Abstract
Routine characterisation of activated sludge and identification of the filamentous population by microscopic and/or other non-culture dependent techniques can assist in diagnosing the aetiology of poor performance of wastewater treatment works (WWTWs). In South Africa, most facilities rely solely on physicochemical indicators, treating reactors as ‘black-boxes’, with the result that process adjustments are often delayed, to the detriment of the environment. This study was performed in order to gain insight into the filamentous population found in activated sludge in Cape Town WWTWs, to compare these with other global and local literature findings, and to build capacity in this science. Physicochemical and plant performance parameters, in terms of nutrient removal and settling, were obtained from routine operational data and assessed in conjunction with the microscopic analyses of activated sludge samples taken over a 6-month period. Hypotheses on the links between filament types and/or plant configurations and/or operational parameters were formulated using existing literature. In order of prevalence, the five most common dominant filament species in 96 activated sludge samples were: Eikelboom Type 0092, Eikelboom Type 1851, nocardioforms, Microthrix parvicella and Eikelboom Type 021N. In order to compile a statistically significant database, it is recommended that an extensive nationwide study is conducted to link filament types with plant configurations, operational parameters and geographical locations. Keywords : activated sludge, bulking, identification, filament, Type 0092
Highlights
The successful treatment of wastewater is reliant on the continued presence of a robust microbial consortium
96 samples taken from 5 Modified Ludzack-Ettinger (MLE), 7 University of Cape Town (UCT) and 4 5SB reactors at 11 WWTWs were analysed
In terms of overall prevalence, some notable differences between the three studies were found, the most important being the fact that Eikelboom Type 0092 was not identified in any of the six WWTWs from KZN, but was present in almost all samples from the other two studies (44 WWTWs)
Summary
The successful treatment of wastewater is reliant on the continued presence of a robust microbial consortium. A variety of bacteria grow in filamentous forms that may or may not form part of the floc structure (Eikelboom, 2000; Jenkins et al, 2004). Some filament types form bridges between flocs or have hydrophobic cell walls that hamper floc settling and cause sludge bulking and/or foaming. Particular process conditions are strongly associated with the proliferation of ‘bulking’ filament types (Eikelboom, 2000; Jenkins et al, 2004; Lakay et al, 1999). Microscopic analysis of activated sludge is a simple, cost-effective procedure that can add value to the arsenal of tests currently performed at laboratories affiliated to WWTWs. At present, expertise in filament identification is only available at the East Rand Water Care company (ERWAT), Received 8 April 2014; accepted in revised form 7 October 2014
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