A Study of Factors Affecting the Incidence and Growth Rates of Fungi in Sewage Bacteria Beds

Abstract

The problems caused by fungi growing in sewage bacteria beds were examined and the need for a study of the autecology of these fungi under simulated bed conditions discussed. The literature on fungi in this habitat was reviewed, with particular reference to factors influencing their occurrence and growth there. Dominant fungi isolated from bacteria bed film at two Birmingham area works were studied in culture on various media to extend taxonomic knowledge and plan continuous culture work. One fungus not recorded previously in the Birmingham area, Subbaromyces splendens, and one not previously recorded from bacteria beds, Fusarium reticulatum, were isolated. Temperature:growth relationships were studied quantitatively in batch culture for five species of these fungi. A continuous culture apparatus was designed to permit accumulation and daily weighing of fungal biomass; terminal dry weight determinations of standing crop were also made. The method proved satisfactory in preliminary trials with five species of bacteria bed fungi and was used to assess the effect of temperature, nature, concentration and method of dosing of feed, scouring effect of high liquid flow and the effect of competition from bacteria on Sepedonium sp. or Ascoidea rubescens. Sterilised sewage or synthetic solutions were used as feeds; sterilisation of sewage by tyndallisation did not prove entirely reliable, but autoclaving resulted in inhibition of fungal growth. Intermittent dosing had a marked inhibitory effect on the growth of Sepedonium sp. at a dosing interval of 8½ minutes, but A. rubescens was only slightly affected. Other factors tested all had appreciable effect on fungal growth, except for liquid scour which was without detectable effect at this dose interval. The relationship of these results to bacteria bed conditions is discussed.