Simple methods for evaluating the population of naidids in drinking water treatment plants

Abstract

The use of biofiltration ozonation followed by biofiltration in drinking water to improve the physicochemical and biological qualities of drinking water can promote the development of macro-invertebrates in filters colonized by bacteria. The passage of invertebrates in filtered water should be avoided both from an aesthetic point of view and from the potential of bacteria growth support on their surface. This paper focuses on the development of two simple methods to estimate the population of members of the naidid family from the class of oligochaetes in biofilters and in water. The first method involves a naidid column trap used to concentrate naidids present in the effluent of biofilters. During the study, the concentrations of naidids recorded in the biofilter effluent studied varied from 0 naidid per m3 in cold water (1°C) to 20 naidids per m3 in warm water (22°C). The second method enumerates naidids in a sample of biofilter media taken using a core sampler. Typical naidid densities encountered ranged from the limit of detection (1 naidid per 4 mL) in cold water (1°C) to 25 naidids per mL in warm water (25°C) at the surface of the biofilter. Statistical analyses done on the second method have shown that samples taken at the surface of the filter media at depths between 0 and 200 mm were statistically different from those taken at deeper levels and represented the maximum naidid densities measured in the biofilter studied.Key words: drinking water, biofiltration, population of naidids.