sewpcc upgrading/expansion preliminary … upgrading/expansion preliminary design report section 22...

SEWPCC Upgrading/Expansion Preliminary Design Report

SECTION 22 – ADDITIONAL TREATMENT OPTIONS

Table of Contents

22.0 ADDITIONAL TREATMENT OPTIONS.......................................................................22.1 22.1 INTRODUCTION..........................................................................................................22.1

22.1.1 Background ....................................................................................................22.1 22.1.2 Purpose ..........................................................................................................22.2 22.1.3 Design Requirements .....................................................................................22.2

22.2 PROCESS DESCRIPTIONS........................................................................................22.2 22.2.1 Option G: Activated Sludge/High Rate Modified Johannesburg BNR

with IFAS Media and Side Stream Treatment ................................................22.2 22.2.2 Option K: High Purity Oxygen Phoredox Process (A/O) followed by

Separate Stage Nitrification in a Moving Bed Biofilm Reactor (MBBR), Post-Nitrification with Methanol Addition and Side Stream Treatment ...........22.4

22.2.3 Option L: High Purity Oxygen BNR Followed by Separate Stage Nitrification in Moving Bed Biofilm Reactor (MBBR) and Side Stream Treatment .......................................................................................................22.7

22.2.4 Option C-1: High Rate Activated Sludge Process with Chemical Phosphorus Removal and Side Stream Treatment for Wet Weather Flows (CEPT)..........22.9

22.2.5 Option K-1: HPO with Chemical Phosphorus Removal followed by Separate Stage Nitrification in a Moving Bed Biofilm Reactor (MBBR), Post-Denitrification with Methanol Addition and Side Stream Treatment for Wet Weather Flows (CEPT) ......................................................................22.9

22.2.6 Options L-1: HPO with Chemical Phosphorus Removal followed by Separate Stage Nitrification in Moving Bed Biofilm Reactor (MBBR) and for Wet Weather Flows (CEPT) ....................................................................22.10

22.3 PROCESS MODELING .............................................................................................22.10 22.3.1 Limitations of Process Modeling...................................................................22.10 22.3.2 Modeling Approach.......................................................................................22.11 22.3.3 Model Development and Assumptions .........................................................22.11 22.3.4 Modeling Results ..........................................................................................22.12 22.3.5 Evaluation of Bioreactor Volumes Using Process Simulation Software .......22.12 22.3.6 Secondary Clarifier Sizing ............................................................................22.13

22.4 FACILITY LAYOUT ....................................................................................................22.13 22.4.1 Site Plan .......................................................................................................22.13 22.4.2 Common Components..................................................................................22.13

22.5 BIOREACTORS .........................................................................................................22.15 22.5.1 Purpose ........................................................................................................22.15 22.5.2 Existing Facility.............................................................................................22.15 22.5.3 Proposed Facility ..........................................................................................22.15 22.5.4 Constructability .............................................................................................22.17

22.6 SOLIDS SEPARATION (SECONDARY CLARIFIERS)..............................................22.18

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SEWPCC UPGRADING/EXPANSION PRELIMINARY DESIGN REPORT

22.6.1 Purpose ........................................................................................................22.18 22.6.2 Existing Facility.............................................................................................22.18 22.6.3 Proposed Facility ..........................................................................................22.18 22.6.4 Constructability .............................................................................................22.19

22.7 PRIMARY SLUDGE FERMENTATION......................................................................22.20 22.7.1 Purpose ........................................................................................................22.20 22.7.2 Existing Facility.............................................................................................22.20 22.7.3 Proposed Facility ..........................................................................................22.20 22.7.4 Constructability .............................................................................................22.20

22.8 INTERMEDIATE PUMPING STATION ......................................................................22.21 22.9 METHANOL STORAGE AND FEED SYSTEM..........................................................22.21 22.10 SOLIDS HANDLING ..................................................................................................22.22

22.10.1 Purpose ........................................................................................................22.22 22.10.2 Existing Facility.............................................................................................22.22 22.10.3 Projected Sludge Quantities .........................................................................22.22 22.10.4 Proposed Facility ..........................................................................................22.22

22.10.4.1 Sludge Thickening .......................................................................22.23 22.10.4.2 Sludge Storage............................................................................22.23

22.10.5 Constructability .............................................................................................22.24 22.11 EFFLUENT DISINFECTION ......................................................................................22.24

22.11.1 Purpose ........................................................................................................22.24 22.11.2 Design Flows................................................................................................22.24 22.11.3 Existing Facility.............................................................................................22.25 22.11.4 Proposed Facility ..........................................................................................22.25 22.11.4 Constructability .............................................................................................22.26

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SEWPCC UPGRADING/EXPANSION PRELIMINARY DESIGN REPORT

22.0 Additional Treatment Options

22.1 INTRODUCTION

22.1.1 Background

Section 8 – BNR Process Options presented twenty-two alternatives for upgrading the SEWPCC to achieve the effluent criteria in the Environment Act Licence for the SEWPCC. Based on the preliminary evaluation in Section 8, twelve of the process options were screened out for technical reasons. The remaining ten short-listed options were evaluated in further detail and screened by the Project Team at Workshop No. 1, which was held on May 6, 2006. At this Workshop, the Project Team selected the four treatment process (Options B, C, D and I) that they felt were the most appropriate options and warranted further evaluation. These four options were then developed in further detail and are explained in Section 17 – Facility Layouts.

The City retained an Independent Review Team (IRT) to review and comment on the Draft SEWPCC PDR. An IRT review Workshop was held on August 20, 2007. At this Workshop it was suggested by the IRT to develop a treatment option around the existing HPO system to the same level of detail as the four short-listed options presented in Section 17. This additional treatment options is:

• Option K - High Purity Oxygen Phoredox process (A/O) followed by separate stage nitrification in a Moving Bed Biofilm Reactor (MBBR), post-denitrification with methanol addition and side stream treatment.

In addition to Option K, the Project Team decided that Option G, developed previously by Stantec as one of the ten short-listed options, deserved further review for the purpose of completeness of the SEWPCC PDR. This additional treatment option is described as follows:

• Option G - Activated Sludge/High Rate Modified Johannesburg BNR process with IFAS media and sidestream treatment.

On August 15, 2007 the City received a proposal for the development of a proposed treatment option from M2T Technologies. As presented, this proposal did not meet the effluent criteria, but it was felt that the technology could have potential for the SEWPCC project. Therefore, the Project Team directed Stantec to develop this option along with the other two additional treatment options. This option is discussed as:

• Option L - High Purity Oxygen Activated sludge BNR followed by separate stage nitrification in Moving Bed Biofilm Reactor (MBBR) with Side Stream Treatment.

Suppliers have also challenged the City’s position with regard to biological nutrient removal. The Terms of Reference (TOR) for engineering services for the SEWPCC project specified the implementation of a biological nutrient removal process. The four treatment alternatives (Option

22.1

SEWPCC UPGRADING/EXPANSION PRELIMINARY DESIGN REPORT Additional Treatment Options March 31, 2008

22.2

B, C, D and I) presented in Section 17 and the three additional treatment options (G, K and L) detailed in this section, achieved this objective. However, suppliers claimed that the TOR should have allowed for chemical Phosphorus (P) removal in order to take advantage of significant cost savings. Since several of the options that had been evaluated for biological nutrient removal could be easily reconfigured for chemical P removal, it was decided that for the purpose of completeness of the report to evaluate three chemical P removal options. These three (3) alternatives are essentially the same as Option C, K and L except that instead of biological phosphorus removal, chemical precipitation of phosphorus is utilized.

The basic principle of chemical phosphorus removal is precipitation followed by clarification. For the purpose of the evaluation alum addition was considered to precipitate the soluble phosphorus that remains following uptake (through bacterial synthesis). The chemical P removal alternatives are referred to as Options C-1, K-1 and L-1.

22.1.2 Purpose

This section provides details associated with the proposed improvements that are required to meet the design effluent quality criteria, for each of the six additional treatment options. Each of the BNR options are discussed in detail, starting with a process description and following through a discussion of each component of the treatment processes involved. The intent is to provide similar information for these three additional BNR treatment options as was provided for the four short-listed options. The chemical phosphorous removal options are modifications of previously detailed options and therefore only a description is provided. This information is then used in Section 24 – Short-Listed Treatment Options to compare and rate these three options along with the earlier short-listed options.

22.1.3 Design Requirements

Section 7 - Design Requirements presents the key design requirements that form the basis of the evaluations in this section. While it is recognized that Manitoba Conservation has clarified some of the assumptions used in the earlier work, the design philosophies and approaches remain consistent with those used for the other four short-listed options in order to facilitate a fair evaluation process. None of the clarifications provided by Manitoba Conservation are deemed to favor any of the alternatives being evaluated.

22.2 PROCESS DESCRIPTIONS

22.2.1 Option G: Activated Sludge/High Rate Modified Johannesburg BNR with IFAS Media and Side Stream Treatment

Option G includes a high rate Modified Johannesburg (MJ) BNR process and side stream physical-chemical treatment of flows > 175 ML/d. The MJ process consists of a sequence of pre-anoxic, anaerobic, anoxic and aerobic cells in series to remove organics, solids, nitrify, denitrify and remove phosphorus using a similar sequence of biological reactors as Option C.


This option was presented as Option G and was short-listed as one of the twelve BNR options for the SEWPCC. However, this option was dropped in the BNR Workshop when the twelve process options were narrowed down to four (4) options for future evaluation.

In Option G, raw wastewater is introduced to the pre-anoxic cell (no oxygen) along with return activated sludge (RAS) recycled from the final clarifiers. In this zone, the RAS is denitrified to protect the anaerobic zone from nitrates. In the next cell (anaerobic zone), volatile fatty acids (VFA) generated from the primary sludge are contacted with the activated sludge (AS) /wastewater mixture and specific bio-P organisms that initiate a metabolic pathway to store carbon as poly hydroxyl butyrate (PHB) internally under anaerobic conditions (no oxygen, no nutrients). In the next cell in the series, nitrates recycled at a high rate from the last aerated cell in the bioreactor are denitrified by denitrifying bacteria using carbon in the incoming waste as a source of carbon. Nitrogen is removed from the wastewater as nitrogen gas. This series of pre-anoxic, anaerobic, anoxic cell which are mixed vertically using propeller mixers, occupy about 36 percent of the bioreactor volume.

22.3

One of the key features of this option (as compared to the option C presented earlier) is the use of a neutral buoyancy plastic media or biofilm carrier elements on which attached growth of micro-organisms takes place in the aerobic zones of the bioreactor. Besides the suspended

growth MLSS (which varies from 3000 ~ 4000 mg/L), attached growth or biofilm occurring on the surface of the media effectively increases the overall biomass inventory in the aerobic zone by 25 percent to 40 percent (thereby reducing the required aerobic volume by about 25 ~ 30 percent). This combined suspended growth and attached growth is referred to as the integrated fixed film activated sludge process or IFAS. The incorporation of fixed-film biomass in the aeration tank increases the biomass inventory of the system without actually increasing the mixed liquor

suspended solids and solids loading to the secondary clarifier (since the media is retained within the aeration tank). The increased biomass also effectively increases the solids retention time (SRT) or sludge age of the system by about 2.5 times which allows nitrification at low temperature or shorter system SRT. The larger mass of organisms in the bioreactor facilitate a very stable biological process particularly at high flows and loads as there is less potential for the washout of nitrifying organisms.

An aeration grid located at the bottom of the reactor supplies oxygen to the biofilm along with the mixing energy required to keep the media suspended and completely mixed within the reactor. Media retention screens are incorporated in the tank walls at the end of the aerobic zone to retain the media within the aerobic tanks. Periodically a portion of the attached growth will slough off and become part of the MLSS which will settle out in the secondary clarifiers and either be returned as RAS or wasted to remove solids, BOD and phosphorus. Primary sludge fermentation will be required to generate VFA’s for biological phosphorus removal.


22.4

Although several types of media are available in the market, for the purpose of this evaluation the concept was developed around polyethylene media with a density slightly lower than water. The key design features of this proprietary media are summarized below:

• Length = 7 mm

• Diameter = 9 mm

• Specific Area = 500 m2/m3

• Percent of tank filled with media = 40 percent

• Media Specific Volume = 0.13 m3/m3

• Type of aeration system = Medium Coarse bubble

• Design and capacity of media retention screen = 304 L SS, 222 ML/d with maximum headloss of 50 mm

A process schematic of this option is shown in Figure 22.1.

Advantages

• IFAS media reduces the overall bioreactor size required for the MJ process.

• IFAS media provides protection of nitrifiers for high flows and the nitrification process recovers quicker than a suspended growth system.

• IFAS improves sludge settleability characteristics.

• Reduced solids load on clarifier.

Disadvantages

• IFAS is not a common technology in Canada (no operating plants).

• Proprietary technology.

• Media is expensive and requires replacement over time.

• Dewatering of the bioreactors is difficult due to the presence of the media.

22.2.2 Option K: High Purity Oxygen Phoredox Process (A/O) followed by Separate Stage Nitrification in a Moving Bed Biofilm Reactor (MBBR), Post-Nitrification with Methanol Addition and Side Stream Treatment

This option was developed on the basis of keeping the existing HPO bioreactors for carbon removal followed by separate stage nitrification in an MBBR followed by denitrification. In this option, additional anaerobic tankages are added upstream of the HPO bioreactors to provide an anaerobic-aerobic sequence in order to implement biological phosphorus removal. This anaerobic-aerobic configuration is commonly referred to as the A/O or Phoredox process.

Thickener

FinalSettling

P

PRAS 0.7 Q

Air

BlendTank

VFA

2.5 to 3.0 Q

Sludge Haulage to NEWPCC

RawWastewater (Q)

GritRemoval

PrimarySedimentation/CEPTScreen

Bypass Flows 175 ML/d

Alum as required

Fermenter

125 M

L/d

4% Solids

FinalSettling

Compressed Air BlowersCompressed Air Blowers

P

PWAS To Thickener

BlendTankBlendTank

VFA

UV

to NEWPCC

RawWastewater (Q)

GritRemovalScreen

required

Figure 22.1: Option G

IFAS media


Four parallel anaerobic cells are proposed immediately south of the existing HPO bioreactor trains to which primary effluent is directed. The anaerobic cells also receives volatile fatty acids (VFA) generated from the primary sludge fermentation to enable the bio-P organisms to release phosphorus and store carbon as poly hydroxyl butyrate (PHB) internally. The mixed liquor from the HPO process is directed to the expanded secondary clarifiers and the settled sludge (underflow) is recycled at the rate of 50 percent of the maximum month flow back to the anaerobic zone. The proposed Phoredox process will be operated as a high-rate process with a very short SRT of 2.5 days. The operation of the system under a short SRT optimizes biological phosphorus removal and also allows a major portion of the influent phosphorus removal via synthesis (i.e. phosphorus removed due to uptake by microorganisms for cell synthesis while performing carbon or BOD5 removal).

The effluent from the secondary clarification contains high levels of TKN, mostly in the form of ammonia-nitrogen. In order to implement nitrification at the SEWPCC, a moving bed biofilm reactor (MBBR technology) would be utilized. As in Option G, the MBBR is a flow-through attached growth process that utilizes bioreactor tanks partially filled with plastic media or sponges as carrier material. The basic principles of an MBBR is the same as the IFAS, except that, MBBRs operate with practically no suspended mixed liquor. The carrier material facilitates the growth of nitrifiers that achieve nitrification within a short retention time (typically less than 3 hours). An aeration grid located at the bottom of the reactor supplies oxygen to the biofilm along with the mixing energy required to keep the media suspended and completely mixed within the reactor. Media retention screens, as required for the IFAS, are incorporated in the tank walls to prevent the loss of media. Periodically a portion of the attached growth will slough off and become part of the solids leaving the system to the downstream processes. By the time wastewater leaves the MBBR, almost all of the ammonia-nitrogen is converted to nitrates. To meet the effluent requirements for the SEWPCC, approximately 25 percent of the maximum month flows can be bypassed around the MBBR trains and denitrification filters, and blended downstream of the denitrification filter with the treated effluent. Retrofitting the proposed MBBRs into the hydraulic grade line of the proposed SEWPCC requires an intermediate pump station to deliver a pumped flow from the underground effluent channel (downstream of the clarifiers). This also enables the MBBR effluent to flow by gravity to the downstream denitrification filter, UV disinfection system and through the outfall to the Red River.

22.5

The purpose of the denitrification filter is to convert the nitrates in the influent of the system to nitrogen gas. However, as most of the carbon resources in the sewage are depleted by this time, an external carbon source in the form of methanol is added to the influent stream to facilitate the denitrification process. For the purpose of this memorandum, a patented “anoxic” biological aerated filter (BAF) was considered for denitrification. The media acts as a filter for the physical removal of the suspended solids as well as


22.6

provides adequate surface area for the attachment of biofilm.

To meet the effluent requirement for the SEWPCC, approximately 35 percent of the treated MBBR effluent can be bypassed around the denitrification filter. The remaining 65 percent of the MBBR effluent is first brought to a common inlet feed channel above the denitrification filter basin where it flows down to the bottom of individual cells by gravity. Upon entering the individual cells, the wastewater flows upwards through the filter media. The media is composed of specially treated spherical polystyrene beads covered by active biomass (see above figure). Ceiling plates with regularly spaced nozzles are used to retain the filter media in the cell. The nozzles allow the treated effluent to enter a common reservoir above the filters, which in turn is used to provide flow during backwash sequences.

Growth of biomass and the retention of suspended solids in the filter media make periodic backwashing necessary. Backwash intervals typically vary from 24 to 72 hours and are triggered either when an operator adjustable time limit has expired or when the head loss across the filter exceeds a pre-determined set point. Effluent that collects in the common treated effluent reservoir flows down through the filter by gravity, causing the media to fluidize. The process air grid located below the media is used to supply scouring air during the backwash sequence. The grids are regularly spaced pipe laterals with small orifices that produce a uniform, coarse bubble pattern over the full cross-section of the filter.

In backwash mode, the feed to the cell to be washed is stopped, and the backwash valves at the bottom of the filter are opened to allow gravity flow of the effluent from the top clear water storage tank to a backwash holding tank located at the end of the filter gallery. The backwash waste storage tank receives the backwash liquid produced during a backwash. The plant is designed to allow only one cell to backwash at a time. The backwash storage tank acts as a flow and TSS load equalization tank, as backwash liquid is produced over a very short period of time. From this tank, the backwash liquid is pumped on a continuous or semi-continuous basis to the head of the primary clarifiers.

The methanol feed system is comprised of methanol storage tanks and feed pumps. Special care is required to handle methanol which is an explosive liquid. As such all the system components associated with the methanol storage and feed system will be explosion proof. For optimal feed of this chemical, a PLC based feed system complete with on-line nitrate-nitrite analyzers will be included for the SEWPCC upgrade/expansion.

A proposed process schematic of this option is shown in Figure 22.2.

Advantages

• Continued use of the existing HPO system.

• A smaller plant footprint compared to conventional suspended growth processes.

• Individual process components can be optimized.

Vent CO2 and O2

PPWAS To

Thickener

Pure Oxygen

BlendTankSludge Haulage

to NEWPCC

RawWastewater (Q)

GritRemoval



Alum as required

Fermenter

Pressure Swing O2Generating System

4% Solids

FinalSettlingSettling

UV

PPWAS To

ThickenerRAS 0.25 – 0.5 Q

BlendTankBlendTank

VFA

GritRemoval


Alum as

Fermenter

125 M

L/d

MBBR Tank Anoxic BAFP


0.75 Q

0.25 Q

P

Filter backwash stream

~ 0.1 Q

0.25 Q

Air

Methanol

Figure 22.2: Option K

Thickener


22.7

• The MBBR media provides protection of nitrifiers for high flows and the nitrification process recovers more quickly than a suspended growth system.

• Provides flexibility to modify flow split to individual process units to optimize treatment costs.

Disadvantages

• This option will produce much more sludge (from the Phoredox process) compared to Options B, C, D, I, G or L.

• There are no operating MBBR plants in Canada.

• This process option uses two proprietary technologies.

• Media is expensive and will require replacement over time.

• Significant operations and safety issues related to the use of methanol for denitrification.

• Higher operating costs. Also, methanol is a bio-fuel and its demand is likely to increase in the future, adding a high risk of cost escalation.

• Need to control oxygen concentration in recycle stream to the anerobic zone.

• Operators will have three different biological treatment processes to operate. This will require more operator attention and increased operation time.

• Need to control methanol dose to denitrification filters to prevent BOD spikes in the final effluent.

22.2.3 Option L: High Purity Oxygen BNR Followed by Separate Stage Nitrification in Moving Bed Biofilm Reactor (MBBR) and Side Stream Treatment

The Option L was developed on the basis of keeping the existing HPO bioreactors for mainstream process followed by a separate stage, side stream nitrification in an MBBR tank. In this option additional pre-anoxic, anaerobic and anoxic tanks are added upstream of the HPO bioreactors similar to that of modified Johannesburg process or option D. The main stream processes provide biological nutrient removal while ammonia removal is achieved in the MBBR tanks.

Additional pre-anoxic, anaerobic and anoxic tanks are proposed to be constructed immediately north and south of the existing HPO reactors. The mixed liquor from the HPO process would be directed to the expanded secondary clarification facility and about 70 percent of the settled sludge would be recycled back to the pre-anoxic zone. The pre-anoxic zone is essential to protect the anaerobic zone from nitrates that may be recycled from the secondary clarifiers.

The anaerobic cells would receive primary effluent and supernatant from the fermenters. Volatile fatty acids (VFA) generated during primary sludge fermentation enable the bio-P


22.8

organisms to release phosphorous and store carbon as poly hydroxyl butyrate (PHB) internally. The anoxic cell receives both primary effluent and nitrified effluent from the MBBR reactors. Denitrifying bacteria remove nitrites using organic carbon from the mainstream process. The HPO reactors remove the remaining organic carbon and contain bio-P microorganisms for phosphorous uptake. In addition, the proposed mainstream configuration is operated under short SRT (3.5 days), which allows a major portion of the influent phosphorous removal via synthesis. At this short SRT nitrification is unlikely to occur in the main stream reactors. The use of the MBBR process results in a smaller footprint compared to the conventional suspended growth processes (such as option C or D).

The effluent from the secondary clarification contains high levels of TKN, mostly in the form of ammonia-nitrogen. In order to implement nitrification a moving bed biofilm reactor (MBBR) is utilized. A portion of the secondary effluent is diverted to the MBBR tanks for nitrification and later brought back to the anoxic zone for nitrogen removal. The MBBR is a flow-through attached growth process contained in bioreactor tanks that are partially filled with media as carrier material. The basic principle of an MBBR is the same as the IFAS, except the MBBR operates with practically no suspended mixed liquor. The carrier material facilitates the growth of nitrifiers that achieve nitrification within a short retention time (typically less than 3 hours although some media suppliers claim as low as 1 hour). An aeration grid located at the bottom of the reactor supplies oxygen to the biofilm along with the mixing energy required to keep the media suspended and completely mixed within the reactor. Periodically a portion of the attached growth will slough off and become part of the solids leaving the system to the downstream processes. By the time wastewater leaves the MBBR, almost all of the ammonia-nitrogen is converted to nitrates. In order to meet the effluent requirements for the SEWPCC, approximately 90 percent of the maximum month flows would have to be passed through the MBBR trains. Retrofitting the proposed MBBRs into the hydraulic grade line of the proposed SEWPCC expansion/upgrade requires an intermediate pump station to deliver a pumped flow from the underground effluent channel (downstream of the clarifiers). This also enables the MBBR effluent to flow by gravity to the downstream anoxic zone in the mainstream process. The increased flow through the secondary clarifiers resulting from the significant recycle from the MBBR trains, necessitates the addition of three 45.7 m diameter clarifiers to the existing SEWPCC facility.

A proposed process schematic of this option is shown in Figure 22.3.

Advantages:

• Continued use of the existing HPO system.

• A smaller footprint compared to conventional suspended growth processes.

• The MBBR media provides protection of nitrifiers for high flow and the nitrification process recovers quicker than a suspended growth system.

4% Solids

Thickener

FinalSettling

PPRAS 0.7 Q

Pure Oxygen

BlendTankSludge Haulage

to NEWPCC

RawWastewater (Q)

GritRemoval



Alum as required

Fermenter

125 M

L/d

4% Solids

FinalSettling


PPWAS To Thickener

BlendTankBlendTank

VFA

UV

to NEWPCC

RawWastewater (Q)

Screen

Alum as required

MBBR Tank

0.9 Q

Vent CO2 and O2 Pressure Swing O2Generating SystemP

Air

Figure 22.3: Option L


22.9

• Due to short SRT in the mainstream system a higher portion of phosphorous is taken up by synthesis, which results in a smaller fermentation facility.

• Use of organic carbon from the mainstream bioreactors to achieve denitrification.

Disadvantages:

• This option will produce a much higher sludge quantity than options B, C, D or I.

• There are no operating MBBR plants in Canada.

• This process uses a proprietary technology.

• Media is expensive and will require replacement in time.

• Additional clarification area required due to high recycle rate to and from MBBR tanks.

• More complicated operation due to numerous processes.

22.2.4 Option C-1: High Rate Activated Sludge Process with Chemical Phosphorus Removal and Side Stream Treatment for Wet Weather Flows (CEPT)

This is the same as option C with the following changes:

• The Pre-anoxic and Anaerobic portion of the bioreactor tankages are eliminated. The new process configuration now represents a Modified Ludzack-Ettinger (MLE) process i.e., anoxic zone followed by aerobic zone with internal mixed liquor recycle.

• The three (3) primary sludge fermenters will no longer be required.

• The proposed stand-by chemical feed system will be expanded to provide the primary means of chemical precipitation of phosphorus. Alum solution (48% strength) will be dosed directly to the last stage of the aerobic zone.

• Sludge thickening and holding capacity will be expanded to accommodate increased sludge production.

22.2.5 Option K-1: HPO with Chemical Phosphorus Removal followed by Separate Stage Nitrification in a Moving Bed Biofilm Reactor (MBBR), Post-Denitrification with Methanol Addition and Side Stream Treatment for Wet Weather Flows (CEPT)

This is the same as Option K with the following changes:

• The Anaerobic zones of the proposed bioreactor tankages are eliminated. The existing HPO tanks will continue to provide carbonaceous BOD5 removal as per current practice.

• The two (2) primary sludge fermenters will no longer be required.


22.10

• The proposed stand-by chemical feed system will be expanded to provide the primary means of chemical precipitation of phosphorus. Alum solution (48% strength) will be dosed directly to the last stage of the existing HPO tanks.


22.2.6 Options L-1: HPO with Chemical Phosphorus Removal followed by Separate Stage Nitrification in Moving Bed Biofilm Reactor (MBBR) and for Wet Weather Flows (CEPT)

This is the same as Option L with the following changes:

• The Pre-anoxic and Anaerobic portion of the bioreactor tankages are eliminated. The existing HPO tanks will continue to provide carbonaceous BOD5 removal as per current practice.

• The proposed stand-by chemical feed system will be expanded to provide the primary means of chemical precipitation of phosphorus. Alum solution (48% strength) will be dosed directly to the last stage of the existing HPO tanks.


22.3 PROCESS MODELING

A preliminary process modeling of the three (3) additional BNR options was undertaken to:

• Characterize anticipated performance for each alternative under the design flow and loading conditions for the most challenging condition, which is during spring maximum month.

• Identify operational advantages and disadvantages of each option to serve as an input to the final process selection based on modeling.

• Predict sludge production rates.

• Identify chemical dose requirements (alum, methanol, etc.)

22.3.1 Limitations of Process Modeling

The results and conclusions presented in this section are based upon analysis of SEWPCC wastewater samples collected between March 2006 and February 2007. For additional details, please refer to Section 15.


22.11

22.3.2 Modeling Approach

In general, the same modeling approach was chosen as described in Section 15. The previously developed synthetic flows database was used here for the modeling of the most critical conditions. Based on previous experience with modeling of the response of the four short listed options, it was found that the most challenging condition for the process design was the spring maximum month in year 2031. The combination of high flows, high nitrogen loads and low temperatures require that the bioreactor be pushed to approximately 150 percent of the design capacity to meet the effluent quality limits.

All three (3) of the additional processes discussed in this section involve a proprietary technology: Option G requires IFAS media, Option K requires an MBBR process and denitrifying filters, Option L requires an MBBR process. BioWin software was initially developed to model activated sludge processes, but recently introduced the ability to model fixed film (biofilm) biomass activity. It should be noted that BioWin is a mechanistic model with output predicted based on theoretical considerations. Modeling phenomena as complex as biofilm is not at this time fully understood. In fact, BioWin uses a one-dimensional model of the biofilm processes that occur in three dimensional space (Takacs, I. 2007. Personal communication. Envirosim). Suppliers of fixed film media prefer to rely at this time on the empirical models that are based on historical plant performance data (Morris, M. 2007. Personal Communication. AnoxKaldnes) or use BioWin software after applying “realistic adjustment … to the default values…” (Warakomski, A. and M. Morper (2005). Process Modeling IFAS and MBBR Systems Using Linpor. Rocky Mountain Water Environment Association, Albuquerque, NM, USA.)

Due to the difficulties and uncertainties related to the mechanistic modeling of the fixed film media response to changing input parameters, namely the dynamic simulation situation, it was decided to verify the response of the BioWin model versus the empirical models used by the media supplier. Maximum month conditions in spring were used as critical parameters. It should be noted that fixed film media support the growth and retention of nitrifying organisms due to the very long SRT of the biofilm. The maximum month in spring is characterized by the highest nitrogen load entering the plant. Therefore, if the suspended and fixed biomass can remove nitrogen during this critical period, for this level of assessment, it can be considered that the system would perform adequately during the remaining part of the year. It should be remembered that more detailed modeling of the selected treatment option will be conducted as part of the Conceptual Design.

The overall approach to the reactor sizing and process modeling for the three additional treatment options is summarized in the following sections.

22.3.3 Model Development and Assumptions

For all model development and assumptions see Section 15.2.2.


22.12

22.3.4 Modeling Results

Based on the previous modeling experience and recommendations from the suppliers, the following sizes of bioreactors and clarifiers were used for modeling purposes:

Table 22.1 - Reactor Sizes Used for the Modeling of Three Additional Treatment Options Option Design Flows and

Logic Reactor Sizes Physical/chemical

Side Stream For Wet Weather Treatment

Main Stream System Additional Treatment for Nitrogen Control

G Design flow 83.5 ML/d treats up to 125 ML/d (175 ML/d in the summer)

Total Volume 26.5 ML PreAnoxic – 1.3 ML Anaerobic – 1.8 ML Anoxic – 6.4 ML Aerobic – 17.0 ML (IFAS)

Not required Treats up to 125 ML/d

K Design flow 83.5 ML/d treats up to 125 ML/d (175 ML/d in the summer); post nitrification and denitrification treats up to 81.8 ML/d

Total Volume 8.64 ML Anaerobic – 2.0 ML Aerobic – 6.64 ML (existing HPO)

Total Volume 10.54 ML MBBR – 9.8 ML Anoxic BAF – 0.74 ML (for denitrification)

Treats up to 125 ML/d

L Design flow 83.5 ML/d treats up to 125 ML/d (175 ML/d in the summer); side stream MBBR treats up to 100 ML/d

Total Volume 12.7 ML PreAnoxic – 1.3 ML Anaerobic – 1.8 ML Anoxic – 3.0 ML Aerobic – 6.64 ML (existing HPO)

Total Volume 5.75 ML MBBR – 5.75 ML

Treats up to 125 ML/d

22.3.5 Evaluation of Bioreactor Volumes Using Process Simulation Software

The initial bioreactor volume estimates were confirmed using BioWin ™ process simulation software. The results of static models are presented in Table 22.2. For details regarding static modeling, refer to Section 15.

Table 22.2 - Summary of Static Modeling Results

Design Flow Temperature

SRT

(main stream)

Overall Reactor Volume

MLSS in main stream Effluent quality, mg/L

Effluent pH

Option MLD Celsius days ML mg/L TSS CBOD TN TP

Option G 111 10 10 26.5 4340 7.4 4.3 9.83 0.32 6.5

Option K 111 10 2.5 19.2 4258 8.6 7.7 12.84 0.30 6.5

Option L* 111 10 3.5 17.7 3330 12.2 7.5 14.4 0.52 7.2 a excludes Anoxic BAF

* Note: The MBBR volume proposed by M2T for Option L is 2.3 ML with 30% recycle. Stantec’s modeling shows a larger MBBR requirement with 90 percent recycle due to a 30 percent underestimation of TKN load by M2T. When these results were provided to M2T for discussions, they refused to participate.


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22.3.6 Secondary Clarifier Sizing

The sizing of secondary clarifiers was based on the following: • average SOR = 24 m3/m2 d, maximum SOR = 50 m3/m2 d • average SLR = 6 kg/m2 hr, maximum SLR = 9 kg/m2 hr It was assumed that all new clarifiers would be sized to match the existing 45.7 m dia. secondary clarifier. The total existing clarification area is 3400 m2. The additional secondary clarification requirements for each of four alternatives are presented in Table 22-3. Table 22.3 - Additional Clarification Requirements of Three Additional Options

Option G Option K Option L

Number of clarifiers added 2 2 3

Diameter (m) 45.7 45.7 45.7

Added clarification area (m2) 3280 3280 4920

Total surface area (including existing 3400 m2) 6680 6680 8320

Solids Loading Rate, (kg/m2.d Predicted by BioWin) 122.1 111.3 115.5

22.4 FACILITY LAYOUT

The key components of the three additional treatment options are detailed in the following sections.

22.4.1 Site Plan

The site plans associated with the three additional treatment options are shown in Figures 22.4, 22.5 and 22.6.

22.4.2 Common Components

There are several components for the three (3) proposed/additional treatment options that are common to the options presented earlier in this report. These common components are described in detail in Section 17: Facility Layout and are therefore not repeated here. For the purpose of this report, only a brief listing of these components are being provided to facilitate an understanding of the overall concept for each of the treatment options. These components are summarized below:


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Liquid Waste Disposal Facility

The system components and facility layouts are the same as developed earlier for the options B,C, D, and I. These include the following:

• Septage Unloading.

• Automated Septage Receiving Station (ASRS).

• Equalization Chambers.

• Discharge to the Interceptor.

• Odor Control.

Plant Inlet Works and Raw Sewage Pumping

The plant inlet works receives wastewater via the 1980 mm South Winnipeg Interceptor Sewer, which discharges to the plant inlet chamber. Two transition channels, each equipped with sluice gates at the upstream end, deliver wastewater from the inlet chamber to the raw sewage pumping well. The raw sewage pumping facility is comprised of a wet well and dry pit pumping area. As presented in Section 17, it is proposed that one of the existing 68 ML/d pumps will be replaced with a 114 ML/d pump. This will result in a firm pumping capacity of approximately 300 ML/d and a total pumping capacity of approximately 410 ML/d.

Screening Facility

One additional 12 mm climber screen will be added to the existing screening facility, bringing the total peak screening capacity to 490 ML/d, which is more than sufficient to accommodate the total pumping capacity of 410 ML/d for the proposed SEWPCC upgrade and expansion.

Grit Removal

The existing grit removal system is comprised of 2 – 9.1 m square aerated grit tanks with a dedicated air blower, grit pump and classifier for each tank. The proposed improvements include two additional vortex grit removal systems complete with grit pumps and classifiers. The total hydraulic capacity of the new grit removal system would be 150 ML/d under peak flow conditions (or 75 ML/d per grit tank). This would bring the total grit removal capacity to 420 ML/d under peak flow conditions based on a capacity 270 ML/d for the existing grit removal facility.

Inlet Channels

The preliminary treatment facility includes flow channels that convey wastewater from the pump discharge, through the unit processes of preliminary treatment and eventually, to the primary treatment facility. Benching in the dead zones in combination with a grit flushing system is proposed to help reduce the problem of grit accumulation in the channels.


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Odor Control

The HVAC system for the expanded preliminary treatment facility would be designed to collect foul air from the facility and convey it via an underground foul air duct to the Odor control facility that is proposed as part of the Septage Facility.

Primary Clarifiers

There are currently three (3) primary clarifiers at the SEWPCC. The proposed primary treatment facilities are the same for the four short-listed treatment options and include construction of one additional rectangular primary clarifier fitted with lamella plate settlers. The new clarifier would also be equipped with chemical feed facilities to provide chemically enhanced primary treatment using alum and polymer. The new clarifier would have a surface area of 702 m2 with a peak rated capacity of 125 ML/d.

22.5 BIOREACTORS

22.5.1 Purpose

The bioreactors are the heart of the biological treatment process. Within the reactors, a diverse group of micro-organisms is grown either as a suspended growth culture (e.g., ASP) or as a biofilm (e.g., MBBR and IFAS) through cell metabolism to oxidize organic material in the sewage. In addition to removal or reduction of the organic material, the process includes anoxic, anaerobic and aerobic conditions to provide nitrification, denitrification and phosphorus removal.

22.5.2 Existing Facility

The existing biological treatment process is comprised of a high purity oxygen (HPO) system with four bioreactor trains. Please refer to Section 17 for details.

22.5.3 Proposed Facility

The proposed improvements for each of the three (3) additional treatment options are quite different from each other. Option G is based on the Modified Johannesburg (MJ) biological nutrient removal (BNR) system with Integrated Fixed Film in the aerobic zone. Options K and L utilize the existing HPO bioreactors for carbon removal with additional tankage providing the anaerobic zone for Option K, and pre-anoxic, anaerobic and anoxic zones for Option L. Options K and L utilize a Moving Bed Biofilm Reactor (MBBR) that utilizes a free floating neutral density media for separate stage nitrification. Option K incorporates a tertiary denification step following the MBBR with methanol as an external carbon source. Figure 22.4, 22.5 and 22.6 (Site Plan) illustrate the location and size of the proposed bioreactors for each Option with respect to the existing SEWPCC layout.

Similar to the basis of design discussed for Options B, C, D and I, the proposed bioreactors provide biological phosphorus removal, nitrification and denitrification by bringing active microbial growth in contact with wastewater. Depending on the option, the bioreactor design


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incorporates a combination of anoxic, anaerobic and aerobic zones to meet the target effluent requirements for the SEWPCC. For Options G and L, raw wastewater is introduced to the pre-anoxic zone along with return activated sludge (RAS) recycled from the secondary clarifier. In this zone, the RAS is denitrified to protect the anaerobic zone from nitrates. In the next zone, which is anaerobic, volatile fatty acids (VFA) generated from the primary sludge fermentation process are brought in contact with the mixed liquor from the pre-anoxic and anoxic zones and under these anaerobic conditions, specific bio-P organisms initiate a metabolic pathway to internally store carbon as poly hydroxyl butyrate (PHB).

The pre-anoxic, anaerobic, and anoxic zones of the proposed bioreactor configuration are mixed vertically using propeller mixers. For Option G, the aerobic zones are provided with a fine bubble diffused air system along the floor of the reactor, which provides oxygen to promote the required biological reactions. High Purity Oxygen generated by the existing PSA system provides the same function for Options K and L. Organic carbon is degraded by the micro-organisms in the activated sludge to carbon dioxide, water and more bacteria cells. Organic nitrogen is converted to ammonia by the heterotrophic bacteria and subsequently nitrifying bacteria convert the ammonia to nitrates. The nitrates are dentrified in a suspended growth anoxic zone for the recycled stream (Options G and L) or in a separate stage denitrification filter (Option K). Granular phosphorus contained in the organisms is removed in the final settling tanks and wasted to the solids handling process. The residual organics, solids not oxidized in the bioreactor and the phosphorus contained in the organisms, is also removed in the final settling tanks and wasted to the solids handling process.

As indicated previously, each of the three (3) short-listed treatment options differ from each other. Option G includes constructing new IFAS activated sludge (AS) MJ BNR reactors and converting the existing HPO AS bioreactors to AS MJ BNRs. Options K and L are based on maintaining the existing HPO AS process but adding additional tankages and separate stage nitirifcation and denitrification (Option K only). The following table summarizes the process parameters and bioreactor sizing for each of the three (3) short-listed options. Refer to Section 22.3 (Process Modeling) for details regarding bioreactor sizing for each of the short-listed treatment options.

Table 22.4 – Bioreactor Details

Description Units Option G Option K Option L

Treatment Capacity ML/d 111 111 111

Number of Suspended Growth Bioreactor Trains

Each 5 (includes IFAS) 4 (existing HPO) and 4 (anaerobic)

4 (existing HPO) and 2 (pre-anoxic

and anoxic) Number of Attached Growth Bioreactor Trains

Each N/A 3 (MBBR) and

6 (denitrification filters)

3 (MBBR)


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Description Units Option G Option K Option L Total Bioreactor Volume/Area

ML or m2 26.5

• 8.64 (suspended growth)

• 11.3 (MBBR) • 210 m2 (denit.

filters)


• 5.75 (MBBR)

Bioreactor Volume or Area per Train

ML or m2 5.3


• 3.8 (MBBR) • 42 m2 (denit.

filters)

• 1.66 (HPO) • 3.05 (Others) • 1.92 (MBBR)

Pre-Anoxic Zone

Total Volume ML 1.3 N/A 1.3

Each Zone/Train ML 0.26 N/A 0.65

Anaerobic Volume

Total Volume ML 1.8 2.0 1.8

Each Zone/Train ML 0.36 0.5 0.9

Anoxic Zone

Total Volume ML or m2 6.4 210 m2 of anoxic denitrification filter 3.0

Each Zone/Train ML or m2 1.28 42m2/filter bed 1.5

Aerobic Zone

Total Volume ML 17.0 6.64 (existing HPO tanks)

6.64 (existing HPO tanks)

Each Zone/Train ML 3.4 1.66 1.66

The bioreactors will incorporate interconnecting tunnels (Option G only), walkways and pipe galleries between existing and new facilities. The proposed improvements include checker plate covers over the bioreactors to reduce odor emissions from the treatment process. It is acknowledged that this may lead to some operational and maintenance access concerns and as such, this issue will require further discussion with the City. The additional cost to provide a building over the bioreactors has been included as a separate line item in the opinion of probable cost.

22.5.4 Constructability

The implementation of all three options will impact the ongoing operation of the plant during construction. Options K and L will involve minimal changes to the existing HPO bioreactor but


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will required the addition of haulage ahead of the HPO bioreactors as well as a lift station following the existing secondary clarifies. These additional components must be added within the existing hydraulic profile while keeping the plant operational.

In order to implement Option G, it will be necessary to complete construction, startup and commissioning of the new BNR bioreactors (and secondary clarifiers) and the corresponding waste and return activated sludge facilities prior to converting the existing HPO AS reactors to the BNR process. In addition, it will likely be necessary to operate the new BNR reactors for a fairly significant period of time prior to commencing work on the existing reactors to ensure the new BNR process achieves equilibrium conditions and produces an effluent that meets the limits established for the project. However, in terms of time required for construction for Option K and Option L will be similar, while Option G would likely be constructed within a similar time frame as Option C.

22.6 SOLIDS SEPARATION (SECONDARY CLARIFIERS)

22.6.1 Purpose

The main objective of the secondary clarifiers is solids-liquid separation of the mixed liquor prior to discharging effluent to the disinfection facility and outfall sewer. The secondary clarifiers also serve to remove solids from the treatment process for further processing. Mixed liquor is introduced to the clarifier, which provides quiescent conditions to promote settling of solids. Clear liquid from the surface of the clarifier flows over a weir to subsequent downstream treatment processes.


The SEWPCC is currently equipped with three (3) center column siphon feed and peripheral overflow type secondary clarifiers with a central bridge driving mechanism that supports and rotates a center cage with two sludge rake arms and two scum blades. Two (2) of the existing clarifier are 33.5 m in diameter and the third is 45.7 m in diameter. Please refer to Section 17 for more details.


The size and capacity of the proposed secondary clarifiers for each of the three (3) additional treatment options are the same except for Option L. In particular, Options G and K required two (2) additional 45.7 m Ø secondary clarifiers, while Option L requires three (3) additional 45.7 m Ø secondary clarifiers. It is important to note that sizing of the proposed clarifiers was based on standardization to match the size of the existing 45.7 m Ø. Figure 22.4, 22.5, and 22.6 (Site Plan) illustrate the proposed location of the new secondary clarifiers for each option with respect to the plant layout.


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The proposed secondary clarifiers are the same style as the existing clarifiers, with the exception that the City prefers helical sweeps for the control of return activated sludge age. In particular, the center column siphon feed and peripheral overflow type secondary clarifiers are proposed for each short-listed treatment option. Sizing of the clarifiers was completed as part of the process modeling and the following table summarizes the secondary clarifier design parameters for each of the four options. Refer to Section 22.3 for details associated with the process modeling.

Table 22.5 – Proposed Secondary Clarifier Design Parameters

Clarifier Dimensions (Each) Option G Option K Option L

Number of Additional Clarifiers 2 2 3

Diameter (m) 45.7 45.7 45.7

Side Wall Depth (m) 4.6 4.6 4.6

Volume (m3) 7544.0 7544.0 7544.0

Surface Area (m2) 1640.0 1640.0 1640.0

Weir Length (m) 144 144 144 The existing layout of the secondary clarifier influent channel includes provision for installation of a new 45.7 m Ø secondary clarifier adjacent to FST-3. The proposed facility layouts for the final clarifiers are based on constructing the clarifiers as part of a new secondary influent flow distribution facility rather than constructing one of the new clarifiers adjacent to FST-3. This will improve constructability and reduce the potential impacts of construction on operation of the existing facility. The feasibility of installing one of the new secondary clarifiers adjacent to FST-3 will be evaluated in detail during conceptual design of the preferred treatment option.

Operation of the proposed secondary clarifiers includes pumping waste sludge from the secondary clarifiers to the existing sludge holding tank, which forms part of the proposed solids handling facility. Details associated with solids handling are discussed in a subsequent section. The proposed improvements include geodesic dome covers over the final clarifiers. The additional cost to delete the geodesic dome covers and provide a building over the final clarifiers has been included as a separate line item in the opinion of probable cost.


The impacts of the proposed modifications to the secondary treatment facility on constructability and maintaining plant operations are the same for all three (3) additional options. The new secondary clarifiers can be constructed adjacent to the existing facility without interrupting plant operation. Temporary shutdowns of some of the clarifiers may be required for interconnections between the new and existing influent and effluent channels.


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22.7 PRIMARY SLUDGE FERMENTATION

22.7.1 Purpose

The purpose of primary sludge fermentation is to produce soluble organics such as short-chain volatile fatty acids (SCVFAs), which provide the carbon source necessary in the biological nutrient removal (BNR) process for biological phosphorus removal. Primary sludge fermentation is implemented in instances where there is insufficient easily degradable organic matter in the wastewater that can be used as a carbon source.

Primary sludge fermentation is an anaerobic process that is typically provided as a standalone unit process. There are various configurations for fermenters including activated primary tanks (APT), complete mix fermenters, static fermenters and two-stage fermenters.


The existing SEWPCC is an HPO activated sludge plant that does not include primary sludge fermentation. Accordingly, there are no existing primary sludge fermentation facilities.


The proposed facilities include circular fermenters. Figure 22.4, 22.5 and 22.6 (Site Plan) illustrate the proposed location of the new primary sludge fermentation process for each Option with respect to the existing plant layout.

The proposed improvements include 3 – 21.3 m Ø primary sludge fermenters for Option G and 2 – 21.3 m Ø units for Options K and L. The fermenters are a static type design utilizing a picket fence style mechanism similar to a primary clarifier. The fermenters provide solids residence time and mixing of primary sludge and the VFAs, which are released in the sludge blanket. An elutriation pump is utilized to rinse the VFAs for feeding directly to the anaerobic zone of the bioreactors. As indicated previously, only the non-chemical primary sludge will be conveyed to the fermenters. Chemical sludge generated from the primary clarifiers will be conveyed directly to the solids handling process. The fermenters provide a solids retention time of approximately 5 days and waste solids from the fermenters will be conveyed directly to the new sludge holding tank. The fermenters are fitted with geodesic dome covers, similar to the secondary clarifiers.


The proposed primary fermentation facility is basically a standalone process for each of the three additional treatment options that will have minimal impacts from a constructability and plant operation perspective. Option G will have a slightly higher impact on constructability and plant operations due to conversion of the existing HPO bioreactors.


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22.8 INTERMEDIATE PUMPING STATION

The hydraulic grade line through the SEWPCC is already fairly tight during wet weather events. The inclusion of an additional two processes in Option K and an additional process in Option L, between the secondary clarifiers and UV disinfection facility necessitate the addition of an intermediate pump station. For both these options, the combined secondary effluent (from both existing and proposed secondary clarifiers) may be pumped to the MBBRs to overcome the hydraulic grade line of the existing components. The pumping station consists of a wet well with pumps located in a dry pit with staircase access from the ground level. The summary of key components of the intermediate pumping station are as follows:

• Overall Footprint = 11 m x 15 m

• Building Footprint = 6.3 m x 11 m

• Total Depth = 10.5 m

• Number of Pumps = 4 with VFD

• Flow Capacity = 25 MLD ~ 175 MLD

• Number of Wet Wells = 2

• Size of each Wet Well = 4.85 x 8 m

22.9 METHANOL STORAGE AND FEED SYSTEM

Option K requires on external carbon source to sustain denitrification. For the purpose of this evaluation, methanol will be used as the external carbon source. Methanol is a colorless liquid with alcohol-like odor. Methanol is highly explosive and is classified as an “Allied Petroleum Product” for storage purposes. For Option K, methanol consumption is estimated at 5000 L/day (average dose rate of 70 mg/L of 99.85 percent purity methanol). Methanol will be dosed to the influent of the denitrification filter through an “explosion proof” chemical feed system. Above ground horizontal double-walled steel tanks are proposed for methanol storage and supported on a concrete foundation. For safety reasons, the head-space of the storage tanks will be pressurized with nitrogen gas. A summary of the key design parameters and process components are as follows:

• Average Methanol Dose = 70 mg/L

• Average Methanol Consumption = 5000 L/day

• Number of Storage Tanks = 2

• Capacity per Tank = 94,000 L


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• Total Storage Capacity = 188,000 L

• Estimated days of storage = 37

• Number of Chemical Feed Pumps = 3

• Storage Tank Dimensions = 11 m (length) and 3.5 m (diameter)

22.10 SOLIDS HANDLING

22.10.1 Purpose

The solids handling process is comprised of sludge thickening and storage. The purpose of sludge thickening is to reduce the volume of liquid sludge in order to optimize the size of the storage facility and minimize ongoing operational costs associated with hauling sludge offsite to the NEWPCC for further processing. Sludge storage is provided to allow periodic hauling of sludge from the plant.


The sludge recirculation and truck loading system provides temporary storage of sludge and scum from the primary and secondary sedimentation tanks. Stored sludge is pumped into tanker trucks and hauled to the NEWPCC where it is digested, dewatered and disposed of. Please refer to Section 17 for additional details.

22.10.3 Projected Sludge Quantities

The waste activated sludge production and concentrations were estimated as part of the process modeling that was completed for each of the short-listed treatment options and the following table summarizes the sludge characteristics for each.

Clarifier Number Units Option G Option K Option L

Sludge Production Rate m3/d 2890 3130 2890 Refer to Section 22.3 for details related to the process modeling completed to date.


The proposed solids handling facility is comprised of sludge thickening and storage. Dissolved air floatation (DAF) is proposed for thickening and a new sludge storage facility has been included in the facility layout. The proposed solids handling process is the same for each of the four short-listed treatment options however, there are some differences in the sizing of the facility for each option. Figure 22.4, 22.5, and 22.6 (Site Plan) show where the solids handling facility for each option is located on the site in relation to the existing plant. The following sections provide technical details associated with the thickening and storage facilities.


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22.10.4.1 Sludge Thickening

The DAF process is described in detail in Section 17.

With respect to the SEWPCC, it is proposed to pump waste sludge only from the secondary clarifiers and convey it to the existing sludge holding tank. From this point, sludge will be fed to the DAF unit for processing and the thickened sludge approximately at 3 percent solids will be conveyed to a new sludge storage facility located in the same vicinity as the DAF process. The purpose of wasting sludge to the existing sludge holding tank is to provide equalization or balancing to allow a constant feed of sludge to the DAF units. The following is a summary of the sludge thickening process design parameters for each of the three additional treatment options.

Table 22.6 – Proposed Sludge Thickening Design Parameters

Design Parameter Units Option G Option K Option L

Sludge Production (m3/d) m3/d 2890 3130 2890

Influent Solids Concentration (percent) percent 0.4 0.4 0.4

Effluent Solids Concentration (percent) percent 3.0 3.0 3.0

Solids Loading Rate (at peak capacity) kg/m2/d 108 108 108

Hydraulic Loading Rate (at peak capacity) m3/m2/d 24 24 24

Required DAF Surface Area m2 120 130 120

Number of DAF Units each 4 4 4

Length of Each DAF Unit m 9.0 9.0 9.0

Width of Each DAF Unit m 3.3 3.6 3.3

Depth of Each DAF Unit m 2.5 2.5 2.5 It is noted that chemical primary sludge and waste solids from the fermenters cannot be conveyed to the DAF unit for thickening due to the potential for the release of phosphorus in the supernatant produced by the DAF unit, which is returned to the head end of the plant. This could have a negative impact on plant performance since it would increase the phosphorus loading to the facility. As such, chemical primary sludge and waste solids from the fermenters would be conveyed directly to the new sludge storage facility.

22.10.4.2 Sludge Storage

The thickened sludge from the DAF would be pumped to a sludge holding tank, which would be located in the vicinity of the DAF process. The holding tank has been designed to provide 3 days of storage so that sludge hauling can be suspended over the course of a holiday weekend. The following is a summary of the design parameters associated with the sludge holding tank for each of the treatment options.


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Table 22.7 – Proposed Sludge Holding Tank Design Parameters


Sludge Quantity m3/d 430 470 430

Days of Storage days 3 3 3

Volume of Sludge Holding Tank m3 1290 1410 1290

Number of New Sludge Holding Tanks each 3 3 3

Volume per Sludge Holding Tank m3 430 470 430

Length of Each Sludge Holding Tank m 20.0 21.0 20.0

Width of Each Sludge Holding Tank m 9.0 9.0 9.0

Depth of Each Sludge Holding Tank m 2.5 2.5 2.5 At this stage in development of the project, it was assumed that sludge from the proposed SEWPCC storage facility will continue to be hauled to the NEWPCC for further processing.


The proposed solids handling facility is basically a standalone process for each of the three additional listed treatment options and it will have minimal impact from a constructability and plant operation perspective. In addition, all options generally have the same degree of impact on constructability and plant operations.

22.11 EFFLUENT DISINFECTION

22.11.1 Purpose

Disinfection, in contrast to sterilization or complete elimination of all organisms, is the selective inactivation or destruction of pathogenic organisms. It does not destroy all of the organisms present but reduces the number of active pathogenic organisms to specified levels. Refer to Section 17 for more details.

22.11.2 Design Flows

Table 22.8 – Proposed Disinfection Facility Design Capacity

Description Option G Option K Option L

Total Raw Sewage Pumping Capacity (ML/d) 410 410 410

Primary Treatment Capacity (ML/d) 300 300 300

UV Disinfection Capacity (ML/d) 175 175 175

Raw Storm Bypass (ML/d) 115 115 115


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Description Option G Option K Option L

Primary Effluent Bypass (ML/d) 125 125 125

Total Bypass Flow (ML/d) 235 235 235 It is noted that the storm bypass flow rate is basically the difference between the total raw sewage pumping capacity and the capacity of the UV disinfection facility for each option.


The existing UV disinfect facility is comprised of a final effluent chamber, UV influent chamber, UV disinfection channels and equipment, effluent chamber, outfall chamber and a wet weather bypass chamber. Presently, disinfection only takes place during dry weather flows between the months of May and September inclusive. The UV System capacity is 100 ML/d. For further details, please refer to Section 17.

The current configuration of the secondary effluent and bypass conduits at the SEWPCC results in blending of all flows, including bypass flows, upstream of the existing UV facility. The existing plant does not include provision for disinfection of storm bypass flows. Accordingly, during storm flow events that exceed 100 ML/d, all flows combine upstream of the UV facility and are discharged to the Red River without disinfection. This configuration and mode of operation is negatively impacting disinfection results.


The proposed disinfection facility for each of the three (3) additional treatment options is comprised of an expansion to the existing UV disinfection facility and construction of new storm bypass disinfection facilities similar to the concepts discussed in Section 17.

The expanded UV facility is located immediately adjacent to the existing facility and the required capacity of 175 mL/d is the same for all three alternative treatment options. The following table summarizes the proposed UV design parameters for each option.

Table 22.9 – Proposed UV Disinfection Facility Design Parameters


Peak Hydraulic Capacity ML/d 175 175 175

Number of New UV Reactors each 1 1 1

Capacity of Each New UV Reactor ML/d 75 75 75


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The impacts of the proposed modifications to the disinfection facility on constructability and maintaining plant operations are the same for each of the three additional treatment options. The new UV disinfection facility can be constructed adjacent to the existing facility without interrupting operation. Temporary shutdowns will be required for interconnections between the new and existing influent and effluent channels as well as work related to separating the existing secondary and bypass flows.

sewpcc upgrading/expansion preliminary … upgrading/expansion preliminary design report section 22...

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