5. Screen
• First unit operation
• Objective
• Removal of coarse and fine objects, which may get entangled
in mechanical equipment e.g., grit chambers, sedimentation
tanks, etc.
• protection of pump impellers.
• Coarse screenings
• Rocks, twigs, leaves, paper, plastic rags and other materials
6. Oil & Grease Removal
• Objectives :
• Protect tank walls of subsequent sewage treatment plant
facilities from grease deposits.
• Protect the biological processes, especially air diffusers from
grease deposits.
• They adversely affect bacteria and protozoa life which is
essential in bio-treatment.
• They are difficult to digest, hence the cost of digestion is
increased.
• Oil and grease remover is absolutely necessary, if there is no
primary settling in sewage treatment plant.
9. Activated sludge processes (ASPs)
• ASP is an aerobic, continuous flow, treatment system that uses sludge with active
populations of microorganisms to breakdown organic matter in wastewater
• Activated sludge is a flocculated mass of microbes
• The organic load (generally coming from primary treatment operations such as
settling, screening or flotation) enters the reactor where the active microbial
population (activated sludge) is present.
• The reactor is continuously aerated.
• The mixture then passes to a secondary settling tank where the cells are settled.
• The cells are recycled in order to maintain sufficient biomass to degrade the
organic load as quickly as possible
10. Objective
• To reduce the water and organic content of sludge -> easy to handle
• To make it suitable for final disposal or reuse
Sources
• Water Treatment
• Alum waste - gelatinous waste;
- difficult to dewater
• Iron sludge - Inorganic in nature
• sand / silt
• suspended solids
• Activated Carbon
• Non biological decomposition
• Filter backwash ( solid: 0.01-0.1%)
• Softening units (soda/lime)
General aspects of sludge treatment
11. Fundamentals of Biological Treatment
• Objectives
• To coagulate and remove non-settlable colloidal solids
• To stabilize organic matter/substances
• To remove trace toxic organics
• To remove nutrients
• To reduce inorganic concentration
• All these carried out by microbes
• Based on form of carbon required
Autotrophs (photo-auto/chemo-auto) &
Heterotrophs (photohetero/chemohetero)
• Based on energy source
Phototrophs & Chemotrophs (chemo-organo/chemo-auto)
12. • Most of the enzymatic reactions involve redox reactions i.e.,
addition/removal of oxygen/hydrogen
• The electron acceptor is based on surrounding medium and cellular
characteristics
• In anaerobic reactions – an oxidized compound is electron
acceptor
• In aerobic reactions – oxygen is acceptor
• Environmental factors that influence microbial growth
• Temperature
Psychrophilic – (-10 to 30 deg.C) opt. 12–18 0C
Mesophilic – (20 to 50 deg.C) opt. 25-40 0C
Thermophilic – (35 to 75 deg.C) opt. 55-65 0C
facultatives
Fundamentals of biological treatment
13. Trickling filters
• A trickling filter (TF) is a aerobic attached growth type wastewater
treatment system that biodegrades organic matter and can also be
used to achieve nitrification.
• The wastewater trickles through a circular bed of coarse stones or
plastic material. A rotating distributor (a rotating pipe with several
holes across it) evenly distributes the wastewater from above the
bed.
• The microorganisms in the wastewater attach themselves to the
bed (also known as the filter media), which is covered with
bacteria.
• The bacteria break down the organic waste and remove pollutants
from the wastewater.
15. Anaerobic fluidized bed process
• A combination of suspended growth and attached growth process
• Anaerobic microbes grow on the surface of the medium, expanding
the apparent volume of the medium; hence this reactor is also
designated an "expanded bed reactor"
16. Disinfection
• Any process to destroy or prevent the growth of microbes
• Intended to inactivate the microbes by physical, chemical or
biological processes
• Inactivation is achieved by altering or destroying essential
structures or functions within the microbe
• Inactivation processes include denaturation of:
– proteins (structural proteins, transport proteins, enzymes)
– nucleic acids (genomic DNA or RNA, mRNA, tRNA, etc)
– lipids (lipid bilayer membranes, other lipids)
17. Disinfection
• Partial destruction of disease causing (pathogenic) organisms
• Characteristics of an ideal disinfectant
• Availability
• Deodourizing ability
• Homogeneity
• Extraneous material interaction
• Non-corrosive and non-staining
• Toxic to microbes but non-toxic to higher organisms
• Penetration
• Solubility and stability
18. Properties of an Ideal Disinfectant
• Broad spectrum: active against all microbes
• Fast acting: produces rapid inactivation
• Effective in the presence of organic matter, suspended
solids and other matrix or sample constituents
• Nontoxic; soluble; non-flammable; non-explosive
• Compatible with various materials/surfaces
• Stable or persistent for the intended exposure period
• Provides a residual (sometimes this is undesirable)
• Easy to generate and apply
• Economical
19. Disinfectant Action
• Damage to cell wall and disturbance in cell permeability –
phenolics and detergents
• Damage to protoplasm and cell molecules – Radiation
• Molecular alterations and Inhibition of enzyme activity – Chlorine
and other halogens
• Factors that influence action
• Contact time
• Concentration (chemical)
• Intensity/nature (physical)
• Temperature
• Organisms
• Nature of w/w
20. Disinfection methods
Chemical Physical Mechanical Radiation
Halogens (Cl)
Ozone
Phenolics
Alcohols
Metals
Detergents,
etc.
Heating
Solar
insolation
Chemical
precipitators
and biofilters
Gamma rad.&
Cobalt-60 rad.
21. Properties of Water Disinfectants
• Free chlorine: HOCl (hypochlorous) acid and OCl- (hypochlorite ion)
– HOCl at low pH and OCl- at high pH; HOCl more potent germicide than OCl-
– strong oxidant; relatively stable in water (provides a disinfectant residual)
• Chloramines: mostly NH2Cl: weak oxidant; provides a stable residual
• Chlorine dioxide, ClO2,: strong oxidant; unstable (dissolved gas)
Concerns due to health risks of chemical disinfectants and their by-products
(DBPs), especially free chlorine and its DBPs
• Ozone, O3: strong oxidant; provides no residual (too volatile, reactive)
• UV radiation
– low pressure mercury lamp: low intensity; monochromatic at 254
nm
– medium pressure mercury lamp: higher intensity; polychromatic 220-280
nm)
– reacts primarily with nucleic acids: pyrimidine dimers and other alterations
• Boiling: efficient kill; no residual protection; issues ->
fuel/environmental costs
22. Reverse Osmosis Method for
Cleaning Water
http://lpt.lanxess.com/uploads/tx_lxsmatrix/01_lewabrane_manual_ro_theory.pdf
23. Contents:
What is membrane
What is osmosis
Design of RO method
RO method in plant
Future technological challenges
24. What is membrane?
A membrane is a selective barrier; it allows some things
to pass through but stops others. Such things may be
molecules, ions, or other small particles.
26. A membrane is a selective barrier that permits the
separation of certain species in a fluid by
combination of sieving and diffusion mechanisms.
Membranes can separate particles and
molecules and over a wide particle size range and
molecular weights.
Membrane Processes
27. Types of Membrane
Based on our applications, there are four
common types of membranes:
Reverse Osmosis
Nanofiltration
Ultrafiltration
Microfiltration
30. Osmosis
• Osmosis is the movement of pure solvent (most of the
time it is water) across a semi-permeable membrane
• At first the concentration of solute is very high on the left.
• But over time, the water moves across the semi-
permeable membrane and dilutes the particles.
31. Osmosis
Diffusion of water across a selectively permeable membrane (a barrier that allows
some substances to pass but not others). The cell membrane is such a barrier.
Small molecules pass through – ex: water
Large molecules can’t pass through – ex: proteins and complex
carbohydrated
32. Reverse Osmosis
In Reverse Osmosis a pump is used to raise the pressure and the feed
is distributed among a number, n, of modules. The reject is collected
and taken for further treatment, disposal or sale. The permeate is
recovered and constitute the clean stream.
Feed
Reject
Permeate
Reverse Osmosis Performance
Reverse Osmosis can be used in a legion of applications. Some of them
are: seawater desalting, treatment of cheese whey, metal finishing
solutions, bleach and dye plant effluent and waste water from sewage
treatment works.
33. If clean water and water with some concentration of solute are
separated by a semi-permeable membrane (permeable to only
water) water will be transported across the membrane until
increases hydrostatic pressure on the solute side will force the
process to stop.
Pressure requirements are based on osmotic pressure for R.O
34. Features of Reverse Osmosis
It requires energy. Therefore, where the energy Is available but
drinking water is not available
For water treatment, R.O. application mostly use for
desalination.
Permeate: almost pure water containing low concentration of ions
Concentration: having high concentration of small particles and
dissolved ions
35. Technology Involved for Large Scale RO Plant
Design of membrane
Design of integrated system
Automation
36. Design integrated system
The purpose of the integrated design is to optimize the design of
the plant (in this case by minimizing the size of the tanks) taking
into account the control strategy. The main purpose of the control
is to be able to supply a water demand over a given timeframe
taking into account a series of restrictions
37. Future Challenges
Designing of membrane. It has not fully developed yet. Important
development is needed to achieve high water flux
Economy: It is not economically viable since it requires enormous
amount of energy; only rich countries can afford it
Integration: Integration with a suitable post-treatment
Sources of water: Water from multiple sources are difficult to
handle
These need to be addressed based on a total
system approach
