Investigating the Functional and Structural Adaptation Changes of Biofilm Communities Toward Better Azo-dye Wastewater Treatment
Mihaela Belouhova *
Department of General and Applied Hydrobiology, Faculty of Biology, Sofia University “St. Kliment Ohridski”, Sofia, Bulgaria.
Yana Topalova
Department of General and Applied Hydrobiology, Faculty of Biology, Sofia University “St. Kliment Ohridski”, Sofia, Bulgaria.
*Author to whom correspondence should be addressed.
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.
Keywords: Biofilm, FISH, digital analysis, azo-dye, unculturable, cooperative relationships.