FORM-2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2006
COMPLETE
Specification
(See Section 10 and Rule 13)
A WASTEWATER TREATMENT SYSTEM USING A BIOREACTOR AND A METHOD THEREOF
THERMAX LIMITED
an Indian Company
of D-13, MIDC Industrial Area, R.D. Aga Road,
Chinchwad, Pune - 19,
Maharashtra, India
The following specification particularly describes the invention and the manner in which
it is to be performed.

FIELD OF THE INVENTION
The present invention relates to wastewater treatment.
Particularly, the present invention relates to wastewater treatment using a
bioreactor.
BACKGROUND OF THE INVENTION & PRIOR ART
Extensive quantity of wastewater is generated everyday from residences, industries, institutes and commercial establishments. A treatment for wastewater is required to make it suitable for the purpose of recycling and reuse or disposal into the environment. Generally, wastewater generated from residences is directly disposed through the sewers, however, incase of industries and commercial establishments, the government regulations require the wastewater to be treated to a regulatory standard before it can be disposed of in the sewer.
Wastewater treatment mainly comprises three stages; a pre-treatment stage for removing materials that can be easily collected from the raw wastewater and disposed of, a secondary treatment stage for substantially reducing the organic content of wastewater and a tertiary treatment stage for further removing the organics and nutrients to enhance the quality of the effluent. Optionally, the effluent can be further treated in an effluent polishing stage that includes disinfection and filtering of the effluent.
Conventional wastewater treatment units require a high initial capital investment, operation and maintenance is difficult and costly and these units acquire a large foot-print area. Also, the conventional processes generate

extensive amount of sludge, disposal cost of which accounts to 60% of the operating cost. Most of the large-scale industries have a wastewater treatment unit of their own for treating the wastewater generated. However, in the case of small and medium scale industries and commercial establishments like hotels, hospitals, offices, educational institutions, manufacturing units, food processing units, husbandry and dairy farms; which generate less volume of wastewater with high organic content; treating the wastewater becomes highly expensive. Thus, there is a requirement for a system for wastewater treatment that is cost-effective, easy to operate, compact and produces less sludge.
Biological processes employing bioreactors are commonly used in such cases as they are economical and effective. These bioreactors are fixed-film treatment processes where active microorganisms grow as a film on the surface of a media filled within the reactor. In these processes, the wastewater is passed through the reactor, wherein the nutrients present in the wastewater are utilized by microorganisms that are present on the film. Treatment can be achieved aerobically or anaerobically. The various conventional bioreactors include trickling filters, fluidized bed reactors, rotating biological contactors, fixed bed reactors and moving bed reactors.
In a fixed bed reactor the media on which the biofilm containing active microorganisms is formed remains stationary during the process. An advantage of this process is the large surface area available for the growth of biofilm. However, in this process the reactor gets clogged due to sludge particles. In the case of moving bed reactors the media within the reactor is in an undefined mobile state. In the moving bed bioreactors there is no

clogging due to sludge. However, the degree of filling of media in these reactors has to be low in order to avoid the collisions between elements of the media; thus, the surface area available for the growth of biofilm is less.
Various attempts have been made to provide a compact system for wastewater treatment using a bioreactor provided with media that are maintained in fluidized or moving conditions. Some of these disclosures are given in the prior art below.
WO Patent No. 2007077298 discloses a water purification unit consisting of a rotary type bioreactor having a circular or elliptical cross-section tank filled with carrier elements. In the above cited document, the bioreactor is provided with aeration means disposed in supply passages which are arranged within a protective cover surrounding the tank partially. This arrangement of the aeration means provides a spinning motion to the carrier elements around the tank's longitudinal central axis where due to a centrifugal force the carrier elements will move along the edges of the tank wall forming an inactive or dead zone towards the longitudinal central axis of the bioreactor.
WO Patent No. 2009026686A1 discloses a wastewater treatment system having twin fluidized beds in the form of columns, where wastewater and solids coated with active microorganisms are continuously passed through a first anoxic/anaerobic bed and a second aerobic bed. Wastewater and solids attain an upward flow after entering the above system at separate inlets, both provided at the lower end of the first bed; this can result in a dead zone in the upper portion of the column. In the above disclosure, wastewater and

solids are continuously pumped between the two beds and the beds are to be maintained in a fluidized condition, so the energy input required by the system is high. In the above system, conduit means used to carry wastewater and solids between the two beds can get clogged due to sludge.
JP Patent No. 2004314062(A) discloses a method and apparatus for wastewater treatment using a fluidized bed bioreactor. The wastewater is first pretreated by flocculation and/or electrolysis followed by which it is saturated with oxygen by an oxygen dissolving device before passing through the bioreactor. The oxygen dissolving device is used to obtain high oxygen transfer efficiency, thus, increasing the organic matter degradation efficiency. However, the requirement of a pretreatment and oxygen dissolving device make the system expensive.
JP Patent No. 10211495 discloses a method for treating polluted water by using a cylindrical fluidized bed reactor filled with carrier media and provided with rotary blades located concentric with the central shaft of the reactor for providing a gentle uniform circulating motion to the carrier media. Aeration is provided by air diffusion plates provided at the lower part. The above disclosed apparatus cannot have a high degree of filling of the carrier media as there is a possibility of the carrier media colliding with the rotary blades and loosing the biofilm formed on the surface. Also, a biofilm might be formed on the surface of the rotating blades reducing their speed, this will result in decreased efficiency and increase in the demand of air.

In the prior art, it is seen that the existing fluidized, moving or rotating bed bioreactor systems are unable to provide complete mixing which results in the formation of inactive or dead zones. Formation of dead zones decreases the efficiency of the process and increases the demand for air. Thus, there is a requirement for a bioreactor that eliminates the formation of dead zones during operation. Also, the existing bioreactor systems have a multi-component assembly which makes the treatment process complex and costly. Another drawback of the existing bioreactor systems is reduced oxygen transfer efficiency which causes an increase in the demand of air adding to the operation cost. To eliminate this drawback some of the processes use additional techniques like membrane diffusers, pure oxygen purging and oxygen dissolving devices to increase the oxygen transfer efficiency; these enhancements add on to the initial and operating cost of the system. Thus, there is a need for a bioreactor system for wastewater treatment that is cost-effective, easy to operate and overcomes the drawbacks of the conventional and existing systems.
OBJECTS OF THE INVENTION
An object of this invention is to provide a system for organic wastewater treatment using a bioreactor.
Another object of this invention is to provide a system for organic wastewater treatment using a bioreactor which has no dead or inactive zones.
Yet another object of this invention is to provide a system for wastewater treatment that requires less initial investment.

Still another object of this invention is to provide a system for wastewater treatment that is economical, reduces the operation and maintenance cost and is easy to operate.
One more object of this invention is to provide a system for wastewater treatment that has higher oxygen transfer efficiency, thus, reduced aeration cost.
Still one more object of this invention is to provide a system for wastewater treatment that can be installed underground and may not occupy any space on the ground.
Yet one more object of this invention is to provide a system for wastewater treatment that is compact and uses small foot print area.
An additional object of this invention is to provide a system for wastewater treatment that reduces the volume of sludge generated.
Another additional object of this invention is to provide a system for wastewater treatment that requires less energy input.

SUMMARY OF THE INVENTION
In accordance with the present invention, a system for the treatment of organic wastewater is provided, said system comprising:
• a filtration unit adapted to receive raw organic wastewater and remove particles of size greater than 3 mm therefrom;
• a bioreactor, said bioreactor comprising:
i. a hollow operatively horizontal tubular body having an inlet at one end adapted to receive wastewater from said filtration unit and an outlet at the other end for discharging treated wastewater and sludge from within said tubular body;
ii. a plurality of perforations at or near the operative upper most region of the wall of said tubular body, said perforations linearly extending along the wall of said tubular body;
iii. a bed of polymeric media provided inside said tubular body, said polymeric media adapted to support the growth of active microorganisms;
iv. air injection means comprising:
■ at least one central air purging tube provided along the central longitudinal axis of said tubular body, said central tube containing linear orthogonally spaced apart sets of perforations;
■ a plurality of air purging elements provided within said tubular body, said purging elements containing linear perforations to purge air into said tubular body and

adapted to angularly displace said polymeric media; and ■ air supply means connected to said central tube and said purging elements to supply air; v. air venting means attached to said tubular body in communication with said linear perforations on said wall of said tubular body;
• a clarification unit adapted to receive discharge from said bioreactor, said clarification unit comprising a settling tank, a sludge discharge outlet and a treated wastewater discharge outlet.
Typically, in accordance with the present invention, an equalization tank adapted to receive the filtrate from said filtration unit is provided for storing the wastewater.
Preferably, in accordance with the present invention, chemicals are added to the wastewater in said equalization tank to adjust the pH in the range of pH 6.5 to pH 8.5.
In accordance with the present invention, said central tube helps in preventing the formation of any dead or inactive zones towards the centre of said tubular body by purging air at the central axis.
Preferably, in accordance with the present invention, said plurality of air purging elements are in the form of tubes located on the inner surface of the wall of said tubular body.

Typically, in accordance with the present invention, said plurality of air purging elements are fitted at the operative lower portion of said tubular body.
Additionally, in accordance with the present invention, if a cross-section is taken of said tubular body with said plurality of air purging elements fitted therein, said plurality of air purging elements preferably subtend an angle of 90° at the central axis of said tubular body.
Preferably, in accordance with the present invention, said plurality of air purging elements are perforated in a manner that the flow of air from said purging elements is tangential.
Additionally, in accordance with the present invention, the tangential purging of air angularly displaces said polymeric media in said tubular body to give it a revolving impetus about the central axis of said tubular body.
In accordance with the present invention, the degree of filling of the elements of said polymeric media in said tubular body is 25% to 80% of the volume of said tubular body.
Typically, in accordance with the present invention, the density of the elements of said polymeric media is slightly less than or equal to that of water.

Preferably, in accordance with the present invention, the elements of said polymeric media are spherical containing cavitations to obtain optimal rotation inside said tubular body.
Additionally, in accordance with the present invention, the spherical structure of the elements of said polymeric media causes the elements of said polymeric media to rotate while revolving around the central axis.
In accordance with the present invention, a method for treating organic wastewater is provided, said method comprising the following steps:
(i) filtering raw wastewater to remove particles of size greater
than 3 mm, by passing through a filtration unit; (ii) feeding filtered wastewater to a bioreactor consisting of a
hollow tubular body; (iii) supporting waste digesting microorganisms on a bed of
polymeric media contained inside said tubular body; (iv) aerating said bioreactor by air injecting means, said air
injecting means provide a rotating motion to said bed ; (v) discharging treated wastewater and sludge from a outlet from
said bioreactor; and (vi) separating treated wastewater and sludge in a clarification unit.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The invention will now be described with the help of the accompanying drawings, in which,

FIGURE la and FIGURE lb illustrates a schematic diagram of the side view and front view respectively of the bioreactor, in accordance with the present invention;
FIGURE 2 illustrates a cross-sectional view of the bioreactor showing the arrangement of the central air purging tube and air purging elements in the bioreactor and the direction of movement of the polymeric media and the air bubbles in the bioreactor, in accordance with present invention;
FIGURE 3 illustrates a schematic diagram of the air purging element of the bioreactor, in accordance with the present invention;
FIGURE 4a and FIGURE 4b illustrates a schematic diagram of the front view and top view respectively of the air vent, in accordance with the present invention;
FIGURE 5 illustrates the flow diagram of the method for treating organic wastewater, in accordance with the present invention;
FIGURE 6 illustrates a graph showing the performance of the wastewater treatment system of the present invention in terms of reduction in COD;
FIGURE 7 illustrates a graph showing the performance of the wastewater treatment system of the present invention in terms of reduction in BOD;
FIGURE 8 illustrates a graph showing the performance of the wastewater treatment system of the present invention in terms of reduction in TSS;

FIGURE 9 illustrates a graph showing the residence time distribution analysis for the system of the present invention comparing experimental and simulated data;
FIGURE 10 illustrates the Dissolved Oxygen (DO) profile in a conventional fluidized bed aerobic bioreactor;
FIGURE 11 illustrates the plot of Log (Cs - CT) Vs T for a conventional fluidized bed aerobic bioreactor;
FIGURE 12 illustrates the Dissolved Oxygen (DO) profile for the bioreactor of the system of the present invention; and
FIGURE 13 illustrates the plot of Log (Cs - CT) Vs T for the bioreactor of the system of the present invention.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The invention will now be described with reference to the accompanying drawings which do not limit the scope and ambit of the invention. The description provided is purely by way of example and illustration.
In accordance with a preferred embodiment of the present invention, FIGURE 1(a) and FIGURE 1(b) illustrates a schematic diagram of the bioreactor from the side view and the front view respectively, wherein the bioreactor is represented by the numeral 100. The bioreactor 100 has a tubular body 102 which defines a hollow 104. The tubular body 102 is

provided with a plurality of perforations 120. The plurality of perforations 120 is located along the length of the tubular body 102. The perforations 120 are located at or near the upper most region of the wall of the tubular body 102 and linearly extend along the wall of the tubular body 102. An air venting means 118 is provided to enclose the perforations 120. The tubular body 102 is provided with an inlet 124 and an outlet 126 at opposite ends of the tubular body 102. Wastewater is fed into the tubular body 102 through the inlet 124. The wastewater is treated in the tubular body 102 and the treated wastewater and sludge are discharged from the outlet 126. The bioreactor 100 is provided with air injection means. The air injection means comprises a central tube 106 and a plurality of air purging elements 110.
FIGURE 2 illustrates the cross-sectional view of the bioreactor 100 showing the arrangement of the central air purging tube 106 and the plurality of air purging elements 110. The central air purging tube 106 is provided along the central longitudinal axis of the tubular body 102. The central air purging tube 106 is provided with linearly located orthogonally spaced apart perforations 202 so that the air entering from a first air supply means 108 purges radially in all four directions in the central region of the hollow 104 of the tubular body 102. The air purged into the tubular body 102 through the central air purging tube 106 from the perforations 202 represented by direction arrows 204 helps in preventing the formation of any dead or inactive zones around the central axis of the tubular body 102.
FIGURE 3 illustrates a schematic diagram of the air purging element 110. The air purging elements 110 are typically in the form of tubes located inside the tubular body 102 such that the central longitudinal axis of the

tubular body 102 is parallel to the longitudinal axis of the air purging elements 110. Typically, the air purging elements 110 are fitted at the operative lower surface of the inner surface of the wall of the tubular body 102. The air purging elements 110 are provided with a plurality of perforations 208 along the length of the air purging elements 110. If a cross-section is taken of the tubular body 102 with the purging elements 110 fitted therein, the purging elements 110 preferably subtend an angle of 90° at the central axis of the tubular body 102. Air is purged through a second air supply means 112 into the tubular body 102 through the perforations 208 of the air purging elements 110. The air purged through the air purging elements 110 is adapted to be discharged tangentially as represented by the direction arrow 210 to cause the polymeric media 114 to revolve around the central axis of the tubular body 102. The quantity of air pumped in each of the air purging elements 110 can be equal or can be manipulated by controlling the flow of air using regulating valves which are attached to each of the air purging elements 110.
FIGURE 4(a) and FIGURE 4(b) illustrates a schematic diagram of the air venting means 118 from the front view and the top view respectively. The air venting means 118 is provided in communication with the linear perforations 120 provided on the wall of the tubular body 102. The air venting means 118 is provided with an air vent pipe 122 for discharging excess air and off-gases from the hollow 104 of the tubular body 102 into the atmosphere. The height of the air vent pipe 122 is adjusted such that the treated water from the bioreactor 100 does not flow out through the air vent pipe 122.

The bioreactor 100 is provided with polymeric media 114, shown in FIG. 1(a) and FIG. 1(b). The polymeric media 114 typically has a density slightly less than or equal to that of water such that during the operation of the bioreactor 100, the polymeric media 114 remains in a fluidized condition. The elements of the polymeric media 114 provide support and surface for the growth of active microorganisms. The polymeric media 114 further helps in creating turbulence between the wastewater and the air which helps in providing optimum diffusion of the air in the wastewater. The degree of filling of the elements of the polymeric media 114 is 25% to 80% of the volume of the tubular body 102. The elements of the polymeric media 114 used can be of different shapes but preferably spherical media containing cavitations is used to obtain optimal revolving and rotational motion. The spherical structure of the elements of the polymeric media 114 will cause the polymeric media to rotate while revolving around the central axis of the tubular body 102.
Raw wastewater is filtered through a filtration unit, shown in FIG. 5, to remove particles of size greater than 3mm from the raw wastewater. The filtered wastewater is sent to an equalization tank, shown in FIG. 5, for storage and/or pH adjustment. From the equalization tank, shown in FIG. 5, the wastewater is pumped into the bioreactor 100 at a predetermined rate through the inlet 124. The operation of the bioreactor 100 containing the polymeric media 114 is initiated by continuously recycling filtered wastewater from the filtration unit through the bioreactor 100 to obtain a stabilized growth of active microorganisms on the surface of the polymeric media 114 contained in the bioreactor 100. Air is purged through the bioreactor 100 through the central air purging tube 106 and the air purging

elements 110. The recycling of wastewater is continued until the treated wastewater obtained at the outlet 126 of the tubular body 102 contains 150 ppm to 300 ppm of sludge. After obtaining 150 ppm to 300 ppm of sludge in the treated wastewater, the recycling of wastewater is stopped and a continuous treatment process is started wherein the wastewater is continuously fed into the bioreactor 100 through the inlet 124 and discharged from the bioreactor 100 through the outlet 126.
In the treatment process, shown in FIG. 5, the wastewater from the equalization tank is continuously supplied to the bioreactor 100 through the inlet 124. The air purged tangentially from the air purging elements 110 displaces the wastewater and the polymeric media 114 supporting the active microorganisms in the tubular body 102 giving the wastewater and the polymeric media 114 a unidirectional revolving impetus. The unidirectional impetus given to the polymeric media 114 eliminates collision of the elements of the polymeric media 114 with each other, thus preventing wastage of energy of the purged air, as compared to a conventional moving bed type biological reactor. The central air purging tube 106 purges air in all directions in the central region of the hollow 104 of the tubular body 102 and thus prevents formation of dead or inactive zones around the central region of the hollow 104 of the tubular body 102.
The air bubbles leaving the air purging elements 110 of the air injection means while moving in the upward direction collide with the polymeric media 114 and as a result move the polymeric media 114 and split the air bubbles into smaller bubbles 116. The smaller air bubbles 116 attain a revolving motion along with the polymeric media 114 in the tubular body

102 for a longer duration and thus provide effective oxygen transfer. When air resides in the bioreactor 100 for a longer duration, more oxygen is diffused in the wastewater. This helps in enhancing the growth process of the active microorganisms which results in the degradation of more organic matter and consequently improves the treatment process. Again, when air resides in the bioreactor 100 for a longer duration, the demand of air is reduced and consequently the operating costs are reduced as compared to a conventional aerobic wastewater treatment processes. After completion of the process, treated wastewater and sludge are discharged from the bioreactor 100 through the outlet 126 and is transferred to a clarification unit, shown in FIG. 5, for separation of the treated wastewater and sludge.
The sludge settles at the bottom of the clarification unit, shown in FIG. 5, and is discharged from a sludge discharge outlet while the treated effluent is discharged from the clarification unit, shown in FIG. 5, from a treated wastewater discharge outlet and is stored for end applications. The final treated effluent obtained using the method of the present invention consists of 20 ppm to 30 ppm of sludge. Therefore, the final treated effluent is suitable for reuse in gardening, washing, cleaning and landscaping. Post treatment can be provided to further purify the final treated effluent. The final treated effluent can be passed through a chlorine contact tank for disinfection. The disinfected water can be further purified by passing through a dual-media sand filter and activated carbon bed.

EXPERIMENTAL DATA
The wastewater treatment system of the present invention was used in a sewage treatment plant for treating municipal sewage of capacity 10 m3/d. Inlet COD and inlet BOD of the municipal sewage treated using the system ranged from 400-550 mg/1 and 150-220 mg/1, respectively. The treated effluent was discharged along with sludge and sent to a clarification unit. The final treated effluent COD and BOD was 60-80 mg/1 and 19-28 mg/1, respectively. Thus, it was observed that by using the system of the present inventions COD and BOD could be reduced by 85% and 88 %, respectively. The results also showed that the system of the present invention can be effectively used in significantly reducing the Total Dissolved Organic Solids (TDOS), Total Suspended Solids (TSS), Total Kjeldhal Nitrogen (TKN) and Total Phosphates (TP) of the wastewater.
TRIAL RESULTS
A. Performance Study
TABLE 1: Biological treatment performance of the wastewater treatment system of the present invention, having a flow capacity of 10 m3/d.

Parameters Before Treatment After treatment % Reduction
PH 7.1 -7.5 7.3 - 7.9 -
COD (mg/L) 156-506 27-80 84
BOD (mg/L) 87-179 19-28 84
TSS (mg/L) 78- 192 20-30 84
Ammoniacal Nitrogen- N (mg/L) 12-27 3-8 71
Phosphate(mg/L) 14-18 6-8 66

From TABLE 1, it is observed that by using the system of the present invention, the BOD, COD and TSS is reduced by 84% while the ammoniacal nitrogen and phosphates is reduced by 71 % and 66%, respectively.
TABLE 2: Performance of the system of the present invention, in terms of reduction in COD.

Sample No. Date of Sample Flow (m3/day) Inlet COD (mg/Lit) Outlet COD
(nig/Lit.)
1 02/06/09 10 203 64
2 11/06/09 10 373 72
3 12/06/09 10 286 80
4 14/06/2009 10 290 43
5 16/06/2009 10 224 45
6 19/06/2009 10 180 27
7 20/06/2009 10 464 75
8 21/06/2009 10 360 71
9 22/06/2009 10 506 62
10 25/06/2009 10 387 79
11 26/06/2009 10 392 62
12 18/07/2009 10 413 67
13 21/07/2009 10 349 63
14 23/07/2009 10 247 54
15 24/07/2009 10 238 58
16 27/07/2009 10 204 71
17 29/07/2009 10 227 59
18 30/07/2009 10 207 43
19 31/07/2009 10 330 60
20 04/08/09 10 318 53
21 07/08/09 10 425 77
22 18/08/2009 10 279 53
23 20/08/2009 10 162 28
24 24/08/2009 10 156 38
25 25/08/2009 10 160 30
26 27/08/2009 10 178 50
27 28/08/2009 10 336 44
28 02/09/09 10 320 78
29 07/09/09 10 381 76
30 14/09/2009 10 369 69
31 16/09/2009 10 327 70
32 25/09/2009 10 312 46
33 17/10/2009 10 291 51
34 04/11/09 10 253 76

From TABLE 2, it is observed that by using the system of the present invention, a substantial COD reduction can be achieved. FIGURE 6 shows a graphical representation of the performance of the system of the present invention in terms of the reduction in COD.
TABLE 3: Performance of the system of the present invention, in terms of reduction in BOD and TSS.

Sample No. Date of Sample Flow (m3/day) Inlet
BOD
(mg/Lit.) Outlet
BOD
(mg/Lit) Inlet TSS
(mg/Lit.) Outlet
TSS
(rag/Lit.)
1 02/06/09 10 117 21 96 24
2 21/06/2009 10 156 24 192 30
3 30/07/2009 10 122 19 92 21
4 24/08/2009 10 87 20 78 20
5 7/9/2009 10 179 28 164 26
6 4/11/2009 10 136 23 106 23
From TABLE 3, it is observed that by using the system of present invention the BOD and TSS in the effluent produced is substantial less. FIGURE 7 and FIGURE 8 show a graphical representation of the performance of the system of present invention in terms of reduction in BOD and TSS, respectively. From the above results, it can be inferred that by using the system of the present invention, the COD, BOD, and TSS is reduced well within the government disposal limits.
B. Hydrodynamic Study
Residence time distribution (RTD) analysis is very useful to access the design of the continuously operating chemical process equipment and optimize their operating parameters. Radiotracer techniques are commonly used for measurement of RTD for flowing process material in pilot as well

as full-scale industrial systems, to determine flow parameters such as mean residence time (MRT), bypassing, extent of dead volume, and degree of mixing. Herein is discussed, radiotracer investigations carried out for the measurements and analysis of RTD of wastewater in the system of the present invention.
A series of radiotracer experiments were carried out to measure the residence time distribution (RTD) of the wastewater in the system of the present invention and evaluate its hydrodynamic performance.
The measured RTD data was simulated using a tanks-in-series model, where FIGURE 9 shows the graphical representation of the RTD analysis for the system of the present invention, comparing the experimental and model simulated RTD's, for best fit values of the model parameters. From FIGURE 9, it is clear that the experimental and simulated data (for MRTs) are in agreement with each other. The results of simulation (tank number, N) indicate that the reactor behaves as a continuously stirred tank reactor or ideal mixer at all the operating conditions used in the study.
From the RTD experiments carried out on the bioreactor (refer FIG. 9), it can be concluded that:
■ No bypassing/short-circuiting and any other flow abnormality was observed in the bioreactor;
■ Mean residence times (MRT's) have been determined at different operating conditions and were found to be marginally higher than the theoretical mean residence times. This could be due to presence of small stagnant volume inside the bioreactor, probably inside the packing elements;

■ Tanks-in-series model was found suitable to describe the flow behavior of the bioreactor and the results of the model simulations indicated that the bioreactor behaved as an ideal stirred tank reactor (tank number, N=l);
■ The flow pattern or dynamics of wastewater was not affected by varying air and liquid air flow rates. Therefore, a combination of air flow of 7 m /h and liquid flow rate of 12.5 m /day are the optimized conditions to operate the reactor.
■ The hydrodynamic behavior of the bioreactor was found to be as per the design criteria and hence the design of the bioreactor was validated. The results of the RTD analysis obtained in present pilot-scale system could be used to scale-up the process; and
■ Radiotracer technique was successfully applied to investigate the mixing characteristics of wastewater, optimize the operating conditions and validate the design of the bioreactor.
C. Oxygen Transfer Rate Study
Oxygen transfer or aeration plays an important role in biological wastewater treatment processes. Many different types of aeration systems have been developed over the years to improve the energy efficiency of oxygen transfer processes. A comparative evaluation on oxygen transfer efficiency of conventional fluidized bed bioreactor and the bioreactor of the system of the present invention was attempted.
A conventional fluidized bed aerobic bioreactor in which air is purged at the bottom leading to random fluidization of the packing material is fabricated in such a way that the working volume and water depth in the bioreactor will

be identical with the bioreactor of the present invention. The packing volume in both the bioreactors (25 % V/V) is kept constant and oxygen transfer rate experiments were conducted by purging equal amount of air (11 m /hr) in both the bioreactors.
Oxygen transfer rate and efficiency in the conventional fluidized bed aerobic bioreactor:
FIGURE 10 illustrates the Dissolved Oxygen (DO) profile in the bioreactor at 11 m /hr air flow rate and 25 °C temperature.
Oxygen transfer rate and Oxygen transfer efficiency is calculated at 11 m3/hr air flow rate and is shown in TABLE 4, where
♦ DO is Dissolved Oxygen, (mg/L);
♦ Cs is steady state Dissolved Oxygen saturation concentration at 25 °C, (mg/L);
♦ CT is Dissolved Oxygen concentration at time T, (mg/L);
♦ KLA is volumetric mass transfer coefficient, (1/hr);
♦ OTR is oxygen transfer rate, (kg/hr); and
♦ OTE is oxygen transfer efficiency.
KLA is the slope of plot Log (Cs - CT) Vs T (shown in FIGURE 11) and determined as follows.

TABLE 4: Oxygen transfer rate (OTR) and oxygen transfer efficiency (OTE) for conventional fluidized bed aerobic bioreactor.

Time (Mins.) DO
(mg/1) Cs
(mg/l) CS-CT
(mg/1) Log(Cs-CT) KLA
(1/hr) OTR
(kg/hr) OTE,
%
0 0 8.2 8.2 2.1041342 2.01 0.009938646 0.370845
5 0.8 8.2 7.4 2.00148

10 1.9 8.2 6.3 1.8405497

15 3.1 8.2 5.1 1.6292406

20 3.9 8.2 4.3 1.458615

25 4.5 8.2 3.7 1.3083328

30 5.1 8.2 3.1 1.1314021

Oxygen transfer rate and efficiency in the bioreactor of the system of the present invention:
FIGURE 12 illustrates the Dissolved Oxygen (DO) profile in the bioreactor of the present invention at 11 m3/hr air flow rate and 25 °C temperature. KLA is the slope of the plot Log (Cs - CT) Vs T (shown in FIGURE 13) and determined as follows.
TABLE 5: Oxygen transfer rate (OTR) and oxygen transfer efficiency (OTE) for the bioreactor of the system of the present invention.

Time
(Mins.) DO
(mg/1) Cs
(mg/1) CS-CT
(mg/I) Log (Cs -CT) (1/hr) OTR
(kg/hr) OTE,
%
0 0 8.2 8.2 2.1041342 4.452 0.022013359
5 2.7 8.2 5.5 1.7047481

0.82 J 394
10 4.5 8.2 3.7 1.3083328

15 5.5 8.2 2.7 0.9932518

20 6A 8.2 1.8 0.5877867

25 1 8.2 1.2 0.1823216

30 7.3 8.2 0.9 -0.105361

From the above oxygen transfer rate studies, it is observed that the DO profile of both the bioreactors indicates that the oxygen transfer rate is higher in the bioreactor of the present invention in comparison to the

bioreactor of the conventional system. Also, the higher value of volumetric mass transfer coefficients in the bioreactor of present invention indicates higher oxygen transfer efficiency than the conventional bioreactor. It is known that a greater oxygen transfer rate and oxygen transfer efficiency aids in reducing the aeration costs of the bioreactor. Therefore, it can be said that the bioreactor of the present invention reduces the operating costs of the treatment system in comparison to the conventional bioreactors.
TECHNICAL ADVANCEMENT
A system for organic wastewater treatment using a bioreactor is provided, as described in this invention has several technical advantages including but not limited to the realization of:
• the system for wastewater treatment using a bioreactor that has no dead or inactive zones;
• the system for wastewater treatment that requires less initial investment;
• the system for wastewater treatment that is economical, reduces the operation and maintenance cost and is easy to operate;
• the system for wastewater treatment that has higher oxygen transfer efficiency, thus, reduced aeration cost;
• the system for wastewater treatment that can be installed underground and may not occupy any space on the ground;
• the system for wastewater treatment that is compact and uses small foot print area;
• the system for wastewater treatment that reduces the volume of sludge generated; and

• the system for wastewater treatment that requires less energy input.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the invention, unless there is a statement in the specification specific to the contrary.
In view of the wide variety of embodiments to which the principles of the present invention can be applied, it should be understood that the illustrated embodiments are exemplary only. While considerable emphasis has been placed herein on the particular features of this invention, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principle of the invention. These and other modifications in the nature of the invention or the preferred embodiments will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

We claim:
1) A system for the treatment of organic wastewater, said system comprising:
• a filtration unit adapted to receive raw organic wastewater and remove particles of size greater than 3 mm therefrom;
• a bioreactor, said bioreactor comprising:
i. a hollow operativeiy horizontal tubular body having an inlet at one end adapted to receive wastewater from said filtration unit and an outlet at the other end for discharging treated wastewater and sludge from within said tubular body; ii. a plurality of perforations at or near the operative upper most region of the wall of said tubular body, said perforations linearly extending along the wall of said tubular body;
iii. a bed of polymeric media provided inside said tubular body, said polymeric media adapted to support the growth of active microorganisms;
iv. air injection means comprising:
■ at least one central air purging tube provided along the central longitudinal axis of said tubular body, said central tube containing linear orthogonally spaced apart sets of perforations;
■ a plurality of air purging elements provided within said tubular body, said purging elements containing

linear perforations to purge air into said tubular
body and adapted to angularly displace said
polymeric media; and ■ air supply means connected to said central tube and
said purging elements to supply air; v. air venting means attached to said tubular body in communication with said linear perforations on said wall of said tubular body;
• a clarification unit adapted to receive discharge from said bioreactor, said clarification unit comprising a settling tank, a sludge discharge outlet and a treated wastewater discharge outlet.
2) The system as claimed in claim 1, wherein an equalization tank adapted to receive the filtrate from said filtration unit is provided for storing the wastewater.
3) The system as claimed in claim 2, wherein chemicals are added to the wastewater in said equalization tank to adjust the pH in the range of pH6.5to pH8.5.
4) The system as claimed in claim 1, wherein said central tube helps in preventing the formation of any dead or inactive zones towards the centre of said tubular body by purging air at the central axis.

5) The system as claimed in claim 1, wherein said plurality of air purging elements are in the form of tubes located on the inner surface of the wall of said tubular body.
6) The system as claimed in claim 1, wherein said plurality of air purging elements are fitted at the operative lower portion of said tubular body.
7) The system as claimed in claim 1, wherein if a cross-section is taken of said tubular body with said plurality of air purging elements fitted therein, said plurality of air purging elements preferably subtend an angle of 90° at the central axis of said tubular body.
8) The system as claimed in claim 1, wherein said plurality of air purging elements are perforated in a manner that the flow of air from said purging elements is tangential.
9) The system as claimed in claim 8, wherein the tangential purging of air angularly displaces said polymeric media in said tubular body to give it a revolving impetus about the central axis of said tubular body.
10) The system as claimed in claim 1, wherein the degree of filling of the elements of said polymeric media in said tubular body is 25% to 80% of the volume of said tubular body.
11) The system as claimed in claim 1, wherein the density of the elements of said polymeric media is slightly less than or equal to that of water.

12) The system as claimed in claim 1, wherein the elements of said polymeric media are spherical containing cavitations to obtain optimal rotation inside said tubular body.
13) The system as claimed in claim 12, wherein the spherical structure of the elements of said polymeric media causes the elements of said polymeric media to rotate while revolving around the central axis.
14) A method for treating organic wastewater, said method comprising the following steps:
(i) filtering raw wastewater to remove particles of size greater
than 3mm, by passing through a filtration unit; (ii) feeding filtered wastewater to a bioreactor consisting of a
hollow tubular body; (iii) supporting waste digesting microorganisms on a bed of
polymeric media contained inside said tubular body; (iv) aerating said bioreactor by air injecting means, said air
injecting means provide a rotating motion to said bed ; (v) discharging treated wastewater and sludge from a outlet from
said bioreactor; and (vi) separating treated wastewater and sludge in a clarification unit.