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Module 14 Conventional Filtration Drinking Water Operator Certification Training Module 14 Conventional Filtration Updated February 2014 This course includes content developed by the Pennsylvania Department of Environmental Protection (Pa. DEP) in cooperation with the following contractors, subcontractors, or grantees: The Pennsylvania State Association of Township Supervisors (PSATS) Gannett Fleming, Inc. Dering Consulting Group Penn State Harrisburg Environmental Training Center MODULE 14: CONVENTIONAL FILTRATION Topical Outline Unit 1 – Conventional Water Treatment Overview I. Purpose of Conventional Water Treatment A. Compliance with Regulations B. Production of Safe Drinking Water II. Terms and Definitions A. Clarification B. Coagulation C. Colloids D. Conventional Filtration E. Disinfection F. Floc G. Flocculation H. Sedimentation I. Sludge J. Turbidity III. Conventional Water Filtration Process Flow A. Source Water B. Chemical Addition C. Pretreatment D. Filtration E. Disinfection F. Corrosion Control G. Water Distribution Bureau of Safe Drinking Water, Department of Environmental Protection Drinking Water Operator Certification Training i MODULE 14: CONVENTIONAL FILTRATION Unit 2 – Mixing, Coagulation, and Flocculation I. Mixing II. Coagulation A. Coagulant Chemicals B. Basic Coagulant Chemistry C. Process Control D. Chemical Safety III. Flocculation A. Floc Formation B. Performance Considerations C. Types of Flocculators D. Flocculation Basins Unit 3 – Sedimentation/Clarification I. Principles of Operation A. Settling Characteristics B. Sedimentation Basin Characteristics C. Operating Parameters II. High Rate Sedimentation Process A. Tube or Plate Settlers B. Specialized Processes III. Sedimentation Mathematical Calculations A. Theoretical Detention Time B. Surface Loading C. Mean Velocity D. Weir Loading Rate Bureau of Safe Drinking Water, Department of Environmental Protection Drinking Water Operator Certification Training ii MODULE 14: CONVENTIONAL FILTRATION Unit 4 – Filtration I. General Overview of Conventional Filtration A. Process Description B. Filtration Mechanisms II. Types of Filters A. Gravity B. Pressure III. Filter Control Systems A. Purposes B. Common Control Systems IV. Performance Considerations A. Filter Media B. Filter Underdrains C. Operational Criteria D. Backwashing V. Process Calculations A. Filtration Rate B. Backwash Rate VI. Record Keeping Bureau of Safe Drinking Water, Department of Environmental Protection Drinking Water Operator Certification Training iii MODULE 14: CONVENTIONAL FILTRATION Unit 5 – Operation of Conventional Filtration Facilities I. Normal Operation A. Process Performance Monitoring B. Process Controls and Equipment C. Process Support Equipment D. Housekeeping E. Laboratory Testing II. Process Start-up and Shutdown Procedures A. Start-up Procedures B. Shut Down Procedures III. Abnormal Operation A. Changes in Source Water Quality B. Increased Filtered Water Turbidity C. Record Keeping IV. Conventional Filtration Process Trouble Shooting A. Source Water Quality B. Process Quality – Coagulation/Flocculation C. Process Quality – Sedimentation D. Process Quality – Filtration Bureau of Safe Drinking Water, Department of Environmental Protection Drinking Water Operator Certification Training iv Unit 1 – Conventional Water Treatment Overview Learning Objectives Understand the purpose for Conventional Water Treatment and relevant regulations Use vocabulary appropriate to conventional filtration of water in discussing the process. Follow the Typical Process Flow Diagram and identify the four major conventional filtration processes. Bureau of Safe Drinking Water, Department of Environmental Protection 1-1 Drinking Water Operator Certification Training PURPOSE OF CONVENTIONAL WATER TREATMENT The purpose for Conventional Water Treatment is two-fold. Compliance with Regulations The primary purpose for Conventional Water Treatment is to comply with the Environmental Protection Agency (EPA) and Pennsylvania Department of Environmental Protection (Pa. DEP) regulations requiring filtration as a mandatory "treatment technique" for all surface water supplies. This "treatment technique" must be operated so as to produce filter effluent that has a turbidity less than 0.3 ntu in 95% of all monthly samples taken at four hour intervals. Turbidity Turbidity is a physical characteristic of water and is an expression of the optical property that causes light to be scattered and absorbed by particles and molecules rather than transmitted in straight lines through a water sample. It is caused by suspended matter or impurities that interfere with the clarity of the water. These impurities may include clay, silt, finely divided inorganic and organic matter, soluble colored organic compounds, plankton and other microscopic organisms. Typical sources of turbidity in raw water sources include: Waste discharges Runoff from watersheds Algae or aquatic weeds and products of their breakdown Humic acids and other organic compounds resulting from decay of plants, leaves High iron concentrations which give waters a rust-red coloration Heavy rains flushing into a water reservoir (can greatly increase raw water turbidity) Excessive turbidity in drinking water is aesthetically unappealing and may also represent a health concern. Turbidity can provide food and shelter for pathogens. If not removed, turbidity can promote re-growth of pathogens in the distribution system, leading to waterborne disease outbreaks, which have caused significant cases of gastroenteritis. Although turbidity is not a direct indicator of health risk, numerous studies show a strong relationship between removal of turbidity and removal of protozoa. As discussed in further detail, systems rely heavily on the coagulation and sedimentation process to remove turbidity from water. Relevant Regulations Surface Water Treatment Rule – Major components include: o Requires disinfection of all surface supplies. o Establishes treatment techniques to achieve at least 99.9% removal or inactivation (referred to as “3-log removal”) of Giardia lamblia cysts and 99.99% (referred to as “4-log” removal) of viruses. o Systems must be operated by “qualified personnel.” o Establishes criteria for operating without filtration. o Establishes “CT” as the basis for disinfection. o Establishes suitable filtration technologies and performance criteria for removal of turbidity and Giardia. o Establishes sampling requirements and MCL’s for combined filter effluent turbidity to monitor performance of the filtration system. Bureau of Safe Drinking Water, Department of Environmental Protection 1-2 Drinking Water Operator Certification Training PURPOSE OF CONVENTIONAL WATER TREATMENT Interim Enhanced Surface Water Treatment Rule - This rule builds upon the Surface Water Treatment Rule to improve control of microbial pathogens and address risk trade-offs with disinfection byproducts. Major components include: o Systems that are required to filter under the Surface Water Treatment Rule must achieve at least 99% (2-log) removal of the protozoan Cryptosporidium. Systems are considered to be in compliance with this requirement if filter effluent turbidity requirements are met. o Strengthened filter effluent turbidity requirements. Combined filter effluent turbidity must be below 0.3 NTU in at least 95% of the turbidity measurements taken, and measurements must be taken at least every four hours. Combined filter effluent turbidity must be below 1.0 NTU at all times. Effluent turbidity of all individual filters must be monitored continuously. Long Term I Enhanced Surface Water Treatment Rule - This rule was put in place to improve control of microbial pathogens, specifically the protozoan Cryptosporidium, and to address risk trade-offs with disinfection by-products. However, this rule applies to public water systems that serve fewer than 10,000 people. Major components include: o All systems covered by this rule must achieve at least 99% (2-log) removal or inactivation of Cryptosporidium. o Strengthened filter effluent turbidity monitoring requirements, as described in the Interim Enhanced Surface Water Treatment Rule. Stage I Disinfectants and Disinfection Byproduct Rule - This rule sets maximum contaminant levels (MCL’s) for total trihalomethanes (TTHM’s) and the total of five haloacetic acids (HAA5). It also sets maximum disinfectant residual concentrations for chlorine, chloramines, and chlorine dioxide. Major components include: o Applies to all public water systems that add a disinfectant during any part of the water treatment process. o Sets MCL for TTHM’s at 0.08 mg/L (80 parts per billion or ppb) and MCL for HAA5 at 0.06 mg/L (60 ppb). o Sets MCL for chlorite (a by-product of chlorine dioxide) at 1.0 mg/L and MCL for bromate (a by-product of ozone) at 0.01 mg/L (10 ppb). o Sets maximum residual disinfectant levels (MRDL’s) of 4.0 mg/L (as Cl2) for chlorine, 4.0 mg/L (as Cl2) for chloramines, and 0.8 mg/L for chlorine dioxide (as ClO2). o Requires removal of total organic carbon (TOC) present in the raw water by enhanced coagulation (for systems using conventional treatment). Chemical disinfectants react with organic carbon in the raw water to form by-products. Long Term 2 Enhanced Surface Water Treatment Rule (LT2): This rule became effective in PA in December 2009. It builds upon the earlier surface water treatment rules to address higher risk public water systems for protection measures beyond those required for existing regulations. Higher risk systems include filtered water systems
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