pond-based treatment and tertiary treatment

8/10/2019 Pond-based Treatment and Tertiary Treatment

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WASTEWATER TREATMENTTERTIARY TREATMENT

PROCESS AND STABILIZATION PONDS

DR. SUDIPTA SARKAR


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STABILIZATION PONDS

Waste or Wastewater Stabilization Ponds (WSPs) are artificial man-made

lagoons in which blackwater, greywater or faecal sludge are treated by

natural occurring processes and the influence of solar light, wind,microorganisms and algae.

These are natural or semi-engineered processes for cost-effective

wastewater treatment where required degree of treatment is achieved with

minimal use of mechanical, civil and electrical facilities. These are popular

for small communities because of their low construction and operatingcosts.

These are essentially biological treatment processes with natural facilities

spread over a vast area of land.

The effluent still contains nutrients (e.g. N and P) and is therefore

appropriate for the reuse in agriculture (irrigation) or aquaculture (e.g. fish-or macrophyte ponds) but not for direct recharge in surface waters.

The ponds can be used individually or in series of an anaerobic, facultative

and aerobic (maturation) pond.


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TYPES OF STABILIZATION PONDS

1. Anaerobic Ponds 2. Facultative Ponds 3. Aerobic Ponds 4. Maturation Ponds

Anaerobic Treatment Ponds are deep ponds (2 to 5 m) devoid of dissolved

oxygen, where sludge is deposited on the bottom and anaerobic bacteria break

down the organic matter by anaerobic digestion, releasing methane and carbon

dioxide.

Anaerobic Ponds

The anaerobic pond serves to:

a)Settle undigested material and non-degradable solids as bottom sludge

b)Dissolve organic material

c)Break down biodegradable organic material

BOD Loading:

400-3000 kg/(ha.d)

Detention Period: 5 -50 days

BOD removal efficiency: 50-85%Volume can also

be calculated

considering organic loading

in the range of 100 to 350 g

BOD/m3/day

NH3 80 mg NH3-N/L


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Facultative Ponds

CO2+NH3+CH4

It functions aerobically at the

surface but anaerobic conditions

prevail at the bottom. The aerobic

zone kept at the top is effectiveagainst release of odorous gases. It

is most suited pond treatment

method.Facultative

Facultative= aerobic + anaerobic

There is a diurnal variation in the

concentration of dissolved oxygen.At peak sun radiation, the pond

will be mostly aerobicdue to algal

activity, while at sunrise the pond

will be predominantly anaerobic.

Daytime pH is high, as algae use bicarbonate ions to convert to new algae. NH3produced due to anaerobic digestion volatilizes out to atmosphere. pH above 9 also

ensures killing of pathogens and E. Coli present in wastewater.

FPs help to: a) treat wastewaterthrough sedimentationand aerobicoxidationof

organic material b)Reduce odor c)Reduce some disease-causing microorganismsif

pHraises d) Store residues as bottom sludge


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Maturation Pond

Maturation ponds are shallower (1 to 1.5 m), with 1 m being optimal. The recommended

hydraulic retention time is 15 to 20 days. If used in combination with algae and/or fish

harvesting, this type of pond is also effective at removing the majority of nitrogen andphosphorus from the effluent.

These are essentially designed forpathogenremoval and retaining suspended stabilized

solids.

The principal mechanisms for fecal bacterial removal in facultative and maturation ponds are

HRT, temperature, high pH (> 9), and high light intensity. Fecal bacteria and other pathogensdie off due to the high temperature, high pH or radiation of the sun leading to solar

disinfection


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DESIGN OF A FACULTATIVE POND (AS PER IS 5611)

Step 1.Find out the surface

area of the tank based on the

rate of application of BOD5

influent to the stabilization

pond

Step 2.Find out the detention

period using the formula:

tk

i

e

eL

L1

tkL

L

i

e

11

1

Le and Liare effluent and influent BOD5, t is the detention time, k1is BOD rateconstant

For plug flow

For continuously

mixed system

Natural and constructed systems do not exactly follow either plug flow or

completely mixed systems, hence corrections in the form of dispersion numbers

are to be incorporated.


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Step 3.Find out the surface area and the depth. The optimal depth is 1.5 m. If the

calculation shows less than 1 m depth, minimum depth to be provided is 1 m.

Step 4.calculate sludge accumulation based on the design data of accumulation

rate of 0.07 cum/ person/ year. The desludging period is normally taken to beequal to 6-12 years. Add depth for accumulation of sludge.

Step 5.Find out the sizes of the stabilization pond. Take length as double the

width. Provide a free board of 0.5 m to 1 m.


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DESIGN OF A FACULTATIVE POND

Consider that desludging interval is equal to 6 years. Consider that the pond is exactly in

between a plug flow and completely mixed flow reactor


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Typical Process flow DiagramDifferent Treatment Blocks

Bar Screens Grit RemovalPrimary Clarifier

O2

Aeration

tank

Secondary

ClarifierNutrient

Removal

D

I

S

P

OS

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 biol. 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 remainingin 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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Nutrients Removal

Basic nutrients present in the domestic wastewater are

Nitrogen (ammonia, nitrite, nitrate)

Phosphorus (soluble and insoluble) Sulfate

Other compounds of nitrogen & phosphorus

Problems associated with nutrients presence in wastewater are accelerate the eutrophication

stimulate 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


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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++ 2 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 N2gas, but require a carbon source

NO3-

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

(organic matter) (cell mass)DenitrificationProcess


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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 (BOD in Wastewater)

Neutral pH (pH 7)

Conc of nitrate

Denitrification

Separate-stage denitrification process using a separate carbon source

O2

Denitrification

clarifier

Return sludge

Effluent

EffluentMedia

Carbon

source


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Phosphorus Removal

Chemical Precipitation

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

Reacts with alkalinity

Alum (Aluminum Sulfate)precipitation

Iron precipitation

pond-based treatment and tertiary treatment

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