Waste Water Treatment Technology

7/30/2019 Waste Water Treatment Technology

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Waste water Treatment Processes

Introduction

Sewage Treatment Processes:A. Preliminary

B. Primary

C. SecondaryD. Tertiary


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Introduction

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Definitions:

Sewage:The content of sewer or drains

Sewage Treatment:Removing of impurities so that the remaining waste water canbe safely returned to the river or sea and become part of thenatural water cycle again.


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Compositions:

Human waste

paper

Food

Grease

Mineral matter

and almost any things that can be carried by water

Introduction Contd


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4 2003 John Wiley and Sons Publishers

Fig 21.21 Diagram of sewage treatment processes.


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Disease-Causing Agents

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Sewage Treatment Processes

Preliminary

Primary

Secondary

Tertiary


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Solids like wood

paper, rags andplastic are removed

by screens

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Preliminary Treatment

Sewage Treatment Processes Contd
http://www.dcs.ex.ac.uk/water/image2/screene2.gif


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The remaining solids that passed from thepreliminary treatment are removed

About 70% of solids settle out at this stage

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Primary Treatment



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Secondary Treatment


Biological treatment to reduce organic matter in the waste

stream

Aerobic bacteria is the main cause for this reduction

The chemical reaction:

Organic matter CO2 + H2OBacteria

O2


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This process can be

speeded up by blowing air

into tanks of sewage

These treatment units are

called Aeration Tanks.


Secondary Treatment


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Bacteria Found in the Sewage

Aerobic

Require dissolved

oxygen for their

existence

Ex: Earobacter

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Facultative

Can grow with or

without oxygen

Ex: Salmonella

Anaerobic

Exist in the absence of

dissolved oxygen

Ex: Sulfate Reducer


Secondary Treatment


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Several forms of tertiary treatment are available for

example:

1. Passing the effluent over grass plots

2. Retaining the effluent in lagoons

3. Filtering through sand beds

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Tertiary Treatment



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Advantages

Long history in the

industry - known

Easy to operate

Easy to construct

Disadvantages

Requires large waterpumps

Operation smothers

the nitrifying biofilm Needs frequent

backwashing

Sand Filters


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Advantages

Good air exchange

Simple to construct

Almost any material

will work

Disadvantages

Uneven surface

wetting

May promote solids

retention & be hard toclean

Trickle Filters


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Advantages

Good air exchange Least maintenance of

all biofilters

Automatically

maintains a thin biofilm

Most efficient Biofilter

Disadvantages

No solids removal

Have to maintain

rotation

Needs space

Industrial RBC


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Advantages

Constant movementof beads promotes

thin biofilm

Large surface for

nitrification

Disadvantages

Hard to maintain constantbead movement

Beads tend to stick together

Loss of Beads from the

filter

May promote growth of

heterotrophic bacteria

Fluidized Beds


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Filter Type Maintenance CloggingPotential OxygenLimitedMechanicalAbility

Sand Filter high high yes goodUndergravel

Filter high high yes good

Plenum low medium yes noneTrickle Filter medium medium no noneRBC low low no noneFluidizedBed med-high medium yes goodBead Filter high high yes good

Filter Comparison


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Activated sludge is a process for treating sewage and industrial

wastewaters using air and a biological floc composed of bacteria

and protozoans.
http://en.wikipedia.org/wiki/Sewagehttp://en.wikipedia.org/wiki/Wastewater_treatmenthttp://en.wikipedia.org/wiki/Wastewater_treatmenthttp://en.wikipedia.org/wiki/Wastewater_treatmenthttp://en.wikipedia.org/wiki/Wastewater_treatmenthttp://en.wikipedia.org/wiki/Wastewater_treatmenthttp://en.wikipedia.org/wiki/Sewage


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oxidizing carbonaceous matter: biological matter.

oxidizing nitrogeneous matter: mainly ammonium and

nitrogen in biological materials.

removing phosphate.

driving off entrained gases carbon dioxide, ammonia,

nitrogen, etc.

generating a biological floc that is easy to settle.

generating a liquor that is low in dissolved or suspended

material.
http://en.wikipedia.org/wiki/Biological_matterhttp://en.wikipedia.org/wiki/Ammoniumhttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Phosphatehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Ammoniahttp://en.wikipedia.org/wiki/Ammoniahttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Phosphatehttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Ammoniumhttp://en.wikipedia.org/wiki/Biological_matter


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Activated sludge process

Activated sludge is a biochemical process for treating sewage and

industrial wastewater that uses air (or oxygen) and microorganisms tobiologically oxidize organic pollutants, producing a waste sludge (or

floc) containing the oxidized material.

Any oxidizable material present in a natural waste will be oxidized bothby biochemical (bacterial) or chemical processes. The result is that the

oxygen content of the water will be decreased.

Oxidizable material + bacteria + nutrient + O2 CO2 + H2O + oxidized

inorganics

S-- + 2 O2 SO4--

NO2- + O2 NO3

-
http://en.wikipedia.org/wiki/Biochemicalhttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Microorganismhttp://en.wikipedia.org/wiki/Flochttp://en.wikipedia.org/wiki/Redoxhttp://en.wikipedia.org/wiki/Biochemistryhttp://en.wikipedia.org/wiki/Inorganic_chemistryhttp://en.wikipedia.org/wiki/Inorganic_chemistryhttp://en.wikipedia.org/wiki/Biochemistryhttp://en.wikipedia.org/wiki/Redoxhttp://en.wikipedia.org/wiki/Flochttp://en.wikipedia.org/wiki/Microorganismhttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Biochemical


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In general, an activated sludge process includes:

An aeration tank where air (or oxygen) is injected and thoroughly

mixed into the wastewater. A settling tank (usually referred to as a "clarifier" or "settler") to

allow the waste sludge to settle. Part of the waste sludge is recycled to

the aeration tank and the remaining waste sludge is removed for further

treatment and ultimate disposal.


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Trickling filter system

A bed of filter medium upon which a

layer of microbial slime is promoted and

developed.

An enclosure or a container which

houses the bed of filter medium.

A system for distributing the flow of

wastewater over the filter medium.

A system for removing and disposing of

any sludge from the treated effluent.

The treatment of sewage or other

wastewater with trickling filters is

among the oldest and most well

characterized treatment technologies.

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Waste Water Treatment Technology