Observations on the anaerobic membrane-filter technique for coliform counts in Nigerian surface waters

The applicability of the anaerobic membrane filtration method to faecal coliform counts was tested on 88 water samples from the Port Harcourt area of the Rivers State of Nigeria. Seventy-eight streams/rivers and ten untreated distributive sources were analysed. High levels of suspended residues necessitated the filtration of 1-2 ml of the raw and 5-10 ml of diluted samples of the surface waters. Anaerobic incubation, overall, decreased the nonfaecal coliforms (NFCs) and faecal coliforms (FCs) by 69.32% and 48.86% respectively. Percent decrease of mean NFC and FC count in 21 streams sampled at random, was 8.85% and 20.88%, respectively. Results from a stream and a faecally polluted beach of a tidal river sampled periodically were variable. The NFCs and FCs decreases in the stream sample by 5.4% and 7.6% respectively were not significant. For the beach samples, the 9.8% reduction in NFCs was significant (p = 0.01), but the 4.19% increase in FCs was not. Seventy percent of the distributive samples gave zero FC counts. Anaerobic incubation reduced to zero FCs in 2 samples and NFCs in 5 samples. It is concluded that the advantages of anaerobic incubation are not commensurate with the increased expenditure which invariably is incurred in the routine analysis of these waters.