A novel approach for methylene blue removal by calcium dodecyl sulfate enhanced precipitation and microbial flocculant GA1 flocculation

A novel approach was proposed for the removal of methylene blue (MB), a soluble cationic dye, from aqueous solution by calcium dodecyl sulfate (Ca(DS) 2 ) enhanced precipitation which was based on the solubilization of sodium dodecyl sulfate (SDS) on MB and Ca 2+ effect on SDS micelles, and microbial flocculant GA1 (MBFGA1) flocculation. The independent and interactive effects of factors, such as SDS, Ca 2+ and MBFGA1 dosages, on the MB removal and interaction between SDS and Ca 2+ were investigated. The response surface methodology (RSM), environmental scanning electron microscope (ESEM) and energy dispersive spectrometer (EDS) analysis were employed to discuss the interaction mechanism between SDS and Ca 2+ , and MB removal mechanism. The results showed that MB and SDS removal efficiency could reach 98.63% and 88.97%, respectively, with pH (10), MB (50   mg/L), SDS (8   mM), Ca 2+ (5   mM) and MBFGA1 (4   mL/L). Under the optimal conditions, residual SDS and Ca 2+ concentrations in the upper phase were 0.88   mM and 1.27   mM, respectively, which reached the K sp of Ca(DS) 2 . The concentration consumption ratio between SDS and Ca 2+ was 2.0. The interaction between SDS and Ca 2+ was depended on the SDS-Ca 2+ concentration ratio in aqueous solution rather than the CMC of SDS. When Ca 2+ concentration was relatively sufficient, SDS micelles containing the solubilized MB (SDS-MB micelles) would disassemble to generate MB loaded Ca(DS) 2 particles (CDS-MB particles) which would be flocculated by MBFGA1. Whereas, when SDS concentration was superfluous relatively, SDS micelles formed in the upper phase would redissolve the CDS-MB particles in flocs.