## 1 Introduction
pH is one of the most important parameters, as it can improve or weaken removal efficiency by affecting the solubility of metal ions as well as the physical properties, structure, and availability of active sites on the surface of the adsorbent [11, 15, 16]. A high adsorbent dosage provides a higher number of active sites, and consequently increases the adsorption capacity until equilibrium is reached at which an excess adsorbent does not further improve removal efficiency [15]. The adsorption capacity can be further increased by reducing the particle size of the adsorbent, as there is then a higher surface area and the limitations caused by mass and diffusional transfer are decreased. This allows molecules to reach sorption sites more easily, and the capture of the adsorbate occurs in a shorter time [15, 17, 18]. Furthermore, the adsorption capacity increases as the contaminant concentration rises, which is calculated by isothermal models that estimate the maximum sorption capacity of the adsorbent (q\({}_{\rm m}\)) at a given temperature  
Figure 1: Adsorption mechanisms: (**A**) chemisorption monolayer; (**B**) physisorption multilayer; and (**C**) ion exchange adsorption. given the possible adsorption mechanisms [17; 19]. Langmuir and Freundlich isotherms are two of the most common models employed to describe different bioadsorbents. However, the Dubinin-Radushkevic, Temkin, and other models have been used in specific cases, e.g., where the carbonaceous material capacity is defined by neither layer-by-layer adsorption nor a constant adsorption potential, or when the adsorption behavior is characterized by uniform energy distribution [20; 21; 22]. The adsorption kinetics indicate the influence of the contact time, which depends on the adsorbate concentration, temperature, and adsorbent characteristics (surface and pore size). There are several kinetic models; however, two that are generally applied in bioadsorbent studies are the pseudo-first and pseudo-second order models [23]. Both models deduce the sorption occurring on localized sites without interaction among the adsorbed ions until it reaches a maximum point on the saturated monolayer [24]. In the context of the current relevance and application of bioadsorbents for water bioremediation, although many authors have reported on several options for the removal of a wide range of contaminants, at present this information is distributed across many studies focused on a single type of contaminant or bioresidue. The present paper seeks to organize this vast amount of information into three major categories of low-cost agricultural adsorbents, namely, grains and seeds, fruits and vegetables, and herbage and forage waste, for the removal of the main groups of pollutants (heavy metals, industrial chemicals, nutrients, and pharmaceuticals) found in different water sources. Bioadsorbents derived from these three categories are described and compared here along with information on both adsorbents and the key parameters that influence the adsorption process. We sought to compile the largest collection of information on bioadsorbents reported to date in a single bibliographical source in order to allow future researchers to easily determine the most suitable alternative in each case.