Edinburgh Napier University

  Wastewater activated sludge treatment plants are among the most common
forms of biotechnological application. These plants breakdown influents of
organic and non-organic matter using a complex bacterial consortia in an
aerobic aqueous suspension. One of the most persistent and widespread
problems associated with these plants is the formation of thick viscous
chocolate coloured scums or foams on the surface of the aeration tanks of the
plants. These foams can reach depths of 1.0-1.5 metres and can transfer to the
secondary clarifiers and into open water sources. They not only reduce
operational efficiency of the plants but they have also been associated with the
transfer of pathogens such as Mycobacteria, nocardioform actinomycetes and
the opportunistic pathogen Nocardia jarcinica.
This investigation had two main aims:
1. To analyse two WWTP with very different characteristics to identify the
causative organisms and factors of foaming in them both.
2. To design a sampling strategy for further investigations into foaming
In this study the molecular techniques to permeabilise the actinomycetes (the
probable foam causing organisms) and hybridise them with specific
oligonucleotide probes for use in Fluorescent in situ hybridisations (FISH)
were evaluated. In addition four novel 16S rRNA oligonucleotides were
designed to detect Nocardia species in environmental samples. FISH using a
nested set of probes covering Rhodococcus spp, Gordonia spp, Nocardia spp
and the mycolata was evaluated for use in the detection and enumeration of target orgamsms in situ allowing the spatial make up of environmental
filamentous flocs to be examined.
The operational data from a large pharmaceutical waste water treatment plant
was obtained which provided a comprehensive study of the day-to-day
workings of the aeration basin over a three-month period, during which a
foaming incidence occurred. This data was analysed statistically to find
possible indicators of the causes of foaming. Several conclusions were made
about the causes of foaming in this plant.
An alternative PCR-ELISA methodology was devised to produce semIquantitative
enumeration of actinomycetes within environmental samples.
A sampling regime was devised for the further study of foaming in activated
sludge systems. This regime incorporates the use of FISH; PCR-ELISA to
identify and characterise the bacterial consortia within the mixed liquor
suspended solids of activated sludge plants, and analysis of the physical
characteristics of the plants. A combination of these techniques will
eventually allow not only control of foaming but also prevention.