Module IV Wastewater treatment methods

Online Lecture 16
Waste Water Treatment Methods
Waste Water Treatments
Module IV

Contents
• Nitrification and De-nitrification – Phosphorous removal –
Heavy metal removal – Membrane Separation Process–
Reverse osmosis– Chemical Oxidation–Ion Exchange – Air
Stripping and Absorption Processes – Special Treatment
Methods –Disposal of Treated Waste
• Common Effluent Treatment Plants (CETPs): Need, Planning,
Design, Operation & Maintenance Problems

Sambhaji Lake, Solapur
Eutrophication

Introduction
• Urine, human excreta, and food processing wastes are the
primary sources of nitrogen for municipal wastewater.
• Domestic wastewater typically has a total nitrogen content
that is about one-fifth of the biochemical oxygen demand
(BOD), with typical nitrogen concentrations ranging from 20
to 70 mg/L.
• About 60% to 70% is ammonia-nitrogen, and 30% to 40%
percent is organic nitrogen, with less than 1% nitrite and
nitrate nitrogen

A. Nitrification
• Nitrification is an oxidation process (loss of electrons or gain
of the oxidation state by an atom or compound takes place).
• This process starts with the ammonium which gets oxidized
into nitrite (NO2
-), this action is performed by the bacteria
Nitrosomonas sp.
• Later on, this nitrite (NO2-) gets oxidized into nitrate (NO3
-),
and this action is performed by the Nitrobacter sp.

• The bacteria are autotrophic, and the reaction is
performed under aerobic condition.
• The importance of this step in the nitrogen cycle is the
conversion of ammonia into nitrate, as nitrate is the
primary nitrogen source present in the soil, for the plant.
• Though nitrate is toxic to the plants.
• The activity of nitrifying bacteria gets slower in acidic
solution, and are best at pH between 6.5 to 8.5
and temperature vary from 16 to 35°C.

B. Denitrification
• Denitrification is the reduction process, where the
nitrate is removed in the form of nitrogen and is
converted to nitrogen gas.
• The action is performed by bacteria
like Bacillus, Aerobacter, Lactobacillus, Spirillum, Pseudo
mona

• The bacteria are heterotrophs, and the action is completed
under anaerobic condition.
• Even the small amount of oxygen may hamper the process,
but there is a need of organic carbon.
• Denitrification is useful for wastewater treatment, aquatic
habitats.
• The denitrification is performed best at pH between 7.0 to
8.5 and at the temperature between 26 to 38°C.

In Short
• The biological process where ammonium (NH4+) is oxidized
and converted into the nitrate (NO3-) is called as nitrification,
while denitrification is biological process involves the
conversion of nitrate (NO3
-) into nitrogen gas (N2).
• The precursor of the nitrification process is ammonia, and
the end product is nitrate, whereas nitrate is the precursor of
the denitrification process and nitrogen is the end product.

Differentiation between Nitrification and
Denitrification
BASIS FOR
COMPARISON
NITRIFICATION DENITRIFICATION
Meaning The part of nitrogen cycle where
ammonium (NH4+) is converted into
nitrate (NO3-) is called nitrification.
Denitrification is the level
where reduction of nitrate
(NO3-) is made into nitrogen
gas (N2).
The process involves Nitrifying bacteria like Nitrobacter,
Nitrosomonas.
Denitrifying bacteria like
Spirillum, Lactobacillus,
Pseudomonas, Thiobacillus.
Grows slowly. Grows rapidly.
Requires aerobic condition. Requires anaerobic condition.

The microbes Autotrophic. Heterotrophic.
Precursor Ammonium . Nitrate.
End product Nitrate. Nitrogen.
pH and
Temperature
The process occurs at the pH
between 6.5 to 8.5 and
temperature between 16 to
35 degree C.
The process occurs at the pH
between 7.0 to 8.5 and
temperature between 26 to
38 degree C.
Importance Provides nitrate to the plant,
which acts as the important
nitrogen source.
Denitrification is used in
wastewater treatment and is
beneficial for aquatic habitats.

• Controlling phosphorous discharged from municipal and
industrial wastewater treatment plants is a key factor in
preventing eutrophication of surface waters.
• Phosphorous is one of the major nutrients contributing in the
increased eutrophication of lakes and natural waters.
• Phosphate removal is currently achieved largely by chemical
precipitation, which is expensive and causes an increase of
sludge volume by up to 40%. An alternative is the biological
phosphate removal (BPR).

1. Chemical methods
• Phosphate precipitation
• Chemical precipitation is used to remove the inorganic forms of phosphate
by the addition of a coagulant and a mixing of wastewater and coagulant.
The multivalent metal ions most commonly used
are calcium, aluminium and iron.
1) Calcium:
• it is usually added in the form of lime Ca(OH)2. It reacts with the natural
alkalinity in the wastewater to produce calcium carbonate, which is
primarily responsible for enhancing SS removal.
• Ca(HCO3)2 + Ca(OH)2 → 2CaCO3 ↓+ 2H2O
• Akalinity lime calcium carbonate ppt

• As the pH value of the wastewater increases beyond about 10, excess
calcium ions will then react with the phosphate, to precipitate in
hydroxylapatite:
• 10 Ca2+ + 6 PO4
3- + 2 OH- ↔ Ca10(PO4)*6(OH)2 ↓
• Because the reaction is between the lime and the alkalinity of the
wastewater, the quantity required will be, in general, independent of
the amount of phosphate present.
• It will depend primarily on the alkalinity of the wastewater.
• Neutralisation may be required to reduce pH before subsequent
treatment or disposal.

2) Aluminium and Iron:
• Alum or hydrated aluminium sulphate is widely used precipitating
phosphates and aluminium phosphates (AlPO4). The basic reaction is:
• Al3+ + HnPO4
3-n ↔ AlPO4 + nH+
• Ferric chloride or sulphate and ferrous sulphate also know as
copperas, are all widely used for phosphorous removal. The basic
reaction is:
• Fe3+ + HnPO4
3-n ↔ FePO4 + nH+
• Ferric ions combine to form ferric phosphate (FePO4).
• They react slowly with the natural alkalinity and so a coagulant aid,
such as lime, is normally add to raise the pH in order to enhance
the coagulation.

Strategies
The main phosphate
removal processes are
(see picture):
1.Treatment of
raw/primary wastewater
2.Treatment of final
effluent
of biological plants
(postprecipitation)
3.Treatment contemporary
to the secondary biologic
reaction (co-precipitation).

2. Biological Removal
• The principal advantages of biological phosphorous
removal are reduced chemical costs and less sludge
production as compared to chemical precipitation.
• In the biological removal of phosphorous, the
phosphorous in the influent wastewater is
incorporated into cell biomass, which is subsequently
removed from the process as a result of sludge wasting.

• The reactor configuration provides the P accumulating
organisms (PAO) with a competitive advantage over
other bacteria.
• So PAO are encouraged to grow and consume
phosphorous.
• The reactor configuration in comprised of an anaerobic
tank and an activated sludge activated tank.
•

• In the anaerobic zone: Under anaerobic conditions, PAO
assimilate fermentation products (i.e. volatile fatty
acids) into storage products within the cells with the
concomitant release of phosphorous from stored
polyphosphates.
• Acetate is produced by fermentation of COD, which is
dissolved degradable organic material that can be easily
assimilated by the biomass.
•

• Using energy available from stored polyphosphates, the
PAO assimilate acetate and produce intracellular
polyhydroxybutyrate (PHB) storage products.
• Concurrent with the acetate uptake is the release of
orthophosphates, as well
as magnesium, potassium, calcium cations.
• The PHB content in the PAO increases as the
polyphosphate decreases.

• In the aerobic zone: energy is produced by the
oxidation of storage products and polyphosphate
storage within the cell increases.
• Stored PHB is metabolized, providing energy from
oxidation and carbon for new cell growth. Some
glycogen is produced from PHB metabolism.
• The energy released from PHB oxidation is used to
form polyphosphate bonds in cell storage.
•

• The soluble orthophosphate is removed from
solution and incorporated into polyphosphates
within the bacterial cell.
• PHB utilisation also enhances cell growth and
this new biomass with high polyphosphate
storage accounts for phosphorous removal.
• As a portion of the biomass is wasted, the stored
phosphorous is removed from the biotreatment
reactor for ultimate disposal with the waste sludge.

Flowsheet for Phosphorus removal

Online Lecture 17
Module IV

Heavy metal removal
• Methods for treating industrial wastewater containing heavy metals
often involve technologies for reduction of toxicity in order to meet
technology-based treatment standards.
• Physico-chemical removal processes such as;
1. Adsorption,
2. Ion exchange,
3. Membrane filtration- Reverse Osmosis (RO)
4. Electrodialysis,

1. Adsorption
• Recently this process is recognized widely for removal of heavy metals
from wastewater.
• Many cheap adsorbents had been developed lately.
• These adsorbents are widely use for treatment of wastewater containing
heavy metals.
• These adsorbents are derived from the waste products generated from
industrial activities, waste generated from agriculture and natural
materials.
• Adsorption can be defined as a mass transfer process which transfers the
substance from the liquid phase to the surface of a solid and becomes
bound by physical and chemical interactions.

• It’s a three-step treatment process 1 the pollutant is transferred to
the sorbent surface from bulk solution 2 adsorption on particle
surface 3 transportation within the sorbent particle..
• This technique is very cost effective.
1.Adsorption on modified natural materials
2.Adsorption on industrial by-products
3.Bio-sorption

Adsorption
• One of the most commonly used techniques for removing
organics and heavy metals involves the process of
adsorption, which is the physical adhesion of chemicals on
to the surface of the solid.
• The effectiveness of the adsorbent is directly related to the
amount of surface area available to attract the particles of
contaminant.

• The most commonly used adsorbent is a very porous
matrix of granular activated carbon, which has an
enormous surface area ( @1000 m2/g).
• Adsorption on activated carbon is perhaps the most
economical and technically attractive method available for
removing soluble organics such as phenols, chlorinated
hydrocarbons, surfactants, and colour (dyes) and odour
producing substances from waste water.

• adsorbate: material being adsorbed.
• Adsorbent: material doing the adsorbing. (examples
are activated carbon or ion exchange resin).
• Generally some combination of physical and chemical
adsorption is responsible for activated carbon
adsorption in water and wastewater.

Physical adsorption:
• Van der Waals attraction between adsorbate and
adsorbent.
• The attraction is not fixed to a specific site and the
adsorbate is relatively free to move on the surface.
• This is relatively weak, reversible, adsorption capable
of multilayer adsorption.

Chemical adsorption:
• Some degree of chemical bonding between adsorbate and
adsorbent characterized by strong attractiveness. Adsorbed
molecules are not free to move on the surface.
• There is a high degree of specificity and typically a
monolayer is formed.
• The process is rarely reversible.

Difference between Osmosis and
RO

• Reverse osmosis (RO) is a membrane-technology filtration
method that removes many types of large molecules and ions
from solutions by applying pressure to the solution when it is
on one side of a selective membrane.
• The result is that the solute is retained on the pressurized
side of the membrane and the pure solvent is allowed to pass
to the other side.
• To be "selective," this membrane should not allow large
molecules or ions through the pores (holes), but should allow
smaller components of the solution (such as the solvent) to
pass freely.

• Commonly used membrane is Cellulose Acetate
• Pre-treatment of wastewater is needed to avoid membrane
fouling.
• High COD and BOD can also affect membrane.
• Flushes away impurities and does not collect them.
• It can remove almost everything. It allows only water (H2O)
to pass
• Very efficient but Cost is high
• Can remove everything from water and wastewater.

Applications of RO
• Applications include treatment and recycle of wastewaters
generated from metal finishing and plating operations; printed
circuit board and semiconductor manufacturing (treatment and
recycle of rinse waters used in electroplating processes);
automotive manufacturing (treatment and recycle of water used
for cleaning and painting); food and beverage (concentration of
wastewater for reuse and reduction of BOD prior to discharge);
groundwater and landfill leachate (removal of salts and heavy
metals prior to discharge).

3. Electrodialysis
• Electrodialysis is an electrochemical process whereby
electrically charged particles, ions, are transported from a
raw solution (retentate, diluate) into a more concentrated
solution (permeate, concentrate) through ion-selective
membranes by applying an electric field.
• When a salt solution is under the influence of an electric field,
as is the case in an electrodialysis module, the charge carriers
in the solution come into motion.

• This means that the negatively charged anions migrate
towards the anode and the positively charged cations
towards the cathode.
• In order to separate salts from a solution, ion-selective
membranes, through which only one type of ion can
permeate in an ideal case, are arranged in the solution
perpendicular to the electric field.

• Thus negatively charged particles (anions) can pass through
an anion exchange membrane on their way to the anode but
are selectively retained by the upstream cation exchange
membrane.
• This separation stage results in a concentration of electrolytes
in the so-called concentrate loop and a depletion of charge
carriers in the so-called diluate loop.

Applications
1. Nitrogen removal from drinking water (nitrate,
ammonium)
2. Desalination of organic substances
3. Concentration of salts, acids and bases
4. Removal of heavy metals

4. Ion exchange
• This technique has been used extensively to remove
hardness, and iron and manganese salts in drinking water
supplies.
• It has also been used selectively to remove specific
impurities and to recover valuable trace metals like
chromium, nickel, copper, lead and cadmium from
industrial waste discharges.

• For example:
NiSO4 + Ca(OH)2 →Ni(OH)2 + CaSO4
• In this reaction, the nickel ions of the nickel sulphate (NiSO4) are
exchanged for the calcium ions of the calcium hydroxide
Ca(OH)2 molecule.
• Similarly, a resin with hydrogen ions available for exchange will
exchange those ions for nickel ions from the wastewater solution.
The reaction can be written as follows:
(R–SO3H)2 + NiSO4 = (R-SO3)2Ni + H2SO4
• R indicates the organic portion of the resin and SO3 is the immobile
portion of the ion active group.

• Two resin sites are needed for nickel ions with a plus 2 valence
(Ni+2). Trivalent ferric ions would require three resin sites.
(R–SO3)2Ni + H2SO4 –> 2(R-SO3H) + NiSO4
• This step is known as regeneration.
• In general terms, the higher the preference a resin exhibits for a
particular ion, the greater the exchange efficiency in terms of resin
capacity for removal of that ion from the wastewater solution.
• Greater preference for a particular ion, however, will result in
increased consumption of chemicals for regeneration.

Online Lecture 18
Module IV

1. Air Stripping
• Air stripping is a technique in which wastewater and air are
intensively brought in contact with each other.
• This causes the volatile compounds present in wastewater to be
transferred into the air.
• The air containing VOC must be treated in an air treatment system.
• A stripper only needs a small surface area; 5x5 m2 is sufficient for a
stripper with a capacity of 100 m3/hour.

• The space taken by an air treatment unit varies greatly.
• The main set-up types are the stripping tower or stripping column
and the plate stripper.
• The stripping tower is based on the counter-flow principle,
where a vertical column is filled with packing material.
• The plate stripper is based on the cross-flow principle, where the
liquid flow is intensively aerated via a perforated plate.
• The stripping process is cheap and reliable, and provides
relatively good substance transfer. One of the disadvantages of
this process is that it is susceptible to pollution.

Air Stripping
Packing
material

Application
• In both inorganic and organic chemistry, stripping is used for the
removal of volatile organic substances, sulphur compounds (H2S,
phosphine) and NH3. Stripping is normally carried out on the
concentrated partial flow;
• Air stripping is used in the pharmaceutical sector for the removal of
chlorinated solvents from wastewater;
• Air stripping is primarily implemented for the removal of volatile
organic matter (incl. chlorinated hydrocarbons) from wastewater.
• In a variety of sectors, air stripping is implemented for the removal
of chlorinated solvents from wastewater:

Disadvantage
• Air containing VOC is released.
• Air treatment could possibly be needed (e.g. active carbon
system, bio-filter).
• Depending on the influent, the location and the installation,
extra measures may be needed to prevent odour and noise
problems.

2. MBBR - Moving Bed Bio-Reactors
Process Description
• MBBRs biologically treat wastewater by circulating moving media in
aerobic, activated-sludge environments.
• The moving media is typically a floating plastic substrate colonized by a
community of bacteria.
• These bacteria form a biofilm on the plastic surface. Increased levels of
biofilm enhance the biological treatment process by introducing a more
robust microbial community.
• In addition to the biofilm attached to the plastic carriers, biomass in the
system also exists in the form of suspended flocks.
• At smaller scales* in India, MBBR tanks were found to be constructed of
reinforced concrete or mild steel.
• Some suppliers also offer fiber reinforced polymer (FRP) tanks.

Advantages
• Can operate at high organic loads
• Is less prone to hydraulic overloading than other STP types
• Is relatively easy to operate—does not require advanced skills for
operation/maintenance
• Generally has lower capital costs than MBR-based systems
• Eliminates issues with media becoming clogged (compared to fixed
film systems)

Disadvantages
• Is a manually operated process
• Generally offers a lower level of wastewater
treatment than MBR-based systems

Process Description
• SBRs are based on the activated-sludge treatment process. SBRs use a
batch approach in which secondary sewage treatment occurs in a
single tank.
• In the first stage of SBR treatment, influent is added to the batch-
reactor tank and aerated.
• Following aeration, the wastewater is allowed to settle. Finally, the
treated wastewater is removed from the top of the tank using a
decanter valve, pump, or airlift tube.
• At smaller scales*in India, SBR tanks were found to be constructed of
reinforced concrete or mild steel.
3. SBR- Sequential Batch reactors

Advantages
• Allows for react, settle, and decant phases to occur within the
same tank
• Does not require secondary clarifiers or return-activatedsludge
(RAS) lines
• Generally has lower capital costs than MBR-based systems
• Is an automated process**

Disadvantages
• Can face issues with high peak flows—unless already factored into
design
• Requires higher skill level for maintenance, due to more complex
system setup (automation/instrumentation)
• Generally offers a lower level of wastewater treatment than MBR-
based systems

4. Membrane Bioreactor (MBR)
• Membrane bioreactors (MBRs) combine two treatments processes:
the activated-sludge process and membrane filtration.
• Wastewater is first aerated in a bioreactor tank, where
microorganisms are present in the form of suspended flocks.
• Then, a microporous membrane is used for solid/liquid separation.
This configuration eliminates the need for secondary clarifiers.
• At smaller scales* in India, MBR tanks were found to be constructed
of mild steel. As such, civil costs (or costs associated with
constructing reinforced concrete structures—e.g., tanks,
foundations) are minimal.
• Note that MBRs can also be added to existing MBBRs as retrofits.

Advantages
• Generally offers higher level of wastewater treatment than
MBBR-or SBR-based systems
• Does not require secondary clarifiers
• Is an automated process**

Disadvantages
• Typically has higher capital costs than MBBR-or SBR-based
systems
• Requires membrane replacement approximately every 3 years
• Requires higher skill level for maintenance, due to more
complex system setup (automation/instrumentation)

5. Common Effluent Treatment Plants (CETP)
• The concept of common effluent treatment plant has been accepted as
a solution for collecting, conveying, treating, and disposing of the
effluents from the industrial estates.
• The effluent include industrial wastewaters and domestic sewage
generated from the estate.
• This CETP concept helps small and medium scale industries to dispose
of their effluents. Otherwise it may not be economical for these
industries to treat their wastewaters or there may be space constraints.
• Some of these industries may require to give preliminary treatment (for
removal of solids) so that the receiving sewers can be maintained free
flowing.
•

• It may be required to correct pH or removal of specific pollutant
before the industry discharges in CETP
• CETP is designed on the basis of:
– Quality and flow rate of the wastewater.
– Effluent standard required by CETP.
– Possibility of recycle and reuse of treated wastewater.
– Availability of land, manpower, energy and expertise in specific
treatment methods.
– Willingness of the industries located in the industrial estate to
contribute towards the capital and operating expenses of CETP.

• CETPs are classified in two categories –
• (i) Homogenous : Industries producing similar goods in that
industrial area are contributing. E.g., tanneries, paper, etc.
• (ii) Heterogenous : industries producing widely divergent
goods are placed together. E.g., chemical, dairy, soft drink,
canneries, pharmaceuticals, etc.
• Designing the treatment plant for the former is easier than the
later due to difficulty in estimating characteristics of the
combined wastewater.

Advantages of providing CETP
– Small and medium scale industries are not required to treat their
wastewater separately.
– Assured wastewater treatment hence better control over
pollution.
– Concerned pollution control agency have to monitor only one
treatment plant for its performance.
– Participating industries have commitment to generate
wastewaters acceptable to CETP.
– Industries are responsible for finding ways to minimize pollution
load and reduce water consumption to the extent possible.

Drawbacks
– There could be conflict among the industries about the
wastewater quality and quantity on which the cost of treatment
depends.
– Failure of pay may result in not allowing this industry to
discharge wastewater.

Objective questions
1. Pick out the odd one
i. Microfiltration, filtration, Nanofiltration, adsorption.
2. _______________ membrane is commonly used in RO process.
3. ____________ ________ is excellent adsorbent because of its very
high surface area.
4. For RO, pretreatment is needed to avoid ________ _________.
5. ___________ and __________ are types of CETPs.
6. ______________combine two treatments processes: the activated-
sludge process and membrane filtration.

7. ___________ use a batch approach in which secondary sewage
treatment occurs in a single tank.
8. MBBRs biologically treat wastewater by circulating ______media in
aerobic, activated-sludge environments.
9. __________ technique is used to remove hardness and heavy metals
from water and wastewater respectively.
10. Commonly used membrane in RO is ___________.
11. Pre-treatment of wastewater is needed to avoid _____ ______in RO.
12. The biological process where ammonium (NH4+) is oxidized and
converted into the nitrate (NO3-) is called as ___________,
while _________ is biological process involves the conversion of nitrate
(NO3
-) into nitrogen gas (N2).

Theory Questions
Q1. Write Short note on
1. Electrodialysis
2. Reverse Osmosis
3. Ion Exchange
4. CETP
5. MBBR
6. SBR
7. MBR
Q2. Differentiate between Physical adsorption and Chemical Adsorption
Q3. Explain Nitrification and Denitrification
Q4. Explain Phosphorus removal from wastewater.

Module IV Wastewater treatment methods

Module IV Wastewater treatment methods

More Related Content

What's hot

Similar to Module IV Wastewater treatment methods

More from Dr. shrikant jahagirdar

Recently uploaded

In this document

Module IV Wastewater treatment methods