External nitrification in biological nutrient removal activated sludge system (original) (raw)
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Proceedings of the Water Environment Federation, 2001
A biological nutrient removal (BNR) activatedsludge (AS) scheme incorporating external nitrification in a fixed media system is evaluated. A laboratory scale investigation of the scheme indicates that it holds considerable potentialfor BNRAS system intensification through major reduction in sludge age and oxygen demand and significant improvement in sludge settleability. Because the BNRAS system is not required to nitrtfy, its anoxic mass fraction can be considerably enlarged at the expense of the aerobic mass fraction creating conditions that (i) allow it to achieve high N removals with domestic wastewaters with high TKN/COD ratios and (ii) promote anoxic P uptake polyphosphate accumulating organisms (PAO) to develop in the system. From this, andearlier investigations with conventional BNR systems, it appears that anoxic P uptake biological excess P removal (BEPR) is only about 2/3rds of aerobic P uptake BEPR. Inclusion of anoxic P uptake PAOs in, and exclusion of nitrtfiers from, the BNRAS system are not essentialfor the scheme. However, conditions that promote aerobic P uptake to maximize BEPR, are also conducive to nitrifier growth, which, if supported in the BNRAS system, would require virtual complete nitrification in the fixed media system to avoid nitrate interference with BEPR. Before the scheme can be implemented at large scale, an engineering and economic evaluation is required to quantify its potential benefits and savings.
Biotechnology and Bioengineering, 2003
A systematic lab-scale experimental investigation is reported for the external nitrification (EN) biological nutrient removal (BNR) activated sludge (ENBNRAS) system, which is a combined fixed and suspended medium system. The ENBNRAS system was proposed to intensify the treatment capacity of BNR-activated sludge (BNRAS) systems by addressing two difficulties often encountered in practice: (a) the long sludge age for nitrification requirement; and (b) sludge bulking. In the ENB-NRAS system, nitrification is transferred from the aerobic reactor in the suspended medium activated sludge system to a fixed medium nitrification system. Thus, the sludge age of the suspended medium activated sludge system can be reduced from 20 to 25 days to 8 to 10 days, resulting in a decrease in reactor volume per ML wastewater treated of about 30%. Furthermore, the aerobic mass fraction can also be reduced from 50% to 60% to <30% and concommitantly the anoxic mass fraction can be increased from 25% to 35% to >55% (if the anaerobic mass fraction is 15%), and thus complete denitrification in the anoxic reactors becomes possible. Research indicates that both the short sludge age and complete denitrification could ameliorate anoxic aerobic (AA) or low food/microorganism (F/M) ratio filamentous bulking, and hence reduce the surface area of secondary settling tanks or increase the treatment capacity of existing systems. The lab-scale experimental investigations indicate that the ENBNRAS system can obtain: (i) very good chemical oxygen demand (COD) removal, even with an aerobic mass fraction as low as 20%; (ii) high nitrogen removal, even for a wastewater with a high total kjeldahl nitrogen (TKN)/COD ratio, up to 0.14; (iii) adequate settling sludge (diluted sludge volume index [DSVI] <100 mL/g); and (iv) a significant reduction in oxygen demand.
Water science and technology : a journal of the International Association on Water Pollution Research, 2002
In this paper the advantages and disadvantages of denitrifying PAOs (polyphosphate accumulating organisms) in conventional BNRAS (biological nutrient removal activated sludge) and external nitrification BNRAS (ENBNRAS) systems are evaluated, with experimental data exhibiting a range of anoxic P uptake from low (<10%) to very high (>60%). The results indicate that the specific denitrification rate of the PAOs on internally stored PHB COD is about 1/5th of that of the "ordinary" heterotrophic organisms on SBCOD, and the PAOs contribute little (maximum 20%) to the denitrification in BNRAS systems even when the anoxic P uptake is high (60% of the total P uptake). Considering the unpredictable nature of anoxic P uptake and the reduction in BEPR it causes compared with aerobic P uptake BEPR, it is concluded that anoxic P uptake does not add a significant advantage to the BNR system.
Biological Nutrient Removal in Municipal Wastewater Treatment: New Directions in Sustainability
Journal of Environmental Engineering, 2012
To control eutrophication in receiving water bodies, biological nutrient removal (BNR) of nitrogen and phosphorus has been widely used in wastewater treatment practice, both for the upgrade of existing wastewater treatment facilities and the design of new facilities. However, implementation of BNR activated sludge AS systems presents challenges attributable to the technical complexity of balancing influent chemical oxygen demand (COD) for both biological phosphorus (P) and nitrogen (N) removal. Sludge age and aerated/unaerated mass fractions are identified as key parameters for process optimization. Other key features of selected BNR process configurations are discussed. Emerging concerns about process sustainability and the reduction of carbon footprint are introducing additional challenges in that influent COD, N, and P are increasingly being seen as resources that should be recovered, not simply removed. Energy recovery through sludge digestion is one way of recovering energy from influent wastewater but which presents a specific challenge for BNR: generation of sidestreams with high nutrient and low COD loads. Technologies designed specifically to treat these side-stream loads are overviewed in this paper. Finally, relatively high levels of nitrous oxide emissions, a powerful greenhouse gas, have been shown to occur in the BNR process under certain conditions, particularly in the presence of high nitrite concentrations. The advantages of using process modeling tools is discussed in view of optimizing BNR processes to meet effluent requirements and to meet goals of sustainability and reducing carbon footprints.
Water Science and Technology, 2016
Mainstream partial nitritation and Anammox (PN/A) has been observed and studied in the step-feed activated sludge process at the Changi water reclamation plant (WRP), which is the largest WRP (800,000 m3/d) in Singapore. This paper presents the study results for enhanced biological phosphorus removal (EBPR) co-existing with PN/A in the activated sludge process. Both the in-situ EBPR efficiency and ex-situ activities of phosphorus release and uptake were high. The phosphorus accumulating organisms were dominant, with little presence of glycogen accumulating organisms in the activated sludge. Chemical oxygen demand (COD) mass balance illustrated that the carbon usage for EBPR was the same as that for heterotrophic denitrification, owing to autotrophic PN/A conversions. This much lower carbon demand for nitrogen removal, compared to conventional biological nitrogen removal, made effective EBPR possible. This paper demonstrated for the first time the effective EBPR co-existence with PN/...
Biological Nutrient Removal: Design Snags, Operational Problems and Costs
Water and Environment Journal, 1995
The EC urban waste water treatment Directive will lead to some sewage-treatment works in the UK having to remove nitrogen and phosphorus. The paper reviews the basic biological processes which are available for retrofitting existing activated-sludge plants to achieve this removal, and then points to some of the problems which are encountered with these processes in other countries. The authors make suggestions as to how these problems can be overcome in design and operation. The paper also provides a cost comparison of different ways of uprating an existing nitrifying activated-sludge plant to achieve nitrification/ denitrification and phosphorus removal.
Factors affecting the biological nitrogen removal from wastewater
Process Biochemistry, 2006
The paper presents the results of full-scale research concerning the temperature, the sludge age and the COD/N ratio in wastewater effect on nitrification and results of batch tests examined the additional carbon source in wastewater and the initial nitrate concentration in anoxic zone effect on the denitrification rate, time and efficiency. It was stated that the sludge age increase above 20 days lessened the unfavorable effect of low temperatures (under 15 8C) and stabilized the nitrification process. The highest effectiveness of nitrification (above 95%) were achieved when the COD/N ratio was lower than 4, higher parameter values destabilized process especially with low temperature. The batch test showed that delivering an additional carbon source in the form of acetic acid solution to the biological treatment process with pre-denitrification is favorable to the denitrification process and that above particular dose (the VFA/N ratio equal to 1.67 mg CH 3 COOH/mg N) the further denitrification rate increase did not occur. The effect of initial nitrate concentration in the anoxic zone on the denitrification rate is less distinct. #
MATEC Web of Conferences
Water utilities, commercial and industrial establishments are required to upgrade or install new treatment systems to comply with the revised effluent standards issued by the Department of Environment and Natural Resources – Environment Management Bureau (DENR – EMB) which now includes removal and monitoring of nutrients (nitrogen and phosphorus components). One solution is to utilize a biological nutrient removal technology (BNRT) system capable of removing nutrients from sewage. The on-going study aims to investigate the performance of the pilot-scale system in the removal of nutrients from sewage. The designed pilot-scale anaerobic-anoxic-oxic (A2O) process with a total hydraulic retention time of 8.37 hrs. was operated in an existing sewage treatment plant (STP). System modification was adapted to ensure continuous operation. Dissolved oxygen (DO) and temperature of each compartment were evaluated after 45 days of system modification. The DO of the anaerobic and oxic compartment...
Nitrite and nitrate inhibition thresholds for a glutamate-fed bio-P sludge
Chemosphere, 2021
Enhanced biological phosphorus removal (EBPR) is an efficient and sustainable technology to remove phosphorus from wastewater. A widely known cause of EBPR deterioration in wastewater treatment plants (WWTPs) is the presence of nitrate/nitrite or oxygen in the anaerobic reactor. Moreover, most existing studies on the effect of either permanent aerobic conditions or inhibition of EBPR by nitrate or free nitrous acid (FNA) have been conducted with a "Candidatus Accumulibacter" or Tetrasphaera-enriched sludge, which are the two major reported groups of polyphosphate accumulating organisms (PAO) with key roles in full-scale EBPR WWTPs. This work reports the denitrification capabilities of a bio-P microbial community developed using glutamate as the sole source of carbon and nitrogen. This bio-P sludge exhibited a high denitrifying PAO (DPAO) activity, in fact, 56% of the phosphorus was uptaken under anoxic conditions. Furthermore, this mixed culture was able to use nitrite and nitrate as electron acceptor for P-uptake, being 1.8 μg HNO 2-N⋅L − 1 the maximum FNA concentration at which P-uptake can occur. Net P-removal was observed under permanent aerobic conditions. However, this microbial culture was more sensitive to FNA and permanent aerobic conditions compared to "Ca. Accumulibacter"-enriched sludge.
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.