# Unravelling the Environmental Application of Biochar as Low-Cost Biosorbent: A Review
## 4 Biochar Adsorption of Emerging Contaminants  
Presently, the so-called \"emerging contaminants\" as the result of anthropogenic activities are being released into the environment and have been detected in surface water, groundwater, drinking water and wastewater treatment plant effluents in trace amounts. In recent years, the development of new and more sensitive methods of analysis has made it possible to alert people to the presence of these micropollutants. Just in the case of Europe, more than 700 of these compounds have been reported [71]. Thus, a standard pharmaceutical product such as ibuprofen has been detected in several scenarios, such as wastewater treatment plant effluents (0.038 \(\mu\)g/L) [72], surface water (6-780 ng/L) [73], groundwater (4-2250 ng/L), and drinking water (4-50 ng/L) [74]. In the same scenarios, it is also possible to find pesticides such as atrazine in surface water (1.29 \(\mu\)g/L) [75] or dyes such as disperse blue 373 or disperse red 1 in the effluents of a wastewater treatment plant in a range of 0.03-0.35 \(\mu\)g/L [76]. These facts confirm that the current wastewater treatment plants are not designed to remove these micropollutants.  
In this context, it should be noted that one of the main handicaps for proper treatment is their low concentration, and the adsorption process stands out. However, the large variety of micropollutants requires the design of new and more specific adsorbents, so the use of unmodified or modified biochar opens up a field of possibilities. In Table 2, the recent research on the application of biochar in the restoration of aquatic environments containing several organic contaminants is summarized.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c} \hline \hline
**Biochar** & **Pyalysis** & **Procedure** & **Pollustant** & **N(C)** & **H(C)** & **O(C)** & **C(C)** & **Surface Area** & **Isochron Model** & **Unregular** & **Sorption Mechanism** & **Ref.** \\ \hline \multirow{4}{*}{Pount-shell} & \multirow{4}{*}{400 \({}^{\circ}\)  
These results confirm that biochar produced in the laboratory can adsorb organic pollutants at a similar level to commercial activated carbon. As an additional advantage, the regeneration of biochar can be easily carried out through different treatments (Figure 3), such as microwave irradiation, thermal or chemical treatment [91; 92; 93], including by extraction with organic solvents or by direct degradation on the biochar surface using advanced oxidation processes [94; 95; 96].  
The adsorption mechanism to remove organic compounds depends on the nature of the pollutants and the properties of biochar, which vary greatly with the selected feedstock and the thermochemical process used. For example, when the temperature is increased, the aromaticity, hydrophobicity and surface area of biochar also increase, which makes it a suitable adsorbent for hydrophobic organic compounds. In addition, by application of other traditional or emerging technologies (such as coating, physical or chemical activation, nanotechnology and/or biotechnology) it is possible to create additional active sites to favor the removal of these organic pollutants [75; 76]. Therefore, due to the diversity of synthesized biochar as well as the variety of organic compounds with different properties, the recent developments in this issue focusing on the most abundant organic contaminants (dyes, pharmaceuticals and personal care products) are summarized.