The microbiology of biological phosphorus removal in activated sludge systems

Abstract

Activated sludge systems are designed and operated globally to remove phosphorus microbiologically, a process called enhanced biological phosphorus removal (EBPR). Yet little is still known about the ecology of EBPR processes, the microbes involved, their functions there and the possible reasons why they often perform unreliably. The application of rRNA-based methods to analyze EBPR community structure has changed dramatically our understanding of the microbial populations responsible for EBPR, but many substantial gaps in our knowledge of the population dynamics of EBPR and its underlying mechanisms remain. This review critically examines what we once thought we knew about the microbial ecology of EBPR, what we think we now know, and what still needs to be elucidated before these processes can be operated and controlled more reliably than is currently possible. It looks at the history of EBPR, the currently available biochemical models, the structure of the microbial communities found in EBPR systems, possible identities of the bacteria responsible, and the evidence why these systems might operate suboptimally. The review stresses the need to extend what have been predominantly laboratory-based studies to full-scale operating plants. It aims to encourage microbiologists and process engineers to collaborate more closely and to bring an interdisciplinary approach to bear on this complex ecosystem.

The Chemical Nature of Phosphorus in Subtropical Lake Sediments

“…Although the absence of polyphosphate in the uppermost 5 cm of sediment may be a methodological artifact, a similar phenomenon has been reported elsewhere (Carman et al 2002;Reitzel et al 2006aReitzel et al , 2007. Bacteria can store polyphosphate if sufficient organic carbon and phosphate are available under alternating aerobic/anaerobic conditions (Gächter and Meyer 1993;Mino et al 1998;Seviour et al 2003), which probably accounts for differences in the occurrence of polyphosphate in the lakes studied here: Lake Apopka sediments contain large amounts of labile carbon and experience alternating aerobic-anaerobic conditions, whereas Lake Annie sediments contain high organic carbon but are always anaerobic and Lake Okeechobee sediments undergo oscillating aerobic-anaerobic conditions but contain little labile organic carbon (Torres 2007). Similar results were reported for a series of Scandinavian lakes (Carman et al 2002): high polyphosphate concentrations were detected in Lake Gömmaren, with well-oxidized sediments and high organic matter content; smaller concentrations of polyphosphate were detected in Lake Långsjön, with oscillating aerobicanaerobic conditions; and no polyphosphate was detected in Lake Flaten, with constant anoxic conditions.…”

Metagenomic analysis of two enhanced biological phosphorus removal (EBPR) sludge communities

“…Both choices yield models fitting some stochiometic ratios properly and others less optimally, depending on the system (a summary can be found in Schuler et al 3 ). As pointed out by Seviour et al 35 , the main weak point of most EBPR studies is that the structure and functional relationships of the populations involved are mainly unknown. For example, in the case of Maurer et al 34 the sludge was obtained from a pilot scale treatment plant fed municipal wastewater (as opposed to acetate) and was subsequently exposed to only two EBPR cycles.…”

Structure and function of the microbial community in a full-scale enhanced biological phosphorus removal plant

“…Our understanding of the microbiology of EBPR WWTPs is to a large extent obtained from culture-independent studies using enriched cultures in well-controlled laboratory-scale reactors by using the full-cycle rRNA approach (Amann, 1995), as reviewed in detail by Mino et al (1998) and Seviour et al (2003). Some potentially important micro-organisms involved in the EBPR process have been identified in such laboratory-scale reactors, but only a few of them have been shown to be important in full-scale WWTPs.…”

“…The general understanding of design and operation of activated-sludge WWTPs has increased significantly in the last two decades, but occasionally EBPR WWTPs still suffer from suboptimal operation and breakdown of the P-removal process. These problems are believed to be due to poor understanding of the structure of the microbial community in EBPR WWTPs and insufficient knowledge of the ecophysiology of the key microbial populations.Our understanding of the microbiology of EBPR WWTPs is to a large extent obtained from culture-independent studies using enriched cultures in well-controlled laboratory-scale reactors by using the full-cycle rRNA approach (Amann, 1995), as reviewed in detail by Mino et al (1998) and Seviour et al (2003). Some potentially important micro-organisms involved in the EBPR process have been identified in such laboratory-scale reactors, but only a few of them have been shown to be important in full-scale WWTPs.…”