improved bio-tower technology municipal sewage treatment

Transcription

IMPROVED BIO-TOWER TECHNOLOGY
FOR
MUNICIPAL SEWAGE TREATMENT Regd. Office : ‘Henabh Center’, 1326, Shukrawar Peth, Off. Bajirao Road, PUNE : 411 002 (INDIA), Tel. : 24473299 (5 Lines) 24474696, (Voice Mail) Fax : 0091‐20‐24473185. E‐mail : [email protected] Web Site : www.hnbc.in
IMPROVED BIO-TOWER TECHNOLOGY FOR MUNICIPAL SEWAGE
TREATMENT
The treatment scheme consists of A) Primary Treatment Units, B) Secondary Treatment
Units, C) Solid liquid separation Units and D) Disinfection Arrangement.
PROCESS DIAGRAM
PRIMARY
TREATMENT
SECONDARY
TREATMENT
DISINFECTION
TREATMENT
Stilling Chamber
Fine screen Channel
Grit Chamber
Parshall Flume
Distribution Chamber
Improved Bio-Towers
Aeration tanks
Secondary Settling
Chlorine
Contact
Tank
SLUDGE
HANDELING
SYSTEM
Primary Treatment Units consist of Stilling Chamber, Fine Screen Channel, Grit
Chamber, Flow measurement arrangement and Distribution Chamber
Stilling Chamber reduces the velocity of the incoming sewage before it enters the fine
screen channel.
Fine Screen Channel is designed to remove the particles of size more than 5 mm. Drum type
fine screens are proposed in the plant. Separated solids will be taken on conveyor belt and
collected at bottom through chute.
Grit Chamber is designed to remove inorganic matter of specific gravity more than 2.5 and
size more than 0.15 mm. The settled grit is removed from the chamber by grit mechanism to
the side channel. Grit is removed by grit screw from the channel and taken to bottom
through chute. While doing this grit is washed with the help of grit wash pumps to separate
organic matter attached to grit if any.
After grit chamber flow is measured and taken to distribution chamber to distribute the flow
to the Improved Bio-Towers.
Secondary Treatment Units consist of Improved Bio-Tower, Mixing Chamber and
Aeration Tank.
IMPROVED BIO‐TOWER TECHNOLOGY FOR MUNICIPAL SEWAGE TREATMENT
1 TRICKLING FILTERS with rock packing have been a common simple and low energy
process used for secondary treatment since early 1900s. The concept of a trickling filter
grew from the use of contact filters in England in the late 1890s. Biological growth on the
media surface converts the organic waste material in to stable by-products such as CO2,
H2O using microorganisms mainly the bacteria. The old plants used mainly Rock as the
surface for the attached growth biological systems. This media had disadvantages due to
heavy weight, elaborate supporting structure, water tight peripheral walls designed to take
lateral thrust, low voltage, potentials for plugging, fly nuisance, poor wetting characteristics,
etc. Even though the problems with rock media were leading and increased use of
suspended growth biological systems, the advantageous of the process as such prevented the
systems from going in to oblivion.
Advantages of Attached Growth Fixed Film Bio-Filters Over Suspended Growth
Activated Sludge Process Plants for Waste Water Treatment

Attached growth systems are more suitable to take shock loads in terms of hydraulic
and organic disturbances as compared to suspended growth systems.
Very high capacity to take organic load.
Trouble free operations even under difficult conditions.
Reliable and consistent nitrification, both in summer & winter operations.
Low power consumption - to the tune of up to half of conventional ASP and 1/4th of
Extended Aeration plant.
Very low skilled operation, control and maintenance requirements and thus low
operation and maintenance costs.
Low sludge production and easily drainable sludge.
8 .Much smaller secondary settling tanks due to higher settling rates of the sludge
produced.
Lower residual suspended solids concentration in treated wastewater.
Cost effective combinations with other treatment methods.
Improved plastic media design have significantly reduced tower sizes and costs and
enhanced their capacities and efficiencies.
Installation depths up to 6.0 m require no intermediate supports. Higher installation
depths with intermediate supports can be provided. This combined with efficient
geometry can offer a very compact plant.
2 General Advantages of Improved Bio-Tower Application:

Long life of over 30 years - UV stabilized material.
Large specific surface areas to accommodate large microbial growth.
Very large voids from 90 to 97%
Very weight easy to handle and simpler for supporting structure.
The distribution pattern provides utilization of the complete surface area.
Large depth - say 6 to 8 m., allows considerable saving of land.
Due to cross flow configuration. The liquid has about 4 times higher detention time.
8 It has very low resistance to airflow leading to maximum contact of air, waste
water & bio mass.
Low resistances to airflow and the mixing caused at the cross over points in the fill
lead to optimum aeration.
Good wetting, continuous air movement and thinner biological growths eliminate fly
nuisance.
Due to continuous redistribution of water flow, plastic media has a very high
resistance to plugging.
Settled effluents TSS is much lower with Improved Bio-Tower.
No elaborate peripheral walls required because modules are self-supporting, only
cladding suffices.
Requires no elaborate under drain system.
AERATION BY NATURAL DRAUGHT
Plastic Media have increased the BOD5
removal levels 90% apart from increasing the
organic and hydraulic Loading rates. The
plastic media offer very low resistance to air,
provides Maximum contact of air, waste &
bio mass, provide thousands of crossover
points per m3, thus leading to a very good
aeration by natural draught or ventilation.
The air requirement is met by providing
Ventilation openings in the wall, at the bottom of the Improved Bio-Tower, having a size of
4- 6% of the cross-sectional area of the Bio-Filter. This way a daily air volume of more than
100 m3 air per m3 of fill circulates to provide the necessary oxygen to the microorganisms.
3 The Oxidation of Organic matter in
waste water and synthesis of new
microbial cells takes place in following
way
Oxidation
COHNS
Organic matter
+ O2 -------------Æ
Bacteria
CO2 + NH3 +C5H7NO2 + Other end products
New cells
Endogenous respiration
C5H7NO2
New cells
+ 5O2 ----------Æ 5CO2 + 2H2O + NH3 + energy
Bacteria
SIMPLE SUPPORT SYSTEM
The modules on the bottom layer are
installed with the longer sides at right angles
to the support beams. The module supports
can be nominal 100 to 150 mm beams at 600
mm or 900 mm centers. This is possible due
to the strength of the module that requires
supports at only 2 points and it’s lightweight.
Such simple supports, widely spaced,
maximize the flow of air and water through
the media and the plenum area, with least
obstruction. The support system is designed
for about 400 kg/m2 per M of media depth. Below the support beams a base slab, with
approx. 4% slope, collects the treated liquid into a central or peripheral channel.
LONGER RETENTION TIME
4 The 60 cross flow characteristics provide about 3 to 4 times more detention time than the
other media such as rock, since no free fall of liquid can take place inside the media. Due to
this configuration, the wastewater is distributed over the entire surface inside the media,
resulting in a thin liquid film. This leads to sufficient time being available for the Biological
process and a high reduction of BOD.
LOW CONSTRUCTION COST
The media is self-supporting, strong and can be cut to fit into any regular shaped Improved
Bio-Tower. With no lateral thrust or pressure on the peripheral surrounding walls, these
walls can be of a cheap construction and of a simple nature. Normally Exterior cladding
consists of easily available AC or plastic sheets.
DISTRIBUTION SYSTEM
The system of interconnected channels in the
plastic media makes it possible to use either a
rotary distributor or a fixed nozzle system to
achieve the desired wetting. The fixed nozzle
system can be adapted to any regular shaped
media plan including the circular trickling
filters and is ideally suited for the rectangular
or square tanks. The efficiency is independent
of the distribution system at the top since the
internal redistribution system in the module
starts to operate immediately on the wastewater hitting the top layer. In over 6000 mixing
points per m3, the liquid film is broken up and re-mixed, a turbulence of vital importance
for efficient transfer of oxygen and the dissolved organic matter between the liquid and the
bio mass.
DESIGN OF IMPROVED BIO-TOWERS
In biological treatment of waste waters many parameters such as the BOD and COD levels,
origin, waste and ambient temperatures, pH, nutrient balance, presence of toxic matters, etc.
interact in such a way that each plant be designed individually. Domestic sewage usually
contains all the necessary nutrients and trace minerals for biological action within the tower
and the design of Improved Bio-Towers for its secondary treatment differs to a certain
extent from the normal design of a high rate unit.
The design of a Improved Bio-Tower is based on various design equations such as the
modified VELZ equation for which the values of the constants have been experimentally
5 determined and fixed for these media. Further, based on the empirical data collected over
the years, design curves have been developed for the organic loading for different ambient
temperature ranges. Since it is also necessary to have a minimum amount of wastewater to
utilize fully all the available surface area within a Bio-filter, design curves have also been
developed for the hydraulic load or the wetting rates for different distribution systems and
the selected depths of media. Due to the very high efficiency of these filters, no
recirculation is normally necessary. However, recirculation of the Bio-filter effluent must be
undertaken to satisfy the wetting rate recommendations if they are not otherwise.
THE MODULE
The modular medium for high rate Improved Bio-Tower is manufactured from plastic/ rigid
PVC, Which is chemically resistant to water soluble substances occurring in municipal and
industrial waste waters. It is also resistant to rot, bacterial, fungal or growths of other
microorganisms.
PROPERTIES OF PLASTIC MEDIA:

Specific Surface Area (sq m/cum)
: 90 to 200
Void ratio
: 90 to 97 %
Number of mixing points per cum
: Up to 10000
Sheet thickness (mm)
: 0.3 to 1.0
Weight kg/cum
Dry
Wet (operational)
: 30 to 45
: 350 to 650
WINTER TIME OPERATION AND ICE FORMATION:
It is known that fixed film or attached growth processes are more stable at lower
temperatures due to the various advantages that this system offers in terms of the conducive
conditions for the required microbial growth. Apart from these advantages, the high void
ratio and geometry of plastic media are key factors is increasing efficiency and minimizing
ice formations. Rock and other media present large, horizontal surfaces where the falling
liquid can splash back and form ice coatings on adjacent surfaces. It is on record, that even
in subzero cold spells no ice formation on the Improved Bio-Tower surface is observed,
even when the adjoining walls and area are under a blanket of snow.
6 NITRIFICATION:
Cross flow media Improved Bio-Towers
with a more compact array of sheets can be
used to achieve consistent, high level
nitrification (> 90%conversion) when
operating at a low BOD waste stream (up
to
30
mg/l)
containing
NH3-N
concentrations up to 25 mg/1. This is a
highly efficient and cost effective
application for which separate design data
and curves have been developed. Final
effluent NH3-N concentrations in the range
of 0.5-2.0 mg/1 can; easily be obtained.
Nitrification takes place in following way
2NH4+ + 3O2 --------------------Æ 2NO2 - + 4H+ + 2H2O
Nitroso-bacteria
2NO2 - + O2 --------------------Æ 2NO3
Nitro-bacter
IMPROVED BIO-TOWER:
As described earlier after primary treatment raw sewage is taken to Improved BIOTOWER, where sewage is spread on packed bed of Plastic/PVC medium where fixed film
of microorganism is formed over media. Biological degradation of organic matter present in
sewage occurs as trickling sewage comes in contact with biological film formed over plastic
media. This method is based on empirical data collected over the years, design curves have
been developed for various organic loading and different temperature ranges. About 50 %
organic load is removed without use of power. The reactions taking place across the fixed
film or microbial layer is explained in the figure below.
Mixing Chamber:
The sewage after partial treatment in Improved Bio-Tower is then taken to Mixing Chamber
where recirculation sludge from secondary clarifier is mixed with partially treated sewage
and the sewage is taken to Aeration tank.
7 Aeration Tank:
About 50 % organic load is removed in
Improved Bio-Tower. Further the sewage
received from Improved Bio-Tower is
taken to aeration tank. Air is introduced
through air diffuser. Remaining organic
load is reduced to achieve outlet
parameter as per the norms as mentioned
above. The process taking place in
aeration tank is similar to that taking
place in ASP as follows
The partially treated sewage from Improved Bio-Tower with about 50% of BOD will then
flow to Aeration Tank. The aeration tank is provided with suitable numbers of air diffusers
to supply required oxygen to develop and maintain MLSS concentration. The hydraulic
retention time of this unit is maintained as per the requirement and guidelines of CPHEEO
manual.
This is suspended growth process and the microorganisms responsible for treatment are
maintained in liquid suspension by appropriate mixing methods. In our case we are
maintaining microorganisms in suspension with the help of air diffuser by providing
sufficient air considering mixing requirement.
The organic matter in the waste water is utilized by microorganisms partly for metabolism
and partly for cell synthesis i.e. new bacteria generation. This can be explained as follows
Endogenous respiration
C5H7NO2
New cells
+ 5O2 ----------Æ 5CO2 + 2H2O + NH3 + energy
Bacteria
Oxidation
COHNS
Organic matter
+ O2 -------------Æ
Bacteria
CO2 + NH3 +C5H7NO2 + Other end products
New cells
Proper removal of organic matter from the sewage depends on the population of
microorganisms present in the aeration tank which is called MLSS or the Mixed Liquor
8 Suspended Solids. The MLSS in the aeration tank is maintained by recirculating part of the
sludge separated in the secondary clarifier. The excess sludge generated is taken to sludge
thickener for reducing its volume and for further dewatering.
Solid liquid separation units:
These are secondary clarifier and Centrifuge Unit
Secondary Clarifier:
The aerated sewage is taken to secondary clarifier.
The design of settling tank is done as per CPHEEO
norms .After settling supernatant is transferred for
disinfection and settled sludge is partly recirculated
for maintaining MLSS in aeration tank and excess is
taken for thickening.
Centrifuge Unit:
The excess sludge collected from secondary clarifier
is taken to sludge thickener with the help of
centrifuge feed pumps the volume of sludge is
reduced and sent for disposal in landfill or dumping
yard.
Disinfection Arrangement:
Disinfection arrangement consists of Chlorine Contact Tank and Chlorination System
Chlorine Contact Tank:
The effluent or supernatant from Secondary Clarifier is
collected in chlorine contact tank. The supernatant is
disinfected in chlorine contact tank by adding suitable
dose of chlorine for reducing MPN of coliforms and
finally the sewage is ready for disposal.
9 Chlorination System:
Chlorination system covering chlorine tonners, chlorinators, water feed pumps, piping,
booster pumps etc. as per explosive department norms are provided in chlorination room.
Advantages of “Improved Bio-Tower Technology”:

Only Column-Beam structure suffices Tower can be constructed even up to 9.0 m
which saves lot of land.
Withstands shock loads.
Sludge generated in Improved Bio-Tower is highly thick and having higher density
which settles faster leads to smaller clarifier size giving better effluent quality.
Sludge production is less than that produced in ASP or any other aerobic treatment
method requires less sludge handling mechanism.
No problem of sludge deposition. Improved Bio-Tower is continuously aerated due
to natural draft thereby avoids any odor related problems. System is always ready to
receive effluent in case of interrupted power supply.
Only power requirement is to lift the effluent to the top of tower. Compared to ASP
this energy saving is more than 50-60%.
Easy operation and maintenance. No foaming problems. No recirculation of sludge
required. No skilled staff is required.
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