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NOTES ON ACTIVATED SLUDGE PROCESS CONTROL

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  • _________________________________

    NOTES ON ACTIVATED SLUDGE PROCESS CONTROL

    _________________________________

    Prepared By: State of Maine Department of Environmental Protection

    ___________________________________________

    2009

  • Notes on Activated Sludge Process Control Page i

    PREFACE

    The Federal Water Pollution Control Act Amendments of 1972 (Public Law 92-500) established the National goals to restore and maintain the chemical, physical and biological integrity of the Nations waters.

    In August 1973, the US EPA published its definition of secondary treatment. Three major effluent parameters were defined: 5 day Biochemical Oxygen Demand (BOD5), total suspended solids (TSS) and pH. Secondary plants treating municipal wastewater are limited to 30 mg/L monthly average, 45 mg/L weekly average and 85 percent removal of BOD5 and TSS.

    The BOD determination involves the measurement of the dissolved oxygen used by microorganisms in the biochemical oxidation of organic matter. The BOD test bottle is incubated for 5 days at 20oC (see Laboratory Summary Appendix A). A typical BOD curve is shown in Figure P-1. The BOD5 of secondary effluents consists of two major components a carbonaceous demand resulting from the oxidation of carbon and a nitrogenous demand resulting from the oxidation of nitrogen. That is,

    BOD5 = CBOD5 + NBOD5

    Figure P-1 The BOD curve, (a) Normal curve for oxidation of organic matter, (b) The influence of nitrification.

  • Notes on Activated Sludge Process Control Page ii

    Total solids are defined as all the matter that remains as residue upon evaporation at 103 to 105oC. Total solids can be classified as either suspended solids or filterable solids by passing a known volume of liquid through a filter. The filter is commonly chosen so that the minimum diameter of the suspended solids is about 1 micron. The suspended solids fraction includes the settleable solids that will settle to the bottom of a cone shaped container (called an Imhoff cone) in a 60 minute period and those solids which are retained on a filter and heated for one hour at 103-105oC (see Figure P-2).

    Figure P-2 Classification and size range of particles found in wastewater.

    The measure of pH is the hydrogen ion concentration. pH is used to express the intensity of the acid or alkaline condition of a solution. The scale of pH ranges from 0 to 14, with 7 being neutral. The effluent limit for pH is typically 6 to 9.0

    There are four major biological processes used for wastewater treatment. These four major groups are: aerobic process, anoxic processes, anaerobic processes and a combination of the aerobic/anoxic or anaerobic. The aerobic processes include suspended growth process (such as activated sludge and aerated lagoons) and attached growth facilities which include trickling filters and Rotating Biological Contactors (RBDs). Maine has about 70 activated sludge treatment plants, 17 aerated lagoons, nine RBCs, two trickling filters and two activates biolfilter (a combination of tricking filter and activated sludge) plants.

    The objectives of the activated sludge wastewater treatment plants are to coagulate and remove the nonsettlable colloidal solids and to stabilize the organic matter.

    The purpose of activated sludge wastewater treatment plants was to accelerate the forces of nature under controlled conditions in treatment facilities of comparatively small size.

  • Notes on Activated Sludge Process Control Page iii

    In the removal of carbonaceous BOD, the coagulation of nonsettleable colloidal solids and the stabilization of organic matter are accomplished biologically using a variety of microorganisms, principally bacteria.

    The microorganisms are used to convert the colloidal and dissolved carbonaceous organic matter into various gases and cell tissue.

    Because the cell tissue has a specific gravity slightly greater than that of water, the resulting tissue can be removed from the treated liquid by gravity settling.

    Studies in the early 1980s by the United States Environmental Protection Agency (EPA), the Water Pollution Control Federation (WPCF), and the General Accounting Office (GAO), indicate that 50 percent or more of the wastewater treatment facilities nationwide were failing to meet their discharge permit requirements. Those reports cited the lack of adequate training for operators as a major factor limiting the performance of these facilities.

    Congress acknowledged the need for improvements in operator training programs and through the use of add-on funds in Section 104 (g)(1) of the Clean Water Act directed EPA to make grants to State training centers and agencies to provide on-site, over-the-shoulder training. The State of Maine has received Section 104(g)(1) funds for over twenty years.

    The State of Maines legislature also recognized the need for operator training and established the Joint Environmental Training Coordinating Committee (JETCC) to provide state-wide training opportunities.

    Notes on Activated Sludge Process Control was started in the spring of 1987 by the DEPs Operation and Maintenance Division to served as a training resource for JETCC and during 104(g)(1) on-site training. It soon became evident that a set of notes was necessary to enable the person receiving the training to concentrate on the fundamental concepts without fear of missing the details. This collection of notes was prepared for use by wastewater treatment plant operators as a reference to help improve activated sludge plants performance through increased understanding of process control principles.

    After over 20 years of experience providing training and technical assistance this collection of notes was updated in 2009 by the staff of the Maine Department of Environmental Protection, Division of Water Quality Management.

  • Notes on Activated Sludge Process Control Page 1

    TABLE OF CONTENTS

    PREFACE ............................................................................................................................. i TABLE OF CONTENTS ...................................................................................................... 1 LIST OF FIGURES............................................................................................................... 2

    SECTION

    I. INTRODUCTION ............................................................................................. 3 II. FUNDAMENTALS........................................................................................... 3 III. MICROORGANISMS.......................................................................................15 IV. ACTIVATED SLUDGE PROCESS MODIFICATIONS .................................18 V. SOLIDS ACCUMULATION ............................................................................22 VI. COMPLETE MIX ACTIVATED SLUDGE EQUATIONS .............................28 VII. SOLIDS SEPARATION....................................................................................32 VIII. SOLIDS FLUX THEORY.................................................................................35 IX. MASS BALANCE.............................................................................................42 X. NITRIFICATION ..............................................................................................46 XI. PROCESS CONTROL WHAT CAN BE CONTROLLED? .........................52 XII. AERATION RATE CONTROL........................................................................54 XIII. RETURN SLUDGE RATE CONTROL ...........................................................58 XIV. WASTE ACTIVATED SLUDGE CONTROL .................................................64 XV. PROCESS MONITORING ...............................................................................70 XVI. TROUBLESHOOTING.....................................................................................76 XVII. GLOSSARY ......................................................................................................84

    APPENDIXES A. LABORATORY SUMMARY B. DESIGN AND OPERATING PARAMETERS C. THE MICROBIOLOGY OF ACTIVATED SLUDGE D. ACTIVATED SLUDGE MICROBIOLOGY PROBLEMS AND THEIR CONTROL E. NUTRIENT DEFICIENCY CALCULATIONS F. RETURN CHLORINATION (BULKING) CALCUALTIONS G. SETTLEABILITY TEST PROCEDURES H. OUR TEST PROCEDURES I. MICROSCOPIC TEST PROCEDURES J. ACTIVATED SLUDGE OBSERVATIONS K. ORP RANGES L. CORE-TAKER PROCEDURES M. MCRT RELATIONSHIP TO F/M N. FINAL CLARIFIER SOLIDS FLUX O. TROUBLESHOOTING CHARTS P. TROUBLESHOOTING ACTIVATED SLDUGE PROCESSES Q. NITRIFICATION SRT CALCULATIONS R. PROCESS CONTROL CALCULATIONS S. WET WEATHER OPERATING PLAN T. SAMPLE MANUAL OF OPERATIONS U. MICROBIOLOGY FOR WASTEWATER TREATMENT PLANT OPERATORS V. ALKALINIATY AS A PROCESS CONTROL INDICATOR

  • Notes on Activated Sludge Process Control Page 2

    LIST OF FIGURES

    Number Page

    P-1 The BOD curve ................................................................................................... i P-2 Classification and size range of particles found in wastewater........................... ii 1.01 Bacteria cell metabolism ................................................................................... 4 2.01 Synthesis and oxidation of organic matter ........................................................ 7 2.02 Energy conversion

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