Transcript Industrial Microbiology and Fermentation Technology

29. Treatment of Wastes in Industry
METHODS FOR THE DETERMINATION OF
ORGANIC MATTER CONTENT IN WASTE
WATERS
• If waste water discharged into a natural water is
rich in degradable organic matter, large numbers
of aerobic microorganisms will develop to break
down the organic matter.
• Use up the available oxygen and as a consequence
fish and other aquatic life will die.
• Anaerobic bacteria will develop following the
exhaustion of oxygen.
• Result in foul odors.
• Dissolved Oxygen
• The Biological or Biochemical Oxygen
Demand (BOD) Tests
• Permanganate Value (PV) Test
• Chemical Oxygen Demand (COD)
• Total Organic Carbon (TOC)
• Total Suspended Solids (TSS)
• Volatile Suspended Solids (VSS)
Dissolved Oxygen
• Dissolved oxygen is one of the most important
means of determining the organic matter content
of waters.
• The heavier the amount of degradable material
present in water, the greater the growth of aerobic
organisms and hence the less the oxygen content.
• The Winkler method is widely used for
determining the oxygen in water.
• Membrane electrodes are now available for the
same purpose.
The Biological or Biochemical
Oxygen Demand (BOD) Tests
• It is a measure of the oxygen required to decompose
the organic matter in a body of water over a five-day
period at 20°C.
• In carrying out the test, two 250-300 ml bottles are
filled with water whose BOD is to be determined.
• The oxygen content of one is determined immediately
by the Winkler method and in the other at the end of
five days incubation at 20°C.
• The difference between the two is the BOD.
• Many industrial wastes contain materials
which are either difficult to degrade or
which may even be toxic to the organisms.
• In such cases an inoculum capable of
degrading the materials must be developed
by enrichment and introduced into the
bottles.
Permanganate Value (PV) Test
• Determines the amount of oxygen used up by a
sample in four hours.
• It gives an idea of the oxidizable materials present
in water.
• The method records the oxidation of organic
materials such as phenol and aniline as well as
those of sulfide, thiosulfate, and thiocyanate and
would be useful in some industries.
• However because oxidation is incomplete it is not
favored by some workers.
Chemical Oxygen Demand (COD)
• The total oxygen consumed by the chemical
oxidation of that portion of organic materials in
water which can be oxidized by a strong chemical
oxidant.
• It is a more rapid test than BOD, the method can
be used for a wider variety of wastes.
• Furthermore, when materials toxic to bacteria are
present it is perhaps the best method available.
• Its major disadvantage is that bulky equipment
and hot concentrated sulfuric acid are used.
Total Organic Carbon (TOC)
• Total organic carbon provides a speedy and
convenient way of determining the degree of
organic contamination.
• A carbon analyzer using an infrared detection
system is used
• The amount of carbon will be expressed in mg/L.
• TOC provides a more direct expression of the
organic chemical content of water than BOD or
COD.
Total Suspended Solids (TSS)
• Total Solids include both total suspended solids, the
portion of total solids retained by a filter and total
dissolved solids, the portion that passes through a
filter.
• Total solids can be measured by evaporating a water
sample in a weighed dish, and then drying the residue
in an oven at 103 to 105°C.
• To measure total suspended solids (TSS), the water
sample is filtered through a preweighed filter.
• The residue retained on the filter is dried in an oven at
103 to 105°C.
• TSS can also be measured by analyzing for total solids
and subtracting total dissolved solids.
Volatile Suspended Solids (VSS)
• Volatile suspended solids (VSS) are those
solids (mg/liter) which can be oxidized to
gas at 550°C.
• Most organic compounds are oxidized to
CO2 and H2O at that temperature;
• Inorganic compounds remain as ash.
WASTES FROM MAJOR
INDUSTRIES
Typical Components of an Oil Refinery Waste Water
Typical Effluent Loads from Pulp
and Paper Manufacture
Typical Effluent Loads from Food
industries
SYSTEMS FOR THE
TREATMENT OF WASTES
(i) The degradable organic compounds in the waste
water (carbohydrates, proteins, fats, etc.) are
broken down by aerobic microorganisms mainly
bacteria and to some extent, fungi.
• The result is an effluent with a drastically reduced
organic matter content.
(ii) The materials difficult to digest form a sludge
which must be removed from time to time and
which is also treated separately.
• Aerobic breakdown of raw waste-water and
anaerobic breakdown of sludge.
Aerobic Breakdown of Raw Waste
Waters
• The activated sludge system
• The trickling filter
• Rotating discs
The activated sludge system
(a) It uses a complex population of microorganisms of
bacteria and protozoa;
(b) This community of microorganisms has to cope with an
uncontrollably diverse range of organic and inorganic
compounds some of which may be toxic to the organisms.
(c) The microorganisms occur in discreet aggregates known
as flocs
(d) Some of the settled biomass is recycled as ‘returned
activated sludge’ inoculate the incoming raw sewage
because it contains a community of organisms adapted to
the incoming sewage.
(e) The solid undigested sludge may be further treated into
economically valuable products.
Organisms involved in the activated
sludge process
• The organisms involved are bacteria and
ciliates (protozoa).
• A wide range of bacteria are involved,
including Pseudomonas, Achromobacter,
Flavobacterium to name a few.
Efficiency of activated sludge
treatments
• The efficiency of any system is usually determined by
a reduction in the BOD of the waste water before and
after treatment.
• Efficiency depends on the amount of aeration, and the
contact time between the sludge and the raw waste
water.
• Thus in conventional activated sludge plants the
contact time is about 10 hours, after which 90-95% of
the BOD is removed.
• When the contact time is less (in the high-rate
treatment) BOD removal is 60-70% and the sludge
produced is more.
• With longer contact time, say several days,
BOD reduction is over 95% and sludge
extremely low.
• In the closed tank system or where there is
great oxygen solubility, contact time could
be as short as 1 hour but with up to 90%
BOD reduction along with substantially
reduced sludge.
The trickling filter
• No sludge is returned to the incoming waste water.
• Rather the waste water is sprayed uniformly by a
rotating distributor on a bed of rocks 6-10 ft deep.
• The water percolates over the rocks within the bed
which are 1-4 ft in diameter and is collected in an
under-drain.
• The liquid is then collected from the under drain
and allowed in a sedimentation tank which is an
integral component of the trickling filter.
• The sludge from the sedimentation tank is
removed from time to time.
Section through Trickling Filter Bed
Microbiology of the trickling filter
• A coating of microorganisms form on the stones as
the waste water trickles down the filter and these
organisms break-down the waste.
• Fungi, algae, protozoa and bacteria form on the
rocks.
• As the filter ages the aerobic bacteria which are
responsible for the breakdown of the organic
matter become impeded,
• The system becomes inefficient and flies and
obnoxious smells may result.
• The microbial coating sloughs off from time to
time.
Rotating discs
• Consist of closely packed discs about 10
ft in diameter and 1 inch apart.
• Discs made of plastic or metal may
number up to 50 or more and are mounted
on a horizontal shaft which rotates slowly,
at a rate of about 0.5-15 revolutions per
min.
• During the rotation, 40-50% of the area of
the discs is immersed in liquid at a time.
• A slime of microorganisms, which decompose the
wastes in the water, builds up on the discs.
• When the slime is too heavy, it sloughs off and is
separated from the liquid in a clarifier.
• It has a short contact time and produces little
sludge.
• The rotating disc system can be seen as a
modification of the tricking filter in which the
waste water is spread on rotating discs rather than
on a bed of rocks.
Structure of Rotating Discs
(Rotating Biological Contactor)
TREATMENT OF THE SLUDGE:
ANAEROBIC BREAKDOWN OF SLUDGE
 Sludge consists of microorganisms and those materials which are
not readily degradable particularly cellulose.
 The solids do not exceed 5%.
 The goals of sludge treatment are:
- to stabilize the sludge and reduce odors,
- remove some of the water and reduce volume,
- decompose some of the organic matter and reduce volume,
- kill disease causing organisms and disinfect the sludge.
 Caustic chemicals can be added to sludge or it may be heat treated
to kill disease-causing organisms.
 Following treatment, liquid and cake sludges are usually spread on
fields, returning organic matter and nutrients to the soil.
Anaerobic Digestion of Sludge
• The commonest method of treating sludge however
is by anaerobic digestion.
• By allowing the sludge to decompose in digesters
under controlled conditions for several weeks.
• Digesters themselves are closed tanks with
provision for mild agitation, and the introduction of
sludge and release of gases.
• About 50% of the organic matter is broken down to
gas, mostly methane.
• Amino acids, sugars alcohols are also produced.
The broken-down sludge may then be de-watered
and disposed of by any of the methods described
above. Sludge so treated is less offensive and
consequently easier to handle.
• Organisms responsible for sludge breakdown are
sensitive to pH values outside 7-8, heavy metals,
and detergents and these should not be introduced
into digesters.
• Methane gas is also produced and this may
sometimes be collected and used as a source of
energy.
Example : Sewage Waste Water
Treatment
• Primary Treatment
– physical separations, removing large objects
• Secondary Treatment
– Reduce the organic load of the sewage to acceptable
levels before releasing it to natural waterways
• Tertiary Treatment
– A physicochemical process employing precipitation,
filtration, and chlorination to sharply reduce the
levels of inorganic nutrients, especially phosphate
and nitrate, from the final effluents
Example : Waste Water
Treatment Technology
Anoxic sludge digester (only the top of the tank
is shown, the remainder is underground.
Inner working of a
sludge digestor
2 stage digestion
Major microbial processes
occurring during sludge
digestion
Anaerobic Wastewater Treatment
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Breweries
Dairy and cheese production
Fish processing
Leachate treatment
Pulp/paper
Meatpacking
Distilleries
Municipal waste
Anaerobic
Wastewater Treatment
• Similar configurations to activated sludge, aerobic
reactors, but no oxygen.
• Used more with industrial wastewaters
– Intermittent flows
– High COD
• Uses less energy, makes less sludge, makes CH4
(energy), but…..
• Biomass grows slowly, acidifies, partial treatment,
no extra P or N removal
Anaerobic Wastewater Treatment:
Considerations
• Mesophilic (25 to 35°C) conditions
advantageous
• Long Retention Time: e.g. 20 days at 30° C
• May need to add CaCO3 to buffer
• May need to add nutrients
• Sensitive to
– Toxic metals and organics
– Ammonia
Microbiology of Anaerobic
Treatment
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CO2 or organics are e- acceptors
C is from CO2 or organic compounds
Energy is from organic compounds or H2
Slow growing bacteria
Conversions and
operative groups
of bacteria
in anaerobic digestion.
Anaerobic digester microbiology
• 1: extracellular hydrolysis (e.g. cellulase)
• 2: fermentation leading to organic acids,
acetate, CO2 and H2
• 3: fermentation leading to acetic acid
(CH3COOH), H2 and O2
• 4: methanogenesis leading to CH4, CO2 and
H2O
Methanogenesis
• By methanogens; which are archaea
• By either
– Hydrogen utilizers (1/3)
– Acetate-splitters (2/3)
• pH sensitive (7 – 7.2)
• Lowers H2 which facilitates acetate formers
What happens in digestion?
• Stabilization
– Reduce pathogen content
– Reduce odors
• Volatile solids reduction (about 60%)
• Gas production (70% CH4, 30% CO2)
(anaerobic only)
Biosolids Disposal
• Land application: fertilizer (bulk or
bagged)
– Surface disposal: dedicated lagoons or other
sites
– Pathogen and vector reduction
• Class A: low pathogens and treatment choices
specified (nurseries, gardens, golf courses)
• Class B: lesser treatment (agriculture, landfill)
– incineration
Aerobic sewage treatment processes: trickling filter
Aeration tank of an activated sludge installation
in a metropolitan sewage treatment plant
Inner workings of an activated sludge installation
A small-scale activated sludge operation used to process dairy waste