Nitrification and denitrification in ACS

Nitrogen: Environmental and Wastewater Concerns The presence of nitrogenous or nitrogen-containing wastes in the finale¿uent of an activated sludge process can adversely impact or pollute

Nitrification and Denitrification in the Activated Sludge Process

Michael H Gerardi

A John Wiley & Sons, Inc., Publication

Nitrification and Denitrification in the Activated Sludge Process

Nitrification and Denitrification in the Activated Sludge Process

Michael H Gerardi

A John Wiley & Sons, Inc., Publication

This book is printed on acid-free paper z y

Copyright ( 2002 by John Wiley and Sons, Inc., New York All rights reserved Published simultaneously in Canada.

No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning or otherwise, except as permitted under Sections 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 750-4744 Requests to the Publisher for permission should

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Library of Congress Cataloging-in-Publication Data:

Gerardi, Michael H.

Wastewater microbiology : nitrification/denitrification in the activated sludge process / Michael H Gerardi.

p cm.

Includes bibliographical references.

ISBN 0-471-06508-0 (cloth : alk paper)

1 Sewage—Purification—Nitrogen removal 2 Nitrification 3 Sewage— Purification—Activated sludge process I Title.

Printed in the United States of America.

10 9 8 7 6 5 4 3 2 1

L Vernon Frye

andthe men and women of the

Williamsport Sanitary Authority

andWilliamsport Municipal Water Authority

The author extends his sincere appreciation tojoVanna Gerardi for computer support

andCristopher Noviello for artwork used in this text

Contents

viii CONTENTS

29 Free Molecular Oxygen 151

31 Monitoring and Correcting Accidental Denitrification 159

CONTENTS ix

Within the last 15 years much interest and use of microbiologicalprinciples of wastewater treatment have been successfully applied tothe activated sludge process These principles include the use of themicroscope for process control and a better understanding of the mi-croorganisms, especially the bacteria that are involved in the degra-dation of wastes

Of special interest to wastewater treatment plant operators are thebacteria that degrade nitrogenous wastes—the nitrifying bacteria—and the bacteria that degrade carbonaceous wastes—the cBOD-removing bacteria Both groups of bacteria need to be routinely moni-tored and operational conditions favorably adjusted to ensure desirednitrification However, operational conditions do change, often in avery short period of time, and an undesired change in operational con-ditions can adversely a¤ect the bacteria within the activated sludgeprocess and its ability to degrade wastes

Regardless of discharge permit limitations, activated sludge cesses that are and are not required to nitrify and denitrify do nitrifyand denitrify Often these plants develop a form of incomplete ni-trification or undesired denitrification that is responsible for an oper-ational upset, an increase in operational costs, and noncompliancewith a discharge limitation Therefore, with a minimum of technicaljargon and numerous tables and illustrations, this book addresses themicrobiological principles of the bacteria and operational conditionsthat a¤ect nitrification and denitrification in the activated sludge pro-

pro-xi

cess The book is target for operators who are responsible for the dailyoperation of the activated sludge process regardless if the process

is or is not required to nitrify or denitrify Each chapter is prepared

to o¤er a better understanding of the importance of nitrification anddenitrification and the bacteria involved in nitrification and denitri-fication The book provides the operator with process control andtroubleshooting measures that help to maintain permit complianceand cost-e¤ective operation

Nitrification and Denitrification in the Activated Sludge Process isthe first book in the Wastewater Microbiology series by John Wiley

& Sons This series is designed for operators and provides a biological review of the organisms involved in wastewater treatment,their beneficial and detrimental roles, and the biological techniquesavailable for operators to monitor and regulate the activities of theseorganisms

micro-Michael H GerardiLinden, Pennsylvania

xii PREFACE

Part I

Overview

Nitrogen: Environmental and Wastewater Concerns

The presence of nitrogenous or nitrogen-containing wastes in the finale¿uent of an activated sludge process can adversely impact or pollutethe quality of the receiving water Principle nitrogenous wastes thatpollute the receiving water are ammonium ions (NHþ4), nitrite ions(NO
2), and nitrate ions (NO
3) Ions are chemical compounds thatpossess a negative (–) or positive (+ ) charge Significant pollutionconcerns related to the presence of nitrogenous wastes include dis-solved oxygen (O2) depletion, toxicity, eutrophication, and methemo-globinemia (Table 1.1)

To reduce the adverse impacts of nitrogenous wastes upon the ceiving water, an activated sludge process may be required by stateand federal regulatory agencies to lower the quantity of nitrogenouswastes in its final e¿uent The activated sludge process would have

re-to nitrify and denitrify the nitrogenous wastes A nitrification ment usually is issued as an ammonia (NH3) discharge limit, and adenitrification requirement usually is issued as total nitrogen or totalkjeldahl nitrogen (TKN) discharge limit (Table 1.2)

require-DISSOLVED OXYGEN DEPLETION

The discharge of nitrogenous wastes to the receiving water results indissolved oxygen depletion The depletion occurs through the con-sumption of dissolved oxygen by microbial activity

3

First, ammonium ions are oxidized to nitrite ions, and nitrite ionsare oxidized to nitrate ions within the receiving water (Figure 1.1) Theoxidation of each ion occurs as dissolved oxygen is removed from thereceiving water by bacteria and added to ammonium ions and nitriteions Second, ammonium ions, nitrite ions, and nitrate ions serve as

a nitrogen nutrient for the growth of aquatic plants, especially algae.When these plants die, dissolved oxygen is removed from the receiv-ing water by bacteria to decompose the dead plants (Figure 1.2)

TOXICITY

All three nitrogenous ions can be toxicity to aquatic life, especiallyfish Ammonium ions and nitrite ions are extremely toxic, and nitriteions are the most toxic of the three nitrogenous ions

TABLE 1.1 Pollution Concerns Related to Excess

NHB4, NOC2, and NOC3

Nitrogenous

NHþ4 Overabundant growth of aquatic plants

Dissolved oxygen depletion Toxicity as NH 3

NO
2 Overabundant growth of aquatic plants

Dissolved oxygen depletion Toxicity

NO
3 Overabundant growth of aquatic plants

Dissolved oxygen depletion Toxicity

Methemoglobinemia

TABLE 1.2 Permit Requirements for Nitrification and Denitrification Requirement Description Nitrification/Denitrification

nBOD Nitrogenous biochemical oxygen

demand

Nitrification/denitrification NOD Nitrogenous oxygen demand Nitrification/denitrification TKN Total kjeldahl nitrogen Nitrification/denitrification

4 NITROGEN: ENVIRONMENTAL AND WASTEWATER CONCERNS

Although ammonium ions are the preferred nitrogen nutrient formost organisms, ammonium ions are converted to ammonia with in-creasing pH (Figure 1.3) It is the ammonia at an elevated pH that istoxic to aquatic life.

EUTROPHICATION

While phosphates (PO42
) are the primary source of eutrophication,nitrogenous wastes contribute significantly to this water pollutionproblem Eutrophication refers to the discharge of plant nutrients,primarily phosphorus and nitrogen, in undesired quantities to bodies

of freshwater, such as lakes and ponds The presence of undesiredquantities of plant nutrients stimulates the rapid growth or blooms of

Figure 1.1 Oxidation of ammonium ions and oxidation of nitrite ions Under propriate conditions nitrification occurs when oxygen is removed from water, or a water film, and added to ammonium ions to produce nitrite ions, or added to nitrite ions to produce nitrate ions Although many organisms such as algae, bacteria, fungi, and protozoa are capable of nitrifying ammonium ions and nitrite ions, a specialized group of nitrifying bacteria is primarily responsible for nitrification in water and soil.

ap-Figure 1.2 Oxygen used during decomposition of dead plants As large blooms

of aquatic plants die in the water, a large diversity of bacteria and fungi quickly remove large quantities of dissolved oxygen and decompose the plant tissue into carbon dioxide, water, ammonium ions, phosphate ions, and sulfate ions The bacteria and fungi transform some of the organic material from the plant tissue into new bacterial and fungal cells.

EUTROPHICATION 5

aquatic plants, including algae When these plants die, the bodies offreshwater rapidly fill with those parts of the plants that do not de-compose Eutrophication results in the rapid ‘‘aging’’ of the bodies offreshwater as they are lost quickly over time due to the accumulation

of parts of plants that do not decompose

Eutrophication also results in additional water pollution problems.These problems include fluctuations in dissolved oxygen concentra-tion with the growth and death of aquatic plants, the clogging ofreceiving water caused by the sudden bloom of aquatic plants, andthe production of color, odor, taste, and turbidity problems associatedwith the growth and death of aquatic plants

Figure 1.3 pH and the conversion of ammonia and ammonium ions The tive quantities of ammonia and ammonium ions in water are determined by the pH

rela-of the water As the pH rela-of the water decreases, ammonium ions are favored As the pH of the water increases, ammonia is favored At a pH value of 9.4 or higher, ammonia is strongly favored.

6 NITROGEN: ENVIRONMENTAL AND WASTEWATER CONCERNS

The term ‘‘methemoglobinemia’’ or ‘‘blue baby syndrome’’ refers tothe disease experienced by an infant who consumes groundwater con-taminated with nitrate ions When an infant consumes formulae madewith groundwater contaminated with nitrate ions, the ions are easilyconverted to nitrite ions in the infant’s digestive tract The nitrite ionsthat enter the infant’s circulatory system bond quickly to the iron inthe hemoglobin or red blood cells (Figure 1.4)

Figure 1.4 Methemoglobinemia If nitrate-contaminated groundwater is used as

a potable or drinking water supply, the presence of nitrate ions represents a nificant health concern for infants Nitrate ions may be present in the groundwater due to the overuse of fertilizers, malfunction of septic tanks, or the discharge of high levels of nitrate ions in the effluent of wastewater treatment plants When an infant consumes nitrate ions from potable water used to prepare baby formula, the nitrate ions are quickly reduced to nitrite ions in the infant’s digestive tract When the nitrite ions enter the infant’s circulatory system, they bind quickly and tightly to the iron within the red blood cells or hemoglobin Once bonded to the red blood cells, oxygen can no longer be transported in adequate quantities throughout the infant’s body.

sig-METHEMOGLOBINEMIA 7

The presence of nitrite ions on the iron prevents the hemoglobinfrom obtaining oxygen as it passes through the infant’s lungs Thelack of oxygen throughout the infant’s body causes the infant’s skin

to turn blue, thus the term ‘‘blue baby syndrome.’’ If insu‰cient gen is present in the infant’s brain, paralysis or death may occur.Methemoglobinemia usually is associated with rural communitieswhere potable water is obtained from groundwater Methemoglo-binemia has no warning sign, and although it can occur in adults, itoccurs more rapidly in an infant’s due to their lower body pH andlower body weight as compared to adults

oxy-Although many activated sludge processes are required to nitrify

in order to satisfy an ammonia discharge limit, often activated sludgeprocesses that are not required to nitrify, do nitrify As long as oper-ational conditions are favorable for nitrification to occur, nitrificationwill occur

If nitrification is not properly monitored and regulated, an sired form of nitrification may occur This undesired form of nitrifi-cation might result in increased operational costs, operational upsetconditions, and violations of discharge requirements (Table 1.3) Be-cause of increased water quality concerns, a nitrification requirementwill play a greater role in the treatment of nitrogenous wastes in acti-vated sludge processes

unde-Although many activated sludge processes are required to denitrify

in order to satisfy a total nitrogen discharge limit, often activatedsludge processes that are not required to denitrify, do denitrify Aslong as operational conditions are favorable for denitrification to oc-cur, denitrification will occur

If denitrification is not properly monitored and regulated, sired denitrification might result in increased operational costs, oper-

unde-TABLE 1.3 Operational Problems Associated with an Undesired Form of Nitrification

Increased operating

costs

Increased aeration demand to oxidize NHþ4 to NO
3Increased chlorine demand to control filamentous growth Increased chlorine demand to control coliform bacteria Operational upset Clumping of solids in secondary clarifiers due to

denitrification Permit violation Interference with effective control of coliform bacteria

8 NITROGEN: ENVIRONMENTAL AND WASTEWATER CONCERNS

ational upset conditions, and violations of discharge requirements(Table 1.4) Because of increased water quality concerns, a denitrifi-cation requirement will play a greater role in the treatment of nitro-genous wastes in activated sludge processes.

Because many activated sludge processes nitrify and denitrify, a view of the microbiology of nitrification and denitrification is desir-able for process control, troubleshooting, and cost-e¤ective operation

re-A review begins with an overview of nitrogen, nitrogenous wastes orcompounds, the activated sludge process, and the bacteria involved

in the treatment of wastes

TABLE 1.4 Operational Problems Associated with Undesired

Denitrification

Increased operating costs Increased use of metal salts/polymers to thicken and

capture solids in clarifiers Operational upset Clumping of solids in secondary clarifiers due to

denitrification Permit violation Discharge of elevated level of total suspended solids

(TSS)

METHEMOGLOBINEMIA 9

Organic compounds that contain nitrogen are considered nitrogen’’ compounds An example of an organic-nitrogen compound

‘‘organic-is urea (NH2CONH2) Urea is a major chemical component of urine.Although fresh, domestic wastewater is rich in urea, this compounddegrades quickly in the sewer system through bacterial activity Inthe sewer system, a large diversity of bacteria adds water to urea Theaddition of water to urea ‘‘splits’’ the compounds into ammonium ionsand carbon dioxide (CO2) The ‘‘hydrolysis’’ of urea, namely, the ad-dition of water by bacteria to split a compound into smaller com-pounds, results in the release of ammonium ions in the sewer system.Examples of inorganic compounds that contain nitrogen and are

of concern to wastewater treatment plant operators include nium ions, nitrite ions, and nitrate ions These ions are the mostimportant nitrogenous compounds that should be monitored for cost-e¤ective operations, permit compliance, and process control for acti-vated sludge processes that are and are not required to nitrify

ammo-11

All elements are made of atoms that contain a large and positivelycharged nucleus that is surrounded by small and negatively chargedelectrons (Figure 2.1) The electrons orbit the nucleus and may beshared between elements When electrons are shared between ele-ments, chemical bonds and chemical compounds are formed (Figure2.2) For example, one atom of nitrogen and three atoms of oxygenshare electrons The sharing of electrons forms chemical bonds toproduce one molecule of NO
3 Although the nitrogen atom and theoxygen atoms shared the electrons, the oxygen atoms pull the elec-trons more closely to their nuclei Because the electrons are pulledclosely to the oxygen atom, the charge on the nitrogen atom becomesless negative, perhaps positive.

When oxygen is added to nitrogen, the nitrogen atom undergoesoxidation; that is, the nitrogen atom loses electrons Oxidation of ni-trogen results in a decrease in negative charge or an increase in posi-tive charge due to the loss of electrons Nitrification is the addition ofoxygen to nitrogen Nitrification is the oxidation of nitrogen

When oxygen is removed from nitrogen, the nitrogen atom goes reduction; that is, electrons are returned to the nitrogen atom orthe nitrogen atom gains electrons Reduction of nitrogen results in

under-a decreunder-ase in positive chunder-arge due to the gunder-ain of electrons cation is the removal of oxygen from nitrogen Denitrification is thereduction of nitrogen

Denitrifi-TABLE 2.1 Examples of Organic Compounds

Isopropyl alcohol CH 3 CHOHCH 3

TABLE 2.2 Examples of Inorganic Compounds

Name of

the Compound

Formula of the Compound

Nitrification and denitrification are chemical reactions that occurinside living cells or bacteria Because these chemical reactions occur

in living cells, they are considered ‘‘biochemical’’ reactions

With all biochemical reactions there are starting compounds or actants and final compounds or products (Equation 2.1) In some bio-chemical reactions intermediate compounds may be formed (Equation2.2) Intermediate compounds usually do not accumulate However,under appropriate conditions, intermediate compounds may accumu-late; for example, nitrite ions are intermediate compounds that mayaccumulate under appropriate operational conditions The accumu-lation of nitrite ions is undesired

re-Figure 2.1 The atom The atom contains three basic components, the proton, the neutron, and the electron The proton and neutron are grouped together at the center or core of the atom and give the atom its weight The neutron has no charge, while the proton is positively charged The electron spins around the core

of the atom and is negatively charged If the number of electrons and protons in the atom are equal, the atom has a neutral charge However, when atoms share electrons, the atoms may become positively or negatively charged depending on the number of shared electrons that spin around the core of each atom.

THE OXIDATION STATES OF NITROGEN 13

Reactants! Products ð2:1ÞReactants! Intermediates ! Products

Figure 2.2 Atoms sharing electrons When a nitrogen atom and an oxygen atom share electrons, the electrons orbit the core of the oxygen atom more than the core of the nitrogen atom Therefore the nitrogen atom becomes positive in charge (oxidized), while the oxygen atom becomes negative in charge (reduced; that is, its charge is lowered or reduced).

14 THE OXIDATION STATES OF NITROGEN

fication (reduction) in an activated sludge process Numerous tion states of nitrogen in the activated sludge process are presented inTable 2.3.

oxida-It is the –3 oxidation state of nitrogen in the ammonium ion that

is preferred by the bacteria in the activated sludge process as their trogen nutrient In this oxidation state in the ammonium ion, nitro-gen is incorporation or assimilated into cellular material (C5H7O2N).Nitrate ions and nitrite ions can be used as a nutrient source for ni-trogen However, nitrate ions and nitrite ions are used only after am-monium ions are no longer available and the oxygen on each ion isremoved and ammonium ions are produced The production of am-monium ions inside the bacterial cells ensures the presence of a –3oxidation state for nitrogen

ni-TABLE 2.3 Nitrogenous Compounds Produced during Nitrification and Denitrification

Nitrogenous Compound Chemical Formula Oxidation State of N

Nitrogenous Compounds

Because of the many oxidation states of nitrogen, many nitrogenouscompounds enter activated sludge processes in domestic wastewater.The diversity of compounds may vary greatly depending on theindustrial discharges that contain nitrogenous waste Examples ofnitrogenous compounds that are found in industrial wastewater in-clude analine, chelating agents, corrosion inhibitors, dairy waste, andslaughterhouse waste

Analine is used in the manufacturing of dyes, photographic icals, and drugs Some chelating agents are organic-nitrogen com-pounds that are used to hold metals such as copper and iron in solu-tion Nitrites are used in corrosion inhibitors in industrial processwater Dairy waste contains nitrogen-containing proteins, includingcasein, and many proteins are present in the meat and blood fromslaughterhouse waste

chem-Domestic wastewater contains organic-nitrogen compounds and monium ions Nitrogen in domestic wastewater originates from pro-tein metabolism in the human body In fresh domestic wastewater,approximately 60% of the nitrogen is in the organic form, such as pro-teinaceous wastes, and 40% of the nitrogen is in the inorganic form,such as ammonium ions Organic compounds such as amino acids,proteins, and urea are the principle organic-nitrogen compounds indomestic wastewater, while ammonium ions are the principle inor-ganic compound in domestic wastewater

am-17

Unless discharged by specific industries, nitrite ions and nitrate ionsare not found in municipal sewer systems Conditions within the sewersystems are not favorable for the oxidation of ammonium ions ornitrite ions; that is, nitrification does not occur.

AMINO ACIDS

Amino acids are organic-nitrogen compounds that contain the boxylic acid group (–COOH) and the amino group (–NH2) Theamino group in all amino acids is always bonded to the carbon next

car-to the carboxylic acid group (Figure 3.1) Amino acids are thestructural compounds, or building blocks, that form proteins Duringbacterial degradation of amino acids, the amino group is released(Figure 3.2)

Deamination is the biochemical reaction responsible for the release

of the amino group Deamination of amino acids can occur in thesewer system and the aeration tank, and deamination can occur in thepresence or the absence of dissolved oxygen Amino acids that aresimplistic in structure may be degraded in the sewer system Aminoacids that are complex in structure may be degraded in an aerationtank

When the amino group is released in wastewater, it is quickly verted to the ammonium ion (Equation 3.1) This conversion occurs

con-in wastewater due to the presence of hydrogen ions (Hþ)

NH2þ 2Hþ! NHþ

Figure 3.1 Structure of an amino acid Regardless of the structure or size of an amino acid, all amino acids contain a carboxyl group (aCOOH) and an amino group (aNH 2 ) In an amino acid such as cyteine, an amino group can be found on the carbon (C) that is bonded to the carboxyl group.

18 NITROGENOUS COMPOUNDS

Proteins are organic-nitrogen compounds that contain amino acids.Proteins are colloids and are complex in structure As colloids, theyhave a large surface area and are suspended in wastewater Due totheir colloidal nature and complex structure, bacterial degradation ofproteins is very slow, and deamination usually occurs in an aerationtank containing high concentrations of solids and a very long aera-tion time

Figure 3.2 Deamination When amino acids undergo deamination, the amino groups present on the amino acid are removed by bacterial activity Here the de- aminating bacterium, Citrobacter, removes the amino group from the amino acid glycine Once removed, the amino group is quickly converted to an ammonium ion.

PROTEINS 19

Proteins must be adsorbed to the surface of bacteria and solublized

to simplistic compounds that can enter the bacterial cells in order to

be degraded Proteins that are not degraded in an aeration tank arewasted from the tank with the solids and degraded in a digester Whenproteins degrade, amino acids are released Deamination of aminoacids results in the production of ammonium ions

Proteins make up the much of the cytoplasm or jellylike materialwithin the bacterial cell and serve as a structural component in thebacterial cell wall Bacterial enzymes and flagella also are proteina-ceous in composition When bacteria die in an activated sludge pro-cess, these cellular components are released and serve as food for liv-ing bacteria As these cellular components are degraded, ammoniumions are produced in the activated sludge process

UREA

Urea is a significant component of urine Urea is a simplistic nitrogen compound that contains two amino groups In the sewersystem urea undergoes hydrolysis resulting in the production of am-monium ions (Equation 3.2) Hydrolysis is the lysis or ‘‘splitting’’ or

organic-a molecule with the organic-addition of worganic-ater through borganic-acteriorganic-al organic-activity.Bacteria use the enzyme urease to split urea

In the sewer system many organic-nitrogen compounds are rapidlyhydrolyzed and deaminated Due to hydrolysis and deamination inthe sewer system, the influent concentration of ammonium ions toactivated sludge processes receiving domestic wastewater is usually

15 to 30 mg/l Although the ammonium ion concentration enteringthe aeration tanks of these processes is relatively high, additionalammonium ions are released in the aeration tanks as complex aminoacids, proteins, and additional nitrogenous wastes are degraded

20 NITROGENOUS COMPOUNDS

to 20 mm in length Because of the very small size of bacteria, theycan be examined only by using a microscope at high-power magnifi-cation Often, a staining technique, such as Gram staining, is used toexamine the bacteria during microscopic work The Gram stainingtechnique is provided in Appendix I.

All bacteria possess a cell wall, a cell membrane, cytoplasm, somes, ribosomes, and inclusions or storage granules (Figure 4.3).The cell wall surrounds the bacterium and gives the organism itssti¤ness and shape The cell wall also provides protection and helps

meso-to regulate the movement of compounds in and out of the cell Thecell membrane is a very thin and flexible structure located immedi-ately beneath the cell wall The cell membrane also helps to regulatethe movement of compounds in and out of the cell Invaginations ofthe cell membrane are the mesosomes The invaginations may takethe shape of tubules, vesicles, or lamellae The function of the meso-somes is unknown

The cytoplasm fills the interior of the cell and is surrounded by thecell membrane The cytoplasm makes up the bulk content of the cell

It contains a variety of colloids and fluids as well as storage granules

21

or inclusions The cytoplasm also contains the mitochondria andribosomes The mitochondria are the sites where substrate (food) isdegraded, while the ribosomes are the sites where protein synthesisoccurs Inclusions or storage granules consist of food, oils, poly-phosphates, and sulfur.

Some bacteria contain a capsule and flagellum (Figure 4.4) Thecapsule is a gelatinous slime and provides additional protection for

Figure 4.1 Patterns of bacterial growth There are several common patterns

of growth for bacteria These patterns include individual (a), pairs (b), irregular clusters (c), chains or filamentous (d), groups of four or tetrads (e), and cubes or sarcinae (f).

22 BACTERIA

Figure 4.2 Shapes of bacterial cells Most bacterial cells have one of three shapes These shapes are spherical or coccus (a), rod-shaped or bacillus (b), and helical or spirillum (c) The helical shape is the least rigid of the three bacterial shapes.

BACTERIA 23

Figure 4.3 Major structural components of the bacterial cell Significant, tural features of the bacterial cell consist of the cell wall, the cell membrane, the cytoplasm, the mesosome, and the ribosomes Also contained within the cyto- plasm are a variety of granules that may consist of stored food such as starch or inorganic materials such as sulfur deposits.

struc-Figure 4.4 Bacterial capsule and flagellum In addition to the major structural components of the cell, some bacteria may possess a capsule and a flagellum The capsule provides additional protection for the cell, while the flagellum provides locomotion.

24 BACTERIA

the cell The slime helps to flocculate bacterial cells together, and italso holds particulate and colloidal wastes to the surface of the bac-terium.

The flagellum is a proteinaceous, whiplike structure that provideslocomotion for the cell Most bacteria are highly motile when theyare young This locomotive ability is lost when bacteria are incorpo-rated into floc particles (Figure 4.5) or the flagellum is lost throughaging

Bacteria enter the activated sludge process through inflow and filtration (I/I) as soil and water organisms and as fecal organisms indomestic wastewater Bacteria in the activated sludge process may besuspended in the water or bulk solution surrounding the floc particles

in-or incin-orpin-orated into floc particles Bacteria are present in the vated sludge process at relatively high numbers They are commonlyfound in millions per milliliter of bulk solution or billions per gram

acti-of floc particles or solids

Figure 4.5 The floc particle The basis structure of a floc particle consists of numerous bacteria that ‘‘stick’’ together or agglutinate The bacteria consist of floc-formers such as organotrophs, non-floc formers such as nitrifying bacteria, and filamentous bacteria The non-floc formers are adsorbed to the floc particle through the coating action from secretions by ciliated protozoa and other higher life forms Filamentous bacteria grow within the floc particle and extend from the perimeter of the floc particle into the bulk solution The filamentous bacteria pro- vide the floc particle with strength and permit the floc particle to grow in size.

BACTERIA 25