# Paper-Mill Wastes for Bioethanol Production in Relation to Circular Economy Concepts: A Review
## 5 RPS for Energy Applications
### Economic Aspects of CE in the Paper Industry  
Paper waste management poses a major economic burden on paper and cardboard producers and recyclers. This burden has dramatically increased in recent years, due to the increase in e-commerce and shipments and the growing need for cardboard boxes and containers [59]. These challenges are also accompanied by major fluctuations in paper and cardboard prices, initially started by a major reduction of more than 300% in cardboard prices, due to the high-volume importation of cheap cardboard from China in recent years, which left the paper recycling sector \"in a crisis situation\" [173]. A more recent case study in Catalonia, Spain, showed a major drop of 73% in paper and cardboard prices from 74.5 \(\upxi\) \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Raw Material** & **Ethanol Production (g/L)** & **Yield (\%)** & **References** \\ \hline Recycled paper sludge & 14.9 & 9.44 & [5] \\ Recycled paper sludge & 5.6–6.3 & 67.9–76.8 & [63] \\ Virgin pulp sludge & 34.2 & 66.9 & [152] \\ Primary sludge & 25–30 & 94.5–95.7 & [165] \\ Primary sludge & 30.7–58.8 & 90 & [166] \\ Primary sludge & 37.2 & 23.5 & [167] \\ Kraft pulp & 30–38 & 16.8–20.2 & [7] \\ Kraft pulp & 5.88 & 4.5 & [168] \\ Kraft pulp & N/A & 12–20 & [169] \\ Spent sulfite liquor & 8.1 & 49 & [170] \\ Spent sulfite liquor & 9 & 25 & [171] \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Ethanol production from papermaking process waste by-products. to 20 \(\epsilon\) during 2018-2019 [174]. Recently, cardboard prices have been moving up, which is explained by the end of inventory hoarding that characterized the post-pandemic recovery. However, it is too soon to determine if these price increases will stay and be repeated [175]. Furthermore, the necessity for waste handling and shipments to landfills/treatment sites, as mostly practiced, contributes substantially to the economic burden of the paper industry. The necessity for the paper and carboard industry to shift toward a CE is demonstrated by the cost of unit cargo for truck shipments that can be estimated to range between 40-180 USD/ton of waste (for a 1000 km distance), according to the truck fullness ratio and additional tax fees [176]. A recent publication by the Ministry of Land, Infrastructure, Transport and Tourism of Japan issued a transportation rate of 7.63 USD/km for a 20-ton truck (with a volume capacity of 75 m\({}^{3}\)) [177]. This has led to several works evaluating full life cycle assessments (LCAs) in the paper industry, analyzing water and raw materials and end waste-products for the possibility of further use, thus increasing economic feasibility [60; 178; 179]. Moreover, PS valorization into valuable energy products holds high potential for environmental benefits. A case study conducted on a virgin pulp mill has shown that the use of PS bioenergy for ethanol and bio-gas production has the potential to reduce energy demand by 10%, while reclaiming 82% of the water from the PS. As a result, greenhouse gas emissions (GHGs) will be reduced by three times, and solids suitable for land spreading will be produced as well [180]. To date, carbon taxes and emissions trading system (ETSs) cover 20% of global emissions. Since these tools increasingly take central places in GHG emissions regulations, this approach can be much more beneficial economically, saving high carbon fees [181]. Integration of ethanol production may transform P&P mills into biorefineries, allowing them to diversify production and increase profitability. For example, several works have assessed the techno-economic potential for repurposing kraft mills into ethanol production plants [182; 183]. Although sulfite pulps correspond to only 2% of annual wood pulps [22], additional papers have suggested the conversion of sulfite mills into integrated biorefineries [184; 185]. Bioethanol production integration into existing paper mills can maximize the use of raw material and reduce operational costs.