Intensified depolymerization of aqueous polyacrylamide solution using combined processes based on hydrodynamic cavitation, ozone, ultraviolet light and hydrogen peroxide

• First depiction of combined processes based on hydrodynamic cavitation and ozone.
• Intensified intrinsic viscosity reduction of polyacrylamide solutions.
• Role of ozone and H2O2 in enhancing the depolymerization has been established.
• HC in combination with UV and H2O2 is the best treatment approach.

The present work deals with intensification of depolymerization of polyacrylamide (PAM) solution using hydrodynamic cavitation (HC) reactors based on a combination with hydrogen peroxide (H2O2), ozone (O3) and ultraviolet (UV) irradiation. Effect of inlet pressure in hydrodynamic cavitation reactor and power dissipation in the case of UV irradiation on the extent of viscosity reduction has been investigated. The combined approaches such as HC + UV, HC + O3, HC + H2O2, UV + H2O2 and UV + O3 have been subsequently investigated and found to be more efficient as compared to individual approaches. For the approach based on HC + UV + H2O2, the extent of viscosity reduction under the optimized conditions of HC (3 bar inlet pressure) + UV (8 W power) + H2O2 (0.2% loading) was 97.27% in 180 min whereas individual operations of HC (3 bar inlet pressure) and UV (8 W power) resulted in about 35.38% and 40.83% intrinsic viscosity reduction in 180 min respectively. In the case of HC (3 bar inlet pressure) + UV (8 W power) + ozone (400 mg/h flow rate) approach, the extent of viscosity reduction was 89.06% whereas individual processes of only ozone (400 mg/h flow rate), ozone (400 mg/h flow rate) + HC (3 bar inlet pressure) and ozone (400 mg/h flow rate) + UV (8 W power) resulted in lower extent of viscosity reduction as 50.34%, 60.65% and 75.31% respectively. The chemical structure of the treated PAM by all approaches was also characterized using FTIR (Fourier transform infrared) spectra and it was established that no significant chemical structure changes were obtained during the treatment. Overall, it can be said that the combination of HC + UV + H2O2 is an efficient approach for the depolymerization of PAM solution.