Conditioning factors of iron ochre biofilm formation on geotextile filters

Abstract

This paper presents a study of ochre formation on geotextile filters. Ochre is a substance found sticking to solid surfaces of drainage systems and may cause clogging. Ochre formation is discussed based on the new concepts of biofilm development. Ochre formation is the result of microbial colonization and its affinity to iron compounds naturally found in seepage water. The aerobic–nonaerobic interface in drainage systems is a very favourable locale for optimum development of iron bacteria. Laboratory studies were done to verify the influence of intrinsic characteristics of the geotextiles and environment on ochre formation. Because flow condition was not considered in the tests, however, these results may not represent real field performance of geotextile filters. Tests of biofilm formation were conducted in Erlenmeyer flasks containing culture mediums for iron bacteria and geotextile samples. Nonwoven polyester, nonwoven polypropylene, and woven polypropylene geotextiles were used in the tests. The study was performed considering different levels of iron concentration, available dissolved oxygen, and pH. Laboratory tests have shown the fundamental importance of iron bacteria activity, type of geotextile, and environmental conditions on ochre formation.Key words: ochre, clogging, filtration, biofilm, geosynthetics.