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Washington, DC, United States
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Kinyua M.N.,Columbia University | Elliott M.,Old Dominion University | Wett B.,ARA Consult GmbH | Murthy S.,DC Water Authority | And 2 more authors.
Chemical Engineering Journal | Year: 2017

This paper quantifies the effect of varying solids retention time (SRT), hydraulic retention time (HRT) and dissolved oxygen (DO) concentrations on extracellular polymeric substances (EPS) production and subsequently effluent quality, carbon capture (bioflocculation) and carbon redirection (settling) in a high rate activated sludge A-stage system treating domestic wastewater. Two pilot-scale A-stage reactors were set-up with HRTs of 30 and 60 min. Cascade DO control was used to maintain 3 DO set-points of 0.5, 1.0 and 1.5 mg/L. A mixed liquor suspended solids (MLSS) concentration of 3000 mg/L was maintained and the waste activated sludge (WAS) flow was varied to achieve SRTs of 0.28 and 0.56 day. EPS fractions and the protein and polysaccharide concentrations of the mixed liquor were measured. Operation at the 0.56 day SRT and 1.0 mg/L DO resulted in the highest total suspended solids (TSS), total COD (tCOD), particulate COD (pCOD), and colloidal (cCOD) removal. The best overall performance in terms of bioflocculation (cCOD removal) and carbon capture (percent COD in the WAS) occurred at the 0.56 day SRT and coincided with decreasing total EPS concentrations but the settling characteristics of the sludge were better at the 0.28 day SRT. Overall, low correlations were found between EPS production and system performance. It is likely that at the high loading rate of the A-stage system, EPS production did not play a major role compared to the influence of operating parameters on effluent quality, carbon capture and redirection. © 2017


Regmi P.,Old Dominion University | Miller M.W.,Virginia Polytechnic Institute and State University | Holgate B.,Old Dominion University | Bunce R.,Hazen and Sawyer | And 5 more authors.
Water Research | Year: 2014

This work describes the development of an intermittently aerated pilot-scale process (V=0.34m3) operated without oxidized nitrogen recycle and supplemental carbon addition optimized for nitrogen removal via nitritation/denitritation. The aeration pattern was controlled using a novel aeration strategy based on set-points for reactor ammonia, nitrite and nitrate concentrations with the aim of maintaining equal effluent ammonia and nitrate+nitrite (NOx) concentrations. Further, unique operational and process control strategies were developed to facilitate the out-selection of nitrite oxidizing bacteria (NOB) based on optimizing the chemical oxygen demand (COD) input, imposing transient anoxia, aggressive solids retention time (SRT) operation towards ammonia oxidizing bacteria (AOB) washout and high dissolved oxygen (DO) (>1.5mg/L). Sustained nitrite accumulation (NO2-N/NOx-N=0.36±0.27) was observed while AOB activity was greater than NOB activity (AOB: 391±124mgN/L/d, NOB: 233±151mgN/L/d, p<0.001) during the entire study. The reactor demonstrated total inorganic nitrogen (TIN) removal rate of 151±74mgN/L/d at an influent COD/NH4+-N ratio of 10.4±1.9 at 25°C. The TIN removal efficiency was 57±25% within the hydraulic retention time (HRT) of 3h and within an SRT of 4-8 days. Therefore, this pilot-scale study demonstrates that application of the proposed online aeration control is able to out-select NOB in mainstream conditions providing relatively high nitrogen removal without supplemental carbon and alkalinity at a low HRT. © 2014 Elsevier Ltd.


Regmi P.,Brown and Caldwell | Holgate B.,Hazen and Sawyer | Miller M.W.,Virginia Polytechnic Institute and State University | Park H.,Columbia University | And 4 more authors.
Biotechnology and Bioengineering | Year: 2016

As nitrogen discharge limits are becoming more stringent, short-cut nitrogen systems and tertiary nitrogen polishing steps are gaining popularity. For partial nitritation or nitritation-denitritation systems, anaerobic ammonia oxidation (anammox) polishing may be feasible to remove residual ammonia and nitrite from the effluent. Nitrogen polishing of mainstream nitritation-denitritation system effluent via anammox was studied at 25°C in a fully anoxic moving bed bioreactor (MBBR) (V=0.45m3) over 385 days. Unlike other anammox based processes, a very fast startup of anammox MBBR was demonstrated, despite nitrite limited feeding conditions (influent nitrite=0.7±0.59 mgN/L, ammonia=6.13±2.86mgN/L, nitrate=3.41±1.92mgN/L). The nitrogen removal performance was very stable within a wide range of nitrogen inputs. Anammox bacteria (AMX) activity up to 1gN/m2/d was observed which is comparable to other biofilm-based systems. It is generally believed that nitrate production limits nitrogen removal through AMX metabolism. However, in this study, anammox MBBR demonstrated ammonia, nitrite, and nitrate removal at limited chemical oxygen demand (COD) availability. AMX and heterotrophs contributed to 0.68±0.17 and 0.32±0.17 of TIN removal, respectively. It was speculated that nitrogen removal might be aided by denitratation which could be due to heterotrophs or the recently discovered ability for AMX to use short-chain fatty acids to reduce nitrate to nitrite. This study demonstrates the feasibility of anammox nitrogen polishing in an MBBR is possible for nitritation-denitration systems. © 2016 Wiley Periodicals, Inc.


Regmi P.,Brown and Caldwell | Holgate B.,Hazen and Sawyer | Fredericks D.,Hazen and Sawyer | Miller M.W.,Virginia Polytechnic Institute and State University | And 3 more authors.
Water Science and Technology | Year: 2015

This paper deals with an almost 1-year long pilot study of a nitritation-denitritation process that was followed by anammox polishing. The pilot plant treated real municipal wastewater at ambient temperatures. The effluent of high-rate activated sludge process (hydraulic retention time, HRT = 30 min, solids retention time = 0.25 d) was fed to the pilot plant described in this paper, where a constant temperature of 23 °C was maintained. The nitritation-denitritation process was operated to promote nitrite oxidizing bacteria out-selection in an intermittently aerated reactor. The intermittent aeration pattern was controlled using a strategy based on effluent ammonia and nitrate + nitrite concentrations. The unique feature of this aeration control was that fixed dissolved oxygen set-point was used and the length of aerobic and anoxic durations were changed based on the effluent ammonia and nitrate + nitrite concentrations. The anaerobic ammonia oxidation (anammox) bacteria were adapted in mainstream conditions by allowing the growth on the moving bed bioreactor plastic media in a fully anoxic reactor. The total inorganic nitrogen (TIN) removal performance of the entire system was 75 ± 15% during the study at a modest influent chemical oxygen demand (COD)/NH4+-N ratio of 8.9 ± 1.8 within the HRT range of 3.1-9.4 h. Anammox polishing contributed 11% of overall TIN removal. Therefore, this pilot-scale study demonstrates that application of the proposed nitritation-denitritation system followed by anammox polishing is capable of relatively high nitrogen removal without supplemental carbon and alkalinity at a low HRT. © 2015 IWA Publishing.


Regmi P.,Brown and Caldwell | Bunce R.,Hazen and Sawyer | Miller M.W.,Virginia Polytechnic Institute and State University | Park H.,Columbia University | And 4 more authors.
Biotechnology and Bioengineering | Year: 2015

This work describes the development of an intermittently aerated pilot-scale process (V=0.45m3) operated for optimized efficient nitrogen removal in terms of volume, supplemental carbon and alkalinity requirements. The intermittent aeration pattern was controlled using a strategy based on effluent ammonia concentration set-points. The unique feature of the ammonia-based aeration control was that a fixed dissolved oxygen (DO) set-point was used and the length of the aerobic and anoxic time (anoxic time ≥25% of total cycle time) were changed based on the effluent ammonia concentration. Unlike continuously aerated ammonia-based aeration control strategies, this approach offered control over the aerobic solids retention time (SRT) to deal with fluctuating ammonia loading without solely relying on changes to the total SRT. This approach allowed the system to be operated at a total SRT with a small safety factor. The benefits of operating at an aggressive SRT were reduced hydraulic retention time (HRT) for nitrogen removal. As a result of such an operation, nitrite oxidizing bacteria (NOB) out-selection was also obtained (ammonia oxidizing bacteria [AOB] maximum activity: 400±79mgN/L/d, NOB maximum activity: 257±133mgN/L/d, P<0.001) expanding opportunities for short-cut nitrogen removal. The pilot demonstrated a total inorganic nitrogen (TIN) removal rate of 95±30mgN/L/d at an influent chemical oxygen demand: ammonia (COD/NH4+-N) ratio of 10.2±2.2 at 25°C within the hydraulic retention time (HRT) of 4h and within a total SRT of 5-10 days. The TIN removal efficiency up to 91% was observed during the study, while effluent TIN was 9.6±4.4mgN/L. Therefore, this pilot-scale study demonstrates that application of the proposed on-line aeration control is capable of relatively high nitrogen removal without supplemental carbon and alkalinity addition at a low HRT. © 2015 Wiley Periodicals, Inc.


Nogaj T.,University of Central Florida | Randall A.,University of Central Florida | Jimenez J.,Brown and Caldwell | Takacs I.,Dynamita SARL | And 4 more authors.
Water Science and Technology | Year: 2015

This study describes the development of a modified activated sludge model No.1 framework to describe the organic substrate transformation in the high-rate activated sludge (HRAS) process. New process mechanisms for dual soluble substrate utilization, production of extracellular polymeric substances (EPS), absorption of soluble substrate (storage), and adsorption of colloidal substrate were included in the modified model. Data from two HRAS pilot plants were investigated to calibrate and to validate the proposed model for HRAS systems. A subdivision of readily biodegradable soluble substrate into a slow and fast fraction were included to allow accurate description of effluent soluble chemical oxygen demand (COD) in HRAS versus longer solids retention time (SRT) systems. The modified model incorporates production of EPS and storage polymers as part of the aerobic growth transformation process on the soluble substrate and transformation processes for flocculation of colloidal COD to particulate COD. The adsorbed organics are then converted through hydrolysis to the slowly biodegradable soluble fraction. Two soluble substrate models were evaluated during this study, i.e., the dual substrate and the diauxic models. Both models used two state variables for biodegradable soluble substrate (SBf and SBs) and a single biomass population. The A-stage pilot typically removed 63% of the soluble substrate (SB) at an SRT <0.13 d and 79% at SRT of 0.23 d. In comparison, the dual substrate model predicted 58% removal at the lower SRT and 78% at the higher SRT, with the diauxic model predicting 32% and 70% removals, respectively. Overall, the dual substrate model provided better results than the diauxic model and therefore it was adopted during this study. The dual substrate model successfully described the higher effluent soluble COD observed in the HRAS systems due to the partial removal of SBs, which is almost completely removed in higher SRT systems. © IWA Publishing 2015.


PubMed | DC Water Authority, ARA Consult GmbH, Virginia Polytechnic Institute and State University, University of Central Florida and 3 more.
Type: Journal Article | Journal: Water science and technology : a journal of the International Association on Water Pollution Research | Year: 2015

This study describes the development of a modified activated sludge model No.1 framework to describe the organic substrate transformation in the high-rate activated sludge (HRAS) process. New process mechanisms for dual soluble substrate utilization, production of extracellular polymeric substances (EPS), absorption of soluble substrate (storage), and adsorption of colloidal substrate were included in the modified model. Data from two HRAS pilot plants were investigated to calibrate and to validate the proposed model for HRAS systems. A subdivision of readily biodegradable soluble substrate into a slow and fast fraction were included to allow accurate description of effluent soluble chemical oxygen demand (COD) in HRAS versus longer solids retention time (SRT) systems. The modified model incorporates production of EPS and storage polymers as part of the aerobic growth transformation process on the soluble substrate and transformation processes for flocculation of colloidal COD to particulate COD. The adsorbed organics are then converted through hydrolysis to the slowly biodegradable soluble fraction. Two soluble substrate models were evaluated during this study, i.e., the dual substrate and the diauxic models. Both models used two state variables for biodegradable soluble substrate (SBf and SBs) and a single biomass population. The A-stage pilot typically removed 63% of the soluble substrate (SB) at an SRT <0.13 d and 79% at SRT of 0.23 d. In comparison, the dual substrate model predicted 58% removal at the lower SRT and 78% at the higher SRT, with the diauxic model predicting 32% and 70% removals, respectively. Overall, the dual substrate model provided better results than the diauxic model and therefore it was adopted during this study. The dual substrate model successfully described the higher effluent soluble COD observed in the HRAS systems due to the partial removal of SBs, which is almost completely removed in higher SRT systems.


PubMed | DC Water Authority, Virginia Polytechnic Institute and State University, ARA Consult, Brown and Caldwell and 3 more.
Type: Journal Article | Journal: Biotechnology and bioengineering | Year: 2015

This work describes the development of an intermittently aerated pilot-scale process (V=0.45m(3) ) operated for optimized efficient nitrogen removal in terms of volume, supplemental carbon and alkalinity requirements. The intermittent aeration pattern was controlled using a strategy based on effluent ammonia concentration set-points. The unique feature of the ammonia-based aeration control was that a fixed dissolved oxygen (DO) set-point was used and the length of the aerobic and anoxic time (anoxic time 25% of total cycle time) were changed based on the effluent ammonia concentration. Unlike continuously aerated ammonia-based aeration control strategies, this approach offered control over the aerobic solids retention time (SRT) to deal with fluctuating ammonia loading without solely relying on changes to the total SRT. This approach allowed the system to be operated at a total SRT with a small safety factor. The benefits of operating at an aggressive SRT were reduced hydraulic retention time (HRT) for nitrogen removal. As a result of such an operation, nitrite oxidizing bacteria (NOB) out-selection was also obtained (ammonia oxidizing bacteria [AOB] maximum activity: 40079mgN/L/d, NOB maximum activity: 257133mgN/L/d, P<0.001) expanding opportunities for short-cut nitrogen removal. The pilot demonstrated a total inorganic nitrogen (TIN) removal rate of 9530mgN/L/d at an influent chemical oxygen demand: ammonia (COD/NH4 (+) -N) ratio of 10.22.2 at 25C within the hydraulic retention time (HRT) of 4h and within a total SRT of 5-10 days. The TIN removal efficiency up to 91% was observed during the study, while effluent TIN was 9.64.4mgN/L. Therefore, this pilot-scale study demonstrates that application of the proposed on-line aeration control is capable of relatively high nitrogen removal without supplemental carbon and alkalinity addition at a low HRT.


PubMed | DC Water Authority, Virginia Polytechnic Institute and State University, ARA Consult, Brown and Caldwell and 3 more.
Type: Journal Article | Journal: Biotechnology and bioengineering | Year: 2016

As nitrogen discharge limits are becoming more stringent, short-cut nitrogen systems and tertiary nitrogen polishing steps are gaining popularity. For partial nitritation or nitritation-denitritation systems, anaerobic ammonia oxidation (anammox) polishing may be feasible to remove residual ammonia and nitrite from the effluent. Nitrogen polishing of mainstream nitritation-denitritation system effluent via anammox was studied at 25C in a fully anoxic moving bed bioreactor (MBBR) (V=0.45m(3) ) over 385 days. Unlike other anammox based processes, a very fast startup of anammox MBBR was demonstrated, despite nitrite limited feeding conditions (influent nitrite=0.70.59 mgN/L, ammonia=6.132.86mgN/L, nitrate=3.411.92mgN/L). The nitrogen removal performance was very stable within a wide range of nitrogen inputs. Anammox bacteria (AMX) activity up to 1gN/m(2) /d was observed which is comparable to other biofilm-based systems. It is generally believed that nitrate production limits nitrogen removal through AMX metabolism. However, in this study, anammox MBBR demonstrated ammonia, nitrite, and nitrate removal at limited chemical oxygen demand (COD) availability. AMX and heterotrophs contributed to 0.680.17 and 0.320.17 of TIN removal, respectively. It was speculated that nitrogen removal might be aided by denitratation which could be due to heterotrophs or the recently discovered ability for AMX to use short-chain fatty acids to reduce nitrate to nitrite. This study demonstrates the feasibility of anammox nitrogen polishing in an MBBR is possible for nitritation-denitration systems.


PubMed | DC Water Authority, Virginia Polytechnic Institute and State University, ARA Consult, Brown and Caldwell and 2 more.
Type: Journal Article | Journal: Water science and technology : a journal of the International Association on Water Pollution Research | Year: 2015

This paper deals with an almost 1-year long pilot study of a nitritation-denitritation process that was followed by anammox polishing. The pilot plant treated real municipal wastewater at ambient temperatures. The effluent of high-rate activated sludge process (hydraulic retention time, HRT=30 min, solids retention time=0.25 d) was fed to the pilot plant described in this paper, where a constant temperature of 23 C was maintained. The nitritation-denitritation process was operated to promote nitrite oxidizing bacteria out-selection in an intermittently aerated reactor. The intermittent aeration pattern was controlled using a strategy based on effluent ammonia and nitrate+nitrite concentrations. The unique feature of this aeration control was that fixed dissolved oxygen set-point was used and the length of aerobic and anoxic durations were changed based on the effluent ammonia and nitrate+nitrite concentrations. The anaerobic ammonia oxidation (anammox) bacteria were adapted in mainstream conditions by allowing the growth on the moving bed bioreactor plastic media in a fully anoxic reactor. The total inorganic nitrogen (TIN) removal performance of the entire system was 7515% during the study at a modest influent chemical oxygen demand (COD)/NH4+-N ratio of 8.91.8 within the HRT range of 3.1-9.4 h. Anammox polishing contributed 11% of overall TIN removal. Therefore, this pilot-scale study demonstrates that application of the proposed nitritation-denitritation system followed by anammox polishing is capable of relatively high nitrogen removal without supplemental carbon and alkalinity at a low HRT.

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