# Paper-Mill Wastes for Bioethanol Production in Relation to Circular Economy Concepts: A Review
## 4 CE Aspects of Paper Manufacturing and Bioethanol Production  
### CE in Pulp and Paper Mills  
As businesses and bureaucracies increasingly digitalize, paper mills must become more competitive by becoming more efficient. The paper industry also faces continuous demand to reduce harmful pollutants releases into water and air [105]. Publications from governmental institutions report that embracing a circular economy would bolster the EU's effort to achieve climate neutrality by 2050 [106]. Therefore, the P&P industry is motivated to convert its processes to circular economy systems, including feeding recycled paper into production [23]. One challenge is that, due to sanitary and other implications, less than 80% of paper can be recycled. Moreover, constructions such as beverage packaging, which includes plastic and aluminum, require additional setup of waste sorting [105]. In this respect, European mills are better positioned than competitors in less developed countries that do not have enough recycled paper to feed their paper mills. The paper recycling rate in Germany, for reference, is above 80%, while it is less than 30% in India [73; 76]. The inadequate availability of indigenous wastepaper for papermaking in India is mainly attributed to the fact that, although most of the consumed paper is collected, it is used for multiple purposes such as wrapping and not solely for paper production. 95% of the wastepaper collection system is in the hands of the unorganized sector, and there is no legislation that could promote resource recycling [52]. As China, and gradually other Asian countries, have increasingly restricted the import of recovered fiber (as well as other recovered materials), the dynamics have shifted. While prices of old corrugated containers (OCCs) and other papers for recycling have plummeted in North America and Europe, prices of domestic Chinese OCCs have risen drastically, challenging both the price and availability of recycled-based corrugated board [18]. With the growing needs worldwide, it appears that the collection of yesterday's consumption is not sufficient for tomorrows' manufacturing. Research is being conducted to improve that ratio. For example, banning toxic inks as an increasing factor in the value of paper recovery is being investigated [53]. A case study of CE in the papermaking industry is the CE papermaking park in China, which piloted a governmental program of advanced CE. Instead of local energy supply that is inefficient for each manufacturer alone, the essence of this park is the centralization of power and heat supply, water supply, solid waste treatment, and wastewater treatment for many papermaking plants together. Energy recycling from the steam line is utilized for cooling water or heat. Solid waste such as paper and de-inking sludge is recovered to produce bobbin paper, which is used for reel cores production. Paper sludge can also be used together with coal in combustion for power supply due to its high calorific value of about 1500 kJ/kg. Environmentally, this method raises a challenge of ash generation, which requires a proper solution such as use in the cement industry [107]. Other studies demonstrate the crucial role of policymakers in the implementation of CE aspects in the forest-wood sector. For example, the forest-wood sector suffers from regulatory inconsistencies like subsidies for wood-waste incineration practices, which act in contrast to the need for incentives for upcycling and reuse practices [108]. Paper sludge originates from the waste stream, which can be dealt with following various CE guidelines and benchmarks [109]. The potential utilization of wastewater in paper mills as a resource for process refeeding has been supported by calculations [8]. However, the challenge lies in achieving a complete system closure and effluent reutilization in kraft mills, as prolonged zero discharge operation often leads to issues like corrosion from chlorides and sulfur [29].