Effect of exogenous carbon sources on removal of inorganic nutrient by the nitrification-denitrification process (original) (raw)
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The effect of an anoxic zone on biological phosphorus removal by a sequential batch reactor
Bioresource Technology, 2004
Nitrate can affect phosphate release and lead to reduced efficiency of biological phosphorus removal process. The inhibition effect of remaining nitrate at the anaerobic/anoxic phases was investigated in a lab scale sequencing batch reactor. In this study the influence of denitrification process on reactor performance and phosphorus removal was examined. The experiments were carried out through simultaneous filling and decanting, mixing, mixing-aeration and settling modes. Glucose and acetate were used as carbon sources. The proposed treatment system was capable of removing approximately 80% of the influent PO4-P, 98% NH4-N and 97% COD at a SRT of 25 days. In the fill/decant phase, anoxic and anaerobic conditions prevailed and a large quantity of nitrate was removed in this stage. In the anoxic phase the remaining nitrate concentration was quickly reduced and a considerable amount of phosphate was released. This was attributed to the availability of acetate in this stage. For effective nitrogen and phosphate removal, a short anoxic phase was beneficial before an aerobic phase.
Biotechnology Letters, 1998
The nitrogen removal potential of phosphate accumulating organisms under anoxic conditions has been evaluated using a laboratory scale sequencing batch reactor fed with synthetic wastewater and operated in a sequence of anaerobic, anoxic and aerobic periods. The phosphate uptake rate under anoxic conditions was lower than that under aerobic conditions. However, in the presence of an external substrate such as glucose and acetate, the fate of phosphate was dependent on the substrate type; phosphate release occurred in the presence of nitrate as long as acetate was present and glucose did not cause any phosphate release. The nitrate uptake rate was also much lower with glucose than acetate. The results implied that poly-hydroxyalkanoates could be oxidized by nitrate and phosphate uptake during the anoxic phase should be introduced into process modeling. © Rapid Science Ltd. 1998
Water Research, 2002
In this paper, research on the growth performance of phosphate-accumulating organisms (PAOs) was conducted based on literature and experimental investigations on biological nutrient removal (BNR) activated sludge (BNRAS) systems. The research aims at presenting the occurrence of denitrifying PAOs (DPAOs), abstracting information on the kinetics and stoichiometry of PAOs under anoxic conditions and determining the conditions that stimulate the PAO growth under anoxic conditions. The research results indicate that the PAOs are capable of utilizing nitrate as electron acceptor instead of oxygen in BNRAS systems, particularly in external nitrification BNRAS (ENBNRAS) systems. However, the growth yield of PAOs under anoxic conditions should be reduced to about 70% of that under aerobic conditions, and further the stoichiometric coefficient for anoxic P uptake per PHB COD utilized should be reduced to about 80% of that under aerobic conditions as the DPAOs show a significantly lower BEPR performance and use the influent RBCOD less ''efficiently'' compared with aerobic PAOs (APAOs). The research results also indicate that the major factor influencing the occurrence of DPAOs and associated anoxic P uptake is the nitrate load into the anoxic reactor, i.e. the nitrate load should be large enough or exceeds the denitrification potential of ordinary heterotrophic organisms (OHOs), i.e. non-PAO organisms in the anoxic reactor to stimulate DPAOs in the system as the specific denitrification rate of OHOs (K 0 2 OHO ) is significantly larger than that of PAOs (K 0 2 PAO ). In terms of this competition, if the nitrate load into the main anoxic reactor is less than the denitrification potential of OHOs, then the OHOs will outcompete PAOs for using the limited nitrate, while if the nitrate load in the main anoxic reactor exceeds the denitrification potential of OHOs, then the PAOs would have opportunities to use the ''excess'' nitrate and so develop in the system. The other factors that influence DPAOs include the system aerobic mass fraction, sequence of reactors and frequency of sludge alternation between the aerobic and anoxic states. Although it does appear that these factors above may significantly influence the fraction of DPAOs (Z G ), the quantitative relationship between these factors and Z G is not known, and the experimental observations indicate that this will be system-specific, and require calibration for each situation. r
Anoxic biological phosphorus removal in a full-scale UCT process
Water Research, 1997
Akstract-Enhanced biological phosphorus removal is based on the selective enrichment of bacteria accumulating inorganic polyphosphate, obtained at a cyclic regime of alternating anaerobic and aerobic conditions. In the University of Cape Town (UCT) process for combined nitrogen and phosphorus removal, polyphosphate-accumulating bacteria will also be exposed to nitrate in the anoxic zone, i.e. an electron acceptor that may be utilized as well as the oxygen of the aerobic zone. During a l-year study of the full-scale UCT process run at Oresundsverket, Helsingborg, special attempts were made to quantify the relative contribution of an anoxic phosphate uptake at full-scale conditions: the dominant chemical oxygen demand (COD) uptake in the anaerobic zone could be identified as poly-/~-hydroxy-alkanoates (PHA). PHA accumulation was at its largest during a test period with acetate added as an extra carbon source. At least one-third of the COD consumed in the anoxic zone could be identified as PHA. The anoxic sludge contained increased amounts of polyphosphate and reduced amounts of free orthophosphate compared to the anaerobic zone, approaching the levels of aerobic sludge. The metal bound orthophosphate remained largely unaffected, at a level of 25-30% of the total phosphorus content. After correction for the sludge recycling of the system, the formation of inorganic polyphosphate in the anoxic zone itself was estimated to be 30% of the total. When the metabolic activity was tested under controlled conditions in batch, the anaerobic sludge of the plant showed a high denitrifying activity accompanied by a phosphorus uptake and a simultaneous consumption of intracellular PHA corresponding to 2 g-COD/g-N, i.e. half the theoretical value needed for denitrification when biomass growth is included. It is concluded that intracellular PHA played a major role as a carbon source for denitrification in this full-scale UCT process, with a corresponding phosphate uptake also in the anoxic zone. The biological nitrogen and phosphorus removal must, therefore, be regarded as interconnected.
Water Science and Technology, 1995
The ecolog-microbiological structure of activated sludge in nittificalion-denittificalion biological excess phosphorus removal (NDBEPR) systems in classic version with real wastewaters and in the presence of inhibitor o-nitrophenol (oNP) has been investigated. The amount of the essential physiological groups microorganisms (aerobic-heterotrophic. nitrifying. denitrifying. phosphorus removing bacteria (Poly P. Poly P denitrifying). nitrophenols-degrading and heterotrophic ammonia releasing bacteria) has been dermed in the presence of low and high oNP-eoncentrations. The dynamics of activated sludge microbial structure has been discussed in effect on treatment efficiency towards different parameters-COD, P043-elimination. ammonia-oxidatioo. oNP elimination. The results show that oNP decreases efficiency of biotreatment from 26% to 80% with the increasing of oNP concentration from 9.35 to 85.44 mg/l. The large flexibility and compensative possibilities of AS structure in NDBEPR systems have been established. The amount of poly P and oNP degrading bacteria is increased at high oNP coocentration (85.44 mgll). These microbial groups play the important buffer role for stabilization of BEPR in the presence of inhibitor, as weD as for the biodetoxication of oNP.
Advancing post-anoxic denitrification for biological nutrient removal
Water Research, 2011
The objective of this research was to advance a fundamental understanding of a unique post-anoxic denitrification process for achieving biological nutrient removal (BNR), with an emphasis on elucidating the impacts of surface oxygen transfer (SOT), variable process loadings, and bioreactor operational conditions on nitrogen and phosphorus removal. Two sequencing batch reactors (SBRs) were operated in an anaerobic/aerobic/anoxic mode for over 250 days and fed real municipal wastewater. One SBR was operated with a headspace open to the atmosphere, while the other had a covered liquid surface to prevent surface oxygen transfer. Process performance was assessed for mixed volatile fatty acid (VFA) and acetate-dominated substrate, as well as daily/seasonal variance in influent phosphorus and ammonia loadings. Results demonstrated that post-anoxic BNR can achieve nearcomplete (>99%) inorganic nitrogen and phosphorus removal, with soluble effluent concentrations less than 1.0 mgN L À1 and 0.14 mgP L À1. Observed specific denitrification rates were in excess of typical endogenous values and exhibited a linear dependence on the glycogen concentration in the biomass. Preventing SOT improved nitrogen removal but had little impact on phosphorus removal under normal loading conditions. However, during periods of low influent ammonia, the covered reactor maintained phosphorus removal performance and showed a greater relative abundance of polyphosphate accumulating organisms (PAOs) as evidenced by quantitative real-time PCR (qPCR). While GAOs were detected in both reactors under all operational conditions, BNR performance was not adversely impacted. Finally, secondary phosphorus release during the post-anoxic period was minimal and only occurred if nitrate/nitrite were depleted post-anoxically.
Journal of Chemical Technology and Biotechnology, 2006
In this study, the effect of various factors such as C:N ratio, carbon source, percentage P content in the sludge influencing the simultaneous denitrification and enhanced biological phosphorus removal was investigated in batch tests on bean and tomato waste sludge from an upflow anaerobic sludge blanket reactor–anoxic/aerobic system and municipal sludge from a circulating fluidized bed bioreactor. A correlation between the change in redox potential and rate of P release was developed. Interestingly, maximum P release was observed at positive redox potential in some of the batch tests. Simultaneous denitrification and P release under anoxic conditions was observed during all the batch tests. Sludge acclimatization improved the efficiency of the sludge and proved independency of maximum specific denitrification rate and P content of sludges. The contribution of denitrifying PAOs to anoxic P uptake was determined through the denitrification control test at an initial level of PO4-P of 100–120 mg dm−3. Copyright © 2006 Society of Chemical Industry
A mathematical model based on the simulation software AQUASIM was developed to validate an anaerobic/aerobic/anoxic (AOA) process that enables simultaneous nitrogen and phosphorus removal in a single reactor by adding external organic carbon to preclude excess aerobic phosphate uptake by polyphosphate-accumulating organisms (PAOs) and provide phosphate for denitrifying PAOs (DNPAOs). Aerobic batch tests after anaerobic phosphate release with different chemical oxygen demand (COD) concentrations indicated that the effect of COD concentration on the phosphate uptake preclusion could be expressed by a simple formula. The reduction factor reflecting the formula, which retards the aerobic phosphate uptake in the presence of COD, was added to the process rates of aerobic polyphosphate storage and PAOs growth in the model. The improved model, which included the reduction factor, reasonably matched the experimental result regarding aerobic phosphate uptake behavior whereas the model without it did not; thus, the former precisely predicts the AOA process behavior. #