JOURNAL OF INFORMATION, KNOWLEDGE AND RESEARCH IN
CIVIL ENGINEERING
HIGH PURITY OXYGEN ACTIVATED SLUDGE
PROCESS FOR TREATING EFFLUENT:- OPEN TO
ATMOSPHERE SYSTEM
1ASHISH
1
GULABANI, 2 DR. PROF. N.S. VARANDANI.
Student of M.E. 4th Semester Environmental Engg. Dept. L.D. College of Engineering
2
Head of the Environmental Engg. Dept. L.D. College of Engineering.
1
ashuchem87@gmail.com
ABSTRACT : There are many of the problems of wastewater treatment – in both municipal and industrial
wastewater treatment plants – are the result of insufficient oxygen. The consequences are inadequate
purification or even anaerobic decomposition processes, giving rise to highly offensive odors. The systematic
input of pure oxygen at critical points along the wastewater chain solves these problems quickly, flexibly and
efficiently.
Many activated sludge plants built years ago are no longer able to handle today’s increased requirements
concerning waste water purification. Because of greater pollutant loads, the installed aeration systems are unable
to supply the micro-organisms with enough oxygen.
This is an attempt to throw some options to handle the increasing load of the pollutant in the wastewater
treatment for existing activated sludge process for the wastewater treatment with the help of pure oxygen.
1. INTRODUCTION
High purity activated sludge process is not the new
technology, it is the existing one, But not widely
applicable due to higher operating cost and
maintenance cost and also with the main requirement
of the completely closed system to recycle of the
oxygen and to utilize the maximum amount of
oxygen in the process rather then wasting it in
atmosphere.
Now, our efforts to make this process technically and
economically viable for the conventional activated
sludge process i.e. open to atmosphere system, for
that idea is to increase the concentration of oxygen in
the supply of air as all are aware that in the
atmosphere approximate 20% of oxygen is available
so to increase that concentration from 20%, & up to
60-70 % depends on the dissolve rate requirement
with keeping in mind that minimum amount of
oxygen is wasted in the atmosphere.
There is literature available for the pure oxygen
system, keeping those advantages and disadvantages
in mind this study has been carried out. Listing out
the advantages and disadvantages of the High purity
oxygen activated sludge process for giving an
overview of the future need & scope for the study.
Problems that can arise in waste water treatment
plants:
1.
Lack of oxygen in existing activated
sludge plants, as a result of:

Increased waste water inflow

Increased concentration of pollutants

Greatly fluctuating pollutant load

More thorough purification dictated by
stricter legal requirements
2.
Failure of aeration systems, caused by:

Defective compressors for diffused aeration

Damage to mechanical surface aerators
3.
Inadequate elimination of nitrogen.
Should the existing aeration system be enlarged?
To increase the aeration capacity in overloaded
activated sludge tanks, there is usually no choice but
to enlarge the aeration equipment – a costly
undertaking. It may be necessary, for example, to
install larger surface aerators, additional compressors,
as well as air diffusers. But such measures quickly
run up against the following constraints:

The space requirement is too great; the
activated sludge tank is too small to accommodate
any more equipment.

Uneconomical and inefficient oxygen
transfer, due to injection of too much air at points
crowded too closely together.
And because the aeration facility must be designed
from the outset to cope with the maximum load, high
investment costs are involved.
Advantages of Using Pure Oxygen

Low investment costs

Quick and economic solutions to problems

Focused injection of oxygen

Increased efficiency without enlarging
facilities

Low maintenance requirement

Optimum oxygen utilization

Flexible oxygen injection

High oxygen concentrations attainable
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JOURNAL OF INFORMATION, KNOWLEDGE AND RESEARCH IN
CIVIL ENGINEERING
II. Aim
“To increase the in situ capacity of activated sludge
process by doing study on pilot scale by introducing
the pure oxygen and with the ultimate goal of the
study is to make smaller footprint”
III. Future Needs & scope of Study:
One line sentence for understanding the needs &
scope “Smaller Footprint”
Needs & Scope

As per current scenario for an available land
& the continually increasing cost in construction
sector.

It is hard to invest a corers of rupees for an
effluent treatment, and also the governing factor for
this study is increased use of water against the
“Scarcity of Water” & stringent rules & regulation by
the government, it has become necessity for an
industries to reuse or recycle or to control the quality
of an effluent generated form premises.

Seeing above needs if this study outcomes
with a positive results then it will be helpful in many
industries for increasing the treatment capacity &
load on a present ETP & to serve the other objectives.
iv. The process: activated sludge process literature
A basic activated sludge process consists of several
interrelated components:

An aeration tank where the biological
reactions occur

An aeration source that provides oxygen and
mixing

A tank, known as the clarifier, where the
solids settle and are separated from treated
wastewater

A means of collecting the solids either to
return them to the aeration tank, (return activated
sludge [RAS]), or to remove them from the process
(waste activated sludge [WAS]).

Aerobic bacteria thrive as they travel
through the aeration tank. They multiply rapidly with
sufficient food and oxygen. By the time the waste
reaches the end of the tank (between four to eight
hours), the bacteria has used most of the organic
matter to produce new cells. Various types of
Activated sludge processes.

The organisms settle to the bottom of the
clarifier tank, separating from the clearer water. This
sludge is pumped back to the aeration tank where it is
mixed with the incoming wastewater or removed
from the system as excess, a process called wasting.
The relatively clear liquid above the sludge, the
supernatant, is sent on for further treatment as
required.
Various types of ASP.
1.
Completely mixed activated sludge process.
2.
Conventional dispersed plug flow activated
sludge process
3.
Contact stabilization activated sludge
4.
High purity oxygen activated sludge
5.
Oxidation ditch (extended
aeration)
activated sludge process
6.
Sequencing batch reactor (SBR) activated
sludge process
7.
Microfilter membrane bioreactor (MMBR)
High purity oxygen activated sludge Process
Advantages

Five times oxygen transfer rate over air

Smaller volume

Higher MLSS concentration possible, but
limited by secondary settler capacity
Disadvantages
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JOURNAL OF INFORMATION, KNOWLEDGE AND RESEARCH IN
CIVIL ENGINEERING

Very expensive: covered tanks, high energy
cost for O2 generation, gas recirculation equipment

Headspace
CO2
accumulation
and
associated pH drop requires alkalinity addition

No flexibility (all aerobic processes)

Nitrification is problematic – low pH, short
HRT produces high biomass at short SRT

Settling problems have been reported
Alternative options for oxygen supply & their
comparisons.
Cryogenic Distillation
Performance
Comparisons
(% Purity)
Power Needs (KWh/Ton O2)
control the cost of generation of oxygen, but mainly
concentrating the above three for the supply option
for oxygen. So comparing the above three
technologies.
V. Details of the pilot study
Scale selected

Pilot scale: i.e Combination of theoretical
scale study & with Oxygen cylinder as a source of
pure oxygen on pilot scale.
Place: - Pilot scale study at Effluent Treatment Plant
ARVIND LIMITED, SANTEJ (A Textile Industry)
Ion Transport Membrane Pressure
swing
(ITM)
Adsorption (PSA)
+
99.99%
99 %
85-94%
259
162
36
Operating Temperature
(In ˚C)
Low
800-900
Ambient
Operating
Pressure
Maximum is 13,000 kPa
Maximum is 7,000 kPa
Maximum is 150 kPa
FCI (For 1 MTPD O2) in Rs.
Approx 11.1
Approx 7.5
Approx <<5
Lacs
Operating Cost in Rs. / MT
O2 Production
Approx 120
Approx 88
Approx 10
Per DAY Basis
There are two possible ways for supplying the
additional oxygen
1)
Oxygen cylinder or other outside source
or
2)
On site oxygen generator units

Oxygen cylinders or other outside source
Oxygen cylinders are the good option for the
small scale unit where the requirement of oxygen is
less as compare to large scale unit. While seeing the
large scale requirement it is not suggested to use the
oxygen cylinder.
The other factor considering the safety
involved in the operating plant with oxygen cylinder
and the main factor to be consider is the availability
of an oxygen cylinder from any near by place or city
with minimum transportation cost which leads to
saving an fixed capital investment in the operation
So this option of supplying the oxygen is only
advisable if the company is small scale unit.

On site oxygen generator units
Alternative technologies for onsite oxygen generation
Unit

Cryogenic Distillation

Ion Transport Membrane (ITM)

Pressure swing Adsorption (PSA)
And there are more technologies available and also
some modifications done in the above technologies to
(Photograph showing pilot scale plant at site.)
Details of the Pilot Plant at initial level of study:

Flow : 65-70 m3/Day

Tank Size (m) : 4.5 x 4.5 x 2.5

I/L COD : 550 ppm Avg.

I/L BOD : 250 ppm

O/L COD (to achieve) : 80 ppm

O/L BOD (to achieve) : 10 ppm

MLSS concentration : 2000

MLVSS concentration : 1550 ppm

DO : 2.5 ppm

pH : 7.65

HRT (present) : 18-20 hrs
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JOURNAL OF INFORMATION, KNOWLEDGE AND RESEARCH IN
CIVIL ENGINEERING
For observing the effect due to the following variable
parameters on the aerobic treatment
Variable parameters:

Flow m3/Day : 80, 90, 100, 120

MLSS ppm : 2000, 2500, 2800, 3000

Observations to be done

Air requirement

Power Consumption

HRT
Result
MLSS : 2500 ppm
DO : 2.5 ppm
O/L COD : 90-120 ppm
O/L BOD : 10-25 ppm
HRT : 16 Hrs
Result
MLSS : 3000 ppm
DO : 2.5 ppm
O/L COD : 60-120 ppm
O/L BOD : 10-25 ppm
HRT : 15 Hrs
Overall Result in Percentage
improvement : 15-20 %
vi. Result & Discussions
[5]
http://www.icheme.org/literature/conference
s/gasi/Gasification%20Conf%20Papers/Session%204
%20presentation-Allam%20et%20al.pdf (comparison
of alternatives)
[6]
http://www.psaplants.com/psa-gasplants.html
[7]
http://www.industrialgasplants.com/pressure
-swing-adsorption.html
[8]
http://www.lindeindia.com/userfiles/image/File/O2%20Plants/Oxygen
%20Generatation%20by%20PSA.pdf
The above results shows that with the study it has
successfully improved in capacity with the increase
in the HRT in the sense that one can handle more
effluent in the effluent treatment plant in that extra
saved time and it is observed to be savings in power
consumption also which is found to be half of the
existing value.
CONCLUSION
After doing this study, It is found that it is technically
possible to apply the High purity Activated Sludge
process in the open to air system. The power cost
calculation is done & it is found to be very cheap &
almost 50% less compare to existing scenario but it
involves higher capital investment at the initial level
which has a payback period of approx 5 yrs. Post
maintenance will be another problem cause it
requires highly skilled person to get involved at the
process which makes the process more costly So, for
a small scale industry which has very low effluent
load are not advisable to go for this process while for
larger scale unit it still required to think before going
for this process cause of post maintenance cost.
REFERENCES
[1]
S B Thakore B I Bhatt.(2007), Introduction
to Process Engineering and Design; TATA
MCGRAW-HILL;
[2]
Ruthven, D., Farooq, S. and Knaebel, K.
(1993); Pressure Swing Adsorption; VCH NewYork;
[3]
Metcalf & Eddy, Inc. (2003). Wastewater
Engineering: Treatment and Reuse, 4th edition,
McGraw Hill, Inc.;
[4]
http://www.mvsengg.com/products/psaoxyg
en/ (Cost of Production of O2 )
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