## 4 Conclusions  
The use of sewage sludge as a low-cost precursor for the preparation of activated carbons to removal neonicotinoid pesticides, e.g., Acetamiprid, thiamethoxam, and imidalcoprid, is a sustainable way to solve the serious problem of sludge management while being in accordance with the concept known as a circular economy. The synthesized activated carbons showed heterogeneous textural properties (micro-mesoporous character)--a characteristic of activated carbons obtained from waste and perhaps also as a result of the heterogeneous nature of the precursor used. The maximum specific surface area (S\({}_{\text{BET}}\) = 558 m\({}^{2}\)/g) was obtained for the AC synthesized using ZnCl\({}_{2}\) as the impregnation agent. Relatively slow adsorption kinetics were obtained for all the materials as a result of the steric hindrance caused by the molecules adsorbed, that is, due to the relatively large molecular size of the pesticides in relation to the medium pore size of the activated carbons; thus, the equilibrium times were longer when THM was used, since this is the largest of the tested molecules. Despite this, very high equilibrium adsorption capacities were obtained: using AC-ZnCl\({}_{2}\), q\({}_{\text{e}}\) values of 128.9, 126.8, and 166.1 mg/g for ACT, THM, and IMD, respectively, were obtained. Besides this, it is important to highlight the behavior observed in the removal of THM onto the AC-Fe(NO\({}_{3}\))\({}_{3}\) and AC-Fe\({}_{2}\)(SO\({}_{4}\))\({}_{3}\) activated carbons, since simultaneous contributions of adsorption and reaction phenomena were observed; this is possibly due to the high content in Fe of these materials. Regarding the adsorption isotherms, it is interesting that, in general, they showed a multilayer profile, which indicates an important contribution of the mesoporous in the adsorption process.  
For all these reasons, the use of sewage sludge to produce activated carbons has great potential as it is a sustainable solution for the management of this kind of waste, and the  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Biomass Source** & **Pesticide** & \begin{tabular}{c} **Adsorption Capacity** \\ **(mg/g)** \\ \end{tabular} & \begin{tabular}{c} **S\({}_{\text{BET}}\)** \\ **(m\({}^{2}\)/g)** \\ \end{tabular} & \begin{tabular}{c} **t\({}_{\text{e}}\)** \\ **(min)** \\ \end{tabular} & **Reference** \\ \hline _Ricinodendron_ & Imidacloprid & 43.48 & 1179 & 90 & [48] \\ _heudelotii_ shells & 39.37 & 6 & 40 & [49] \\ \begin{tabular}{c} \end{tabular} & Accetamiprid & 35.70 & 688 & 240 & [50] \\ \
\begin{tabular}{c} \end{tabular} & Imidacloprid & 8.68 & 535 & 240 & [51] \\
\begin{tabular}{c} \end{tabular} & Imidacloprid & 313.00 & 660 & 720 & [52] \\ \hline \hline \end{tabular}
\end{table}
Table 7: Adsorption capacity values of pesticides onto adsorbents derived from biomass.  
resulting activated carbons can be considered capable of competing with conventional adsorbent materials synthesized from fossil fuels.  
Conceptualization, E.S.-S., S.A.-T. and M.L.; methodology, E.S.-S. and L.C.; software, E.S.-S. and L.C.; formal analysis, E.S.-S., S.A.-T. and M.L.; investigation, E.S.-S., L.C. and S.A.-T.; resources, V.I.A. and J.G.; data curation, E.S.-S., L.C. and S.A.-T.; writing--original draft preparation, E.S.-S., L.C. and S.A.-T.; writing--review and editing, E.S.-S., L.C., S.A.-T. and M.L.; supervision, V.I.A. and J.G. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Regional Government of Madrid provided through Project P2018/EMT-4341 and Project IND2019/AMB-17114.  
Not Applicable.  
The study did not report any data.  
The authors declare no potential conflicts of interest with respect to the research, authorship, and/or publication of the article.