## 4 Conclusions  
This study aimed to optimize the sorption procedure by applying alternative sorbents--biochar and bentonite--in the co-action of ionic liquids such as benzalkonium chloride or Aliquat 336 for the removal of the chromium complex of reactive azo dye Reactive Black 8 from wastewater. The preliminary tests proved that alternative sorbents biochar (BC) and bentonite (BT) do not achieve the sorption capacities of virgin powdered active carbon (PAC) or montmorillonite (MTM), respectively. On the other hand, we proved that the co-action of BC or BT with ionic liquid BAC is the most promising method of RB8 separation from model wastewater. The amount of 2 g L\({}^{-1}\) of BAC in co-action with 1 g L\({}^{-1}\) of BT resulted in higher than 98% RB8 \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Treatment Method**} & **Quantity of Used** & **Initial** & **Decolorization** & **Removal** & \multirow{2}{*}{**Ref.**} \\  & **Reagents per Gram of** & **Concentration of** & & **Efficiency** & & **COD** \\ \hline Biological treatment & _Physalis minima_ L. & 30 mg L\({}^{-1}\) RB8 & 75.7\% & – & [9] \\ Fenton reaction & 0.5 g H\({}_{2}\)O\({}_{2}\) + 0.17 g Fe\({}^{2+}\) & 400 mg L\({}^{-1}\) RB8 & 81\% & 62\% & [15] \\ Fenton reaction + & 0.5 g H\({}_{2}\)O\({}_{2}\) + 0.17 g Fe\({}^{2+}\) & 400 mg L\({}^{-1}\) RB8 & 89\% & 84\% & [15] \\ Photocatalytic oxidation & 20 g CoMoO\({}_{4}\) & 50 mg L\({}^{-1}\) RB8 & 91.5\% & – & [16] \\ Electrooxidation + & \(\Pi\)/R\({}_{2}\)-iPO\({}_{2}\) anode + & 100 mg L\({}^{-1}\) RB8 & 62.9\% & 32.4\% & [17] \\ sonification & steel cathode & 106.7 g nano ZnO & 75 mg L\({}^{-1}\) RB8 & 94\% & – & [19] \\ Adsorption & 20 g Fe powder & 100 mg L\({}^{-1}\) RB8 & 86\% & – & [18] \\ Ion exchange via IL & 2 g BAC * & 1000 mg L\({}^{-1}\) RB8 & 99.1\% & 88.8\% & this work \\ Ion exchange via IL & 6 g A336 & 1000 mg L\({}^{-1}\) RB8 & 98.9\% & 39.2\% & this work \\ Adsorption & 40 g PAC & 1000 mg L\({}^{-1}\) RB8 & 97.9\% & 87.4\% & this work \\ Adsorption & 40 g BC & 1000 mg L\({}^{-1}\) RB8 & 70.8\% & 61.2\% & this work \\ Adsorption & 40 g MTM & 1000 mg L\({}^{-1}\) RB8 & 48.4\% & 37.8\% & this work \\ Adsorption & 40 g BT & 1000 mg L\({}^{-1}\) RB8 & 18.9\% & 10.7\% & this work \\ Co-action of sorbent and IL & 1 g BT + 2 g BAC * & 1000 mg L\({}^{-1}\) RB8 & 92.\% & 94.6\% & this work \\ Co-action of sorbent and IL & 2 g BC + 1.5 g BAC * & 1000 mg L\({}^{-1}\) RB8 & 99\% & 94.6\% & this work \\ \hline \hline \end{tabular}  
* Note: Doses of 50% aq. BAC.  
\end{table} 
Table 2: Comparison of treatment methods applied for wastewater polluted with RB8 dye. removal efficiency after 30 min of action. The comparable removal efficiencies were obtained using as high as 40 g L\({}^{-1}\) of virgin PAC after at least 180 min of action. The equilibrium sorption capacity of the BT in co-action with BAC reaches a value greater than 489 mg g\({}^{-1}\). This high sorption capacity can be explained by the parallel effect of several proposed mechanisms: (i) sorption, (ii) the formation of less polar ion pairs and (iii) the separation of formed ion pairs using a BT sorbent. However, the separation of RBS (7 g L\({}^{-1}\)) from real wastewater established slightly worse results due to the complex matrix of the wastewater sample. For comparable removal efficiency of RB8 dye from real wastewater, it is required to apply an only 1.4 times higher dose of BAC and 4 times higher dose of BT than the optimized dosages applied within the RB8 removal from model wastewaters. The application of alternative sorbents BC or BT decreases the costs of the developed separation process for RB8 dye removal from wastewater. Moreover, the addition of BAC to the used alternative sorbent BC or BT decreases the dosage of BC or BT and provides the required removal efficiencies of both the RB8 dye and/or residual BAC from wastewaters.