UNIT IIWASTEWATER BIOTREATMENT

Biological treatment of waste water

Methods Aerobic : removal of

organic pollutants in wastewater by bacteria that require oxygen to work

End products: Water and carbon dioxide and biomass

Anaerobic :bacteria digests biosolids in the absence of oxygen

End products: methane and carbon dioxide gas and biomass

Aerobic Biological TreatmentSteps Primary secondary Tertiary treatments

Aerobic Biological Treatment Technologies1) Conventional Activated Sludge Process (CASP) System

2) Cyclic Activated Sludge System (CASS)

3) Membrane Bioreactor (MBR)

4) Biofilm reactors in aerobic biological wastewater treatment:

- Trickling Filters

- Integrated Fixed Film Activated Sludge (IFAS) System

- Submerged Aerobic Fixed Film Reactor

- Fluidized Bed Bioreactor

- Hybrid Biofilm/suspended Growth processes

- Rotating biological contactors

Conventional Activated Sludge Process (CASP) System most common and oldest biotreatment process

used to treat municipal and industrial wastewater

wastewater after primary treatment i.e. suspended impurities removal is treated in an activated sludge process based biological treatment system comprising aeration tank followed by secondary clarifier.

The aeration tank is a completely mixed or a plug flow (in some cases) bioreactor

where specific concentration of biomass (wide variety of microorganisms) (measured as mixed liquor suspended solids (MLSS) is maintained along with sufficient dissolved oxygen (DO) concentration (typically 2 mg/l)

biodegradation of soluble organic pollutants (measured as Chemical oxygen demand (COD) and Biological oxygen demand (BOD)

The aeration tank is provided with fine bubble diffused aeration pipework at the bottom to transfer required oxygen to the biomass and also ensure completely mixed reactor.

The aerated mixed liquor from the aeration tank overflows to the secondary clarifier unit to separate out the biomass and allow clarified, treated water to the downstream filtration system for finer removal of suspended solids.

The separated

biomass is

returned

to the aeration

Tank by means of

return

activated sludge

(RAS) pump.

Activated sludge plant

Cyclic Activated Sludge System (CASS) Cyclic Activated Sludge System (CASS) - one of the most

popular sequencing batch reactor (SBR) processes employed to treat municipal wastewater and wastewater from a variety of industries including refineries and petrochemical plants.

This technology offers several operational and performance advantages over the conventional activated sludge process.

The CASS SBR process performs all the functions of a conventional activated sludge plant (biological removal of pollutants, solids/liquid separation and treated effluent removal)

by using a single variable volume basin in an alternating mode of operation, thereby dispensing with the need for final clarifiers and high return activated sludge pumping capacity.

The Cyclic Activated Sludge System (CASS), incorporates a high level of process sophistication in a configuration which is cost and space effective and

offers a methodology that has operational simplicity, flexibility and reliability that is not available in conventionally configured activated sludge systems.

The reactor basin is divided by baffle walls into three sections

Zone 1: Selector,

Zone 2: Secondary Aeration,

Zone 3: Main Aeration). Sludge biomass is intermittently recycled from Zone 3 to the Zone

1 to remove the readily degradable soluble substrate and favor the growth of the floc-forming microorganisms.

System design is such

that the sludge return rate

causes an approximate daily

cycling of biomass in the

main aeration zone through

the selector zone. No special mixing equipment

or formal anoxic mixing

sequences are

required to meet the effluent

discharge objectives.

CASS utilizes a simple repeated time-based sequence which incorporates:

1 & 2) Aeration (for biological reactions)

2) Settle (for solids-liquid separation)

3) Decant (to remove treated effluent)

Characteristics of aerobic activated sludge: Overall, activated sludge must contain a microorganisms capable of

producing all enzyme systems required for the biodegradation of both soluble and insoluble pollutants.

Activated sludge contains prokaryotes (bacteria) and Eukaryotes (Protozoa and fungi)

The primary consumers of organic wastes are the heterotrophic (An organism that cannot synthesize its own food and is dependent on complex organic substances for nutrition) bacteria

The majority of the bacterial genera in activated sludge are Gram-negative

Pseudomonas, Arthrobacter, Comamonas, Lophomonas, Zoogloea, Sphaerotilus, Azotobacter, Chromobacterium, Achromobacter,Flavobacterm, Bacillus, and Nocardia.

Certain genera Sphaerotilus or Nocardia-causes poor settling Many types of protozoa : 50,000 cells/ml

Design of activated sludge process• The main parameters that have to be taken into account

when designing activated sludge systems are:

• Influent : Characteristics must be known before treatment

- Flow rate of the inflow of waste water

- Substrate concentration in inflow of waste water (For e.g. BOD)

- Active biomass concentration in inflow of wastewater

• Kinetic data and stoichiometric coefficients• Sludge recycle rate • Sludge wasting rate• Oxygen uptake rate

hydraulic loading rate, HLR kg BOD/m3/day =

raw BOD (kg/m3) x flow rate (m3/day)

aeration volume (m3)

hydraulic retention time (HRT, h) =

reactor volume (m3)

flow (m3/h)

sludge loading rate SLR, kg BOD/kg MLSS/day =

raw BOD (kg/m3) x flow rate (m3/day)

MLSS (kg/m3) x aeration tank volume (m3)

Membrane Bioreactor (MBR) Latest technology for biological degradation of soluble organic

impurities.

Extensively used for treatment of domestic sewage but for industrial waste treatment applications, its use has been

somewhat limited or selective.

MBR is an improvement of CASP, where the secondary clarifier is replaced by a membrane unit for the separation of treated water from the mixed solution in the bioreactor

System comprises of activated sludge process with the biomass separation carried out by membrane process

Separation of biomass using membrane provides filtered quality final effluent – can reuse

Biofilm reactors in aerobic biological wastewater treatment

2 categories:

(1) Fixed-medium systems : biofilm media are static in the reactors and the biological reactions take place in the biofilm developed on the static media, and

(2) Moving-medium systems : biofilm media are kept continually moving by means of mechanical, hydraulic, or air forces.

Biofilms can be used in various types of reactors

Trickling filters and biological towers

Rotating biological contactors

Fed Batch Reactors (FBRs)

Granular media filters

Fluidized bed biofilm reactors

Hybrid biofilm/suspended growth processes

TricklingFilters

Flow Diagram for Trickling Filters

Recycle

Primaryclarifier Trickling

filter

Finalclarifier

Wastesludge

FinaleffluentInfluent

Trickling Filters• Not a true filtering or sieving process• Material only provides surface on which

bacteria to grow• Can use plastic media

– lighter - can get deeper beds (up to 12 m)– reduced space requirement– larger surface area for growth– greater void ratios (better air flow)– less prone to plugging by accumulating slime

Trickling Filters

Filter Material

Typical Trickling Filter

Random Packing Structured Media

Bio-towers

Trickling Filter• Tank is filled with solid media

– Rocks

– Plastic

• Bacteria grow on surface of media

• Wastewater is trickled over media, at top of tank

• As water trickles through media, bacteria degrade BOD

• Filter is open to atmosphere, air flows naturally through media

• Treated water leaves bottom of tank, flows into secondary clarifier

• Bacterial cells settle, removed from clarifier as sludge

• Some water is recycled to the filter, to maintain moist conditions

Trickling Filter System

Trickling Filter Process

Types of Trickling Filters

• Standard or low rate– single stage rock media units– loading rates of 1-4 m3 wastewater/m2 filter cross-sectional area-day– large area required

• High rate– single stage or two-stage rock media units– loading rates of 10-40 m3 wastewater/m2 filter cross-sectional area-day– re-circulation ratio 1-3

• Super rate– synthetic plastic media units- Plastic media depths of 5-10 m

• modules or random packed• specific surface areas 2-5 times greater than rock• much lighter than rocks• can be stacked higher than rocks

– Loading rates of 40-200 m3 wastewater/m2 filter cross-sectional area-day

Design Criteria for Trickling FiltersT a b le 10 .5

T y p ic a l D e s ig n C r ite ria fo r T r ic k li ng F il te rs

Ite m L o w -ra te filte r H ig h-ra te f ilte r S up er- ra te f ilte r

H yd ra u l ic loa d in g (m 3/m 2-d ) 1 - 4 10 - 40 40 - 20 0

O rg a n ic loa d in g (k g B O D 5/m 3-d) 0 .0 8 - 0 .32 0.3 2 - 1 .0 0.8 - 6.0

D e p th (m ) 1 .5 - 3 .0 1.0 - 2.0 4.5 - 12 .0

R e c irc u la tio n ra tio 0 1 - 3 1 - 4

F ilte r m e d ia R o c k , s la g, e tc . R o ck , s la g,syn th e tic s

F ilte r f lie s M a n y Fe w , la rva e a rew ash e d a w a y

Fe w o r no ne

S lo ug h in g I nte rm itte n t C o nt in uo u s C o nt in uo u s

D o sin g inte rv a ls < 5 m in < 1 5 s C o nt in uo u s

E f flue n t U sua l ly fu l lyn it rif ied

N itr ifie d a t lowlo ad in g s

N itr ifie d a t lowlo ad in g s

Submerged Aerobic Fixed Film Reactor

cost-effective method of waste water treatment

sewage sanitation that is primarily used in residential and commercial complexes

This equipment primarily works on the three stages that are Primary Settlement, Secondary Treatment and Final Settlement / Clarification

Improved treatment quality

particularly for small to medium sized treatment plants where available land is limited, and where full time operational manning would be uneconomical

A well built Submerged Aerated Filter plant has no moving parts within its main process zones, any serviceable items will be positioned to access easily without disrupting the ongoing sewage treatment

Fluidized Bed Bioreactor

Fluidized bed bioreactors (FBR) have been receiving considerable interest in wastewater Treatment.

A fluidized bed bioreactor consists of microorganism coated particles suspended in wastewater which is sufficiently aerated to keep the gas, liquid and the solid particles thoroughly mixed.

capable of achieving treatment in low retention time because of the high biomass concentrations that can be achieved .

successfully applied to an aerobic biological treatment of industrial and domestic wastewaters.

Rotating Biological ContactorRotating Biological Contactors, commonly called RBC’s, are used in wastewater treatment plants (WWTPs).

The primary function of these bio-reactors at WWTPs is the reduction organic matter.

Very effective for low strength organic wastes

Rotating Biological Contactors

RBC Schematic

Wastewater

Film of Microorganisms

Rotation

• Design of Rotating Biological Contactors Organic loading rate ( g BOD per m3 disc area per day) Hydraulic retention time (d) Diameter of discs (m) Number of discs Depth of submergence of rotating disc (m) Rate of rotation (rpm)

PrimarySettling

SludgeTreatme

nt

SecondarySettling

Sludge Treatment

Hybrid Biofilm/suspended Growth processes Activated sludge process can be enhanced in terms of capacity

and reliability through the introduction of biofilm media that

create hybrid biofilm/suspended growth system

Existing activated sludge-upgraded by adding biofilm surface

area inside the aeration basin

The goal is to increase the total mass of active bacteria in the

system and to increase the SRT

Suspended and biofilm bacteria have different SRTs

Biofilm SRT-longer- which makes it especially important for

accumulating slow growing species such as nitrifiers

Eg: Activated biofilter

• In the settler MLVSS--- maintained around 2,500 mg/L

• BOD loading--- 9 Kg BOD5/m3/day

Anaerobic waste-water treatment Anaerobic treatment is often performed for solids and high-strength

industrial waste-waters (upto 1,00,000 COD). both facultative and obligate anaerobic microorganisms, in the

absence of oxygen are being involved in the anaerobic waste water treatment.

They biodegrade the organic pollutant to generate methane, carbon dioxide and biomass.

The microbiology of these anaerobic digestion processes is complex. Their efficient and stable operation requires a microbial population

containing at least 3 different interacting microbial groups.

1) Fermentative/hydrolytic bacteria (group 1)

2) Acetogenic bacteria (group 2)

3) Methanogenic bacteria (group 3)

There are 3 stages: 1)Hydrolysis

2) Acetogenesis

3) Methanogenesis

The first stage of the process, hydrolysis

involves

the hydrolysis of complex organic wastes (proteins, fatty acids and polysaccharides) by the hydrolytic bacteria.

The hydrolysis of these wastes results in the production of simplistic, soluble organic compounds (amino acids, volatile acids and alcohols).

The second stage of the process, acetogenesis,

involves

the conversion of the volatile acids and alcohols to substrates such as

- acetic acid or acetate (CH3COOH) and

- hydrogen gas by acetogenic bacteria

further that can be used by methane-forming bacteria. The third and final stage of the process, methanogenesis,

involves

the production of methane and carbon dioxide from the products of acetogenesis process by methanogenic bacteria.

Overview of anaerobic digestion processes

Several reactor designs exist for anaerobic treatment. simple conventional mixed sludge reactors

utilized primarily to treat solid waste materials such as primary and secondary sludges,

anaerobic filter or upflow anaerobic sludge blanket (UASB) digester.

Conventional methods for the disposal of sludges and other solid wastes:

Methods routinely used for the disposal of final sludges and other

solid wastes are as follows.

1) Landfilling

2) Incineration

1) Landfilling: used for agricultural, industrial and urban wastes. materials can leach into adjacent water courses when unsuitable

sites are used. expensive due to a lack of suitable landfill sites.

2) Incineration: routinely used for solids. For sludges, the system operates with limited energy input

due to their high calorific value, leading to self combustion.

However, there may be problems with the disposal of residue ash, as it often contains high concentrations of heavy metals.

The types of bacteria within an anaerobic digester :

- saccharolytic bacteria

- proteolytic bacteria fermentative bacteria

- lipolytic bacteria

- methane-forming bacteria 3 important bacterial groups in anaerobic digesters with respect to

the substrates utilized by each group. These groups include

- the acetate-forming (acetogenic) bacteria (AFB),

- the sulfate-reducing bacteria (SRB),

- the methane-forming bacteria (MFB).

ACETATE-FORMING BACTERIA (AFB) Acetate-forming (acetogenic) bacteria grow in a symbiotic

relationship with methane-forming bacteria. Acetate serves as a substrate for methane-forming bacteria.

Eg: when ethanol (CH3CH2OH) is converted to acetate, carbon dioxide is used and acetate and hydrogen are produced.

CH3CH2OH + CO2 CH3COOH + 2H2

When AFB produce acetate, hydrogen also is produced.

If the hydrogen accumulates and significant hydrogen pressure occurs, the pressure results in termination of activity of acetate-forming bacteria and lost of acetate production.

However, methane-forming bacteria utilize hydrogen in the production of methane so that a significant hydrogen pressure does not occur.

CO2 + 4H2 CH4 + 2H2O

AFBs are obligate hydrogen producers and survive only at very low concentrations of hydrogen in the environment.

They can only survive if their metabolic waste—hydrogen—is continuously removed.

This is achieved in their symbiotic relationship with hydrogen-utilizing bacteria or methane-forming bacteria.

Acetogenic bacteria reproduce very slowly. Generation time for these organisms is usually greater than

3 days.

SULFATE-REDUCING BACTERIA (SRB) SRB also are found in anaerobic digesters along with AFB and

MFB. If sulfates are present, SRB such as Desulfovibrio

desulfuricans multiply. Their multiplication or reproduction often requires the use of

hydrogen and acetate—the same substrates used by MFB

When sulfate is used to degrade an organic compound, sulfate is reduced to H2S.

Hydrogen is needed to reduce sulfate to H2S.

The need for hydrogen results in competition for hydrogen between two bacterial groups, SRB and MFB.

When SRB and MFB compete for hydrogen and acetate

SRB obtain hydrogen and acetate more easily than MFB under low-acetate concentrations.

At substrate-to-sulfate ratios <2, SRB out-compete MFB for acetate. At substrate-to-sulfate ratios between 2 and 3, competition is very

intense between the two bacterial groups. At substrate-to-sulfate ratios >3, MFB are favored.

METHANE-FORMING BACTERIA (MFB) MFB are known by several names

- Methanogens

-Methanogenis bacteria

-Methane forming bacteria

- Methane producing bacteria morphologically diverse group of organisms that have

many shapes, growth patterns, and sizes. The range in diameter sizes of individual cells is

0.1–15 µm. Filaments can be up to 200 µm in length. Motile and non motile bacteria as well as spore-

forming and non-spore-forming bacteria can be found.

MFB are some of the oldest bacteria and are grouped in the domain Archaebacteria (from arachae, meaning “ancient”).

The domain thrives in heat. MFB are

- oxygen-sensitive,

- fastidious anaerobes

- free-living terrestrial and aquatic organisms. MFB found in habitats that are rich in degradable organic

compounds. In these habitats, oxygen is rapidly removed through

microbial activity. MFB also have an unusually high sulfur content:

Approximately 2.5% of the total dry weight of the cell is sulfur.

MFB has several unique characteristics

1) a “nonrigid” cell wall and unique cell membrane lipid,

The cell wall lacks muramic acid, and the cell membrane does not contains an ether lipid as its major constituent.

2) substrate degradation that produces methane as a waste

3) specialized coenzymes.

- coenzyme M and

- the nickel containing coenzymes F420 and F430. Coenzyme M is used to reduce CO2 to CH4.

The nickel-containing coenzymes are important hydrogen carriers in methane-forming bacteria.

Anaerobic Reactor Technologies a number of novel anaerobic reactor configurations have

been developed. 2 types

- Conventional

- High rate Anaerobic digesters (Ads)

ConventionalEg: Anaerobic batch reactor (Anaerobic lagoons)

High-rate AD(Many types of reactors)

Stratified Homogeneous due tomixing

Intermittent feeding and withdrawal Continuous or intermittantfeeding and withdrawal

HRT based on liquid input is 30-60 days HRT based on liquid inputis 15 days or less

VS loading: 500-1600 kg/m3.day VS loading: 1600-1800kg/m3.day

High-rate anaerobic reactors Completely mixed anaerobic digester (AD) Anaerobic contact process (ACP) Anaerobic sequencing batch reactor (ASBR) Anaerobic packed bed or anaerobic filter Anaerobic fluidized and expanded bed reactors Upflow anaerobic sludge blanket (UASB) reactor Anaerobic baffled reactor (ABR) 2-Phase AD Process

Completely mixed ADWastewater and anaerobic bacteria are mixed

together and allowed to react. When the organic pollutant

is reduced to

desired level,

treated

wastewater is

then removed

Can be operated in either batch or continuous mode

At least 10 days of SRT and HRT are required because of slow growing methanogens.

This necessitates a reactor with a very large volumeLarge volume requirements wash-out of

microorganisms in effluent pose serious problems and make ADs unsuitable for use with most industrial wastewaters

Anaerobic contact process (ACP) Link between high biomass concentration, greater

efficiency and smaller reactor size is the idea of ACP. Settling of anaerobic sludge in a settling tank and its return

back to the reactor allows further contact between biomass and raw waste.

due to sludge recycling, the SRT is no longer coupled to the HRT.

As a result, considerable

improvements in

treatment efficiency can

be achieved. Disadvantage :

poor sludge settlement

arose from gas

formation by anaerobic

bacteria in settling tank.

Although simple in concept, individual units make ACP more complex than other high rate ADs.

Anaerobic Sequencing Batch Reactor (ASBR) Anaerobic sequencing batch reactor (ASBR) process is a

batch-fed, batch-decanted, suspended growth system and is operated in a cyclic sequence of four stages:

- feed,

- react,

- settle

- decant.

Since a significant time is spent in settling the biomass from the treated wastewater, reactor volume requirement is higher than for continuous flow processes.

Not require - additional biomass settling stage or solids recycle.

No feed short-circuiting is another advantage of ASBRs over continuous flow systems.

Operational cycle-times for the ASBR can be as short as 6 hours if biomass granulation is achieved.

Anaerobic Filter (Packed Bed) Anaerobic filter is a fixed-film biological wastewater

treatment process in which a fixed matrix (support medium) provides an attachment surface that supports the anaerobic microorganisms in the form of a biofilm.

Treatment occurs as wastewater flows upwards through this bed and dissolved pollutants are absorbed by biofilm.

Anaerobic filters were the first anaerobic systems that eliminated the need for solids separation and recycle while providing a high SRT/HRT ratio

Various types of support material can be used

- plastics,

- granular activated carbon (GAC),

- sand,

- reticulated foam polymers,

- granite,

- quartz and stone. These materials have exceptionally high surface area to

volume ratios (400 m2/m3) and low void volumes. Its resistance to shock loads and inhibitions make

anaerobic filter suitable for the treatment of both dilute and high strength wastewaters.

Limitations: deterioration of the bed structure through a gradual accumulation of non-biodegradable solids.

This leads eventually to channelling and short-circuiting of flow, and anaerobic filters are therefore unsuitable for wastewaters with high solids contents.

Additionally, there is a relatively high cost associated with the packing materials.

Anaerobic Filter Packings

Fluidized Bed Reactor (FBR) In order to achieve fluidization of the biomass particles,

units must be operated in an upflow mode. Rate of liquid flow and the resulting degree of bed expansion

determines whether the reactor is termed a fluidized bed or expanded bed system.

Expanded bed reactors have a bed expansion of 10% to 20% compared to 30% to 90% in fluidized beds.

In FBR, biomass is attached to

surface of small particles

(anthracite, high density plastic

beads, sand etc.) which are kept

in suspension by upward velocity

of liquid flow.

Effluent is recycled to dilute incoming waste and to provide sufficient flow-rate to keep particles in suspension.

Large surface area of support particles and high degree of mixing that results from high vertical flows enable a high biomass conc. to develop and efficient substrate uptake.

Biomass concentration: 15-40 g/l The greatest risk with FBR is the loss of biomass particles

from the reactor following sudden changes in particle density, flow rate or gas production.

In practice, considerable difficulties were experienced in controlling the particle size and density of flocs due to variable amounts of biomass growth on particles.

Therefore FBRs are considered to be difficult to operate.

Upflow Anaerobic Sludge Blanket (UASB) Reactor The problem associated with anaerobic filters and FBRs

has led to development of unpacked reactors that still incorporate an immobilized form of particulate biomass.

most widely used high-rate anaerobic system for domestic & industrial wastewater treatment.

UASB reactor is based on that anaerobic sludge exhibits inherently good settling properties, provided the sludge is not exposed to heavy mechanical agitation.

Adequate mixing is provided by an even flow-distribution combined with a sufficiently high upflow velocity, and by agitation that results from gas production.

Biomass is retained as a blanket or granular matrix, and is kept in suspension by controlling the upflow velocity.

Wastewater flows upwards through a sludge blanket located in lower part of reactor, while upper part contains a three phase (solid, liquid, gas) separation system.

Three-phase separation device is the most characteristicfeature of UASB reactor.

It facilitates the collection of biogas and also provides internal recycling of sludge by disengaging adherent biogas bubbles from rising sludge particles.

Superior settling characteristics of granular sludge allows higher sludge concentrations

Granular sludge development is now observed in UASB reactors treating many different types of wastewater.

Granulation Granulation is a process in which a non-discrete

flocculent biomass begins to form discrete well-defined granules.

These vary in dimension and appearance depending on the wastewater and reactor conditions, but generally have a flattened spherical geometry with a diameter of 1-3 mm.

Mechanism of biomass granulation has been widely studied the objective being that the rate and extent of granule

formation could be

manipulated,

particularly in

wastewaters that

show little intrinsic

propensity to granulate

(e.g. fat and oil containing

effluents).Anaerobic sludge granules from a UASB reactor

treating effluent

Expanded Granular Sludge Bed (EGSB) Reactor

Hybrid (UASB+Packed Bed) Reactor

Anaerobic Baffled Reactor (ABR)Anaerobic baffled reactor (ABR) consists of a number of

UASB reactors connected in series. In ABR, wastewater passes over and under the

staggered vertical baffles as it flows from inlet to outlet. Advantages: Unique baffled design enables ABR to

reduce biomass washout, hence retain a high active biomass content.

It can recover quickly from hydraulic and organic shock loads.

No special gas or sludge separation equipment is required

Owing to its compartmentalized configuration, it may function as a two-phase anaerobic treatment system with separation of acidogenic and methanogenic biomass.

ABR has a simple design and requires no special gas or sludge separation equipment. It can be used for almost all soluble organic wastewater from low to high strength.

Considering its simple structure and operation, it could be considered a potential reactor system for treating municipal wastewater in tropical and sub-tropical areas of developing countries

Anaerobic Membrane Bioreactor (AMB) AMB is still in development stage.

Advantages: Higher biomass concentrations in AMB reduce the size of

reactor and increase organic loadings. Almost complete capturing of solids (much longer SRT)

results in maximum removal of VFAs and degradable soluble organics and provide a higher-

quality effluent.

Maximum capture of effluent SS improves greatly the effluent quality.

Longer SRT and low effluent SS concentration allow AMB to compete with aerobic treatment processes.

High liquid velocities across the membrane and gas agitation systems might be used to minimize fouling.

Disadvantages Organic fouling problems are typically caused by

accumulation of colloidal material and bacteria on the membrane surface.

High pumping flow rates across the membrane may lead to the loss of viable bacteria due to cell lysis.

Developments in membrane design and fouling control measures could make AMB a viable technology in future.

2-Phase AD Process Two-phase AD implies a process configuration employing

separate reactors for acidification and methanogenesis. These are connected in series, allowing each phase of

digestion process to be optimized independently since the microorganisms concerned have

- Different nutritional requirements

- Physiological characteristics

- pH optima

- Growth and nutrient

uptake kinetics and

- Tolerances to

environmental stress

factors

Advantages of Two-Phase AD Improvement in process control Disposal of excess fast growing acidogenic sludge

without any loss of slow growing methanogens Degradation of toxic materials in the first phase (protects

the sensitive methanogens) Precise pH-control in each reactor Higher CH4 content in biogas from methanogenic phase

Increased loading rate possible for methanogenic stage

Disadvantages of Two-Phase AD High sludge accumulation in the first phase Lack of process experience and so more difficult to

operate Difficulty in maintaining a balanced segregation of the

phases.

Advantages of Two-Phase AD Improvement in process control Disposal of excess fast growing acidogenic sludge

without any loss of slow growing methanogens Degradation of toxic materials in the first phase (protects

the sensitive methanogens) Precise pH-control in each reactor Higher CH4 content in biogas from methanogenic phase

Increased loading rate possible for methanogenic stage

Disadvantages of Two-Phase AD High sludge accumulation in the first phase Lack of process experience and so more difficult to

operate Difficulty in maintaining a balanced segregation of the

phases.

Nitrogen and phosphorous removal

Biological Nitrogen Removal

• Uptake into biological cell mass• Nitrification (conversion to Nitrate)

• Denitrification (conversion to N2 gas)

NITRIFICATION

Nitrogens are introduced into waste water in the forms of ,

• Urine• Food processing waste• Chemical cleaning agents• Many other industrial waste

Negative Impacts of Nitrogen on the Environment

•Nitrate in drinking water can cause Blue Baby Syndrome Increased levels of nitrate in water supplies can increase the acidity of the water and make toxic metals such as mercury more solubleGrowth of nuisance algae can cause decreased water quality and cause fish kills

DEFINITION

Nitrification is a microbial process of removing the nitrogen from environment with the help of nitrifying bacteria which are called nitrifiers.

• Nitrosomonas (ammonia to nitrite)• Nitrobacter (nitrite to nitrate)

Majority of ammonia (gas) is converted to ammonium (ion).

The equilibrium between gas and ionic forms are maintained by pH of water.

More acidic solution leads to ionic form(6-9)

More basic solution leads to gas form (12)

Molecular mechanism

First step nitrification: (nitrosifying bacteria)

ammonia is converted in nitrite with the help of autotrophs which can produce ammonia mono oxygenase (hydroxyl amine) as well as hydroxyl amine oxydo reductase (nitrite)

NH3 + O2 → NO2 + 3H+ + 2e−

NH2OH +  H2O → NO2 + 5H+ + 4e−

Second step nitrification : (nitrifying bacteria)

Nitrite which is produced in the first step can be converted in to nitrate with the help of nitrite oxydoreductase.

NO2 +  H2O → NO3 + 2H+ + 2e−

Total Kjeldahl Nitrogen(TKN)

NITROGEN CYCLE

NITRIFYING BACTERIA

• Autotrophs • Chemolithotrophs• Obligate aerobes• ANAMMOX micro organisms

Basic Design

THE INFLUENCE OF ENVIRONMENTAL FACTORS

• Alkalinity (50-150 mg/l in the form of CaC03)• Temperature• pH (6-9)• Toxic substances• Oxygen concentration• Concentration of the substances

NH4+

NO3-

Carbon Source

(Methanol)

Aeration

Media Fill Media Fill

Mechanical Mixing

Influent Effluent

Nitrification Denitrification

NO3- N2 (gas)

Alkalinity

Nitrification Tank Design•Nitrification rate of 1 gNH4

+-N/m2d (Kaldnes)•Decided on 30% Fill•Ammonia-N Load of 1250 lb/d•Reactor Volume of 130,000 ft3

•Depth of 12 ft•Length to Width 2:1 used•HRT 3.9 hrs

Media Design and Characteristics-7 mm Long and 10 mm Diameter-Density of 0.96 g/cm3 -Surface Area of 500 m2/m3

-Typical Fill of 30-50%

Aeration Requirements• Course Bubble Diffusers used to

Suspend Media and Oxygen Requirements

• Oxygen Transfer Rate of 1%/ft depth Results in 11% Oxygen Transfer Rate (Kaldnes)

• Based on earlier stoichiometry 4.6 gO2/gNH4

+-N (Nitrification)• Ammonia Loading used to

determine 110 kgO2/hr

• Standard Oxygen Transfer Rate Determined

• Air Flow Rate then Determined 4000ft3/min

)(,,

20,

CCF

CAOTRSOTR

HTs

s

)/270.0)((min/60(_

32 airmkgOhSOTE

SOTRflowAir

Alkalinity RequirementsStoichiometry NH4

++2HCO3-+2O2→NO3

-+2CO2+3H2O

7.14 g Alkalinity as CaCO3/g N is required

Design Considerations•Assumed Influent Alkalinity of 120 mg/L as CaCO3

•Desired Effluent Alkalinity of 80 mg/L as CaCO3

•Alkalinity Required used for Nitrification is 164 mg/L as CaCO3

•Alkalinity Addition Needed is 124 mg/L as CaCO3

•Total Alkalinity Required 6,200 lbs/d •Strictly Based on Stoichiometry (Further Investigation Needed)

Full nitrification: ammonium less than 2mg/l nitrite less than 0.5 mg/l• To reduce 1 pound of BOD 1.2 pounds of

oxygen is required• To reduce 1pound of ammonium to nitrite 4.6

pounds of oxygen is required.

Nitrification processes

• One sludge activated process• Two sludge activated process• Biofilm nitrification processs• Hybrid process• ANNAMOX process

One sludge activated process

• Both heterotrophic and nitrifying bacteria coexist in a single mixed liquor that simultaneously oxidizes ammonium and organic BOD.

• It has one reactor and one settler for all types of biomass.

• One sludge nitrification otherwise called as one stage nitrification, because it has only one reactor stage.

Two sludge activated process

• Two stage is an attempt to reduce the competition between heterotrophs and nitrifiers by oxidizing most of the organic BOD in a first stage, while ammonium is oxidized in second stage.

• Here two stages are available. Both stage produce their own biomass which are recycled with respective stages.

• The first sludge is essentially free of nitrifiers, while the second stage has full of nitrifiers, since all the nitrification and only a small amount of BOD oxidation occurs there.

Biofilm nitrification• The nitrifying bacteria are being attached to a solid surface in

the form of a biofilm.• Biofilm structures are heterogeneous• physical factors influencing biofilm structure are hydraulic

erosion, detachment,mass transfer, shape of the substrate.• Chemical factors- physico-chemical environment, substrate

concentration, type of substrate• During nitrification the nitrifying bacteria grow continuously

and hence there is a growth of the thickness of the biofilm. If this is not balanced by a corresponding detachment of the biofilm for trickling filters, the biofilm will be too thick resulting in clogging of the trickling filters. It is therefore desirable to have a stable state with equilibrium between growth and detachment.

Hybrid Biofilm/suspended Growth processes

• Activated sludge process can be enhanced in terms of capacity and reliability through the introduction of biofilm media that create hybrid biofilm/suspended growth system

• Existing activated sludge-upgraded by adding biofilm surface area inside the aeration basin

• The goal is to increase the total mass of active bacteria in the system and to increase the SRT

• Suspended and biofilm bacteria have different SRTs• Biofilm SRT-longer- which makes it especially important for

accumulating slow growing species such as nitrifiers• Eg: Activated biofilter• In the settler MLVSS--- maintained around 2,500 mg/L• BOD loading--- 9 Kg BOD5/m3/day

ANAMMOX process

• ANAMMOX, an abbreviation for ANaerobic AMMonium OXidation, is a globally important microbial process of the nitrogen cycle.

• If only half of the ammonia nitrogen in a wastewater flow were oxidized just to nitrite, then the remaining ammonia nitrogen and the nitrite nitrogen that has been formed could be converted to nitrogen gas by anammox bacteria in an anaerobic (absence of oxygen) environment.

• The discovery of ANAMMOX is one of the most startling ones in environmental biotechnolgy.

• ANAMMOX bacterium uses ammonium as its donor and nitrite as its electron acceptor. The energy reaction is,

• NH4+ + NO2

- = N2 + 2H2O

• The yield and specific growth rate reported for ANAMMOX are low.

DENITRIFICATION PROCESS

HIGHLIGHTS

Physiology of Denitrifying Bacteria

Tertiary Denitrification

One- sludge denitrification

INTRODUCTION

• Denitrification is a microbially facilitated process of nitrate reduction

• Performed by a large group of heterotrophic facultative anaerobic bacteria

• Ultimately produce molecular nitrogen (N2) through a series of intermediate gaseous nitrogen oxide products.

• This respiratory process reduces oxidized forms of nitrogen in response to the oxidation of an electron donor such as organic matter.

• The preferred nitrogen electron acceptors in order of most to least thermodynamically favourable include nitrate (NO3

−), nitrite (NO2−), nitric oxide (NO), nitrous oxide (N2O)

finally resulting in the production of dinitrogen (N2) completing the nitrogen cycle.

• Since denitrification can lower leaching of NO3 to groundwater, it can be strategically used to treat sewage or animal residues of high nitrogen content.

• Denitrification allows for the production of N2O, which is a greenhouse gas that can have a considerable influence on global warming.

SCHEMATIC OF DENITRIFICATION PROCESS

CONDITIONS

Anaerobic Conditions

Heterotrophic and Autotrophic Bacteria

Nitrite or Nitrate is electron acceptor

Carbon Source Required

Neutral pH (pH 7)

DENITRIFYING BACTERIA• A group of bacteria that reduce nitrates or nitrites to nitrogen containing gases.

• Important as it allows nitrogen to be recycled back into the atmosphere.

• Denitrifying heterotrophic bacteria only exist in environments where oxygen is limited.

• Denitrifying bacteria use reactive nitrogen and organic carbon as substrates to perform denitrification.

• Denitrification is one of the few ways to permanently remove reactive nitrogen from ecosystems. Since excess reactive nitrogen in water contributes to serious water quality and human health problems like toxic algal blooms and bowel cancer, denitrification in streams can be considered a valuable ecosystem service.

• Potential examples include Thiobacillus denitrificans, Micrococcus denitrificans, Paracoccus denitrificans and Pseudomonas.

• Genes known in microorganisms which denitrify include nir (nitrite reductase) and nos (nitrous oxide reductase).

PHYSIOLOGY

Denitrification process proceeds in a stepwise manner:

Very low conc. of the electron donor or too high DO can lead to accumulation of denitrification intermediates. (NO2

-, NO and N2O).

- i) a low conc. of the electron donor limits the supply of electrons to drive the reductive half-reactions.

- ii) a high DO tends to repress the nitrite and nitrous oxide reductases before the nitrate reductase is suppressed.

pH values outside the optimal range of 7 to 8 can lead to accumulation of intermediates.

- In low acidity waters, pH control can become an issue, because denitrification produces strong base.

Characteristics :

• Short, rodshaped, Gram-negative

• Grows as a facultatively anaerobic chemolithotroph

• Coupling the oxidation of inorganic sulfur compounds to the reduction of oxidized nitrogen compounds

• The optimum conditions for denitrification are pH 6.85 at 32.8°C, and optimal growth conditions are pH 6.90 at 29.5°C.

• Widely found in soil, mud, fresh-water and marine sediments, sewage and industrial waste treatment ponds

• T. denitrificans can remediate natural groundwater and engineered water treatment systems by removing excess nitrate

Thiobacillus denitrificans

Application :

• In T. denitrificans, sulfide is oxidized by a series of reactions catalyzed by a sulfide/sulfite oxidoreductase, similar to that found in some SRB.

• T. denitrificans finds use in environmental remediation, particularly for nitrate removal.

• Excess nitrogen can cause problems such as eutrophication and methemoglobinemia (blue baby syndrome), caused primarily by discharge of waste waters and overuse of fertilizers.

• Thiobacillus denitrificans is an autrophic denitrifier, which has the competitive advantages of not needing an external carbon source to be added to the process, and not producing as much sludge.

• Sulfur-based systems that T. denitrificans thrive in have been considered as a viable solution to remove nitrate from groundwater and surface water that have been contaminated, as well as remediating waste waters with high nitrate levels such as nitrified leachate. Thiobacillus denitrificans is able to reduce not only nitrate, but nitrite as well.

Characteristics :

• A coccoid shaped gram negative bacteria. Includes a double membrane with a cell wall.

• They live in the soil in either aerobic or anaerobic environments and also have the ability to live in many different kinds of media including C1 and sulfur.

• They can either use organic energy sources, such as methanol or methylamine, or act asChemolithotrophs.

• A feature of this bacteria is its ability to single-handedly convert nitrate to dinitrogen in aprocess called denitrification.

Paracoccus denitrificans

Application :

• Finds application in the construction of a bioreactor, a tubular gel containing two bacteria, for the removal of nitrogen from wastewater.

• Paracoccus denitrificans has the unusual ability of reducing nitrite to nitrogen gas.

• In this bioreactor, Paracoccus denitrificans is paired up with Nitrosomonas europaea, which reduces ammonia to nitrite. This system simplifies the process of removing nitrogen from wastewater.

TYPES OF DENITRIFICATION PROCESS

Tertiary denitrification : exogenous electron donor is needed and added.

One sludge denitrification : donor already present in the waste-water.

TERTIARY TREATMENTNutrient Removal, Solids Removal, and

Disinfection

Why is tertiary treatment needed?

• To remove total suspended solids and organic matter those are present in effluents after secondary treatment.

• To remove specific organic and inorganic constituents from industrial effluent to make it suitable for reuse.

• To make treated wastewater suitable for land application purpose or directly discharge it into the water bodies like rivers, lakes, etc.

• To remove residual nutrients beyond what can be accomplished by earlier treatment methods.

• To remove pathogens from the secondary treated effluents.

• To reduce total dissolved solids (TDS) from the secondary treated effluent to meet reuse quality standards.

• To provide additional treatment when soils or receiving waters cannot.

Biological Denitrification

• A modification of aerobic pathways (no oxygen)– Same bacteria that consume carbon material aerobically

• Denitrifying bacteria obtain energy from the conversion of NO3

- to N2 gas, but require a carbon source

NO3- + CH3OH + H2CO3 C5H7O2N + N2 + H2O + HCO3

-

Organic matter Cell mass

Denitrification (cont.)

• Separate denitrification reactor or• Combined Carbon Oxidation-nitrification-

denitrification reactor– A series of alternating aerobic and anoxic stages– Reduces the amount of air needed– No need for supplemental carbon source

Combined Nitrification/Denitrification(note alternating regions of aerobic and anoxic)

Tertiary Denitrification using Activated Sludge

• SRT (5 d) >>HRT

• High cell concentration increases reaction rate

DayPer System Leaving Sludge Mass

SystemIn Sludge MassSRT

Biofilm Process

• Submerged fixed beds of rocks, sand, limestone, or plastic media.

• Fluidized beds of sand, activated carbon, and pellets of ion-exchange resin.

• Circulating beds of a range of lightweight particles.

• Membrane bioreactors (membrane supplies H2 and is the attachment surface) .

• HRT can be less than 10 minutes.

• Recalcitrant Forms of Nitrogen

• Adequate Nutrients

• Partially Denitrified Versus Full Nitrogen Load as Nitrate

• Final barrier of treatment prior to disinfection

• Ammonia bleed through from upstream process (partial

nitrification).

LIMITATIONS IN TERTIARY DENITRIFICATION SYSTEM

ONE-SLUDGE DENITRIFICATION

One-sludge denitrification The water contains an electron donor that can drive denitrification.

- One-sludge denitrification uses the BOD in the influent of a wastewater to drive denitrification

Two goals in one-sludge denitrification :

1) Providing aerobic conditions that allow full nitrification

2) Providing anoxic conditions and Reserving BOD (organic electron donor) for denitrification.

In one sludge denitrification, the TKN must be oxidized to NO3-- N without

oxidizing all the BOD before denitrification takes place.

-Total Kjeldahl nitrogen (TKN) = organic BOD and reduced nitrogen (NH4+)

Basic One-Sludge Strategies

Three basic strategies for reserving organic electron donor while nitrification takes place :

1) Biomass storage and decay

2) Classical predenitrification

3) Simultaneous nitrification with denitrification

Biomass storage and decay

The synthesis of biomass stores electron equivalents that originally came from the BOD and can be released through endogenous respiration to drive denitrification.

It is called Wuhrmann biomass decayer (Swiss engineer K. Wuhrmann, 1964)

Biomass storage and decay has limited applicability by itself and is not often employed as a stand-alone process due to two shortcomings:

1) Endogenous respirations has slow kinetics

o high conc. of MLVSS (operating problems with settler and recycle) and a long HRT in a anoxic tank

o high capital costs are necessary

2) The decay of biomass always releases NH4+-N from the anoxic step although at

concentrations lower than in the influent.

Biomass storage and decay

Classical Predenitrification- The first tank (anoxic) ; the influent BOD (electron donor) is directly

utilized for denitrification. - The second tank (aerobic); the influent TKN is nitrified to NO3

- and any remained BOD is oxidized.

- The nitrate formed in the aerobic tank is recycled to an anoxic tank

Advantages:

i) direct use of influent BOD for denitrification - reduces aeration costs for the removal of BOD.

ii) faster kinetics than with biomass storage and decay

iii) no release of NH4+-N in the effluent

Disadvantage:

i) large mixed-liquor recycle rate - increases costs of piping and pumping.

Classical Predenitrification

Three factors allow all reactions to occur simultaneously.

1) Various nitrogen reductases using N as e- acceptor are repressed only when the D.O. conc. is well above 1 mg/L.

2) However, inhibition of the nitrogen reductase is not severe when the D.O. conc. is less than 1 mg/L.

3) D.O. conc. is depressed inside the aggregates that normally form in treatment systems; thus, denitrification can occur inside the floc (or biofilm), as long as the electron donor (BOD) penetrates inside.

- When D.O. concentration is poised at a suitably low level (< ~ 1 mg/L), anoxic denitrification can occur in parallel to the aerobic reactions of nitrification and aerobic BOD oxidation.

Simultaneous nitrification with denitrification

Advantages:

• Simultaneous nitrification with denitrification offers all the advantages of predenitrification, but overcomes the main disadvantage, the high recycle rate.

• Maintaining a low D.O. conc. throughout one reactor creates an infinitely high recycle ratio and allows essentially 100 percent N removal.

Drawback :

• The combinations of SRT, HRT, and D.O. conc. that guarantee reliability are not known yet.

Simultaneous nitrification with denitrification

Variations on the Basic One-Sludge processes

Barnard process

- No exogenous electron donor needs to be added.• chemical costs are reduced over tertiary denitrification.

- Some of the influent BOD is oxidized with nitrate as the electron acceptor (not O2).

• aeration costs are reduced compared to alternative systems that oxidize all BOD and nitrify the reduced

- nitrogen forms in the influent with O2 .

- Full or nearly full N removal is achieved• protecting receiving waters at risk from cultural eutrophication.

Benefits of One Sludge Denitrification

Phosphorous removal

Major Use: Fertilizer (Triple Superphosphate, Monoammonium Phosphates)Other Uses:• surfactants• cleaners • metal treating• lubricants• fire retardants• tooth paste

Environmental ImpactsProblem: Fertilizer Runoff and Product WasteResult: Eutrophication-Water body receives excess nutrients

that stimulate primary production (algae, nuisance plants)

Negative Effects• Health (Algae releases neurotoxins)• Depletes Dissolved Oxygen• Fish Kills

Phosphorous can be removed from wastewater prior to biological treatment, after biological treatment

Chemical precipitation: PO4

3- with Ca2+, Al3+ or Fe3+

Methods for the removal as part of the microbial treatment process:

• Precipitation by metal-salts addition to a microbiological process

• Normal phosphorous uptake into biomass• Enhanced biological phosphorous uptake into biomass

Form of phosphates

Ortho Phosphate(Soluble)

plusMetal Salts

(Soluble)

form

Insoluble Phosphorus Compounds

Chemical Phosphorus Removal

Chemical RemovalChemical Removal

M+3 +( M+3 = Metal in Solution )

Metals used are: Aluminum, Al

Iron, Fe

PRECIPITATION

PO4-3 MPO4

Precipitation by metal-salts addition to a microbiological process

Al3++ PO4

3- AlPO4

Undergo competing acid/base complex reaction

results formation of protonated species- pH-important role

There are two important disadvantages associated to chemical treatment method: (1) a certain overdosing of metal salts is necessary to obtain the required low effluent phosphorus values,

resulting in high costs of chemicals and a significant increase of excess sludge production(2) the accumulation of ions (increased salt content) may seriously restrict the reuse possibilities of the effluent

Total PhosphorusOrganic

Phosphorus

Condensed (Poly) Phosphates

OrthoPhosphates Ortho

Phosphates

Metal SaltAddition

Chemical Phosphorus Removal

Normal phosphorous uptake into biomass: Stoichiometric fromula for the

biomass can be modified to include this amount of P.

C5H7O2NP0.1 has a formula weight of 116 g/mol, of which P is 2.67%

Sludge wasted from the process removes P in proportion to the mass rate of sludge VSS wasted (QwXv

w) A steady state mass balance on total

P is P0 and P =influent and effluent total P

concentrations, Q=influent flow rate

Biological P Removal-Enhanced biological phosphorous removal (EBPR)

PAO - Phosphate Accumulating Organisms

Heterotrophic Bacteria Break Down OrganicsFermentation

Volatile Fatty Acids (VFAs) Acetate (Acetic Acid)

Anaerobic Conditions

AnaerobicFermentationAcetate ProductionSelection of Acinetobacter/PAOP Released to Produce Energy

Mechanism for uptake of phosphorous by biological method:

phosphate accumulating organisms (PAOs) store polyphosphate as an energy reserve in intracellular granules

Under anaerobic conditions, in the presence of fermentation products, PAOs release orthophosphate, utilizing the energy to accumulate simple organics and store them as polyhydroxyalkanoates (PHAs) such as poly-β-hydroxybutyrate (PHB)

Under aerobic conditions, the PAOs grow on the stored organic material, using some of the energy to take up orthophosphate and store it as polyphosphate

Phosphorus Removing Mechanism

Facultative bacteria EnergyAcetate plusfermentation

products

PO4

3-

SubstrateAcinetobacter spp.

Anaerobic

(Phosphorusremoving

bacteria, slowgrower)

Aerobic

PHB

PO4

3-

PHBEnergy

BOD + O2

New biomass

+

CO2 + H2O

Poly-P

Poly-P

Important Considerations

Adequate Influent BOD ( Enough O2 demand to achieve anaerobic conditions)

BOD:P 20:1

Adequate Anaerobic Detention Time 1-3 hrs (Not so long as to reduce sulfate to sulfide-septicity)

Adequate Aerobic Detention Time 4-5 hrs. (Enough time for BOD removal & Nitrification)

Biological P Removal

Low Effluent Suspended SolidsBelow 20 mg/L (SS result in P in effluent)

Sludge Handling(Supernatant P can overload P removal system)

Benefits

Biological P Removal

No Chemical Feed (Usually, Sometimes)

Lower CostSafetyNo Tramp MetalsNo Chemical Sludge Produced

Inhibits Growth of Filamentous Organisms(Cycling between Anaerobic & Aerobic)

Biological P Removal

Most often Used Processes

A/OPhostrip

A2/OConcentric Ring Oxidation Ditch

Sequencing Batch Reactor

Head End of Aeration Tank Baffled and Mechanically Mixed

Primary Effluent and RAS Produce Anaerobic Conditions

Phosphorus Released

“Luxury Uptake” of Phosphorus in Aerated End

A/O Process(Anaerobic/Oxic)

A/O Process

A2/O (Anaerobic/Anoxic/Oxic)

(Anaerobic/Oxic)

Phostrip

Some Return Sludge Diverted to Anaerobic StripperPhosphorus Released

Elutriated (Washed) to a Precipitation Tank

Precipitated With Lime – Sludge Removed

Concentric Ring Oxidation Ditch

AnaerobicAerobic

Aerobic

Three Aeration Tanks in Concentric Rings

Concentric Ring Oxidation Ditch

Wasting Aerobicthe Bio-solids Removes

Phosphorus

Three Aeration Tanks in Concentric Rings

Sequencing Batch Reactor

Sequencing Batch Reactor

Batch Treatment in Sequence of Steps

AnaerobicP Release

AerobicP Taken Up by

Biomass.

P Removed in Sludge

Static Fill

Mixed Fill

React Fill

React

Settle

Decant

Waste

Idle

D.O.

Ortho-P