FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
i
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
Sludge treatment plant and method of treating sludge
APPLICANTS
Pratibha Industries Limited, Universal Majestic, 14th Floor, P L Lokhande Marg, Off . Ghatkopar Mankhurd Link Road, Govandi, Mumbai - 400 043, Maharashtra, India, an Indian Company
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner
in which it is to be performed:

FIELD OF THE INVENTION
This invention relates to a sludge treatment plant and a method of treating sludge.
This invention also relates to a water treatment plant and a method of treating sludge generated in the water treatment plant.
BACKGROUND OF THE INVENTION
Water which is absolutely essential for the survival of life on earth is becoming scarce day by day and it is a matter of grave concern for the entire world. Serious efforts are being made all over the world to conserve water and to prevent wastage of water. Sources of water are mainly surface water and ground water. Many a time surface water and ground water is turbid and contaminated with particulate materials and microbes and is not fit for human consumption as such. Water is also getting polluted and contaminated due to various reasons like increasing industrialization and urbanization and accidental spillage or careless release of effluents and wastes into water bodies. Effluents and wastes released into or dumped on the ground accidentally or otherwise also ultimately reach and pollute water bodies, especially during rainy seasons. Contaminated or polluted water is treated in water treatment plants in order to remove the turbidity and impurities and microbial contamination and to render the water suitable for human consumption.
Typically a water treatment plant comprises a raw water inlet chamber, a flash mixer unit connected to the raw water inlet chamber, a flocculation and settling unit connected to the flash mixer unit, a filtration unit connected to the flocculation and settling unit and a disinfection unit connected to the filtration unit. Raw water from the water inlet chamber is

agitated and mixed in the flash mixer unit and fed into the flocculation and settling unit. Dissolved and suspended particles in the water are coagulated or flocculated in the flocculation and settling unit by adding coagulants such as iron or aluminium salts like ferric sulphate or chloride or aluminium sulphate or polymers. The coagulated particles settle down at the bottom of the flocculation and settling unit as sediments. Supernatent flows into and is filtered in the filtration unit to remove all the particulate impurities. Filtered water flows into the disinfection unit where it is disinfected with disinfectants like chlorine, chloramines or chlorine dioxide before it enters the distribution system to ensure that potentially dangerous microbes are killed. A large water treatment plant also comprises a distribution chamber for distributing water into the flash mixer unit.
While treating water in water treatment plants, waste in the form of sludge is generated both in the flocculation and settlement unit and filtration unit thereof. The sludge generation is approximately 5 to 6 % of the total quantity of the treated water. Sludge contains substantial quantity of water and is unstablised. The sludge is often disposed of into drains or into the open environment. Sludge disposal not only causes pollution and environmental problems but also results in substantial loss and wastage of water. Disposal of sludge is also problematic as it requires a suitable site or location for disposal. Disposal also may require additional cost by way of transportation and labour. The following Table is illustrative of the loss or wastage of water in sludges:

Table
1 Water Treatment Plant Capacity | Quantum of sludge generated Quantum of water
lost in the sludge
M3/day Kg/day M3/day
1000 2045 60
5000 10225 300
10000 20450 600
50000 102250 3000
100000 204500 6000
Sludge treatment plants are in use for recovery of water from the sludge. Typically a sludge treatment plant comprises a settler and a centrifuge and optionally a sludge drying bed. The settler is normally a tube settler or a settling tank. A tube settler comprises a network of tubes arranged in a staggered manner. The sludge is allowed to settle down in the settler and the solids or sludge particles are removed from the settler at intervals of time. The solids are taken to the centrifuge to further separate water from the solids by centrifugal action. In case the sludge treatment plant includes a sludge drying bed, the solids in the centrifuge are again taken to the sludge drying bed for further separation of water from the solids. The solids generated in the centrifuge without further treatment in the sludge drying bed or the solids generated in the sludge drying bed are made into cakes and are generally used for land filling applications or as a substitute for earth. Water recovered in the settler, centrifuge and sludge drying bed is recycled into the raw water inlet chamber of the water treatment plant for further treatment. Substantial quantity of water in the sludge is thus recovered in the sludge treatment plant. As a result, the quantity of solids generated in the sludge treatment plant for

disposal is also considerably reduced thereby reducing problems associated with sludge disposal.
A main disadvantage with a sludge treatment plant is that it is necessary to provide a long residence time for the sludge in the settler to allow the solids in (he sludge to settle down. As a result of the residence time for the sludge in the settler, the sludge treatment takes longer time and the efficiency of operation of the sludge treatment plant is reduced. Further, as is known, parameters like concentration of the sludge in the water being treated in a water treatment plant varies, especially during rainy seasons. As the solids are withdrawn from the water treatment plant at intervals of time, variations in the solids content in the incoming sludge will cause overloading or shock loadings of the settler of the sludge treatment plant. This may cause malfunctioning of the sludge treatment plant and further reduce the efficiency of operation of the sludge treatment plant. A tube settler or settling tank is very large in size and requires correspondingly large foot print area for occupation. Because of the large size and large land requirement, capital cost of the settler is very high. Power consumption by a centrifuge is very high. Centrifuge being an essential component of the sludge treatment plant, power consumption and operational cost of the plant are correspondingly increased. Because of the large size of the plant, capacity of the plant is also high. This may cause under utilization of the capacity of the plant.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention there is provided a sludge treatment plant comprising a reactor thickener and a sludge drying bed, wherein the reactor thickener comprises a vessel defining an inner reaction zone, an outer clean water zone and a hopper bottom settling zone, the inner

eaction zone opening onto a sludge blanket formed on the hopper bottom settling zone and xtending into the clean water zone, the reaction zone comprising a sludge inlet, weighting agent dosing inlet and a pH control agent dosing inlet, the reaction zone further comprising a plurality of spaced apart agitators and a rotary scraper disposed for rotation about vertical axes, the rotary scraper comprising a flat body disposed underneath the sludge blanket, the clean water zone opening at the top thereof into a launder around the clean water zone,the launder having a clean water outlet and the hopper bottom settling zone being provided with a sludge drainage line fitted with a control valve, the sludge drying bed having a sludge inlet connected to the sludge drainage line of the reactor thickener and a clean water outlet and a sludge outlet.
According to an embodiment of the invention the sludge treatment plant further comprises a centrifuge having a sludge inlet, a sludge outlet, a slush outlet and a clean water outlet and wherein the sludge drying bed comprises a sludge inlet, a sludge outlet, a slush inlet and a clean water outlet, the sludge inlets of the sludge drying bed and centrifuge being connected to the sludge drainage line of the reactor thickener, the slush outlet of the centrifuge being connected to the slush inlet of the sludge drying bed.
According to the invention there is also provided a method of treating sludge, wherein the method is carried out in a sludge treatment plant comprising a reactor thickener and a sludge drying bed and wherein the reactor thickener comprises an inner reaction zone, an outer clean water zone and a hopper bottom settling zone, the inner reaction zone being open at the bottom thereof and wherein the method comprises treating the sludge in the inner reaction zone by agitating the sludge and dosing the sludge with a weighting agent and a pH control

agent to maintain the pH of the sludge in the reaction zone between 7.5 to 7.8, allowing the sludge particles to settle down at the hopper bottom settling zone of the reactor thickener and form a sludge blanket extending upto the bottom of the inner reaction zone and into the clean water zone, allowing the water in the reaction zone to percolate through the sludge blanket into the clean water zone and rise up in the clean water zone and flow out under the force of a head difference between the sludge in the reaction zone and water in the clean water zone, maintaining the thickness of the sludge blanket constant by stirring the sludge blanket and withdrawing the sludge in the sludge blanket at the hopper bottom settling zone of the reactor thickener at a controlled rate and treating the withdrawn sludge in the sludge drying bed to further separate water from the sludge.
According to an embodiment of the invention the method is carried out in a sludge treatment plant which further comprises a centrifuge and wherein part of the sludge from the reactor thickener is treated in the sludge drying bed and the remaining part of the sludge from the reactor thickener is treated in the centrifuge and wherein the slush from the centrifuge is also treated in the sludge drying bed to further separate water from the sludge.
According to the invention there is also provided a water treatment plant comprising the above sludge treatment plant, wherein the sludge outlets of the flocculation and sealing unit and filtration unit of the water treatment plant are connected to the sludge inlet of the reactor thickener and the clean water outlets of the reactor thickener and sludge drying bed and centrifuge, if any, are connected to the raw water inlet chamber of the water treatment plant.

According to the invention there is also provided a method of treating sludge generated in a water treatment plant comprising the above sludge treatment plant, wherein the method is carried out as described above.
The following is a detailed description of the invention with reference to the accompanying drawings, in which : .
Fig 1 is a block diagram of a sludge treatment plant according to an embodiment of the invention;
Fig 2 is a schematic plan view of the reactor thickener of the sludge treatment plant of Fig 1:
Fig 3 is a schematic cross sectional view of the reactor thickener of Fig 2;
Fig 4 is an isometric view of a flow channel of the reactor thickener of Fig 2; and
Fig 5 is a block diagram of a water treatment plant comprising the sludge treatment plant of Figs 1 to 4.
As illustrated in Figs 1 to 4 of the accompanying drawings, the sludge treatment plant 1 comprises a reactor thickener 2, a sludge drying bed 3 and a centrifuge 4. The reactor thickener 2 comprises a vessel 5 defining an inner reaction zone 6, an outer clean water zone 7 and a hopper or conical bottom settling zone 8. The inner reaction zone opens onto a sludge blanket 9 formed on the hopper bottom settling zone and extending into the clean water zone.

The reaction zone further comprises a sludge inlet 10, weighting agent dosing inlet 11 and a pH control agent dosing inlet 12. A plurality of spaced apart agitators 13 and a rotary scraper 14 are disposed in the reaction zone for rotation about vertical axes. The rotary scraper comprises a flat body 15 disposed underneath the sludge blanket and having a vertical shaft 16 at the centre thereof. The clean water zone opens at the top thereof into a launder 17 around the clean water zone. The launder has a clean water outlet 18. The hopper bottom settling zone is provided with a sludge drainage line 19 fitted with a controlled valve 20. The sludge drying bed has a sludge inlet 21 connected to the sludge drainage line 19 of the reactor thickener and a clean water outlet 22, a sludge outlet 23 and a slush inlet 24. The centrifuge comprises a sludge inlet 25 connected to the sludge drainage line of the reactor thickener, a sludge outlet 26, a clean water outlet 27 and a slush outlet 28 connected to the slush inlet 24 of the sludge drying bed. The clean water outlets 18, 23 and 26 of the reactor thickener. sludge drying bed and centrifuge respectively are connected to a common clean water carrier line 29. The clean water zone comprises a plurality of spaced apart flow channels 30 across the clean water zone. The flow channels communicate with the launder. The sidewalls of the flow channels are perforated (perforations marked 31).
Preferably the agitators 13 and rotary scraper 14 are driven by a variable speed or frequency drive mechanism. The drive mechanism has not been illustrated and described as such is not necessary for understanding the invention. The drive mechanism may be configured in known manner. Preferably the control valve is a telescopic valve. Preferably the weighting agent is polyelectrolyte and the pH control agent is lime (calcium oxide).

Sludge (not shown) is fed into the reaction zone (6) of the reactor thickener 2 via the sludge inlet 10 and dosed with a weighting agent and a pH control agent via the respective inlets 11 and 12. The pH of the sludge in the reaction zone is maintained between 7.5 to 7.8 with the pH control agent. The sludge in the reaction zone is also agitated with the agitators 13. The sludge particles are allowed to settle down at the hopper bottom settling zone 8 of the reactor thickener and form the sludge blanket 9. Water in the reaction zone is allowed to percolate through the sludge blanket into the clean water zone 7 and rise up in the clean water zone and flow into the launder 17 via the flow channels 30 through the perforations 31 in the sidewalls of the channels under the force of a head difference maintained between the sludge in the reaction zone and water in the clean water zone. The thickness of the blanket is maintained constant by stirring the sludge blanket with the rotary scraper 14 and withdrawing the sludge in the sludge blanket at the hopper bottom settling zone of the reactor thickener at a controlled rate by operating the control valve 20 in the drainage line 19. The hopper or conical bottom settling zone of the reactor thickener facilitates settlement of the sludge.
Part of the sludge being withdrawn from the reactor thickener is treated in the centrifuge to separate water from the sludge. The remaining part of the sludge from the reactor thickener and the slush from the centrifuge are fed into the sludge drying bed. Sludge and slush are treated in the sludge drying bed to further separate water from the sludge and slush. Water recovered in the sludge drying bed and centrifuge and the reactor thickener is collected via the common clean water carrier line 29 and reused. Final sludge from the sludge drying bed and centrifuge are disposed of. It is to be understood that as the sludge being drained out from the reactor thickener is in small lots or quantities, the entire sludge can be treated in the sludge drying bed. Therefore, the centrifuge is optional and the capital cost, energy

consumption and operational cost of the sludge treatment plant of the invention are correspondingly reduced.
The water treatment plant 32 as illustrated in Fig 5 of the accompanying drawings comprises a raw water inlet chamber 33, distribution chamber 34 connected to the raw water inlet chamber, a flash mixer unit 35 connected to the distribution chamber, a flocculation and settling unit 36 connected to the flash mixer, a filtration unit 37 connected to the flocculation and settling unit and a disinfection unit 38 connected to the filtration unit. Dosing inlets of the distribution chamber for chemicals like chlorine, lime and alum are marked 39, 40 and 41, respectively. Disinfectant dosing inlet of the disinfection unit is marked 42. The sludge outlets 43, 44 of the flocculation and settling unit and filtration unit rspectively are connected to the sludge inlet 10 of the reactor thickener 2 of the sludge treatment plant 1 of Figs 1 to 4. Common clean water carrier line 29 of the sludge treatment plant is connected to the raw water inlet chamber. 45 is another raw water inlet for the raw water inlet chamber for additional raw water supply. Raw water is treated in the water treatment plant of Fig 5 in the usual manner. Sludge generated in the flocculation and settling unit and filtration unit of the water treatment plant is treated in the sludge treatment plant 1 of Figs 1 to 4 as described earlier. The distribution chamber is optional and only a large water treatment plant may comprise the distribution chamber
The following experimental example is illustrative of the invention but not limitative of the scope thereof:

Example 1
A sludge treatment plant of Figs 1 to 4 comprising only the reactor thickener and sludge
drying bed and designed for a capacity of treating sludge of 6 MGD (million gallons per day)
was used in the experiment. The sludge was generated by a water treatment plant of capacity
100 MGD. There were 4 agitators and the agitators were operated at a speed of 225 RPM.
The rotary scraper was operated at a speed of 15 RPM. Polyelectrolyte was dosed at the rale
of 0.5 mg per litre. Lime was dosed at the rate of 3 mg per litre. The sludge was drained out
from the reactor thickener at the rate of 1339 cubic meters per day. Water recovered from the
sludge treatment plant was 26 millions liters per day (26 Mld) and quantum of sludge
produced by the sludge treatment plant was 290 m /day. The turbidity of water recovered
from the sludge treatment plant was about 50 NTU whereas raw water treated in the water
treatment plant had a turbidity of about 100 NTU. It is quite evident from this experiment
that the sludge treatment plant of the invention helps to recover considerable quantity of
water from the sludge which would have been otherwise wasted and that the quantum of
sludge to be finally disposed of also reduced substantially thereby correspondingly reducing
problems associated with sludge disposal and that the water recovered in the sludge treatment
plant was of a better quality. The sludge generated was stabilised.
A main advantage of the invention is that considerable quantity of water in the sludge is recovered and reused. As a result wastage of water is eliminated and the amount of sludge for disposal is substantially reduced and the sludge generated is stabilised thereby corresponding reducing problems associated with sludge disposal. As the sludge is being continuously

drained out from the reactor thickener in lots, the sludge lots can be treated in the sludge drying bed without the centrifuge. Therefore, the centrifuge is optional thereby correspondingly reducing investment cost, energy consumption and operational cost. According to the invention the sludge in the reaction zone of the reactor thickener is continuously agitated and dosed with a weighting agent and a pH control agent. Because of the agitation of the sludge in the reaction zone and because of the treatment of the sludge with weighting agent and because of the pH control of the sludge between 7.5 to 7.8. effective separation between the water and the solids in the sludge in the reaction zone takes place. The suspended particles in the sludge in the reaction zone agglomerate into scttable size particles to achieve better settlement. Dissolved metal hydroxides impurities in the sludge also precipitate and agglomerate.
While the water percolate through the sludge blanket, the sludge blanket effectively traps sludge particles which are generated in the reaction zone of the reactor. As the sludge blanket is continuously stirred with the rotary scraper consistency of the solids in the sludge blanket and thickness of the sludge blanket is maintained. Preferably the agitators and the rotary scraper are rotated with variable speed or frequency to prevent concentration or accumulation of solids at locations in the reaction zone of the reactor thickener and in the sludge blanket. Because of the agitation in the reaction zone, the weighting agent and pH control agent are well dispersed in the sludge in the reaction zone. This helps to agglomerate suspended solid particles in the reaction zone and settle the same. As a result of all this, effective separation between the water and solids takes place, agglomeration of the suspended and dissolved impurities takes place and settlement of the solid impurities takes place and the performance efficiency of the sludge treatment plant is improved.

As the clean water rises up in the clean water zone of the reactor thickener under the force of head difference between the sludge in the reaction zone of the reactor thickener and the clean water in the clean water zone of the reactor thickener, no additional energy input is required to force the clean water out of the launder of the reactor thickener. Further, as the sludge blanket thickness is maintained by continuously withdrawing sludge from the reactor thickener at a controlled rate, variations in the incoming sludge parameters like variations in the solid content or concentration of the sludge and resultant shock loadings on the sludge treatment plant do not affect the performance efficiency of the sludge treatment plant. The agitation rate of the sludge in the reaction zone of the reactor thickener and the stirring rate of the sludge blanket at the bottom of the hopper bottom settling zone of the reactor thickener and dosing of the weighting agent and pH control agent and withdrawal rate of the sludge from the reactor thickener are all selected and controlled as required depending upon the incoming sludge parameters. Because of this, the invention provides flexibility to handle incoming sludges of varying parameters and malfunctioning of the sludge treatment plant is avoided. Operational efficiency of the plant is thus maintained.
As a result of the effective separation between the solids and water in the reaction zone of the reactor thickener and the effective settlement of the solids in the sludge and the continuous withdrawal of the solids accumulated at the bottom of the reactor thickener, residence time for the sludge in the reactor thickener is reduced and performance efficiency of the plant is further improved.

The reactor thickener is small and compact as compared to a tube settler or settling tank. Because of the use of the reactor thickener in the place of a tube settler or settling tank, foot print area for occupation of the reactor thickener is reduced. As a result, capital cost and space requirement of the sludge treatment plant is considerably reduced. Being compact, capacity of the plant is also fully and optimally utilised.
The above embodiments of the invention are by way of examples and should not be construed and understood to be limiting the scope of the invention. The agitator and the rotary scraper can also be driven with a constant speed or frequency drive mechanism. The control valve need not be telescopic valve. Any other control valve can be used. Dosing chemicals in the reaction zone of the reactor thickener may include other chemicals also depending upon the composition or constitution of the sludge. Besides polyclectrolyte any other weighting agent can be used. Instead of lime any other pH control agent can be used. The bottom settling zone of the reactor thickener need not be hopper or conical shaped. Instead the bottom of the reactor thickener can be any other shape. The reactor thickener configuration and construction can be different. The flow channels are optional. Instead of flowing through the flow channels, the clean water may flow into the launder directly. The number of agitators can be different. Such variations of the invention including those discussed in the earlier part of the specification are obvious to those skilled in the art and are to be construed and understood to be within the scope of the invention.

We claim :
1) A sludge treatment plant comprising a reactor thickener and a sludge drying bed. wherein the reactor thickener comprises a vessel defining an inner reaction zone. an outer clean water zone and a hopper bottom settling zone, the inner reaction zone opening onto a sludge blanket formed on the hopper bottom settling zone and extending into the clean water zone, the reaction zone comprising a sludge inlet, weighting agent dosing inlet and a pH control agent dosing inlet, the reaction zone further comprising a plurality of spaced apart agitators and a rotary scraper disposed for rotation about vertical axes, the rotary scraper comprising a flat body disposed underneath the sludge blanket, the clean water zone opening at the top thereof into a launder around the clean water zone, the launder having a clean water outlet and the hopper bottom settling zone being provided with a sludge drainage line fitted with a control valve, the sludge drying bed having a sludge inlet connected to the sludge drainage line of the reactor thickener and a clean water outlet and a sludge outlet.
2) The sludge treatment plant as claimed in claim 1, which further comprises a centrifuge having a sludge inlet, a sludge outlet, a slush outlet and a clean water outlet and wherein the sludge drying bed comprises a sludge inlet, a sludge outlet, a slush inlet and a clean water outlet, the sludge inlets of the sludge drying bed and centrifuge being connected to the sludge drainage line of the reactor thickener, the slush outlet of the centrifuge being connected to the slush inlet of the sludge drying bed.

3) The sludge treatment plant as claimed in claim 1 or 2, wherein the clean water zone comprises a plurality of spaced apart flow channels across the clean water zone and communicating with the launder, the sidewalls of the channels being perforated,
4) The sludge treatment plant as claimed in any one of claims 1 to 3. wherein the agitators and the rotary scraper are driven by a variable speed or variable frequency drive mechanism.
5) The sludge treatment plant as claimed in any one of claims 1 to 4, wherein the control valve is a telescopic valve.
6) A method of treating sludge, wherein the method is carried out in a sludge treatment plant comprising a reactor thickener and a sludge drying bed and wherein the reactor thickener comprises an inner reaction zone, an outer clean water zone and a hopper bottom settling zone, the inner reaction zone being open at the bottom thereof and wherein the method comprises treating the sludge in the inner reaction zone by agitating the sludge and dosing the sludge with a weighting agent and a pH control agent to maintain the pH of the sludge in the reaction zone between 7.5 to 7.8, allowing the sludge particles to settle down at the hopper bottom settling zone of the reactor thickener and form a sludge blanket extending upto the bottom of the inner reaction zone and into the clean water zone, allowing the water in the reaction zone to percolate through the sludge blanket into the clean water zone and rise up in the clean water zone and flow out under the force of a head difference between the sludge in the reaction zone and water in the clean water zone, maintaining the thickness of the sludge blanket constant by stirring the sludge blanket and withdrawing the

sludge in the sludge blanket at the hopper bottom settling zone of the reactor thickener at a controlled rate and treating the withdrawn sludge in the sludge drying bed to further separate water from the sludge.
7) The method as claimed in claim 6, wherein the method is carried out in a sludge treatment plant which further comprises a centrifuge and wherein part of the sludge from the reactor thickener is treated in the sludge drying bed and the remaining pari of the sludge from the reactor thickener is treated in the centrifuge and wherein the slush from the centrifuge is also treated in the sludge drying bed to further separate water from the sludge.
8) The method as claimed in claim 6 or 7, wherein the sludge in the reaction zone and the sludge blanket at the hopper bottom settling zone are agitated and stirred respectively at variable speeds or frequencies
9) The method as claimed in any one of claims 6 to 8, wherein the weighting agent is polyelectrolyte and the pH control agent is lime (calcium oxide).
10) A water treatment plant comprising a sludge treatment plant as claimed in any one of claims 1 to 5, wherein the sludge outlets of the flocculation and settling unit and filtration unit of the water treatment plant are connected to the sludge inlet of the reactor thickener and the clean water outlets of the reactor thickener and sludge drying bed and centrifuge, if any, are connected to the raw water inlet chamber of the water treatment plant.

11) A method of treating sludge generated in a water treatment plant comprising the sludge treatment plant as claimed in any one of claims 1 to 5, wherein the sludge treatment is carried out in the sludge treatment plant as claimed in any one of claims 6 to 9.