An investigation of techniques to identify the causes of foaming in activated sludge waste water
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.