Title of Invention

"AN IMPROVED TREATMENT PLANT FOR TEXTILE WASTEWATERS AND AN IMPROVED PROCESS THEREOF"

Abstract An improved treatment plant for textile wastewaters, which comprises a screen chamber (25) for removing particles and floating bodies above 50 mm diameter, having wastewater inlet (24), characterized in that the outlet of the said screen chamber being connected through a grit chamber (26) so as to re me inorganic silt having specific gravity ≥2.65, and a conventional parshall flume (27) so as to regulate and measure wastewater flow, to the inlet (44) of an equalisation basin (28) having a plurality of improved high speed floating aerators (49) and for providing a constant wastewater level of 0.5 to 1.0 m below the inlet and retention time of 5 to 7 hours, the outlet of the said equalisation basin (28) being connected to a flash mixer (29) being provided with separate dosing tanks (30,31,32) of ferrous sulphate (30), polyelectrolyte (31) and lime (32) for neutralising and coagulating the wastewater. the outlet of said mixer (29) being connected to a centre feed radial distribution system (34) of a circular clariflocculator (33) so as to provide retention time of 4 to 6 hours and having a separated clarification zone (36), sludge withdrawal outlet (61), and peripheral outlet (59), the said sludge outlet (61) being connected (42) to sludge drying beds (40) having an outlet for filtrate(43) connected to the inlet of equalization basin (28), the said peripheral outlet (59) being connected in parallel to a plurality of bays of aeration tank (36) having a plurality of improved high speed floating aerators (65), the output of the said aeration tank (36) being connected to a secondary clarifier (37) so as to provide retention time of 3 to 5 hours and having a sludge withdrawal outlet (85), a peripheral outlet (84) and treated effluent outlet (41), the said sludge outlet (85) being connected to the said sludge drying beds (40) and the peripheral outlet (84) being connected (38) to the inlet of aeration tank (36)
Full Text The present invention relates to an improved treatment plant for textile wastewaters and an improved process thereof.
The improved equipment (treatment plant) and process for treatment of textile
wastewaters of the present invention enables treatment of wastewaters containing high
total dissolved solids (TDS) in the range of 10,000 to 20,000 mg/l, and provides
improved resistance to hydraulic and organic shock loads incorporating, process of
equalization in an equalization basin with reduced retention time, neutralization process
comprising of a flash mixer for coagulation and neutralisation, physico-chemical process
comprising a clariflocculator with increased retention time for efficient suspended solids
(SS) separation and reduction in chemical oxygen demand (COD), biological aerobic
'process, comprising of an aeration tank and a secondary clarifier for efficient separation
of suspended solids and the reduction of biochemical oxygen demand (BOD), by
minimizing the total treatment time by 12 hours for treatment.

A conventional treatment plant for textile wastewaters as depicted in figure 1 of
the drawings accompanying this specification comprises of the processes of screen removal (1), grit removal (2), equalization (3), neutralization, comprising of lime (4) and acid (5) dosing tanks, chemical mixing tanks (6), neutralization tank (7) and sludge drying beds (8), physico-chemical process consisting of flash mixer (9), lime (10), ferrous sulphate (11), polyelectrolyte (12) and a clariflocculator (13) with flocculation zone (14) and clarification zone (15) and aerobic biological process consisting of an aeration tank (16) and a secondary clarifier (17). Treated effluent (18) is discharged either onto land or into surface water. Activated sludge is recycled (19) to the inlet of aeration tank (16) and excess biological sludge (20) and chemical sludge (21) are sent to drying beds (22) and the filtrate (23) from drying beds (8) and (22) is sent to equalization basin (3). Additional units that are essentially required in conventional process have been highlighted in figure 1. In conventional process, the total time required for treatment is about 50 hours and a separate unit is essentially required for wastewater neutralization, thus increases the cost of treatment.
Screening is the process wherein a screen chamber is used, to remove large floating bodies and particles above 50 mm diameter to prevent damage of pumps, whereas in grit removal process, inorganic sand and silt having specific gravity 2.65 and

above are removed and thus wear and tear of impellers of aerators and pumps are avoided.
The function of equalization process is to dampen the wide variation in wastewater characteristics and making it uniform for further treatment in physico-chemical process. Conventionally, wastewater in equalization process is retained for about 16 to 24 hours for this purpose.
Reference may be made to David H.F. Liu and B'ela G. Liptak, Environmental Engg. Handbook, Second Edition, 1996, wherein the process of equalization levels out operation parameters such as flow, pollutant levels, and temperature over a time frame, "normally 24 hours" minimizing the effects of these parameters in the downstream treatment. Reference may be made to Wastewater Engineering: Treatment, Disposal, Reuse, third edition, Metcalf and Eddy Inc. 1995, wherein a conventional equalization process comprising of a basin and made up of earthen or lined material has normally a trapezoidal cross section. In conventional equalization process, free board required depends on the surface area of the basin and local wind conditions, and a concrete pad is essentially required at the bottom to prevent the erosion. The disadvantages of conventional equalization process are:
i) Prevention of wind induced erosion in the upper portion of the basin ii) Prevention of embankment failure by suitable drainage in high groundwater
zones and iii) To attend to the problem of floatation due to large volume of the basin.
Neutralization is the process wherein the pH of wastewater is adjusted in the range of 7-8.5, which is ideal for application of most the coagulants and microbial activity. In conventional treatment plant, neutralization process consisting of chemical dosing and mixing tanks, neutralization tank and sludge drying beds are essentially provided. Following are the drawbacks of neutralization process provided in conventional treatment plant:
i) Additional units for chemical storage and dosing are required ii) Additional units for chemical mixing and sludge drying are required iii) Cost and time required for treatment are increased

iv) Large quantity of sludge is produced and poses problems in disposal.
In conventional physico-chemical process, comprising of a clariflocculator wherein colloidal and fine suspended solids and COD and to some extent BOD are removed from the wastewater. Conventional physico-chemical process comprising of a clariflocculator has certain disadvantages from the standpoint of efficiency of separation of fine suspended solids and reduction in chemical oxygen demand. It also produces sludge, having moisture content 98-99% and requires large units for sludge dewatering and handling. Reference may be made to Manual on Sewerage and Sewage Treatment, Second Edition, 1993: Central Public Health and Environmental Engineering Organization, wherein a conventional physico-chemical process comprising of a clariflocculator has expected efficiencies for reduction of suspended solids (SS), COD and BOD of the order of 40 to 60%, 30 to 50% and 20 to 40%, respectively. These efficiencies correspond to design values for retention time of 2 to 2.5 hrs, side water depth (SWD) 3.5 to 4.5 m, and average and peak overflow rate 25 to 35 and 50 to 60, m3/m2.d respectively, With the said design values, a clariflocculator of conventional physico-chemical process is often associated with the problem of reduction of fine SS, BOD and COD to the expected efficiencies, and is not capable of withstanding shock loads prevalent in large capacity textile wastewater treatment plants.
Reference may be made to Manual of Practice, Wastewater Treatment Plant Design, Water Pollution Control Federation; 1977 wherein short term flow variations resulting from a constant speed pump cycling on and off cause pulsating turbulence in the clarification zone. Turbulence in the clarification zone of a clarifier is also a cause of reduced sedimentation efficiency.
Of the biological means of treating textile wastes, trickling filtration, activated sludge process, and dispersed growth aeration have been found most successful. Reference may be made to Liquid Waste of Industry; Theories, Practices and Treatment: N.L. Nemerow, 1971, wherein, trickling filter is advantageous from the standpoint of flexibility, lower operating cost and capability of handling shock loads, but has certain disadvantages. Reference may be made to The Treatment of Industrial Waste, Edmund B. Besselievre, P.E. 1969 wherein loss of head necessary to operate

the revolving distributors (usually 1.0 to 17m) above the centerline of the distribution arms, Ventilation duct for the underlain system, Odor and fly nuisance in the intermittent operation, final sedimentation units to collect the bacterial slime periodically unloaded from the bed media.
Activated sludge process gives greater BOD and suspended solids reduction, but has following disadvantages. Reference may be made to The Treatment of Industrial Waste: Edmund B. Besselievre, P.E. 1969 wherein high cost of operation and maintenance is involved, difficulty of dewatering sludge, slow recovery from damage to the activated culture by shock loads, large units are required to provide long retaintion time; usually 12 to 48 hours and requires highly qualified supervision. Reference may be made to Environmental Engineer's handbook, 2nd Edition, David H. F. Liu and B'ela G. Lipta'K 1996, wherein the conventional activated sludge process is susceptible to shock and toxic loading conditions since longitudinal mixing is absent in aeration tanks.
The conventional activated sludge process in practice for textile wastewater essentially employs:
(I) A conventional plug flow aeration tank wherein the particles retain their identity
and remain in the tank for a time equal to theoretical retention time. This type of
flow is approximated in long tanks with high length to width ratio. Reference may
be made to Wastewater Engineering: Treatment, Disposal, Reuse, third edition,
Metcalf and Eddy Inc. 1995, wherein the conventional plug flow aeration tank is
susceptible to shock loads.
(II) A conventional completely mixed continuous flow aeration tank (square and/or
circular) wherein the organic load and the oxygen demand in the aeration tank
are uniform throughout the tank. Reference may be made to Wastewater
Engineering: Treatment, Disposal, Reuse, third edition, Metcalf and Eddy Inc.
1995, wherein the BOD removal efficiency in completely mixed continuous flow
aeration tank with high rate aeration is 75-90%.
Dispersed growth aeration takes a minimum of operation and maintenance and does away with the sludge problem. However, BOD reduction is low as compared to activated sludge treatment.

The function of secondary clarification is to remove BOD and SS, which can not be removed by the physico-chemical process. Reference may be made to: Manual on Sewerage and Sewage Treatment, Second Edition, 1993; Central Public Health and Environmental Engineering Organization wherein the design values adopted for conventional secondary clarified process for retention time is 1.5 to 2.0 hours, depth 3.5 to 4.5 meter and overflow rate 8 to 15 (Average), 25 to 35 (Peak) m3/m2.d and solids loading rate 25 to 120 (Average), 170 (Peak) Kg/m2.d. With the said design values a conventional secondary clarifier is often associated with the problem of separation of suspended solids and BOD reduction to the extent to meet the effluent standards adopted for discharge of treated effluent either onto land or into water body.
Effluent from secondary clarification is some times directly discharged for disposal onto land or into stream without giving tertiary treatment, hence it is very essential to remove the SS and reduce BOD to the extent of meeting the effluent standards.
Reference may be made to "Process for treating waste water" U.S. Patent No. 4,200,520 dated April 29, 1980, wherein waste water from a textile plant and other manufacturing process is purified. The raw waste water comprising bleach & rinse waste and dye & salt waste are input to a balancing tank which is intended to provide uniform waste and to eliminate surges. However, the suitable hydraulic retention time (HRT) to ensure a uniform waste composition has not been described.
The waste water having temperature 60 to 82°C (140 to 180°F) is passed through heat exchanger before going to composite tank. In the composite tank, the waste is treated with a reducing agent such as sodium bisulfite, introduced to neutralize any excess hydrogen peroxide. The waste water is then pumped to a flash mixer, wherein it is treated with traditional flocculants and lime is concurrently added to maintain pH of approximately 8-9.5. In the aforerefered process, the pH range that can be neutralized in flash mixer has not been clearly addressed, however the process of neutralisation in flash mixer for wide range of pH has been clearly described in this invention.

After flash mixer, waste is pumped to a flocculator where it is allowed to flocculate for approximately 30 minutes. The liquid is then pumped to a clarifier wherein sludge settles at the bottom and clear supernatant is withdrawn from the top. The settled sludge from clarifier is pumped to vacuum filters, which add to the cost of treatment and require attendance towards operation & maintenance, whereas the same can be avoided using drying beds which treats sludges naturally, especially in tropical countries like India. The filtrate from vacuum filters is combined with clarified effluent in surge tank, that may impart, the quality of clarified effluent whereas the filtrate obtained from drying beds is mixed with the equalized waste water as described in this invention. The process of flocculation & clarification are practiced independently hence additional pumping of waste water is required. Further, no suitable hydraulic retention time (HRT) for clarification of supernatant as well as thickening of sludge is described. Hence, the efficiency of clarifier can not be obtained. In the above process, waste water is pumped through all the stages, like from flash mixer to flocculator and then to clarifier however, the wastewater is conveyed by using gravity flow as described in this invention which in turn makes the treatment system less energy intesive. The clear supernatant from clarifier is pumped to a surge tank, intended for temporary retention. No suitable HRT for surge tank is described herein. Provision of a surge tank after clarifier clearly indicates that the following sand filter can not sustain frequent variation in hydraulic & organics shock loads. Waste water from surge tank is pumped to sand filter, wherein residual SS are removed and provision is made for back wash of sand filter. The back wash discharge is caused to pass to a waste storage balancing tank, to be combined with raw textile plant effluent for further treatment. This may introduce additional turbidity and suspended solids in the raw wastewater.
The filtrate from sand filter is neutralized to a pH range of 5.0 to 6.0 using acid such as sulphuric acid and a water softening agent such as sodium hexametaphosphate is then added, before being passed through reverse osmosis membrane. The above process requires two stage neutralization of waste water, and the treated effluent has pH 5.4, which can not be discharged directly on inland surface water or on to land.

the performance of the treatment process described by way of example indicates that the process can be effectively used to treat waste water having total suspended solids 156 mg/L, chemical oxygen demand 795 mg/L, biochemical oxygen demand 310 mg/l, total dissolved solids 6904 mg/L and pH 8.5. Whereas the treatment plant and process, described in the present invention can handle wide range of characteristics. Further, the process described in US Patent No 4,200,520 does not involve any biological means of treating textile wastewater, and uses primary and tertiary (advance) treatments, which are neither cost effective nor suitable for large scale treatment of textile waste water as described in this invention.
Reference may be made to US Patent No. 4313824 dt. 2/2/1982 wherein the waste water treatment system and process are disclosed, which are particularly suitable for use in industrial plants having existing drainage trench networks through which normal plants effluents, component leakages and accidental spills are allowed to flow. Effluent having relatively low ranges of concentration of impurities are directed into isolated trenches or a pipe net work located in the trenches to discharge to the waste water treatment system. A series of dams are provided at locations throughout the trench network so that the effluents having higher ranges of concentration of impurities are hold behind the dams.
Low concentration effluents are passed through a cleaning system which comprises demineralizing and deionizing means for removing impurities. The resulting clean water is then returned to the plant, for reuse. Periodically, the demineralizing and deionizing means are back flushed into a further system, wherein the impurities in the backflush liquid are concentrated for disposal in solid form. The high concentration effluents from the plant are passed directly to above referred cleaning system.
In the above treatment system and process, the presence of low and high concentrations of impurities in waste water are neither described qualitatively nor quantitatively. Secondly, the methodology or type of treatment e.g. primary, secondary and or tertiary treatment for the industrial effluents has not been stated. Hence, the efficiency of waste water treatment system & process is also not obvious. It has been stated that the invention was developed for use in a battery manufacturing facility and

can be adopted for use in any industrial plant which produces large volumes of effluents having relatively low concentrations of impurities and rather small volumes of effluents having high concentration of impurities. The boundaries of high & low volumes of effluents are not described, which give the capacity or capability of waste water treatment system and process, especially in industrial effluent treatment. Moreover, the word 'impurity' whether of low or high concentration does not specify the limits and types of parameters, used to evaluate the performance & efficiency of waste water treatment system & process, to limit the scope of the invention.
The main object of the present invention is to provide an improved treatment plant for textile wastewaters and an improved process thereof which provides resistance to hydraulic and organic shock loads and reduces the total treatment time by 12 hours for wastewater containing high total dissolved solids (TDS).
Another object of the present invention is to provide an equalization process comprising of an equalization basin with reduced retention time of six hrs as compared to 16 hrs in conventional treatment plant.
Yet another object is to provide a physico-chemical process comprising of a clariflocculator with increased retention time of 5 hrs as compared to 2.5 hrs in conventional treatment plant and enhanced efficiency of reduction of SS and COD over conventional physico-chemical process.
Still another object of the present invention is to provide an aerobic biological process comprising of an aeration tank that operates simultaneously in completely mixed continuous flow for mixing and tapered aeration plug flow for organic loading, and secondary clarification process comprising of a secondary clarifier with increased retention time of five hrs as compared to 2.5 hrs in conventional secondary clarification process for providing improved resistance to hydraulic and organic shocks loads with efficient separation of SS and reduction of BOD as compared to conventional process.
A further object is to provide a treatment plant and process which obviates the drawbacks of conventional treatment plant and process for treatment of textile waste waters.
The improved treatment plant for textile wastewaters and a process thereof of the present invention provides a reduced total treatment time of 30-40 hrs as compared to 40 - 59 hrs in conventional process. This is effected by passing the intake wastewater containing fine suspended solids and biodegradable organic substances through an improved equalization basin, having a retention time of 5 to 7 hrs (as compared to 16 to 24 hrs in conventional process) wherein a constant water level of 1 m is maintained below the inlet and also has a provision for mixing arrangement using improved high speed floating aerators such as described and claimed in our copending Patent Application No. 254/Del/2000 dated. 16.03.2000; An Improved Mechanical Floating Aerator for Oxygen Transfer for Biological Treatment of Wastewater) along the length of the basin. Passing the effluent from the said equalization basin through a flash mixer wherein lime is added for neutralization/pH adjustment, and ferrous sulphate and polyelectrolyte are added for coagulation by stirring the wastewater for 3 to 5 minutes. Passing the effluent from the said flash mixer to an improved clariflocculator and retaining for 4 to 6 hrs (as compared to 2 - 2.5 hrs in conventional process) for separating chemical sludge containing suspended solids; passing the effluent containing fine SS, BOD and high TDS from the said clariflocculator through an aeration tank and retaining for 18-22 hrs (as compared to 27-30 hrs in conventional process) which, operates in completely mixed continuous flow conditions. Passing the effluent containing mixed liquor suspended solids from the said aeration tank to a secondary clarifier and retaining for 3-5 hrs (as compared to 2 - 2.5 hrs in conventional process) for separating biological sludge containing fine SS; thereafter obtaining treated wastewater.
In the drawings accompanying this specification:
Figure 2 represents a schematic diagram of the improved treatment plant of the present
invention, wherein the various parts are:
24- Inlet, 25- Screen chamber, 26-Grit chamber, 27- Parshall flume, 28-Equalization basin, 29- Flash mixer, 30- Ferrous sulphate dosing tank, 31-Polyelectrolyte dosing tank, 32- Lime dosing tank, 33- Clariflocculator, 34-Flocculation zone, 35- Clarification zone, 36 - Aeration tank, 37- Secondary
clarifier, 38- Returned activated sludge, 39- Excess biological sludge, 40- Sludge
drying beds, 41- Treated effluent, 42- Chemical sludge and 43- Filtrate to inlet.
Figure 3 represents schematic diagram of details of improved equalization basin, (28)
wherein the various parts are:
44- Inlet 45- Length, 46- Total depth, 47- Effective depth, 48- Free board, 49-High
speed floating aerator, 50- Maximum allowable operating water level, 51 Minimum
required operating level, 52-Outlet and 53- Bottom of tank.
Figure 4 represents sectional elevation of details of c1ariflocculator (33), wherein the
various parts are:
54- Center feed radial distribution inlet, 55- Flocculation zone, 56- Flocculators,
57- Baffle wall, 58- Clarification zone, 59-Peripheral outlet 60- Bottom, 61- sludge
withdrawal outlet and 62- Side water depth.
Figure 5a represents schematic diagram of details of improved aeration tank (36),
wherein the various parts are:
63- Inlet for effluent from primary clarifier, 64- Aeration tank, 65- High speed floating
aerators, 66- Baffle wall, 67- Outlet to secondary clarifier, 68- Returned activated
sludge, 69- Width of one aeration tank and 70- Length of aeration tank.
Figure 5b represents sectional elevation of details of improved aeration tank, wherein
the various parts are:
71- Inlet chamber, 72- Aeration tank, 73- High speed floating aerators, 74- Baffle wall,
75- Outlet to secondary clarifier, 76- Returned activated sludge, 77Effective depth,
78- Length of aeration tank and 79- Free board
Figure 6 represents sectional elevation of details of secondary clarifier used in
improved secondary clarification process, wherein the various parts are:
80- Center feed radial distribution inlet, 81- Steel baffle wall, 82- Bottom of clarifier,
83- Clarification zone, 84- Peripheral outlet, 85- Sludge withdrawal outlet and 86- Side
water depth.
Figure 7 represents pH variation at inlet and outlet of improved equalization process,
wherein 87 -pH variation at inlet, 88-pH variation at outlet.
Accordingly, the present invention provides a n improved treatment plant for textile wastewaters, which comprises a screen chamber (25) for removing particles and floating bodies above 50 mm diameter, having wastewater inlet (24), characterized in
that the outlet of the said screen chamber being connected through a grit chamber (26) so as to reme inorganic silt having specific gravity > 2.65, and a conventional parshall flume (27) so as to regulate and measure wastewater flow, to the inlet (44) of an equalisation basin (28) having a plurality of improved high speed floating aerators (49) and for providing a constant wastewater level of 0.5 to 1.0 m below the inlet and retention time of 5 to 7 hours, the outlet of the said equalisation basin (28) being connected to a flash mixer (29) being provided with separate dosing tanks (30,31,32) of ferrous sulphate (30), polyelectrolyte (31) and lime (32) for neutralising and coagulating the wastewater, the outlet of said mixer (29) being connected to a centre feed radial distribution system (34) of a circular clariflocculator (33) so as to provide retention time of 4 to 6 hours and having a separated clarification zone (36), sludge withdrawal outlet (61), and peripheral outlet (59), the said sludge outlet (61) being connected (42) to sludge drying beds (40) having an outlet for filtrate(43) connected to the inlet of equalization basin (28), the said peripheral outlet (59) being connected in parallel to a plurality of bays of aeration tank (36) having a plurality of improved high speed floating aerators (65), the output of the said aeration tank (36) being connected to a secondary clarifier (37) so as to provide retention time of 3 to 5 hours and having a sludge withdrawal outlet (85), a peripheral outlet (84) and treated effluent outlet (41), the said sludge outlet (85) being connected to the said sludge drying beds (40) and the peripheral outlet (84) being connected (38) to the inlet of aeration tank (36).
In an embodiment of the present invention the equalization basin length (45) to breadth ratio is of the order of 2:3, total depth (46) is in the range of 3.5 m to 4.5 m, effective depth (47) is in the range of 3 to 4 m, free board (48) is in the range of 0.5 to 1.0 m and provided with a plurality of improved high speed floating aerators (49) capable of providing mixing level of the order of 20 watts/m3,
In another embodiment of the present invention the circular clariflocculator is provided with a center feed radial distribution inlet (54) to a flocculation zone (55) having flocculators (56) capable of providing slow mixing @ 10 to 15 rpm; a circular baffle wall (57) capable of preventing short circuiting and minimizing pulsating
turbulence in the
clarification zone (58, 36); and having bottom (60) slope of 1 in 12 and sludge sump having sludge withdrawal outlet (61).
In yet another embodiment of the present invention the aeration tank (36) is provided with a vertical baffle wall (66, 74) of about 1 m depth at a distance of 0.5 to 1.0 m from the outlet (67), length (70, 78) to breadth (69) ratio in the range of 2.5 to 4.0 and breadth/width 12 to 15 m, effective depth (77) in the range of 3 to 3.5 m, free board (79) in the range of 0.5 to 1.0 m and provided with a plurality of improved high speed floating aerators (65) capable of providing mixing level of the order of 20 watts/m3.
In still another embodiment of the present invention the secondary clarifier (37) is provided with a center feed radial distribution inlet (80), a steel baffle wall (81) having diameter of about 3 m and depth of 1.5 to 2.0 m capable of preventing short circuiting in the clarification zone (83) and having bottom (82) slope of 1 in 12 and sludge slump having sludge withdrawal outlet (85).
In a further embodiment of the present invention the improved high speed floating aerators used is such as described and claimed in our copending patent application no. 254/Del/2000.
Accordingly, the present invention provides an improved process for the
treatment of textile wastewaters using the improved treatment plant of the present
invention, which comprises:
(i) passing the intake wastewater through a screen chamber (25), grit chamber (26) and parshall flume (27) to an equalization basin, having retention time of 5 to 7 hrs wherein a constant water level of 1 m below the inlet is maintained and also has a provision for mixing arrangement through improved high speed floating aerators (49) along the length of the basin (45);
(ii) passing the equalized effluent from the said equalization process through a flash mixer (29) wherein lime (32) is added for pH neutralization/adjustment, and ferrous sulphate (30) and polyelectrolyte (31) are added for coagulation by stirring the wastewater for 3 to 5 minutes;
passing the neutralized effluent from the said neutralization process in the flash mixer to a clariflocculator capable of providing retention time of 4 to 6 hrs for separating colloidal and fine suspended solids;
(iv) subjecting the effluent from the said clariflocculator to aerobic biological process in a multi bay aeration tank (36) capable of providing mixed continuous flow for mixing and tapered aeration plug flow for organic loading and retention time of 18 to 22 hrs and containing flock forming bacteria;
(v) passing the effluent containing mixed liquor suspended solids from the said aerobic biological process of aeration tank through secondary clarifier (37)having 3-5 hrs retention time, thereafter obtaining treated wastewater.
In an embodiment of the improved process of the present invention pH neutralization/adjustment of wastewater having pH of the order of 7-9 is effected by using about 400-mg/L ferrous sulphate, about 400-mg/L lime and 5 to 10 mg/L polyelectrolyte.
In another embodiment of the improved process of the present invention pH neutralization of wastewater having pH of the order of 10-11 is effected by using 500 to 600 mg/L ferrous sulphate and 5 to 10 mg/L polyelectrolyte.
In yet another embodiment of the improved process of the present invention pH neutralization of wastewater having pH of the order of 5-6 is effected by using 100 to 200 mg/L ferrous sulphates, 500 to 600 mg/L lime and 5 to 10 mg/L polyelectrolyte.
In still another embodiment of the improved process of the present invention the flock forming bacteria used is a microbial culture such as Pseudomonas Aeruginosa, Bacillus Subtilis.
An improved treatment plant and an improved process thereof of the present invention as depicted in figure 2, wherein wastewater enters the plant through inlet (24) and then into screen chamber (25) wherein large floating bodies and particles above 50 mm diameter are segregated. Wastewater enters in to grit chamber (26) wherein inorganic silt and sand having specific gravity 2.65 and above are removed. Wastewater
passes through parshall flume (27) wherein flow is regulated and measured. Wastewater enters in equalization basin (28) wherein improved high-speed floating aerators equalize wastewater and characteristics are made uniform. Equalization basin (28) is connected to flash mixer (29), wherein ferrous sulphate (30), polyelectrolyte (31) and lime (32) are added for neutralization and coagulation. The clariflocculator (33) receives wastewater from flash mixer (29) by gravity through a center feed radial distribution system wherein the floes are formed in flocculation zone (34) and separated from the bottom of the clarification zone (35) of clarifier and clarified wastewater enters by gravity equally in three bays of aeration tank (36), wherein the BOD and suspended solids are reduced. The wastewater enters in secondary clarifier (37) by gravity from the center wherein the biologically activated sludge is recycled (38) to the aeration tank (36) and excess biological sludge (39) is sent to drying beds (40) and treated effluent (41) is discharged by gravity into the stream. Chemical sludge (42) from the clariflocculator (33) is sent to drying beds (40) and the filtrate (43) is again brought to the inlet of equalization basin (28) of the plant.
The improvement in the treatment plant and process at various stages due to the non-obvious inventive steps resulting in a novel treatment plant and process for textile wastewaters has been described below:
Wastewater in an improved treatment plant enters in equalization process comprising of an equalization basin as depicted in figure 3 through inlet (44). The equalization basin has rectangular shape with its length (45) to breadth ratio 2 to 3, total depth (46) 3.5 to 4.5m and effective depth (47) 3 to 4 m and free board (48) 0.5 -1.0m. Improved high speed floating aerators (49) are installed to provide a mixing level of 20 W/m3. The maximum allowable operating water level (50) is at the bottom of the inlet (44) and minimum required operating level (51) is maintained one meter below the maximum water level (50). The outlet (52) is provided one meter above the bottom (53) to ensure minimum allowable operating level to protect aerators during cleaning. The bottom (53) is made of reinforced concrete to avoid the problem of erosion and uplift especially in area where groundwater table is high. The minimum required operating level (51) is always maintained to equalize the wastewater continuously. Wastewater entering from the inlet (44) of the basin gets mixed with the equalized wastewater
through improved high speed floating aerators and replaces the one near outlet (52). This geometry of the basin and inlet and outlet arrangements with continuous mixing along the length of the basin levels out operation parameters especially pH over a time frame of 6 hours thus minimizes the effects of pH on down stream wastewater treatment. The equalization basin has long rectangular shape and can be used as pre-aeration tank for minimizing the effect of organic loading (BOD) in the following secondary treatment. The time required in the improved equalization process is thus reduced by 10 hrs as compared to the conventional process.
Wastewater from equalization basin (28) containing suspended solids and biodegradable organic substances is conveyed to neutralization process comprising of a flash mixer (29) as depicted in figure 2, where ferrous sulphate (30) and polyelectrolyte (31) are added as coagulants and lime (32) for pH neutralization and/or adjustment. Wastewater is retained in flash mixer (29) for about 3 to 5 minutes for rapid mixing of chemicals. Wastewater with pH 7 to 9 requires about 400 mg/l ferrous sulphate (30) and lime (32) each and 5 to 10 mg/l polyelectrolyte (31). Highly alkaline waste with pH 10-11 requires 500 to 600 mg/l ferrous sulphate (30) and 5 to 10 mg/l polyelectrolyte (31) and lime (32) need not be added. Similarly, wastewater with reasonably low pH 5 to 6 requires 500 to 600 mg/l lime (32), ferrous sulphate (30) 100 to 200 mg/l and polyelectrolyte (31) 5 to 10 mg/l. Rapid mixing in flash mixer for about 3 to 5 minutes brings pH in the suitable range (7 to 8.5) for biological treatment. This arrangement is therefore capable of handling wide range of pH between 5 to 11 without a separate provision for neutralization, essentially provided in the conventional treatment plant as highlighted in figure 1.
Wastewater from flash mixer enters by gravity into physico chemical process comprising of a circular clariflocculator used in improved treatment plant as depicted in figure 4. Wastewater through a center feed radial distribution inlet (54) is uniformly distributed in the flocculation zone (55) wherein the flocculators (56) provide slow mixing @ 10 to 15 rpm for floes formation. The wastewater in the flocculation zone (55) is retained for about 20 to 30 minutes, which enhances floes formation and a baffle wall (57) prevents short-circuiting and subsequently minimizes pulsating turbulence in the clarification zone (58). The floes formed in the flocculation zone (55) settles in the
clarification zone (58) before reaching the peripheral outlet (59) of the clarifier. The sludge is collected at the bottom (60) having slope 1 in 12 and separated from the sludge withdrawal outlet (61) and sent to sludge drying beds (40) and the filtrate (43) is brought to the inlet of equalization basin (28) as depicted in figure 2. The design values for average and peak overflow rates are 12 to 15 and 25 to 30 m3/m2.d respectively, and side water depth (62) of 2.5 to 4.5 m and retention time of 4 to 6 hours This configuration of improved physico-chemical process is capable of handling varying hydraulic loads and enables 60 to 80% removal of SS and 50 to 70% reduction in COD as against the efficiencies of 40 to 60% and 30 to 50% for SS and COD respectively in conventional process.
Primary clarified wastewater (63) from improved physico-chemical process enters by gravity in aerobic biological process comprising of an aeration tank (64), equally in all the three compartments as depicted in figure 5a. Improved high speed floating aerators (65) ensure complete mixing and oxygen transfer required for biological degradation of wastewater. A baffle wall (66) also shown in (74) of figure 5b of about 1 m depth and at a distance of 0.5 to 1.0 m from the outlet to secondary clarifier (67) is provided to reduce short-circuiting. Settled activated biological sludge is recycled (68) to the inlet (63) of aeration tank. The length (70) to breadth (69) ratio is kept between 2.5 to 3.0 and width 12 to 15 meters. The effective depth (77) of the tank as shown in figure 5b is provided in the range of 3 to 3.5 meters, free board (79) 0.5 to 1.0m and retention time 20 hours as compared to 27 hrs in conventional process. This configuration of aerobic biological process consisting of an aeration tank in activated sludge process operates under completely mixed continuous flow conditions so far as the mixing is concerned and simultaneously operates in tapered aeration plug flow so far as the organic loading is concerned. The configuration of aeration tank also incorporates features of extended aeration process, which requires low organic loading and long retention time. Special microbial culture which is a flock forming bacteria viz. Pseudomonas Aeruginosa, Bacillus Subtilis has been developed for treatment of wastewater having high total dissolved solids concentration. Wastewater containing high total dissolved solids gets thoroughly mixed (20 watts/m3) through improved high speed floating aerators (65) of figure 5a thus ensures complete mixing and oxygen transfer while traveling from inlet (63) to outlet (67) of figure 5a. The oxygen
requirement gradually decreases along the length of the tank as wastewater progresses from inlet (63) to outlet (67) of figure 5a.
The above configuration of improved aerobic biological process comprising of an aeration tank is capable of withstanding the hydraulic and organic shock loads and improves BOD reduction especially for textile wastewaters having high total dissolved solids concentration in the range of 10,000 to 20,000 mg/l and thus obviates the drawbacks of conventional activated sludge process used for treatment of textile wastewater in large capacity plants.
Wastewater after aeration enters by gravity to secondary clarification process comprising of a secondary clarifier as depicted in figure 6 through a center feed radial distribution inlet (80). A steel baffle wall (81) of 3-m diameter and 1.5 rn to 2.0 m depth is provided to prevent the short-circuiting. Biological floes (Biomass) formed in the aeration process start settling at the bottom (82) of the clarification zone (83) while traveling from inlet (80) to the peripheral outlet (84) of secondary clarifier. The biological floes trap the fine suspended solids and settle at the bottom (82) having slope 1 in 12, and are separated from the sludge withdrawal outlet (85). The excess biosludge is sent to drying beds (40) and the filtrate (43) is brought to the inlet of equalization basin (28) as depicted in figure 2. The design values for average and peak surface overflow rate are 5 to 8 and 10 to 15 m3/m2.d, respectively and average and peak solids loading rate 12 to 15 and 70 kg/m2.d, respectively. Side water depth (86) is kept 2.5 to 5.0 meters and retention time of the clarifier between 3 to 5 hours. This configuration and functioning of improved secondary clarification process consisting of a secondary clarifier is capable of handling varying hydraulic loads and improves SS and BOD reduction by 20 to 30% over conventional secondary clarification process.
The following example is given by way of illustration and therefore should not be construed to limit the scope of the present invention
Example -1
In order to examine the effectiveness of the improved treatment plant and an improved process thereof, a comparison of conventional and improved treatment plant is illustrated below:
An improved treatment plant as depicted in figure 2 of this specification was subjected to effluent flow rate of 6810 m3/d (6.81 MLD), and a conventional treatment plant as depicted in figure 1 of this specification subjected to flow rate of 5000 m3/d (5.0 MLD). The typical major raw wastewater characteristics with wide variation are presented in Table 1. The raw wastewater was simultaneously pumped to both the plants from a common intake well.
Table 1: Typical Raw Wastewater Characteristics
(All values except pH are in mg/L)
(Table Removed)
Wastewater in an improved process of equalization was retained for about six hours. The results of improved equalization process are depicted in figure 7 of the drawings accompanying this specification, through pH variation at inlet (87) and outlet (88) of equalization basin. This was achieved by maintaining a constant wastewater level (51) 1-m below the inlet (44) and providing long rectangular shape with improved high speed floating aerators (49) as shown in figure 3. This ensured complete equalization of wastewater and the pH variation was leveled out at the outlet (88) in six hours. A batch of wastewater entering in equalization basin replaces the wastewater near outlet (52), which had already been equalized. In conventional equalization process, about 16-hrs retention time was required to level out the pH variation as shown in figure 7.
Equalized wastewater was then pumped to neutralization process comprising of a flash mixer. The required dose of chemicals viz. ferrous sulphate, polyelectrolyte and lime in improved treatment plant for neutralization of wastewater having pH in the range of 7 to 9 were 400 mg/l, 5 to 10 mg/l and 400 mg/l respectively. Highly alkaline waste with pH 10-11 required 500 to 600 mg/l ferrous sulphate and 5 to 10 mg/l polyelectrolyte
and lime was not added. Wastewater having reasonably low pH range of 5 to 6 required 500 to 600 mg/l lime, ferrous sulphate 100 to 200 mg/l and polyelectrolyte 5 to 10 mg/l. Whereas in conventional neutralization process separate neutralization units consisting of chemicals dosing and mixing tanks, neutralization tank and additional sludge drying beds are essentially required as highlighted in figure 1.
In the improved treatment plant and process thereof wastewater neutralised in the pH range of 7 to 8.5 entered into clariflocculator by gravity, through a center feed radial distribution system and retained in the flocculation zone for 30 minutes, wherein slow mixing @ 10-15 rpm enhances floc formation. The colloidal and fine suspended particles were trapped in the floes, which settled out at the bottom of clarification zone in 5-hrs retention time. Typical one-week performance evaluations of physico-chemical processes in improved and conventional treatment plants are presented in Table 2.
Table 2: Performance evaluation of physico-chemical Process in Improved and
Conventional Treatment Plants
(All values except pH are in mg/L)

(Table Removed)


n- % Efficiency
The SS and COD reduction in improved treatment plant varied from 60 to 80% and 50 to 70% respectively. Whereas in conventional treatment plant the maximum SS and COD reductions were 52 and 50% respectively.
The clarified wastewater entered by gravity in improved aeration process equally in all the three compartments as shown in figure 5a. The wastewater was retained for 20 hrs in aeration process where improved high-speed floating aerators ensured
complete mixing and O2 transfer for biodegradation of organic matter. Biological floes formed during the process enter for secondary clarification of wastewater through a center feed radial distribution inlet. Biological floes being heavier than water of specific gravity 1.01 - 1.02 settled in the secondary clarifier while travelling from inlet to peripheral outlet.
In order to study the effect of shock loading the improved and conventional treatment plants were subjected to variable flow rates. The impact of flow variation was observed in physico-chemical and biological process with respect to SS and COD and SS and BOD respectively. Typical shock loading analyses for 8-hrs for improved and conventional physico-chemical and biological processes are reported in, Table 3 respectively.
Table 3: Shock Loading Analysis (All values except pH are in mg/L)

(Table Removed)



The average flow rates in improved and conventional treatment plants were 284 m3/hr and 208 m3/hr respectively. In improved treatment plant the values of SS and BOD were within the stipulated standards for discharge into surface water and had a range of 74 to 90 mg/l and 20 to 26 mg/L, respectively, whereas in conventional process, values of SS and BOD were not within the prescribed limits and had a range of 168 to 228 and 60 to 98 mg/L, respectively. Conventional treatment plant could not withstand the impact of flow variation since the retention time in primary and secondary clarification process was less as compared to improved process and the biological process operated in conventional activated sludge process wherein longitudinal mixing was absent, thereby affected the biological metabolism. The improved treatment plant
was capable of handling shock loads since retention time in primary and secondary clarification process is increased by 2 to 2.5 times of conventional clarification process and biological process involved the features of completely mixed flow conditions for mixing and tapered aeration plug flow for organic loading, thus provided resistance to shock loads.
Textile wastewaters in improved treatment plant is thus equalized in 1/3 to 1/2 of the time required for conventional equalization process i.e. wastewater in an improved equalization process is equalized in 6 hrs as compared to 16 hrs in conventional equalization process thereby reducing time of equalization by 10 hours. Increase in retention time in primary and secondary clarification process from 2.5 hours to 5 hours enhances the separation of fine suspended solids by 20 to 40% and COD and BOD reduction 20 to 30% as compared to conventional clarification process and provides resistance to hydraulic shock loads. The aeration process is operated in extended aeration mode at low food to microorganism ratio with 20 hours retention time and incorporates the features of completely mixed continuous flow conditions for mixing and tapered aeration plug flow for organic loading provides resistance to hydraulic and organic shock loads and increases the efficiency of BOD reduction of wastewater containing high TDS. The main advantages of the present invention are:
1. The overall cost of treatment process for textile wastewaters is reduced by
decreasing the total retention time of treatment by 12 hours.
2. Equalization process comprising of small equalization basin with retention time of
6 hours can be used for equalization of wastewater thereby reducing the cost of
construction, operation and maintenance.
3. No separate provision for neutralization process is required, thus minimizes
sludge production and subsequently, its handling.
4. Efficiency of primary and secondary clarification is increased in separating
suspended solids and reducing COD and BOD.
5. Wastewater containing high TDS can be treated in aeration process with
improved resistance to hydraulic and organic shock loads and BOD reduction.
6. The treated wastewater can be safely disposed off into streams and can be
reused for irrigation and/or green belt development.




We claim:
1 ) An improved treatment plant for textile wastewaters, which comprises a screen chamber (25) for removing particles and floating bodies above 50 mm diameter, having wastewater inlet (24), characterized in that the outlet of the said screen chamber being connected through a grit chamber (26) so as to reme inorganic silt having specific gravity ≥ 2.65, and a conventional parshall flume (27) so as to regulate and measure wastewater flow, to the inlet (44) of an equalisation basin (28) having a plurality of improved high speed floating aerators (49) and for providing a constant wastewater level of 0.5 to 1.0 m below the inlet and retention time of 5 to 7 hours, the outlet of the said equalisation basin (28) being connected to a flash mixer (29) being provided with separate dosing tanks (30,31,32) of ferrous sulphate (30), polyelectrolyte (31) and lime (32) for neutralising and coagulating the wastewater, the outlet of said mixer (29) being connected to a centre feed radial distribution system (34) of a circular clariflocculator (33) so as to provide retention time of 4 to 6 hours and having a separated clarification zone (36), sludge withdrawal outlet (61), and peripheral outlet (59), the said sludge outlet (61) being connected (42) to sludge drying beds (40) having an outlet for filtrate(43) connected to the inlet of equalization basin (28), the said peripheral outlet (59) being connected in parallel to a plurality of bays of aeration tank (36) having a plurality of improved high speed floating aerators (65), the output of the said aeration tank (36) being connected to a secondary clarifier (37) so as to provide retention time of 3 to 5 hours and having a sludge withdrawal outlet (85), a peripheral outlet (84) and treated effluent outlet (41), the said sludge outlet (85) being connected to the said sludge drying beds (40) and the peripheral outlet (84) being connected (38) to the inlet of aeration tank (36).
2. An improved treatment plant as claimed in claim 1 wherein the equalization basin
length (45) to breadth ratio is of the order of 2:3, total depth (46) is in the range of 3.5
m to 4.5 m, effective depth (47) is in the range of 3 to 4 m, free board (48) is in the
range of 05 to 1.0 m and provided with a plurality of improved high speed floating
aerators (49) so as to provide mixing level of the order of 20 watts/m3.
3. An improved treatment plant as claimed in claim 1 wherein the circular
clarifloccutator is provided with a center feed radial distribution inlet (54) to a flocculation zone (55) having flocculators (56) so as to provide slow mixing @ 10 to 15 rpm; a circular baffle wall (57) so as to prevent short circuiting and minimizing pulsating turbulence in the clarification zone (58, 36); and having bottom (60) slope of 1 in 12 and sludge sump having sludge withdrawal outlet (61).
(4) An improved treatment plant as claimed in claim 1 wherein the aeration tank (36) is
provided with a vertical baffle wall (66, 74) of about 1 m depth at a distance of 0.5 to
1.0 m from the outlet (67), length (70) to breadth (69) ratio in the range of 2.5 to 4.0
and breadth/width 12 to 15m, effective depth (77) in the range of 3 to 3.5 m, free
board (79) in the range of 0.5 to 1.0 m and provided with a plurality of high speed
floating aerators (65) so as to provide mixing level of the order of 20 watts/m3
(5) An improved treatment plant as claimed in claim 1 wherein the secondary clarifier
(37) is provided with ; a center feed radial distribution inlet (80), a steel baffle wall (81)
having diameter of about 3 m and depth of 1.5 to 2.0 m so as to prevent short
circuiting in the clarification zone (83) and having bottom (82) slope of 1 in 12 and
sludge slump having sludge withdrawal outlet (85).
(6) An improved process for the treatment of textile wastewaters using the improved
treatment plant for textile wastewaters as claimed in claims 1 to 6, which comprises:
i). passing the intake wastewater through a screen chamber (25), grit chamber (26) and parshall flume (27) to an equalization basin, having retention time of 5 to 7 hrs wherein a constant water level of 1 m below the inlet is maintained and also has a provision for mixing arrangement through improved high speed floating aerators (49) along the length of the basin (45);
ii). passing the equalized effluent from the said equalization process through a flash mixer (29) wherein lime (32) is added for pH neutralization/adjustment, and ferrous sulphate (30)) and polyelectrolyte (31) are added for coagulation by stirring the wastewater for 3 to 5 minutes;
iii). passing the neutralized effluent from the said neutralization process in the flash mixer to a c1ariflocculator so as to providing retention time of 4 to 6 hrs for separation of colloidal and fine suspended solids;
iv). subjecting the effluent from the said c1ariflocculator to aerobic biological process in a multi bay aeration tank (36) so as to providing mixed continuous flow for mixing and tapered aeration plug flow for organic loading and retention time 18-22 hrs and containing floc forming bacteria;
v). passing the effluent containing mixed liquor suspended solids from the said aerobic biological process of aeration tank through secondary clarifier (37) having 3-5 hours retention time, thereafter obtaining treated wastewater.
7) An improved process as claimed in claim 7 wherein the pH neutralization / adjustement of wastewater having pH of the order 7 to 9 is effected by using 400 mg/L ferrous sulphate, 400 mg/L lime and 5 to 10 mg/L polyelectrolyte,
improved process as claimed in 7 wherein the pH neutralization of wastewater having pH of the order of 10 to 11 is effected by using 500 to 600 mg/L ferrous sulphate and 5 to 10 rng/l polyelectrolyte,
9) An improved process as claimed in 7 wherein the pH neutralization of wastewater
having pH of the order of 5 to 6 is effected by using 100 to 200 mg/L ferrous sulphate
and 500 to 600 mg/llime and 5 to 10 mg/L polyelectrolyte,
10) An improved process as claimed in claim 7 wherein the flock forming bacteria
used is a microbial culture such as Pseudomonas Aeruginosa, Bacillus Subtilis.
11) An improved treatment plant for textile wastewaters substantially as herein
described with reference to the example and figures 2 to 6 of the drawings
accompanying this specification,

Documents:

227-del-2002-abstract.pdf

227-del-2002-claims.pdf

227-del-2002-correspondence-others.pdf

227-del-2002-correspondence-po.pdf

227-del-2002-description (complete).pdf

227-del-2002-drawings.pdf

227-del-2002-form-1.pdf

227-del-2002-form-18.pdf

227-DEL-2002-Form-2.pdf

227-del-2002-form-3.pdf


Patent Number 231615
Indian Patent Application Number 227/DEL/2002
PG Journal Number 13/2009
Publication Date 27-Mar-2009
Grant Date 06-Mar-2009
Date of Filing 14-Mar-2002
Name of Patentee COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH
Applicant Address RAFI MARG,NEW DELHI,100 001,INDIA
Inventors:
# Inventor's Name Inventor's Address
1 SANTOSH NARAIN KAUL WASTEWATER TECHNOLOGY DIVISION NEERI,NEHRU MARG,NAGPUR 440 420 MAHARASHRTA,INDIA
2 GIRISH RAMESH POPHALI WASTEWATER TECHNOLOGY DIVISION NEERI,NEHRU MARG,NAGPUR 440 420 MAHARASHRTA,INDIA
3 TAPAS NANDY WASTEWATER TECHNOLOGY DIVISION NEERI,NEHRU MARG,NAGPUR 440 420 MAHARASHRTA,INDIA
PCT International Classification Number C02F 1/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA