treatment of wastewater introduction

8/13/2019 Treatment of Wastewater Introduction

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Treatment of Wastewater

- Introduction

- Preliminary Concepts

PRADEEP KUMAR

SUDIPTA SARKAR


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Wastewater Discharge Regulations (Excerpts)

Parameter and

unit

Into

Surface

Water

Into

Public

Sewer

Into

Irrigation

Water

Into coastal

water

pH 5.5 -9.0

BOD, 3day,

27deg C, mg/L

30 350 100 100

COD, mg/L 250 - - 250

TSS, mg/L 100 600 200 100

TDS, mg/L 2100 2100

Oil and Grease,

mg/L

10 20 10 20

Dissolved

phosphates, as P,

mg/L

5 - - -

Nitrate, as NO3,

mg/L

10 - - 20

SS particle size,

micron

850 - - -


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Normal Pollutant Loads vis--vis Discharge Standard into

Surface Water in Wastewater

Parameter and unit Into

Surface

Water

Untreated Domestic Wastewater

Weak Medium Strong

pH 5.5 -9.0

BOD, 3day, 27deg C,

mg/L

30 100 200 400

COD, mg/L 250 250 500 1000

TSS, mg/L 100 100 250 350TDS, mg/L 2100 250 500 850

Oil and Grease, mg/L 10 50 100 150

Dissolved

phosphates, as P,

mg/L

5 4 8 15

Nitrate, as NO3, mg/L 10 0 0 0

SS particle size,

micron

850 Not

known

Not

known

Not

known

Total Coliform,

no/100 mL

- 106-107 107-108 108-109


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RAW

WATER

TREATED WATER

WASTEWATER

TEATED

WASTEWATER

WASTEWATER TREATMENT PLANT

WATER TREATMENT PLANT


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CLASSIFICATION OF WASTEWATER TREATMENT METHODS

Once the quality of wastewater is assessed, and the regulations and discharge limits are

finalized, the degree of treatment can be determined by comparing the quality with the

target effluent characteristics

TEATED WASTEWATER

WASTEWATER TREATMENT PLANT

WASTEWATER

Three basic operations:a) Physical Unit ProcessesApplication of Physical forces predominate in physical

unit operations. Example: Screening, Mixing, flocculation, Sedimentation,

filtration, floatation, and gas transfer are typical physical unit operation

b) Chemical Unit Processes- Removal of contaminants by chemical reaction either by

adding chemicals or changing conditions so that chemical reactions occur. Typical

examples: Precipitation, adsorption, disinfection, etc.

c) Biological Unit Processes- Removal of contaminants by biologically active elements

such as microbes. Biodegradable components are removed. Nutrients are also

destroyed.


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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

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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Primary Settling Tanks

Aeration TanksSecondary Settling TanksSludge Thickener

Sludge Digester

Tertiary

Treatment

facilities

Methane Gas storage


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PRELIMINARY TREATMENTREMOVAL OF OVER-SIZED SOLIDS

Two Different Types of Treatment facilities for preliminary treatment:

a) Screens

b) Grit Chambers

Screens are provided for separation of larger-sized floating or suspended particles in

wastewater.

Unless the screens are used, larger sized floating objects such as plastic bags, bottles,

rags, etc. and other objects such as tree branches, leaves, large-sized debris would enter

the machineries in the Wastewater treatment plant and damage the equipment .

Grit Chambers are provided for separation of larger-sized objects such as rubbles, sand,

ash, clinkers, egg shells, bone chips, etc. from the raw wastewater entering the

treatment plant.

Unless a grit chamber is used the inorganic larger objects of abrasive nature would

enter the treatment plant and negatively impact the operation of the rotating

machineries in the treatment plant.


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SCREENS

Screens are for the protection of the treatment plants machineries from getting

choked by the floating objects. So, they are located before the entry of treatment

plant or before a pumping well or any other sewer outfall.

Three different quality of Screens:

a) Coarse Screen

b) Medium Screen

c) Fine Screen

Coarse screen is used purely for protection

purposes; restricts the entry of large floating

objects with size greater than 50 mm

Medium screen has clear openings of 25- 50 mm size. The bars are about 10 mm

thick on the upstream side and taper slightly to the downstream side. Typical size ofthe bars are 10 mm X 50 mm, the larger dimension is arranged along the direction

of flow.

Fine screens are mechanically cleaned devices, with opening size less than 25 mm.

The opening shape may vary from square to circular; it can get clogged very easily

so its use is restricted to industrial wastewaters.


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COARSE SCREENS

MANUALLY CLEANED SCREENS

Manual bar screens have little or no motorized

cleaning equipment therefore must beperiodically cleaned manually by hand.

Scheduled cleaning as often as necessary to

ensure unobstructed flow of the waste stream.

Screenings removed manually from the bar

screen are conveyed to a perforated plate todrain excess water before being disposed of.

Maintaining the manual bar screen labor is intensive.

If removal of screenings from the bar screen is infrequent, flooding and overflow occursdue to clogging.

The bar screen channel should be designed in such a way as to reduce the build up of grit

and other debris directly upstream and downstream of screen.


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The continuous belt bar screen is

equipped with cleaning elements that

are fixed to an endless belt used toremoved objects from the waste stream.

The number of elements attached to the

belt is determined by the depth of the

channel.

The cleaning elements include hooks

that stick out to augment the screening

capture of larger object and rags from

the wastewater.

MECHANICAL SCREENS


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When designing any wastewater treatment process at a wastewater treatment

facility, head loss calculations should be performed. To obtain the head loss through

the bar screen the following equations is used:

h = 1 ((V12V2

2)/2g)

0.7

where: h = head loss, mV2 = approach velocity, m/s

V1= velocity through bar opening, m/s

g = acceleration from gravity

0.7 = head loss coefficient

treatment of wastewater introduction

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