Abstract When old corrugated cardboard (OCC) is returned to the paper mill for repulping and reuse, the starch, which is added to the paper surface as a reinforcement agent, is dissolved into the pulping process water. Most of the OCC pulping wastewater is recycled to save precious water resources; however, during the water recycling process, the accumulation of dissolved starch stimulates microbial reproduction, which causes poor water quality and putrid odor. This problem seriously affects the stability of the papermaking process and product quality. In this study, phosphomolybdic acid (H 3 PMo 12 O 40 , abbreviated as PMo 12 ) was utilized to oxidatively degrade the waste starch present in papermaking wastewater to monosaccharides, realizing the resource utilization of waste starch. The results showed that the optimized yield of total reducing sugar (73.54 wt%) and glycolic acid (11.05 wt%)was achieved at 145 °C with 30 wt% PMo 12 , which is equivalent to 84.59 wt% starch recovered from wastewater. In addition, the regeneration of the reduced PMo 12 was realized applying a potential of 1 V for 2 h. Overall, this study has theoretical signi ¦ cance and potential application value for resource utilization of waste starch in OCC pulping process and cleaner management of OCC waste paper. Introduction In the production of corrugated paper and liner paper, starch is often used as a paper surface enhancer because of its low cost, environmental protection, and degradability (Li et al. 2013; Wang C 2020). However, when the old corrugated cardboard (OCC) waste paper made from corrugated cardboard boxes and test liner is returned to the paper mill for pulping and papermaking, most of the starch on the paper surface is dissolved into the water during dissociation of waste paper ¦ bers. The starch, which accumulates abundantly in the papermaking system, has a serious effect on the papermaking production, particularly regarding environmental impact, stability of the system operation, and product quality. Simultaneously, the accumulated starch also causes proliferation of microorganisms(Zhu et al. 2017), which results in rot and smell and further deterioration of the production system, the environment, and product quality (Lin et al. 2020; Miao et al. 2012). Generally, anaerobic fermentation is used for the production of biogas, wastewater treatment, and energy recovery (Chaterjee et al. 2019; Sun et al. 2011). According to the China Paper Association report in 2019(Association 2020), the total production of corrugated cardboard containers in China is 44 million tons, accounting for 40.9% of total paper production. Commonly, starch consumption is approximately 40–60 kg for every ton of paper ¦ bers; the total consumption of starch based on the above reports is 1.76–2.64 million tons every year, which is equivalent to 303,000~455,000 ha of ¦ elds (the average yield of corn starch is 5800 kg/ha)(Lin et al. 2020). This implies the wasting of a large amount of food. Polyoxometalates (POMs) are polymetallic oxygen cluster compounds consisting of a metal–oxygen octahedron, which have become a research hotspot in many ¦ elds due to their low corrosivity and environmental protection (Guo et al. 2019; Wang and Yang 2015). POMs are considered as water-soluble metal oxide nanoparticles (Du et al. 2017; Wu et al. 2016), and have both acidic and redox characteristics, as well as unique "pseudo-liquid phase" characteristics (Long et al. 2010). Therefore, it is more e ¨ cient
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