This document discusses conventional wastewater treatment processes and their applicability. It begins by outlining the objectives and presentation outline. The fundamental principles of conventional treatment are then described, including physical, chemical, and biological unit operations and processes. The main conventional treatment processes are explained in detail, including preliminary, primary, secondary, tertiary, and sludge treatment stages. Applications in Nepal are discussed. Strengths and limitations are provided. Finally, emerging alternative technologies are presented as potential solutions to challenges with conventional wastewater treatment.

1. 2018-07-30

2. Objectives Of The Presentation
 To discuss the physical, chemical, and biological
processes applied for sewage purification and complex
interactions among them occurring in wastewater
treatment system.
 To discuss the principles, fundamentals and applicability
of conventional wastewater treatment processes.
 To analyse the reliability and challenges of conventional
wastewater treatment in developing countries like Nepal.
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3. Presentation Outline
Introduction
Fundamental principles of conventional wastewater
treatment
Conventional wastewater treatment processes
Applicability of conventional wastewater treatment
Applications in context to Nepal
Strength and Limitations
Challenges to conventional wastewater treatment
1.
2.
3.
4.
5.
6.
7.
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4. 1. Introduction
 Conventional wastewater treatment is a term that applies
to a standard method of wastewater treatment , that can
reduce the objectionable properties of water-carried
waste and render it less dangerous and repulsive to
man.
Conventional
wastewater
treatment
Industrial
wastewater
treatment
Radioactive
wastewater
treatment
Sewage
treatment
Agricultural
wastewater
treatment
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5. 2. Fundamental Principles
 It consists of a combination of physical, chemical and
biological processes and operations to remove solids,
organic matter, and sometimes, nutrients from
wastewater.
Physical unit
operations
• Screening
• Mixing
• Flocculation
• Sedimentation
• Floatation,
etc.
Chemical unit
processes
• Chemical
precipitation
• Gas transfer
• Adsorption
• Ion exchange
• Electrodialysis
, etc.
Biological unit
processes
• Activated
sludge
process
• Tricking
filtration
• Sludge
digestion, etc.
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6. 3. Conventional Wastewater Treatment
Processes
Fig 3. Typical Conventional wastewater plant
Source: Google image
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7.  Wastewater while undergoing treatment goes through
following processes:-
a) Preliminary treatment
b) Primary treatment
c) Secondary (or biological) treatment
d) Tertiary (or advanced) treatment
e) Sludge treatment and disposal
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8. Preliminary treatment3.1.
 Removes following:-
a. Large objects - using bar screens
b. Heavy settleable inorganic solids - using grit
chambers
c. Fats and greases - using floatation units and
skimming tanks
 Protects pumps and equipment from damage
Fig 3.1. Preliminary treatment
Source: Google image
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9. Primary Treatment3.2.
 Involves settling or
sedimentation tanks for
primary sedimentation.
 To remove a large fraction
(50-70) % of the total
suspended solids and
around (25-40) % of the
total BOD in wastewater.
 Lowers the operational
problems in next treatment
processes.
Fig 3.2.Circular primary settling tank
Source: B.C. Punmia, Ashok. K.
Jain(1998)
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10.  To remove readily biodegradable BOD that has
escaped primary treatment.
 Also removes suspended and non- settleable colloidal
solids through biofilm or biological flocs.
Secondary Treatment (Biological Treatment)3.3.
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11. • Microorganisms convert organic matter into gases.
• Cell tissues are attached to some inert medium like
rock, slag or especially designed ceramic or plastic.
• Eg: bio filter, rotating biological contractors, etc.
Attached
(fixed film)
growth
process
• Cell tissues are in suspension with liquid in reactor by
employing either natural or mechanical mixing.
• Eg: Activated sludge process, Aerated lagoons, etc.
Suspended
growth
process
• Consists of both suspended as well as attached
growth processes.
• Eg: 1) Activated sludge, trickling filter
2) Trickling filter, activated sludge
3) Facultative lagoons
Combined
processes
Types of secondary treatment
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12. a) Biofilter Process
 A biofilter is a bed of media on which
microorganisms attach and grow to form a biological
layer called biofilm.
 Biofiltration was first introduced in England as a
trickling filter for wastewater treatment.
 It uses bioreactor containing living material to capture
and biodegrade contaminants.
 Biofilter process is usually aerobic.
 Filtering media may be organic or inorganic.
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13.  Advantages of biofilter
• Low operational cost
than activated sludge
and less supervisio.
• Less subject to
loading and hydraulic
shock.
• Can remove about
80% of SS and about
75 to 80% of BOD.
 Drawbacks of biofilter
process
• Bioclogging and flow
channeling.
Fig 1. A typical complete trickling
filter system for treating
wastewater.
Source: Beychok, Milton R.(1967)
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14. b) Activated Sludge Process
 A suspended process
because it maintains
adequate biological mass
in suspension within the
liquid in aerator.
 Increases speed for waste
decomposition by sludge
recirculation.
 Secondary clarifier is used
to settle solids for sludge
removal. Fig. 3.3.1.(b) Flow diagram of
activated sludge process
Source: B.C. Punmia, Ashok. K.
Jain(1998)
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15. Only done if necessary.
Removes suspended, colloidal and dissolved solids,
nutrients such as nitrogen, phosphorus, etc.
Suspended and organic matters remained after
secondary treatment are removed to provide high
quality of water.
 Disinfection is a type of advanced treatment used to
remove pathogens, that involves injection of chlorine
solution at head end of chlorine contact basin.
Tertiary (Advanced) Treatment3.4.
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16. Table 3.4. selected advanced wastewater treatment processes
Source: B.C. Punmia, Ashok. K. Jain(1998)
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17. Fig. 3.3.1.(b) Flow diagram for sludge treatment and disposal
Source: B.C. Punmia, Ashok. K. Jain(1998)
Sludge Treatment And Disposal3.5.
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18.  Wastewater reclamation and reuse systems should
contain both design and operational requirements
necessary to ensure reliability of treatment.
Reliability features include:-
• Alarm systems
• Standby power supplies
• Treatment process duplications
• Emergency storage or disposal of in adequately
treated wastewater
• Monitoring devices
• Automatic controllers
 Where disinfection is required, several reliability
features must be incorporated into system to ensure
uninterrupted chlorine feed.
4. Applicability Of Conventional Wastewater
Treatment
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19. Strength
 Relatively high removal of
TSS and BOD.
 Capacity to treat large
amount of wastewater in
small area unlike non-
conventional systems.
 Highly efficient.
 Waste sludge can be
used in composting.
Limitations
 Complex operations.
 Expensive spare parts.
 High priced chemical
additives.
 Energy intensive, requires
constant high electrical
energy .
 Issue of ecological disposal of
sludge waste.
 Overall high cost of design,
construction, supervision and
maintenance.
6. Strength and Limitations
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20. Fig. Existing conventional wastewater treatment plants in Nepal
Source: Nyachhyon (2006)
5. Applications In Context To Nepal
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21. Fig. Conventional activated sludge WWTP in Guheshwori, Nepal
Source: http:/www.bagmati.gov.np/

22. Some of the modern wastewater treatment alternatives are
described below:-
 DEWATS (Decentralized Wastewater Treatment Solution)
 Comparatively small mass of wastewater.
 Easy operation and low maintenance.
 Low investment.
 High efficiency.
 Types:-
a) Aerobic digestion process:
• Bacterial process in presence of oxygen.
• Reduces volume of sludge and makes it suitable
for subsequent use.
• Unlike energy consuming aerobic process ,it
produces biogas with organic fertilizer.
7. Challenges to conventional wastewater
treatment
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23. b) Constructed wetland
• Unlike conventional WWTP, it uses biological
technology natural processes.
• No additional energy required.
• Cost efficient.
• Simple in operation and maintenance.
• Reed bed WWTP is most used in Nepal.
Sunga community WWTP in Kathmandu valley is a
reed bed WWTP.
 Chemically enhanced primary treatment (CEPT)
 Operates at twice the rate of conventional primary
treatment.
 Use of metal salts for coagulation-flocculation.
 Heavy metals are precipitated out.
 Cost 60% of conventional biological treatment.
 Can handle relatively high influent rates.
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24.  Advanced Integrated Pond System (AIPS)
 Suitable for highly variable rates of flow.
 Bio – digestor uses anaerobic micro organisms.
 No sludge to be removed or wasted.
 Energy efficiency - no moving parts in reactor.
 Half cost of conventional treatment with higher quality
effluent.
 Sequencing Batch Reactor (SBR)
 Occupies less land space than activated sludge as all
steps of activated sludge is combined in single basin.
 Biological aerobic process
 Process steps are not continuous like conventional
but carried out in batches in one single basin.
 Less energy consumption.
 Good alternative at local level.
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25. Thank you for listening!!
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