Neutralization IWM

8/13/2019 Neutralization IWM

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Industrial and Hazardous Waste

Management


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Pre-Treatment

Coagulation

and

Precipitation

Equalization Neutralization

Flotation

Sedimentation

FiltrationSpill Basin


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Introduction

Law of mass action

The mathematical product of the H+

and-

OH ion concentration,expressed as moles/Litre is always equal to 10-14 .

Many wastes contain acidic or alkali materials that require tobe neutralized prior to discharge to receiving water body orprior to chemical or biological treatment.

For biological treatment ,pH should be maintained between

6.5 to 8.5 to ensure optimum biological activity.

The CO2produced during biological oxidation also provides abuffer capacity , which reacts with caustic and acidicmaterials


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Introduction

Organic matter +O2+ bacterial cellsCO2+ H2OHCO3 +

HCO3 CO3

+

+ pH=8.9

CO3

+H2OHCO3

+-OH pH=9


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Neutralization

Process of adjusting the pH of water or wastewater throughaddition of an acid or a base, depending on the target pHand process requirements.

Water or wastewater is generally considered adequatelyneutralized if;

1. Its damage to metals, concrete , or other material is minimal.

2. Its has little effect on fish and aquatic life.

3. It has no effect on biological matter.


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Neutralization

Alkalinity & Acidity

Important source of alkalinity and acidity in natural waters isfrom the carbonate system

Water and wastewater pH controlling ions are HCO3 , [+],

[CO3],[-OH ]

It is determine by titration

pH above 8.3 , two steps take place:

1. pH shifted to 8.3

2. pH shifted to 4.5


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Methods of Neutralization

1. Mixing acidic and alkaline waste streams

2. Passing acid wastes through limestone beds

3. Mixing acid wastes with lime slurry

4. Adding the proper proportion of concentrated solutions of caustic

soda (NaOH) or soda ash (Na2CO3) to acid wastes

5. Adding compressed CO2to alkaline wastes

6. Adding H2SO4to alkaline wastes


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Neutralization of Acidic wastewater

1. Mixing acidic and alkaline waste streams

This can be accomplished within a single plant operation orbetween neighboring industrial plants.

Acid and alkaline wastes may be produced individually within oneplant and proper mixing of these wastes at appropriate times canaccomplish neutralization


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1. Acid wastes neutralization through limestone beds

Passing acidic wastewater through beds of limestone by pumpingthe waste through the bed depending on :

1. Head available

2. Cost involved for neutralization

Two systems involved:

1. Up flow system

2. Down flow system

For down flow system the maximum hydraulic loading rate is 1

gal/min.ft2



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CaCO3+ H2SO4 CaSO4+ H2CO3

The above reaction will continue as long as:

1. excess limestone is available (met by simply providing asufficient quantity of limestone)

2. in an active state( water should not contain lime stonecoating substances such as sulphuric acid or metal salts orhydrochloric acid)

pH is related to the bed depth.



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Limestone Bed


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Problem 1

1. Acid wastes neutralization through limestone beds.

A wastewater flow of 100 gallons/min with 0.1N H2SO4requiredneutralization prior to secondary treatment. This flow is to be neutralized

to a pH of 7 using limestone bed(data given below). Designed aneutralization system specifying

(a) most economical bed depth of limestone

(b) weight of acid per day to be neutralized

(c) limestone requirements on an annual basis

Depth (ft3) 0.5 1 2 3 4

HLR ( gal/ft2.hr) 42 180 850 1440 1600


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Problem 2

1. Acid wastes neutralization through limestone beds.

A wastewater flow of 200 gallons/min with 0.2N HCL required

neutralization prior to secondary treatment. Calculate

(a) weight of acid required on annual basis

(b) limestone requirements on an annual basis


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2. Mixing Acid wastes with Lime Slurries

Depends on type of lime used.

Magnesium fraction of lime is most reactive in strongly acidic

solution and useful below pH 4.2.

Basicity factor

Neutralization can be done by using sodium hydroxide,

sodium carbonate, ammonium hydroxide or magnesium

hydroxide.



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1. CO2Treatment for Alkaline Waste streams

Bottled CO2 is aplied to wastewater as compressed air is applied to

activated sludge process.

It forms a weak acid (carbonic acid) when dissolved in water.

The cost may be prohibitive , when the quantity of alkaline waste is

large

Neutralization of Alkaline wastewater


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2. H2SO4Treatment for Alkaline Waste streams

2NaOH + H2SO4 Na2SO4+ 2H2O

Costly but common method

Storage and feeding equipment requirements are low as a result ofits great acidity

Difficult to handle because of its corrosiveness

Neutralization of Alkaline wastewater


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Selection Criteria(Neutralizing agent)

1. Reaction rate

2. Sludge production and disposal

3. Safety during handling and equipment

4. Side reactionincluding dissolved solids, scale formation and heat

5. Effect of overdosing


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Multistage Neutralization


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Problem

1. 100 gallons/min of wastewater is highly acidic and requiresneutralization prior to secondary treatment. This flow is to be

neutralized to a pH of 7 by lime. Titration are shown in figure fromwhich a 2 stage neutralization system will be used with the total limeconsumption of 2250 mg/l. The first stage requires 2000 mg/l and thesecond stage 250 mg/l.

(a) Determine the amount of lime required in lb/day.

(b) Also determine the size of neutralization tank. Assume detentiontime 5 min

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Neutralization IWM

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