## 3 Obtaining Waste-Based Bioadsorbents
### Raw Wastes as Bioadsorbents
[72] employed coconut coil dust without chemical modification to remove MB, resulting in pH-dependent monolayer adsorption behavior. [PERSON] [76] studied the MB adsorption process employing a jackfruit peel biobed. This biowaste was sliced and dried at 70 \({}^{\circ}\)C, then ground and sieved to obtain a particle size range of 0.5-1 mm. Banana, orange, and pomelo peels represent another low-cost method, adsorbing MB and other dye pollutants such as methyl orange, rhodamine-B, congo red, methyl violet, amido black 10 B, proicon orange, violet 17 (V-17), direct red 23, direct red 80, and reactive blue 114 without requiring chemical treatment. The waste peels in these studies were dried in the sunlight and a hot air oven at 60 or 120 \({}^{\circ}\)C, and the resulting material was crushed with a mill and sieved to obtain a particle size < 500 \(\upmu\)m [67, 80, 81, 83, 95, 96]. Low-cost adsorbents derived from herbage and forage have been studied for the removal of dyes generated from different industries. Caulfilower leaves were dried and pulverized to achieve a higher adsorption capacity for MB in synthetic aqueous solutions [70]. [PERSON] et al. [84] evaluated the leaves and stems from potato plants as biodegradable material for the removal of MB and malachite green; leaves boiled and dried at 60 \({}^{\circ}\)C showed better adsorption efficiency than stems for both dyes at same particle sizes (100-150 \(\upmu\)m). [PERSON] et al. [69] employed raw and chemically, magnetically, and non-magnetically modified versions of barley straw to remove four water-soluble dyes (bismarck brown Y, crystal violet, MB, and safranin O). The barley straw was cut and sieved into fine particles (\(\sim\)0.15-2 mm diameter) and a fraction was magnetically modified by microwave-synthetized magnetic iron oxides followed by treatment with citric acid, then dried at 50 \({}^{\circ}\)C until reaching a constant weight. Macro- and micronutrients that alter the microbial dynamics in ecosystems have been removed by employing bioadsorbents. Fluoride, one of these pollutants, was removed from contaminated underground water using natural banana-peel powder in a fixed-bed design. This biomaterial was dried at 50 and 60 \({}^{\circ}\)C and then ground to obtain a particle size of 200 \(\upmu\)m for the batch experiments [68]. Mangosteen pericarps, passion fruit rinds, red onion peels, and red dragon fruit peels were used to make an anthocyanin-based adsorbent to attract iodide ions (I\({}^{-}\)). These raw materials were dried at 60 \({}^{\circ}\)C, ground, and sieved to obtain particles of 0.5-0.711 mm [79]. Additionally, phosphates were extracted employing peanut husk improved with Fe\({}_{3}\)O\({}_{4}\) as an adsorption assistant, as this increases ionic attraction and provides a cheaper recovery method than centrifugation or filtration. This oxide was combined with iminodiacetic acid (IA) and zirconium (Zr) to increase the efficiency and selectivity of the peanut husk-based magnetic material [82]. As for pharmaceuticals, coffee and rice husks were tested by [PERSON] et al. [71] in a variety of particle sizes (from <75 to 500 \(\upmu\)m) to retain the antibiotic norfloxacin in distilled and municipal water. Both natural adsorbents were dried at 60 \({}^{\circ}\)C, ground to powder, and sieved; particles < 75 \(\upmu\)m proved to be the best option for norfloxacin adsorption. Another cereal byproduct, rice straw, was dried at the same temperature, pulverized, and passed through a mesh sieve (<150 \(\upmu\)m) to test its ability to remove clofibric acid and carbamazepine from aqueous solutions at different pH values and adsorbent concentrations [85].