Claims:We Claim:
1. A process for reducing chemical oxygen demand (COD) in an effluent discharged during viscose manufacturing, comprising the following steps:
a) mixing a predetermined quantity of the effluent in a tank with a predetermined quantity of ferrous sulphate to obtain a mixture;
b) circulating the mixture obtained in step a) through a pump and then mixing a predetermined quantity of hydrogen peroxide to the mixture to obtain another mixture; and
c) circulating the mixture obtained in step b) through a hydrodynamic cavitator for a reaction time of 5 to 60 minutes and at a pressure of 1 to 4 barg,
wherein the ratio of hydrogen peroxide to ferrous sulphate in the mixture obtained in step c) is between 1:2 to 1:4 and the COD in the mixture obtained in step c) is 40% to 90% less than the COD of the effluent at the start.
2. The process as claimed in claim 1, wherein a temperature of the effluent ranging from 25°C to 60°C is maintained throughout the process.
3. The process as claimed in claim 1, wherein the hydrodynamic cavitator is with venturi type or orifice type nozzle.
4. The process as claimed in claim 3, wherein the hydrodynamic cavitator is operated at an effluent flow velocity of 30 – 60 m/s at venturi.
5. The process as claimed in claim 3, wherein the hydrodynamic cavitator is operated at an effluent flow velocity of 40 – 60 m/s at orifice.
6. The process as claimed in claim 1, wherein the COD in the mixture obtained in step c) is less than 150mg/L.
7. A process for reducing chemical oxygen demand (COD) in an effluent discharged during viscose manufacturing, comprising the following steps:
a) mixing a predetermined quantity of the effluent in a tank with a predetermined quantity of sodium hypochlorite solution to obtain a mixture; and
b) circulating the mixture obtained in step a) through a pump and then through a hydrodynamic cavitator for a reaction time of 5 to 60 minutes and at a pressure of 1 to 4 barg,
wherein the COD in the mixture obtained in step (b) is 40% to 75% less than the COD of the effluent at the start.
8. The process as claimed in claim 7, wherein the hydrodynamic cavitator is with venturi type or orifice type nozzle.
9. The process as claimed in claim 8, wherein the hydrodynamic cavitator is operated at an effluent flow velocity of 30 – 60 m/s at venturi.
10. The process as claimed in claim 8, wherein the hydrodynamic cavitator is operated at an effluent flow velocity of 40 – 60 m/s at orifice.
11. The process as claimed in claim 7, wherein the COD in the mixture obtained in step b) is less than 150mg/L.
12. The process as claimed in claim 7, wherein a temperature of the effluent ranging from 25°C to 60°C is maintained throughout the process.
, Description:FORM 2
THE PATENT ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006

COMPLETE SPECIFICATION
(See section 10 and rule 13)

TITLE OF THE INVENTION:
A process for reducing chemical oxygen demand (COD) in an effluent discharged during viscose manufacturing.

APPLICANT:
Aditya Birla Science & Technology Company Pvt Ltd, an Indian Company, having address at Plot No. 1 & 1- A/1, MIDC Taloja, Tal. Panvel, Dist. Raigad 410208, India

PREAMBLE TO THE DESCRIPTION:
The following specification particularly describes this invention and the manner in which it is to be performed.

FIELD OF THE INVENTION
[001] The present invention relates to a process for reducing chemical oxygen demand (COD) in an effluent discharged during viscose manufacturing. Specifically, the invention relates to a process for COD reduction of viscose effluents in the range of 50-150 mg/L.
BACKGROUND OF THE INVENTION
[002] In Viscose Staple fibre (VSF) process, huge quantity of effluent is generated. The primary impurities in the effluent are in the form of organics and dissolved solids. The effluent discharge specifications, in terms of chemical oxygen demand and total dissolved solid (TDS) are becoming more stringent. More specifically, COD is required to reduce in the range of 50-150 mg/L. Removal of both organic pollutants and heavy metals is required to meet water quality standards/environmental regulations.
[003] In VSF effluent streams, the major contributors to COD are hemicellulose and fatty acids which are complex organic molecules. It is known that Hydrodynamic cavitation (HC) produces local stress zones having extremely high temperature (~5000 K) and pressure (~500 atm) which are effective in breaking the C-C bonds, generating hydroxyl radicals that can oxidize complex organic molecules and thus reducing the COD. Alternatively, chemicals like Fenton reagent and hypochlorite solution are also known to reduce COD by virtue of generating highly reactive hydroxyl and hypochlorite free radicals respectively, which can oxidize complex organic molecules into simpler molecules.
[004] The existing processes for treatment of viscose process effluent includes primary treatment and secondary treatment. While primary treatment is in the form of sedimentation, pH adjustment, coagulation, and flocculation which remove suspended impurities, the secondary treatment comprises of biological treatment and clarifier which reduces the organic impurities (COD and BOD) in the effluent. Due to inherent limitations of residence time and COD/BOD ratio of these treatments, the final COD of treated effluent cannot be reduced to levels below 100-250 mg/L in most viscose plants. Thus, a tertiary treatment process is desirable which is likely to serve two benefits: i) reduce COD to 50-150 mg/L and ii) meet feed COD requirements for reverse osmosis process in a zero liquid discharge scheme.
[005] Moreover, traditional methods for degrading such complex molecules include biological treatment which is an extremely slow process with reaction times up to 24 hours. Despite long hours of biological treatment, the treated effluent COD is observed to be in the range of 100 – 250 mg/L. Moreover, with discharge limits for COD in wastewater reaching as low as 50 mg/L in some locations and the rising levels of water pollution affecting the global population, the current situation needs improvements and thus a need of tertiary treatment for further reduction of COD is desirable. Additionally, as the industries move towards the goal of zero liquid discharge, the COD of wastewater effluent will inevitably have to be reduced using tertiary methods to recover water for reuse.
[006] Hence, a strong need exists for a process that can solve some of the problems of the prior art.
SUMMARY OF THE INVENTION
[007] According to an embodiment of the present invention, there is provided a process for reducing chemical oxygen demand (COD) in an effluent discharged during viscose manufacturing, comprising the following steps:
a) mixing a predetermined quantity of the effluent in a tank with a predetermined quantity of ferrous sulphate to obtain a mixture;
b) circulating the mixture obtained in step a) through a pump and then mixing a predetermined quantity of hydrogen peroxide to the mixture to obtain another mixture; and
c) circulating the mixture obtained in step b) through a hydrodynamic cavitator for a reaction time of 5 to 60 minutes and at a pressure of 1 to 4 barg,
wherein the ratio of hydrogen peroxide to ferrous sulphate in the mixture obtained in step c) is between 1:2 to 1:4 and the COD in the mixture obtained in step c) is 40% to 90% less than the COD of the effluent at the start.
[008] According to another embodiment of the present invention, there is provided a process for reducing chemical oxygen demand (COD) in an effluent discharged during viscose manufacturing, comprising the following steps:
a) mixing a predetermined quantity of the effluent in a tank with a predetermined quantity of sodium hypochlorite solution to obtain a mixture; and
b) circulating the mixture obtained in step a) through a pump and then through a hydrodynamic cavitator for a reaction time of 5 to 60 minutes and at a pressure of 1 to 4 barg,
wherein the COD in the mixture obtained in step (b) is 40% to 75% less than the COD of the effluent at the start.
BRIEF DESCRIPTION OF THE DRAWINGS
[009] Figure 1 depicts a batch process for COD reduction in viscose process effluent, in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[010] As set out in the claims, the present invention eliminates or reduces the aforementioned problems of the prior art by providing a process for COD reduction in viscose effluent using hydrodynamic cavitation and chemical oxidation. The present process results in reduction of COD of the effluents from 250 mg/L to 30 mg/L.
[011] According to an embodiment of the present invention, a predetermined quantity of the effluent is taken in a tank and mixed with a predetermined quantity of ferrous sulphate to obtain a mixture. This mixture is then circulated through a pump and a predetermined quantity of hydrogen peroxide is mixed to it to obtain a second mixture. This mixture is then circulated through a hydrodynamic cavitator for a reaction time of 5 to 60 minutes and at a pressure of 1 to 4 barg. The COD in this mixture is in the range of 30 mg/L to 150mg/L. Preferably, the ratio of hydrogen peroxide to ferrous sulphate in the second mixture is between 1:2 to 1:4 and the COD in the second mixture is 40% to 90% less than the COD of the effluent at the start.
[012] The present invention consists of a process which is effective in breakdown of complex organic molecules, such as hemicellulose and fatty acids, which decreases the chemical oxygen demand (COD) present in the viscose process effluent. The present process shows synergistic effect, to the degree of 2-3 times, by resulting in generation of highly reactive hydroxyl/hypochlorite radicals. These free radicals further attack and break the C-C bonds in a complex molecule thereby degrading them into simpler molecules like CO2 and H2O. The effluent is preferably mixed with Fenton reagent or Sodium/Calcium Hypochlorite. Both these chemicals produce highly reactive free radicals which can break the C-C bond. This in addition to the free radicals generated due to cavitation in a venturi/orifice device (cavitator) which provides a synergistic effect of being capable of reducing COD levels which traditional bioreactors cannot achieve.
[013] Preferably, the temperature of the effluent ranging from 25°C to 60°C is maintained throughout the process. The hydrodynamic cavitation reactors employed in this process can be of two types based on the nozzles, either venture type or orifice type. Preferably, the hydrodynamic cavitator is operated at an effluent flow velocity of 30 – 60 m/s at venturi and the hydrodynamic cavitator is operated at an effluent flow velocity of 40 – 60 m/s at orifice.
[014] According to another embodiment of the present invention, there is provided a process for reducing chemical oxygen demand (COD) in an effluent discharged during viscose manufacturing which comprises of mixing a predetermined quantity of the effluent in a tank with a predetermined quantity of sodium hypochlorite solution to obtain a mixture. This mixture is then circulated through a pump and then through a hydrodynamic cavitator for a reaction time of 5 to 60 minutes and at a pressure of 1 to 4 barg. The COD in this mixture is in the range of 30 mg/L to 150mg/L which is 40% to 75% less than the COD of the effluent at the start.
[015] Preferably, the temperature of the effluent ranging from 25°C to 60°C is maintained throughout the process. For temperatures > 60 °C vapour pressure of the effluent become higher which can decrease the effects of cavitation. On the other hand, for temperatures less than 25°C, vapour pressure of effluent becomes lower, which can also decrease the cavitation effects Preferably, the hydrodynamic cavitator is operated at an effluent flow velocity of 30 – 60 m/s at venturi and the hydrodynamic cavitator is operated at an effluent flow velocity of 40 – 60 m/s at orifice. Higher velocities result into enhanced cavitation effects, i.e., greater hydroxyl radical formation and greater mixing effects.
[016] Concentration of H2O2 is kept higher than the theoretical requirement, but at the optimum, to overcome the issues of recombination of free radicals or scavenging by H2O2. Excellent COD reduction was observed for different ratios of H2O2:FeSO4.7H2O. Additionally, the reaction time of even 15 min is beneficial for large scale operation. Finally, a minimum dosage of 150:600 (H2O2:FeSO4.7H2O, mg/L) was found to achieve the target decrease in COD (i.e. < 150 ppm) which could benefit several VSF plants across India. Additionally, the samples simulated with initial COD of ~100 ppm also showed reduction in COD by 59 % with the dosing of 150:600 ppm (H2O2:FeSO4.7H2O). It has been observed that the ratio of H2O2:FeSO4.7H2O is critical in achieving the desired reduction in COD. The reason for reduction in COD is attributed to the nature of COD being similar across VSF plants, which constitutes of hemicellulose and fatty acids.
[017] Moreover, the present process is environment friendly as it does not use sodium aluminate that is used in the prior art processes thereby avoiding the huge sludge generation and handling issue of sodium aluminate due to solidification.
[018] Advantages and benefits of the process according to the embodiments of the present invention would become more apparent from the below experimental details to a person skilled in the art.
[019] Experimental Data:
[020] Process steps for COD reduction of viscose effluents using sodium hypochlorite and HC:
a) The feed tank was filled with effluent, keeping the drain valve closed.
b) Thereafter, 500–2000 mg/L of 4-10 % available chlorine solution of sodium hypochlorite was added into the effluent and the valve to cavitator was opened completely.
c) The pump was on and allowed normal flow through the cavitator.
d) The operating pressure was increased to 2-4 barg by adjusting the opening of valve. The pressure was kept constant for 5-60 minutes of reaction time. The valve was released, and the pump was switched off. The sample was collected from the feed tank via the drain valve. The collected sample is the final treated sample with COD < 50 -150 mg/L.
[021] Figure 1 depicts a batch process for COD reduction in viscose process effluent. The untreated feed sample is collected in a tank wherein it is dosed with either Fenton reagent or Hypochlorite and is circulated through the hydrodynamic cavitator for 15 minutes. The final treated sample is then analysed for COD with wet chemistry that involves acidic digestion and measurement with titration/spectroscopy. The difference between the initial and final COD values gives the percentage reduction.
Table 1
Experiment Chemical dosing Initial COD (mg/L) Final COD (mg/L) % Reduction
HC NA 200 170 15
HC+Fenton H2O2:FeSO4.7H2O=1500:3270 mg/L 203 30.4 85
HC+Fenton H2O2:FeSO4.7H2O=750:1635 mg/L 200 30 85
HC+Fenton H2O2:FeSO4.7H2O=550:1199 mg/L 250 30.4 88
HC+Fenton H2O2:FeSO4.7H2O=450:980 mg/L 250 44.8 82
HC+Fenton H2O2:FeSO4.7H2O=350:1050 mg/L 250 52.8 79
HC+Fenton H2O2:FeSO4.7H2O=250:1050 mg/L 250 76.8 69
HC+Fenton H2O2:FeSO4.7H2O=150:600 mg/L 250 106 58
HC+Fenton H2O2:FeSO4.7H2O=150:600 mg/L 107 27 75
HC+Hypo NaOCl = 1000 mg/L 220 112 49
HC+Hypo NaOCl = 500 mg/L 250 111 56
HC+Hypo NaOCl = 500 mg/L 107 29 73
[022] Table 1 lists the experimental data obtained for different schemes of chemical dosing with and without hydrodynamic cavitation. The ratio of H2O2:FeSO4.7H2O is critical based on the initial COD which was optimized at 150:600 mg/L for initial COD of 100 – 250 mg/L. While, this ratio suffices for obtaining nearly 50 % COD reduction, further reduction is also possible by increasing the chemical dosing in appropriate ratio as shown in the table. In addition, dosing hypochlorite up to 500 mg/L in combination with hydrodynamic cavitation is also found to be effective in COD reduction and is an attractive alternative as it avoids generation of any suspended impurities during the process. Higher hypochlorite dosing of 1000 mg/L is also effective but runs the risk of producing adsorbable organic halides (AOX) beyond discharge norms of 1 mg/L and hence not recommended.
[023] The foregoing description of specific embodiments of the present invention has been presented for purposes of description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obvious modifications and variations are possible in light of the above teaching.