1. Hybrid Advanced Oxidative Pre-treatment of Complex Industrial Effluent for Biodegradability Enhancement
Dr. (Ms) Kiran Paradkar
CSIR-National Environmental Engineering Research Institute (NEERI)
Nagpur, INDIA
April 28, 2017

2. Genesis & Motivation
Complex /recalcitrant effluents with high COD-color are generated from industries such as distillery, heterocyclic chemicals, API manufacturing (8-500 LWastewater/kgproduct)
Advanced oxidation processes (AOPs) are mostly used for complete mineralization and are capital and energy intensive
AOPs are set of chemical treatment procedures designed to remove organics by oxidation via hydroxyl radical mechanism
Need for development of advanced oxidation based pretreatment process for selective biodegradability enhancement
Hybrid combination (synergism) of AOPs can be a potential option for biodegradability enhancement and lowering energy requirements
Biodegradability enhancement of complex effluent can facilitate integration with subsequent biological processes like anaerobic digestion for biogas generation and/or aerobic biooxidation
April 28, 2017

3. Objectives
Evaluation of Hydrodynamic-Cavitation, Wet air oxidation based Advanced Oxidation Processes for pretreatment of model complex effluent to enhance biodegradability
Evaluation of the mechanism of pretreatment
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4. Model Complex Wastewater- Biomethanated distillery wastewater
Characteristics
Raw complex waste water
Desirable for anaerobic digestion pH
7.64
6.5-8
COD (mg/L)
40,000
>10,000
BOD (mg/L)
7015 -
VFA: Alkalinity ratio
0.022
BOD: COD ratio
0.17
>0.4
April 28, 2017

5. Cavitation
Cavitation is the generation, subsequent growth and collapse of cavities releasing large magnitudes of energy over a very small interval of time and over a small location
In Hydrodynamic cavitation (HC) cavities are generated by passing liquid via a venturi/orifce resulting in conditions similar to acoustic cavitation/ultrasound but at comparatively much larger scale of operation and with much better energy efficiencies
Important effects of cavitation phenomena are generation of very high temperatures & pressures locally with overall ambient operating conditions, release of highly reactive free radicals, generation of micro-turbulence and liquid circulation enhancing the rates of transport processes
In water at 25oC, it is possible to achieve temp. as high as 5000K and pressures of bar by collapse of cavitation bubbles
April 28, 2017

6. Wet Air Oxidation
Wet air oxidation is aqueous phase oxidation of organic material at elevated temperature ( oC) and pressure ( bar)
Oxygen solubility in water decreases with temp to 0.85 ppm near 100oC under atm conditions and then increases with increasing temp to an infinite value at 374.1oC, the critical point of water. This enhanced solubility of oxygen in aqueous solutions provides a strong driving force for oxidation
Longer molecules are oxidized to various intermediate products. Most of the initial intermediates formed are unstable except low molecular weight carboxylic acid which are resistant to further oxidation
Complex molecules
A + O2 C k1 k2 k3
B + O2
A : Unstable intermediates
B : Carboxylic acids
C : End products
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7. Abbreviations HYCA/HC: Hydrodynamic Cavitation WAO: Wet Air Oxidation
VFA: Volatile Fatty Acids
COD: Chemical Oxygen Demand
BOD: Biochemical Oxygen Demand
BI: Biodegradability Index; BOD5:COD ratio
BDWW: Biomethanated Distillery Wastewater
April 28, 2017

8. The CAVOX (HYCA+ WAO) Concept
CAVOX is a recent hybrid technique and potential treatment/pre- treatment option for recalcitrant waste streams
Advantage of hybrid technique is mainly due to identical controlling reaction mechanism leading to an enhanced generation of hydroxyl radicals, which eventually can result in higher oxidation rates
Hybrid method can synergistically combine for higher energy efficiency and oxidation in comparison to standalone cavitation or wet oxidation
Selective pretreatment targeting enhanced biodegradation and biogas recovery can be achieved by developing hybrid pretreatment process
April 28, 2017

9. Summary of cavitation for complex model wastewater at various conditions
April 28, 2017

10. Pretreatment of complex wastewater by Wet Air Oxidation
0.88
0.63
0.4
0.2
Original COD : 40,000 mg/L, BI : 0.17
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11. Profile of VFA in WAO pretreated model wastewater
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12. Comparison of cavitation and WAO as stand alone and combined (CAVOX) pretreatment for biodegradability enhancement
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13. Biogas generation Post WAO Pretreatment
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14. Proposed Mechanism of Pretreatment
FTIR analysis indicated the dissociation and reorientation of complex organic compounds in the untreated B-DWW to new and simpler organic compounds in comparison to the untreated sample
Intense bands were found in the ranges 1600–1300,1200–1000 and 800–600 cm-1 which indicated that strong OH bonds are produced in treated sample over control
investigation on 1H NMR spectrum of untreated and treated sample has shown signals at d 7.4 ppm d 8.0 ppm in only the untreated sample, indicative of presence of aromatic groups in the untreated sample which were not observed in WAO treated samples, probably because of breakdown of aromatic compounds by wet oxidation into simpler aliphatic compounds
Important structural feature of Melanoidin (major coloring compound in original sample) is the peak of C=N and C=C conjugated bonds. The pretreatment aids in cleavage of the C=N (azomethane) and C=C(ethylinic) linkage producing more hydroxyl groups in (3400 cm-1) pretreated sample over the control
This is indicative of conversion of complex molecules to simpler ones
April 28, 2017

15. Summary & Conclusions
Synergistic combination of Hydrodynamic Cavitation-Wet Air Oxidation is a potential high performance pretreatment concept
Biodegradability Index > favours anaerobic digestion for biogas generation
WAO pretreatment indicated possibility to enhance BI greater than 0.4 for its utilization in biogas production
Hybrid pretreatment could retain 50% COD with an BI of 0.55, indicating suitability of coupling with biological systems
Hybrid pretreatment concept can be applied to similar complex wastes for enhancing biodegradability and biofuel recovery
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16. Future Needs
Understanding Complete Mechanism and postulating possible pathway of pretreatment for application to similar complex effluents containing large number of complex (known and unknown) constituents
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17. Publications
Wet Air oxidation as a Pretreatment Option for Selective Biodegradability Enhancement and Biogas Generation Potential from Complex Effluent. Bioresource Technology (2012)
Cavitationally induced Biodegradability enhancement of a Distillery Wastewater. Journal of Hazardous materials (2012)
Kinetics of Wet Air Oxidation Pretreatment and Biodegradability of a Complex Wastewater. J. of Environmental Chemical Engg. (2014)
Wet Air Oxidation Induced Enhanced Biodegradability of Distillery Effluent. J. of Environmental Management (2014)
Advanced Oxidative Pretreatment of Complex Effluents for Biodegradability Enhancement and Color Reduction. In: Advances in Biodegradation & Bioremediation of Industrial Waste, Taylor & Francis, CRC Press (2015)
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18. Thank You Acknowledgements
Department of Science and Technology for Financial Support
Thank You
Dr.R.A.Pandey, CSIR-NEERI, Nagpur, India
Prof.Dr.A.B.Pandit, ICT, Mumbai, India
Dr.S.N.Mudliar, CSIR-CFTRI, Mysore, India
April 28, 2017

19. Sample calculation for preliminary cost estimation of hydrodynamic cavitation treatment to facilitate biogas formation
Biogas formed in the Cavitaionally pretreated B-DWW (13 bar, 25% Dilution, 50 minutes, BI: 0.32) = 400 ml in 2 L of pretreated B-DWW
Biogas formed in the control system = 60 mL
Additional biogas formed due to hydrodynamic cavitation pretreatment = (400-60) mL
= 340 ml in 2 L of pretreated B-DWW
Total Biogas formed in 6 lit of Cavitaionally pretreated B-DWW = 340 (mL) × (6/2)
= 1.02L
Total electrical energy consumed = pump power × total treatment time
= 1.1 kW × (50/60) h
= 0.92 kWh
Biogas formed per unit energy consumed = 1.02 (L) / 0.92 kWh
= 1.11 L/kWh
Power cost in India for heavy industry = 0.13 US$/kWh
Cost for the additional biogas formation = 1.11 (L/kWh) / 0.13 (US$/kWh)
= 8.5 L/ US$
= 0.12 US$/L
% COD reduction: Exp-70%, BI : 0.32, COD:19,000mgL-1 , Control-12%, BI:0.17, COD : 28,754 mgL-1
Duration: 40 days
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