Production of a value added compound from the H-acid waste water—Bioflocculants by Klebsiella pneumoniae

A novel strain (designated as ZCY-7) which could convert H-acid into bioflocculants was isolated from H-acid wastewater sludge. Conditions for bioflocculants production were optimized by response surface methodology (RSM) and determined to be inoculum size 9.65%, initial pH 7.0, and CODCr of the H-acid wastewater 520 mg/L. The highest flocculating efficiency achieved for kaolin suspension was 95.1%, after 60 h cultivation. The yielded bioflocculant was mainly composed of polysaccharide (82.4%) and protein (14.2%), and maintained its flocculating activity in 0.4% (w/w) kaolin suspensions over pH 2–8 and 20–80 °C. Fourier transform infrared (FTIR) spectra showed that amino, amide and hydroxyl groups were present in the bioflocculant molecules. A viable alternative treatment technology of H-acid wastewater using this novel strain is suggested, which could largely reduce bioflocculants costs. In addition, flocculating mechanism investigation reveals that the bioflocculant could cause kaolin suspension instability by means of charge neutralization firstly and then promoted the aggregation of suspension particles by adsorption and bridge. It is evident from the results that H-acid wastewater could be used as a source to manufacture bioflocculants.