Lectut CE 202 PDF Tertiary Treatment

8/18/2019 Lectut CE 202 PDF Tertiary Treatment

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WASTEWATER TREATMENT – TERTIARY TREATMENT

PROCESS

SUDIPTA SARKAR


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Typical Process flow Diagram –

Different Treatment Blocks

Bar Screens Grit RemovalPrimary Clarifier

O2

Aeration

tank

Secondary

ClarifierNutrient

Removal

D

I

S

P

O

S

A

L

Dewatered

Sludge to

landfill

AnaerobicDigester

Gravity Sludgethickener

Filter Press

Screenings Grit

PRELIMINARY PRIMARY SECONDARY TERTIARY

Advanced

Treatments

SLUDGE PROCESSING


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Treated Wastewater Effluent Still Contains…

• A portion of initial organic load (residual BOD)

– Carbon matter, depletes O2, causes biomat growth

• TSS (total suspended solids)

– Depletes O2• NH3 (ammonia)

– Toxic to fish, depletes O2, a nutrient that promotes biological growth

• NO3- (nitrate)

– Toxic to babies, drinking water regulated, a nutrient

• Total P (total phosphorus)

– A nutrient

• Pathogens (bacteria/viruses)

– Disease causing

There is a need of tertiary treatment to tackle the contaminants still remaining

in the treated effluent

• To better protect public health and environment from creating a potentially

hazardous condition such as eutrophication

• To provide additional treatment when soils or receiving waters cannot

naturally degrade the small amount of contaminant released.


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Problems associated with nutrients presence in wastewater are

• accelerating the eutrophication

• stimulating the growth of algae & rooted aquatic plants

• aesthetic problems & nuisance

• depleting D.O. concentration in receiving waters

• Toxicity towards aquatic life

• increasing chlorine demand

• presenting a public health hazard

• affecting the suitability of wastewater for reuse

Nutrients Removal

Basic nutrients present in the domestic wastewater are

– Nitrogen (ammonia, nitrite, nitrate)

– Phosphorus (soluble and insoluble. Orthophosphate, polyphosphate. Organic P)

– Sulfate

– Other compounds of nitrogen & phosphorus


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Control and Removal of Nitrogen (Biologically):

• Removal of Nitrogen by Nitrification/Denitrification Processes:

– It is a two step processes

Conversion of Ammonia to Nitrite (Nitrosomonas)

NH4+ + 1.5 O2 Bacteria (Nitrosomonous) NO2

- + 2 H+ + H2O

Conversion of Nitrite to Nitrate (Nitrobacter)

NO2- + 0.5 O2 (Nitrobactor) NO3

-Nitrification

Process

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

Process

There is another reaction, mediated by a special group of bacteria, known as ANAMMOX

(ANaerobic AMMonium OXidation) bacteria, recently discovered in the year 2000, which

directly produces nitrogen from nitrite as per the following reaction:

NH4+ + NO2- N2 + 2H2O


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SuspendedGrowth SeparateStage Nitrification

Single State Nitrification

Nitrification Processes

The following factors affect nitrification:

a) Conc. of NH4+ and NO2

-, b) BOD/TKN ratio (BOD should be gone/removed) ;

c) Dissolved oxygen conc. (need oxygen); d) Temperature; e) pH (7.5 to 8.6)


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• Need low (no) oxygen (< 1 mg/L)

• Need carbon source (Methanol or alternative)

• Neutral pH (pH 7)

• Concentration of nitrate

Denitrification

Separate-stage denitrification process using a separate carbon source

Air

Return SludgeReturn Sludge

Source of Organic

carbon (methanol or

alternative

NitrificationTank

Nitrification

Clarifier

Denitrification

Clarifier

Denitrification

tank

Effluent

Waste Sludge Waste Sludge

Anoxic Zone


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Combined Nitrification-Denitrification Process – Oxidation Ditch

The influent stream is discharged into the upstream limit of the anoxic zone , organicloading of the wastewater serves for the denitrification purpose. The wastewater at

the end of the anoxic zone has the organic load as well as ammonia source, it is put

into extended aerobic zone where nitrification occurs. Because there is no polishing

stage provided at the end of aerobic region for denitrification, the nitrogen removal

efficiency is low, about 50-60%. Effluent is taken just before the anoxic zone.

Controlling the Dissolved oxygen level is crucial to the efficiency of the system.


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Four-stage Plug Flow Bardenpho Process

Separate reaction zones are used for carbon oxidation nitrification and anoxic denitrification. The influent

initially enters into anoxic denitrification zone where nitrified mixed liquor is recycled from subsequent

combined carbon oxidation nitrification compartment. The carbon in the wastewater is used to denitrify

the recycled nitrate. Organic loading is high, the process of denitrification proceeds rapidly. Ammonia

passes on unchanged to the next compartment.

In the 2nd compartment, ammonia of the wastewater gets nitrified, because of extended aeration.

In the 3rd compartment, denitrification need is rather low; it is carried out anoxically by the utilization of

endogenous carbon source still remaining.

In the 4th compartment, aeration is done to strip the nitrogen gas out of the system, so that the final

sludge is not fluffy and settles down well in the clarifier.


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Enhanced Biological Phosphorus Removal

Phosphorous appears in the wastewater as orthophosphate (PO43-), Polyphosphate (P2O7)

and organically bound phosphorus. Polyphosphate and org-P account up to 70% of total P

in the wastewater. Microbes need P for cell synthesis and energy transport. 10-30 percentof P is thus removed in the secondary treatment process where new cells are synthesized

and wasted. In order to attain even lower P concentration at the outlet, additional uptake

of P by the microbes is required.

When some aerobic microbes such as Acinetobactor is subjected to anaerobic situation,phosphorus is released from the cells. If the microbes are then subjected to aerobic zone,

they tend to uptake more phosphorus than needed because they want to store more

phosphorus to counteract the future stressed situation.

Thus, microbes when subjected to alternate anaerobic and aerobic situations, tend to

extract more P from the wastewater.


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PAO- Phosphorus

accumulating

organism

A/O Process for P removal

Net Result:

Phosphorus

accumulation by the

microorganism. And,removal as

Phosphate-rich

sludge


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Inorganic Phosphorus Removal

• Chemical Precipitation

– Calcium (lime) addition at high pH (>10)

– Alum precipitation

– Precipitation with ferric hydroxide


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Combined Nitrogen and Phosphorus Removal

A2/O Process

Anaerobic Anoxic Aerobic

Air

Wastewater

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Lectut CE 202 PDF Tertiary Treatment

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