OPTIMIZATION STUDY OF THE ST. MARY'S WASTEWATER TREATMENT PLANT

Transcription

1 XCG File No.: October 26, 2016 OPTIMIZATION STUDY OF THE ST. MARY'S WASTEWATER TREATMENT PLANT Prepared for: B.M. ROSS & ASSOCIATES LIMITED 62 North Street Goderich, Ontario N7A 2T4 Prepared by: XCG CONSULTANTS LTD. Suite 300, 2620 Bristol Circle Oakville, Ontario L6H 6Z7 TM docx

2 Optimization Study of the TABLE OF CONTENTS TABLE OF CONTENTS 1. INTRODUCTION OBJECTIVES EXISTING WASTEWATER TREATMENT Treatment Objectives and Compliance Requirements SUMMARY OF HISTORIC REVIEW AND CAPACITY ASSESSMENT Recent Developments Industrial Wastewater Fertilizer Registration INTENSIVE SAMPLING Intensive Sampling Results SECONDARY CLARIFIER STRESS TESTING Stress Test Results Baseline Conditions Large Secondary Clarifier Small Secondary Clarifier BIOLOGICAL PROCESS MODELLING Model Setup Model Calibration and Validation Determining Design SRT OPPORTUNITIES FOR OPTIMIZATION Secondary Treatment Capacity Solids Treatment Capacity WAS Thickening Anaerobic Digestion Dewatering General Recommendations SUMMARY REFERENCES...46 TM docx ii

3 Optimization Study of the TABLE OF CONTENTS TABLES Table 3.1 ECA Objectives and Compliance Limits...5 Table 4.1 Summary of Historic Review and Capacity Assessment (XCG, 2014)...6 Table 4.2 Equivalent Capacity of Sludge Treatment Unit Processes...8 Table 5.1 Intensive Sampling Results - Liquid Treatment Train...13 Table 5.2 Intensive Sampling Results - Solids Treatment Train...14 Table 6.1 Baseline Secondary Clarifier Performance...16 Table 7.1 BioWin Model Calibration Results...31 Table 7.2 Summary of Modelled Raw Wastewater Quality...35 Table 8.1 Recommended Supplementary Sampling...42 Table 9.1 Recommended Supplementary Sampling...44 Table 9.2 Updated Capacity Assessment of the St. Mary s WWTP...45 FIGURES Figure 3.1 Process Flow Diagram of the...4 Figure 5.1 Process Flow Diagram of the...11 Figure 6.1 Peak Flow Testing - Large Secondary Clarifier Effluent TSS...17 Figure 6.2 Peak Flow Testing - Large Secondary Clarifier Effluent TP...18 Figure 6.3 Peak Flow Testing - Large Secondary Clarifier SOR and SLR...19 Figure 6.4 Peak Flow Testing - Large Secondary Clarifier Sludge Blanket Profiles..19 Figure 6.5 Sustained Peak Flows - Large Secondary Clarifier Effluent TSS...21 Figure 6.6 Sustained Peak Flows - Large Secondary Clarifier Effluent TP...21 Figure 6.7 Sustained Peak Flows - Large Secondary Clarifier Sludge Blanket Profiles...22 Figure 6.8 Peak Flow Testing - Small Secondary Clarifier Effluent TSS...23 Figure 6.9 Peak Flow Testing - Small Secondary Clarifier Effluent TP...24 Figure 6.10 Peak Flow Testing - Small Secondary Clarifier SOR and SLR...25 Figure 6.11 Peak Flow Testing - Small Secondary Clarifier Sludge Blanket Profiles..25 Figure 6.12 Sustained Peak Flows - Small Secondary Clarifier Effluent TSS...26 Figure 6.13 Sustained Peak Flows - Small Secondary Clarifier Effluent TP...27 Figure 6.14 Sustained Peak Flows - Small Secondary Clarifier Sludge Blanket Profiles...28 Figure 7.1 Schematic of BioWin Model Set Up for the...29 Figure 7.2 Historic and Model Predicted Final Effluent cbod5 Concentrations...33 Figure 7.3 Historic and Model Predicted Final Effluent TAN Concentrations...34 Figure 7.4 Model Predicted Effluent TAN Concentration v. SRT...35 Figure 8.1 Optimal Operating Point for Secondary Treatment at Historic Average BOD5 Concentration...37 Figure 8.2 MLSS Concentrations and Secondary Treatment Capacities at Varying BOD5 Concentrations...38 Figure 8.3 MLSS Concentrations at 5,560 m 3 /d and Varying BOD5 Concentrations...39 APPENDICES Appendix A Intensive Sampling Program Laboratory Analysis Results Appendix B Stress Testing Laboratory Analysis Results TM docx iii

4 Optimization Study of the INTRODUCTION 1. INTRODUCTION The St. Mary's Wastewater Treatment Plant (WWTP) is owned by the Town of St. Mary's (the Town) and operated by the Ontario Clean Water Agency (OCWA), and provides secondary treatment for wastewater from the Town. The plant is operated under amended Environmental Compliance Approval (ECA) No VLLLP, amended April 22, The plant is rated for an average day flow (ADF) capacity of 5,560 m 3 /d and a peak flow capacity of 14,250 m 3 /d. The Town had initiated a Class Environmental Assessment (Class EA) to identify a preferred alternative to address projected growth in the Town. Over the course of the Class EA, it was identified that the projected growth did not necessitate any increase in plant capacity beyond the average day rated capacity. Consequently, the Town determined that the future treatment needs of the Town of St. Mary's could potentially be addressed through optimization of the existing plant. B.M. Ross and Associates Limited (BM Ross), in association with XCG Consultants Ltd. (XCG), were retained by the Town to undertake an Optimization Study of the St. Mary's WWTP. TM docx 1

5 Optimization Study of the OBJECTIVES 2. OBJECTIVES The objectives of the Optimization Study are the following: To develop a better understanding of the practical capacities of individual key unit processes at the (i.e. bioreactors, secondary clarifiers); To identify opportunities to increase the capacities of these key unit processes through process or operational changes; and, To identify opportunities to increase the capacities of key unit processes through physical changes or modifications. TM docx 2

6 EXISTING WASTEWATER TREATMENT 3. EXISTING WASTEWATER TREATMENT The is a modified Ludzack-Ettinger (MLE) biological nutrient removal (BNR) process with integrated sludge management that consists of headworks processes, an MLE activated sludge process, disinfection and sludge management. Raw wastewater passes through an automatically cleaned bar screen prior to being pumped to a detritor tank (grit removal) and comminutor. A grit classifier removes excess water prior to disposal. The plant was designed such that during wet weather and other high flow events, flows in excess of the plant capacity can bypass the entire plant at the lift station downstream of the mechanical screen and flow directly to the Thames River outfall. Historically, extremely high flows correspond with high river levels, limiting the ability to physically bypass the plant. Preliminary treated wastewater flows from the headworks to two continuously mixed anoxic tanks. Mixed liquor from the anoxic tanks flows to an inlet chamber, where flow is equally split to three rectangular aeration tanks, each equipped with tapered fine bubble diffusers. Mixed liquor is recycled to the anoxic tank by two internal recirculation pumps. The was originally designed to allow secondary bypass in the event of high flows; however, plant hydraulics were modified when the plant was converted to the BNR process. Consequently, gates that would formerly allow secondary bypass are kept closed. Secondary clarification of the mixed liquor occurs in four circular secondary clarifiers, two large (diameter = m) and two small (diameter = m) clarifiers. Flows to the secondary clarifiers are controlled by a flow splitting mechanism to control hydraulic and solids loading to each clarifier. Return activated sludge (RAS) is directed to a RAS splitter box, which controls the flow split to the anoxic tanks. Waste activated sludge (WAS) flow is controlled by adjusting the overflow weir in the RAS splitter box. Disinfection of secondary effluent is by UV disinfection, with backup chlorination in case emergency disinfection of plant effluent is required. Final plant effluent is discharged to the Thames River. WAS is stored in the WAS equalization tanks prior to thickening by a rotary drum thickener (RDT). The thickened WAS (TWAS) is sent to the TWAS storage/transfer tank prior to stabilization in the anaerobic digesters. Stabilized sludge (biosolids) is withdrawn from the secondary digester, dewatered by a centrifuge and stored in the dewatered sludge tank prior to further treatment in the Lystek process. Polymer can be added upstream of the RDT or the centrifuge to increase solids removal. The Lystek-processed biosolids are stored in the existing sludge storage tanks prior to removal. A portion of the Lystek product is recycled to the anoxic tanks and to the anaerobic digesters (approximately 2 m 3 /d and 3 m 3 /d, respectively) to enhance the performance of the BNR and stabilization processes. The digester supernatant, RDT filtrate and centrifuge centrate are returned to the anoxic tanks. Additional detail on the historic operation and performance of the St. Mary s WWTP can be found in the Historic Review and Capacity Assessment of the (XCG, 2014) completed as part of the Class EA. A flow schematic of the is provided in Figure 3.1. TM docx 3

7 EXISTING WASTEWATER TREATMENT Figure 3.1 Process Flow Diagram of the TM docx 4

8 EXISTING WASTEWATER TREATMENT 3.1 Treatment Objectives and Compliance Requirements The operates under amended ECA Number VLLLP amended April 22, It has a rated ADF capacity of 5,560 m 3 /d and peak capacity of 14,250 m 3 /d. The ECA specifies effluent concentration objectives for carbonaceous biochemical oxygen demand (cbod5), total suspended solids (TSS), total phosphorus (TP), total ammonia nitrogen (TAN), dissolved oxygen (DO) and E. coli. Monthly and daily concentration compliance limits are included for cbod5, TSS, TP, and TAN. The effluent compliance limit for E. coli is 200 organisms/100 ml (monthly geometric mean density) from May 1 to November 30, although E. coli objectives are specified year round. The effluent objectives, monthly and daily compliance limits are shown in Table 3.1. Table 3.1 ECA Objectives and Compliance Limits Parameter Effluent Objectives Monthly Average Concentration Compliance Limits Daily Concentration cbod mg/l 15 mg/l 25 mg/l TSS 10.0 mg/l 15 mg/l 25 mg/l TP 0.7 mg/l 1.0 mg/l 1.0 mg/l TAN 2.5 mg/l 6.0 mg/l 8.0 mg/l DO (1) 4.0 mg/l - - E. Coli (2) May 1 to November organisms / 100 ml 200 organisms / 100 ml - December 1 to April organisms / 100 ml - - ph Notes: 1. Minimum concentration objective. 2. Based on monthly geometric mean density. TM docx 5

9 SUMMARY OF HISTORIC REVIEW AND CAPACITY ASSESSMENT 4. SUMMARY OF HISTORIC REVIEW AND CAPACITY ASSESSMENT As part of the Class EA, a Historical Review and Capacity Assessment of the St. Mary's WWTP was completed based on available data. Table 4.1 summarizes the results of the capacity assessment. Additional detail on the capacity assessment can be found in the Historic Review and Capacity of the St Mary's WWTP (XCG, 2014) Table 4.1 Summary of Historic Review and Capacity Assessment (XCG, 2014) Treatment Unit Capacity Assessment Average Day Flow Max Day Flow Peak Flow Headworks ,250 m 3 /d (1) Bioreactors 5,220 m 3 /d (2) - - Secondary Clarifiers - 14,410 m 3 /d 20,050 m 3 /d RAS Pumping 8,840 m 3 /d - - Oxygenation 83,300 m 3 /d - - Disinfection ,250 m 3 /d (1) WAS Thickening 4,130 m 3 /d (2) - - Anaerobic Digestion 2,625 m 3 /d (2) - - Biosolids Dewatering 3,270 m 3 /d (2) - - Lystek Process 25,000 m 3 /d (2) - - Biosolids Storage 3,300 m 3 /d Overall Capacity 2,625 m 3 /d 14,410 m 3 /d 14,250 m 3 /d Notes: 1. Based on ECA rated peak flow capacity. Capacity should be confirmed during preliminary design. 2. Based on maximum month BOD5 loading. Based on Table 4.1, the has an equivalent ADF capacity of 2,625 m 3 /d limited based on the anaerobic digestion process. It should be noted that the sludge management does not determine the capacity of the liquid treatment process, which is about 5,220 m 3 /d based on the bioreactor capacity. The liquid treatment train has a maximum daily flow (MDF) capacity of 14,410 m 3 /d, limited by the secondary clarifiers, which is equivalent to an ADF of approximately 5,620 m 3 /d (based on the equivalent peak factor of 2.56 using the ECA rated plant ADF and peak flow capacities). The peak flow capacity of the liquid treatment train is 14,250 m 3 /d based on the ECA rated capacity of the existing headworks and UV disinfection system. The equivalent ADF capacity of the existing headworks and UV disinfection system is approximately 5,560 m 3 /d, which is equivalent to the current ECA rated ADF capacity of the plant. The following points summarize key findings of the historic review of the St. Mary's WWTP: Industrial wastewater accounted for approximately 18% of raw wastewater flows to the. Wastewater quality from these industries are not typically TM docx 6

10 SUMMARY OF HISTORIC REVIEW AND CAPACITY ASSESSMENT monitored; however, based on the surcharge agreements with some of the industries, a large portion of the loading to the plant (potentially up to 2/3 in the case of BOD5) may be from industrial sources. The actual wastewater strength from major industries should be verified through an industrial wastewater sampling and characterization program; Historically, the bioreactors have operated at annual average MLSS concentrations ranging 4,540 mg/l in 2011 to 5,419 mg/l in 2012, for an average of approximately 5,000 mg/l from 2010 to The historic MLSS concentration is well above the typical design range for an MLE process of 1,500-4,000 mg/l (WEF, 2010). Operation at the elevated MLSS concentration may be a result of the high organic loading to the plant and maintaining the system SRT, but does not appear to have negatively impacted performance of the plant. The capacity of the bioreactors is about 5,220 m 3 /d based on a design solids retention time (SRT) of 10 days, and a MLSS concentration of 4,600 mg/l. The capacity is lower than the ECA rated capacity of 5,560 m 3 /d primarily due to historically high organic loading to the bioreactors; Based on a design surface overflow rate (SOR) of 37 m 3 /m 2 d, the clarifiers have a (peak hourly flow) PHF capacity of 20,054 m 3 /d. Based on a design max day solids loading rate (SLR) of 170 kg/m 2 d, the MDF capacity of the secondary clarifiers is 14,410 m 3 /d; The historic average alum dosage of 33 mg/l was well below the typical alum dosage range of 110 to 225 mg/l (MOE, 2008) while the effluent TP from the St. Mary's WWTP consistently met daily and monthly effluent TP objectives and limits. In part, this could be due to the ratio of influent BOD5 to TP in the raw wastewater closely matching nutrient requirements for biomass growth of 1 g of phosphorus per 100 g of BOD5 (Metcalf and Eddy, 2003); The estimated equivalent ADF capacity of the RDT is 4,130 m 3 /d. This is lower than the ECA rated capacity of the plant and is likely due to the high historic organic loading to the and its impact on the WAS mass generation rate; The equivalent ADF capacity of the anaerobic digester is estimated at 2,625 m 3 /d, which is less than half of the ECA rated ADF capacity of the plant. The historic WAS mass generation rate is much higher per unit of wastewater treated than typical values, which negatively impacts the equivalent ADF capacity of the digesters; Due to limited historic sampling data from process streams between unit processes, it is not possible to assess the performance of the anaerobic digesters or Lystek process in terms of volatile solids (VS) destruction, nor is it possible to quantify the impact of recycling of the Lystek product on the performance of the digester. Sampling of the intermediate sludge and biosolids product between unit processes is recommended to better assess the performance of the individual unit processes with respect to VS destruction; The estimated equivalent ADF capacity of the centrifuge is 4,580 m 3 /d. This is lower than the ECA rated capacity of 5,560 m 3 /d and is likely due to the high historic organic loading to the and its impact on the WAS mass generation rate; Based on the minimum cycle time and operation 8 hours per day, 5 days per week, the equivalent ADF capacity of the Lystek process is 25,000 m 3 /d; and, TM docx 7

11 SUMMARY OF HISTORIC REVIEW AND CAPACITY ASSESSMENT Based on providing 240 days of onsite storage at a solids concentration of 7.4% total solids (TS), the equivalent ADF capacity of the biosolids storage is approximately 3,300 m 3 /d. A reduction in the BOD5 loading to the plant would increase the equivalent ADF capacity of the biosolids storage. Additionally, according to the conceptual design, the sludge storage was sized based on a minimum solids concentration of 10% TS in the Lystek biosolids product. Increasing the solids concentration in the Lystek product to 10% would result in approximately 25% additional equivalent capacity. 4.1 Recent Developments Industrial Wastewater As part of the Historic Review and Capacity Assessment (XCG, 2014), it was noted that as much as 18 percent of the wastewater flow to the was attributed to industries, potentially representing up to 2/3 of the BOD5 loading to the plant. Industrial loading, however, is dependent on the industries currently in operation and discharging to the collection system, (seasonal) variations in production and changing operations. Since the completion of the Historic Review and Capacity Assessment, the Town has been working with industries to reduce their loadings to the plant. According to Operations Staff, these efforts combined with changes to the industries discharging to the, have resulted in a reduction in BOD5 concentrations by almost 13 percent (down from 390 mg/l to approximately 340 mg/l) in A reduction in BOD5 concentration and loading would result in an increase in secondary treatment capacity as well as in the equivalent capacities of the sludge management unit processes (i.e. WAS thickening, anaerobic digestion, biosolids dewatering, the Lystek process and biosolids storage). Based solely on a reduction in raw wastewater BOD5 concentration from 390 mg/l to 340 mg/l, the equivalent capacities of the sludge treatment unit processes increased by 13% as compared to the equivalent capacities estimated in the Historic Review and Capacity Assessment. Table 4.2 presents the equivalent ADF capacities of the sludge treatment unit processes at a raw wastewater BOD5 concentration of 340 mg/l. The equivalent capacities from the Historic Review and Capacity Assessment are included in the table for comparison. Table 4.2 Treatment Unit Equivalent Capacity of Sludge Treatment Unit Processes Reduced BOD Loading Equivalent ADF Capacity (1) Historic Review and Capacity Assessment WAS Thickening 4,679 m 3 /d 4,130 m 3 /d Anaerobic Digestion 2,972 m 3 /d 2,625 m 3 /d Biosolids Dewatering 3,705 m 3 /d 3,270 m 3 /d Lystek Process 28,311 m 3 /d 25,000 m 3 /d Biosolids Storage 3,786 m 3 /d 3,300 m 3 /d Notes: 1. Based on maximum month BOD5 loading. TM docx 8

12 SUMMARY OF HISTORIC REVIEW AND CAPACITY ASSESSMENT Based on Table 4.2, with a reduced BOD5 concentration of 340 mg/l, the capacities of the WAS thickening, anaerobic digestion and biosolids dewatering unit processes are all still lower than the ECA rated ADF capacity of 5,560 m 3 /d. The impact of the reduced BOD5 loading on bioreactor capacity is discussed in Section Fertilizer Registration In October 2015, the Lystek product generated at the, called LysteGro TM, was registered as a biofertilizer under the Canadian Food Inspection Agency (CFIA). Registration as a fertilizer under the CFIA is site-specific, and includes a detailed review and evaluation of the product over a period of a year or longer. As a registered fertilizer, the LysteGro TM product is not considered a sewage sludge waste product and therefore is not subject to the same restrictions as biosolids with respect to land application and storage. Consequently, LysteGro TM may be land applied year round, and may be stored with no specific storage or permitting requirements. The removal of restrictions with respect to storage of the biofertilizer produced at the St. Mary's WWTP eliminates the impact of biosolids storage limitations on the capacity of the plant. TM docx 9

13 INTENSIVE SAMPLING 5. INTENSIVE SAMPLING An intensive sampling program was conducted at the over seven business days from February 9, 2015 to February 15, 2015 as part of the optimization study. The objective of the intensive sampling program was to evaluate the performance of individual unit processes and to characterize the wastewater throughout the plant. The data were also used for the purposes of biological modelling to review the biological treatment capacity of the. Figure 5.1 presents the sampling locations in the liquid and solid treatment trains at the St. Mary's WWTP. Of the locations shown, samples of the raw wastewater, blended internal recycle, and secondary effluent were 24-hour composite samples collected using an autosampler. All other samples were discrete grab samples collected manually. A number of samples collected from Day 4 to Day 7 were analyzed as a sludge matrix rather than as a wastewater matrix. This had an impact on the parameters and the units in which the results were reported; Anoxic tank effluent and MLE recycle streams were not decanted prior to bottling, which may have impacted the laboratory results due to continued biological activity; RDT filtrate on Day 6 was notably higher than the rest of the results and may be due to a polymer delivery issue at the RDT. Similarly, no TWAS sample was collected on that day as the unit was taken offline; and, No biosolids sample was collected on Day 7 due to inadequate flow to the sampling location. A list of the various parameters analyzed as part of this study is included below. Total COD (tcod), filtered COD (fcod) and flocculated and filtered COD (ffcod) Total BOD5 (tbod5), carbonaceous BOD5 (cbod5) and filtered cbod5 (fcbod5) Total phosphorus (TP) and dissolved reactive phosphorus Total Kjeldahl nitrogen (TKN), total ammonia nitrogen (TAN), Nitrate + Nitrite Nitrogen Alkalinity (CaCO3 equivalent) Total suspended solids (TSS) and volatile suspended solids (VSS) ph Dissolved Oxygen (DO) 5.1 Intensive Sampling Results Table 5.1 summarizes the results of the liquid treatment train sampling. Table 5.2 summarizes the results of the intensive sampling of the solids treatment train. The laboratory analysis results from the intensive sampling program are included in Appendix A. The following general observations were based on the results of the intensive sampling program. The raw wastewater concentrations are representative of a high strength wastewater with respect to BOD5, and medium strength with respect to TSS, TKN and TP (Metcalf & Eddy, 2003). The results of the sampling program were consistent with the Historic TM docx 10

14 INTENSIVE SAMPLING Review and Capacity Assessment with respect to BOD5 and TSS, and higher strength for TKN and TP. As discussed in Section 4.1.1, the Town has been working with industries to reduce the loading to the plant. Since the completion of the intensive sampling program, preliminary results indicate a reduction in BOD5 concentrations to approximately 340 mg/l. Although still considered a high strength wastewater in terms of BOD5 concentration, this is a significant reduction as compared to the results of the intensive sampling program as well as historic values. Figure 5.1 Process Flow Diagram of the The impact of industrial wastewater on the raw wastewater quality is dependent on the industries currently in operation and discharging to the collection system, (seasonal) variations in production and changes to operations. As a result, where wastewater composition includes significant industrial contributions, raw wastewater strength and composition can vary significantly throughout the year. Therefore, the duration of the program (7 days) may be insufficient to adequately capture the variability inherent in the type of wastewater treated at the and obtain representative wastewater characterization. Based on estimated flows, recycle streams (RDT filtrate, centrate and Lystek recycle) are equivalent to approximately 5% of the raw wastewater organic (BOD5 and TKN) loading to the plant. Based on Table 5.2 and assuming that supernatant was not withdrawn from the primary digester, the VS destruction in the primary digester was about 25%, and 36% through primary and secondary digestion, which are lower than the typical value of 56% at an hydraulic retention time (HRT) of 15 days. TM docx 11

15 INTENSIVE SAMPLING The primary purpose of the intensive sampling program was to collect data on the sludge processes. At the time of the intensive sampling program, there were operational issues that resulted in the high MLSS. However, the elevated MLSS would have limited impact on the results of the sludge sampling as the effects on the sludge treatment train would not be observed immediately, but only under consistent operation at elevated MLSS concentrations over an extended period of approximately 2 weeks or longer, equivalent to the retention of solids in the bioreactors (or SRT). TM docx 12

16 INTENSIVE SAMPLING Table 5.1 Intensive Sampling Results - Liquid Treatment Train Average Concentration (mg/l) Parameter Raw Wastewater Secondary Effluent RDT Filtrate Centrate Lystek Recycle Anoxic Tank MLE Recycle MLSS RAS tcod ,500 3,627 51,000 (1) 8,433 9,300-12,333 fcod ffcod tbod ,800 (1) 2,367 2,600-3,200 cbod ,900 (1) 1,667 1,700-2,167 fcbod TSS ,157 8,867 65,714 7,214 7,943 7,871 10,214 VSS ,886 6,291 40,486 5,610 5,887 6,224 7,937 TKN , TAN Nitrite Nitrate Nitrite + Nitrate TP , Orthophosphate ph Alkalinity ,200 6,300 (1) (2) 357 Notes: Unless otherwise noted, sample results based on 3 samples analyzed as wastewater matrices and 4 samples analyzed as sludge matrices. 1. Based on the results of 1 sample analyzed as wastewater matrices. 2. Based on the results of 3 samples analyzed as wastewater matrices. TM docx 13

17 INTENSIVE SAMPLING Table 5.2 Intensive Sampling Results - Solids Treatment Train Average Concentration (TS, VS - %, Alkalinity mg/l as CaCO3) Parameter TWAS RDT Filtrate Biosolids Centrate Hauled Biosolids (1) Lystek Recycle (2) Primary Digested Sludge Dewatered Biosolids (3) WAS TS VS ph Alkalinity (3) 3,633 (3) 2,200 (3) - 6, (1) Notes: Unless otherwise noted, sample results based on 3 samples analyzed as wastewater matrices and 4 samples analyzed as sludge matrices. 1. Based on 2 samples analyzed as wastewater matrices and 4 samples analyzed as sludge matrices. 2. Based on 6 samples analyzed as sludge matrices and 1 sample analyzed as a wastewater matrix. 3. Based on 7 samples analyzed as sludge matrices. TM docx 14

18 SECONDARY CLARIFIER STRESS TESTING 6. SECONDARY CLARIFIER STRESS TESTING Hydraulic stress testing was conducted to measure the performance of the secondary clarifiers under high flow and solids loading conditions, and to estimate the maximum hydraulic loading rates permissible before clarifier failure is observed. Over a five day period from November 2 to November 6, 2015, stress testing was completed on one each of the small and large secondary clarifiers at the. Target stress testing conditions were met by closing gates and directing flow preferentially to the test clarifier. In order to supplement the flows to the plant, wastewater stored in the offline secondary clarifiers were returned to the aeration tanks using the plant's RAS pumps. The following summarizes the stress testing conducted on each day of testing: Baseline sampling of the small and large secondary clarifiers was conducted on November 2, Peak flow testing on the small secondary clarifier was carried out from approximately 9:00 AM to 2:00 PM on November 3, Peak flow testing on the large secondary clarifier from 8:30 AM to 2:00 PM on November 4, Sustained peak flow testing of the large secondary clarifier was conducted from 8:30 AM to 3:00 PM on November 5, Sustained peak flow testing of the small secondary clarifier was conducted from 8:30 AM to 3:00 PM on November 6, During the testing period, the following sampling and monitoring activities were performed: Flows through the secondary clarifiers were monitored by installing a temporary velocity-area (VA) flowmeter in the effluent trough of the secondary clarifiers, and flows were recorded throughout the course of the stress tests; An automatic sampler was installed in the effluent channel of each test secondary clarifier to collect secondary effluent samples. During baseline and sustained peak flow testing, each sample consisted of four 15 minute sub-samples to obtain a 1 hour composite sample. During peak flow testing, each sample consisted of two 15 minute sub-samples to obtain a 30 minute composite sample. Each sample was submitted to an accredited laboratory for cbod5, TSS and TP analyses, and analyzed onsite for ortho-phosphorus and ultraviolet transmittance (UVT). The results of the laboratory analysis are included in Appendix B; Grab samples of mixed liquor were also submitted to an accredited laboratory for total TSS analysis; and, A sludge judge was used to monitor the radial profile of the sludge blanket in the test secondary clarifiers. Measurements were taken at 3 points along the radius of the secondary clarifiers. It should be noted that individual RAS flow (from each secondary clarifier) or concentration data were unavailable for this study. For the purpose of calculating secondary TM docx 15

19 SECONDARY CLARIFIER STRESS TESTING clarifier SLR values, it was assumed that the RAS flow from each secondary clarifier was proportional to their relative surface area. 6.1 Stress Test Results Baseline Conditions Preliminary data were collected by XCG staff on November 2, 2015 to obtain a baseline of the operation and performance of the secondary clarifiers under normal operating conditions prior to the initiation of stress testing. At the current flows, the plant is typically operated with the two large secondary clarifiers in service. The two small secondary clarifiers are brought online to provide additional capacity during wet weather events. In order to obtain a baseline of the performance of the small secondary clarifier, one unit was brought online in advance of the stress test. Table 6.1 presents the mixed liquor suspended solids (MLSS) concentration and effluent quality with respect to TSS and TP as well as the onsite measurements of ortho-phosphorus and UVT. Table 6.1 Baseline Secondary Clarifier Performance Sample Location Small Secondary Clarifier Large Secondary Clarifier MLSS 2,800 mg/l Effluent TSS 11 mg/l <10 mg/l Effluent TP mg/l Effluent Ortho-Phosphorus 0.08 mg/l 0.03 mg/l Effluent Turbidity 5.65 NTU 1.83 NTU Effluent UVT 71.3% 74.7% Measured flow through the small secondary clarifier was approximately 443 m 3 /d on November 2, 2015, which resulted in an average SOR of approximately 5.0 m 3 /m 2 d, and a SLR of approximately 55 kg/m 2 d. Concurrently, the flow to the large secondary clarifier was 3,678 m 3 /d, which resulted in an average SOR of approximately 20.2 m 3 /m 2 d, and a SLR of approximately 98 kg/m 2 d. At these average SOR and SLR values, the average effluent TSS from the small secondary clarifier was 11 mg/l and the sludge blanket depths ranged from approximately 1.0 to 2.5 feet across the radius of the clarifier. The effluent TSS from the large clarifier was less than 10 mg/l and the sludge blanket depths ranged from approximately 0.25 to 1 feet. The TSS values corresponded to low effluent turbidities of 5.65 and 1.83 Nephelometric Turbidity Units (NTU) in the small and large secondary clarifier, respectively, resulting in UVT values of 71.3% and 74.7%. The secondary effluent TP was 0.20 mg/l and 0.14 mg/l from the small and large secondary clarifiers, respectively, which are in compliance with the daily effluent TP limit of 1.0 mg/l, and is below the effluent objective of 0.7 mg/l. TM docx 16

20 SECONDARY CLARIFIER STRESS TESTING Large Secondary Clarifier Peak Flow Testing A pre-stress test sample was collected to document the secondary clarifier performance before initiation of the stress test. Effluent TSS and TP were consistent with the baseline sampling, with a TSS value of less than 10 mg/l and a TP concentration of 0.11 mg/l. Figure 6.1 presents the secondary effluent TSS concentrations over the course of the peak flow testing of the large secondary clarifier and the recorded peak flows. Where sample results were less than the minimum detection limit of 10 mg/l, Figure 6.2 presents effluent TP and ortho-phosphorus concentrations and peak flows over the course of the peak flow testing. Figure 6.1 Peak Flow Testing - Large Secondary Clarifier Effluent TSS As shown in Figure 6.1, effluent TSS concentrations were relatively stable with a majority of results being less than 10 mg/l over the course of the stress test. Generally, the effluent TSS exceeded the effluent objective TSS concentration of 10 mg/l at hourly flows surpassing 8,000 m 3 /d, but remained below the daily compliance limit of 25 mg/l throughout the entire stress test. The highest recorded effluent TSS was 21 mg/l, at a peak hourly flow of approximately 8,200 m 3 /d. The secondary clarifier was pushed to a peak instantaneous flow of approximately 10,500 m 3 /d and a sustained flow of 9,400 m 3 /d before the test was discontinued due to hydraulic limitations resulting in a backup of floating sludge and scum in the secondary clarifier distribution chamber. TM docx 17

21 SECONDARY CLARIFIER STRESS TESTING Figure 6.2 Peak Flow Testing - Large Secondary Clarifier Effluent TP The effluent TP remained well below the objective of 0.7 mg/l over the course of the stress test, averaging 0.2 mg/l with a high of 0.3 mg/l. Throughout the stress test, orthophosphorus remained relatively constant with an average concentration of 0.06 mg/l, and represented anywhere from 20% to 90% of the measured effluent TP. This indicates that the secondary clarifier continued to operate consistently over the course of the stress test and was able to maintain performance with respect to effluent phosphorus. In the post stress test period, the effluent TP and ortho-phosphorus increased, which was inconsistent with the effluent TSS in the post stress test period. It is unclear what the cause of this may have been, but it may have been due to the release of the floating sludge from the distribution chamber once the stress test was discontinued. Figure 6.3 presents the SOR and SLR observed in the secondary clarifier during the peak flow testing. Figure 6.4 presents the sludge blanket profile at various flows over the course of the stress test. TM docx 18

22 SECONDARY CLARIFIER STRESS TESTING Figure 6.3 Peak Flow Testing - Large Secondary Clarifier SOR and SLR Figure 6.4 Peak Flow Testing - Large Secondary Clarifier Sludge Blanket Profiles TM docx 19

23 SECONDARY CLARIFIER STRESS TESTING At an hourly flow of 8,200 m 3 /d, the peak hourly SOR was 45 m 3 /m 2 d, which is higher than the MOE Design Guidelines value of 37 m 3 /m 2 d for an activated sludge plant with chemical addition and no primary clarification. Although effluent performance was maintained at flows exceeding 8,200 m 3 /d, hydraulic issues in the distribution chamber prevented continued testing beyond these flows. At a MLSS concentration of 2,900 mg/l, the equivalent peak hourly SLR was estimated at 187 kg/m 2 d, which is higher than the typical design maximum day SLR value 170 kg/m 2 d for a nitrifying activated sludge plant with chemical addition and no primary clarification (MOE, 2008). As can be seen in Figure 6.4, the sludge blanket in the secondary clarifier did not vary significantly over the course of the peak flow testing, remaining at depths of less 3 feet or less throughout the stress test at all three measurement points. This confirms that the secondary clarifier did not fail during the peak flow testing as would have been evident through a sharp rise in sludge blanket depth, loss of sludge blanket definition, and sudden increase in effluent TSS concentration. Sustained Peak Flow Testing The objective of the sustained peak flow test was to demonstrate the performance of the secondary clarifier during a sustained peak flow event. A pre-stress test sample was collected to document the secondary clarifier performance before initiation of the stress test. Effluent TSS and TP concentrations were consistent with the baseline sampling, with a TSS value of less than 10 mg/l and a TP value of 0.14 mg/l. Figure 6.5 presents the effluent TSS concentration from the secondary clarifier over the course of the sustained peak flow testing and Figure 6.6 presents effluent TP and orthophosphorus concentrations over the same period. The average flow over the course of the sustained peak flow testing was 7,150 m 3 /d, resulting in a SOR of 39 m 3 /m 2 d and a SLR of approximately 197 kg/m 2 d with an average MLSS concentration of 3,120 mg/l. Over the duration of the test, no effluent TSS concentrations exceeding 10 mg/l were recorded. Similarly, effluent TP concentrations averaged 0.1 mg/l, which is well below the objective of 0.7 mg/l and the daily limit of 1.0 mg/l. Based on the sustained peak testing, the large secondary clarifiers are capable of maintaining effluent quality with respect to TSS and TP at an SLR of 197 kg/m 2 d, which is higher than the typical value of 170 kg/m 2 d for a nitrifying activated sludge plant with chemical addition and no primary clarification (MOE, 2008). TM docx 20

24 SECONDARY CLARIFIER STRESS TESTING Figure 6.5 Sustained Peak Flows - Large Secondary Clarifier Effluent TSS Figure 6.6 Sustained Peak Flows - Large Secondary Clarifier Effluent TP TM docx 21

25 SECONDARY CLARIFIER STRESS TESTING Figure 6.7 presents the sludge blanket levels in the large secondary clarifier over the course of the sustained peak flow testing. Figure 6.7 Sustained Peak Flows - Large Secondary Clarifier Sludge Blanket Profiles As can be seen in Figure 6.7, the sludge blanket in the secondary clarifier did not vary significantly over the course of the sustained peak flow testing, remaining at depths of less than 3 feet throughout the stress test at all three measurement points. This suggests that the secondary clarifier did not fail and was able to maintain performance over the course of the sustained peak flow testing Small Secondary Clarifier Peak Flow Testing A pre-stress test sample was collected to document the secondary clarifier performance before initiation of the stress test. Effluent TSS was consistent with the baseline sampling, with a TSS value of less than 10 mg/l. The measured effluent TP was slightly elevated as compared to the baseline sample at 0.19 mg/l. Figure 6.8 presents the secondary effluent TSS concentrations over the course of the peak flow testing of the small secondary clarifier and the recorded peak flows. TM docx 22

26 SECONDARY CLARIFIER STRESS TESTING Figure 6.8 Peak Flow Testing - Small Secondary Clarifier Effluent TSS As shown in Figure 6.8, effluent TSS concentrations were relatively stable with a majority of results being less than 10 mg/l over the course of the stress test, and a peak of 15 mg/l occurring during the second hour of the stress test at a flow of approximately 1,400 m 3 /d. The effluent TSS exceeded the effluent objective TSS concentration of 10 mg/l two times over the course of the stress test despite hourly flows exceeding 3,500 m 3 /d, while remaining below the daily compliance limit of 25 mg/l. The small secondary clarifier was pushed to a peak instantaneous flow of approximately 4,565 m 3 /d before the test was discontinued due to the hydraulic limitations in the secondary clarifier distribution chamber. Figure 6.9 presents effluent TP and ortho-phosphorus concentrations and peak flows over the course of the peak flow testing. The effluent TP were consistently below the objective of 0.7 mg/l over the course of the stress test, averaging 0.27 mg/l with a high of 0.34 mg/l. Throughout the stress test, orthophosphorus remained relatively consistent with an average concentration of 0.06 mg/l, and represented anywhere from 12% to 35% of the measured effluent TP. This indicates that the secondary clarifier continued to operate consistently over the course of the stress test and was able to maintain performance with respect to effluent phosphorus. TM docx 23

27 SECONDARY CLARIFIER STRESS TESTING Figure 6.9 Peak Flow Testing - Small Secondary Clarifier Effluent TP In the post stress test period, the effluent TP decreased to below pre-stress test levels, which was expected. This is unlike the effluent response from the large clarifier. The cause for the variation in the post-stress test performance of the two clarifiers is unclear. Figure 6.10 presents the SOR and SLR observed in the secondary clarifier during the peak flow testing. At an hourly flow of 3,521 m 3 /d, the peak hourly SOR was 40 m 3 /m 2 d, which is higher than the MOE Design Guidelines value of 37 m 3 /m 2 d for an activated sludge plant with chemical addition and no primary clarification plant. Although effluent performance was maintained at flows of up to 3,521 m 3 /d, hydraulic issues in the distribution chamber prevented continued testing beyond these flows. At a MLSS concentration of 2,700 mg/l, the equivalent peak hourly SLR was estimated at 135 kg/m 2 d assuming that the proportion of RAS from the secondary clarifiers is proportional to their respective surface areas. Figure 6.11 presents the sludge blanket profile at various flows over the course of the stress test. TM docx 24

28 SECONDARY CLARIFIER STRESS TESTING Figure 6.10 Peak Flow Testing - Small Secondary Clarifier SOR and SLR Figure 6.11 Peak Flow Testing - Small Secondary Clarifier Sludge Blanket Profiles TM docx 25

29 SECONDARY CLARIFIER STRESS TESTING As can be seen in Figure 6.11, the sludge blanket in the secondary clarifier did not vary significantly over the course of the peak flow testing, with an average depth of slightly over 2 feet, with maximum measured depths of 3.5 feet. This confirms that the secondary clarifier did not fail during the peak flow testing as would have been evident through a sharp rise in sludge blanket depth, loss of sludge blanket definition, and sudden increase in effluent TSS concentration. Sustained Peak Flow Testing A pre-stress test sample was collected to document the secondary clarifier performance before initiation of the stress test. Effluent TSS and TP were consistent with the baseline sampling, with a TSS value of less than 10 mg/l and a TP value of 0.16 mg/l. Figure 6.12 presents the effluent TSS concentration from the secondary clarifier over the course of the sustained peak flow testing and Figure 6.13 presents effluent TP and orthophosphorus concentrations over the testing period. Figure 6.12 Sustained Peak Flows - Small Secondary Clarifier Effluent TSS The average flow over the course of the sustained peak flow testing was 3,228 m 3 /d, resulting in a SOR of 36 m 3 /m 2 d and a SLR of approximately 176 kg/m 2 d with an average MLSS concentration of 2,920 mg/l. Over the duration of the test, no effluent TSS concentrations exceeding 10 mg/l were recorded. Similarly, effluent TP concentrations averaged 0.10 mg/l with a peak reading of 0.16 mg/l. The effluent TP was well below the objective of 0.7 mg/l and the daily limit of 1 mg/l. The post test sample showed an elevated TP concentration of 0.49 mg/l. This is inconsistent with the post stress test orthophosphorus and TSS concentrations, both of which decreased after the termination of the stress test. Because the ortho-phosphorus did not increase post stress, the soluble fraction of the TP is unlikely to have the increase in TP. If the elevated TP was a result of the release of floating sludge from the distribution chamber, then the TSS would be expected to be TM docx 26

30 SECONDARY CLARIFIER STRESS TESTING elevated as well. As this was not the case, the accuracy of this analytical result is uncertain, and the discrepancy may have been the result of sampling or analytical error. Based on the sustained peak testing, the small secondary clarifiers are capable of maintaining effluent quality with respect to TSS and TP at an SLR of 176 kg/m 2 d, which is consistent with the typical value of 170 kg/m 2 d for an activated sludge plant with chemical addition and no primary clarification (MOE, 2008). Figure 6.13 Sustained Peak Flows - Small Secondary Clarifier Effluent TP Figure 6.14 presents the sludge blanket profile at various flows over the course of the sustained peak flow testing. As can be seen in Figure 6.14, the sludge blanket in the secondary clarifier did not vary significantly over the course of the sustained peak flow testing, remaining at depths of less than 3.5 feet throughout the stress test at all three measurement points. This suggests that the secondary clarifier did not fail and was able to maintain performance over the course of the sustained peak flow testing. TM docx 27

31 SECONDARY CLARIFIER STRESS TESTING Figure 6.14 Sustained Peak Flows - Small Secondary Clarifier Sludge Blanket Profiles TM docx 28

32 BIOLOGICAL PROCESS MODELLING 7. BIOLOGICAL PROCESS MODELLING 7.1 Model Setup Biological process modelling using the BioWin modelling software, provides a means to evaluate the capacity of a biological treatment system in terms of BOD and TAN removal, and was utilized for simulation of the biological treatment process at the St. Mary's WWTP. The BioWin model of the existing WWTP was configured as shown in Figure 7.1 using the following data: Results from intensive sampling, conducted between February 23 and March 4, 2015; Historic plant data, including raw wastewater quality, final effluent quality, and plant operating conditions; and, Typical raw wastewater characteristics for a municipal wastewater treatment plant. SC3 Alum SC4 Alum Anoxic 1 Aeration Tank 1 Aeration Tank 2 To Disinfection Raw Influent Grit Removal Anoxic 2 Aeration Tank 3 Grit WAS EQ1 AD1 WAS EQ2 Lystek KOH Lystek Product Figure 7.1 Schematic of BioWin Model Set Up for the The bioreactor (anoxic and aerobic) tank volumes were modelled according to the volumes identified in the ECA. It should be noted that although the anoxic tanks are retrofitted primary clarifiers, the HRT provided would be 3 hours at ADF capacity, which is consistent with the typical range of 1-3 hours found in literature (Metcalf & Eddy, 2003). Consequently, it appears that the anoxic volume provided in the retrofitted anoxic tanks are sized sufficiently to meet typical design guidelines. An ideal clarifier was used to model all secondary clarifiers at the plant. This approach involves using a defined percent solids removal across the clarifier based on historic operating data. This is a simple approximation of the solids settling mechanics in a clarifier that does not take into account sludge blanket depths, spatial variations in sludge quality, or changing performance resulting from variability in influent quality or flow. More complex settling models are available within BioWin that require a detailed sampling and analysis program in order to determine the required settling model parameters. As a separate field program was conducted to confirm the capacity of the secondary clarifiers, the focus of this modelling was on the biological treatment capacity of the plant. TM docx 29

33 BIOLOGICAL PROCESS MODELLING Dewatering units were used to model the rotary drum thickener and centrifuge. In BioWin dewatering units are simple processes that model the physical process of separation of solids from the liquid phase based on user input for solids capture percentage, and underflow rate (i.e. filtrate or centrate). Operation of these units was defined based on typical parameters (M&E, 2003) in conjunction with sample results from the intensive sampling program. The Lystek process was modelled using the thermal hydrolysis process unit available in version 4.1 of BioWin. This is a complex process which simulates the breakdown of particulate material in the digested sludge into soluble components. For the purposes of modelling the, default parameters were used for the thermal hydrolysis unit. 7.2 Model Calibration and Validation The model was calibrated according to the procedure for model calibration as detailed in Methods for Wastewater Characterization in Activated Sludge Modelling (WEF, 2003), based on historic plant operating and performance data collected between January and March, 2010, and results from an intensive sampling program (conducted between February 23 to March 4, 2015). Historic plant information was used as the source of data for all streams except solids concentrations for the RDT filtrate, centrate, Lystek influent, and Lystek effluent streams, which were based on data from the intensive sampling program. As noted in Section 5, an intensive sampling program of the was conducted to characterize the wastewater throughout the plant and to evaluate unit process performance where historic data were unavailable. This data were used in the calibration of the biological model to define the performance of unit processes in the liquid and solids treatment trains. Although the intensive sampling program included samples of raw wastewater, the duration of the program (7 days) was insufficient to adequately capture the variability inherent in the type of wastewater treated at the and to obtain wastewater fractions that are representative of the average conditions at the plant. Additionally, the Town has been working with industries to reduce the loading to the plant, with preliminary results showing a reduction in BOD5 strength by as much as 13 percent since the intensive sampling program was conducted. These changes may have also impacted the raw wastewater fractions. Therefore, due to the uncertainty with the industrial impact on the raw wastewater characteristics, and for purposes of modelling, historic raw wastewater quality data and the default BioWin fractions were used to characterize the raw wastewater. The following assumptions were also made for the purposes of modelling at the St. Mary's WWTP: RAS and WAS flows were modelled based on historic operating data; MLE and Lystek recycle flows were set to constant values based on input from Operations Staff; Recycle flows from the RDT, secondary digester, and centrifuge were adjusted to achieve target solids concentrations based on results from the intensive sampling program; TM docx 30