# Low-Cost Biochar Adsorbents for Water Purification Including Microplastics Removal
## 3 Results
### Yields, Surface Areas, and Porosities
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Parameter** & **Pine Bark Biomass** & **Pine Bark Biochar** & **Pine Bark AC 30\% Steam** & **Pine Bark AC 30\% Steam** & **Pine Bark AC 40\% Steam** \\ \hline N\({}_{2}\) gas flow, L/h & - & - & 66 & 300 & 300 & 300 \\ Particle size & large & large & small & small & large & small & large \\ Carbon, wt-\% & \(53\pm 3\) & \(77\pm 2\) & \(81\pm 3\) & \(84\pm 2\) & \(90\pm 7\) & \(85\pm 2\) & \(91\pm 2\) \\ Nitrogen, wt-\% & \(0.13\pm 0.02\) & \(0.043\pm 0.02\) & \(0.14\pm 0.01\) & \(0.11\pm 0.00\) & \(0.21\pm 0.06\) & \(0.17\pm 0.03\) & \(0.11\pm 0.02\) \\ Hydrogen, wt-\% & \(5.8\pm 0.03\) & \(3.1\pm 0.1\) & \(0.69\pm 0.08\) & \(0.67\pm 0.01\) & \(0.70\pm 0.05\) & \(0.67\pm 0.03\) & \(0.74\pm 0.01\) \\ Sulfur, wt-\% & \(0\pm 0\) & \(0\pm 0\) & \(0\pm 0\) & \(0\pm 0\) & \(0\pm 0\) & \(0\pm 0\) & \(0\pm 0\) \\ Oxygen, wt-\% & \(41\pm 0\) & \(13\pm 0\) & \(2.4\pm 0.2\) & \(3.6\pm 0.4\) & \(3.5\pm 0.4\) & \(3.0\pm 0.2\) & \(2.8\pm 0.1\) \\ Ash, wt-\% & \(1.4\pm 0.0\) & \(4.7\pm 0.7\) & \(5.8\pm 0.1\) & \(5.7\pm 0.3\) & \(5.6\pm 0.1\) & \(6.2\pm 0.1\) & \(6.1\pm 0.1\) \\ \hline
**Parameter** & **Sproce Bark Biomass** & **Sproce Bark Biochar** & **Sproce Bark AC 30\% Steam** & **Sproce Bark AC 30\% Steam** & **Sproce Bark AC 40\% Steam** \\ \hline N\({}_{2}\) gas flow, L/h & - & - & 66 & 300 & 300 & 300 \\ Particle size & large & large & small & small & large & large \\ Carbon, wt-\% & \(47\pm 0.1\) & \(68\pm 3\) & \(65\pm 1\) & \(68\pm 3\) & \(63\pm 2\) & \(65\pm 4\) & \(57\pm 4\) & \(69\pm 8\) \\ Nitrogen, wt-\% & \(0.42\pm 0.02\) & \(0.62\pm 0.05\) & \(0.53\pm 0.04\) & \(0.45\pm 0.03\) & \(0.40\pm 0.01\) & \(0.42\pm 0.04\) & \(0.46\pm 0.02\) & \(0.43\pm 0.08\) \\ Hydrogen, wt-\% & \(5.7\pm 0.07\) & \(2.5\pm 0.1\) & \(0.70\pm 0.03\) & \(0.60\pm 0.01\) & \(0.60\pm 0.04\) & \(0.65\pm 0.03\) & \(0.61\pm 0.03\) & \(0.60\pm 0.08\) \\ Sulfur, wt-\% & \(0\pm 0\) & \(0\pm 0\) & \(0\pm 0\) & \(0\pm 0\) & \(0\pm 0\) & \(0\pm 0\) & \(0\pm 0\) & \(0\pm 0\) \\ Oxygen, wt-\% & \(42\pm 0\) & \(12\pm 0\) & \(4.7\pm 0.1\) & \(3.9\pm 0.3\) & \(5.3\pm 0.2\) & \(5.1\pm 0.5\) & \(5.2\pm 0.1\) & \(4.9\pm 0.6\) \\ Ash, wt-\% & \(5.4\pm 0.1\) & \(11\pm 1\) & \(15\pm 0\) & \(24\pm 1\) & \(13\pm 1\) & \(15\pm 0\) & \(12\pm 0\) & \(18\pm 0\) \\ \hline \end{tabular}
\end{table} 
Table 4: Elemental composition of the studied biomasses, biochars, and activated biochars. The surface areas of the activated biochars increased as a function of the burn-off, however the results were also influenced by pore formation. Large particles exposed to 30% steam, for example, had lower burn-off than small particle size AC (24.5% vs. 28.7%) but higher surface area because of the relatively greater quantity of micropores. The particle size effect was more substantial with pine bark, but the smaller particle size of both bark biochars yielded a slightly greater surface area, as the smaller particle size provides more reaction surface for the steam. The total burn-off of pine bark biochar because of activation increased in a more linear fashion than that observed for spruce bark biochar (Figure 2). The surface areas of the spruce bark ACs were considerably lesser than those of pine bark ACs. This result may have been due to the high quantity of ash in the spruce bark (Table 4), which can cause pore blockage. The pore size distributions of pine and spruce bark ACs remained similar, consisting of primarily micropores. Increasing the activation time and temperature may have resulted in an increase in the quantity of larger pores. Some of the observed differences between pine and spruce bark biochars and ACs may be an artefact of the non-homogenous nature of the biomasses. The bark residues may contain some amounts of stem wood, for example, that has a different pore structure than the bark.