## 1 Introduction  
Through industrialization and excessive use of chemicals worldwide, environmental pollution has resulted in heavy metals releasing into the environment and other toxic contaminants [1, 2]. Heavy metals in the environment are a severe problem to address in today's world due to their high toxicity, mobility in the environment, and non-biodegradability [3]. Among them, Cr (VI) and Ni (II) are discharged in effluents from mining, electroplating, refining, and other industrial wastewaters, which can cause potential damage to the ecosystem and human and animal health, even at low concentrations [4, 5]. In addition, high concentrations may cause cell membrane damage, alter enzyme activities, disrupt cell function, cause birth damage, cancer, skin lesions, and kidney and hepatic damage [6]. Cr (VI) is considered a priority dangerous pollutant since it usually occurs in the form of chromate (CrO\({}_{4}\)\({}^{2-}\)) or dichromate (Cr\({}_{2}\)O\({}_{7}\)\({}^{2-}\)) ions and easily crosses biological barriers, being carcinogenic, in addition to being about 500 times more toxic and mobile than chromium (III) [7]. Ni (II), in high concentrations, is toxic and in humans, it can cause dermatitis, pulmonary fibrosis, decreased bodyweight, cardiovascular diseases, liver and kidney damage, gastrointestinal upset, and cancer [8]. For this reason, efforts have been made to remove heavy metals present in effluents through the implementation of different technologies such as solvent extraction, membrane filtration, ion exchange, reverse osmosis, chemical precipitation, oxidation, photocatalysis, among others [9]. However, these methods have limitations, such as the generation of toxic chemical sludge, incomplete metal removal, low efficiency, high energy, and reagent requirements [10]. Thus, bio adsorption is presented as a good and effective alternative technique recommended for removing heavy metal ions from water due to its low cost and ease of operation, minimal generation of toxic sludge, short operation time, the possibility of recovery, and final disposal of metals [11]. This process often uses low-cost adsorbents mainly of biological origin [12]. Various adsorbents have been tested for the removal of heavy metals from aqueous solutions with promising results based on living biomass (fungi, algae, and bacteria) and agricultural biomass (husks, sawdust, agricultural and agro-industrial wastes) [13; 14; 15; 16; 17]. Different lignocellulosic biomasses have been used in heavy metal remotion, such as millet [18], lime [19; 20], rice husks [18; 21], black walnut bark [22], eucalyptus [23], palm residues [24], plantain [25], and kenaf [26], among others [27; 28; 29; 30; 31], presenting high removal yields. The use of bio adsorbents of residual lignocellulosic origin has advantages, such as low cost, high availability, and excellent performance at high and low concentrations [32]. Additionally, different techniques have been studied to reuse bio adsorbent materials to extend their useful life and recover the contaminants from a concentrated solution after each desorption cycle, thus using solvents as NaOH, HCl, and acetic acid, and organic solvent mixtures [33]. Regarding the final disposal of the adsorbents, once they are aged after the desorption cycles, practices have been studied to get rid of this waste, such as recycling in the cement matrix, re-filling of the road, stabilization soil, stabilization/solidification processes, and soil correction and as a liming agent, among others [34]. The large volumes of waste generated by agro-industrial exploitation require the generation of alternatives for their use. One process that produces the most waste is starch production since its yield is close to 20% [35].