Homogenisation and Dilution in Metabolic Evaluation of Activated Sludge Rich in Chloroflexi

The biological wastewater treatment systems are mostly based on the activated sludge method and endangered by exploitation problems connected to sludge bulking and/or foaming. Chloroflexi bacteria often cause bulking episodes and should be investigated in that matter, especially regarding the unusual metabolic activities. The aim of the study was to evaluate if the activity of microbial populations measured by the Biolog system is changing in reaction to diluent and homogenisation. The thesis was it that it differs for activated sludge samples with high and low abundance of Chloroflexi. The systematic review was performed to identify and fill a research gap concerning the best approach to study metabolism of activated sludge of various origins. We tested samples of municipal and industrial sludge with differing abundance of Chloroflexi and showed that activity of distinct types of sludge is influenced incongruously by preparation. The homogenisation unified the composition of activated sludge and influenced the microbial communities responsible for the hydrolysis of complex sugars. The homogenised sludge showed activity for the same substrates as the non-homogenised one, but the carbohydrate uptake was higher for the second one. Dilution with supernatant also influenced the metabolism. Substrate uptake was lower for 60% of the substrate groups for the less diluted sludge. On the other hand, the higher dilution of activated sludge inoculum resulted in a bigger spectrum of the substrates assimilated by bacteria on EcoPlate. Interestingly the type of diluent and time of homogenisation do not significantly affect the results within the same wastewater treatment plant.