## 5 Water Treatment Employing Bioadsorbents
### Bioadsorbents Based on Fruits and Vegetables
#### 5.2.2 Industrial Contaminants  
Removing dyes from aqueous solutions can be a difficult task with conventional treatment methods. However, the bioadsorbent application of fruit biowastes as AC or raw material has been studied for dye removal (Table 4). For instance, watermelon rind-based AC adsorbed brilliant green, remazol brilliant blue reactive, basic red 2, and orange G, showing removal efficiencies of 98, 94.5 \(\pm\) 2.5, 75 and 85%, respectively, at 30 \({}^{\circ}\)C and q\({}_{\rm m}\) values in the range of 27.4-333.3 mg/g [3]. It is important to mention that the dye adsorption was both endothermic (remazol brilliant blue reactive and basic red 2) and exothermic (brilliant green and orange G). In the same study a dominance of ion-exchange sorption towards MB was present, with maximum capacity values of 188.6-489.8 mg/g and removal efficiencies from 83% to 98%. The models that best described the kinetic and equilibrium data were pseudo-second order and Langmuir isotherm. Additionally, coconut co prior powder without chemical treatment exhibited a monolayer adsorption capacity of 29.50 mg/g for MB under optimal conditions (30 \({}^{\circ}\)C and pH 6.0), achieving maximum removal efficiency when the adsorbent dosage increased from 0.05 to 0.20 g [72]. In this case, the authors determined that the Temkin isotherm model was adequate to describe the adsorption behavior, as it considers that the adsorption heat of the molecules decreases linearly along the surface by adsorbent-adsorbate interactions. Depending on the initial adsorbent concentration, after 180 min of contact time the removal efficiency for MB using jackfruit peels without pre-treatment varied from 58.2 to 89.8% with a maximum adsorption capacity of 285.71 mg/g [74]. AC from pineapple waste was identified as another efficient bioadsorbent for MB recovery, presenting an outstanding adsorption capacity (288.34 mg/g) and removal efficiencies from 67 to 76%, according to the Langmuir isotherm [48]. Other biowastes of interest include pomelo and banana peels; the former exhibited a maximum MB removal efficiency of 83% with a q\({}_{\rm m}\) of 133 mg/g, while the latter reached a maximum adsorption capacity of 15.9 mg/g at the same temperature (30 \({}^{\circ}\)C) and different pH (8 and 6, respectively) [67, 96]. Pomelo peels without any chemical treatment were studied by [PERSON] et al. [83], retaining antraquinonic dye reactive blue 114 from aqueous solutions; adsorption reached equilibrium (16.3 mg/g) within a 90 min reaction time, with a maximum removal efficiency of 96%. Congo red is another widely-used dye with carcinogenic properties that needs to be monitored and removed from water sources. [PERSON] et al. [3] reported that AC from watermelon rinds adsorbed it at a capacity of up to 17 mg/g, with efficiency above 100% when using sonication and modification with TiO\({}_{2}\) nanoparticles. When the adsorption was assisted by the ultrasound method, the acoustic waves caused the water to create gas bubbles or cavities, increasing the surface area and facilitating contact between the dye and the biosorbent [106]. Coir pith presented notable removal percentages of Congo red under acidic conditions, varying from 30.5 to 66.5% depending on the dye concentration [46]. This bioseduine is interesting for violet acid recovery, because after thermal treatment it exhibited up to 78.7% dye removal and attained equilibrium after the first 10 min of adsorption [46]. Congo red was removed using orange peel with a maximum removal efficiency reaching up to 76.6% at pH 5 and decaying to 49% at pH 12 [80]. Banana peel was evaluated for the adsorption of Congo red, methyl orange, methyl violet, and amido black 10B at initial concentrations of 100 mg/g, achieving maximum adsorption capacities of 11.2, 17.2, and 7.9 mg/g, respectively [67]. The Langmuir and Freundlich isotherms were used to describe the adsorption behaviors, with the latter a better fit for the data.