sewage treatment

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Sewage and Treatment
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sewage

• Sewage is a water-carried waste, in solution or
  suspension, that is intended to be removed from a
  community.
• Known as domestic or municipal wastewater, it is
  more than 99 water and is
• characterized by volume or rate of flow, physical
  condition, chemical and toxic constituents, and
  its bacteriologic status.
• It consists mostly of greywater (from sinks,
  tubs, showers, dishwashers, and clothes washers),
  blackwater (the water used to flush toilets,
  combined with the human waste that it flushes
  away) soaps and detergents and toilet paper
  (less so in regions where bidets are widely used
  instead of paper).
• Whether it also contains surface runoff depends
  on the design of sewer system.

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Characteristics of sewage

• Temperature
• pH
• Colour and Odour
• Solids
• Nitrogen and Phosphorous
• Chlorides
• Organic materials
• BOD and COD

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BOD and COD

• Organic matter conc measured
• Essential difference are in the Oxidant utilized
  and the operational conditions imposed during the
  test.
• TOC
• The BOD of the sewage is the amount of oxygen
  required for the biochemical decomposition of
  biodegradable organic matter under aerobic
  conditions.
• The oxygen consumed in the process is related to
  the amount of decomposable organic matter.
• The general range of BOD observed for raw sewage
  is 100 to 400 mg/L. Values in the lower range are
  being common under average Indian cities.

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COD

• Chemical Oxygen Demand (COD)
• The COD gives the measure of the oxygen required
  for chemical oxidation. It does not differentiate
  between biological oxidisable and non oxidisable
  material.
• Ratio of the COD to BOD does not change
  significantly for particular waste and hence this
  test could be used conveniently for interpreting
  performance efficiencies of the treatment units.
• In general, the COD of raw sewage at various
  places is reported to be in the range 200 to 700
  mg/L.

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Wastewater Treatment Technologies

• Bioremediation
• Coagulation/Floc
• Membrane Filtration
• Filtration/Gravity
• Adsorption
• Activated sludge
• Mineralization within microbes

• Oxidation (Ozone)
• Thermal Oxidation
• Encapsulation
• Evaporation

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• Primary treatment - solid substances, floating
  objects removed-screening chambers.
• Secondary treatment biological
  treatment-aerobic and anaerobic
• Tertiary treatment nutrient rich-eutrophication-
  biological ponds-disinfection-UV treatment.

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Primary treatment

• Solid substances and floating objects have to be
  removed by passing the waste through screens or
  nets in chambers called screening chambers
• Grid chambers- large stones-remove coarse
  particulate materials.
• Hydrocyclones or centrifugal separators
• Sedimentation /floation tank-emulsifiction/foamin
  g agent/coagulant/flocculant

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Secondary treatment

• Dissolved organic matter
• Organic debris
• Particulate materials
• Aerobic decomposition
• Carbonaceous organic matter O2
  CO2
• Nitrogenous organic matter O2
  NO32-
• Sulphurous organic matter O2
  SO42-
• Phosphorous organic matter O2
  PO42-

Aerobic and anaerobic
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Trickling filters

• Trickling filter consists of a bed of highly
  permeable media to which microorganisms are
  attached and through which wastewater is
  percolated or trickled.
• The filter media usually consist of rocks,
  varying in size from 25 to 100 mm in diameter.
  The depth of the media varies from 0.9 to 2.5 m
  and 1.8 m is most common.
• The liquid wastewater is distributed over the top
  of the bed by a rotary distributor as sprays. The
  wastewater trickling from the top, comes in
  contact with the biological media and get rid of
  its nutrients (carbohydrates,proteins etc).
• The under drain system is important both as a
  collection unit and as a porous structure through
  which air can circulate.
• The collected liquid is passed to a settling tank
  where the solids are separated from the treated
  wastewater.

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• TFs enable organic material in the wastewater to
  be adsorbed by a population of microorganisms
  (aerobic, anaerobic, and facultative bacteria,
  fungi, algae, and protozoa) attached to the
  medium as a biological film or slime layer
  (approximately 0.1 to 0.2 mm thick).

zoogleal film. The organic material is then
decomposed by the aerobic microorganisms in the
outer part of the biological layer. As the layer
thickness through microbial growth, oxygen cannot
penetrate through the entire thickness of the
medium , and anaerobic organisms develop within.
As the biological film continues to grow, the
microorganisms near the free surface lose their
ability to cling to the medium which is away may
get detached. The detached slime layer goes down
along with wastewater- sloughing. Sloughing is
primarily a function of organic and hydraulic
loading of the filter. The sloughed solids are
transported to the secondary clarifier.
Biological process in filter bed
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Activated sludge (ASP)

• Activated sludge is a process for treating sewage
  and industrial wastewaters using air and a
  biological floc composed of bacteria and protozoa
  (active sludge).
• The carbonaceous organic matter of wastewater
  provides an energy source for the production of
  new cells for a mixed population of
  microorganisms in an aquatic aerobic environment.
  
• The microbes convert carbon into cell tissue and
  oxidized end products that include carbon dioxide
  and water.
• A limited number of microorganisms may exist in
  activated sludge that obtain energy by oxidizing
  ammonical nitrogen to nitrate nitrogen in the
  process known as nitrification.
• Leads to deposition of flocculant sludge golden
  brown sludge.
• Activity is measured by rate of oxygen
  consumption in definite time schedule.
• Pretreatment such as sedimentation, chemical
  treatment, oxidation..needed before sludge
  digestion to reduce load or aeration processs.
• Chlorine gas injected-prevent bulking and
  contraction of humus.
• Oxidation is performed-Oxidation ponds.

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Purposes

• In a sewage (or industrial wastewater) treatment
  plant, the activated sludge process is a
  biological process that can be used for one or
  several of the following
• Oxidizing carbonaceous biological matter.
• Oxidizing nitrogeneous matter mainly ammonium
  and
• nitrogen in biological matter.
• Removing phosphates.
• Driving off entrained gases such as carbon
  dioxide, ammonia,
• nitrogen, etc.
• Generating a biological floc that is easy to
  settle.
• Generating a liquor that is low in dissolved or
  suspended material.

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Arrangement

• The general arrangement of an activated sludge
  process for removing carbonaceous pollution
  includes the following items
• Aeration tank where air (or oxygen) is
  injected in the mixed liquor.
• Settling tank (usually referred to as "final
  clarifier" or "secondary settling tank") to allow
  the biological flocs (the sludge blanket) to
  settle, thus separating the biological sludge
  from the clear treated water.
• Treatment of nitrogenous matter or phosphate
  involves additional steps where the mixed liquor
  is left in anoxic condition (meaning that there
  is no residual dissolved oxygen).

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Conventional Activated Sludge process
Food Microbes O2
New cells Energy CO2 H2O
NH3 (org. waste) (sludge)
nutrients (surplus sludge) Wastewater rich
in organics blended with return sludge rich in
microorganisms is called Mixed Liquor. The
microbes grow in number to remove both insoluble
and soluble organic from wastewater, stabilize
them and they themselves flocculate to form into
clumps which settle in the secondary
sedimentation tank by gravity. The process
derived its name from the fact that sludge
containing active microorganisms is returned to
increase the available biomass and to speed up
the reaction.
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Biological components

• Bacteria, fungi, protozoa, and rotifers
  constitute the biological component, or
  biological mass of activated sludge.
• In addition, some metazoa, such as nematode
  worms, may be present.
• However, the constant agitation in the aeration
  tanks and sludge recirculation are deterrents to
  the growth of higher organisms.
• The species of microorganism that dominate a
  system depends on environmental conditions,
  process design, the mode of plant operation, and
  the characteristics of the secondary influent
  wastewater.
• While both heterotrophic and autotrophic bacteria
  reside in activated sludge, the former dominate.
• Heterotrophic bacteria obtain energy from
  carbonaceous organic matter in influent
  wastewater for the synthesis of new cells. At the
  same time, they release energy with the
  conversion of organic matter into stable
  compounds such as carbon dioxide and water.
• Important genera of heterotrophic bacteria
  include Achromobacter, Alcaligenes, Arthrobacter,
  Citromonas, Flavobacterium, Pseudomonas, and
  Zoogloea.

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EUTROPHIC ATION
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Environmental Impacts of Eutrophication
Decrease in the transparency of water
Development of anoxic conditions (low oxygen
levels) Increased algal blooms Loss of
habitat (e.g. Sea grass beds) Change in
dominant biota (e.g. Changes in plankton
and macrophyte community structure or
changes in fish composition)
Decrease in species diversity Change in the
aesthetic value of the water body
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caused by a few species of dinoflagellates and
the bloom takes on a red or brown color. Red
tides are events in which estuarine, marine, or
fresh water algae accumulate rapidly in the water
column, resulting in coloration of the surface
water. It is usually found in coastal areas
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When plankton called dinoflagellates grow too
numerous near shore, the single-celled algae can
stain the water a reddish-brown, causing
so-called red tides that are often toxic to
people and fish alike. Certain dinoflagellates
species also produce bioluminescence, and when
night falls at the beach, the teeming algae can
make the shallows glow an electric blueOut at
sea, dinoflagellates use bioluminescence as a
sort of 'burglar alarm' when disturbed, the
plankton flash or light up, essentially creating
a glowing trail that leads right to their
assailant. This silent signal alerts predators
higher up in the food chain about the
dinoflagellates' nemesis. 'The burglar alarm is
a scream for help,' Widder says. 'The best chance
you have when you're getting attacked is to
attract something bigger than what is eating
you.'" (Hadhazy 2009)
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• Chemical precipitation has long been used for P
  removal.
• The chemicals most often employed are compounds
  of calcium, aluminum, and iron.
• Chemical addition points include prior to primary
  settling, during secondary treatment, or as part
  of a tertiary treatment process
• 5Ca2 7OH- 3H2PO4-
  CA5OH(PO4)36H2O

hydroxyapatite
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Biological method

• Assimilation
• Incorporation of the P as an essential element
  in biomass, particularly through growth of
  photosynthetic organisms (plants, algae, and some
  bacteria, such as cyanobacteria).
• Traditionally, this was achieved through
  treatment ponds containing planktonic or
  attached algae, rooted plants, or even floating
  plan ts (e.g., water hyacinths, duckweed).

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Process of Phosphate removal

• Certain micro-organisms in sludge will, in
  different conditions, release or take up large
  quantities of phosphorus.
• They are first induced to release phosphates,
  creating a concentrated phosphate solution.
• A second stage of phosphate uptake can then be
  induced, the micro-organisms taking up even more
  P than initially released, and removing nearly
  all the phosphates from whatever water the sludge
  is mixed with.
• This process can be manipulated to transfer P
  from waste water either to sludge (organic
  phosphates stored in micro-organisms) or to a
  side-stream of supernatant liquid containing high
  P concentrations.

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Phosphate accumulating organisms

• In the first oxygen-free zone,
• phosphate accumulating micro-organisms take up
  short-chain fatty acids (which can be obtained
  from organic materials in waste waters or
  sludges) using cellular polyphosphates as an
  energy source.
• They thus deplete their cellular phosphate
  levels, releasing phosphates into the supernatant
  liquid.
• Under anaerobic conditions, in the presence of
  fermentation products, PAOs release
  orthophosphate, utilizing the energy to
  accumulate simple organics and store them as
  polyhydroxyalkanoates (PHAs) such as poly-ß-
  hydroxybutyrate (PHB).
• Under aerobic conditions , the PAOs then grow on
  the stored organic material, using some of the
  energy to take up orthophospha te and store it
  as polyphosphate.
• The bio P removal lies in the exposure of
  organism to aerobic and anaerobic conditions.
• Acinetobacter,Pseudomonas and Nocardia

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Aerobic
Anaerobic
Pi

• e

acetate
Acetic acid
polyphosphate
energy
C-reserves
Pi
Transport and storage of simple organics such as
acetate require energy-ie is obtained from
polyphosphate reserves with the release of Pi
The organic matter is oxidized to produce Energy
and reaccumulation of phosphates into
polyphosphates
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• Decomposition of organic material- nitrogen from
  protein is released-ammonia nitrogen-process
  nitrification/denitrification
• Nitrifying bacteria are autotrophs, requiring
  only inorganic chemicals as the starting point
  for their energy metabolism and growth.
• Thus ammonia is taken up and oxidised to provide
  the energy required for growth. Carbon dioxide is
  used as the carbon source, and this is
  metabolised into organic carbon compounds inside
  the bacteria - a process which also requires
  energy.
• The process of ammonia oxidation is referred to
  as nitrification, and is carried out by two
  different groups of nitrifiers. The most abundant
  genus is Nitrosomonas but there are other
  nitrifiers as well. The overall reaction is
• NH4 O2 nitrification NO3- 2H
  2O
• Nitrosomonas
• NO3- organic matter
  N2 CO2 H2O
• 
  Nitrobacter
  
• 
  released

Nitrogen removal from waste water
Denitrification
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Denitrification reactor
In a third stage, oxygen is provided by aeration
and the P-depleted micro-organisms take up nearly
all the available phosphates from their
environment using the substrate stored in their
cells, and taking up more phosphates than they
initially released.
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