Kassim Olasunkanmi Badmus Ninette Irakoze Leslie Petrik Treatment of textile wastewater using combined Hydrodynamic cavitation, Fenton process and Nano zero valent Iron Kassim Olasunkanmi Badmus Ninette Irakoze Leslie Petrik

Oxidizing and reducing agents Textile wastewater contains both organic and inorganic chemical substances used in the complex processes of textile production. Wastewater Organic Organic acids Thickeners Dyes Detergents Textile auxiliaries Finishing agents Inorganic Oxidizing and reducing agents Acids Alkalis Salts

Dyes are the dominant content of textile wastewater Complex organic dyes are toxic chemicals with documented biological effect on animals (Akhtar et al. 2016)

Conventional Treatment of Textile Wastewater Method Example Advantages Disadvantages Physical treatment Filtration, Sedimentation, Precipitation, Adsorption. Turbidity and colour removal Amenability for further treatment Inexpensive Low efficiency Microorganism cannot be removed. Chemical treatment Coagulation, Flocculation, Ion exchange, Chemical disinfection. Improved microbial quality Efficient Physical removal Generation of toxic chemical intermediates Use of expensive chemical Require further treatment for solid waste removal. Biological treatment Active filtration, Riverbank filtration, Membrane bio reactor and Soil aquifer treatment. Effective for COD and turbidity removal Need skilled man power Ineffective for colour removal. Toxic intermediates (Cripps et al. 1990).

Cavitation is a Non-chemical Ultrasonic Hydrodynamic

NZVI is a red-ox agent and good source of Fenton catalyst

Combined AOP using FP, NZVI and HC can result in efficient mineralization of persistent organic pollutants in textile wastewater . Orange II sodium salt (OR2) is a representative azo dye. HC NZVI FP

Objectives of the studies Single AOPs Determination of the optimum condition for degradation of OR2 in HC Focus on pH and initial concentration Combined AOPs Investigation of the degradation effect of HC and FP in combined AOP. Investigation of the degradation effect of HC and NZVI in combined AOP. Results Discussion of the best combined AOP on the degradation effect Proposal for the reaction pathway

Experimental method Find the optimum pH for degradation of OR2 in HC at 300 kPa in-let pressure Find the optimum concentration for degradation of OR2 in HC at 300 kPa in-let pressure Apply the optimum conditions for degradation of OR2 in HC Combine FP [10 ppm H202/ 200 mg Fe (2+)] with the HC at 300 kPa in-let pressure, pH 2, 10 ppm OR2 Combine NZVI (20 mg/ L) with HC at optimum conditions in the degradation of OR2

First order kinetic degradation of OR2 in hydrodynamic cavitation jet-loop at varied initial contaminant pH (Initial concentration and pressure are 10 ppm and 300 kPa respectively).

pH 2 was confirmed as the optimum for the generation of OH radicals in an ultrasonicator in our previous experiment. Badmus et. al., 2016

% degradation per 60 minutes First order rate constant (k) and extent of degradation of OR2 at varied contaminant concentration using HC at pH 9.4, 300 kPa inlet pressure Concentration (ppm) % degradation per 60 minutes k X 10-3 min-1 R2 5 21 4.15 0.988 10 16 3.12 0.991 20 13 2.92 0.972

C Ξ cavitation, F Ξ Fenton, N Ξ green nano zero valent iron (gNZVI) CF Ξ combined cavitation and Fenton, CN Ξ combined cavitation and gNZVI while CNF Ξ combined cavitation, gNZVI and Fenton.

FT-IR spectrograph of OR2 and degraded products after an hour treatment time at the optimized conditions showing the peculiar peaks at (cm-1)

FT-IR spectrograph of OR2 and degraded products after an hour treatment time at the optimized conditions of combine AOP showing the presence of new peaks

Conclusion The single AOP is ineffective in mineralization of Azo dyes. Combination of HC, FP and NZVI can result in efficient degradation of Azo dyes. NZVI and HC represent a green replacement for Fenton oxidation in a AOP system. NZVI and HC was successfully combined for the first time in the treatment of wastewater containing OR2. The rate and extent of degradation is significantly high. The method is recommended for tertiary stage of textile wastewater treatment.

Recommendation for further studies LC-MS analysis should be done to elucidate the complete degradation pathway. COD and BOD test should be done to determine the biodegradability of the resulting compounds. Daphnia magna test should be done to estimate the toxicity of the resulting products. The pH range of activity should be investigated in combine AOP using H.C and NZVI

Acknowledgment Prof. Leslie Petrik ENS (staff and students) Royal Society of chemistry/ Dalton Division UWC

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