Treatment of azo dye wastewater by the self-flocculating marine bacterium Aliiglaciecola lipolytica

Microorganisms with capacity to degrade and separate azo dyes from water are potential in developing eco-friendly and cost-effective method for azo wastewatertreatment, challenged for large volume, toxicity and high salinity. Marine bacterium Aliiglaciecola lipolytica (A. lipolytica) was examined to decolorize Congo Red (CR), a typical azo dye in sythesized water. The results showed that the bacterium could achieve aerobic decolorization (more than 90%) and self-flocculation under wide conditions (temperature 25–35°C, initial CR concentration 25–100 mg L−1, salinity 0–20 g L−1, pH 5–6, glucose concentration 4–8 g L−1, and (NH4)2SO4 concentration 1–2 g L−1). It was proved that the dyes were firstly adsorbed onto cells by extracellular polymeric substances (EPS), and about 46% of them were then degraded. This degradation process was through co-metabolism with the glucose and also mediated by azoreductase and intracellular laccase. The azo linkage (-N=N-), the chromophore groups (C-N) and sulfonate groups (−SO3) were cleaved; then the naphthalene rings were decomposed, which made CR into smaller molecules. The bacterium secreted many EPS, especially protein-like and humic acid substances in tightly bound EPS (TB-EPS), which could decrease electrostatic force and increase hydrophobicity of cell surface contributed to dye adsorption and cell self-flocculation. It was stressed that self-flocculation marine bacterium A. lipolytica could provide a promising technique for azo dye wastewater treatment.