Enhanced Precipitation And Microbial Flocculant GA1 Flocculation

Dyes and pigments are widely used in the textile and leather dyeing, printing, pharmaceutical, and cosmetic industries. Discharge of the dyes to the environment have aroused serious concerns all over the world due to the toxicity of dyeing effluents, such as carcinogenic and mutagenic action to aquatic biota and humans. Furthermore, the dyes in surface water imped sunlight penetration and reduce the dissolved oxygen, which cause annoyance to the aquatic biosphere. Methylene blue ?MB?, a soluble cationic dye, is most commonly used in dyeing wools and cottons, coloring paper and as a temporary hair colorant. The MB could enter the human body through the digestive tract and skin, and cause specific harmful effects in human such as vomiting, shock, cyanosis, heartbeat increase, jaundice, quadriplegia, and tissue necrosis. Therefore, taking the effective method to remove MB is very important.In this study, a novel approach was proposed for the removal of MB from aqueous solution by calcium dodecyl sulfate ?Ca?DS?₂? enhanced precipitation and microbial flocculant GA1 ?MBFGA1? flocculation. This method combined the solubilization effect of sodium dodecyl sulfate ?SDS? on MB and the calcium ion effect on SDS micelles containing the solubilized MB ?SDS-MB micelles?, for the first time, to make MB precipitate from aqueous solution in a form of suspended particles, which then were flocculated by MBFGA1. Firstly, this study investigated the effects of SDS dosages, Ca²⁺ dosages, MBFGA1 dosages, MB initial concentration, pH, mixing time on the MB removal efficiency. Next, the independent and interactive effects of important factors, such as SDS, Ca²⁺ and MBFGA1 dosages, on the interaction between SDS and Ca²⁺ were investigated. Based on these investigations, MB removal mechanism and the interaction mechanism between SDS and Ca²⁺ were verified and elaborated by the response surface methodology ?RSM?, Environmental scanning electron microscope ?ESEM? and Energy dispersive spectrometer ?EDS? analysis.The study results showed that the optimal conditions were that SDS, Ca²⁺, MBFGA1 dosages were 8mM,5mM,4mL/L, respectively, MB initial concentration was 50 mg/L, pH was 10, mixing combinations were 5 minutes rapid mixing at 200 rpm and 30 minutes slow mixing at 40 rpm. Under the optimal conditions, the MB and SDS removal efficiency could reach 98.63% and 88.97%, respectively, which indicated that this novel method was high efficient and environmentally feasible.Through the interactive effects analysis of important factors by RSM and the floes analysis by the ESEM and EDS, we could conclude that the interaction between SDS and Ca²⁺ was closely related to the SDS-Ca²⁺ concentration ratio in aqueous solution rather than the CMC of SDS. When Ca²⁺ concentration was relatively sufficient, even if the SDS concentration was more than 1 CMC, the Ca²⁺ could react with the SDS micelles containing the solubilized MB ?SDS-MB micelles? to generate MB loaded Ca?DS?₂ particles ?CDS-MB particles?. However, when SDS concentration was superfluous relatively, the SDS micelles formed in the upper liquid phase would redissolve the CDS-MB particles in flocs gradually, leading to the complete dissolution of flocs finally. Hence, only when Ca²⁺ concentration was relatively sufficient, MB could be removed effectively. At this time, MB was precipitated from aqueous solution in the form of CDS-MB particles which then were flocculated by MBFGA1.The MB removal approach proposed in this study was simple, high efficient, environmentally and economically feasible, so it had wide application prospects and seemed to be promising for the real MB wastewater purification processes.