Phosphate uptake under anoxic conditions and fixed-film nitrification in nutrient removal activated sludge system

Experimental investigation of the external nitrification biological nutrient removal activated sludge (ENBNRAS) system

“…The percent anoxic P uptake varied from 42% to 63% of the total P uptake. From these results, together with those from the previous investigations of the similar DEPHANOX system Sorm et al, 1996), it can be concluded that anoxic P-uptake BEPR is a particular characteristic of the ENBNRAS systems. Thus, information on the factors that stimulate anoxic P-uptake BEPR can generally be obtained from these investigations; Hu et al (2002aHu et al ( , 2002b indicated that these include nitrate load on the main anoxic reactor exceeding its denitrification potential, small aerobic mass fractions, sequence of nitrification then denitrification, and reduced frequency of alternation between anoxic and aerobic states.…”

“…2) is similar to that of the DEPHANOX system, except for inclusion of the small pre-anoxic reactor (∼10% mass fraction) in the underflow recycle to the anaerobic reactor. However, it appears that the DEPHANOX system was developed with the specific objective of stimulating anoxic P uptake and denitrification by PAOs, thereby recapturing the influent RBCOD for denitrification Sorm et al, 1996). With aerobic P-uptake BEPR, the influent RBCOD is lost for denitrification, because, while taken up in the anaerobic reactor, it is utilized (via PHA) with oxygen as terminal electron acceptor only in the aerobic reactor; if the PAOs can be stimulated to denitrify in the anoxic reactor, then some of the stored PHA would be utilized with nitrate as terminal electron acceptor and P uptake, with the result that the same substrate (RBCOD) is utilized for both N and P removal.…”

“…To resolve these difficulties, on the basis of the DEPHANOX system Sorm et al, 1996), Hu et al (2000) proposed a BNRAS scheme in which nitrification is removed from the BNRAS system to an external fixed media, called the external nitrification (EN) BNRAS system. In addition to allowing for a significant reduction in sludge age, removing nitrification from the aerobic reactor of the BNRAS system has other benefits:…”

Model evaluation and optimisation of nutrient removal potential for sequencing batch reactors

“…For example the IWA (formerly IAWQ) Task Group has developed the Activated Sludge Model No.2 (ASM2) incorporating EBPR (Henze et al, 1995). These models, while providing an acceptably reliable description for nitrogen transformations, generally lacked sufficient credibility for the fate of phosphorus, mainly because they did not incorporate sufficient experimental support, and also, the behaviour of phosphate accumulating organisms (PAOs) did not always appear quite predictable (Sorm et al, 1996;Kuba et al, 1997;Ekama and Wentzel, 1999). In the light of recent research Artan et al, 1998;Barker and Dold, 1997), ASM2 was modified as ASM2d to include denitrification by PAOs with reduced anoxic P uptake (Henze et al, 1999).…”

Antibody recognition of an 18 kDa protein possibly involved in phosphate removal by activated sludge

“…The existence of two groups of phosphate accumulating bacteria was postulated: one group capable of utilising only oxygen as electron acceptor and the other group capable of utilising both oxygen and nitrate as electron acceptor, i.e. denitrifying polyP organisms (Mino et al, 1995;Sorm et al, 1996). The anoxic zone sample utilised in the current study was obtained from the second anoxic zone of a modified UCT system.…”