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NITRIFICATION IN PULSED ADSORPTION BEDS A · PDF file 2012. 8. 1. · 2.3.2 Denitrification Microorganisms can use nitrate in two ways, by assimilating into organic matter via ammonia,

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  • '·.

    NITRIFICATION IN PULSED ADSORPTION BEDS

    A Report Presented to the Department of

    Civil Engineering of Lehigh University in Candidacy for the Degree of

    Master of Science in

    Civil Engineering

    '•

    Lehigh University 1972

    -i

  • -iii

    TABLE OF CONTENTS ,.

    ABSTRACT Page

    1V

    .. 1. INTRODUCTION 1 2. THEORETICAL ANALYSIS 3

    2.1 ADSORPTION PHENOMENON 3 2.2 THE NITROGEN CYCLE 4 2.3 THE NITRIFICATION-DENITRIFICATION PROCESS· 6 2.4 ASPECTS OF NITRIFICATION IN PAB UNITS 9

    3. DESCRIPTION OF EXPERIMENT 10

    3.1 TEST APPARATUS 10 3.2 EXPERIMENTAL ANALYSES 17

    4. TEST RESULTS 23

    5. DISCUSSION 27

    5.1 DISCUSSION OF THE TEST RESULTS 27 5.2 OPERATIONAL ANALYSIS 39

    " 6. CONCLUSIONS 41

    7. RECOMMENDATIONS AND FUTURE PERSPECTIVES 42

    8. ACKNOWLEDGEMENT 46

    9. LIST OF FIGURES 47

    10. LIST OF TABLES 48

    11. TERMINOLOGY AND ABBREVIATIONS 49

    12. REFERENCES 51

    13. APPENDICES 52

    14. ABOUT THE AUTHOR 58

  • -iv

    ABSTRACT

    The Pulsed Adsorption Bed (PAB) is a tertiary wastewater .. I treatment process which has shown excellent organic removal in labora-

    tory and field studies.

    Several indications in the initial studies pointed towards

    the feasibility of nitr~fication with the PAB process. A pilot plant

    study was conducted to obtain".information about the nitrification

    effect of the process under various hydraulic and organic loads.

    The results showed that the characteristics of the available

    sewage and the test set-up used did not allow significant nitrifica-

    tion. With other conditions favorable, an effective secondary treat- .. -

    ment and solids retention times sufficiently high enough seem to be

    the strongest requirements to obtain nitrification.

    Despite the failure of this study to demonstrate the pos- .

    sibility of nitrification, the excellent organic removal of the PAB

    / process has been confirmed under different conditions and further

    studies should be able to: optimize the PAB process for complete nitro-

    gen remova 1 .

  • 1. INTRODUCTION

    NITRIFICATION IN PULSED ADSORPTION BEDS

    The goal for sewage treatment during the past three decades

    was removal of suspended matter and biochemical oxygen demand, plus

    -1

    . reduction of bacterial contamination. The usual flow scheme for treat-

    ment facilities was plain sedimentation followed by biological treat-

    ment in activated sludge units or trickling filters, final sedimenta-

    tion and eventually chlorination.

    A large amount of research on the effect of waste discharge

    into natural water courses, demand for future increased water supply,

    as well as official and public concern about ecology have led to a

    demand for further waste treatment. This treatment is generally termed

    advanced or tertiary treatment. The purpose of advanced waste treat-

    ment is the further removal of carbonaceous matter resistant to classical

    biological treatment and additional removal of nitrogen and phosphorous.

    Nitrogenous material can exert appreciable oxygen demand and both elements

    are nutrients which enhance biological growth, or eutrophication in re-

    ceiving water courses.

    It should be noted that both the con~entional activated sludge

    process and the standard rate trickling filters originally were designed

    to produce a highly nitrified effluent. The development of these pro-

    cesses came at a time when biological methods of measuring plant perfor-

    mances were yet unknown and chemical tests, especially tests for the

    different forms of nitrogen were used instead (1). When the BOD test,

  • ..

    measuring carbonaceous oxygen demand primarily, was introduced as

    standard for measuring plant performance, .it was found that sufficient

    purification could be obtained to meet the standards without the long

    detention times necessary for nitrification. This resulted in several

    modifications of the biological processes.

    -2

    Recent research has pointed towards the development of physical-

    chemical treatment processes and improvement' of biological purification

    methods. One process which has gained much attention is adsorption of

    organic material onto granular media. This process combines both

    physical-chemical and biological activities. The media of choice is

    usually activated carbon, but other media like coal or sand are also

    nominal adsorbents, especially if biological activity is enhanced during

    the adsorption process.

    Laboratory work on aerated adsorption columns by R. L. Johnson

    showed excellent organic removal from dilute wastes like secondary treat-

    ment effluents (2). The pulsing appearance of the media due to aeration

    gave the process its name, pulsed adsorption beds (PAB). A pilot plant

    study by S. R. Sedgwick at the sewage treatment plant of Ames, Iowa

    confirmed the laboratory results (3).

    The characteristics of the PAB process and data from the

    original studies (2,3,4) are indicating that appreciable nitrification

    might be obtained in the PAB process. T}.le possibility of nitrification

    would increase the benefits of the process and its field of applicability.

    To confirm these indications and to obtain data about the

    degree of nitrification under different conditions, a PAB pilot plant

    l.

  • . .

    study was conducted at the Bethlehem, Pennsylvania sewage treatment

    plant.

    2. THEORETICAL ANALYSIS

    2.1 ADSORPTION PHENOMENON

    The principle of adsorption is usually expressed with the

    classical Gibbs equation (5)

    r =- _£ ~ Re de where r is the excess surface concentration as weight per unit area,

    c is the bulk concentration of the solute as weight per volume, y

    is the surface tension of the solution, and R and e are the universal

    gas constant and the absolute temperature, respectively •

    Equation 1 indicates a surface concentration higher than the

    bulk concentration for solutes which decrease surface tension, because

    -3

    (1)

    the relative change of surface tension with concentration has a negative

    value for these solutes. Most organic materials produce a decreased

    suface tension and, thus, tend to accumulate on surfaces (4). The /

    Gibbs equation also indicates increasing excess surface concentration

    with increasing bulk concentration. However, the importance of adsorp-

    tion in waste treatment is for further treatment of the dilute secondary

    •effluents. For these waste effluents the increased concentration of

    • foodstuff on solid surfaces provides a more amenable environment for

    organisms. This concentration effect indeed is quite sizable if suffi-

    cient surface is provided (4).

  • . .

    ..

    -4

    2.2 THE NITROGEN CYCLE

    Nitrogen is an element of special interest to sanitary engineers

    since it is essential to the life processes of all organisms. In these

    processes nitrogen appears in many different forms with different elec-

    tronic charges, following a certain scheme known as nitrogen cycle (Fig.

    1). In some of the transformations of nitrogen theN-containing compound

    is used as a source of oxygen and in others the compound itself is oxi-

    .dized to provide energy for synthesis reactions.

    The vast reservoir of nitrogen is the atmosphere where it is

    contained in molecular form as nitrogen gas. During electrical storms

    large amounts of nitrogen are oxidized and washed out by rain as nitric

    acid, HNo3 .

    Plants utilize nitrogen as fertilizer by assimilating riitrate

    or ammonia or in special cases by fixing nitrogen from the air, thus

    transforming inorganic nitrogen into organic nitrogen:

    N03 + co2 + green plants + sunlight

    NH3 + co2 + green plants + sunlight N2 + special bacteria or algae (bl~e-green)

    plant

    } -+protein

    Animals and humans, unable to utilize inorganic nitrogen,

    (2)

    use the plant protein or other animal protein to produce own proteins.

    Organic nitrogen is discharged upon death of organisms and

    in their waste products, fecal matter and urine. The released organic

    matter comes back into the soil,· is washed out into water courses, or

    goes into sewer systems and into waste-treatment facilities. The proteins

  • .,

    Fig. 1

    c: 0 -(/) 0 a.!.... E m 0 N 0

  • ..

    -6

    are readily transformed to ammonia by saprophytic bacteria under aerobic

    or anaerobic conditions.

    I Protein + bacteria -+ ~· (3)

    The nitrogen in urine is largely contained as urea which is rapidly

    hydrolyzed to ammonium carbonate.

    jllz c = 0 + 2~0 urease (NH4) 2co3 I

    (4)

    NH2

    The ammonia released may be used by plants directly and the

    excess ammonia is oxidized to nitrate by nitrifying bacteria. However,

    there is

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