Neutralization of alkaline industrial wastewaters using Exiguobacterium sp.

A facultatively alkaliphilic bacterium capable of lowering the pH of highly alkaline wastewater from 12.0 to 7.5 within just 2.0 h was isolated from industrial wastewater drained sludge of a local beverage industry. The metabolic product which the bacterium produces in order to neutralize alkaline wastewater was found to be carboxylic acid in nature by Fourier Transform- Infrared (FT-IR) spectroscopy. The isolate belongs to genus Exiguobacterium as determined by 16S rRNA gene sequencing and biochemical characterization. It was found to be gram-positive, nonspore-forming, nonmotile, rod shaped, growing aerobically and anaerobically at a wide range of temperatures (5–40 °C), pH (6.5–12.0) and NaCl concentrations(0–9.5%). The strain was able to hydrolyze starch and was catalase positive but lacked oxidase or aminopeptidase activity. Acid was produced from glycerol, cellobiose, d-mannose, mannitol, methyl α- d-glucoside, amygladin and arbutin. From the 16S rRNA gene sequence analysis, the strain appeared to be most similar (99%) to the sequence from Exiguobacterium aurantiacum strain DSM 6208.Neutralization of highly alkaline wastewater without addition of any external carbon source highlights the potential use of the isolate as an alternative to the conventional acid neutralization method for treatment of alkaline wastewater.