Environmental engineers handbook - Chapter 7 ppsx

Sources and Character- istics 7.1 NATURE OF WASTEWATER Flow Rates Wastewater Characteristics Permits and Effluent Limitations 7.2 SOURCES AND EFFECTS OF CONTAM- INANTS Sources of Contaminants Point and Nonpoint Sources Violations of Water Quality Standards Effects of Contaminants Ecological Effects Toxicity Effects Effects of Contaminants on Wastewater Treatment Plants 7.3 CHARACTERIZATION OF INDUSTRIAL WASTEWATER Origins of Industrial Wastewater Wastewater from Process Operations Wastewater from Petroleum Refining Wastewater Discharge Standards Wastewater Characterization Surveys 7.4 WASTEWATER MINIMIZATION Municipal Wastewater Flow Reduction Industrial Wastewater Flow Reduction Pollutant Concentration Reduction 7.5 DEVELOPING A TREATMENT STRATEGY Evaluating Compliance Characterizing Wastewater Selecting Treatment Technologies Monitoring and Analysis 7.6 FLOW AND LEVEL MONITORING Flow Sensors for the Wastewater Industry Magnetic Flowmeters 7 Wastewater Treatment Carl E. Adams, Jr.ԽDonald B. AulenbachԽL. Joseph BollykyԽJerry L. BoydԽRobert D. BuchananԽDon E. BurnsԽLarry W. CanterԽ George J. CritsԽDonald DahlstromԽStacy L. DanielsԽFrank W. DittmanԽWayne F. Echelberger, Jr.ԽRonald G. GantzԽLouis C. Gilde, Jr.ԽBrian L. GoodmanԽNegib HarfoucheԽ R. David HolbrookԽSun-Nan HongԽDerk T.A. HuibersԽFrederick W. Keith, Jr.ԽMark K. LeeԽBéla G. LiptákԽJános LiptákԽDavid H.F. LiuԽFrancis X. McGarveyԽThomas J. Myron, Jr.ԽVan T. NguyenԽJoseph G. RaboskyԽLeRoy H. ReuterԽBernardo Rico- OrtegaԽChakra J. SanthanamԽE. Stuart SavageԽFrank P. SebastianԽGerry L. ShellԽWen K. ShiehԽJohn R. SnellԽPaul L. StavengerԽMichael S. Switzenbaum ©1999 CRC Press LLC Theory Designs and Applications Coriolis Mass Flowmeters Metering Pumps Orifices Wastewater Applications Pitot Tubes Segmental Wedge Flowmeters Variable-Area Flowmeters Purge Flowmeter Variable-Area Flowmeters Venturi and Flow Tubes Vortex Flowmeters Weirs and Flumes Detectors for Open-Channel Sensors Level Sensors Interface Measurement Bubblers Capacitance Probes Conductivity Probes D/P Cells Level Gauges Optical Sensors Resistance Tapes Thermal Switches Ultrasonic Detectors Vibrating Switches 7.7 pH, OXIDATION-REDUCTION PROBES AND ION- SELECTIVE SENSORS Probes and Probe Cleaners pH Measurement Theoretical Review Measurement Electrode Cleaners Installation Methods ORP Probes Principles of ORP Measurement Equipment for ORP Measurement Practical Application of ORP Care of an ORP System Ion-Selective Electrodes Electrode Types Liquid Ion Exchange Electrodes Interferences Advantages and Disadvantages 7.8 OXYGEN ANALYZERS Bypass Filters and Homogenizers Slipstream and Bypass Filters Homogenizers Automatic Liquid Samplers DO Analyzers Polarographic Cell Galvanic Cell BOD, COD, and TOD Sensors Oxygen Demand COD TOD Correlation among BOD, COD, and TOD Total Carbon Analyzers TOC, TC, and TIC FID Aqueous Conductivity 7.9 SLUDGE, COLLOIDAL SUSPENSION, AND OIL MONITORS SS and Sludge Density Sensors Activated Sludge Monitors Slurry Consistency Monitors In-line Consistency Measurement Probe Type Optical Sensor Sludge and Turbidity Monitors Turbidity Units Forward Scattering or Transmission Types Scattered Light Detectors (Nephelometers) Backscatter Turbidity Analyzers Installing the Sludge Monitor Online Monitoring Sampling-Based Sludge Monitoring Colloidal Suspension Monitors Principles of Operation Applications Oil Monitors Environmental Pollution Sensors Sewers and Pumping Stations 7.10 INDUSTRIAL SEWER DESIGN Basic Sewer Systems The Oily Water Sewer Acid (Chemical) Sewer Storm Water Sewer Sanitary Sewer Designing Sewer Systems Develop Plot Plan Lay Out System Classify and Type Surface ©1999 CRC Press LLC ©1999 CRC Press LLC Drainage Establish and Check Slope Design Sewer Determine Sewer Pipe Size Determine Invert 7.11 MANHOLES, CATCH BASINS, AND DRAIN HUBS Sanitary Sewer Appurtenances Manholes Building Connections Depressed Sewers (Inverted Siphons) Industrial Sewer Appurtenances Drain Hubs Catch Basins Floor Drains Manholes 7.12 PUMPS AND PUMPING STATIONS Pump Types and Applications Centrifugal Pumps Positive Displacement Pumps Rotary Screw Pumps Air Pumps Pumping System Design Capacity Head Requirements Suction Lift Specific Speed Horsepower Pump Curves Pumping Station Design Equalization and Primary Treatment 7.13 EQUALIZATION BASINS Purpose of Flow Equalization Flow Equalization Processes Design of Facilities Alternating Flow Diversion Intermittent Flow Diversions Completely Mixed Combined Flow Cumulative Flow Curve Operational Considerations Mixing Requirements Draining and Cleaning 7.14 SCREENS AND COMMINUTORS Screen Openings and Hydraulics Screen Types Hand-Cleaned Bar Screens Mechanically Cleaned Bar Screens Mechanical Bar Screen and Grit Collector Coarse-Mesh Screens Fine Screens Microscreens Hydrasieves Volume of Screenings Disposal of Screenings Comminutors Rotating Cutters Oscillating Cutters Barminutors 7.15 GRIT REMOVAL Characteristics of Grit Grit Removal Devices Gravity Settling Aerated Grit Chamber Detritus Tanks Hydrocyclones 7.16 GREASE REMOVAL ANDSKIMMING Grease Traps and Grease Interceptors Grease Removal by Air-Aided Flotation Scum Collection Skimming Devices Rotatable Slotted-Pipe Skimmers Revolving Roll Skimmers Belt Skimmers Flight Scrapers Floating-Pump Skimmers 7.17 SEDIMENTATION Types of Clarifiers Horizontal Flow Clarifiers Solid-Contact Clarifiers Inclined-Surface Clarifiers Design Factors Detention Time Surface Overflow Rate Weir-Overflow Rate Dimensions Inlet Structure Outlet Structures Sludge Removal 7.18 FLOTATION AND FOAMING Gas–Particle Contact Gas Solubility and Release Pressurization Systems Process Design Variables Hydraulic and Solids Loadings Chemical Additions Foaming Process Process Variables 7.19 SLUDGE PUMPING AND TRANSPORTATION Types of Sludge Raw Sludge Activated Sludge Filter Humus Chemical Sludge Physical Characteristics of Sludge Transport of Sludge in Closed Conduits Sludge Pumps Piston Pump Diaphragm Pump Screw Pump Air-Lift Pump Centrifugal Pump Conventional Biological Treatment 7.20 SEPTIC AND IMHOFF TANKS Treatment Characteristics Septic Tanks Imhoff Tanks Septic Tank Design Imhoff Tank Design 7.21 CONVENTIONAL SEWAGE TREATMENT PLANTS Selection of Specific Processes Pretreatment Processes Settling or Clarification Chemical Treatment Biological Oxidation Disinfection Sludge Thickening, Conditioning, and Disposal Secondary Treatment 7.22 WASTEWATER MICROBIOLOGY Nutritional Requirements Microbial Enzymes Environmental Factors Affecting Microbial Growth Temperature Effects pH Effects Oxygen Requirements and Microbial Metabolism Microbial Populations Bacteria Fungi Protozoa, Algae, and Invertebrates General Growth Pattern of Bacteria 7.23 TRICKLING FILTERS Process Description Process Microbiology Process Flow Diagrams Process Design Velz Equations NRC Equations Eckenfelder Equation (Plastic Media) Germain/Schultz Equations (Plastic Media) Underdrains Filter Media Clarifiers Design Procedures Treatability Factor Determination List of Abbreviations 7.24 ROTATING BIOLOGICAL CONTACTORS Process Description Process Flow Diagrams Process Design Operating Problems Biological Disks 7.25 ACTIVATED-SLUDGE PROCESSES Process Description Process Microbiology Process Flow Diagrams Design Concepts Organic Loading Microorganism Concentration Contactor Retention Time Artificial Aeration ©1999 CRC Press LLC ©1999 CRC Press LLC Liquid-Solids Separation Effluent Quality Process Costs Process Kinetic Models CFSTR Model PF Model CFSTR-in-Series Model Contact-Stabilization Activated-Sludge Process Step-Aeration Activated-Sludge Process Process Design Operational Problems 7.26 EXTENDED AERATION Process Description Process Flow Diagrams Process Design 7.27 PONDS AND LAGOONS Process Microbiology Stabilization Ponds Aerobic Ponds Facultative Ponds Anaerobic Ponds Aerated Lagoons Anaerobic Lagoons Dimensions Applications Costs 7.28 ANAEROBIC TREATMENT Process Description Process Microbiology Environmental Factors Treatment Processes Anaerobic Contact Process USB Reactor Anaerobic Filter AFBR Anaerobic Lagoons 7.29 SECONDARY CLARIFICATION Process Description Design Trickling Filters and RBCs Activated-Sludge Processes Geometric Configurations 7.30 DISINFECTION Chlorine Chemistry Prechlorination/Postchlorination Factors Affecting Chlorine Disinfection Free-Available Chlorine Chloramines and Combined Available Chlorine Rate of Kill Chlorine Dosage Chlorination System Design Methods of Feeding Chlorinator Sizing Control Method Selection Auxiliary Components Ozonation Ozone Characteristics Dosage and Performance Advanced or Tertiary Treatment 7.31 TREATMENT PLANT ADVANCES Secondary Equivalent (80 to 90% BOD reduction) Pure Oxygen Moving Carbon Bed Adsorption Secondary Equivalent plus Phosphate Removal Lime Precipitation of Phosphorus Ferrous Precipitation of Phosphate Alum and Ferric Precipitation of Phosphate Sludge Heat Treatment Process Physicochemical Treatment (PCT) Hydrolysis-Adsorption Process Tertiary Equivalent (95% BOD reduction plus phosphate removal) Colorado Springs Treatment Plant Rye Meads Treatment Plant South Lake Tahoe Reclamation Plant Windhoek Reclamation Plant Hydrolysis Adsorption Process 7.32 CHEMICAL PRECIPITATION Process Description Types of Chemicals Used pH Adjusting Chemicals Flocculation Aids Chemical Sludge Production Unit Operations Rapid Mixing Flocculation Solids Contact Liquid–Solids Separation Design Considerations 7.33 FILTRATION Special Filters Filtration Enhanced by Applied Chemical Coagulants Selection and Operation of Filters Filtration Enhanced by Equipment Design General Design Parameters Diatomaceous Earth Filters Microscreening Moving-Bed Filters Membrane Filtration Ultrafiltration Membranes in Activated- Sludge Processes Ultrafiltration Membranes Ultrafiltration Process Ultrafiltration Devices Sewage Treatment Applications High-Rate Granular Filtration Definitions Removal Mechanisms Removal Efficiency System Components and Design Optimization Applications Limitations 7.34 COAGULATION AND EMULSION BREAKING Colloidal Behavior and Inorganic Coagulants Colloidal Pollutants Colloidal Properties Destabilization of Colloidal Suspensions Inorganic Coagulants Practical Applications Laboratory Determination of Coagulant Doses Flocculation with Organic Polyelectrolytes Flocculants Coagulant Aids Design Considerations Instrumentation and Control Applications Coagulation Systems System Description Preparation of Coagulant Solutions Engineering Design Considerations Settling or Flotation Coagulation Followed by Settling Coagulation Followed by Flotation Coagulation in Sludge Handling Emulsion Breaking Types of Emulsions Stability of Emulsions Emulsion Breaking Methods Treatment of Waste Emulsions Future of Emulsion Breaking Organics, Salts, Metals, and Nutrient Removal 7.35 SOLUBLE ORGANICS REMOVAL Using Oxygen Instead of Air Oxygen Application Techniques Use of Oxygen in Bioremediation Use of Oxygen in Handling Industrial Wastewater Biological Fluidized-Bed Wastewater Treatment Aerobic Fluidized-Bed Treatment of Municipal Wastewater Aerobic Fluidized-Bed Treatment of Industrial Wastewater Anaerobic Wastewater Treatment with Attached Microbial Films 7.36 INORGANIC SALT REMOVAL BY ION EXCHANGE Ion-Exchange Reaction Structural Characteristics Ion-Exchange Characteristics Process Applications Role of Resin Types Cocurrent Countercurrent Application of Ion Exchange Waste Metal Processing Ion-Exchange Equipment Process Conclusion 7.37 DEMINERALIZATION Demineralization by Distillation Distillation Processes Corrosion and Scaling Flash Distillation Systems ©1999 CRC Press LLC ©1999 CRC Press LLC Vertical Tube Evaporators Vapor Compression Evaporators Demineralization by Electrodialysis Principles of Electrodialysis Electrodialysis Processes Sizing of Electrodialysis Units Membranes Applications Demineralization by Freezing Energy Requirements Indirect-Contact Freezing Process Direct-Contact Freezing Process Hydrate Process Costs Demineralization by Reverse Osmosis Pretreatment Desalination Experience Wastewater Applications 7.38 NUTRIENT (NITROGEN AND PHOSPHOROUS) REMOVAL Nutrient Removal Mechanisms Phosphorous Removal Nitrogen Removal Ion Exchange Phosphorus Removal Processes Anaerobic/Oxic (A/O) Process OWASA Nutrification Process Sequencing Batch Reactors PhoStrip Process Chemical Precipitation Nitrifying/Nitrogen Removal Systems Systems without Internal Recycling Systems Using Internal Recycling Streams Simultaneous Phosphorous and Nitrogen Removal Processes A 2 /O Process Improved A 2 /O Process Modified Bardenpho Process UCT/VIP Processes Biodenipho Process Chemical Treatment 7.39 NEUTRALIZATION AGENTS AND PROCESSES Process Description Common Neutralization Reagents Lime Limestone Sodium Hydroxide (caustic) Soda Ash Ammonia Acidic Reagents 7.40 pH CONTROL SYSTEMS Nature of the pH Process Nonlinear Controllers Process Equipment and Reagent Delivery Reagent Delivery Systems Mixing and Agitation Control Dynamics Tank Connection Locations Sensor Locations Equalization Tanks Controller Tuning Dead Time Exceeding Time Constant PID Controller Tuning Batch Controller Tuning Control Applications Feedback Control Systems Feedforward Control Systems Feedback-Feedforward Combination Control Optimization and Auto-Start-Up Batch Control of pH 7.41 OXIDATION-REDUCTION AGENTS AND PROCESSES Process Description Application of the Nernst Equation Titration Curve Oxidation Processes—Cyanide Destruction First-Stage Reaction Second-Stage Reaction Oxidizing Reagents Reduction Processes—Hexavalent Chrome Removal 7.42 ORP CONTROL (CHROME AND CYANIDE TREATMENT) ORP Measurement ORP Control Chemical Oxidation Cyanide Waste Treatment Batch Treatment of Cyanide Chlorinator Controls Continuous Cyanide Destruction Chemical Reduction Chrome Waste Treatment Batch Chrome Treatment First Stage Second Stage Precipitation 7.43 OIL SEPARATION AND REMOVAL Oil Sources Oil Properties Treatment Chemical Treatment Physical Treatment Ultimate Disposal Typical Treatment Systems Sludge Stabilization and Dewatering 7.44 STABILIZATION: AEROBIC DIGESTION Theory and Mechanisms Digestion of Primary Sludge Digestion of Secondary Sludge General Background Consid- erations Design Considerations Development of Design Criteria Design Example Summary 7.45 STABILIZATION: ANAEROBIC DIGESTION Conventional and High-Rate Digesters Physical Design Digester Dimensions and Accessories Gas Production and Heating Requirements Digester Sizing Anaerobic Digester Design Example Digester Dimensions Gas Holder Sizing Primary Digester Heating Requirements 7.46 SLUDGE THICKENING Gravity Thickening Gravity Thickener Design Example Flotation Thickening Pressurized Recycling Design Example 7.47 DEWATERING FILTERS Domestic Wastewater Filtration versus Clarification of Primary Domestic Waste Primary Sludge Activated and Digested Sludge Industrial Wastewater Filter Aids Solids Concentrated by Physical Methods Solids Derived from Chemical Reactions Combined Domestic and Industrial Wastewaters Filtration Tests and Sizing Calculations Continuous Rotary Filters Filter Presses and Other Batch Pressure Filters Filter Sizing Example Batch versus Continuous Filters Cake Washing Batch Tests in Pressure Filters with Variable Pressure Deep-Bed Filter Designs Precoat Filters Outdoor Sand-Bed Filters Tank-Type, Deep-Bed Filters 7.48 DEWATERING: CENTRIFUGATION Imperforate Bowl (Basket) Knife Centrifuge Applications Limitations and Maintenance Solid Bowl Conveyor Centrifuge Operating Variables Applications Auxiliary Equipment Maintenance Disc Centrifuge with Nozzle Discharge Applications Limitations and Maintenance ©1999 CRC Press LLC ©1999 CRC Press LLC Auxiliary Equipment Performance Correlation Laboratory Testing Selection of Centrifuge Two-Stage Centrifugation Heat Treatment Processes Recovery of Chemical Additives Selected Applications and Trends Alternate Dewatering Methods 7.49 HEAT TREATMENT AND THERMAL DRYERS Porteous Heat Treatment Process Thermal Dryers Dryer Types Operation and Economics Sludge Disposal 7.50 SLUDGE INCINERATION Multiple-Hearth Radiant Incineration Process Description Construction Auxiliary Equipment Equipment Selection and Process Design Exhaust Gases—Air Pollution Odor Control Ash Residue New Developments Characteristics of Multiple-Hearth Systems Reuse of Incinerator Ash Fluidized-Bed Incineration Process Description Hydraulic Characteristics Solid Waste Incineration Sludge Incineration Wet Oxidation Process Description Limit on Air Usage Sewage Sludge Applications Other Applications Flash Drying or Incineration Process Description Flash Drying versus Other Processes Value of Heat-Dried Sludge 7.51 LAGOONS AND LANDFILLS Design and Operation Continuous-Fill Lagoons Fill and Dry Lagoons Freeze and Thaw Health Considerations Engineering Considerations Operation 7.52 SPRAY IRRIGATION Physical and Biological Nature Temperature and Shock Load Effects Wastewater Pretreatment System Description Design Criteria and Parameters Infiltration Techniques Overland Techniques Conclusions 7.53 OCEAN DUMPING Effects Regulation Illegal Dumping Sludge Pipelines and Marine Fills Disposal Methods 7.54 AIR DRYING Area Needed Mechanical Sludge Removal Chemical and Physical Conditioning Freezing Vacuum Underdrains Optimum Depth for Various Sludge Degree of Dryness Composting Partially Dried Sludge Mechanized Removal Maintenance of Sand Beds Costs and Sales 7.55 COMPOSTING Process Description Process Fundamentals Raw Material Selection and Mixture Moisture Management ©1999 CRC Press LLC Aeration Time Design Special Considerations Stability and Product Quality Pathogens Odors and Odor Control Summary and Conclusions [...]... Habitat modification Pesticides Priority organics SS Flow alteration pH impaired mi 67, 059 51 ,74 7 47, 545 35,151 28,2 87 21,914 20,258 20 ,70 1 nr 20,819 15,565 55,9368 impaired acres 70 2,8 57 1 ,79 3,022 1, 072 ,184 129,286 2, 672 ,4 27 243,482 nr nr 2 47, 3 17 731,993 677 ,413 192,153 impaired sq mi 312 3 279 1 876 178 1 431 nr nr 105 9 17 4 67 nr 36 Sources of Pollution Rivers Lakes and Reservoirs Estuaries Agriculture Municipal... impaired mi 103,439 27, 994 24,884 24,015 18,129 15,568 15,459 55,9810 55 ,71 88 55,2836 55,9266 impaired acres 1,996 ,77 2 593,518 1,4 07, 8 27 301,398 973 , 077 318,446 106,502 106,398 846,892 3015 403,080 impaired sq mi 1 074 2038 3 07 91 179 0 615 89 640 11 37 359 189 Source: U.S EPA, 1992 Notes: nr ϭ not reported In addition to the causes and sources listed, thermal modifications impair 9 970 river mi Taste and... 40–41 New York: Holt, Rinehart and Winston U.S Congress 1 972 Federal Water Pollution Control Act Amendments of 1 972 PL 9 2-5 00, 92nd Congress, S 277 0, 18 October 1 972 U.S Environmental Protection Agency (EPA) 1992a Storm water management for construction activities—Developing pollution prevention plans and best management practices EPA 832-R-9 2-0 05 Washington, D.C.: Office of Water (September) ——— 1992b... supporting Not supporting Not assessed Total mi 4 07, 162 43,214 134, 472 62,218 1,153,000 1,800,000 acres 8, 173 ,9 17 2,902,809 3, 471 ,633 3,940, 277 20,910,000 39,400,000 Estuaries sq mi 15,004 3052 6 573 2064 8931 35,624 Source: U.S Environmental Protection Agency (EPA), 1992, National water quality inventory: 1990, Report to Congress (Washington, D.C.) TABLE 7. 2.5 CAUSES AND SOURCES OF SURFACE WATER POLLUTION... because of their varying environmental requirements, form communities characteristic or associated with physical and chemical conditions For example, the presence of immature insects, certain mollusks, TABLE 7. 2.6 NATIONAL AMBIENT WATER QUALITY IN RIVERS AND STREAMS: VIOLATION RATES, 1 975 –1989 Year FC Bacteria 1 975 1 976 1 977 1 978 1 979 1980 1981 1982 1983 1984 1985 1986 19 87 1988 1989 36 32 34 35 34... Civil Engineers 1 977 ) Large municipalities have variations from 1.25 to 1.5 average flow When storm water runoff goes into municipal sewerage systems, the maximum flow rate is often two to four times the average dry-weather flow (Water Pollution Control Federation and American Society of Civil Engineers 1 977 ) ©1999 CRC Press LLC Source: Water Pollution Control Federation and American Society of Civil Engineers, ... served Employee Customer Employee Toilet room Employee Guest Employee 2–4 7 13 9–15 1–5 10–16 400–600 8–12 40–56 7 13 3 10 12 3 13 500 10 48 10 Employee Machine Wash Employee Meal Employee Parking space 7 16 450–650 45–55 7 16 2–4 7 13 1–2 13 550 50 13 3 10 2 Source: Metcalf and Eddy, Inc., 1991 Note: l ϭ gal ϫ 3 .78 54 TABLE 7. 1.4 TYPICAL WASTEWATER FLOW RATES FROM INSTITUTIONAL SOURCES Flow, gal/unit... Without cafeteria and gym School, boarding Range 125–240 5–15 75 –140 5–15 75 –150 5–15 50–120 165 10 100 10 115 10 85 15–30 10–20 5– 17 50–100 Student Student Student Student Typical 25 15 11 75 Source: Metcalf and Eddy, Inc., 1991 Note: l ϭ gal ϫ 3 .78 54 tion, and other nondomestic sources such as industrial wastewater discharges Environmental engineers may need to use population forecasting to project... management for industrial activities— Developing pollution prevention plans and best management practices EPA 832-R-9 2-0 06 Washington, D.C.: Office of Water (September) Water Pollution Control Federation and American Society of Civil Engineers 1 977 Wastewater treatment plant design 10 Washington, D.C 7. 2 SOURCES AND EFFECTS OF CONTAMINANTS Sources of Contaminants Contaminants in municipal wastewater are introduced... 0.18 Municipal wastewater , , , , 70 .0* na† na na 36.0 66.0 na 56.0 na na 69.9 1.5 78 .0 6.1 26.5 4.0 49.0 65 .7 FIG 7. 2.2 Population served by municipal wastewater treatment systems (Reprinted from Council on Environmental Quality 1992, Environmental trends, Washington, D.C.) 1.18 Industrial discharge 1988 *Numbers represent millions of people †na = not available 20.4 0. 27 ,,,,,,,,, ,,,,,,,,, ,,,,,,,,, . LLC Liquid-Solids Separation Effluent Quality Process Costs Process Kinetic Models CFSTR Model PF Model CFSTR-in-Series Model Contact-Stabilization Activated-Sludge Process Step-Aeration. Removal by Air-Aided Flotation Scum Collection Skimming Devices Rotatable Slotted-Pipe Skimmers Revolving Roll Skimmers Belt Skimmers Flight Scrapers Floating-Pump Skimmers 7. 17 SEDIMENTATION. Systems Feedforward Control Systems Feedback-Feedforward Combination Control Optimization and Auto-Start-Up Batch Control of pH 7. 41 OXIDATION-REDUCTION AGENTS AND PROCESSES Process Description