Investigating the Functional and Structural Adaptation Changes of Biofilm Communities Toward Better Azo-dye Wastewater Treatment

Abstract

Aims: The aim of this study was to investigate the functional and structural adaptation changes in three biofilm communities purifying azo-dye contaminated wastewater. Study Design: Three lab-scale sand biofilters were constructed for treating wastewater with azo-dye. The dye amaranth was chosen as model toxicant and its concentration was gradually increased in the wastewater from 10 mg/L up to 55 mg/L. The biofilters functioned for 26 days. Place and Duration of Study: Laboratory of Environmental biotechnology, Sofia University “St. Kliment Ohridski”, 2011-2013 year. Methodology: The residual amaranth concentration, efficiency and rate of its removal were monitored. The diagnostics of the functional structure of the biofilms is based on a cross analysis of data from culturable, culture-independent (fluorescent in-situ hybridization - FISH) and digital (digital image processing) techniques. Results: The efficiency of the biofilters varied from 88.35% up to 95.97%. Three phases of the azo-detoxification process were distinguished. In the early phase of functioning (0-191 h) culturable Pseudomonas sp. had key role in azo-degradation as their part of the community was about 70% for the three biofilters. In the late phase of functioning (191-455 h) the biofilters eliminated 2 times higher concentration of amaranth. The mean value for the part of the microorganisms from g. Pseudomonas, calculated on the base of FISH, remained unchanged (42%). Simultaneously the cultivation techniques showed significantly decreased part of Pseudomonas sp. (4-10%). This suggest an important role of the unculturable Pseudomonas sp. In the ending period (455-623 h) the rate of amaranth removal was increased with 20%. Well-formed zones with high concentration of bacteria from g. Pseudomonas were found in the biofilms which indicated formation of cooperative relationships. Conclusion: This study shows three-stage mechanism of development of amaranth degradation potential. It includes successive importance of culurable, unculturable bacteria and cooperation in the g. Pseudomonas.