Biotechnology in microbiology

 Biotechnological processes are used for wastewater treatment, gas
treatment and disposal of solid wastes in environmental engineering.
 Also, these processes can be utilized for the production of biogas and
hydrogen as new energy resources.
 For preventing environmental pollution in environmental engineering,
activated sludge process, trickling filters, biotrickling filters, oxidation
ponds, anaerobic treatment, composting units and biogas reactors are
used extensively among the waste treatment technologies.

 The methods based on biotechnology in wastewater treatment are:
 activated sludge,
 trickling filters,
 oxidation ponds,
 biofilters and anaerobic treatment.
 Furthermore,
 solid waste composting techniques,
 biotrickling filters and
 biosorption are the examples of biotechnology
applications in environmental engineering

ACTIVATED SLUDGE
 An activated sludge wastewater treatment system has atleast four
components;
 an aeration tank,
 a settling tank
 a return sludge pump and
 a system of introducing oxygen into the aeration tank.
 Wastewater, sometimes pretreated and sometimes not, enters the
aeration tank and is mixed with a suspension of microbes in the
presence of oxygen.
 This mixture is referred to as “mixed liquor.”

 The microbes metabolize the organic pollutants in the wastewater.
 After spending, on average, an amount of time equal to the
hydraulic residence time in the aeration tank, the mixed liquor flows
into the clarifier, where the solids (Mixed Liquor Suspended
Solids- MLSS) separate from the bulk liquid by settling to the
bottom.
 The clarified effluent then exits the system.
 The settled solids are harvested from the clarifier bottom and a
fraction of the settled solids is recycled to the aeration tank whilst
the remainder is discarded.

 Those MLVSS (Mixed Liquor Volatile Suspended Solids) solids that are returned to the
aeration tank are microbes in a starved condition, having been separated from untreated
wastewater for an extended period and are thus referred to as “activated.”
 This process of returning microbes from the clarifier to the aeration tank enables buildup of
their concentrations to high levels (1,800 to 10,000 mg/L) and that, indeed, characterizes the
activated sludge process itself.
 The growth of the microorganisms in flocs is responsible for the metabolism and removal of
organic matter from the liquid.
 Although the presence of a certain number of filaments is important for proper floc formation,
the occurrence of large filamentous bacterial populations is detrimental for sewage treatment as
it causes foam formation or settling problems of the activated sludge in the secondary clarifiers

ACTIVATED SLUDGE PROCESS
 Most common suspended growth process used for municipal water
treatment process
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 Activated sludge plant involves:
 wastewater aeration in the presence of a microbial suspension,
 solid-liquid separation following aeration,
 discharge of clarified effluent,
 wasting of excess biomass, and
 return of remaining biomass to the aeration tank.
 In activated sludge process wastewater containing organic matter is aerated in an aeration
basin in which micro-organisms metabolize the suspended and soluble organic matter.
 Part of organic matter is synthesized into new cells and part is oxidized to CO2 and water to
derive energy.
 In activated sludge systems the new cells formed in the reaction are removed from the
liquid stream in the form of a flocculent sludge in settling tanks.
 A part of this settled biomass, described as activated sludge is returned to the aeration tank
and the remaining forms waste or excess sludge.
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TRICKLING FILTERS
 A very active biological growth forms on the rocks and these organisms
obtain their food from the waste stream dripping through the rock bed.
 It was found that if settled wastewater was passed over rock surfaces, slime
grew on the rocks as mentioned above and the water became cleaner.
 Today this principle is still used, but in many installations plastic media is
used instead of rocks.
 Trickling filters are widely used for the treatment of domestic and
industrial wastes.
 The process is a fixed film biological treatment method designed to remove
BOD and suspended solids.

TRICKLING FILTERS
 Flow diagram of Trickling Filter
Recycle
Primary
clarifier
Trickling
filter
Final
clarifier
Wast
sludg
Influent
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 A trickling filter consists of a
 rotating distribution arm that sprays and evenly distributes liquid wastewater over
 a circular bed of fist-sized rocks, other coarse materials, or synthetic media.
 The spaces between the media allow air to circulate easily so that aerobic conditions
can be maintained.
 The spaces also allow wastewater to trickle down through, around
 and over the media.
 A layer of biological slime that absorbs and consumes the wastes trickling through
the bed covers the media material.
 The organisms aerobically decompose the solids and produce more organisms and
stable wastes that either become part of the slime or are discharged back into the
wastewater flowing over the media.

 This slime consists mainly of bacteria, but it may also include algae,
protozoa, worms, snails, fungi and insect larvae.
 The accumulating slime occasionally sloughs off (sloughings) individual
media materials and is collected at the bottom of the filter, along with the
treated wastewater and passed on to the secondary settling tank where it is
removed.
 The performance of a trickle bed reactor highly relies on the uniformity of
liquid distribution throughout the bed.
 Non-wetted zones in the bed are not colonized by the micro-organisms
rendering a low efficiency of the trickle bed filter.

 Tank is filled with solid media
 Rocks
 Plastic
 Bacteria grow on surface of media
 Wastewater is trickled over media, at top of tank
 As water trickles through media, bacteria degrade BOD
 Bacteria eventually die, fall off of media surface
 Filter is open to atmosphere, air flows naturally through media
 Treated water leaves bottom of tank, flows into secondary clarifier
 Bacterial cells settle, removed from clarifier as sludge
 Some water is recycled to the filter, to maintain moist conditions
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 Can use plastic
media
 lighter - can get
deeper beds (up to
12 m)
 reduced space
requirement
 larger surface area
for growth
 greater void ratios
(better air flow)
 less prone to
plugging by
accumulating slime
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ROTATING BIOLOGICAL CONTRACTORS (RBC)
 The RBC is a fixed film biological treatment device; the basic biological
process is similar to that occurring in the trickling filter.
 Since these contactors allow obtaining high efficiencies in the removal of
dissolved carbon and ammonia with less energy expense than by using
activated-sludge systems, they are widely used in wastewater treatment.
 An RBC consists of a
 series of closely spaced (mounted side by side), circular, plastic (synthetic) disks that are
typically about 3.5 m in diameter and
 attached to a rotating horizontal shaft.
 Approximately 40% of each disk is submersed in a tank containing the
wastewater to be treated.

ROTATING BIOLOGICAL CONTRACTORS
 Rotating Biological Contactors, commonly called RBC’s, are used in
wastewater treatment plants (WWTPs). The primary function of these
bio-reactors at WWTPs is the reduction organic matter.
Wastewater
Film of Microorganisms
Rotation
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 As the RBC rotates, the attached biomass film (zoogleal slime) that
grows on the surface of the disk moves into and out of the
wastewater. While submerged in the wastewater,
 The microorganisms absorb organics; while they are rotated out of
the wastewater, they are supplied with needed oxygen for aerobic
decomposition.
 As the zoogleal slime reenters the wastewater, excess solids and
waste products are stripped off the media as sloughings.
 These sloughings are transported with the wastewater flow to
settling tank for removal.

 Modular RBC units are placed in series simply because a single contactor is not
sufficient to achieve the desired level of treatment.
 Each individual contactor is called a stage and the group is known as a train. Most
RBC systems consist of 2 or more trains with 3 or more stages in each.
 The key advantage in using RBCs instead of trickling filters is that RBCs are easier
to operate under varying load conditions, since it is easier to keep the solid medium
wet at all times.
 Media up 12 feet in diameter
 Shafts as long as 25 feet
 Media areas up to 180,000 square feet per shaft

MEMBRANE BIOREACTORS
 Membrane bioreactor technologies are, as the name suggests, those technologies
that provide biological treatment with membrane separation.
 The term is more appropriately applied to processes in which there is a coupling of
these two elements, rather than the sequential application of membrane separation
downstream of classical biotreatment.
 A conventional municipal water treatment plant usually proceeds through a three
stage process:
 sedimentation of gross solids in the feed water followed by
 aerobic degradation of the organic matter and
 then a second sedimentation process to remove the biomass.
 An MBR can displace the 2 physical separation processes by filtering the biomass
through a membrane.

 As a result the product water quality is significantly higher than that generated by
conventional treatment, obviating the need for a further tertiary disinfection process
(Judd, 2008).
 The 2 most common configurations for membrane bioreactors are:
 submerged membranes and external membranes.
 Submerged type MBRs are preferred more than the external types.
 Some disadvantages of this system include frequent membrane monitoring and
maintenance requirements.
 Besides wastewater treatment, membrane bioreactors are used for the production of
amino acids, antibiotics, anti-inflammatories, anticancer drugs, vitamins, optically
pure enantiomers and isomers, etc

ANAEROBIC TREATMENT
 The anaerobic process comprises a series of phases.
 Initially complex organic compounds such as lipids, proteins and
carbohydrates, if present, are hydrolyzed to simpler organics.
 The latter are then fermented to volatile fatty acids (VFAs) by acidogens.
 The most common of these fatty acids is ethanoic acid.
 Given the production of acids by the process, the system has to be
adequately buffered to avoid pH declines which may adversely impact on
the process’s further progress.
 The acidogens include both facultative and obligate anaerobic bacteria.
 The gaseous by-product of the acidogenic reactions is carbon dioxide.

 Subsequent to the acidogenic phase is the methanogenic phase.
 The methanogens are obligate anaerobes and they convert the fatty acids
from acidogenesis to methane and carbon dioxide.
 This results in substantial decrease in the organic content of the
wastewater.
 The methane generated offers an avenue for energy recovery.
 An indication of impending anaerobic process failure is dropping pH. The
methanogens are sensitive to pH and methanogenesis would stop if pH
drops below 6.2.

 The advantages of anaerobic biotechnology can be summarized as
below;
i) Provision of process stability,
ii) Reduction of waste biomass disposal costs,
iii) Reduction of nitrogen and phosphorus supplementation costs,
iv) Reduction of installation space requirements,
v) Conservation of energy, ensuring ecological and economical benefits,
vi) Elimination of off-gas air pollution,
vii) Avoidance of foaming with surfactant wastewaters,
viii) Biodegradation of aerobic non-biodegradables,
ix) Reduction of chlorinated organic toxicity levels,

COMPOSTING
 The composting process is a controlled biological exothermic oxidation of organic
matter, followed by a maturing phase, carried out by a dynamic and rapid
succession of microbial populations.
 The organic matter is transformed into a final stable humus type product (compost)
through its mineralization and humification (20 or 30% of the volatile solids are
converted in CO2 and H2O).
 This product is a hygienic material, free of unpleasant characteristics, according to
the following reaction.
 Organic Microorganisms Biodegradable + O2 Stabilized organic residuals +
Microbial biomass + CO2+H2O + Heat

BIOSORPTION
 The uptake of both metal and non-metal species by biomass, whether living
or denatured, is commonly termed biosorption.
 Biosorption encompasses physico-chemical mechanisms by which metal
species, radionuclides and so on, are removed from aqueous solutions by
microbial biomass or products.
 In biosorption, the metals are not only removeed from wastes, but also
recovered to reuse for different purposes.
 One of the more common questions aroused by biosorption processes
involves the fate of the biosorbent after the process.
 The common answer to the disposal of the final material is via landfill or
incineration

Biotechnology in microbiology

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