Effects of hydrogen peroxide feeding strategies on the photochemical degradation of polyvinyl alcohol

Abstract

The performance of batch and fed-batch photoreactors with that of continuous photoreactor for the treatment of aqueous polyvinyl alcohol (PVA) solutions is compared. Hydrogen peroxide feeding strategies, residence time, and [H2O2]/[PVA] mass ratio are examined for their impacts on the molecular weight distribution (MWD) of PVA and the total organic carbon (TOC) removal. The results prove that a continuous addition of H2O2 during the degradation reaction ensures the utilization of the produced radicals to minimize the oxidant consumption and maximize the TOC removal and the PVA degradation in a short irradiation time. Also, the MWD of PVA is found to be bimodal and shifted towards lower molecular weights with small shoulder peak indicating a progressive disappearance of the higher molecular weight fractions that is in accordance with the random chains scission mechanism. Besides, the hydrogen peroxide feeding strategies are found to have a great effect on the reduction in H2O2 residuals in the effluent.

ARX and NARX Modeling and Control of a Continuous UV/H2O2 Photoreactor for the Aqueous PVA Degradation

“…The reactions for the degradation of PVA in a tubular flow photoreactor were investigated in our previous studies (Hamad et al, 2019(Hamad et al, , 2016a(Hamad et al, , 2016b(Hamad et al, , 2014. Reaction kinetics is explained in detail in our own previous studies (Hamad et al, 2018).…”

Nonlinear System Identification for Aqueous PVA Degradation in a Continuous UV/H2O2 Tubular Photoreactor

“…The reactions for the degradation of PVA in a tubular flow photoreactor were investigated in our previous studies. − Reaction kinetics is explained in detail in our own previous studies . The general pattern of the degradation pathway of a polymer such as PVA is summarized as follows where P r represents the polymeric compound (PVA).…”

“…The general pattern of the degradation pathway of a polymer such as PVA is summarized as follows where P r represents the polymeric compound (PVA). Under UV light, hydrogen peroxide decomposes into active radicals as follows Both free radicals attack the PVA molecules, where hydrogen is abstracted from the PVA molecule as shown in the following degradation reactions In previous studies, the application of the UV/H 2 O 2 processes for the PVA degradation was typically focused on the pollutant (TOC content) removal, H 2 O 2 residuals, average molecular weight reduction, and the effluent pH in representing PVA degradation efficiencies, H 2 O 2 utilization, and acidic/low-molecular-weight intermediate formation. ,, The results varied under various H 2 O 2 dosages and influent PVA concentrations, with an optimum operating point at a H 2 O 2 /PVA mass ratio of 1.0 at the influent stream. , More importantly, the formation of intermediates during PVA degradation was proven by a decrease in the average molecular weight of pollutants throughout a batch degradation measured by gas permeation chromatography (GPC) analyses and a decrease in pH in the aqueous system. ,,− The decrease in pH further indicated the formation of acidic intermediate throughout the batch PVA degradation process . Hence, in this study, the H 2 O 2 dosage was utilized as the manipulating variable to investigate its effects on TOC removal, effluent pH, and the quality of effluent in terms of H 2 O 2 residuals under steady-state and transient conditions.…”

Modelling and Optimization Study on Biodegradability Enhancement of PVA-Contained Wastewater in a Continuous UV/H2O2 photoreactor

“…High consumption of PVA leads to generating a considerable amount of wastewater containing PVA, which should be treated before discharging to the environment. PVA-contained wastewater is considered recalcitrant and non-biodegradable wastewater due to the long molecular structure of PVA and possessing the ratio of biochemical oxygen demand (BOD5)/chemical oxygen demand (COD) <0.1 [2]. Thus, conventional biological treatment methods are not sufficient to degrade this type of compound.During the last few decades, Advanced Oxidation Processes (AOPs) technique has been extensively studied and vastly proven to be an efficient water/wastewater treatment alternative to degrade recalcitrant/non-biodegradable compounds that may not be easily degraded by conventional biological treatment methods [3].…”

“…High consumption of PVA leads to generating a considerable amount of wastewater containing PVA, which should be treated before discharging to the environment. PVA-contained wastewater is considered recalcitrant and non-biodegradable wastewater due to the long molecular structure of PVA and possessing the ratio of biochemical oxygen demand (BOD5)/chemical oxygen demand (COD) <0.1 [2]. Thus, conventional biological treatment methods are not sufficient to degrade this type of compound.…”