Solid-liquid separation of real cellulose- containing wastewaters by extracellular polymeric substances: Mechanism and cost evaluation

The flocculation feasibilities of tobacco wastewater (TBW) and livestock and poultry wastewater (LPW) by the extracellular polymeric substances (EPS) of Bacillus sp. were evaluated in this study. The average particle sizes of flocs formed by the crude EPS were 45.83 mm and 41.67 mm in TBW and LPW, respectively, which were larger than that formed by chemical flocculants. The removal efficiencies of chemical oxygen demand, ammonia nitrogen and suspended solid achieved by crude EPS were increased more than 50% than that by chemical flocculants. Charge neutralization was dominant in the flocculation of LPW, while chemical reactions between the Fe (III) and reductive substances in TBW played an important role in the flocculation of TBW. The FTIR and XPS results indicated that the sugar derivatives of EPS, especially the hemiacetal and glucoside groups interacted with cellulose molecules. Three-dimensional EEM fluorescence spectra presented three peaks of tryptophan protein, aromatic polysaccharides and polysaccharides, and the peak intensities were enhanced with the addition of cellulose by PARAFAC analysis. Cost evaluation suggested that the generated flocs and supernatants could be further utilized as fertilizer after the solid-liquid separation of LPW, thus one ton of LPW after flocculation by crude EPS might generate a gross profit of $43.51, suggesting that advantages of crude EPS not only on environmental protection but also on flocculation cost. The results of present study implied that the crude EPS of Bacillus sp. have stronger competitiveness in the treatment of cellulose-containing wastewaters comparing to the chemical flocculants, which sheds lights on its potential usage as an alternative bio-flocculant.

Automated summary

The study evaluated the flocculation feasibilities of tobacco wastewater and livestock and poultry wastewater by the extracellular polymeric substances of Bacillus sp. The crude EPS showed larger floc sizes and higher removal efficiencies compared to chemical flocculants. Charge neutralization was dominant in LPW flocculation, while chemical reactions with Fe(III) played a role in TBW flocculation.