Most cold-climate biological food removal facilities feel poor settling mixed liquor during wintertime, resulting in treatment capacity throughput limitations. The Metro Wastewater Reclamation District in Denver, Colorado, operated 2 full-calibration secondary treatment trains to compare the existing biological nutrient removal configuration (Control) to ane that was modified to operate with an anaerobic selector and with hydrocyclone selective wasting (Test) to induce granulation. Results from this evaluation showed that the Test accomplished significantly better settling behaviour than the Command. The deviation in the mean diluted SVI30 between the Test and Control were statistically significant (P < 0.05), with values of 77 ± 17 and 135 ± 25 mL/1000 observed for the Test and Command respectively. These settling results were accompanied by differences in the particle size distribution, with notably college settling velocities commensurate with increasing particle size. The degree of granulation observed in the Exam train was between 32 and 56% of the mass greater than ≥250 μm in particle size whereas 16% of the mixed liquor in the Control was ≥250 μm over the entire study period. The improved settling behaviour of the Test configuration may interpret into an increase of secondary treatment capacity during winter by 32%.

  • Inducing granulation in a full-calibration continuous menses activated sludge system was possible with the awarding of both biological and physical selection pressures.

  • Observations in this study could translate to a price effective intensification solution versus traditional expansion for WRRFs evaluating capacity needs.

Graphical Abstract

Graphical Abstract

Graphical Abstract

Graphical Abstract

Graphical Abstract

The Robert W. Hite Treatment Facility (Hite handling facility) is an 833 meg litre per twenty-four hour period (MLD) water resources recovery facility (WRRF) owned and operated by the Metro Wastewater Reclamation District (Commune) that serves a 2.0 million population equivalent in metropolitan Denver, Colorado. The Hite treatment facility has two parallel liquid treatment complexes (North and South), and a centralized solids handling complex (Figure 1). The North Circuitous, which is the focus surface area of this newspaper, uses a side-stream anaerobic reactor as a biological selector for phosphorus accumulating organisms (PAOs), which supplements the mainstream Modified Ludzack-Ettinger (MLE) procedure to accomplish nitrogen and enhanced biological phosphorus removal (EBPR).

Figure one

The Robert W. Hite treatment facility.

The Robert Due west. Hite treatment facility.

Figure 1

The Robert W. Hite treatment facility.

The Robert West. Hite treatment facility.

Close modal

The North Complex was constructed in the belatedly 1960s to achieve basic secondary handling. The clarifier side h2o depth is 3.05 metres, which is shallow compared to typical design depths of 4.3 to 4.9 metres (Ahuja & Griborio 2017). These shallow Northward Complex clarifiers must operate consistently around their maximum rated design chapters of 147 kg/one thousand2/d to sustain the establish-rated 833 MLD capacity and operate at the solids memory time needed for year-circular nitrogen removal.

There has been a growing interest in aerobic granular sludge (AGS) given the reported improvements in settleability in laboratory-scale studies with sequencing batch reactors (SBR) (Kreuk et al. 2005; Ji et al. 2009; Gao et al. 2011). However, few airplane pilot studies on both SBR and continuous menstruum configurations have been performed (Pishgar et al. 2019), and full-calibration application of AGS is limited to predominantly SBR configurations (Kent et al. 2018). Due to the lack of continuous flow full-scale applications of AGS, the authors opted to evaluate the impact of selective pressures in a total-scale trial. While at that place are configuration differences between AGS and a continuous flow system, key control mechanisms learned from AGS research are applied in this study.

Granules are distinguished from floc by being divers as particles larger than 0.2 mm in bore. To form smoothen and compact granules, typically higher shear is required to maintain a polish granule structure. Granular sludge settles significantly faster than activated sludge, and typically an AGS SVI5 is comparable to SVI30 in conventional activated sludge (Kreuk et al. 2005). Key selective pressures documented to promote granule formation and retentivity are every bit follows: (1) High fraction of readily biodegradable chemic oxygen demand (rbCOD) in the influent stream. A compact granular particle is dependent on the degree of extracellular polymeric substance (EPS) product (Mcswain et al. 2005). In a airplane pilot written report evaluating the impact of nutrient to microorganism (F/M) ratio on EPS production in AGS, it was observed that EPS content and settling velocity linearly increases with increasing F/M ratio (Sturm et al. 2017). It was reported by Sturm et al. that EPS production and the intrinsic settling velocity was maximized at an F/M ratio of ∼0.2 mg rbCOD/mg VSS/d. At these higher F/Ms, the resulting carbon slope results in fully penetrating substrate conditions into the granule structure and avoids improvidence limiting conditions. Floc and filamentous bacteria can typically out-compete granules under rbCOD-limited weather due to mass transfer limitations, which can issue in granule instability, causing elevated effluent total suspended solids (TSS) and worsening settleability (Layer et al. 2019). (2) A physical option force per unit area for larger, denser solids such as hydrocyclones. As granules begin to form, physical selection becomes possible due their increased density relative to more than buoyant floc particles. Information technology has been reported that selectively wasting flocs reduces competition between granules and floc particles for the rbCOD (Loosdrecht et al. 2005). (3) Granule growth requires the presence of electron acceptors such as oxygen, nitrate, and nitrite, and they must exist present in quantities not bad enough to fully diffuse into the granule construction. Electron acceptor-limited conditions can lead to granule instability (Kreuk et al. 2007). (iv) Elevated hydrodynamic shear must be present in order to maintain shine and compact granule structures, which has been reported to facilitate settling and substrate diffusion into the granule (Kreuk et al. 2005; Figdore 2017).

Due to reported successful uses of hydrocyclones to gravimetrically retain granules in deammonification systems (Klein et al. 2012; Wett et al. 2015), the authors opted for this technology for selective wasting. Hydrocyclones operate with no moving parts, and achieve separation through centrifugal forces and their shape. Return activated sludge (RAS) is fed tangentially into the hydrocyclone at a target feed pressure level. As the fluid velocity increases within the body of the hydrocyclones, the denser particles are forced towards the outer perimeter of the hydrocyclone before exiting in the underflow. The lighter solids remain in the inner vortex of the hydrocyclone, and are forced upwardly to exit in the overflow (Bradley 1965).

One of the 12 three-pass North Complex secondary aeration basins (i.e. Examination) was configured for the study independent and yet parallel to the rest of the Due north Complex secondary treatment system. The Exam train receives its proportion of the aforementioned primary effluent as is received by the remaining basins. To promote granulation, modifications to the Exam basin include: (one) incorporation of a front-end zone where the RAS and hydrocyclone underflow recycle is introduced to primary effluent, creating a high gradient F/Grand condition, and (2) installation of hydrocyclones to facilitate a concrete selective pressure towards retention of granules and wasting out of floc particles. The purpose of this paper is to share observations from this try to induce granulation in a total-scale activated sludge system.

Operations

Two identically sized basins (a Exam and Control) were operated from May 7, 2018 to April 19, 2019. The Test basin was modified to be completely isolated from the remainder of the Northward Complex, including a split up primary effluent pumping station designed to mimic full-scale diurnal menses patterns. Both the Command and Exam basins were operated according to the conditions summarized in Table one across three operating periods.

Table ane

Cardinal operating weather condition for test and control secondary treatment trains

Parameter Phase Period i Period 2 Period iii
Testing Goals Evaluate touch of biological selector Evaluate touch on of biological and physical selector Stress testing clarifier
Start Appointment six/5/2018
 11/v/2018
 3/eighteen/2018
Basin Test Control Test Control Test Control
Process configuration Anaerobic – Oxic (AO) Modified Ludzack-Ettinger (MLE) AO – Hydro cyclone MLE Modified AO – Hydrocyclone MLE – EBPR
Pattern capacity Meg Litres per Day (MLD) 33 33 33 33 33 33
Influent menstruum MLD 26.5 ± two 24.3 ± 4.ii 21.1 ± 2 22.1 ± ii.9 23.1 ± 2.1 27.5 ± ane.seven
Gravity thickener effluent flow MLD – – – – 1.15 ± 0.13 –
Dissolved oxygen mg O 2/Fifty 0.53 ± 0.17 0.94 ± 0.four 0.83 ± 0.24 1.thirteen ± 0.26 0.9 ± 0.2 1.31 ± 0.15
Mixed liquor suspended solids mg/L three,526 ± 435 2,826 ± 475 4,219 ± one,038 3,492 ± 361 5,227 ± 607 3,985 ± 513
Mixed liquor volatile suspended solids ratio % 85.5 ± 2.1 84.1 ± one.3 83.v ± 1.2 84.half-dozen ± 2.0 84.4 ± 4.5 85.ix ± 1.viii
F/1000 ratio mg rbCOD/mg VSS/d 0.19 ± 0.02 0.2 ± 0 0.eighteen ± 0.03 0.23 ± 0.03 0.13 ± 0.02 0.19 ± 0
Aerobic solids retention time days 4.6 ± 0.4 6.3 ± 1.half dozen 5.8 ± 0.8 half dozen.eight ± 2.7 six.2 ± 0.6 vi.3 ± 1
RAS recycle % of influent flow 130 ± 10 150 ± 20 160 ± 30 160 ± 20 160 ± 20 130 ± 10
Mixed liquor recycle % of influent flow 0 310 ± l 0 340 ± fifty 0 270 ± xx
% Anaerobic volume % of basin volume xvi.i 0 sixteen.ane 0 16.i 5.5
% Anoxic volume % of bowl volume 0 21.v 0 21.v 0 20.iii
%Aerobic volume* % of bowl volume 83.9 70.2 83.9 lxx.ii 83.nine 66.3
Total basin book Million litres 7.76 7.76 7.76 7.76 7.76 7.76
Hydrocyclone hydraulic ratio OF/UF – – 85/15 – 87/13 –
Hydrocyclone mass flow ratio OF/UF – – 66/34 – 69/31 –
Total mass wasted Metric tons per mean solar day 4.iii ± 0.7 4.0 ± 1.1 4.2 ± 0.9 4.0 ± 0.7 5.5 ± 0.seven 4.7 ± 0.7
Parameter Phase Menstruation ane Period 2 Flow iii
Testing Goals Evaluate touch on of biological selector Evaluate impact of biological and physical selector Stress testing clarifier
Start Appointment 6/5/2018
 11/5/2018
 iii/18/2018
Basin Test Control Test Control Exam Control
Process configuration Anaerobic – Oxic (AO) Modified Ludzack-Ettinger (MLE) AO – Hydro cyclone MLE Modified AO – Hydrocyclone MLE – EBPR
Blueprint chapters Million Litres per Solar day (MLD) 33 33 33 33 33 33
Influent period MLD 26.5 ± 2 24.three ± 4.2 21.ane ± ii 22.1 ± 2.9 23.ane ± 2.i 27.five ± 1.seven
Gravity thickener effluent flow MLD – – – – i.15 ± 0.thirteen –
Dissolved oxygen mg O 2/L 0.53 ± 0.17 0.94 ± 0.4 0.83 ± 0.24 1.13 ± 0.26 0.9 ± 0.ii ane.31 ± 0.xv
Mixed liquor suspended solids mg/L 3,526 ± 435 2,826 ± 475 4,219 ± 1,038 iii,492 ± 361 five,227 ± 607 three,985 ± 513
Mixed liquor volatile suspended solids ratio % 85.5 ± ii.1 84.one ± one.3 83.5 ± 1.2 84.six ± 2.0 84.4 ± 4.5 85.9 ± ane.8
F/M ratio mg rbCOD/mg VSS/d 0.19 ± 0.02 0.2 ± 0 0.18 ± 0.03 0.23 ± 0.03 0.13 ± 0.02 0.19 ± 0
Aerobic solids memory time days 4.half-dozen ± 0.4 6.3 ± 1.6 5.8 ± 0.8 6.8 ± ii.7 6.2 ± 0.vi 6.iii ± 1
RAS recycle % of influent flow 130 ± 10 150 ± 20 160 ± thirty 160 ± xx 160 ± xx 130 ± ten
Mixed liquor recycle % of influent menses 0 310 ± 50 0 340 ± 50 0 270 ± 20
% Anaerobic volume % of bowl volume 16.1 0 16.one 0 sixteen.i 5.5
% Anoxic volume % of basin volume 0 21.5 0 21.five 0 xx.3
%Aerobic book* % of basin volume 83.9 lxx.2 83.ix 70.2 83.nine 66.3
Total basin volume Million litres seven.76 7.76 7.76 7.76 vii.76 vii.76
Hydrocyclone hydraulic ratio OF/UF – – 85/fifteen – 87/13 –
Hydrocyclone mass flow ratio OF/UF – – 66/34 – 69/31 –
Total mass wasted Metric tons per day 4.3 ± 0.7 4.0 ± one.1 4.2 ± 0.9 four.0 ± 0.seven v.5 ± 0.vii four.7 ± 0.7

*Difference in % aerobic volume is due to all Due north Complex secondary basins (including Control) having unaerated zones at the end of the aerobic zone to reduce dissolved oxygen in recycle to anoxic zones. All Test basin aerobic zones were fully aerated equally in that location was no mixed liquor recycle.

From May seven, 2018 until June v, 2018, both the Test and Control basins were operated using commingled solids in a MLE configuration with surface wasting, which is wasting solids from the surface of the aeration basin versus traditional wasting from the clarifier. Menstruation 1: The goal of Period ane was to compare the Command to the Examination basin configured with a biological selector. On June 5, 2018 the Test basin solids were isolated from the rest of the commingled North Circuitous solids and operated in an anaerobic-oxic (AO) process configuration with traditional wasting. The Control basin remained in the MLE configuration. Menstruation ii: The goal of Menstruation 2 was to compare the Control to the Test bowl configured with both a biological and physical selector. On Nov five, 2018, an InDense™ (Globe Water Works, Oklahoma) hydrocyclone sideslip comprised of 8 10 chiliad3/h hydrocyclones was placed in service for selective wasting on the Exam basin, and was operated in an AO-Hydrocyclone configuration until March 18, 2019. Period 3: The goal of Flow iii was to stress exam the clarifier on the Test basin past operating at increasing solids loading rates while comparing clarifier functioning to the Control. On March 18, 2019, the sidestream anaerobic reactor in the North Circuitous was placed into service, changing the configuration of the Control bowl to include a formal anaerobic selector for EBPR at the full scale. This organization was placed in service independent of the study, so the process configurations had to exist modified to business relationship for this system existence placed in service. Functioning of the sidestream anaerobic reactor changes the menses distribution of gravity thickener effluent (GTE) in the N Complex such that it is added directly to the sidestream anaerobic reactor. During Period 1 and Period 2, GTE was mixed in with the principal effluent upstream of the Exam basin's pump station. Modifications were made to the Examination basin to permit for the GTE to be added directly to the anaerobic zone when the sidestream anaerobic reactor is in operation to business relationship for the GTE not being mixed in with the main effluent. This modified AO-Hydrocyclone process menses configuration was implemented to reintroduce GTE to an anaerobic solids contact zone in the Exam bowl. Stress testing of the Test clarifier was achieved by reducing wasting rates to increase the solids inventory, thus increasing the clarifier solids loading charge per unit. Process flow configurations tested throughout all study periods are summarized in Figure 2. The piloting menses ended abruptly during Menses 3 due to mechanical failure of an aeration filigree in the Test basin requiring the arrangement be drained and cleaned for repairs.

Figure 2

Process flow configurations for the Test and Control basin throughout study.

Process period configurations for the Test and Control basin throughout study.

Figure ii

Process flow configurations for the Test and Control basin throughout study.

Process flow configurations for the Test and Control basin throughout study.

Close modal

Wastewater characterization

The Test and Control basins both receive municipal wastewater treated through bar screens, grit screening, and primary sedimentation. The primary effluent, GTE, and clarified secondary effluent were characterized for nutrients, carbon, and solids according to Baird et al. (2017). Floc-filtered chemic oxygen demand (ffCOD) was measured according to the method outlined in Mamais et al. (1993), and is used as a surrogate for rbCOD. Influent feed characteristics for the Test and Control are provided in Tables 2 and iii.

Table ii

Chief effluent characteristics

Parameter Phase Period i Menstruum 2 Menses 3
Date 6/5/2018 11/5/2018 3/18/2018
Total suspended solids mg/L 86 ± 13 110 ± 20 103 ± sixteen
Full alkalinity mg CaCO3/50 238 ± x 241 ± 5 241 ± two
COD mg/L 372 ± 26 484 ± thirty 418 ± 58
Soluble COD mg/L – 235 ± 25 229 ± 36
rbCOD mg/L – 228 ± eleven 168 ± ten
Ammonia mg due north/L 32 ± 13 34 ± 3 32 ± 3
Full Kjedal nitrogen mg N/L forty ± three 47 ± 3 48 ± iii
Orthophosphorus mg P/Fifty 3.ane ± 0.2 3.half-dozen ± 0.3 3.9 ± 0.6
Total phosphorus mg P/50 4.7 ± 0.half-dozen 5.vii ± 0.4 half-dozen.ane ± 0.1
Temperature Celsius 21.6 ± 0.9 16.7 ± ane.5 15.8 ± 0.5
COD:total nitrogen mg/mg North 9.1 ± 0.5 10.1 ± 0.4 8.5 ± ane.3
Parameter Stage Period 1 Menstruation two Period 3
Date half dozen/5/2018 11/5/2018 three/eighteen/2018
Total suspended solids mg/Fifty 86 ± thirteen 110 ± twenty 103 ± 16
Total alkalinity mg CaCO3/L 238 ± 10 241 ± v 241 ± 2
COD mg/L 372 ± 26 484 ± 30 418 ± 58
Soluble COD mg/50 – 235 ± 25 229 ± 36
rbCOD mg/L – 228 ± 11 168 ± ten
Ammonia mg due north/L 32 ± thirteen 34 ± 3 32 ± 3
Total Kjedal nitrogen mg North/L 40 ± iii 47 ± three 48 ± 3
Orthophosphorus mg P/Fifty 3.i ± 0.ii 3.half-dozen ± 0.three three.nine ± 0.6
Total phosphorus mg P/L 4.vii ± 0.half dozen 5.7 ± 0.iv half dozen.1 ± 0.1
Temperature Celsius 21.six ± 0.9 16.seven ± 1.5 15.eight ± 0.5
COD:total nitrogen mg/mg N 9.1 ± 0.5 ten.1 ± 0.iv viii.5 ± 1.3

Table three

Gravity thickener effluent characteristics

Parameter Phase Catamenia 1 Menses 2 Period 3
Appointment half-dozen/five/2018 11/five/2018 three/18/2018
Total alkalinity mg CaCO3/Fifty – 270 ± 18 272 ± iii
COD mg/L – 614 ± 152 604 ± 30
Soluble COD mg/L – 254 ± 27 241 ± 18
rbCOD mg/Fifty – 209 ± 23 178 ± 3
Parameter Phase Menstruum 1 Period 2 Menstruation three
Date 6/five/2018 11/5/2018 iii/18/2018
Total alkalinity mg CaCOthree/L – 270 ± xviii 272 ± three
COD mg/L – 614 ± 152 604 ± 30
Soluble COD mg/Fifty – 254 ± 27 241 ± xviii
rbCOD mg/Fifty – 209 ± 23 178 ± 3

Settling and particle characterization

Sieve assay and dilute Sludge Volume Alphabetize (dSVI) were performed according to methods outlined in van Loosdrecht et al. (2016). Cole Parmer (Vernon Hills, Illinois) standard sieve model numbers 35 (500 μm), sixty (250 μm), and 120 (125 μm) were used to guess particle size distribution. Qualitative microscopy was performed on mixed liquor using an Olympus Life Sciences (Waltham, Massachusetts) BH-ii phase dissimilarity microscope. Where applicable, basic statistics were calculated using a two-tailed Student'southward t-test to evaluate whether any differences observed between the ways of paired datasets were statistically different. For the t-exam, the variances were causeless unequal for each paired test.

Operational challenges

There are inherent challenges associated with operation of a full-scale system. Equipment failure and limited command over certain operational variables can impact testing. This section provides a summary of the main bug experienced.

On January 7, 2019, the RAS volumetric recycle rates were reduced from 160% to 71% of the influent menstruum to detect if this change would help reduce clarifier effluent TSS. Shortly subsequently the RAS rate was intentionally reduced, the gear box of a mixer in the Exam basin anaerobic zone broke and was out of service from January ten, 2019 to February 27, 2019. From January 10, 2019 to January 19, 2019, the mixed liquor suspended solids concentration in the Test basin dropped from 3,479 mg/50 to 2,778 mg/L, a 20% reduction. Ii theories for what caused the turn down in mixed liquor suspended solids are related to the low dSVIs occurring during this menstruation. The reduced RAS flow led to lower fluid velocity in the RAS recycle aqueduct, causing solids deposition in the aqueduct, and solids were settling in the unmixed anaerobic zone. The volumetric RAS recycle charge per unit was increased back to 160% of the total influent menses on Jan 31, 2019, and the gear box to the mixer was finally repaired on February 27, 2019. Additional measures were taken to mitigate the solids loss: (ane) the wasting rate from the Test basin was reduced, and (2) a temporary pumping organization was implemented to pump whatsoever settled solids from anaerobic zone iii into the next zone. After all of the issues were corrected, the mixed liquor suspended solids increased to 4,800 mg/L. It was decided to movement forward with stress testing the clarifier on the Examination basin, which was originally targeted to be washed during Flow 3. Stress testing the clarifier in the Exam train began on February 28, 2019. The operational challenges experienced are summarized in Table 4.

Tabular array 4

Summary of operational challenges that occurred during testing

Operational change Start date Impact Correctional alter Date corrected
Reduced RAS charge per unit to 71% of influent flow i/seven/2019 Possible solids loss in RAS recycle channel Increased RAS rate to 160% of influent flow 1/31/2019
Anaerobic zone mixer gear box malfunction i/10/2019 Possible solids loss in unmixed anaerobic zone Gear box replaced in mixer and mixer placed back in service. Temporary pumping of settled solids. 2/27/2019
Operational change Start engagement Touch on Correctional alter Appointment corrected
Reduced RAS rate to 71% of influent flow 1/7/2019 Possible solids loss in RAS recycle channel Increased RAS rate to 160% of influent flow 1/31/2019
Anaerobic zone mixer gear box malfunction 1/10/2019 Possible solids loss in unmixed anaerobic zone Gear box replaced in mixer and mixer placed back in service. Temporary pumping of settled solids. 2/27/2019

Effluent quality

Average effluent quality for both the Test and Control basins across all 3 testing periods is summarized in Table 5, and all values were below facility belch limits. Until Period 3 the Control basin had lower effluent TSS. Particulate COD in the effluent was college in the Test than in the Command. Nitrogen removal efficiency in the Command was higher than the Test, which is predominantly attributed to the lack of a dedicated anoxic zone in the Test, and potentially due to partial conversion of particulate COD (Wagner et al. 2015a, 2015b). Phosphorus removal in both the Test and Control were comparable across all three testing periods. It is noted that EBPR has occurred in the North Circuitous despite the lack of a defended anaerobic zone. While effluent quality is non a focus of this paper, this information is provided for abyss.

Table five

Summary of Test and Control clarified effluent

Parameter Stage Flow 1 Period 2 Period 3
Date 6/five/2018
 xi/5/2018
 3/xviii/2018
Basin Test Control Test Command Test Command
TSS mg/50 22.7 ± 7.1 13.8 ± 12.7 15 ± 6.0 7.1 ± 2.2 5.vi ± three.7 6.iv ± 3.2
Alkalinity mg/Fifty 127 ± 18 124 ± 11 118 ± 2 136 ± 5 125 ± 12 143 ± 3
COD mg/Fifty 60 ± 20 38 ± 6 47 ± 8 38 ± x fourscore ± 31 forty ± vii
Soluble COD mg/Fifty 22 ± vii 22 ± 1 24 ± 12 33 ± xvi 25 ± 4 32 ± 4
Ammonia mg N/L three.4 ± three.7 0.three ± 0.ane 0.9 ± 1.5 0.9 ± 0.8 0.two ± 0 0.3 ± 0.ii
Nitrate mg N/Fifty v.5 ± 2.ane 3.seven ± 1.nine 6 ± 1.5 0.2 ± 0.3 v.4 ± iii.eight 0.5 ± 0.2
Nitrite mg N/L 0.31 ± 0.23 0.06 ± 0.09 0.46 ± 0.54 0.17 ± 0.1 0.ii ± 0 0.25 ± 0.1
TKN mg N/L 5.1 ± 3.7 3 ± 2 2.7 ± one.7 2.1 ± 0.eight ane.half dozen ± 0.1 1.6 ± 0.iv
Ortho-phosphorus mg P/L 0.00 ± 0.00 0.07 ± 0.07 0.22 ± 0.55 0.eleven ± 0.15 0.09 ± 0.08 0.02 ± 0.01
Full phosphorus mg P/L 0.77 ± 0.32 0.47 ± 0.25 0.39 ± 0.18 0.29 ± 0.07 0.74 ± 0.63 0.27 ± 0.08
Parameter Stage Period ane Period 2 Menstruation 3
Date vi/five/2018
 11/5/2018
 3/18/2018
Bowl Test Command Exam Control Test Control
TSS mg/L 22.7 ± vii.i 13.8 ± 12.vii 15 ± 6.0 7.one ± 2.ii 5.6 ± 3.7 6.four ± 3.two
Alkalinity mg/Fifty 127 ± 18 124 ± 11 118 ± 2 136 ± 5 125 ± 12 143 ± 3
COD mg/L 60 ± twenty 38 ± 6 47 ± 8 38 ± 10 80 ± 31 40 ± 7
Soluble COD mg/L 22 ± seven 22 ± 1 24 ± 12 33 ± 16 25 ± 4 32 ± 4
Ammonia mg N/50 3.four ± three.7 0.3 ± 0.1 0.9 ± 1.5 0.ix ± 0.8 0.ii ± 0 0.3 ± 0.2
Nitrate mg N/L 5.5 ± ii.1 three.seven ± 1.9 half dozen ± 1.five 0.2 ± 0.3 5.4 ± iii.8 0.five ± 0.two
Nitrite mg Due north/L 0.31 ± 0.23 0.06 ± 0.09 0.46 ± 0.54 0.17 ± 0.1 0.2 ± 0 0.25 ± 0.1
TKN mg N/L 5.i ± 3.7 iii ± ii 2.7 ± 1.vii 2.one ± 0.8 ane.vi ± 0.1 ane.6 ± 0.4
Ortho-phosphorus mg P/Fifty 0.00 ± 0.00 0.07 ± 0.07 0.22 ± 0.55 0.11 ± 0.15 0.09 ± 0.08 0.02 ± 0.01
Total phosphorus mg P/L 0.77 ± 0.32 0.47 ± 0.25 0.39 ± 0.18 0.29 ± 0.07 0.74 ± 0.63 0.27 ± 0.08

Settling performance

The Test and Control basins began performance in the same configuration using common mixed liquor inventory. The mean dSVI30 observed in the Exam and Control was 117 ± 6.1 and 113 ± 16.two mL/k respectively (Effigy 3). After Flow i began, the dSVI5 and dSVI30 in the Exam began to diverge from values observed in the Control bowl. The dSVI30 observed in the Control basin increased to values relatively similar to the dSVI5 observed in the Test bowl. The differences in the mean dSVI30 values observed during Flow one were statistically significant (P < 0.05), with values of 93 ± x and 107 ± 29 mL/thou observed for the Test and Control respectively. Higher affluence of PAOs have been attributed to greater biomass density due to the increase in internal polyphosphate content (Schuler & Jang 2007). Every bit shown in Table v, EBPR was occurring throughout the study. 2 months into Catamenia 2 of testing, the dSVIv and dSVIxxx in the Test basin decreased to a low of 64 and 48 mL/g respectively. While the dSVI5 and dSVI30 in the Exam were observed to increase from the depression observed in Jan to values of 97 and 155 mL/g respectively. The differences in the hateful dSVI30 between the Test (76 ± 18 mL/g) and the Control (137 ± 28 mL/g) during Menses ii of testing remained statistically significant (P < 0.05). Period three of testing lasted one month, during which the dSVI30 in both the Test and Control increased. During Menstruation 3, the differences in the mean dSVI30 between the Test (83 ± 12) and Command (127 ± 11) remained statistically meaning (P < 0.05). These results advise that having an anaerobic biological selector in the Test basin initially lowered the dSVI in the Examination equally compared to the Control, and that the addition of a physical selection force per unit area with hydrocyclones further separated the dSVI betwixt the Test and Control.

Figure iii

Comparison of dSVI5 and dSVI30 between the Test and Control.

Comparison of dSVI5 and dSVI30 between the Test and Control.

Effigy 3

Comparison of dSVI5 and dSVI30 between the Test and Control.

Comparison of dSVIv and dSVIxxx betwixt the Test and Command.

Close modal

Clarifier effluent TSS in the Test was variable and higher than the Control during Period i (Figure iv). During the summer months, algae growth in the clarifier effluent launders is a known problem at the Hite treatment facility, and contributes to elevated effluent TSS during the summer. The average clarifier solids loading rates to the Test and control clarifiers were 162 ± 14 and 152 ± nineteen kg/d/mtwo. After the hydrocyclones were placed in service during Flow 2 of testing, the effluent TSS from the Exam clarifier began to decline; however, as summarized in earlier in Table iv, a series of intentional and unintentional operational changes occurred. The RAS was reduced to run into if a reduced solids loading rate would lower effluent TSS. This reduced the solids loading rate to the Exam clarifier from 162 kg/d/m2 to 100 kg/d/1000ii. The loss of the anaerobic zone mixer during Period two further reduced the solids loading rate to the Test clarifier due to a reject in mixed liquor suspended solids. Even at a reduced clarifier solids loading charge per unit, the effluent TSS was observed to increase from beneath four mg/L to above vii mg/L. The RAS volumetric recycle ratio in the Examination was increased back to 160%, which elevated the solids loading charge per unit to the Exam clarifier, and also began increasing the coating depth in the clarifier. Prior to these changes, the average blanket depths in the Test and Control clarifiers were 0.9 ± 0.1 and 1.ii ± 0.2 metres respectively. Later on these operational issues were corrected and the solids inventory in the Test was increased, the coating depths in the Test and Command clarifiers averaged ane.seven ± 0.five and one.three ± 0.4 metres respectively. The effluent TSS from the Test clarifier declined to levels equal to or below effluent TSS from the Control clarifier, fifty-fifty with the Exam clarifier operating at solids loading charge per unit that was 32 ± nine% greater than that of the Control. These results suggest that the extent of granulation achieved was sufficient to allow operation at a higher solids inventory, while maintaining comparable effluent TSS to the existing arrangement.

Figure 4

Clarifier solids loading rate and effluent TSS.

Clarifier solids loading rate and effluent TSS.

Figure 4

Clarifier solids loading rate and effluent TSS.

Clarifier solids loading rate and effluent TSS.

Shut modal

Particle size

Size distribution analysis using sieves began nearly the end of Period i (October 2018) for the Test basin mixed liquor suspended solids, followed by the Control basin during Menstruum 2 of testing (December 2018). Analysis of the Command basin revealed that the total fraction of biomass greater than 250 μm remained relatively consistent at around 16% over the entire testing menstruation. Conversely, results from the size distribution assay of the test basin showed that the full fraction of biomass ≥250 μm (the sum of solids retained on the 250 and 500 μm sieves) began to increase inside ane calendar month later on the start of Menstruum 2, and reached a pinnacle of 56% after 3 months into Period 2 (Effigy 5). Subsequently this maximum was reached, the total fraction of biomass ≥250 μm began to decline, reaching a value of around forty% by the stop of Period 3. Granules inside the size range of 250 to 500 μm began to decline during the menstruum where operational issues forced the alter in wasting, thus driving the mixed liquor suspended solids concentration higher. Particle sizes ≥500 μm in the Exam basin were steady at approximately 2% of the total population until around three months into Period 2, at which time there was a steady increase until the stop of Period iii, reaching a maximum of twenty%. In spite of the failing total fractionation of particles to a higher place 250 μm, the mature and established larger particles connected to increase while the smaller granules decreased.

Figure 5

Particle size distribution of mixed liquor suspended solids from the Test and Control basin.

Particle size distribution of mixed liquor suspended solids from the Examination and Control basin.

Figure 5

Particle size distribution of mixed liquor suspended solids from the Test and Control basin.

Particle size distribution of mixed liquor suspended solids from the Examination and Control basin.

Close modal

During Period 1, the F/Yard ratios for the Examination and Command systems were like, ∼0.two mg rbCOD/mg VSS/d, which is within the range of values reported to be acceptable for achieving 60% granulation in an SBR (Sturm et al. 2017). However, without a strong concrete selection pressure, just a depression fraction of the biomass was of granular fraction. The low caste of granulation observed in the Test bowl during Period one and the Control Bowl during Period 2 and Period iii could be attributed to having an appropriate F/K ratio, plug menstruum conditions in a continuous flow system creating a gradient feast/famine status, and a physical selection force per unit area from the surface wasting strategy employed at the Hite handling facility, which are suggested to be the reasons granules have been observed in other full-calibration continuous menses systems (Downing et al. 2017; Wei et al. 2020). Upon implementation of the hydrocyclones in the Exam bowl during Period 2, the granular fraction began to increase which suggests that the addition of the concrete choice force per unit area from the hydrocyclones was plenty to drive the granular fraction to the degrees observed during this written report. The turn down of the fraction of biomass ≥250 μm during the latter office of Period 2 and into Period 3 could be a combination of these smaller granules transitioning to larger sized granules, and potential instability due to operational challenges that occurred during Menstruum 2. It has been reported that granules display less stability during maturation and growth as operating conditions are more complex (Pishgar et al. 2019), which could explain the dynamics in size distribution observed in this work given the operational challenges experienced during testing. Nonetheless, the long-term stability of granular sludge in a continuous flow organisation will demand to exist adamant in future evaluations.

At that place was a direct correlation with dSVIxxx between the fraction of biomass in the range of 125 to 250 μm. However, an inverse correlation with dSVIthirty is suggested when considered with the fraction of biomass greater than 250 μm (Figure vi). Maintaining a consistent degree of granulation might exist an important consideration for achieving optimum settling behaviour in a continuous flow system.

Figure 6

dSVI30 as a function of the total fraction of biomass between 125 and 250 μm in Test (left graph), and as a function of the total fraction of biomass greater than 250 μm (right graph).

dSVIthirty as a part of the full fraction of biomass between 125 and 250 μm in Test (left graph), and every bit a function of the total fraction of biomass greater than 250 μm (correct graph).

Figure half dozen

dSVI30 as a function of the total fraction of biomass between 125 and 250 μm in Test (left graph), and as a function of the total fraction of biomass greater than 250 μm (right graph).

dSVIthirty as a function of the total fraction of biomass betwixt 125 and 250 μm in Examination (left graph), and equally a function of the total fraction of biomass greater than 250 μm (correct graph).

Close modal

A sieve mass balance was performed around the hydrocyclones during Period 3 of testing. The fraction of biomass ≥500 μm was observed to exist greatest in the underflow stream from the hydrocyclones, while the majority of particles in the overflow are less than 250 μm (Figure 7). Qualitative microscopy performed confirmed the presence of granule-like structures (Figure eight). Given the operating weather tested in this study, these results propose that forming and retaining granular sludge was possible and occurred within three months, which is in line with timeframes reported in other AGS studies (Wagner et al. 2015a, 2015b; Pronk 2017).

Figure 7

Size distribution analysis of hydrocyclone RAS feed, underflow, and overflow.

Size distribution analysis of hydrocyclone RAS feed, underflow, and overflow.

Figure 7

Size distribution analysis of hydrocyclone RAS feed, underflow, and overflow.

Size distribution analysis of hydrocyclone RAS feed, underflow, and overflow.

Shut modal

Figure 8

Microscopic images from Test basin mixed liquor samples collected during Periods 2 and 3. All images at 100x total magnification. (a) Sample collected February 10, 2019. (b) Sample collected March 12, 2019. (c) Sample collected April 6, 2019.

Microscopic images from Test basin mixed liquor samples collected during Periods two and 3. All images at 100x full magnification. (a) Sample collected February ten, 2019. (b) Sample nerveless March 12, 2019. (c) Sample collected April 6, 2019.

Figure eight

Microscopic images from Test basin mixed liquor samples collected during Periods 2 and 3. All images at 100x total magnification. (a) Sample collected February 10, 2019. (b) Sample collected March 12, 2019. (c) Sample collected April 6, 2019.

Microscopic images from Test basin mixed liquor samples nerveless during Periods ii and 3. All images at 100x full magnification. (a) Sample collected February 10, 2019. (b) Sample collected March 12, 2019. (c) Sample nerveless Apr 6, 2019.

Close modal

  • Inducing granulation in a continuous flow activated sludge arrangement was possible with the application of both biological and concrete choice pressures.

  • For the Exam basin, a negative correlation was observed between the fraction of biomass greater than 250 μm and dSVI30, which suggests that maintaining a consequent fraction of granules in a continuous menstruation activated sludge system could be vital for increasing and maintaining intensified secondary treatment capacity through high mixed liquor concentrations and sustained high solids loading rates on secondary clarifiers.

  • The reduction in dSVI in the Test bowl allowed functioning at a solids loading rate to the Test clarifier that was 32% greater than the Control while maintaining equivalent effluent TSS.

  • Under the conditions tested in the study, granulation was observed to occur in a total-scale continuous menses system. The full fraction of biomass larger than 250 μm began to increment after one month of operation, and inside three months peaked at 56%. The fraction of biomass within the range of 250 to 500 μm fluctuated over fourth dimension, while the fraction ≥500 μm continually increased, peaking at xx% before piloting ceased. The long-term stability of granular sludge in a continuous flow activated sludge arrangement is unknown and would demand to be determined in futurity evaluations.

  • Operating in an AO process configuration during Period 1 initially attenuated settleability equally measured by dSVIxxx, and the differences in the means observed between the Examination and Control were statistically significant (P < 0.05), with values of 93 ± 10 and 107 ± 29 mL/g respectively. The differences in the mean dSVI30 observed during hydrocyclone performance in Menstruation ii were statistically significant (P < 0.05), with values of 76 ± 18 and 137 ± 18 mL/chiliad observed for the Test and Control respectively. These results propose that having an anaerobic biological selector in the Test bowl initially moderated the dSVI relative to the Control, and that the addition of a physical selection pressure with hydrocyclones further improved the dSVI.

The observations in this written report suggest that through awarding of primal biological and physical choice pressures, intentional granulation in a continuous period activated sludge system is possible and could be a price effective solution versus traditional expansion for other WRRFs with similar chapters needs. Some of the results presented, while non the focus of this paper, have potential design implications such as:

  • The reduction in the mixed liquor suspended solids that occurred during Period two points to the need to evaluate mixing free energy requirements throughout the organisation as part of design considerations for granulation in a continuous flow system.

  • Operating at college mixed liquor suspended solids in the Test basin during Periods two and three decreased total F/Chiliad ratios from 0.18 to 0.xiii mg rbCOD/mg volatile suspended solids, which could perhaps lead to reduced granule stability. Balancing optimal feed atmospheric condition with an appropriate solids inventory could exist an important operational consideration to sustain optimal selective conditions.

This work has the potential to inform design guidelines for practitioners, as well equally potentially supplement future academic research into key mechanistic principles.

All relevant information are included in the paper or its Supplementary Data.

Ahuja

N.

Griborio

A.

2017

Liquid Stream Fundamentals: Sedimentation

.

Alexandria, Virginia

.

https://doi.org/WSEC-2017-FS-022

.

Baird

R.

Eaton

A. D.

Rice

E. Due west.

2017

Standard Methods for the Examination of Water and Wastewater

, 23rd edn.

American Public Health Clan, American Water Works Association, Water Environment Federation

,

Washington, DC

.

Bradley

D.

1965

The Hydrocyclone

, 1st edn.

Pergamon Press

,

London

.

Downing

L.

Redmond

East.

Klopping

P.

Young

K.

2017

. In:

Water Environment Federation Technical Exhibition and Conference 2017, WEFTEC 2017 7 (Figure 1)

, pp.

4479

–

4483

.

https://doi.org/ten.2175/193864717822155849

.

Figdore

B. A.

2017

Nitrification Bioaugmentation in Mainstream Flocculent Activated Sludge Systems Using Sidestream Aerobic Granular Sludge

.

University of Washington

,

Seattle, WA

.

Gao

D.

Liu

50.

Liang

H.

Wu

W. Thousand.

2011

.

Critical Reviews in Biotechnology

31

(

2

),

137

–

152

.

https://doi.org/10.3109/07388551.2010.497961

.

Ji

M.

Wei

Y.

Lu

S.

Wang

F.

Cheng

L.

2009

. In:

third International Conference on Bioinformatics and Biomedical Applied science, ICBBE 2009

.

https://doi.org/x.1109/ICBBE.2009.5162490

.

Kent

T. R.

Bott

C. B.

Wang

Z. Due west.

2018

.

Biotechnology Advances

36

(

4

),

1139

–

1166

.

https://doi.org/10.1016/j.biotechadv.2018.03.015

.

Klein

A.

Ekstrom

Fifty.

Summers

A.

Wan

J.

Wett

B.

Johnson

C.

Williams

L.

Newman

D.

Green

K.

Melcer

H.

2012

. In:

WEFTEC 2012

,

Sept. 29 – Oct. 3, 2012

,

New Orleans, LA

.

Water Environment Federation

,

New Orleans

, pp.

1

–

14

.

https://doi.org/10.2175/193864712811740774

.

Kreuk

One thousand. M. d.

Heijnen

J. J.

van Loosdrecht

M. C. One thousand.

2005

.

Biotechnology and Bioengineering

ninety

(

vi

),

761

–

769

.

https://doi.org/x.1002/fleck.20470

.

Kreuk

M. 1000. d.

Picioreanu

C.

Hosseini

1000.

Xavier

J. B.

Van Loosdrecht

M. C. One thousand.

2007

.

Biotechnology and Bioengineering

97

(

4

),

801

–

815

.

https://doi.org/10.1002/flake.21196

.

Layer

Thou.

Adler

A.

Reynaert

Due east.

Hernandez

A.

Pagni

M.

Morgenroth

E.

Holliger

C.

Derlon

N.

2019

.

Water Enquiry X

4

,

100033

.

https://doi.org/10.1016/j.wroa.2019.100033

.

Loosdrecht

M. 5.

de Kreuk

M. K.

Heijnen

J. J.

2005

The Unity of Biofilm

. In:

Aerobic Granular Sludge

(

Bathe

Due south.

de Kreuk

1000. K.

McSwain

B. S.

Schwarzenbeck

Due north.

 , eds).

IWA Publishing

,

Clove Crescent, London

, pp.

i

–

5

.

.

Loosdrecht

M. C. 1000. 5.

Nielsen

P. H.

Lopez-Vazquez

C.

Brdjanovic

D.

2016

Experimental Methods in Wastewater Handling

.

IWA Publishing

,

London

.

Mamais

D.

Jenkins

D.

Prrr

P.

1993

.

Water Research

27

(

1

),

195

–

197

.

https://doi.org/10.1016/0043-1354(93)90211-Y

.

Mcswain

B. S.

Irvine

R. L.

Hausner

M.

Wilderer

P. A.

2005

.

Practical and Environmental Microbiology

71

(

two

),

1051

–

1057

.

https://doi.org/x.1128/AEM.71.2.1051-1057.2005

.

Pishgar

R.

Dominic

J. A.

Sheng

Z.

Tay

J. H.

2019

.

Water Research

160

,

81

–

96

.

https://doi.org/10.1016/j.watres.2019.05.026

.

Pronk

Grand.

2017

Aerobic Granular Sludge Continuous Aerobic Granular Sludge in Conventional Wastewater Handling View Project

.

Delft University of Technology

.

https://doi.org/ten.4233/uuid:5ea870b3-671e-4b02-b202-5255d5b58da2

.

Schuler

A. J.

Jang

H.

2007

.

Environmental Scientific discipline and Technology

41

(

5

),

1675

–

1681

.

https://doi.org/ten.1021/es0616074

.

Sturm

B.

Faraj

R.

Figdore

B.

Willoughby

A.

Ford

A.

Bott

C.

Shiskowski

D.

McFall

50.

Downing

L.

2017

Knowledge Development Forum: Balancing Granular Sludge with Activated Sludge Systems for Biological Nutrient Removal

. In:

Water Surroundings Federation Technical Exhibition and Conference 2017, WEFTEC 2017 five

, pp.

3105

–

3121

.

Wagner

J.

Guimarães

L. B.

Akaboci

T. R. V.

Costa

R. H. R.

2015a

.

H2o Science & Technology

71

(

seven

),

1040

–

1046

.

https://doi.org/x.2166/wst.2015.064

.

Wagner

J.

Weissbrodt

D. 1000.

Manguin

5.

Da Costa

H. R.

Morgenroth

E.

Derlon

Due north.

2015b

.

Water Research

85

,

158

–

166

.

https://doi.org/10.1016/j.watres.2015.08.030

.

Wei

S. P.

David Stensel

H.

Quoc

B. Due north.

Stahl

D. A.

Huang

Ten.

Lee

P. H.

Winkler

G. G. H.

2020

.

Water Research

179

,

115865

.

https://doi.org/10.1016/j.watres.2020.115865

.

Wett

B.

Podmirseg

S. M.

Gómez-Brandón

1000.

Hell

M.

Nyhuis

Thou.

Bott

C.

Murthy

S.

2015

.

Water Environment Enquiry

87

(

12

),

2084

–

2089

.

https://doi.org/10.2175/106143015X14362865227319

.

© 2021 The Authors

This is an Open Admission article distributed under the terms of the Creative Eatables Attribution Licence (CC Past-NC-ND 4.0), which permits copying and redistribution for non-commercial purposes with no derivatives, provided the original piece of work is properly cited (http://creativecommons.org/licenses/by-nc-nd/4.0/).