Design Guidelines For Sewage Works
These Design Guidelines for Sewage Works are intended for an audience that includes engineers who are responsible for designing sewage works, ministry engineers responsible for reviewing and approving the designs of such works and the municipalities/owners of the sewage works.
Ministry of the Environment
The Design Guidelines for Sewage Works were prepared under the guidance of the Ontario Ministry of the Environment Sewage Technical Working Group with the assistance of Hydromantis, Inc. in association with XCG Consultants Ltd.. This document underwent review by various branches of the Ontario Ministry of the Environment (MOE) and the following stakeholders and reviewers.
Ministry of the Environment Sewage Technical Working Group
- Vince Pileggi, M.A.Sc., P.Eng., Standards Development Branch, MOE
- Janusz Budziakowski, M.Sc., P.Eng., Env. Assessment and Approvals Branch, MOE
- Mano Manoharan, Ph.D., P.Eng., Standards Development Branch, MOE
- Sumithra Naguleswaran, P.Eng., Standards Development Branch, MOE
- Yixun Shen, M.Sc., Standards Development Branch, MOE
Stakeholders and Reviewers
- Ahmed Sharaf, P.Eng., Ontario Municipal Affairs and Housing (MAH)
- Asim Masaud, P.Eng., Ontario Clean Water Agency (OCWA)
- Bill DeAngles, P.Eng., Consulting Engineers of Ontario (CEO)
- Brian Gage, B.Sc., Ontario Pollution Control Equipment Association (OPCEA)
- Chado Brcic, P.Eng., Association of Municipalities of Ontario (AMO)
- Chris Howard, P.Eng., Association of Municipalities of Ontario (AMO)
- Dave Tidy, P.Eng., Ontario Pollution Control Equipment Association (OPCEA)
- Deanna Barrow, P.Eng., Association of Municipalities of Ontario (AMO)
- Gerry Rupke, M.Eng., P.Eng., Engineering Advisor
- John Haanstra, P.Eng., Ontario General Contractors Association (OGCA)
- Matt Uza, B.A.Sc., Land and Water Policy Branch (LWPB), MOE
- Mike Pearce, P.Eng., Consulting Engineers of Ontario (CEO)
- Mohsen Keyvani, M.Eng., Waste Management Policy Branch (WMPB)
- Pervez Sunderani, P.Eng., Alberta Environment (AENV)
- Tom Copeland, P.Eng., Municipal Engineers Association (MEA)
- Troy Briggs, P.Eng., Water Environment Association of Ontario (WEAO)
- Wayne Parker, Ph.D., P.Eng., University of Waterloo
- Zafar Bhatti, Ph.D., P.Eng., Env. Assessment and Approvals Branch, MOE
- André D. Schnell, M.Eng., P.Eng., Standards Development Branch, MOE
- Bob Putzlocher, M.Eng., P.Eng., Eastern Region, Operations Division, MOE
- Charles Goulet, M.Eng., P.Eng., Ottawa District Office, MOE
- Dave Porter, P.E., Michigan Department of Environmental Quality
- Debra Abbott, P.Geo., Northern Region, Operations Division, MOE
- Gerald Novotny, P.E., Wisconsin Department of Natural Resources
- Heather Brodie-Brown, P.Geo., Standards Development Branch, MOE
- Irmi Pawlowski, P.Geo., Standards Development Branch, MOE
- Jamie Connelly, P.Geo., West Central Region, Operations Division, MOE
- Jeff Markle, M.Eng., P.Eng., Southwestern Region, Operations Division, MOE
- Lou-Ann Cornacchio, Northern Region, Operations Division, MOE
- Mark Wespetal, Minnesota Pollution Control Agency
- Myron Zurawsky, P.Geo., Central Region, Operations Division, MOE
- Parimal Parikh, P.E., Pennsylvania Department of Environmental Protection
- Peter Seto, Ph.D., P.Eng., Environment Canada
- Randy Thorson, P.E., Minnesota Pollution Control Agency
- Robert P. Ryan, M.E.S., R.P.P., Env. Assessment and Approvals Branch, MOE
- Ron Bell, P.E., Ohio Environmental Protection Agency
- Ted Belayneh, P.Geo., Central Region, Operations Division, MOE
- Terry Kirschenman, P.E., Iowa Department of Natural Resources
- Tony Ho, P.Eng., Standards Development Branch, MOE
Since the establishment of the Ontario Water Resources Commission under the Ontario Water Resources Act (1956), the commission engineers used the Ten States Standards for Sewage Works as the reference design guidelines for sanitary engineering practice. These publications were prepared, edited and published, approximately every five years, by the Great Lakes Upper Mississippi River Board of State Public Health Engineers and Great Lakes Board of Public Health Engineers. The commission engineers had also developed and applied internal advisory sewage works design guidelines based primarily on the Ten States Standards and included design, construction and operational experience specific to Ontario.
This practice has continued after the establishment of the Ministry of the Environment in 1973. The Province of Ontario joined the Great Lakes-Upper Mississippi River Board of State and Provincial Public Health and Environmental Managers and the Ten States Standards Wastewater Committee in 1977.
Over the years, engineering design criteria based on generally accepted good engineering practice in Ontario have been developed and the following ministry guidelines were published:
- Guidelines for the Design of Sewage Treatment Works (1980, 1984)
- Guidelines for the Design of Sanitary Sewage Systems (1979, 1985)
- Guidelines for the Design of Storm Sewer Systems (1979, 1985)
- Guidelines for Servicing in Areas Subject to Adverse Conditions (1985)
These guidelines have been revised and updated based on Ontario specific engineering practice, the latest Ten States Standards (Recommended Standards for Wastewater Facilities, 2004) and other relevant North American design guidelines and published as the Design Guidelines for Sewage Works (2008).
The Ontario Ministry of the Environment’s Design Guidelines for Sewage Works is intended for an audience that includes engineers who are responsible for designing sewage works, ministry engineers responsible for reviewing and approving the designs of such works and the municipalities/owners of the sewage works.
It is intended that this Design Guidelines document be used with professional judgment and experience in the design of sewage works and in the engineering review of applications for approval of such systems. The Ministry recognizes that the choice of sewage works designs may be influenced during the planning stages by sustainability issues, such as the cost to design and build sewage works as well as the ongoing cost to operate, maintain, rehabilitate and replace infrastructure.
Designers should note that the ministry has a number of specific guidelines and/or procedures which relate to sewage works that may affect design. Such specific guidelines and procedures take precedence over these Design Guidelines.
Similarly, the use of actual site-specific data is encouraged. Wherever possible, designers are encouraged to use actual data derived from the sewage works monitoring records and characterization studies. Actual data can be compared to the typical values provided in these Design Guidelines for comparison and consideration.
As well, it should be noted that this Design Guidelines document provides design guidance related to established technologies. The fact that other technologies or equipment are not mentioned in the Design Guidelines should not be construed as precluding their use. It is not the intention of the ministry to stifle innovation. The ministry will approve designs of sewage works if the applicant and designer can demonstrate that the works will have a reasonable and substantial chance of success for the particular application. However, design of sewage works using new and innovative technologies and equipment would be approved only where operational reliability and effectiveness of the works has been demonstrated with a suitably-sized prototype operating at its design load in the conditions suitable for the particular application.
Finally, it should be emphasized that this document contains design guidelines. Legislation, including legislated standards and regulations, takes precedence over the Design Guidelines and must be followed. Readers are cautioned to obtain their own legal advice and guidance in this respect.
Chapter 1: Legislative Framework
This chapter provides a brief introduction to the acts and regulations which may be applicable to the design of municipal sewage works which are defined and regulated by the Ontario Water Resources Act (OWRA).
The designers and proponents of sewage works are responsible for understanding and incorporating all relevant federal and provincial requirements in the planning, design, construction and operation of sewage works and obtaining legal advice with respect to this. It is recommended that designers and proponents be aware of any pending legislative requirements that may impact design considerations. It is essential to confirm any legislative requirements with the most up to date version, as changes occur frequently.
1.2 Applicable Legislation Administered by the Ministry
The Environmental Assessment Act (EAA), the Ontario Water Resources Act (OWRA), the Clean Water Act (CWA), the Nutrient Management Act (NMA), the Environmental Protection Act (EPA) and the Environmental Bill of Rights, 1993 (EBR) are statutes administered by the Ontario Ministry of the Environment (ministry) that are applicable to municipal sewage works. These statutes can be accessed from the Ontario e-Laws website or the ministry website under the “e-Laws” link.
Municipal undertakings would follow the approved Municipal Engineers Association (MEA) Municipal Class Environmental Assessment (MEA 2007 or most recent version) planning process and thereby meet the requirements of the EAA. For private undertakings that require EAA approval, reference should be made to the Designation and Exemption Private Sector Developers Regulation (O. Reg. 345/93), made under the EAA.
The statutory requirements for approval of sewage works are contained in Section 53 of the OWRA.
The designer or owner should contact the local District Office of the ministry for pre-submission consultation regarding applications for approval of proposed sewage works.
1.3 Sewage Works Regulations and Supporting Documents
The designer should refer to the regulations under the applicable Acts administered by the ministry as well as the Guidelines and Procedures related to sewage works. Before the design of sewage treatment works can be initiated, the designer needs to determine the effluent quality criteria that the sewage treatment works will need to achieve consistently. Generally, the determination of the effluent criteria will require site specific calculations to ensure consistency with the ministry’s Guideline B-1, Water Management Policies, Guidelines and Provincial Water Quality Objectives.
Guidelines with associated Procedures that should be consulted include:
- Guideline F-5, Levels of Treatment for Municipal and Private Sewage Treatment Works Discharging to Surface Waters (1994):
- Procedure F-5-1, Determination of Treatment for Municipal and Private Sewage Treatment Works Discharging to Surface Waters;
- Procedure F-5-2, Relaxation of Normal Level of Treatment for Municipal and Private Sewage Works Discharging to Surface Waters;
- Procedure F-5-3, Derivation of Sewage Treatment Works Effluent Requirements for the Incorporation of Effluent Requirements into Certificates of Approval for New or Expanded Sewage Treatment Works;
- Procedure F-5-4, Effluent Disinfection Requirements for Sewage Works Discharging to Surface Waters; and
- Procedure F-5-5, Determination of Treatment Requirements for Municipal and Private Combined and Partially Separated Sewer Systems;
- Guideline F-6, Sewer and Watermain Installation: Separation Distance Requirements (1994):
- Procedure F-6-1, Procedures to Govern Separation of Sewer and Watermains;
- Guideline F-8, Provision and Operation of Phosphorus Removal Facilities at Municipal, Institutional and Private Sewage Treatment Works (1994):
- Procedure F-8-1, Determination of Phosphorus Removal Requirements for Municipal, Institutional and Private Sewage Treatment Works
- Guideline F-10, Sampling and Analysis Requirements for Municipal and Private Sewage Treatment Works (Liquid Waste Streams Only) (1994):
- Procedure F-10-1, Procedures for Sampling and Analysis Requirements for Municipal and Private Sewage Treatment Works (Liquid Waste Streams Only)
The designer should ensure that the most current versions of the guidelines and procedures are being used; access is available from the ministry website. The list provided above is for information only and the ministry website, “Forms, Manuals and Guidelines” should be consulted for up-to-date references on currently active procedures and guidelines.
1.4 Other Applicable Legislation
Sewage works may be subject to planning-oriented legislation such as the Planning Act, the Municipal Act, 2001, the Ontario Municipal Board Act and others. In addition, it may be necessary to obtain approval from a number of other organizations which have jurisdiction over all or part of the project, primarily involving the Ministry of Labour. Approvals may be necessary from public bodies and authorities such as Ontario Power Generation, municipal plumbing and/or building departments, conservation authorities and the Federal Government (Parks Canada, the Department of Transportation, the Department of Fisheries and Oceans). Liaison with utility providers such as telephone, power and gas companies and railways may also be required. Designers should familiarize themselves with the requirements of all legislation dealing with sewage works, including relevant sections of the Building Code, the Electrical Safety Code, the Fire Code and labour safety regulations. Existing Ontario legislation may be found at the following “e-Laws” website. Additionally, the Sustainable Water and Sewage Systems Act, 2002, is a provincial statute which many municipalities reference when preparing sewage business plans and when considering the economic viability of proposed projects.
1.5 Ministry Approval Program for Sewage Works
The ministry’s approvals program is designed so that all undertakings requiring approval under the legislation administered by the ministry are carried out in accordance with that legislation and the ministry’s Guidelines and Procedures. The Guidelines and Procedures are intended to provide a consistent approach to various aspects of environmental protection throughout the Province.
The designer of sewage works should consult the newest edition of the ministry document Guide for Applying for Approval of Municipal and Private Water and Sewage Works. This document is intended to provide guidance to applicants requesting approval of municipal and private sewage works (other than industrial sewage works) under Section 53 of OWRA. The guide describes the approval process in general, clarifies the information needed to complete the respective application forms, and outlines the technical information that may be required in support of various applications for approval.
There are Ministry Guidelines and related Procedures that cover effluent quality requirements for sewage treatment plants. Designers should consult with the ministry’s staff from the Regional Office to determine the effluent quality requirements for specific proposals.
Higher levels of treatment, beyond secondary treatment, may be necessary in some watersheds due to limited assimilation capacity or due to critical downstream uses of the receiving water body. Many watersheds in the Province have been designated as requiring higher levels of treatment.
Assuming that a complete and satisfactory application for sewage works is provided and all necessary preconditions (e.g. compliance with the EAA) have been met, the ministry will be able to issue a Certificate of Approval (C of A) that will allow construction and operation of the sewage works. In the case of sewage treatment works, the C of A will outline the effluent quality criteria that need to be complied with and the effluent quality objectives to which the sewage works should be designed to, operated and maintained at all times. The effluent non-compliance limits and effluent quality objectives will generally be provided as both concentrations and mass loadings.
1.6 Legal Considerations
The designer should determine applicable statutes, regulations, guidelines and procedures for the proposed sewage works and ensure familiarity with the treatment, design and approvals requirements. There is a wide range of legislation that may apply to the planning, design, construction and operation of sewage works. While some are referenced here, no attempt is made for this listing to be complete. The user of this guide should obtain legal advice and understand and abide by any applicable legal requirements.
Chapter 2: Project Design Documentation
This chapter provides recommendations regarding documentation to support the design and construction of sewage works. The planning and engineering design of sewage works can vary with the size and complexity of the undertaking and therefore not all documents listed in this chapter may be relevant for a particular project.
The terms used are consistent with the Professional Engineers Ontario (PEO) Guideline Engineering Services to Municipalities (1986; Revised 12/11/98).
The description of technical information and documentation needed to support applications for approval of sewage works are provided in the ministry’s Guide for Applying for Approvals of Municipal and Private Water and Sewage Works.
The process of planning and design involves preparation of a number of separate documents in several phases. The number and complexity of the documents depend on the complexity of the sewage works. The planning and design of new sewage treatment plants require the preparation of several reports and many drawings. The design of a sanitary sewer extension may only require preparation of a single engineering drawing with the basis of design and specifications.
A three stage approach, outlined below, identifies the typical planning and design phases involved towards the development of appropriate project design documentation:
Stage 1 - The recommended approach to meet the project objectives is typically determined through a feasibility and pre-design investigation. Normally, Stage 1 will include: an Environmental Assessment (EA) and the preparation of an Environmental Study Report (ESR), a requirement of the Environmental Assessment Act (EAA) through the approved Municipal Engineers Association (MEA) Municipal Class EA, feasibility studies, master plans and other special services. The terms of the MEA's Class EA, a planning document approved under the EAA for use in planning municipal sewage works, should be referred to and followed throughout the initial planning process, as and if applicable.
Stage 2 - Preliminary design and reports should include preliminary plans and reports in the form of drawings and documents outlining the nature of the project, a summary of the basis of the engineering design, a preliminary cost estimate, project schedule and a description of the extent of services and recommendations. This is sometimes referred to as the “preliminary engineering report”, but should not be confused with pre-design and feasibility studies which are completed in Stage 1.
Stage 3 - Detailed design, final drawings and specifications, should include preparation of: a design brief, final plans (detailed engineering drawings), specifications (for construction, processes, materials and equipment), a final cost estimate, geotechnical and special investigations (e.g., hazardous building material report) and documents required for all approval or permit applications (e.g., permits for construction, approval for waste discharges, stream crossings, air emissions). Detailed engineering drawings include all structural, civil, architectural, mechanical, electrical and Supervisory Control and Data Acquisition (SCADA) drawings required to adequately and completely detail the work being proposed to ensure the works are constructed as designed. A report outlining operation and maintenance requirements may also be necessary.
2.2 Stage 1 Documents
Most designs will require feasibility or pre-design investigations. If an environmental assessment (EA) is necessary, it should be completed in accordance with the requirements of the EAA. For projects that do not require an EA, feasibility studies, treatability and pilot studies, pre-design reports and other special services such as the following may be needed:
- Soils investigation;
- Preparation of feasibility studies comparing alternatives in terms of capital, operation and maintenance costs, land requirements, operating efficiency and energy conservation;
- Obtaining topographic plans or photogrammetric mapping; and
- Other special services which may precede the preliminary design and detailed design services described in Stage 2 and Stage 3.
Where the proposed system incorporates processes for which established guidelines are not available, or include equipment and materials where no reliable data from full scale operation are available (e.g., processes that are new or in development - Section 3.9 -Technology Development), the following information may also be needed depending on the scope and risks involved in the project:
- All available data pertaining to the proposed process, equipment, or material;
- Results of any testing programs which have been undertaken by independent testing agencies, research foundations and universities;
- Identification of any known full-scale applications of the proposed process/equipment/material, including a description of the type of application and the name and address of the person who could be contacted for technical information on the application;
- Discussion of the impact of the potential failure of the proposed process/equipment/material and identification of the measures proposed
- to be undertaken to prevent or remedy any health hazard or noncompliance as a result of such failure; proposed contingencies to modify or replace the proposed process, equipment or material in case of their failure and liabilities associated with the proposal;
- Description of the monitoring, testing and reporting program proposed to be undertaken during the experimental period; and
- The proposed duration of the experimental period.
2.3 Stage 2 Documents
If a preliminary design report is being prepared for the proposed works, it should present the following information, where applicable. If these issues were addressed in an ESR, reference should be made to that document.
- Summary of raw sewage characteristics and design loads;
- Summary of receiving environment investigations and effluent quality criteria;
- Brief description of the proposed facilities including sludge management, where applicable;
- Summary of preliminary design basis, unit operations and process design parameters including information on operational reliability, unit redundancy/back-up (including sludge management facilities);
- Brief description of noise and odour generation potential in context with the separation distance between the sewage treatment plant (STP) and the periphery of the nearest sensitive land-use (buffer zone);
- Description of availability of stand-by power for the STP;
- Documentation of the extent, nature and anticipated population of the area to be serviced, facilities proposed to serve the area and provisions for future expansion of the sewage works to include additional service areas and/or population growth;
- Itemization and discussion of present and future domestic sewage production figures, industrial, commercial and institutional sewage production, infiltration and wet weather inflows used in sizing various components of the sewage collection and/or treatment works;
- Identification of all yard piping including: pipe location, size, depth, material and bedding, suitable inlets and outlets, the design and location of catch-basins, manholes, building connections and other appurtenances;
- Description of all waste streams generated in the STP, including their volumes, composition, proposed treatment and points of discharge;
- Description of the proposed flow metering, sampling and monitoring program, including monitoring of all waste streams;
- Description of the proposed pumping facilities, including the number and capacities of duty and standby pumps and discussion on the ability of the sewage works to treat sewage during power failure events through standby power facilities and/or equalization facilities;
- Brief discussion of the locations of all significant sewage works structures and their proximity to sources of potential water contamination (e.g., lakes, streams, wells) and susceptibility to flooding;
- Consideration and discussion of cost-effective design alternatives in terms of capital and operation and maintenance costs;
- Description of energy efficient systems incorporated into the proposed design to minimize the impact on future energy demands. This should include energy conservation and utilization practices in the selection of process machinery, the location and orientation of structures, use of biogas and the insulation of buildings;
- Identification of suitable procedures and documents for the pre-selection of machinery and equipment;
- Specification of hydraulic grade line;
- Discussion of the design criteria used for proposed sewers including design flows, minimum depth of cover and minimum separation distance from water mains and other utilities;
- Discussion of the planning for any future extensions and/or improvements to the sewage collection and treatment systems;
- Preliminary design plans, all bearing the project title, name of the municipality/owner, name of the development or facility with which the project is associated, name of the design engineer and preparation date and, where applicable, the plan scale, north point, land surveying datum and any municipal boundaries within the area shown. Where pertinent, the following information may need to be provided:
- General layout and size of existing and proposed sewers and location of major components of other existing and proposed works;
- General layout (line diagram) of the works (except for sewers);
- Process Flow Diagrams (PDFs) for the sewage treatment processes, showing all process components, the direction of flow of all raw and treated sewage, the location of all chemical addition points, the maximum flow of all streams entering and leaving each component of the process and a mass balance for all design parameters around each process component;
- Brief description of any renovations or improvements to the existing structures, sewer rehabilitation and flow modifications; and
- Brief description of buildings and other significant sewage works structures in terms of specific document needs (e.g., Code for Digester Gas and Landfill Installations CAN/CGA-B105 and Occupational Health and Safety Act (OHSA)).
2.4 Stage 3 Documents
2.4.1 Design Brief / Basis of Design
A design brief, summarizing the design criteria and presenting the design bases and calculations used in sizing individual components of the sewage works, should be prepared along with final plans and specifications. Where a preliminary report was not prepared or where some parts of the information in the preliminary report are no longer valid or applicable, the design brief should include the applicable information outlined in Section 2.2 - Stage 1 Documents as well as the applicable information outlined in the following subsections:
188.8.131.52 Design Brief - Sewers
- Nature and population of the area served (current and design);
- Design Peak Flow;
- Design data and calculations for individual sewers, including the required capacities;
- Capacity of the existing (or proposed) sewage works to meet the additional demand; and
- Field investigations.
184.108.40.206 Design Brief - Major Facilities
Major facilities include pumping stations, sewage treatment plants, outfalls and combined sewer overflow (CSO) facilities.
- Basic data on the estimated sewage generation rates from the population and area to be served, including:
- Design period;
- Design service population and area and population density;
- Design industrial, commercial and institutional sewage flows;
- Wet weather flow; and
- Design flows (average, peak daily and peak hourly).
- Design flows used in sizing of individual components of the sewage works (outfalls, pumps, channels, treatment process units and storage units, transport and collection facilities);
- Description (types, number and sizes) of all proposed sewage works, process units and equipment, including treatment and disposal facilities and identification of their process design parameters (e.g., screen sizing,
- surface overflow rates and retention times in settling tanks, oxygen levels in aeration tanks, chemical feed rates, chlorine concentration and contact time);
- Detailed process and hydraulic design (or sizing) calculations for all facilities, treatment process units and equipment;
- Accurate hydraulic profiles through treatment plants and pumping stations prepared for minimum and maximum flow conditions to a vertical scale adequate to clearly show the elevations of tank tops, channel and trough inverts, weirs and other features directly affecting the hydraulic gradient;
- PDFs showing all process components (i.e., including type, size, pertinent features, rated capacity of process units and major equipment, tanks, reactors, pumps, chemical feeders), direction of flow for all processes, recycle, backwash and waste streams, the location of all points of chemical addition and treated sewage effluent sampling and monitoring, and indicating the minimum and maximum flow rates of all streams entering and leaving each process component as well as a mass balance for all design parameters around each process component;
- Proposed flow metering system, including raw sewage (influent), recycle/return flows, waste flows and treated sewage (effluent);
- Proposed influent sewage and treated sewage effluent quality monitoring program, identification of sampling points, and frequency of sampling and calibration procedures.
- Procedures for calibrating plant instrumentation;
- Proposed system automation and backup procedures;
- Process Narrative; and
- Proposed rated capacity of the new or expanded sewage treatment plant.
2.4.2 Final Plans and Supporting Documents
All final plans should bear the project title, name of the municipality/owner, name of the development or facility with which the project is associated and name of the design engineer, including a signed and dated imprint of Professional Engineer’s seal and, where applicable, the plan scale, north point, land surveying datum and any municipal boundaries within the area shown.
Engineering plans should include plan views, elevations, sections and supplementary views which, together with the specifications and general layout plans, would provide the working information for finalization of the construction contract for the works. These drawings should show dimensions and relative elevations of structures, the location and outline of equipment, location and size of piping, liquid/water levels, location of utilities and ground elevations.
220.127.116.11 Plans of Sewer Systems
A comprehensive plan of the existing and proposed components of the sewage works should be prepared for projects involving new sewer systems or substantial additions to existing systems. This plan should show:
- All major topographic features including existing and proposed streets, contour lines at suitable intervals, drainage areas, watercourses, municipal boundaries and land surveying datum used (or assumed bench mark);
- Location and size of existing and proposed sewers and manholes; and
- Location and nature of all existing and proposed components of the sewage works associated with the proposed sewers, including any existing sewer manholes and overflows.
Detailed Engineering Drawings
A detailed plan and profile drawings should be provided for the proposed and adjacent sewers. The profiles should have a horizontal scale of not more than 1:1000 and a vertical scale of not more than 1:100. The plan view should be drawn to a corresponding horizontal scale. Detailed engineering drawings should show:
- Location of streets, sewers and manholes;
- Existing and proposed ground surface, size, material and class of pipe, location of valve chambers, manholes and other appurtenances;
- Location of all known existing structures which might interfere with or affect the proposed sewers, especially watermains, storm sewers and other appurtenances;
- Geotechnical information and groundwater table elevations along the sewer route;
- Details include sewer bedding and anchoring, service connections, bridge crossings, stream crossings, support structures for existing structures in the path of construction, trench bracing, thrust blocks, manhole installations; and
- Any additional descriptive specifications and information, not included in a separate specifications document, required to inform the contractor of all project requirements regarding the type and quality of construction materials and prefabricated components, quality of workmanship, testing of structures and materials to meet design standards and operating tests for the completed works and process components (e.g., leak testing of sewers).
18.104.22.168 Plans of Major Facilities
The major facilities include pumping stations, STP and sludge storage facilities.
A comprehensive plan of the existing and proposed sewage works should be prepared for all projects involving new major sewage works. This plan should show:
- Area to be serviced and the location of the proposed sewage works;
- All major topographic features including, but not limited to, drainage areas, existing and proposed streets, watercourses, contour lines at suitable intervals, municipal boundaries, land surveying datum used (or assumed bench mark); and
- Location and nature of all existing and proposed major components of the sewage works associated with the proposed facilities, including pumping stations, treatment plant, storage facilities, and outfalls together with their individual geo-reference coordinates (Universal Transverse Mercator Easting and Northing).
Individual site plans should be provided for all proposed major facilities of the sewage works and modifications/upgrades of such facilities. Each site plan should show:
- The entire property where the facility is to be or is located, including the property lines and identification of the nature of the adjoining lands;
- Topographic features of the property and adjoining lands, including existing and proposed streets, contour lines at suitable intervals, drainage areas, watercourses, the elevation of the highest known flood level, municipal boundaries and the land surveying datum (or assumed bench mark) used;
- Layout, size and nature of the existing, proposed and future structures on the property showing distances from property lines and show residences and other structures on adjoining properties;
- Test borings and groundwater elevations within site limits;
- Utility routing within site limits;
- Each site plan should be developed according to local municipal bylaws and be approved by the local municipality; and
- Each drawing should bear a seal of a professional engineer licensed in Ontario.
General Layout and Detailed Engineering Drawings
The following general layout and detailed engineering drawings should be provided for all new major facilities of the sewage works and modifications or upgrades of existing major facilities:
- Accurate hydraulic profiles through sewage works such as collection facilities, sewage treatment plants or pumping stations, prepared for minimum and maximum flow conditions to a vertical scale adequate to clearly show the elevations of tank tops (top of concrete), channel and trough inverts, weirs and other features directly affecting the hydraulic gradient;
- General layout plans for all major facilities of the works (e.g., layout of all processes together) including all associated process flow channels and piping (show direction of flow), process and ancillary equipment, air and chemical feed lines, points of chemical addition, and waste streams;
- Construction scale plan and profile drawings (with dimensions and elevations) of all facilities proposed to be constructed or modified, including any additional descriptive specifications and information not included in a separate specifications document.
- All engineering discipline drawings as required to adequately characterize the works need to be provided; and
- Process and instrumentation diagrams (P&ID) showing the interconnection and operation control arrangements for all process and ancillary equipment and appurtenances.
Detailed technical specifications should be provided for all sewage works projects. In the case of minor works such as minor sewer extensions, these specifications can generally be noted on the final plans. For more extensive works, separate specifications documents should be prepared.
These specifications should include all construction and installation information not shown on the drawings but required to inform the contractor of all project requirements regarding:
- Type and quality of construction materials and prefabricated components;
- Quality of workmanship;
- Type, size, rating, operating characteristics and quality of mechanical and electrical equipment and installations (e.g., process and ancillary equipment and appurtenances, valves, piping and pipe joints, electrical apparatus, wiring, metering and monitoring equipment, laboratory fixtures and equipment, special tools);
- Type and quality of process materials (e.g., filter media) and chemicals;
- Testing of structures, materials and equipment necessary to meet design standards;
- Margin of error and calibration frequency necessary to meet the performance criteria of effluent monitoring;
- Operating tests for the completed works and process components (e.g. leak testing of sewers and other piping);
- A program for keeping existing sewage works facilities in operation during construction of additional facilities so as to minimize interruption of service;
- Laboratory facilities and equipment;
- The number and design of chemical feeding equipment;
- Procedures for testing, as needed, prior to placing the project in service; and
- Materials or proprietary equipment for facilities including any necessary backflow or backsiphonage protection.
2.5 Sewage Treatment Plant Process Optimization
The designer may optimize an existing sewage treatment plant to obtain additional capacity or improved performance rather than expanding or physically upgrading the plant. The results of any plant optimization investigation, which forms the basis for any proposed design changes, need to be adequately documented or referenced (Section 3.10.3 - Process Re-Rating).
Process optimization needs to ensure that the proposed changes to the existing sewage works will consistently and reliably satisfy the requirements of the C of A.
Process optimization can play an important role in the assessment of an STP ability to increase its capacity or to meet more stringent effluent quality. There are many sources of information on plant process optimization that can be referenced and four ministry sponsored references include:
- Guidance Manual for Sewage Treatment Plant Process Audits (1996);
- The Ontario Composite Correction Program Manual for Optimization of Sewage Treatment Plants (1996);
- Assessment of the Comprehensive Performance Evaluation Technique for Ontario Sewage Treatment Plants (1994); and
- Assessment of the Comprehensive Technical Assistance Technique for Ontario Sewage Treatment Plants (1995).
Chapter 3: General Design Considerations
This chapter describes general design considerations related to the construction, operation and maintenance of municipal sewage works. Topics covered in this chapter include site selection, security, energy conservation, reliability and odour control. Specific details on design considerations for Pumping Stations and Sewage Treatment Plants are provided in Chapter 7 - Pumping Stations and Chapter 8 - Design Considerations for Sewage Treatment Plants.
Sewage pumping and treatment works should be able to handle all flows and loadings to be expected at the works and meet the overall requirements of the works in terms of facility operation, treatment and effluent quality criteria. Designs should anticipate future changes in terms of hydraulic and/or contaminant loadings and provide flexibility in terms of meeting all reasonable expectations.
3.2 Design Basis
Sewage pumping stations and treatment works need to be designed to meet the current and planned development needs, eliminate bypasses and overflows (Section 8.5.6 - Bypasses and Overflows). Further details on the design basis for facilities and treatment process units are contained in their respective sections.
3.3 Site Selection
Sewage pumping station and sewage treatment plant sites should be located as far as practicable from any existing commercial or residential area or any area that will probably be developed within the plant’s design life. The plant site should be separated from adjacent uses by a buffer zone and provided with adequate area for any foreseeable future expansion. Plant outfalls should be placed so as to minimize impacts on public water supply intakes and where applicable, satisfy the requirements of the federal Navigable Waters Protection Act (NWA). Information on site selection for sewage treatment plants is included in Section 8.1 Sewage Treatment Plant Location.
The design of the sewage works should allow for:
- Practicality/ease of construction;
- A phased approach;
- Maintaining operations during construction; and
- Planning for future additions/expansion.
3.4 Operation and Maintenance
All sewage pumping and treatment works should be designed with consideration to operation and maintenance. All equipment should be able to be serviced both routinely and during breakdown with a minimum of disruption, including provisions for isolating equipment, removing equipment and safety. Critical equipment should be provided with backup capacity to ensure uninterrupted operation of treatment process units and pumping facilities. Special attention should be given to areas that would be designated as confined space areas.
Facilities need to be provided for staff, including personnel, laboratory and maintenance facilities. The facilities required will depend on the size and remoteness of the sewage works.
For a sewage treatment plant, personnel facilities are generally located in the administration building. This building would serve the needs of the supervisory staff, the operation and maintenance personnel and often the laboratory staff.
A sewage treatment plant staffed for eight hours or more each day should possess support facilities for the staff.
The following, in conformance with applicable building codes, should be provided:
- Washing and changing facilities. These should include showers, lockers, sinks and toilets sufficient for the entire staff necessary to operate the facility at design conditions. A heated and ventilated mudroom is desirable for changing and storing boots, jackets, gloves and other outdoor garments worn on the job. Each staff member should have separate lockers for street clothes and plant clothes. Separate washing and changing facilities should be available for men and women, with the exception of the mudroom;
- Eating facilities. Provide a clean, quiet area with facilities for storage and eating of light meals;
- Meeting facilities. Provide a place to assemble the plant staff and visitors. In some cases, the meeting facilities and the eating facilities will be the same; and
- Supervisors' facilities. Provide a place where discussions and paper work can be carried out in private.
Small treatment plants that are not staffed 8 hours a day need not contain all of the personnel facilities required for larger plants, but should have a room with a door capable of being locked and contain at minimum a washroom.
Laboratory facilities required will depend on the amount of analytical work conducted onsite. Generally, regulatory samples are sent to an offsite certified laboratory for analysis while process sampling and analysis are done onsite.
Facilities should be provided to allow for adequate maintenance of equipment. Such facilities generally include a maintenance shop, garage, storage space and yard maintenance facilities. Access to nearby municipal garages and other maintenance centres should be considered and duplication of facilities avoided where possible.
Storage space should be provided for spare parts, fuel supplies, oils and lubricants, grounds maintenance equipment and collection system equipment. In larger facilities it may be desirable to have a separate storage building. In smaller facilities it may be desirable to combine storage with the shop or garage so that the stored material can be protected against unauthorized access and use. For design information on storage and handling of chemicals refer to Chapter 20 - Handling of Chemicals.
All basements should have a flood alarm system connected to the central alarm system of the facility.
3.5 Flood Protection
Sewage pumping stations and treatment plants should be protected against flooding. The treatment process units should be located at an elevation higher than the 100-year flood level or otherwise be adequately protected against 100-year flood damage. Newly constructed plants should remain fully operational during a 100-year flood event. Information on flood protection of sewage pumping stations can be found in Section 7.1.2 - Flooding and for sewage treatment plants in Section 8.1.2 - Flood Protection.
Measures should be provided to prevent unauthorized entry of pumping and treatment facilities which may result in personal mishap or disruption of operations. Measures should include:
- Fencing, railings and walls;
- Secured entrance gates;
- Provisions for emergency vehicles (work closely with the local fire department);
- Traffic control signs or signals;
- Provisions for safe transport of chemicals, fuel supplies and sludge; and
- Care should be taken to avoid trapping personnel with these security measures.
Suggested security provisions for remote pumping stations are outlined in Section 7.6 - Alarm Systems.
3.7 Energy Conservation
The designer should consider the use of energy efficient treatment processes and equipment including motors, blowers and diffusers over the life of the equipment or process. The treatment processes and equipment should be evaluated in terms of life-cycle costing to ensure maximum benefits.
3.8 Reliability and Redundancy
Reliability and redundancy criteria should be determined to ensure protection of public health and the environment. Standby or redundant capabilities need to be provided for satisfactory operation of the sewage works during power failures, flooding, peak loads, equipment failure and maintenance shutdowns. Generally, sewage pumping stations and treatment works should be designed so that with the largest flow capacity unit out-of-service the hydraulic capacity of the remaining units can handle the design peak instantaneous flow. The designer should ensure that the sewage flow to any treatment process unit outof-service can be routed to remaining units in service with minimum impact on their performance.
The design of a sewage treatment plant, since it has an effluent discharge into the environment, should be based on the premise that the failure of any single component should not prevent the sewage works from meeting the required effluent quality and quantity criteria, while operating at design flows (i.e., minimum to maximum design flows).
A treatment plant that has strictly defined effluent quality criteria in terms of objectives and non-compliance limits should have a commensurate level of reliability and redundancy of its components. The designer of a sewage treatment plant should consider the following when evaluating and documenting reliability of the proposed treatment components:
- The effluent non-compliance limits and other site specific quality and quantity criteria (i.e., concentrations and loadings) during the full-range of design flows (i.e., minimum to maximum design flows);
- The likelihood of the system having reduced level of treatment or performance;
- The risk to the performance of the system and in turn to the environment, public health and safety if the level of treatment and performance of its components is reduced; and
- The manner and methods by which reliability is provided so that reduced treatment/performance and overflows or bypasses can be eliminated.
As part of the reliability and redundancy analysis of individual process units, equipment or elements, the designer should also consider the definition of the following:
- Critical process element, unit or equipment;
- Critical events:
- Estimated duration of events;
- Actions/safeguards; and
Effect on the effluent quality versus non-compliance limits. This analysis may be carried out using Table 3.1 as an example.
Such a table should then form a part of the Operations and Maintenance Manual to ensure the long-term satisfactory performance of the sewage treatment system.
3.9 Technology Development
Implementation of new technologies and re-rating of existing facilities require special considerations. For the purpose of this Design Guidances document, new technology and proven technology are defined below.
3.9.1 New Technology
Any method, process, or equipment proposed to collect, convey, treat or dispose of sewage that is being tested or has been tested at pilot-scale or at full-scale level, but lacks an established performance record.
3.9.2 Proven Technology
A proven technology has an established performance record and means a technology with:
- A minimum of three separate installations, operated at near design capacity;
- A minimum of three years of operating record at three separate locations; and
- A minimum of three years operating record showing reliable and consistent compliance with the design performance criteria without major failure of either the process or equipment.
The designer should be aware that new technologies may have a higher risk of failure than proven technologies. The degree of risk of failure can be evaluated through review of sequential stages of a new technology development where the risk of failure is reduced with each of the following sequential steps:
- theoretical concept;
- development at the laboratory or bench-scale;
- experimental stage consisting of pilot-scale program and field application testing;
- extensive pilot or full-scale testing; and
- established performance record.
|Element||Example Events||Event Duration||Frequency||Action/ Safeguard||Effect on Effluent|
|Pumps||pump failure||Weeks||1 in 5 years||firm capacity|
|Chemical system||components failure||Minutes||1 in 1 year||alarm, analyzer|
|Chemical system||pump failure||Hours||1 in 3 years||backup system|
|Pretreatment||equipment or process failure||Weeks||1 in 5 years||firm capacity, backup systems or bypasses||none|
|Primary clarifier||replace motor or gear box||Hours||1 in 10 years||spare parts on site||minimal|
|Primary clarifier||equipment failure||Weeks||1 in 5 years||run with unit out of service||minimal|
|Final clarifier||replace motor or gear box||Hours||1 in 10 years||spare motor on site|
bypass to other clarifier, if available
|some degradation of effluent quality for short period of time|
|Liquid-train biological processes||equipment failure||Weeks||1 in 5 years||spare parts on site, run with unit out of service||some degradation of effluent quality|
|Disinfection||equipment failure||Days||1 in 5 years||alarms, spare parts on site||significant impact on effluent quality|
|Biosolids processes||equipment and process failure||Weeks||1 in 5 years||firm capacity or operate with fewer units||minimal|
|Power||power outage||Days||1 in 5 years||alternate grid||none|
|Power||equipment failure||Days||1 in 3 years||generator||minimal|
A new technology that is considered for a site-specific application as part of an experimental or pilot program should meet the following requirements:
- The size of the principal components and duration of the pilot program should be such that physical, chemical and/or biological processes are accurately simulated under representative conditions;
- Process variables normally expected in full-scale application have been simulated;
- All recycle streams have been considered;
- Variations in influent sewage characteristics that can substantially affect performance in full-scale application have been anticipated and simulated;
- The duration of testing has been adequate to ensure stable operating conditions and subsequent consistent performance has been confirmed;
- The service life of high maintenance or replacement items have been accurately estimated;
- Basic process safety, environmental and health risks have been considered and found to be within reasonable limits;
- Types and amounts of all required process additives have been determined and tested; and
- A contingency plan should be in place in the event that the new technology fails to meet the expected performance.
Designers considering a full-scale application of any new treatment technology should evaluate the data and other information of any testing programs which have been undertaken by independent testing agencies necessary to ensure the viability of the proposed treatment technology and application and document their findings in the Design Brief (Chapter 2 - Project Design Documentation).
Note that specific new technologies are not discussed in this Design Guidances document.
3.10 Sewage Treatment Plant Capacity Rating
3.10.1 Design Capacity
In the case of a new municipal sewage treatment plant, a conceptual design capacity will be developed through the Municipal Engineers Association’s Municipal Class Environmental Assessment (i.e., Class EA) process and will be documented in the Environmental Study Report (ESR). Once the ESR has met the requirements of Class EA, this conceptual design capacity will form the basis of detailed engineering design resulting in plans and specifications which, in turn, will be used for obtaining a Certificate of Approval (C of A) from the approving Director at the Ministry of the Environment (ministry). This conceptual design capacity should be documented in the ESR and confirmed as the proposed rated capacity in the final design brief. The rated capacity is the highest average annual flow during which the sewage treatment plant can consistently meet site specific effluent quality criteria. It will be specified in the C of A as the rated capacity of the approved sewage treatment plant.
In cases where an expansion, alteration or modification is required to an existing treatment plant, the proponent will need to determine the applicable Schedule (Schedule A, A+, B or C) of Class EA that is relevant to the undertaking. One of the factors in making this determination is the “existing rated capacity” of the “existing sewage treatment plant” referred to in the Schedules included in Appendix 1 of Class EA document. This “existing rated capacity” is the rated capacity of the sewage treatment plant specified in the existing C of A for the facility. If the proposed undertaking results in flows to the sewage treatment plant that exceed the rated capacity, the expanded flow requirement needs to form the basis of further Municipal Class EA considerations and subsequent detailed engineering design.
3.10.2 Rated Capacity
The rated capacity of a sewage treatment plant, in accordance with the C of A, is defined as the average daily flow which the sewage treatment works have been approved to handle, calculated as the cumulative total sewage flow to the sewage works during a calendar year, divided by the number of days during which sewage was flowing to the sewage treatment works that year. This is equivalent to the Design Average Daily Flow.
In establishing the design capacity of the sewage treatment plant the designer should consider:
- The ability of the sewage treatment plant to consistently produce treated effluent meeting all applicable Ontario regulations, guidelines, procedures and site specific effluent quality criteria;
- The rated capacity should be established by assessing the capacity and performance of each process in isolation and in conjunction with the entire process train operating as a system to identify the process with the lowest treatment capacity that represents the capacity limiting process or the treatment rate of its slowest unit operation that forms the rate controlling step
footnote 1; and
- The flow(s) and loadings into the sewage treatment plant, process components, trains or stages, (the design maximum, minimum, hourly and instantaneous flows for each individual treatment process and the overall plant).
The designer should undertake a detailed design to meet these requirements in the context of the issues addressed in these design guidelines and specifically in Section 8.5 - Major Design Criteria. The rated capacity of the sewage treatment plant will be confirmed in the review of the proposed design by the ministry as part of the C of A application review process and will be included in the C of A issued after the review is completed.
The sewage treatment plant rated capacity, as defined in the final design brief and subsequently in the C of A, is based on the design assumptions at the time of applying for approval. Improvements to operational knowledge, technologies, changes in sewage quality characteristics, conditions of the physical facilities, and process optimization can change the performance of an STP and providing a basis for the re-evaluation of the rated capacity of the STP.
3.10.3 Process Re-Rating
Sewage treatment plant re-rating is the practice of evaluating sewage treatment plants or unit treatment processes to determine if it is possible to consistently operate the STP or unit treatment processes at a higher capacity than the original rated capacity. Process unit or STP re-rating requires at least the following:
- Operational data from continuous operation of a full-scale installation treating or conveying the type and strength of sewage to be treated;
- Automatic indicating, recording and totalizing flow-measurement equipment should be provided. Total flow and other process control measurements should be taken and recorded daily or at a frequency required to verify the operation of the facility or unit process at the proposed re-rated capacity; and
- A proper process audit with stress testing should be carried out, with adequate sample collection and analyses, to demonstrate effectiveness and efficiency under minimum and maximum design flow and loading conditions over extended periods of time such that stable operating conditions have been achieved.
In addition, the following specific elements need to be addressed in all proposals for sewage treatment plant re-rating:
- Impacts of the proposed change on the sewage treatment plant ability to reliably and consistently comply with effluent quality criteria and C of A conditions;
- An evaluation of the potential for the treatment system upset, overflow, by-pass or non-compliance with effluent limits;
- An evaluation of re-rating the sewage treatment plant versus expanding of the plant based on the capacity to accommodate new growth. The community’s historical and anticipated rate of growth should be considered;
- An evaluation of the impact of re-rating the sewage treatment plant on operation and maintenance of the facilities. This evaluation should, at a minimum, include the impact on treatment plant operators, including level of certification needed and the need for additional process control and monitoring; and
- For more detailed information on sewage treatment plant re-rating and treatment processes optimization, the designer is referred to the following ministry documents:
- Guidance Manual for Sewage Treatment Plant Process Audits (1996);
- The Ontario Composite Correction Program Manual for Optimization of Sewage Treatment Plants (1996);
- Assessment of the Comprehensive Performance Evaluation Technique for Ontario Sewage Treatment Plants (1994); and
- Assessment of the Comprehensive Technical Assistance Technique for Ontario Sewage Treatment Plants (1995).
3.11 Emissions of Contaminants to Air
For all sources of emission of contaminants to the air at sewage works (e.g. gases from air striping process, exhaust emissions, noise of standby or stationary generators, noise of air blowers or compressors, odours) the requirements of Section 9 of the Environmental Protection Act (EPA) need to be satisfied.
The Air Pollution - Local Air Quality Regulation (O. Reg. 419/05) made under the EPA specifies the maximum allowable concentration of the specific air contaminants at the point of impingement. Compliance is achieved by maintaining the point of impingement concentrations of the contaminants discharged from the source of emission below the maximum concentrations stipulated in the regulation. Typical points of impingement are the property line and all critical receptors such as building air intakes or windows.
3.12 Sampling and Monitoring Equipment
Sampling devices should be compatible with the needs of the influent and effluent quality monitoring program. The type of sampler and sample container used depends on the parameter being tested in the sample. Sample devices include dippers, vacuum lifts and pumps (peristaltic, positive displacement or centrifugal). The amount of lift should be a design consideration.
Samplers need to maintain a sampling velocity which will prevent the solids in the sample from settling in the sampler lines. Composite samplers should be flow proportional and capable of sampling flow over a 24-hour period. Sampling lines should be large enough to carry suspended matter. A sampler should have a purge cycle to expel any material left in the sample line from the previous sampling. To comply with sample preservation, most samplers will need a means of refrigeration for the sample.
General guidelines to be used for automatic samplers include the following:
- The sampling device should be located near the source being sampled, to prevent sample degradation in the line;
- Long sampling transmission lines should be avoided. If sampling transmission lines are used, they should have velocities sufficient to prevent sedimentation. Provisions should be included to make sample lines removable and easily cleanable. Minimum velocities in sample lines should be 1 m/s (3 ft/s) under all operating conditions;
- Sampler control should consider continuous flow or flushing to ensure a representative sample is taken;
- Samples need to be refrigerated unless the samples are not affected by biological degradation;
- Sampler inlet lines should be located where the flow stream is well mixed and representative of the total flow;
- Sampling access points should be provided for return and recycle lines, sewage inflows and outflows and waste sludge lines; and
- Access to sampling sites should be provided in the design of sewage pumping and treatment facilities to obtain grab samples.
The designer of new sewage works needs to evaluate the existing and proposed hydraulic grade lines to ensure raw sewage or effluent pumping requirements are met under steady state and peak flow conditions for the design life of the facility. The use of gravity flow, where appropriate, may result in lower capital and operating costs, but generally restricts the siting of the treatment works and may not be suitable for use with some treatment processes. Such factors should be carefully evaluated to determine the best possible hydraulic and siting configuration.
3.13.1 Flow Metering
All sewage pumping stations and sewage treatment plants should have flow measuring devices to measure the sewage flow to the works and through the sewage treatment plant, including overflows and bypasses. In addition, flow through unit processes, backwash flow, chemical and gas flows should be metered for monitoring and controlling the treatment processes (Chapter 9 - Instrumentation and Control).
The designer should consider the importance of meter accuracy, specifically as it relates to compliance with C of A effluent quality criteria relating to contaminant loadings.
3.13.2 Flow Distribution
Flow distribution or splitting refers to the separation of a flow stream into two or more smaller streams of a predetermined proportional size. Flow splitting allows unit processes to be used in parallel and applies mainly to liquid streams but can also be used for sludge streams.
22.214.171.124 Flow Splitting Devices
The following devices can be used for flow splitting; many can also be used for flow measurement. These include:
- Flumes - Flumes are open channel structures or devices that produce a headwater (upstream) elevation related to a predictable flow going through the structure as long as the flumes are operating in a non-submerged condition. The higher the flow, the higher the headwater elevation. Two or more identical flumes will pass the same flow with the same upstream head. If two or more identical flumes share the same headwater such as in a splitter box, they will effectively split the flow evenly among the flumes. One advantage in using flumes to split the flow is that they can operate accurately with very little available head. Flumes are not recommended if the flow needs to be split unevenly because the flow is not linearly related to the throat width of the flume;
- Weirs - Weirs are flat plates set in a channel which, like flumes, produce an upstream head proportional to the flow going over the weir. The main advantage of weirs is that they are fairly compact and inexpensive. Their main disadvantage is that they need sufficient head to operate properly. Generally, the weir plate itself has to be in the order of a minimum of two times the maximum head generated behind the weir in height. If the flow is to be split unevenly, suppressed weirs, circular weirs or Cipolletti weirs should be considered;
- Control Valves - Control valves are used to split the flow when little or no head is available or space constraints prohibit the use of a splitter box. There are several valves suitable to control flow splitting. Butterfly valves can be used in large-flow situations where the chance of plugging with stringy materials is low. Pinch valves are ideally suited for flow control when there is no debris in the fluid. Plug valves, ball valves and other valves which do not plug are appropriate for flow splitting control. It is best if the valves are automatic and controlled by a flow signal from each of the individual flow paths. In this way the flow can be instantaneously totaled and divided out in a predetermined way; and
- Symmetry - Symmetry has been relied on to split flows with mixed results. Symmetrical flow splitting relies on the symmetry of the inlet structures to the upstream flow that is being split. One problem with reliance on this type of flow scheme is maintaining complete dynamic symmetry throughout the actual design flow range. Small variations in approach velocity, channel and pipe roughness and downstream head losses can have a major impact on the accuracy of the flow split.
126.96.36.199 Factors Affecting Flow Splitting
The following points should be considered in the design of the various components of the hydraulic flow distribution:
- Upstream Conditions - If the upstream flow velocity is above 0.3 m/s (1 ft/s) significant velocity head can develop. If the flow is not perfectly symmetrical in relation to the splitting devices, the velocity head can develop uneven pressure head on the different flow splitting devices. This causes an uneven or unintended flow split. A sufficient amount of head has to be available upstream of the splitting devices so as not to cause flooding of the upstream processes.
- Inadequate Head or Pressure - If there is insufficient elevation difference between the upstream process and the downstream tanks, the flow splitting devices will not function properly and submergence of the splitting device can occur. When a device is submerged, the tail water depth prevents free fall and an aerated nappe from occurring through the device. The head on the device, in this case, is no longer related in a consistent way to the flow going through the device. If one or more of the devices are submerged, but have the same headwater, the devices cannot reliably split the flow in the required ratio. The results would be unpredictable and inconsistent.
- Approach Conditions - The flow conditions approaching the splitting devices are critical to the success of the flow splitting effort. The flow velocity in the headwater area should be 0.3 m/s (1 ft/s) or less to minimize any potential velocity head, which is described by the equation V2⁄(2g) (where V is velocity and g is acceleration due to gravity). The additional velocity head could turn into pressure head resulting in uneven head loss among the splitting devices, changing the flow split. An uneven approach velocity distribution can also result in an unacceptable change in the flow split.
- Downstream Conditions - Downstream conditions can seriously affect the flow splitting capability of splitting weirs. Sufficient head needs to be available between process units to allow the proper functioning of the flow splitting devices. In particular, the flow splitting device needs sufficient free fall to the tail water for it to work properly.
- Submerged Flow - Submerged flow occurs when the tail water depth is too high to allow free fall through the splitting device. Without free fall, the splitting device will not work properly. Certain devices such as flumes can tolerate a degree of submergence and still function. Weirs need at least 0.3 m (1 ft) of free fall to allow for an aerated nappe. If a device is overly submerged, the flow through the device is affected by the tail water depth, which alters the flow split design.
- Improper Sizing of Primary Device - For satisfactory results, the size of the primary flow splitting device needs to match the flow being divided. If the primary flow splitting device is too large, it will not function properly. A minimum amount of head loss has to be generated through the device: For small flows, at least 0.2 m (0.7 ft) head loss needs to be generated. For larger flows, more head loss is required to split the flow. If the flow over a weir is insufficient it may result in the spillover running down the face of the weir. The nappe is no longer considered aerated and it acts as though it were a submerged flow. This can result in a pulsing of the flow over the weir as the nappe hugs and then separates from the weir. The resulting split flow is unpredictable. If the primary splitting device is too small it will generate too large a head to be accurate. It will also generate excessive head loss which may not be acceptable. Finally, the device would need a higher free fall to function.
3.14 Manuals & Training
3.14.1 Operations Manual
An Operations Manual should be supplied to the sewage treatment plant as an essential part of the design. The Operations Manual should include detailed descriptions and explanations of the treatment processes and operational strategies for meeting the effluent quality criteria specified in the C of A. All standard operating procedures developed for the plant should be included in the Operations Manual. The manual should be provided in standard electronic format and cover the following topics:
- A plant overview and process control philosophy statement;
- Detailed unit operations and chemical dosing for normal operation and emergency situations;
- Simplified system schematics that take into account the spatial relationships involved;
- Descriptions and operational procedures for facility utilities (e.g. Heating, Ventilating, and Air Conditioning (HVAC), plant service water, security);
- General safety information, including provisions to keep Material Safety Data Sheets (MSDSs) up-to-date;
- Spill containment and emergency procedures and reporting;
- Emergency power systems and electrical system operation;
- Security of infrastructure, electronic files and/or programs and response procedures to breaches or intrusions;
- The licensing requirements as indicated in Licensing of Sewage Works Operators Regulation (O. Reg. 129/04) made under the Ontario Water Resources Act and other applicable regulations;
- Monitoring, reporting and documentation procedures;
- Procedures for bringing equipment on-line after maintenance;
- Reliability and redundancy analysis of system components;
- Detailed routine maintenance procedures;
- Alarm notifications and response procedures;
- A list of emergency contacts and locations of contingency plans; and
- A list of major equipment suppliers.
3.14.2 Equipment Manuals
Equipment manuals including parts lists and parts order forms, operator safety procedures and an operational troubleshooting section should be supplied to the owner as part of any proprietary unit installed at the works.
Provisions should be made for operator instructions with documentation at the start-up of any new facility, equipment or process.
3.15 Health and Safety
Consideration needs to be given to the safety of sewage works personnel and visitors. The designer should refer to all applicable codes and regulations under the Occupational Health and Safety Act, the Building Code Act, 1992 and the Fire Protection and Prevention Act, 1997. Items to be considered include noise arresters, noise protection, confined space entry, protective equipment and clothing, gas masks, safety showers and eye washes, handrails and guards, ladders, warning signs, smoke detectors, toxic gas detectors and fire extinguishers.
Equipment and chemical suppliers should also be contacted regarding particular hazards of their products and the appropriate steps taken in the facility design to ensure safe operation. The designer may also refer to the U.S. National Fire Protection Association (NFPA) - NFPA 820 - Standard for Fire Protection in Wastewater Treatment and Collection Facilities.
- footnote Back to paragraph The products of a sequence of processes can be formed no faster than the rate of the slowest step in the sequence. Therefore, if one of the steps in a sequence is slower than all the others, the overall process rate is limited by and is exactly equal to, the rate of this slowest step (the rate controlling step). The rated capacity of the treatment system is therefore based on the rate controlling step under specific operating conditions such as influent sewage quality and flow variations, temperature and effluent quality requirements.