Microbial Ecology of Bulking and Foaming Activated Sludge Treating Tannery Wastewater

Abstract

This study involves a comprehensive survey of the microbial ecology of the activated sludge process treating tannery wastewater, emphasizing evaluation during periods of bulking and foaming. The survey also includes a detailed characterization of process influent and effluent. Observations always associate bulking with significant increase in protozoa species and rotifers, but decrease or disappearance of nematodes. Activated sludge sustained under normal conditions with a sludge volume index lower than 80 ml g⁻¹, exhibits all the properties of a compact and healthy zoogleal floc structure. Three types of filamentous bacteria prevail in the microscopic examinations. Two of the filamentous bacteria, Microthrix parvicella and Nostocoida limicola II, always appear as components of the floc structure under normal conditions and abundant or even excessive levels. The study identifies Gordona spp. as the main microorganism responsible for bulking and foaming, which starts by a Gordona contamination process inside the floc, later branching out and extending through adjacent flocs. When completed, this process increases sludge volume index values to over 200 ml g⁻¹. Microscopic examinations indicate significant morphological differences between filamentous microorganisms observed in this study and reported in the literature mostly for domestic sewage treatment.

Keywords:

• Bulking and foaming
• Gordona
• Microthrix parvicella
• Nostocoida limicola II
• Sludge volume index
• Tannery wastewater

ACKNOWLEDGMENTS

This research was supported by two different research grants, one from the ITU Research Foundation and Development Center and the other from the Scientific and Technical Research Council of Turkey (TUBITAK-Project No:100Y045). The corresponding author acted as the principal investigator in both research projects. The support of the Istanbul Organized Leather Tanning Industrial District I activated sludge treatment plant management, engineers, and technicians is gratefully acknowledged.