Nematodes in wastewater biofilms--appearance and density of species in three biofilter reactors

Population dynamics of nematode species in biofilms of three different biofilter reactors, differing in size (pilot/laboratory scale), operation mode and biofilm carrier, were studied over a period of 1 year. In the biofilm suspension of the pilot system mean nematode density was 118individuals/ml and average biomass 15microg wet weight/ml. Higher mean abundance was found in the two laboratory systems with 2380 and 4411individuals/ml. Mean biomass in the laboratory systems ranged from 209 to 330microg wet weight/ml. There were marked temporal differences in appearance and density of nematode species in all three biofilters. Number of species observed was 3 in the laboratory systems and 5 in the pilot system. The fastest growing species (Paroigolaimella bernensis and Diplogasteritus nudicapitatus) were observed in the pilot reactor in contrast to the more slowly growing species (Diploscapter coronatus and Acrostichus sp.), which dominated in the laboratory reactors. Sexual reproduction was found for all species but of Diploscapter coronatus. When comparing life history traits of the different species with the environmental conditions in the reactors, it seems that the unstable conditions in the pilot reactor favor the fast growing species whereas the stable environment in the laboratory systems allows the growth of species with longer generation times.