Abstract
It is now clear that several of the filamentous bacteria in activated sludge wastewater treatment plants globally, are members of the phylum Chloroflexi. They appear to be more commonly found in treatment plants designed to remove nitrogen (N) and phosphorus (P), most of which operate at long sludge ages and expose the biomass to anaerobic conditions. The Chloroflexi seem to play an important beneficial role in providing the filamentous scaffolding around which flocs are formed, to feed on the debris from lysed bacterial cells, to ferment carbohydrates and to degrade other complex polymeric organic compounds to low molecular weight substrates to support their growth and that of other bacterial populations. A few commonly extend beyond the floc surface, while others can align in bundles, which may facilitate interfloc bridging and hence generate a bulking sludge. Although several recent papers have examined the phylogeny and in situ physiology of Chloroflexi in activated sludge plants in Denmark, this review takes a wider look at what we now know about these filaments, especially their global distribution in activated sludge plants, and what their functional roles there might be. It also attempts to outline why such information might provide us with clues as to how their population levels may be manipulated, and the main research questions that need addressing to achieve these outcomes.
Highlights
The Activated Sludge ProcessTreatment of domestic and industrial wastewater is essential to reduce potentially harmful levels of organic and inorganic compounds and pathogenic microbes to those allowing the treated water to be run into a receiving water body, such that its self-purification ability is not compromised (Catherine et al, 2013; Gaget et al, 2017)
The most popular treatment process globally is activated sludge (Daigger, 2014), and in use for more than 100 years (Lofrano and Brown, 2010; Jenkins and Wanner, 2014). No longer are these seen as disposal systems, but as valuable sources of recycled water, and the biomass or sludge for recovery of chemicals of value. This biomass consists primarily of bacteria and protozoa, which become organized as aggregates called ‘flocs.’ It is generally accepted that the Chloroflexi, the subject of this review, play an important role in providing the filamentous matrix around which desirable strong flocs with rapid settling properties are formed
This review deals with a group of filamentous bacteria, the Chloroflexi, who have been associated with bulking and foaming events in activated sludge plants
Summary
The Activated Sludge ProcessTreatment of domestic and industrial wastewater is essential to reduce potentially harmful levels of organic and inorganic compounds and pathogenic microbes to those allowing the treated water to be run into a receiving water body, such that its self-purification ability is not compromised (Catherine et al, 2013; Gaget et al, 2017). It is clear that several of the filamentous bacteria in activated sludge wastewater treatment plants globally, are members of the phylum Chloroflexi.
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