Synthetic water-soluble polymers are popular in industry and they are produced in large scale owing to their wide spectrum of applications. In particular, the polyvinyl alcohol polymer (PVA), a well-known refractory pollutant, is abundant in wastewater effluents since it is heavily used in industry as paper coating and polarization layer in liquid crystal displays (LCDs). These polymers are non-biodegradable and contaminant to water resources. Alternatively, they can be effectively removed by advanced oxidation processes (AOPs).
This study investigates the photo-oxidative degradation of aqueous PVA solution in UV/H2O2 photoreactors and the effect of hydrogen peroxide feeding strategies on the photoreactor performance. The research covers thoroughly the impact of operating conditions on the polymer number average molecular weight (Mn), TOC content, and H2O2 residual under batch, fed-batch and continuous modes of operation. The experimental results show that the performance of the fed-batch photoreactor was higher than the batch system for similar experimental conditions revealing that the way H2O2 is fed into the system has a considerable effect on the PVA degradation.
The experimental result of batch system was used as a guide to develop a photochemical kinetic model of the PVA degradation in UV/H2O2 batch process that describes the disintegration of the polymer chains in which the statistical moment approach was considered. The model predictions are in good agreement with data.
Realizing the limitations of batch and fed-batch UV/H2O2 processes, an innovative continuous treatment technique was devised to enhance the process performance and to minimize UV dosage. Response surface methodology (RSM), based on Box-Behnken method, was adopted for design set of experiments required to determine the impact of operating variables and their interaction on the process performance.
Finally, the results show that Mn was reduced from 130 kg/mol to 24.9, 20.3, and 2.2 kg/mol, corresponding to percent TOC removal of 41.5, 64.2 and 94.4 and H202 residual of 17, 3 and 1% were achieved in batch, fed-batch (120-min), and continuous (30-min) UV/H2O2 photoreactors, respectively. In addition, the overall power consumption of the process was assessed to determine the economic incentive for continuous feeding strategy and ensure the possibility of the process scale-up.