ST. GEORGE W ATER POLLUTION CONTROL PLANT PROCESS …€¦ · 6. St. George Water Pollution Control Plant Annual Performance Report, Ontario Clean Water Agency, 2004 to 2008. 7. St.

ST. GEORGE WATER POLLUTION CONTROL PLANT PROCESS CAPACITY ASSESSMENT

COUNTY OF BRANT

GAMSBY AND MANNEROW LIMITED CONSULTING PROFESSIONAL ENGINEERS

GUELPH – OWEN SOUND – KITCHENER - LISTOWEL

April 2009 Our File: 109-025

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ST. GEORGE WPCP PROCESS CAPACITY ASSESSMENT COUNTY OF BRANT

EXECUTIVE SUMMARY

Gamsby and Mannerow Ltd. (G&M) was retained by the County of Brant to assess existing process capacity of the St. George Water Pollution Control Plant (WPCP). The plant is a package extended aeration plant with processes including grit removal, secondary clarification, disinfection, tertiary sand filtration, dechlorination and sludge digestion. The rated capacity of the plant is an average flow of 1,300 m3/d (cubic metres per day) with a design peak flow rate of 3,412 m3/d. Based on observations made during a plant tour and discussions with plant operations personnel, various mechanical deficiencies associated with the inlet works, aeration tank, clarifier and tertiary sand filter have been identified. Notwithstanding the correction of the identified mechanical deficiencies, the process analysis detailed herein, clearly demonstrates that the plant cannot handle its rated design capacity of 1,300 m3/d. The plant suffers from sludge bulking, primarily associated with increased flow and BOD loadings. Abnormally high sludge production rates, relative to both design and typical extended aeration rates, constrains sludge processing capacity. Limited biosolids processing capacity at the Paris WPCP necessitates operation at long SRT and high MLSS, thus overloading the secondary clarifier. The simultaneous increase in SVI with flow and BOD loading combined with occasional occurrence of anaerobic zones in the aeration tank point to potential limitations in aeration system performance and/or design. Based on limited available data, we estimate that the existing plant (without any improvements) can achieve reasonable effluent quality at flows up to an average processing capacity of 1,000 m3/d. At this flow rate, the uncommitted hydraulic reserve capacity for the St. George WPCP is determined to be 84 m³/d, which can service approximately 186 people or 53 additional units. Notwithstanding the above conclusion, a more detailed sampling and comprehensive data analysis program is required to verify the estimated 1,000 m3/d average processing capacity prior to approving any additional development.

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TABLE OF CONTENTS

1.0 INTRODUCTION .......................................................................................................................... 1

1.1 Existing Plant Description .................................................................................................. 1

2.0 PROCESS CAPACITY ASSESSMENT........................................................................................ 3

2.1 Equipment Performance...................................................................................................... 3 2.1.1 Inlet Works.......................................................................................................................... 3 2.1.2 Aeration System.................................................................................................................. 3 2.1.3 Secondary Clarifier ............................................................................................................. 5 2.1.4 Tertiary Sand Filter ............................................................................................................. 6 2.2 Process Performance........................................................................................................... 7 2.2.1 Wastewater Characteristics................................................................................................. 7 2.2.2 Compliance Assessment ..................................................................................................... 8 2.2.3 Process Analysis ............................................................................................................... 10

3.0 UNCOMMITTED RESERVE CAPACITY................................................................................. 12

4.0 CONCLUSIONS........................................................................................................................... 13

5.0 RECOMMENDATIONS.............................................................................................................. 14

5.1 Equipment Modifications.................................................................................................. 14 5.2 Additional Sampling & Monitoring.................................................................................. 15 5.3 Process Modifications....................................................................................................... 15 5.4 Plant Expansion ................................................................................................................ 16

LIST OF FIGURES Figure 1 Process Flow Diagram

Figure 2 Diurnal Flow and Temperature Variations

Figure 3 Effluent BOD Concentrations

Figure 4 Effluent TSS Concentrations

Figure 5 Effluent Ammonia Concentrations

Figure 6 Effluent Total Phosphorous Concentrations

Figure 7 Effluent E. Coli Concentrations

Figure 8 Wastewater Flow Rate and MLSS Concentrations In The Aeration Tank

Figure 9 Temporal Variation of Sludge Volume Index

Figure 10 Variations of SVI and Food-To-Microorganisms Ratio

Figure 11 Variations of SVI and BOD Loading

Figure 12 Variations of SVI and Wastewater Flow Data

Figure 13 Correlation of Selected SVI and Flow Data

Figure 14 Secondary Clarifier Operation Diagram

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LIST OF TABLES

Table 1 Process Unit Descriptions

Table 2 Tertiary Filter Design Parameters

Table 2 Raw Sewage Characteristics

Table 3 Detailed Influent Wastewater Characteristics for 2008

Table 4 Monthly Average Effluent Wastewater Characteristics for 2008

Table 5 Annual Average Operating Parameters

REFERENCES

1. Design Brief – St. George WPCP Rerating, County of Brant, KMK Consultants Ltd., June 2003. 2. Design Report – Design Report - Ministry of the Environment Provincial Sewage Works 1-0189-

69, Police Village of St. George, Township of South Dumfries, Triton Engineering Services Ltd., February 1974

3. Metcalf and Eddy Incorporated. Wastewater Engineering Treatment and Reuse, 4th Edition, McGraw Hill, 2003.

4. MOE Design Guidelines for Sewage Works, Ministry of the Environment, 2008. 5. Procedure D-5-1 MOE Calculating and Reporting Uncommitted Reserve Capacity at Sewage

and Water Treatment Plants

6. St. George Water Pollution Control Plant Annual Performance Report, Ontario Clean Water Agency, 2004 to 2008.

7. St. George WWTP Operations Manual, Ontario Clean Water Agency, March 2005. 8. WEF Manual of Practice No.8, Design of Municipal Wastewater Treatment Plants, 1992.

NOMENCLATURE m3/d Cubic Metres per day BOD Biochemical Oxygen Demand MLSS Mixed Liquor Suspended Solids SVI Sludge Volume Index SRT Solids Retention Tim HRT Hydraulic Retention Time TSS Total Suspended Solids RAS Return Activated Sludge WAS Waste Activated Sludge F/M Food to Microorganism Ratio VSS Volatile Suspended Solids ZSV Zone Settling Velocity TKN Total Kjeldahl Nitrogen TP Total Phosphorous C of A Certificate of Approval

Gamsby and Manne row L im i ted . Gue lph . K i tchene r , L i s towe l Owen Sound 255 Woodlawn Rd W. Suite 210, Guelph, ON N1H 8J1 519-824-8150 fax 519-824-8089 www.gamsby.com

ST. GEORGE WPCP PROCESS CAPACITY ASSESSMENT

COUNTY OF BRANT April 28, 2009

Our File: 109-025 1.0 INTRODUCTION

Gamsby and Mannerow Ltd. (G&M) together with process specialists from Conestoga-Rovers and Associates (CRA) were retained by the County of Brant to assess the process capacity of the St. George Water Pollution Control Plant (WPCP). The St. George WPCP is located at 43 Victor Boulevard and serves the community of St. George by means of a gravity collection system. The St. George WPCP is an extended aeration plant currently operated under contract by the Ontario Clean Water Agency. The plant has a rated capacity of 1,300 m3/d and a design peak flow rate of 3,412 m3/d (Ministry of Environment Certificate of Approval 4045-5QRMK91). Current average day flows are approaching 70% of the WPCP rated capacity and the County has requested that a process capacity assessment be completed prior to approving additional development in the community of St. George. This report includes a process performance assessment of the St. George WPCP. Conclusions and preliminary recommendations for optimization and upgrade are provided at the end of the report.

1.1 EXISTING PLANT DESCRIPTION The St. George WPCP, originally built in 1981 with a capacity of 1,063 m3/d, is a package extended aeration plant with processes including grit removal, secondary clarification, disinfection, tertiary sand filtration, and sludge digestion. The plant was rerated in 2002 to a capacity of 1,300 m3/d with upgrades including new fine bubble diffusers, a third positive displacement air blower, inlet channel grinder, dechlorination facilities and larger aerobic sludge digestion facility. Raw wastewater flows to the plant into two parallel grit channels followed by a channel grinder and a bypass manually raked bar screen. Degritted and shredded wastewater receives biological treatment in a circular extended aeration package plant. The aeration tank is an annular ring equipped with fine bubble diffusers complete with a total of three dedicated positive displacement air blowers (2 duty and 1 standby). Mixed liquor from the aeration tank is settled in a circular secondary clarifier located in the center of the package plant. Return activated sludge (RAS) is transferred from the secondary clarifier to the aeration tank by means of an air lift pump. Excess sludge is temporarily stored in the sludge wasting tank and then transferred to the aerobic digester by means of a submersible pump. Secondary effluent is disinfected using sodium hypochlorite with contact time provided in a chlorine contact chamber. Chlorinated secondary effluent is directed to a travelling bridge sand filter for tertiary polishing. Filter effluent is dechlorinated with sodium bisulphate and flows by gravity into Fairchild Creek through a 355mm diameter outfall. An overall process flow schematic is provided in Figure 1 (back of report) and a summary of process unit descriptions is presented in Table 1 below.

1 Certificate of Approval 4045-5QRMK9 has a typographical error as the peak flow rate is identified as 3,900 m3/d.

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ST. GEORGE WPCP – PROCESS CAPACITY ASSESSMENT COUNTY OF BRANT

Table 1. Process Unit Descriptions Process Unit Description Screening Dual Grit Channel Volume Channel Grinder Design Flow Capacity Manually Raked Bypass Bar Screen

1.9 m3 each 90 L/s (7,800 m3/d) 50mm openings

Aeration Tanks Peak Design Flow Average Design Flow Area of Tank Depth of Tank Volume of Tank Diffusers Blower Capacity

45.0 L/s (3,412 m3/d) 15.0 L/s (1,300 m3/d) 193.6 m2 4.4 m 851.6 m3 Stamford Scientific Int. Fine Bubble 1350 m3/hr at 100 kPa

Secondary Clarifiers Diameter SWD Surface Area Total Volume RAS / WAS Air Lift Pump Phosphorous Removal Scum Removal

10.7 m 3.8 m 86.3 m2

356 m3 15.0 L/s (1,300 m3/d) at 4.0 m Ferric chloride Rotating Scum Plate

Tertiary Filters Travelling Bridge Sand Filter Number of Cells Total Filter Surface Area Active Filter Surface Area

Shallow sand filter with anthracite bed 40 21.2 m2 20.7 m2

Outlet Works Disinfection Chlorine Contact Chamber Volume Chlorine Contact Time and Average Flow Dechlorination

Sodium Hypochlorite 26 m3 29 minutes Sodium Bisulphate

Sludge Handling Aerobic Digester Max. Operating Depth Aerobic Digester Total Volume Aerobic Digester Diffusers Digester Air Blower Capacity Sludge Wasting Tank Max. Volume

4.4 m 277.8 m3

Stamford Scientific Int. Coarse Bubble 16.8 m3/hr at 98 kPa 108 m3

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2.0 PROCESS CAPACITY ASSESSMENT 2.1 EQUIPMENT PERFORMANCE

G&M conducted a site visit to the St. George WPCP on April 15, 2009. Based on observations made during the site visit and discussions with plant operations personnel, various mechanical deficiencies associated with the inlet works, aeration tank, clarifier and tertiary sand filters have been identified.

2.1.1 INLET WORKS Due to limited preliminary treatment at the inlet works, as a consequence of lack of screening and inadequate grit removal, accumulations of rags, plastics and filament material have been observed in the aeration tank as shown in Photograph 1. The presence of non-biodegradable solids such as rags, plastics and grit in the treatment process can lead to mechanical failures of pumps and diffusers due to clogging and excessive wear. Operators have indicated that when the air supply to the aerobic digester is turned off for decanting purposes, the coarse bubble diffusers have a tendency to plug when the solids settle. As a result, operators are reluctant to decant the digester in order to reduce maintenance operations with the diffusers. Without adequate plant screening, ongoing operation and maintenance issues such as clogged diffusers and plugged pumps adds to operational challenges requiring extended hours of maintenance for frequent mechanical failures.

2.1.2 AERATION SYSTEM The aeration tank is equipped with fine bubble diffusers consisting of 10 grids of 12 diffusers per grid for a total of 120 diffusers. Each diffuser grid is removable for cleaning and repairs without draining the aeration tank. Since the new fine bubble diffusers were installed in 2002, operators have indicated that on-going maintenance problems have persisted. Frequent mechanical failures of the diffuser support frame, broken distribution headers and inadequate diffuser grid ballasts have resulted in overall poor performance of the aeration system. Evidence of poor diffuser performance can be identified by examining the surface profile of the aeration tank. As shown in Photographs 2 and 3, numerous large air bubbles can be observed at the liquid surface with an overall uncharacteristic turbulent aeration surface profile suggesting uneven air distribution. For comparison purposes, a typical fine bubble diffuser aeration surface profile should be relatively calm with uniformly distributed small bubbles as shown in Photograph 3. Poor diffuser performance and uneven air distribution can lead to inadequate mixing in the aeration tank and potentially the development of zones with low dissolved oxygen levels. The impact of inadequate oxygen distribution on mixing and aeration is further intensified in plug flow aerations tanks due to the inherent lack of longitudinal mixing characteristics. A comprehensive dissolved oxygen profile of the aeration tank would be required to confirm the presence of these low dissolved oxygen zones.

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Photograph 1. Aeration Tank Rags, Large Bubble in Background and Overall Turbulent Surface Profile.

Photograph 2. Aeration Tank Large Bubble and Overall Turbulent Surface Profile.

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Photograph 3. Typical Aeration Tank Fine Bubble Diffuser Surface Profile (Source: North Perth WWTP)

2.1.3 SECONDARY CLARIFIER The secondary clarifier (Photograph 4) is equipped with scum removal and rotating sludge collection systems. Operators indicated that the floating sludge raking mechanism is broken as one of the scraping blades became dislodged and had to be removed. The sludge raking mechanism has not been repaired as there is only one clarifier which cannot readily be taken out of service. In order to ensure proper functioning of the sludge collection system the clarifier raking arm should eventually be repaired. The return activated sludge (RAS) air lift discharge line is supplied with air from the aeration air supply line. During periods of increased oxygen demand requiring multiple blowers to operate, excessive air flow to the air lift pumps is likely. This may result in excessive RAS rates that may impose a solids loading limitation on the secondary clarifies (see discussion in Section 2.2.3). The inability to adequate control the RAS and consequently the WAS flow rates is considered an operational deficiency.

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Photograph 4. Secondary Clarifier Surficial Solids

2.1.4 TERTIARY SAND FILTER

The travelling bridge tertiary sand filter consists of a sand bed overlain by an anthracite bed. Tertiary filter design parameters are summarized in Table 2 below. While originally designed to handle a peak flow of 3,412 m3/d, operator’s experience suggest that the actual filter capacity is on the order of 1,040 m3/d. Above this flow, operators have indicated that the filters become stressed due to high solids “washout” from the clarifier. Operators indicated that a tertiary filter bypass occurred on June 15, 2008 due to heavy rainfalls and increased inflow and infiltration. The reported average day flow for June 15, 2008 was only 816 m3/d; however, instantaneous flow data was not available. While secondary effluent TSS data is not available, it is likely that the sand filters are operating with a high solids loading rate (see Section 2.2.3 for further discussion). High rate of filter media loss has also been identified as a problem with the tertiary sand filter, which is suggestive of frequent backwash cycles typically caused by high solids loading. Lost filter media is topped up as required. The filter is over 28 years old and the media and porous plate underdrain system have not been replaced as there is only one filter which cannot readily be taken out of service. Typical life expectancy of a tertiary sand filter is about 20 to 25 years.

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Table 2. Tertiary Filter Design Parameters

Description Parameter MOE Guideline

Peak Solids Loading Rate (mg/m2.s) 1 95 51 (shallow bed)

83 (deep bed)

Peak Filtration Rate (L/m2.s) 2 2.2 2.1

Notes: 1. Actual data on secondary effluent not available. Solids loading rate based on an assumed secondary effluent TSS of 50 mg/L under “washout” conditions and a peak flow of 3,412 m3/d.

2. Based on a peak instantaneous flow of 3,900 m3/d (peak factor of 3.0). 2.2 PROCESS PERFORMANCE 2.2.1 WASTEWATER CHARACTERISTICS

Table 3 illustrates the annual wastewater average flows and characteristics for 2004 to 2008.

Annual average flows have increased slightly over the last 3 years with a 2006 to 2008 average of 840 m3/d as compared to a 2004 to 2005 average of 818 m3/d. Based on the annual average concentrations presented in Table 2, the BOD/TSS ratio in the raw wastewater for 2004 through 2008 were 0.67, 0.4, 0.56, 1.3 and 0.74 respectively, resulting in an average of 0.59 (excluding the anomaly of 1.3 in 2005). The typical BOD/TSS ratio in municipal wastewaters is usually around 0.85 to 0.9 and thus while the wastewater BOD concentrations are typical of medium strength municipal wastewater, the relatively low BOD/TSS ratio is reflective of abnormally high influent TSS concentrations. While high infiltration/inflow (I/I) may contribute to increased BOD/TSS ratios, the diurnal variation of flows (Figure 2, back of report) does not support high I/I, with a peaking factor of less than two. It should be noted that high influent concentrations of inert solids (i.e. inorganic and non-biodegradable organic suspended solids) adversely impacts treatment plant performance, particularly in long solids retention time (SRT) systems such as this plant. Further information on the soluble BOD, total and soluble COD, and VSS in the raw wastewater is needed to better understand the implications on treatment system performance. The COD (estimated as double the BOD concentration) to TKN ratios for 2004 through 2008 were 7.5, 14, 13, 12.5, and 12.5 respectively, which is typical for municipal wastewater (with the exception of 2004). Similarly, the COD to TP ratios for 2004 to 2008 are 53, 84, 86, 86, and 83 respectively, which is also typical of municipal wastewater (with the exception of 2004). The concentrations of both nitrogen and phosphorous in the raw wastewater are also typical of medium strength municipal wastewater and are not reflective of any nutrient limitations.

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Table 3. Raw Sewage Characteristics

Parameters Average

± Std. Dev. 2004

Average ± Std. Dev.

2005


2006


2007


2008

Typical* Municipal

Wastewater Flow (m3/d) 813 ± 107 822 ± 87 843 ± 98 812 ± 82 864 ± 116 -- CBOD5 (mg/L) 124 ± 29 181 ± 100 169 ± 48 194 ± 57 161 ± 59 190 TSS (mg/L) 186 ± 54 451 ± 388 298 ± 189 151 ± 92 217 ± 59 210 TKN (mg/L) 33 ± 10 26 ± 7 26 ± 3 31 ± 7 26 ± 9 40 TP (mg/L) 4.7 ± 1.1 4.3 ± 1.8 3.9 ± 0.5 4.5 ± 4.1 3.9 ± 1.0 7 pH 7.8 ± 0.2 7.6 ± 0.1 7.8 ± 0.2 7.8 ± 0.2 7.8 ± 0.4 --

*Metcalf and Eddy, 2003.

2.2.2 COMPLIANCE ASSESSMENT

The plant performance data reviewed as part of this assessment primarily included influent and final effluent characteristics as well as aeration tank MLSS and 30-minute settling volume. Without additional unit performance data, the process analysis detailed herein is constrained by the available data. The plant monitoring program primarily focuses on the parameters stipulated in the C of A and is thus more geared towards compliance assessment than optimization of plant operations. The gaps in the data that hinder thorough process analysis will be elaborated upon later. Figure 2 (back of report) illustrates the diurnal variation of wastewater flows and temperatures for 2004 to 2008. It is evident from Figure 2 that the plant is operating below its hydraulic design capacity of 1,300 m3/d (average) and 3,412 m3/d (peak). Wastewater temperature ranged predominantly from 10 to 20°C and averaged around 15°C. At an average temperature of 15°C process kinetics accommodates full nitrification. However, at 10°C biokinetics is limited as the activity of nitrifying bacteria becomes restricted. Figures 3 through 7 (back of report) depict the final effluent BOD, TSS, ammonia, TP, and E. Coli concentrations, respectively, relative to both the design objectives and Ministry of Environment (MOE) compliance criteria. Analysis of the compliance data for 2004 to 2008 reveals the following:

• Only one BOD exceedance of the compliance limit and 8 exceedances of the design objectives were observed;

• Only two TSS exceedances of the compliance limit and 22 exceedances of the design objectives were observed;

• Only two ammonia exceedances of the compliance limits were observed;

• Only four E. Coli exceedances of the compliance limit and 8 exceedances of the design objectives were observed; and

• Numerous exceedances of both the compliance limit and design objectives for TP were observed.

A summary of influent and effluent characteristics for 2008 is presented in Tables 4 and 5, respectively.

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Table 4. Detailed Influent Wastewater Characteristics for 2008

Month cBOD5 (mg/L)

Total Suspended

Solids (mg/L)

Total Phosphorus

(mg/L)

Total Kjeldhal Nitrogen (mg/L)

January 174 219 3.1 23.7 February 197 225 3.4 25.9

March 110 206 2.5 20.4 April 131 162 3.5 21.7 May 141 171 4.8 27.7 June 130 233 5.4 33.0 July 182 233 5.0 30.8

August 199 167 3.7 21.0 September 108 194 4.3 36.0

October 188 192 4.0 20.2 November 177 261 3.3 26.7 December 221 395 3.4 26.7

Yearly Average 161 217 3.9 26.0

Table 5. Monthly Average Effluent Wastewater Characteristics for 2008

Month Temp. (°°°°C)

cBOD5 (mg/L)

Total Suspended

Solids (mg/L)

Total Phosphorus

(mg/L)

Total Kjedhal Nitrogen (mg/L)

Total Ammonia Nitrogen (mg/L)

January 11.8 4.5 1.6 0.2 0.7 0.2 February 10.4 3.5 2.0 0.2 0.8 0.3

March 10.7 5.5 2.2 0.2 1.5 0.7 April 12.3 3.5 1.9 0.2 1.0 0.4 May 14.3 3.3 1.3 0.3 1.2 0.3 June 17.2 2.0 2.1 0.3 0.1 0.1 July 19.2 3.0 1.5 0.3 0.8 0.2

August 19.7 4.0 4.2 0.4 2.5 0.6 September 19.5 3.0 2.2 0.3 2.0 0.2

October 17.5 2.0 1.8 0.3 0.7 0.4 November 15.7 2.5 1.2 0.2 0.5 0.1 December 12.1 2.5 1.3 0.1 1.4 0.1 Average 15.0 3.2 1.9 0.2 1.1 0.3 Design

Objective N/A 5.0 5.0 0.20 N/A

2.01 5.02

Exceedances N/A 3 5 110 N/A 0 MOE

Compliance Criteria

N/A 10.0 10.0 0.3 N/A 3.01 5.02

Exceedances N/A 0 0 61 N/A 0 Notes: 1Summer limit, 2Winter limit

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It thus appears that the plant is readily meeting its MOE compliance requirements for BOD, TSS, ammonia, and E. Coli. The numerous TP exceedances are attributed to inadequate chemical addition for soluble phosphorus removal and are not associated with the inability of the filtration system to remove suspended solids.

2.2.3 PROCESS ANALYSIS Figure 8 (back of report) depicts the temporal variations of wastewater flows and aeration tank MLSS concentrations for 2004 to 2008 while Table 6 summarizes the annual averages of food-to-microorganisms (F/M), MLSS, SVIs and volumetric loadings. Annual average volumetric BOD loadings ranged from 0.1 to 0.18 kg BOD/m3⋅d, well within the 0.1 to 0.3 kg BOD/m3⋅d range for extended aeration plants (Metcalf and Eddy, 2003). Annual average MLSS concentrations ranged from 4,328 to 4,928 mg/L which are at the higher end of the 2,000 to 5,000 mg/L reported for extended aeration plants. Although there is no available data on the aeration tank MLVSS, assuming a 60% volatile component of MLSS (in light of the low raw wastewater BOD/TSS ratio and long SRT) the F/M ratios of Table 6 translate to a range of 0.045 to 0.062 g BOD/g MLVSS⋅d within the 0.04 to 0.1 g BOD/g MLVSS⋅d typical range of extended aeration plants. The MLSS data supports that the plant is running at approximately 40 days SRT; however this figure cannot be confirmed due to lack of available data. Table 6. Annual Average Operating Parameters Parameter 2004 2005 2006 2007 2008

BOD Loading (kg/d) 99 ± 26 145 ± 84 140 ± 48 146 ± 55 138 ± 50

Vol. Loading (kg/m3⋅d) 0.12 ± 0.03 0.18 ± 0.10 0.17 ± 0.06 0.176 ± 0.067 0.167 ± 0.060

MLSS (mg/L) 4328 ± 687 4708 ± 703 4494 ± 763 4891 ± 982 4928 ± 858

SVI (mL/g) 162.9 ±

46.6 157.0 ±

26.1 136.9 ±

33.0 108.6 ±

39.1 144.9 ±

39.1

F/M (gBOD/gTSS⋅d) 0.027 ± 0.008 0.031 ± 0.010

0.033 ± 0.009

0.037 ± 0.005

0.035 ± 0.014

F/M (gBOD/gVSS⋅d)* 0.045 ± 0.013 0.052 ± 0.017

0.055 ± 0.015

0.062 ± 0.008

0.058 ± 0.023

* F/M is based on 60% volatile content of mixed liquor Figure 9 (back of report) depicts the temporal variation of SVI with a range as low as 50 mL/g to as high as 225 mL/g clearly demonstrates that the plant is operating with very dynamic sludge settling characteristics, which has a significant impact on the operation and control of the facility. It should be noted that the acceptable range of SVIs, which is indicative of good settling, is 80 to 120 mL/g. Solids settling is severely hampered at the plant, resulting in significant sludge bulking, as reflected by the high average SVIs reported in Table 6. Figure 10 (back of report) shows the temporal variation of both F/M and SVI and despite the scatter the trend of simultaneous increases in F/M and SVI is discernable, particularly in the data from mid-June 2007 to December 2008. This trend indicates that sludge bulking is not associated with low F/M filamentous organisms but rather increased loadings. Figures 11 and 12 (back of report) both show that the increase in SVI was consistent with an increase in BOD loading and flow. Since

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the plant is only treating domestic wastewater without any substantial industrial or commercial sources, BOD loading is directly proportional to flow, and hence the satisfactory correlation of SVI trends with both flow and BOD loadings. Discussions with the plant operators confirmed that at times, the DO concentrations were at or below 0.5 mg/L, with potentially lower values at other locations as a result of the poor mixing (see discussion in Section 3.3.2). There are numerous filamentous microorganisms that can proliferate at low DO or on anaerobic biodegradation products. Flow and SVI data from July 1, 2007 to December 31, 2008 was further scrutinized as shown in Figure 13 (back of report). Despite the significant scatter, the trend of SVI > 150 mL/g at flows > 1,000 m3/d is undisputable. While SVIs > 150 mL/g were frequently observed at flows in the range of 700 to 1,000 m3/d, SVIs fluctuated mostly in the 100 to 150 mL/g range at the aforementioned flows. However, whenever flows increased beyond 1,000 m3/d invariably SVIs were > 150 mL/g. Using the secondary clarifier surface area of 89.4 m2 (Table 2), the average MLSS concentration of 4,928 mg/L (Table 6), RAS recycle rate of 1,300 m3/d, the 2008 average and peak daily wastewater flows of 864 m3/d and 1,501 m3/d the estimate annual average and peak day solids loading are 120 kg/m2⋅d and 154 kg/m2⋅d respectively. Typical average and peak solids loading rates for extended aeration plants are 120 and 170 kg/m2⋅d (Metcalf and Eddy, 2003). It must be asserted that the aforementioned typical values pertain to sludges with acceptable settling characteristics (i.e. SVIs of 80 to 120 mL/g). Figure 14 (WEF Manual of Practice No. 8, 4th Edition, p. 11-104) shows the impact of SVI on limiting (maximum) solids loading to the clarifiers. At 1% solids concentration in the RAS the limiting flux declines from 215 kg/m2⋅d for an SVI of 150 mL/g to 122 kg/m2⋅d for an SVI of 200 mL/g. At the 1.5% RAS solids, the impact of SVI on solids loading is even more pronounced, as reflected by a drop from 73 kg/m2⋅d at an SVI of 150 mL/g to 24 kg/m2⋅d at an SVI of 200 mL/g. Based on the above information, secondary clarification is limiting the overall performance of the plant as a serious bottleneck, exacerbated by relatively high sludge SVI. The secondary clarifier depth is 3.8 m and the operators indicated that they maintain a sludge blanket thickness of 2 m or greater, leaving only 1.8 m for sludge settling and thickening. This restricted clarifier volume is inadequate for proper clarification, potentially resulting in solids washout to the tertiary filters. During the site visit on April 15, 2009, the clarifier appeared to have high solids content near the surface as shown in Photograph 1. More data on the secondary effluent quality as well as waste sludge flows and solids concentration is needed to further assess clarification efficiency, although it is our opinion that the plant cannot handle flows in excess of 1,000 m3/d with its current high SVIs of about 150 mL/g. Although we do not have performance data to assess the filtration system, it is anticipated that excessive solids carryover in the secondary effluent as a result of the clarifier overload will ultimately overstress filtration, resulting in excessive backwash and potentially exceedance of the suspended solids criterion.

Furthermore, due to recirculation of backwash water to the head of the plant, excessive backwashes may be detrimental to plant operation. Although the available data is insufficient to determine the operating SRT for the treatment system, the SRT estimated on the basis of the annual average waste activated sludge flow rate of 7.0 m3/d, and an estimated 1.2% solids concentration in the WAS is about 40 days. At this sludge age, the estimated plant wastage of about 103 kg SS/d at 864 m3/d is comparable on a prorated basis to the 176 kg SS/d at 1,300 m3/d used in the St. George WPCP Rerating Design Brief

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(2003) to design the digester. Hauled biosolids data for 2007 indicated that a total of 1,849 m3 at an average TSS concentration of 23,933 mg/L was hauled off-site. For 2008, 2,426 m3 at an average TSS concentration of 20,550 mg/L were hauled. Based on the biosolids data, the plant disposed of 0.77 kg SS/kg BOD in 2007 and 0.96 kg SS/kg BOD in 2008, after aerobic digestion. Such sludge production rates are abnormally high for extended aeration plants where biological sludge yields before aerobic digestion is about 0.31 g SS/g BOD (at the typical SRT of 30 days, with a decay coefficient of 0.06 d-1 and true yield of 0.86 g SS/g BOD or 0.6 g VSS/g BOD). Although the efficiency of the aerobic digester appears to be low, the high yield observed in this plant may be attributed to a high concentration of non-biodegradable influent suspended solids, as elaborated in Section 2.1.1. Furthermore, while the 2008 hauled biosolids data translates to an average of 137 kg SS/d, the prorated aerobically digested sludge value (at 2008 average flows) in the 2003 Design Brief is only 101 kg SS/d. It is thus evident that the plant is handling more solids than originally anticipated and designed for. It appears that both the solids removal processes (i.e. secondary clarification and filtration) as well as the sludge digestion systems are severely constrained and represent significant process bottlenecks. It is our understanding that the solids dewatering centrifuge at Paris WPCP, which handles the biosolids from St. George plant, has very limited capacity and is governing the frequency and quantity of solids wastage and final disposal from the St. George WPCP. No comments on the mechanisms of ammonia removal at the plant can be made due to lack of pertinent data resulting in the fact that both biological treatment by nitrification and chemical treatment by breakpoint chlorination contribute to overall ammonia removal. The plant chlorinates with sodium hypochlorite upstream of filtration. Usually, chlorination as the final treatment step is after filtration. The need to control biological growth in the filters by pre-chlorination suggests that biodegradable organics may be escaping in the clarifier effluent.

3.0 UNCOMMITTED RESERVE CAPACITY

In accordance with Ministry of Environment Procedure D-5-1, the uncommitted reserve capacity of the St. George WPCP is determined from calculating the hydraulic rated plant capacity minus the current average sewage flows less the capacity allocated to unconnected servicing commitments. The St. George WPCP has a rated design capacity of 1,300 m3/d as indicated in Certificate of Approval number 4045-5QRMK9. However, as a result of process deficiencies as described in Section 2.0 above, the actual capacity of the WPCP is estimated to be 1,000 m3/d. The uncommitted reserve hydraulic capacity of the St. George WPCP is calculated using the following formula:

Cu = Cr –

( )H

PFL ××

Where, Cu = Uncommitted hydraulic reserve capacity (m³/d) Cr = Hydraulic reserve capacity (m³/d) L = Number of unconnected approved lots P = Existing connected population H = Number of connected residential lots F = Average daily flow per capita (m³/capita/d)

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The average day flow for 2008 was 864 m3/day (see Table 3). Therefore, the hydraulic reserve capacity of the system is estimated as: Cr = 1,000 – 864 = 136 m³/d Based on information collected from the County of Brant’s Planning Department, there were 33 unconnected committed residential lots in 2008 that either are now, or will eventually be serviced by the St. George WPCP. These lots include 31 lots in the Sunnyside subdivision (i.e. Taylor Road), one lot on Russell Crescent and one lot severance on Beverly Street. The County confirmed that each of these lots represents only one residential unit. As per the County of Brant’s Engineering Standards, the average daily domestic flow is 0.45 m3/capita/day and the number of people per residential unit is 3.5. Consequently, the uncommitted reserve capacity of the plant is: Cu = 136 – (33 × 0.45 × 3.5) = 136 – 52 = 84 m³/d An uncommitted reserve capacity of 84 m³/d can service 186 people, which is approximately equivalent to 53 units. The above calculation does not include any flows from the former Parmalat facility, which closed in 2003. Furthermore, the community of St. George does not have any major industries and/or commercial developments and therefore, these flows are accounted for by means of the per capita flow criteria of 0.45 m3/capita/day.

4.0 CONCLUSIONS Notwithstanding the correction of the mechanical deficiencies detailed in Section 2.1, the aforementioned process analysis clearly substantiates that the plant cannot handle its rated design capacity of 1,300 m3/d for the following reasons: 1. The plant suffers from sludge bulking, primarily associated with increased flow and BOD

loadings, although the microbiological characterization of filamentous bacteria is largely unknown;

2. The abnormally high sludge production rates, relative to both design and typical extended

aeration rates constrains sludge processing capacity which coupled with limited biosolids processing at Paris WPCP necessitates operation at long SRT and high MLSS, thus overloading the secondary clarifier;

3. The limited aerobic digestion capacity mandates sludge storage in the clarifier as reflected

by maintenance of a very high sludge blanket (2 m or more), constituting greater than 53% of the overall clarifier depth;

4. The simultaneous increase in SVI with flow and BOD loading combined with occasional

occurrence of anaerobic zones point to potential limitations in aeration system performance and/or design.

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5. Based on the limited data available, we estimate that the maximum current processing

capacity of the St. George WPCP is about 1,000 m3/d. The maximum processing capacity can only be reconfirmed by more detailed and comprehensive data.

In summary, the St. George WPCP has various mechanical and processing deficiencies that limit the maximum processing capacity of the plant. Based on limited available data, we estimate that the existing plant (without any improvements) can achieve reasonable effluent quality at flows up to an average processing capacity of 1,000 m3/d. At this flow rate, the uncommitted hydraulic reserve capacity for the St. George WPCP is determined to be 84 m³/d, which can service approximately 186 people or 53 additional units. Notwithstanding the above conclusion, a more detailed sampling and comprehensive data analysis program is required to verify the estimated 1,000 m3/d average processing capacity prior to approving any additional development.

5.0 RECOMMENDATIONS

5.1 EQUIPMENT MODIFICATIONS

Headworks upgrades to include automatically cleaned screens and improved grit removal should be considered in order to limit the amount of non-biodegradable solids in the system and reduce overall operational and maintenance problems. Based on the photographic documentation of improper mixing of the fine bubble aeration system, it is imperative that the aeration system oxygenation and mixing capacities be determined both in its current state, and after repair and cleaning of the diffusers. It must be asserted that the cleaning of the diffusers and potentially the air headers is a short-term solution, which does not alleviate the long-term impact of mechanical deficiencies. However, given the resources and time required to rectify the aforementioned deficiencies, it is recommended that the operational staff temporarily repair and clean the fine bubble diffusers and conduct oxygenation capacity and mixing tests before and after cleaning/repair. Repairs of the secondary clarifier raking arm are recommended, however, it is recognized that this work is not straightforward as there is only one clarifier is service. This work may need to be delayed until the second treatment train is constructed (see Section 5.4). Upgrades to the air lift pump to provide more efficient pumping and RAS/WAS control is also warranted. Scheduled maintenance of the tertiary filter is also required. Following improvements to the secondary clarifier, it is recommended that the filter be taken out of service and the sand/ anthracite media and porous plate underdrain be replaced. This work should only be undertaken provided the secondary effluent can temporarily meet compliance criteria (may require addition of enhanced coagulant chemicals in the secondary clarifier). However, if the secondary clarifier continues to be overloading with solids, filter media replacement will not alleviate the existing flow capacity restriction of the tertiary filter.

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5.2 ADDITIONAL SAMPLING & MONITORING More detailed characterization of the influent raw sewage to the aeration tank, aeration tank contents, secondary effluent, final effluent, and waste activated sludge is warranted. All the aforementioned waste streams should be analyzed for total and soluble (filtered through 0.45 mm filter paper) BOD, TKN, and TP to better characterize the particulate and soluble fractions of organics, nitrogen and phosphorus. Additionally, waste streams should be analyzed for TSS, VSS, ammonia, nitrates, nitrites, and alkalinity. It must be asserted that this level of detailed analysis of the aeration tank, secondary effluent, and waste activated sludge is necessitated by the atypical operation of the clarifier with a very high sludge blanket, which may induce changes in soluble organics, nitrogen, and phosphorus. Settling characteristics of mixed liquor solids should be measured not only in terms of SVI but also zone settling velocity (ZSV). Furthermore, selected samples of the mixed liquor should be microbiologically profiled to delineate the filamentous microorganisms. Real-time measurements of oxidation-reduction potential (ORP) and dissolved oxygen at selected key locations in the aeration tank are recommended. TSS, VSS, COD, and SCOD concentrations in the aerobic digester as well as the digester supernatant returned back to the aeration tank should also be monitored to facilitate assessment of digester efficiency. The digester supernatant should also be microbiologically characterized as conditions in the aerobic digesters are naturally conducive to the proliferation of specific types of filamentous organisms i.e. the ones that can thrive at low F/M ratios. Additionally, in order to evaluate the filtration system capacity, instantaneous flow data together with hourly secondary and filtered effluents TSS data (based on hourly composite samples) must be collected during peak flow events. Additional sampling and monitoring data should be used to affirm the estimated processing capacity of the plant and be utilized in the design process for future plant expansions.

5.3 PROCESS MODIFICATIONS The wastewater characteristics discussed in Section 2.2.1 highlight the relatively high influent TSS to the extended aeration plant. Should the recommend characterization (Section 5.2) confirm the presence of non-biodegradable volatile suspended solids and/or inorganic suspended solids, both of which tend to be concentrated in the aeration tank by a factor of 40 times (i.e. current SRT/HRT conditions), the plant inevitably must run at high MLSS concentrations due to the severely constrained biosolids processing capacity leading to clarification overload and filtration system stress. In such a case, the recommended solution for the sludge bulking problems is the incorporation of a selector upstream of the aeration tank, to which the RAS is redirected. The selector may need to be designed to operate in an anaerobic, anoxic, or aerobic mode to allow maximum flexibility. The selector would need to be mechanically mixed without excessive agitation to keep the solids in suspension and minimize oxygen transfer. To operate under anoxic conditions, the nitrified mixed liquor must be recirculated from the aeration tank to the selector.

Another advantage inherent to anaerobic and anoxic selector is the hydrolysis of particulate organic matter potentially including non-biodegradable VSS, which will reduce the overall sludge yield. A reduction in the overall organic loading to the plant can also be achieved with a selector. Furthermore, if filament proliferation was an issue, the selector process configuration is known to suppress filament growth and reduce polysaccharides production, thus improving overall sludge settling characteristics.

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5.4 PLANT EXPANSION Although the plant appears to still have some available hydraulic capacity, restricted processing capacity coupled with the numerous mechanical deficiencies do not warrant any increase in wastewater flows without conducting a more detailed and comprehensive analysis to confirm the estimated 1,000 m3/d annual average processing capacity. It should be noted that based on a 1,000 m3/d annual average processing capacity, the plant is currently running at 86% capacity (92% with the additional committed capacity), and thus plans for expansion should be undertaken as soon as possible. In order to meet future servicing requirements for the St. George catchment area, considerations for plant expansion by twinning the existing plant should be considered including an evaluation of disinfection alternatives and biosolids management upgrades. In this way, during periods of low flow, individual treatment processes can be taken out of service without significant process interruptions for necessary maintenance activities.

All of which is respectfully submitted. GAMSBY AND MANNEROW LIMITED Per:

Paul McLennan, P.Eng Per:

Matthew Ballaban, M.Sc., P.Eng

109-025: Process Capacity Assessment of the St. George WPCP Figure 2. Diurnal Flow and Temperature Variations

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109-025: Process Capacity Assessment of the St. George WPCP Figure 3. Effluent BOD Concentrations

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109-025: Process Capacity Assessment of the St. George WPCPFigure 4. Effluent TSS Concentrations

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109-025: Process Capacity Assessment of the St. George WPCP Figure 5. Effluent Ammonia Concentrations

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109-025: Process Capacity Assessment of the St. George WPCP Figure 6. Effluent Total Phosphorous Concentrations

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109-025: Process Capacity Assessment of the St. George WPCPFigure 7. Effluent E. coli Concentrations

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109-025: Process Capacity Assessment of the St. George WPCP Figure 8. Wastewater Flowrate and MLSS Concentrations in the Aeration Tank

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109-025: Process Capacity Assessment of the St. George WPCP Figure 9. Temporal Variation of Sludge Volume Index

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109-025: Process Capacity Assessment of the St. George WPCP Figure 10. Variations of SVI and Food-to-Microrganisms Ratio

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109-025: Process Capacity Assessment of the St. George WPCP Figure 11. Variations of SVI and BOD Loading

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109-025: Process Capacity Assessment of the St. George WPCP Figure 12. Variations of SVI and Wastewater Flow Rate

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109-025: Process Capacity Assessment of the St. George WPCP Figure 13. Correlation of Selected SVI and Flow Data

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Figure 14: Secondary Clarifier Operation Diagram

(adopted from WEF Manual of Practice No. 8, 4th Edition, p. 11-104)

109025_ProcessCapacityAssessment_revised_2009-06-04.doc109025-Figures1-14

ST. GEORGE W ATER POLLUTION CONTROL PLANT PROCESS …€¦ · 6. St. George Water Pollution Control Plant Annual Performance Report, Ontario Clean Water Agency, 2004 to 2008. 7. St.

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