Abstract
Activated sludge is widely used to treat municipal and industrial wastewater globally and the formation of activated sludge flocculates (flocs) underpins the ability to separate sludge from treated water. Despite the importance of activated sludge flocs to human civilization there have been precious few attempts to rationally design fit for purpose flocs using a bottom-up approach based on a solid scientific foundation. Recently we have been developing experimental models for activated sludge floc formation based on the colonization and consumption of particulate organic matter (chitin and cellulose). In this study we lay the foundation for investigation of activated sludge floc formation based on biofilm formation around spheres of the lipid glycerol trioleate (GT) that form spontaneously when GT is introduced into activated sludge incubations. Sludge biomass was observed to associate tightly with the lipid spheres. An increase in extracellular lipase activity was associated with a decrease in size of the colonized lipid spheres over a 25 day incubation. Bacterial community composition shifted from predominantly Betaproteobacteria to Alphaproteobacteria in GT treated sludge. Four activated sludge bacteria were isolated from lipid spheres and two of them were shown to produce AHL like quorum sensing signal activity, suggesting quorum sensing may play a role in lipid spheres colonization and biodegradation in activated sludge. The development of this experimental model of activated sludge floc formation lays the foundation for rational production of flocs for wastewater treatment using lipids as floc nuclei and further development of the flocculate life-cycle concept.
Highlights
The activated sludge process for wastewater treatment is a biotechnology fundamental to human health and represents a model high population density ecosystem for studying microbial interactions [1]
In this study we developed an experimental model of activated sludge floc formation based on glycerol trioleate (GT) as a substrate
To establish an experimental model of floc formation based on interactions between lipids and bacteria in activated sludge, glyceryl trioleate (GT) was added to activated sludge samples at 1% v/v
Summary
The activated sludge process for wastewater treatment is a biotechnology fundamental to human health and represents a model high population density ecosystem for studying microbial interactions [1]. It can be argued that human civilization is dependent on bacterial flocculate formation given the central role of this phenomenon in industrial and municipal wastewater treatment globally. Despite the importance of activated sludge floc formation and function there remain significant knowledge gaps relating to how flocs form, function and change over time. It is unclear how floc development is initiated. There is no mechanistic microbiological description of the ultimate fate of a floc. Put another way, the “lifecycle” of activated sludge flocs is poorly described, possibly because heterogeneity between flocs is rife. A promising approach to addressing these knowledge gaps is to circumvent the challenge of heterogeneity through development and interrogation of experimental models of floc formation
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