The role of nematodes in low rate percolating filter sewage treatment works

The contribution and role of bacterivore nematodes in energy flow in two low rate percolating filter works was calculated based on field sampling and laboratory studies of feeding rates and energy ingestion, growth, reproduction and respiration. At both sewage works energy flow values peaked in May and January corresponding to peaks in nematode density and biomass. Simplified energy flow diagrams related to time are presented expressed for a core extending from the bed surface to its bottom. Nematode ingestion in the filter-beds exercised a distinct effect on the bacterial community such that in order to maintain steady-state conditions a mean bacterial doubling time ranging from 31 to 291 h was necessary at Caton Effluent Treatment Works and 87-4460 h at Carnforth ETW. Localized grazing effects, especially in the upper filter regions, exercised even greater effects, where a doubling time of 4 h may have been required on occasions. Oxygen consumption attributable to nematodes ranged from 0.03 to 2.7% of total community respiration at the two treatment works, suggesting that in general the direct role of nematodes is relatively small and they exert their greatest effect by grazing on bacteria. © 1986.