Removal of Cr from tannery sludge by indigenous sulfur-oxidizing bacteria

The aim of the present study was to examine Cr removal from tannery sludge by bioleaching method using indigenous sulfur-oxidizing bacteria with special emphasis on the influence of bioleaching process on sludge settleability. Chemical leaching with sulfuric acid was designed as the control. The results showed that the inoculation of sulfur-oxidizing bacteria and the addition of elemental sulfur were effective in removing Cr from tannery sludge. After 144 hours of bioleaching, 98% of Cr could be leached. Although it took only 8 hours to reduce the sludge pH from 7.8 to about 2.0 by chemical leaching as compared to 144 hours for bioleaching treatment, chemical leaching removed only 91% of the total Cr. Regardless of bioleaching and chemical leaching treatments, sludge settleability improved considerably with a decrease in sludge pH. Bioleaching treatment performed better than chemical leaching in terms of the percentage of settled sludge and the effluent suspended solids (ESS) content in sludge supernatant. Nevertheless, further work should be carried out to investigate the precise mechanisms leading to such enhanced sludge settleability during sludge bioleaching process.

[1]  X. Y. Li,et al.  Influence of loosely bound extracellular polymeric substances (EPS) on the flocculation, sedimentation and dewaterability of activated sludge. , 2007, Water research.

[2]  V. Tare,et al.  Oxidation of Cr(III) in tannery sludge to Cr(VI): field observations and theoretical assessment. , 2005, Journal of hazardous materials.

[3]  W. Sand,et al.  Bioleaching - a result of interfacial processes caused by extracellular polymeric substances (EPS). , 2003 .

[4]  R. Tyagi,et al.  Bacterial Leaching of Metals from Tannery Sludge by Indigenous Sulphur-Oxidizing Bacteria—Effect of Sludge Solids Concentration , 2003 .

[5]  Kyung-Suk Cho,et al.  Leaching characteristics of heavy metals from sewage sludge by Acidithiobacillus thiooxidans MET. , 2003, Journal of environmental quality.

[6]  A. Fakhru’l-Razi,et al.  Enhanced settleability and dewaterability of fungal treated domestic wastewater sludge by liquid state bioconversion process. , 2003, Water research.

[7]  R. Tyagi,et al.  Extraction of Cr(III) and Other Metals from Tannery Sludge by Mineral Acids , 2001, Environmental technology.

[8]  A. A. Mozeto,et al.  BIOLEACHING OF METALS FROM ANAEROBIC SEWAGE SLUDGE: EFFECTS OF TOTAL SOLIDS, LEACHING MICROORGANISMS, AND ENERGY SOURCE , 2001, Journal of environmental science and health. Part A, Toxic/hazardous substances & environmental engineering.

[9]  R. Tyagi,et al.  Class A Pathogen Reduction in the SSDML Process , 2001 .

[10]  J. Wong,et al.  Removal of heavy metals from anaerobically digested sewage sludge by isolated indigenous iron-oxidizing bacteria. , 2000, Chemosphere.

[11]  I. Suzuki,et al.  Effect of Various Ions, pH, and Osmotic Pressure on Oxidation of Elemental Sulfur by Thiobacillus thiooxidans , 1999, Applied and Environmental Microbiology.

[12]  E. Donati,et al.  The role of exopolymers in the bioleaching of a non-ferrous metal sulphide , 1999, Journal of Industrial Microbiology and Biotechnology.

[13]  R. Tyagi,et al.  Effect of sulfur concentration on sludge acidification during the SSDML process , 1996 .

[14]  J. O’Halloran,et al.  Chromium speciation in tannery effluent—II. Speciation in the effluent and in a receiving estuary , 1996 .

[15]  D. Couillard,et al.  Removal of metals and fate of N and P in the bacterial leaching of aerobically digested sewage sludge , 1993 .

[16]  R. Tyagi,et al.  Bacterial leaching of toxic metals from municipal sludge: influence of sludge characteristics , 1993 .

[17]  R. Tyagi,et al.  Cooperation between two Thiobacillus strains for heavy-metal removal from municipal sludge. , 1992, Canadian journal of microbiology.

[18]  Eun-hee Lee,et al.  Leaching Characteristics of Heavy Metals from Sewage Sludge by MET , 2003 .

[19]  G. Tiravanti,et al.  Pretreatment of tannery wastewaters by an ion exchange process for Cr(III) removal and recovery , 1997 .

[20]  K.S.L. Lo,et al.  Extracting heavy metals from municipal and industrial sludges , 1990 .