# Low-Cost Biochar Adsorbents for Water Purification Including Microplastics Removal
The forest industry has traditionally used these sidestreams for energy production, but this use is increasingly limited because of the \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Pyrolysis**} \\ \hline  & **Fast** & **Intermediate** & **Slow** & **Torrefraction** & **Gasification** \\ \hline Temperature & 500 & 400 & 400 & 300 & 800–900 \\ Residence time & \textless{1 s} & 10–30 s & 1–5 h & Hours-days & s-min \\ Liquid \% & 75 & 40 (2 phases) & 35 & & 1–5 \\ Char \% & 12 & 40 & 35 & 85 & \textless{1} \\ Gas \% & 13 & 20 & 30 & 15 & 95–99 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of different pyrolysis processes with product distributions. growing need to decrease carbon dioxide (CO\({}_{2}\)) emissions from industries. There is a need to find alternative uses for these sidestreams, of which biochar is one possibility. Bio-based carbons are creating a new market segment in water treatment and metallurgy based on their potentially low cost compared with traditional fossil carbons subdued to emission trade. Both applications present \"new\" industrial utilizations with positive export potential for countries with significant forest products industries, both domestically and internationally. Based on the earlier reports on economically feasible raw materials for biochar (e.g., [12; 13]), a range of different wood-based wastes and sidestreams are suitable for biochar production. The steam activation method has been used to produce ACs from various biomasses, such as white spruce sawdust, canola, and wheat straw [14], switchgrass, hard and soft wood [15], oil palm stones [16], oil palm shells [17], and seed cakes [18]. Despite the large volumes generated by the forest products industry, tree bark has not been extensively tested for production of steam activated carbons. Mixed soft wood bark residue has been successfully converted into AC in a small-scale thermogravimetric experiment [19], producing surface areas between 455 and 613 m\({}^{2}\)/g at different temperatures (600-985 \({}^{\circ}\)C). Poplar wood bark biochar has also been used for steam activation with similar surface areas of 547 and 555 m\({}^{2}\)/g at 700 and 800 \({}^{\circ}\)C, respectively [20]. In the present study, we have investigated activated biochar production from two forest industry sidestreams, pine and spruce bark. The suitability of these steam-activated biochars for application to treatment of urban runoff and wastewater purification were investigated by examining the attenuation of selected metals, microplastics, and organic contaminants. Microplastics in stormwaters originate from microscopic plastic spheres or particles that are intentionally added to a product, or from disintegrating plastic and rubber materials. One of the major sources of microplastics is created by traffic through the abrasion of vehicle tires, brakes, and the road surface itself [2]. Vehicle-generated plastic particles can be mobilized by wind and passing traffic, becoming deposited in surface waters, soil, or sediment. Deposition of a large quantity of plastic particles to surface waters can cause significant damage to the aquatic environment and organisms [21; 22; 23; 24]. Recent studies of microplastics removal have focused on agglomerate formation [22; 25] or activated sludge [26]. Biochar and activated biochar also have the potential to retain microplastics. Microplastic particles can be immobilized between biochar particles or, in the case of nano-and micrometer-scale particles, retained within the pore structure. The present study examined microplastics removal by steam-activated biochar generated from pine and spruce bark. The particular focus of the study was on the characteristics of the biochar products, e.g., the particle size and chemical composition, as forest residues may be comprised of highly inhomogeneous raw materials.