Enumeration of protozoan ciliates in activated sludge: determination of replicate number using probability.
A new approach to the enumeration of ciliate protozoa in activated sludge is described. A 25 microL sub-sample volume is optimal for routine analysis using a standard slide and 24 x 24 mm cover slip requiring between 20 and 40 min per sub-sample for full enumeration and identification of species. However, to achieve high probability (>or=95%) of recovering all species large numbers of replicates are required (i.e. 23-47). To achieve high probabilities of recovery using less replicates it is necessary to neglect rare species with low densities (<0.5%); based on the assumption that they do not play a significant role in plant performance. The precise number of replicates required for different probabilities of recovering species is determined by conducting an initial pilot survey analysing a minimum of 8 replicates and using a probability equation to determine the optimum replicate number for that particular plant. Six replicate 25 microL sub-samples provided excellent species recovery (90-95% excluding up to 3 rare species), while analysing just two or three replicates, as commonly used in previous wastewater studies, only gave probabilities of 25 and 50% respectively for the same recovery. Ciliate analysis should be completed within 8h of collection with significant changes in community structure occurring beyond this period.
Dubber
Donata
D
Centre for the Environment, Trinity College, College Green, Dublin 2, Ireland. dubberd@tcd.ie
Gray
N F
NF
D000818:Animals; D016798:Ciliophora / Q000302:isolation & purification*; D015203:Reproducibility of Results; D018401:Sample Size; D012722:Sewage / Q000469:parasitology*; D014865:Waste Disposal, Fluid; D018508:Water Purification
D012722:Sewage