Introduction To
UASB - Process
The heart of the UASB system is the anaerobic reactor based on Upflow Anaerobic Sludge Blanket
process. The reactor consists of a large corrosion resistant tank which
incorporates a unique 3‑phase settler called as GLSS, to separate the sludge,
biogas and effluent. The settler is located at the top of the reactor and is
designed for specific COD reactor loadings and hydraulic throughput.
A flow distribution network is located at the
base of the reactor. This network is
designed to distribute the flow evenly
throughout the bottom of the reactor.
This eliminates short ‑ circuiting and promotes the proper formation of
the sludge flocs which is a critical
factor in reactor operation. The
distribution network is designed to facilitate easy cleaning, thereby
eliminating potential plugging problems.
New bacterial cells formed in the reactor
aggregate into tiny flocs with extremely good settling characteristics. The biogas produced by the bacteria in the
form of small bubbles rises upward through the sludge bed / blanket zones and
provides a natural mixing action. When
the biogas reaches the top of the reactor, it is removed by gas
collectors. A gas‑free zone above the
collector makes possible the settling of finely dispersed solids to the reactor
bottom.
SALIENT FEATURES OF
THE UASB PROCESS
·
High treatment efficiency in terms of BOD & COD
reductions in single stage
·
Very low or practically nil energy requirements
·
Ability to withstand organic and hydraulic shock
loadings
·
Low nutrient requirements
·
Production of Biogas with high percentage of methane
which can be converted into an useful energy resource viz. Heat, Electricity,
etc.
·
Low space requirements due to higher organic loading
rates
·
It is a high rate process i.e. It can operate at high
volumetric loading
·
Low production
of stabilized excess sludge with very good dewatering characteristics
·
Low operation / maintenance costs since very few
moving parts
·
Sludge can be stored for extended periods of time
(bacteria go dormant)
ADVANTAGES OF THE UASB PROCESS OVER CONVENTIONAL
ACTIVATED SLUDGE PROCESS
The “
UASB ” process has been recognized and accepted world wide as the “
Most Cost Effective ” process, due to following direct and inherent
advantages, as compared to traditional conventional system i.e. Activated
Sludge Process :
¨
Higher efficiency and working results.
¨
Compact reactor, hence space reduced to a large
extent.
¨
Very low power consumption (mainly required for feed
pumps only).
¨
Stable process
¨
Production of stabilized excess sludge is low with very good dewatering
characteristics.
¨
Low nutrient requirement, as bacteria retain Nitrogen & Phosphorus
and there is no destruction of cells.
¨
Resistant to shock loadings
¨
Methane rich biogas is produced as a by-product which can be effectively
used either for domestic or industrial purposes.
¨
Volumetric loading rate is high. .
¨
In case of power failure or long shut down, the bacteria go into dormant
stage and plant can be restarted to take full load within short period.
¨
Since the anaerobic digestion takes place in a closed reactor, there is
no foul smell in surrounding area and in the vicinity of E.T.P. Further, the nuisance due to flies,
mosquitoes etc, is totally eliminated.
¨
“UASB” process eliminates large number of pumps / blowers / aerators
etc. hence operating and maintenance cost reduces to a large extent.
The system proposed by us has many advantages over the
Conventional Activated sludge treatment scheme. These are as follows:
- The total capital cost of UASB followed by Extended aeration is
substantially less than the Conventional Activated sludge process.
- The operating electrical power requirement of the UASB + Extended
Aeration is about 50% of that of the conventional ASP.
- The excess sludge generation in the UASB + Extended Aeration is
negligible as compared to the conventional ASP.
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