Wastewater Municipal Tertiary

EE304 ENVIRONMENT ENGINEERING & ABATEMENT PROCESS

EP317 ENVIRONMENT ENGINEERING AND ABATEMENT PROCESS

EG202 ENVIRONMENTAL SCIENCE AND TECHNOLOGY

Content

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EE304 ENVIRONMENT ENGINEERING & ABATEMENT PROCESS EP317 ENVIRONMENT ENGINEERING AND ABATEMENT PROCESS EG202 ENVIRONMENTAL SCIENCE AND TECHNOLOGY

WATER POLLUTION & WASTEWATER

0 Water quality parameter

0 Sources and classification of pollutants

0 Water quality control policy

0 Impact of pollutant to environment and

human

0 Waste water treatment technologies

Municipal Wastewater Treatment

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Tertiary Treatment

Secondary treatment and disinfection may remove over 85% of BOD & suspended solids and nearly all pathogens.

Not significant removal of some pollutants, nitrogen, phosphorus, soluble COD & heavy metals.

Nitrogen and Phosphorus can be available as nutrient and stimulate the growth of toxic cyanobacteria (blue-green algae) therefore contributes to eutrophication in aquatic systems.

Thus Advanced Wastewater Treatment is required


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Tertiary Treatment

AWT of sewage can remove about 99% of the pollutants from raw wastewater and can produce an effluent of almost drinking water quality.

Some of the common AWT processes:

1) Filtration

2) Phosphorus Removal

3) Carbon Adsorption

4) Nitrogen Removal


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Tertiary Treatment


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Tertiary Treatment

The purpose of tertiary treatment is to provide a final treatment stage to further improve the effluent quality before it is discharged to the receiving environment (sea, river, lake, ground, etc.) or reuse.

More than one tertiary treatment process may be used at any treatment plant (Integration System).


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Tertiary Treatment – 1) Filtration

Remove residual suspended solid & residual BOD5, the unsettled mo in secondary clarifiers.

1) Conventional sand filters

often clog, require frequent backwashing can be improved by having larger filter grain sizes at

the top of the filter (lengthen filter runs & reduce backwashing)


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2) Multimedia filter low density coal for the large grain sizes medium density sand for intermediate size high density garnet for the smaller size filter grain

The use of coagulation and sedimentation followed by filtration can yield suspended solids concentration virtually zero.


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Typical layout of a wastewater system including filtration


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Tertiary Treatment – 2) Carbon Adsorption Refractory Organic Compounds (ex. soluble COD) are

resistant to biological breakdown, even after secondary, coagulation, sedimentation and filtration may persist in the effluent.

Most practical available method to remove ROC is by adsorbing them on Activated Carbon.

Carbon is activated by heating in the absence of O2, activation process results in formation of many pores within each carbon particle.


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Tertiary Treatment – 2) Carbon Adsorption Adsorption is accumulation of materials at an interface,

wastewater organic materials accumulate at interface.

Adsorption is a surface phenomena – the greater the surface area of the carbon the greater its capacity to hold organic matter.

After adsorption, AC can be restored by heating it in furnace at a temperature sufficiently high to drive off the adsorbed organic material.


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Tertiary Treatment – 3) Phosphorus Removal Phosphorus in wastewater is primarily in the form of

organic phosphorus and as phosphate (PO43-) compounds.

Chemical phosphorus removal is accomplished by chemical precipitation using one of the 3 compounds.


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Tertiary Treatment – 3) Phosphorus Removal The phosphorus compounds are entrapped in the coagulant

flocs that are formed and settle out.

Precipitation of P requires a reaction basin and settling tank.

To avoid the need for construction of additional tanks, coagulant is added to the wastewater at same point in the conventional process.


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Tertiary Treatment – 4) Nitrogen Removal Biological nitrogen removal is a 2-step process:

1) Nitrification in aerobic environment

2) Denitrification in anoxic environment

N in any soluble form NH3, NH4+, NO2

-, NO3- is a nutrient,

need to be removed.


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Tertiary Treatment – 4) Nitrogen Removal 1) Nitrification

Forced to occur in activated sludge by maintaining a cell detention time of 15 days in moderate climate or 20 days in cold climates.

Bacteria must be present to cause reaction to occur

2) Denitrification


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Tertiary Treatment – 4) Nitrogen Removal

AOB

NOB

Ammonium

Nitrite

Nitrate

Nitrite

Nitrogen

O2

COD

Nitrifiers involved in nitrification: 1) Ammonia Oxidizing Bacteria

AOB 2) Nitrite Oxidizing Bacteria

NOB 3) Oxidize N compound to obtain

energy (energy source) & use inorganic carbon as carbon source for biosynthesis


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AOB

NOB

Ammonium

Nitrite

Nitrate

Nitrite

Nitrogen

O2

COD Denitrifies involved in denitrification: 1) Organic carbon serves as

energy and carbon source

2) External organic carbon source required for rapid denitrification


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Wastewater Municipal Tertiary

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