Prepared by the Operation of Municipal Wastewater Treatment Plants Task Force of the Water Environment Federation

Transcription

1 Operation of Municipal Wastewater Treatment Plants WEF Manual of Practice No. 11 Chapter 24 Physical Chemical Treatment Sixth Edition Prepared by the Operation of Municipal Wastewater Treatment Plants Task Force of the Water Environment Federation Michael D. Nelson, Chair Richard E. Finger John L. Meader, P.E. Robert L. Oerther Under the Direction of the MOP 11 Subcommittee of the Technical Practice Committee 2007 Water Environment Federation 601 Wythe Street Alexandria, VA USA 1

2 About WEF Formed in 1928, the Water Environment Federation (WEF) is a not-for-profit technical and educational organization with 32,000 individual members and 80 affiliated Member Associations representing an additional 50,000 water quality professionals throughout the world. WEF and its member associations proudly work to achieve our mission of preserving and enhancing the global water environment. For information on membership, publications, and conferences, contact Water Environment Federation 601 Wythe Street Alexandria, VA USA (703) IMPORTANT NOTICE The material presented in this publication has been prepared in accordance with generally recognized engineering principles and practices and is for general information only. This information should not be used without first securing competent advice with respect to its suitability for any general or specific application. The contents of this publication are not intended to be a standard of the Water Environment Federation (WEF) and are not intended for use as a reference in purchase specifications, contracts, regulations, statutes, or any other legal document. No reference made in this publication to any specific method, product, process, or service constitutes or implies an endorsement, recommendation, or warranty thereof by WEF. WEF makes no representation or warranty of any kind, whether expressed or 2

3 implied, concerning the accuracy, product, or process discussed in this publication and assumes no liability. Anyone using this information assumes all liability arising from such use, including but not limited to infringement of any patent or patents. Copyright 2007 by the Water Environment Federation All Rights Reserved. Water Environment Research, WEF, and WEFTEC are registered trademarks of the Water Environment Federation. 3

4 Manuals of Practice of the Water Environment Federation The WEF Technical Practice Committee (formerly the Committee on Sewage and Industrial Wastes Practice of the Federation of Sewage and Industrial Wastes Associations) was created by the Federation Board of Control on October 11, The primary function of the Committee is to originate and produce, through appropriate subcommittees, special publications dealing with technical aspects of the broad interests of the Federation. These publications are intended to provide background information through a review of technical practices and detailed procedures that research and experience have shown to be functional and practical. Water Environment Federation Technical Practice Committee Control Group B. G. Jones, Chair A. B. Pincince, Vice-Chair S. Biesterfeld-Innerebner R. Fernandez S. S. Jeyanayagam Z. Li M. D. Nelson S. Rangarajan E. P. Rothstein A. T. Sandy A. K. Umble T. O. Williams J. Witherspoon 4

5 Contents Chapter 24 Physical Chemical Treatment Introduction Fundamentals of the Process Coagulation and Flocculation Sedimentation Filtration Recarbonation ph Adjustment Description of Processes and Process Equipment Coagulants Coagulant Mixing Analytical Tools to Determine Mixing Efficiency Computational Fluid Mixing Flocculation Sedimentation Recarbonation ph Adjustment Filtration Process Control Systems Determining Chemical Dosage Phosphorus Reduction Heavy Metal Removal 5

6 Bacteria and Virus Removal Suspended Solids Reduction Control of Chemical Dosage Chemical Sludge Recycle/Wasting Optimizing Filter Run Time Effluent Quality and Headloss Filter Aids Effects of Polymers Polymer Handling Backwashing of Filters Media Expansion and Suspension Backwash Duration Surface Washing Data Collection Samples Types and Analysis Grab Samples Composite Samples Quality Assurance Plan Reporting to Meet Legal (Permit) Requirements Reporting for Process Monitoring and Control Planned Maintenance Program Why Is A Program Required? Equipment Listing 6

7 Frequency of Checks Conventional Processes Sedimentation Fundamentals of the Process Description of Process and Process Equipment Process Control Systems Normal Process Control Data Collection Planned Maintenance Program Troubleshooting Filtration Fundamentals of the Process Description of Process and Process Equipment Process Control Systems Flowrate Control Filter Aids Filter Backwash Filter Appurtenances Process Monitoring and Control Normal Process Control Filling the Filter Filter Aids Turbidity Monitoring 7

8 Filter Backwashing Recycle of Backwash Flows Data Collection Planned Maintenance Program Troubleshooting Recarbonation Fundamentals of the Process Description of Process and Process Equipment Process Control Systems Normal Process Control Data Collection Planned Maintenance Program Troubleshooting Advanced Processes Soluble Chemical Oxygen Demand Removal Fundamentals of the Process Description of Process and Process Equipment Process Control Systems Normal Process Control Data Collection Planned Maintenance Program Troubleshooting Nitrogen Removal (Includes Ammonia Stripping) 8

9 Fundamentals of the Process Breakpoint Chlorination Ion Exchange Ammonia Stripping Description of Process and Process Equipment Breakpoint Chlorination Ion Exchange Ammonia Stripping Process Control Systems Breakpoint Chlorination Ion Exchange Ammonia Stripping Normal Process Control Breakpoint Chlorination Ion Exchange Ammonia Stripping Data Collection Breakpoint Chlorination Ion Exchange Ammonia Stripping Planned Maintenance Program Breakpoint Chlorination Ion Exchange 9

10 Ammonia Stripping Troubleshooting Breakpoint Chlorination Ion Exchange Ammonia Stripping Phosphorus and Enhanced Suspended Solids Removal Fundamentals of the Process Chemical Coagulation for Enhanced Solids Removal Chemical Coagulation for Phosphorus Removal Description of Process and Process Equipment Process Control Systems Normal Process Control Data Collection Planned Maintenance Program Troubleshooting References 10

11 LIST OF TABLES 24.1 Inorganic chemicals commonly used for coagulation in wastewater treatment Surface loading rates (SLRs) for clarifiers treating common chemically treated effluents a Troubleshooting chart for filtration Tests for recarbonation and lime recalcining Troubleshooting chart for lime recalcining Organic compounds amenable to removal by granular activated carbon Carbon adsorption tests Troubleshooting chart for soluble chemical oxygen demand removal processes. 11

12 LIST OF FIGURES 24.1 In-basin mechanical rapid-mixing device In-line diffusers (a) In-line helical element static mixer (cut-away) and (b) in-line blade element static mixer (cut-away) (a) In-channel rapid-mixing device (schematic) and (b) close-up of in-line rapidmixing device (discharge end) Typical flocculation devices High-rate solids contact clarifier Ballasted media, high-rate clarification system Cross section through a typical gravity filter Typical pressure filter Schematic cross section through an ideal filter, uniformly graded from coarse to fine from top to bottom Schematic of a continuous backwash, up-flow filter Schematic of a cloth media filter and its operational cycles Schematic of operational cycles for a compressible media, upflow-type filter Lime dosage as related to wastewater alkalinity Effects of polymers as filtration aids: (a) polymer dose inadequate, (b) polymer dose excessive, and (c) optimal polymer dose Typical single-stage recarbonation using gas feed system Downflow carbon contactor. 12

13 24.18 Carbon adsorption vessel schematics: (a) series operation, (b) series operationadsorption vessels, (c) series operation adsorption units Types of ammonia stripping towers Alternative points of chemical addition for phosphorus removal: (a) before primary sedimentation, (b) before and/or following biological treatment, (c) following secondary treatment, and (d f) at several locations (known as split treatment ). 13

14 Preface This sixth edition of this chapter was produced under the direction of Michael D. Nelson, Chair. The principal author of this chapter is Sandeep Karkal, P.E. In general, wastewater treatment processes fall into three broad classes: biological, chemical, and physical. Trickling filters, rotating biological contactors, activated sludge, and anaerobic digestion are examples of biological processes. Examples of chemical processes are heavy metal precipitation, phosphorus precipitation, acid or alkali addition for ph control, and disinfection with chlorine or hypochlorite. Processes such as flow measurement, grit removal, primary and secondary clarification/sedimentation, filtration, and centrifugation are examples of physical processes. At the time of this writing, most wastewater treatment plants in the United States provide preliminary, primary, and secondary levels of treatment to wastewater, where the focus is on reducing carbonaceous biochemical oxygen demand (CBOD) and total suspended solids (TSS) to meet discharge permit parameters. However, to further enhance the quality of receiving waters, regulatory agencies are increasingly targeting reductions in parameters such as nitrogen and phosphorus and pollutants such as metals and non-biodegradable soluble organics, in addition to the conventional BOD,, TSS, and fecal coliform parameters. Another area of regulatory and environmentalist focus is in providing additional (tertiary) treatment to secondary effluent to levels where it can be recycled for applications traditionally served by potable water, such as many types of irrigation and industrial uses. Both of these objectives can be addressed by 14

15 physical chemical processes, where either chemical addition can be used to enhance the reduction of conventional parameters such as suspended solids, or new processes can be added to reduce the levels of parameters such as phosphorus and soluble, nonbiodegradable chemical oxygen demand (COD). Accordingly, this chapter mainly addresses the use of physical chemical treatment as it relates to (a) enhanced suspended solids reduction in primary treatment, (b) further reduction of solids in advanced treatment processes following conventional treatment, and (c) reductions in parameters such as phosphorus and soluble, nonbiodegradable COD. Other physical, physical chemical, or chemical treatment methods are discussed extensively elsewhere in this book and the reader is referred to the appropriate chapters. Solids-handling processes that incorporate elements of physical and chemical treatment are also not discussed here, as they too are discussed extensively in other chapters of this book. Advanced biological treatment for nitrogen and phosphorus reduction, which is becoming increasingly more commonplace as opposed to physical chemical removal, especially at larger wastewater treatment plants, is also discussed elsewhere in this book. Review of this chapter was also provided by Daniel A. Nolasco, M.Eng., M.Sc., P.Eng., and Keith Radick. Authors' and reviewers' efforts were supported by the following organizations: City of Frankfort, Frankfort Sewer Department, Frankfort, Kentucky 15

16 Mike Nelson Consulting Services LLC, Churchville, Pennsylvania NOLASCO & Assoc. Inc., Ontario, Canada Novato Sanitary District, Novato, California Floyd Browne Group, Delaware, Ohio West Point Treatment Plant, Seattle, Washington Weston & Sampson Engineers, Inc, Peabody, Massachusetts 16