Industrial Pollution

ENVE 420
Industrial Pollution Control Solid and Hazardous Water
Wastes Air Pollution Pollution

INTRODUCTION
Interrelations between pollution types in an industrial
Dr. Aslıhan Kerç system.

• Productionà one or more materials are used

• Process: includes all the unit operations to obtain
products
• Sub-processes: not directly related with
Raw Material production. Includes supply of energy,
Energy Industrial System Products preperation of materials
By-products • Inputs into an industrial sys: ?
Material + energy
Reuse Wastes Recycle • Outputs: ?
Products + By-products + wastes
Real Wastes • Waste: ?
hazardous If the outputs from an industry do not have
Solid Gas Liquid
Radioactive economic value they are considered as wastes.
 Pollution Management in an Industry Process types
• Examination of the industry as a whole with • Continuous process
all major and sub-processes • Batch process
• Aim: minimize waste production • Semi-batch process
If necessary à change the process (e.g. raw material continuous, production not)

Material and Energy Balance

• Operation of the industry should be known on
daily, weekly and seasonal basis
# shifts / day
Workdays / week
Is there production in weekends?
Is there any seasonal changes within the year?
 Units used in industrial pollution
Flowrates
• Variations in waste flows depending on the • Volume
diversity of the products manufactured and on • Load
process operations. • Concentration
• Process operations
- Batch
- Continuous
Industrial surveys are conducted to determine
waste loadings and variations.

Expression of Flows / Volume Expression of Load

• Time basis • Time basis
m3/h, m3/day kg BOD5 /h, kg BOD5 /day
• Production basis • Production basis
m3/product Textile: kg BOD5 / ton cloth
m3/raw material Sloughter house. Meat processing ind.:
m3/energy used kg SS / kg live weight kill
Metal plating: kg Cadmium / m2 plated area
 Expression of Concentration Population Equivalent
• Pollution loads of an industry can be
• Mass
expressed in terms of people equivalent.
mg/L kg/m3
• Characteristics of domestic wastewater are
• Volume taken as the reference for the conversion
mL /L L/m3
• Percentage L water consumption/ capita-day
mass % volume % Pollution load / capita-day

Classification of Wastewaters
• Wastewaters from process and operations
ENVE 420 • Cooling waters
Industrial Pollution Control • Cleaning of equipment, production areas, buildings
• Wastewaters from sub-processes:
e.g. Boiler waters (blöf), condensate waters,
Wastewater Sources in an Industry regeneration water from softening plants
Dr. Aslıhan Kerç • Wastewater from toilets, baths, cafeterias (domestic
ww characteristics)
• Storm water (rain water), drainage
 Classification of Wastewaters Process water
Each source may have different characteristics. Flowrates and characteristics vary.
Examples:
Should we mix them and treat together? Or not? • Metal plating industry: plating baths
• Fertilizer industry: Chemical solution tanks
If ww generated during cleaning process (cleaning of • Paint industry: ww generated from cleaning of
reactors) contain pollutants, they should be tanks
considered as process water. • Cooling water which is in contact with the
pollutants
• Stom water drainage from storage areas should be
considered as process ww.

Cooling water Cooling water

Used for cooling of raw material, products or If the cooling water is not in direct contact with
equipment the equipment, it is not contaminated,
• Closed loop à No ww generation (or very generally clean
small amount) They may contain small amounts of chemicals
• Open loop à Water is used only once or a few used for corrosion control à generally
times, then discharged negligible. Cause thermal pollution
If the cooling water is in contact with the
H.W. : Cooling water discharge stds equipment they may contain pollutants and
should be considered as process water.
 Cooling water Cleaning water
In some industries cooling water may contain Similar to the cooling water
toxic chemicals. If no contamination à Maybe considered as
Example? domestic ww
Metal industry If contaminated à Handle like process ww

Wastewater from sub-processes Storm water drainage

Sub-process: Not directly related with If collected seperately and does not have
production contaminants à clean
Can be classified in process ww according to its
characteristics
e.g. Boilers: Does not produce highly polluted
ww à may not be considered as an important
process in terms of water pollution
In terms of air pollution à An important process
 Domestic wastewater
From toilets, baths, cafeteria
There should be a seperate collection system for ENVE 420
ww of domestic characteristics. Industrial Pollution Control
If mixed with process ww à all together
considered as process ww. Sources and Characteristics of
Wastewaters
Industrial Waste Survey
Dr. Aslıhan Kerç

Sources and Characteristics of Sources and Characteristics of

Wastewaters Wastewaters
• In any plant there will be statistical variation in • Wide variation in waste flow and characteristics will
waste-flow characteristics. also appear among similar industries.
• Variations depend on: Due to:
– Diversity of products manufactured - Difference in housekeeping
– Process operations - Water reuse
– Process type (batch or continuous) - Variations in production processes

Waste loadings and their variations should be

determined by industrial waste surveys
 INDUSTRIAL WASTE SURVEY INDUSTRIAL WASTE SURVEY

Survey Results are used to determine:

• Develop a flow and • Establish the variation in
material balance for all waste characteristics
- Possibilities for water conservation and resue
processes - from specific process
operations - Variations in flow and in strength (important
- using water
information for the design of treatment facilities)
- producing wastes - from the whole plant

Steps of Industrial Waste Survey Steps of Industrial Waste Survey

STEP 1 STEP 2
Establish sampling and analysis schedule
Develop a sewer map.
Prefer composite samples weighted according to
Consult with the plant engineer, inspect various
flow. Period and frequency of sampling should be
process operations.
established according to the process.
On the map:
e.g. Hourly composited on 8, 12.. 24 h basis
- indicate possible sampling stations
If characteristics highly fluctuate à 1h or 2h
- indicate estimated flow rates. composite
Samples from batch processes should be
composited during the course of the batch dump.
 Steps of Industrial Waste Survey Steps of Industrial Waste Survey
STEP 3 STEP 4
Develop a flow and mateerial balance diagram
Establish statistical variation in significant waste
- Collect survey data characteristics.
- Analyze samples
- Flow-material balance diagram that considers
all significant sources of waste discharge.

Stormwater Control
• Contain and control pollutional discharges from
ENVE 420 stormwater.
Industrial Pollution Control
• Adequate diking around:
- Process areas
Stormwater Control - Storage tanks
Dr. Aslıhan Kerç - Liquid transfer points with drainage into the
process sewer
 Holding Basin
• To retain the contaminated stormwater.
• Located before the connection to the trunk ENVE 4020
sewer. Industrial Pollution Control
• Volume determined based on storm
frequency Wastewater Treatment Processes
(e.g. A ten year storm)
Dr. Aslıhan Kerç

Primary – Secondary Treatment Primary Treatment

• Primary and secondary treatment handle non- • Preparation of wastewater for biological
toxic wastewaters. treatment
• If ww contains toxic compounds, they have to • Removal of large solids by screening, grit
be pretreated before these processes. removal
• Equalization: Levels out the hour to hour
variations in flows and concentrations.
• Spill Pond: Retain slugs of concentrated
wastes that could upset the downstream
processes.
 Primary Treatment Secondary Treatment
• Neutralization: Follows equalization. Streams • Biological degredation of soluble organic
of different pH neutralize each other compounds
• Oil and grease, SS removal by flotation,
sedimentation or filtration Biotreatment:
- Aerobic
- Anaerobic

In-plant Treatment
• Necessary for biological treatment.
• Heavy metals, pesticides pass through primary
treatment and inhibit biological treatment.
• Effective for low volume streams with high
concentration of non-degredable materials.
• Easier to treat a specific pollutant from a small
and concentrated stream than a large dilute
stream.
 In-plant Treatment
• Precipitation
• Activated carbon adsorption ENVE 4020
• Chemical oxidation Industrial Pollution Control
• Air or stream stripping
• Ion exchange EQUALIZATION
• Reverse osmosis Dr. Aslıhan Kerç
• Electrodialysis
• Wet air oxidation

Purpose of using equalization for

Objective of Using Equalization Basins
industrial treatment facilities
• Minimize or control fluctuations in • Dampening of organic fluctuations à prevent
wastewater characteristics and flowrate. shock loading of biological systems
• pH control à Minimize chemical
• Size and type of equalization basin varies with: requirements for neutralization
- Quantity of waste • Minimize flow surges to physical – chemical
- Variability of the wastewater stream treatment. Permit chemical feed rates
compatible with feeding equipment
 Purpose of using equalization for Mixing Requirements for Equaliztaion
industrial treatment facilities Tanks
• Provide continuous feed to biological system • Mixing is required for:
(even when the factory is not operating) - Adequate equalization
• Controlled discharge of wastes to municipal - Prevent settlement of solids
system. Distribute waste loads evenly. - Oxidation of reducing compounds
• Prevent high concentrations of toxic materials - Reduction of BOD by air stripping
from entering the biological treatment plant.
(limited)

Mixing Methods Mixing Methods

1. Distribution of inlet flow and baffling Most common method à Submerged mixers
2. Turbine Mixing
3. Diffused air aeration For readily biodegradable wastes use surface
4. Mechanical aeration aerators à 0.003 – 0.004 kW /m3
5. Submerged mixers
Air requirement for diffused air aeration:
3.5 – 4.0 m3air / m3 waste
Variable volume in the equalization tank à
provide a constant effluent flow Equalization basin equalize
- Flow
Program effluent pumping rate à Discharge or
maximum quantity of waste during periods - Concentration
of low flow
or
Organic loading of treatment plant is
- Both
maintained constant for 24-h.

Flow equalization Concentration Equalization

Plot cumulative flow versus time Equalization basin may be sized to restrict the
Determine maximum volume with respect to discharge to a maximum concentration
constant discharge line
 Equalization volume Patterson and Menez Method
• Volume of completely mixed basins used in • Used to calculate equalization volume when both
treatment can be considered as part of the flow and the strength vary randomly
equalization basin (e.g. Activated sludge) Based on material balance
CiQT + CoV = C2QT + C2V
Example: Total time required for equalization: 16h
Aeration basin: ?
8h
Required equalization: 8 h

Construction details for

Factors effecting need for equalization
equalization basins
1. Influent should be given to the equalization
basin close to the mixing device to prevent short
1. Cost of construction 2. Cost saving by
circuiting
and implementing reducing the effects
2. Cleaning system for grease and scum which can
effective on downstream
accumulate on the walls should be considered
equalization treatment systems
3. An overflow weir should be installed to
discharge wastewater in case of failure of
pumps
4. Spray nozzles should be installed to break the
foams
 Flow Equalization Processes Flow Equalization Processes
2. INTERMITTENT FLOW DIVERSION:
1. ALTERNATING FLOW:
Allows any significant variance in stream
Collects total flow of the effluent for a given parameters to be diverted to an equalization
period of time (normally 24 hours) while a basin for short durations. Diverted flow is then
second basin is discharging. Alternative between bled back into the stream at a controlled rate.
filling-discharging. High degree of equalization Rate at which the diverted flow is fed back into
by leveling all discharge parameters. main stream depends on:
Disadvantage à high construction cost - volume
- variance of the diverted water à to reduce
downstream effect

Flow Equalization Processes Flow Equalization Processes

3. COMPLETELY MIXED COMBINED FLOW: 4. COMPLETELY MIXED FIXED FLOW:
Complete mixing of multiple flows combined at A large completely mixed holding basin before
the front end of the facility. Reduce variance in wastewater treatment facility. Levels variations
each stream by thorough mixing with other of influent stream parameters and provides a
flows. constant discharge.
 Need for neutralization
• Many industrial wastes contain:
ENVE 420
- Acidic
Industrial Pollution Control
- Alkaline materials

NEUTRALIZATION Neutralization is required prior to:

- discharge to receiving waters
Dr. Aslıhan Kerç - chemical or biological treatment

Neutralization requirement for

Types of Neutralization Processes
biological treatment
• For biological treatment pH ? • Mixing acidic and alkaline waste streams
6.5 – 8.5 Requires sufficient equalization capacity
Biological process itself provides a neutralization • Neutralization using chemicals
and buffer capacity due to carbon dioxide
production.
Requirement for pre-neutralization
 Neutralization of Acid Wastes Through
Limestone Beds
• Can be designed as upflow or downflow
• Max hydraulic rate for downflow (unit ?)
4 x 10-2 m3/min m2
Maximum H2SO4 concentration 0.6%
àTo avoid coating of limestone with non-
reactive CaSO4
àTo avoid excessive CO2 evolution which limits
complete neutralization

Neutralization of Acid Wastes Through

Mixing Acid Wastes with Lime Slurries
Limestone Beds
Up –flow beds à higher hydraulic loading • Lime
rates can be used • Slaked lime
• NaOH
• Na2CO3
• NH4OH
• Mg(OH)2

This method is useful below pH 4.2

vf = 2 – 2.4 m3/m2 hr vf = 3 - 40 m3/m2 hr
(~10)
 Mixing Acid Wastes with Lime Slurries Neutralization of Basic (Alkaline) Wastes
• In lime slaking reaction is accelerated by heat • Any strong acid can be used for neutralization
and agitation Sulfuric acid, Hydrochloric acid
• Neutralization can be defined by basicity • Using flue gas for neutralization?
factor. Flue gas that contain 14% CO2 can be used
• Titration of 1 g sample with excess HCl, boiling Bubbled through the waste
15 minutes followed by back titration with
0.5N NaOH to phenol phtalein end point CO2 à H2CO3 reacts with waste
Slow reaction. May be sufficient for pH
adjustment ~ pH 7-8
• Can also be applied in spray towers

• Stepwise addition of chemicals

• Selection criteria for neutralization agents:
- Reaction rate
- Sludge production and disposal ENVE 4020
- Safety Industrial Pollution Control
- Ease of handling
- Cost, Equipment cost HEAVY METALS REMOVAL IN
- Side reeactions (dissolved salts, scale INDUSTRIAL WASTES
formation, heat produced) Dr. Aslıhan Kerç
- Effect of overdosage
 Sources of Heavy Metals Effects of Heavy Metals
• Potential adverse effects of soluble metal
• Heavy metals à present abundance in nature. compounds on human health and on the health of
• Enter water cycle through geochemical organisms, treatment inhibition, aesthetics of the
processes. environment.
• Metals added by human activities: • Certain metals in low concentrations are not only
– Manufacturing harmless , but traces are essential for good
– Construction nutrition.
– Agriculture Co, Cu, Fe, Se, Zn.
– Transportation • Some metal salts on the other hand may be toxic.

Evaluation of toxicity: Examples for Metal Toxicity

• Acute • Soluble copper à gastroenteritis symptoms
• Chronic with nausea
• Synergistic • Chromiumà lung tumors, skin sensitizations,
• Mutagenic / teratogenic inflammation of the kidneys
• Seleniumà Poison in high concentrations,
carcinogen, cause tooth decay.
Acute toxic effects show up quickly upon
ingestion of, or contact with a metal
compound.
 Examples for Metal Toxicity
• Chronic poisoningà e.g. cadmium and lead
accumulate in body tissue • Mutagenic / teratogenic toxicity à when
• Certain metals are more toxic in combination with certain metals combine with organic
other metals or under specific environmental compounds, these substances may produce
conditions changes in genetic makeup or cause abnormal
• e.g. Cadmium toxicity increases in the presence of tissue development in embryos
Cu / Zn. pH, T, hardness, SS, CO2 effect the toxicity. (teratogenicity)
• Lead is more toxic if dissolved oxygen
concentration is low.

Effects of Heavy Metal Content Effects of Heavy Metal Content

• Heavy metal content may affect taste, staining
• If found in irrigation water à may damage
and corrosion characteristics
crops.
• Taste Cu > 1 mg/L
• Continuous exposure of biological systems (in
Fe > 9 mg/L treatment plants) to such metals à biological
Zn > 5 mg/L system can become acclimated (what would
• Fe, Mn stain fixtures, discolor laundry, normally be inhibitory or even toxic).
obstruct pipes with bacteria
• Interference with industrial processes. • Heavy metals accumulate in the solids
e.g. Cu may cause adverse color reactions in produced.
food industry. • Land application !
 Recycling / recovery of heavy
Cost analysis for metal recovery
metals
• Recycling rinse water in metal plating industry • Capital & operating cost
may reduce wastewater generation. Closed vs
loop recovery system may be appropriate for Total benefits from
wastes that are different or expensive to treat.
– reductions in raw material losses
• Recovery systems: Evaporation, reverse – wastewater treatment capacity
osmosis, electrodialysis, electrolytic recovery, – chemicals
ion exchange – sludge disposal fees

Hydroxide ppt / coagulation Hydroxide ppt / coagulation

• Typically heavy metals are dissolved under acidic
• Conventional method of removing heavy metals.
conditions and precipitate under alkaline
Chemical ppt of the metal as hydroxides followed
conditions.
by coagulation of the metal particles into larger,
heavier floc particles which then separate from • pH increase by NaOH (caustic), Ca(OH)2 lime
the water. addition
• Metal concentrations can be reduced to 0.3 – 1.5 • Cu2+ + 2NaOH à Cu(OH)2 + 2 Na+
mg/L • Cu2+ + Ca(OH)2 à Cu(OH)2 + Ca2+
 Hydroxide ppt / coagulation Sedimentation of Metal Flocs
• Often the hydroxide precipitates tend to floc Overflow rate for metal hydroxides:
together naturally. Sometimes coagulant / More often values range between
flocculent aids may be added to enhance 10 – 33 m3/m2d
flocculation, improve sedimentation, ultimately Typically should not exceed 40 m3/m2d
reduce heavy metal concentrations. For very thick floc 60 m3/m2d
• Polyelectrolytes may be used
• Treatability testsà to determine optimum pH Most hydroxide sludge after settling à
and chemical dosages
96 – 99 % water
May be dewatered to 65 – 85 % water

Other Treatment Alternatives for

Dewatering of Metal Sludge
Metal Removal: Adsorption
• Sand drying beds (climate dependent) • Adsorption on
• vacuum filters – activated carbon
• filter presses – aluminum oxides
• Centrifuges – silica clays
• Belt filters – synthetic materials like zeolites and resins.
 HEAVY METALS REMOVAL USING COAGULATION FLOCCULATION
• Heavy metals are precipitated as hydroxide by lime or caustics
addition. pH à minimum solubility
ENVE 4020 • Metal compounds are amphoteric and exhibit a point of
Industrial Pollution Control minimum solubility. pH of minimum solubility varies with
metal.
• Pretreatment of industrial ww to remove substances that will
HEAVY METALS REMOVAL USING COAGULATION interfere with ppt is important.
FLOCCULATION
• Cyanide and ammonia form complexes with metals
Dr. Aslıhan Kerç
àreduce removal

CYANIDE REMOVAL AMMONIA REMOVAL

• Alkaline chlorination Prior to removal of metals ammonia should be removed
• Catalytic oxidation • Ammonia stripping
Cyanide ww containig Ni, Ag à difficult to treat by alkaline • Breakpoint chlorination
chlorination due to slow rxn rate of these complexes

Cyanide ww containing Fe
Ferrocyanide [Fe(CN)64-] oxidized to à Ferricyanide [Fe(CN)63-]
resists further oxidation
Lime precipitation is the most widely method. CHROMIUM REMOVAL
Heavy metals may be precipitated as sulfides and as carbonates
Chromium is found in different forms
as well (eg. Lead)
Hexavalent chromium needs to be reduced:
For arsenic As, Cd à can be coprecipitated with Fe and Al
coagulation. Metal adsobs to alum or iron flocs. Cr6+ à Cr3+ reduction and precipitation
For low effluent requirements à filtration may be necessary to Reducing agents:
remove thiny floc particles - Ferrous sulfate (dry or solution fed)
- Sodium meta-bisulfite (dry or solution fed)
- Sulphur dioxide (gas cylinders)

CHROMIUM REMOVAL CHROMIUM REMOVAL

If Ferrous sulfate is used: Fe2+ à Fe3+ Theoretical quantities of chemicals required à text book
If sulphur dioxide is used: SO2-3 à SO2-4
If SO2 is used, excess (35%) may be needed, since DO present in
Cr6+ + Fe2+ + H+ à Cr3+ + Fe3+ ww also consumes added SO2
(rxn takes place pH<3, acid addition may be required)
H2SO3 + ½ O2 à H2SO4
Cr3+ + 3OH- à Cr(OH)3 (ppt)
When alkali is added, contaminated sludge Fe(OH)3 is formed Acid requirement for pH adjustment à determine with titration
Excess dosage (2.5 times) of ferrous sulfate may be needed
 CHROMIUM REMOVAL in Plating Plants
CHROMIUM REMOVAL in Plating Plants
(Continuous Treatment)
For small plating plants à batch treatment (Q<114 m3/d)
2 tanks; each with a capacity of one day’s flow Acidification Lime
Mixing Tank
Settling Tank
and reduction
1 filling , 1 treatment

Accumulated sludge à can be dewatered on sand drying beds

For Q : 114 – 151 m3/d, batch treament is not feasible for high
flowrates, continuous plants are used.
Retention time 20 min for Surface
is dependent flocculation loading:
on pH 20 m3/d-m2
1 m3/h-m2

CHROMIUM REMOVAL in Plating Plants

(Continuous Treatment)

ENVE 4020 Acidification

and reduction
Lime
Mixing Tank
Settling Tank

Industrial Pollution Control

HEAVY METALS PRECIPITATION FLOW DIAGRAMS

NUMERIC EXAMPLE
Dr. Aslıhan Kerç Retention time 20 min for Surface
is dependent flocculation loading:
on pH 20 m3/d-m2
1 m3/h-m2
Continuous chrome waste treatment system (Eckenfeleder, 2000)

Metal removal example

A plating industry generates wastewater with a flowrate of
Q = 120 m3/day. WW characteristics is as follows:

Cu: 11 mg/L
Zn: 12 mg/L
Cr6+: 50 mg/L
Dissolved O2: 5 mg/L

a) Make treatment process selection for this ww

b) Design the treatment units
c) Calculate the chemical dosages d) Calculate produced sludge amount
 Process selection Reduction of Cr6 to Cr3 by SO2
Continuous treatment plant Cr2O72- + 2H+ + 3 SO2 à 2Cr3+ + 3SO2-4 + H2O
Reduction of hexavalent chromium by SO2
Precipitation of the metals by lime addition Cr: 51.9 O:16 S: 32 H:1
Mixing / flocculation and settling tanks should be designed For Dissolved oxygen

SO2 + ½ O2 à SO3

Reduction of Cr6 to Cr3 by SO2 Metal precipitation with Lime (90% purity)
Cr2O72- + 2H+ + 3 SO2 à 2Cr3+ + 3SO2-4 + H2O For 1 gr of Cr6+ à 2.38 g Ca(OH)2 (90% pure) is needed
For 1 g Cr6+ à 1.85 g SO2 is needed For Cu and Zn à 1.3 g Ca(OH)2 (90% pure) is needed

50 (g/m3) * 120 (m3/d) * 1.85*10-3 = 11.1 kg/day Cr: 51.9 Cu: 63.5 Zn: 65
For Dissolved oxygen
SO2 + ½ O2 à SO3 5(g/m3)*120*4*10-3 = 2.4 kg/day
Total SO2 = 11.1 + 2.4 = 13.5 kg/day
 Metal precipitation with Lime (90% purity) Mixing Tank
For 1 gr of Cr6+ à 2.38 g Ca(OH)2 (90% pure) is needed • Retention time ?
For Cu and Zn à 1.3 g Ca(OH)2 (90% pure) is needed
Cr
2.38 * 50 * 120 * 10-3 = 14.28 kg/day
Cu and Zn
(11 + 12) (g/m3) * 1.3 * 120 * 10-3 = 3.59 kg/day
Total lime: 14.28 + 3.59 = 17.87 kg/day

Mixing Tank Settling Tank

Retention time t = 20 minutes (minimum) Retention time : ?
Q = 120 m3/day = 5 m3/h Surface loading : ?
Volume = 1/3 hr * 5 m3/h = 1.67 m3

Dimensios = 2 x 1 x1
 Settling Tank Settling Tank
Retention time : t≈ 4 hr Retention time : t≈ 4 hr
Surface loading : S0 ≤ 1 m3/m2h Volume = 4 h * 5 (m3/h) = 20 m3
Choose h = 3m
Design of settlings tanks Area = 20 /3 = 7 m2 à D= 3m (can be selected as 4-5 m)
1. Select retention time, calculate volume, choose depth, Surface loading = Q / A = 5 /7 = 0.7 m/h < 1 m/h Ok
calculate surface area, calculate and check surface loading Surface loading : S0 ≤ 1 m3/m2h
OR
2. Select surface loading, choose depth, calculate volume,
calculate and check retention time

Sludge Amount Sludge Amount

Chromium sludge : Chromium sludge :

………. mg Cr(OH)3 / mg Cr 1.98 mg Cr(OH)3 / mg Cr

Cu and Zn Sludge: Cu and Zn Sludge:

……… mg Cu(OH)2 / mg Cu 1.53 mg Cu(OH)2 / mg Cu

 Sludge Amount Sludge Amount
Chromium sludge : Total sludge?
1.98 mg Cr(OH)3 / mg Cr
1.98 * 50 * 120 * 10-3 = 11.88 kg/day Suspended solids content of metal sludge?

Cu and Zn Sludge:
1.53 mg Cu(OH)2 / mg Cu
1.53 * (11+12) * 120 * 10-3 = 4.2 kg/day
Total Sludge ?

ENVE 4020
Sludge Amount
Industrial Pollution Control
Suspended solids content of metal sludge? 1.5 %
FLOTATION
(11.88 + 4.2 ) / (1.5%) = 1072 kg/day (Ref: 1- WPCF – Wastewater Treatment
Plant Design
2- Eckenfelder)

Dr. Aslıhan Kerç

 Objective of Using Flotation Mechanism of Flotation
• Used for • If density of particle < density of water
the removal of: à can be separated by flotation
- Suspended Solids e.g. ?
- Oil and Grease Petroleum industry
from wastewater Edible oil industry
the seperation and concentration of Fiber recycling in paper industry
sludges

Mechanism of Dissolved Air Flotation

Flotation Types
(DAF)
1. Simple flotation • Solid particles in liquid suspension become
2. Flotation with aeration attached to microscopic air bubbles.
3. Dissolved air flotation • Waste flow or a portion of clarified effluent is
4. Electroflotation pressurized to 3.4 – 4.8 atm in the presence of
sufficient air to approach saturation.
5. Vacuum flotation
• When pressurized air-liquid mixture is
released to atmospheric pressure, minute air
bubbles are released from the solution.
 Mechanism of Dissolved Air Flotation Mechanism of Dissolved Air Flotation
(DAF) (DAF)
• Agglomerate rise to the surface to join other • Air-solids mixture à skimmed off from the
particles and form a blanket that can be surface
removed mechanically. • Clarified liquid à removed from the bottom
• Flotation is used primarily to remove light SS. • A portion of the effluent à recycled back to
• Sludge flocs, suspended solids, oil globules are the pressure chamber
floated by the air bubbles which:
– Attach to floc particles
– Become enmeshed in floc particles

Principal components of flotation

Primary variables for flotation design
system
• Pressure • Pressurized pump à elevated pressure to
• Recycle ratio increase solubility
• Feed solids concentration • Air-injection facilities
• Retention period • Retention tank (saturation tank) à 1-3 min
• Back pressure regulation device à constant
For clarification, retention time: 20 – 30 min head on pressurizing pump
loading rate: 0.06 – 0.16 m3/min-m2 • Flotation unit à circular / rectangular with a
skimming device
For thickening: longer tR
DAF Flow Diagram DAF Flow Diagram

DAF Application of flotation

• Flotation is applicable for wastewater
containing high concentration of finely divided
solids:
- Wastes from canneries
- Packing houses
- Oil refineries
- Laundries
Recovered solids may be reusable à source of
fuel
 Induced Air Flotation System Induced Air Flotation System
• A submerged rotor forces the liquid through
disperser openning, creating a negative
pressure.

OIL SEPARATION
• Free oil is floated to the surface of a tank and
then skimmed.
• Design of gravity separators à American
Petroleum Institute (API Separators)
• Removal of oil particles > 0.015 cm
• Effluent oil concentration : 50 mg/L
• Plate separators separate oil droplets > 0.006 cm
• Corrugated plates