## 1 Introduction
Microbial biomass is a low-cost product obtained as a residue of the fermentation processes in the production of antibiotics, beverages, enzymes, and other metabolites. However, it has been reported that the use of live biomass in the processes of biosorption of dyes presents some disadvantages, such as the need for a continuous supply of nutrients and high sensitivity to the dye toxicity [27]. Therefore, a lot of research has focused on using dead biomass for biosorption processes, since it does not require continuous nutrient supply and is not affected by toxic waste [28]; likewise, its regeneration is simple, can be stored for long periods at room temperature, can be reused for many cycles, and can be easily immobilized on inert supports [26]. The surface properties of bacteria, yeasts, fungi, and algae allow them to interact with different types of contaminants. In particular, in the process of dye biosorption, microbial biomass can use mechanisms such as physical and chemical adsorption, electrostatic interaction, ion exchange, complexation, chelation, and micro-precipitation [29]. Thus, the biosorption process will depend on the dye chemical nature (specie, size, ionic charge), type of biomass, specific surface properties, environmental conditions (pH, temperature, ionic strength), and presence of organic compounds, salts, and competing ions [26]. Fungal adsorption by living or dead biomass is commonly used as biological treatments for dye removal in aqueous media. Fungal biomass contains a large number of  
Figure 1: Chemical structure of the Congo red (**A**) and malachite green (**B**) dyes. functional groups, which gives its cell surface a negative charge that allows the efficient biosorption of dyes [30; 31]. However, the process of dye biosorption for fungal biomass can be slow, and the initial pH of the dye solution strongly influences the biosorption [3; 32; 33]. Filamentous fungi such as _Aspergillus niger_, _Phanerochaete chrysosporium_, _Rhizopus arrhizus_, _Cuninghamella elegans_, _Ganoderma applanatum_, and _Pleurotus oostreatus_, among others, have been assessed as an alternative strategy for removing and degrading dyes under in vitro conditions [34; 35; 36; 37; 38; 39; 40; 41]. Concerning the _Trichoderma_ species, previous works have reported that _T. harzianum_ can remove or discolor Rhodamine 6G and Trypan Blue Erioglaucine, and can favor the biosorption of the Orange G dye [42; 43; 44; 45; 46]. In addition, researchers have shown the potential of _T. viride_ for the removal of methylene blue [47]. However, more research is needed to determine the true potential of these species for decolorizing polluted waters. The genus _Trichoderma_ comprises a predominant group of filamentous fungi in terrestrial and aquatic ecosystems widely used in the control of phytopathogenic organisms and industrial processes [48; 49; 50; 51]. The advantages of using species of the genus _Trichoderma_ in the biosorption of dyes are its easy availability, low cost, good mechanical properties, and chemical stability under both alkaline and acid conditions [52]. In this regard, the present study evaluated the capability of either fresh or dry biomass of _T. virens_ and _T. viride_ to remove CR and MG under several dye concentrations. These fungi were selected due to their tolerance to high concentrations of polycyclic aromatic hydrocarbons [53]. In addition, to carry out an objective comparison, under the same conditions, additional absorption experiments were carried out with activated carbon as the sorbent.