## 3 Results and Discussion
### Biosorption Design in the Fixed/Packed Bed (Column) Reactor  
The appropriate selection of the sizes of the fixed/packed bed in a biosorption (column) reactor influences the efficiency of the retention of reactive BRed anionic dye from the treated effluent, the biosorption operating time, the volume of treated effluent and the possibility of using relatively reasonable amounts of biosorbent for the retention of persistent organic pollutants such as organic dyes. This is why it is necessary to obtain experimental data to be properly processed for the determination of the sizes of the biosorption (column) reactor (e.g., for a large industrial setup scale application). Based on the previously obtained experimental data, the following two operating parameters necessary for the design of the biosorption step in an industrial effluent treatment station (Table 4), meaning the mean flow rate of the treated effluent passing through the immobilized biosorbent fixed/packed bed (\(b_{i}\)) and the mean volume of the treated effluent passing through the immobilized biosorbent fixed/packed bed till the maximum admissible concentration attaining of residual dye in the treated effluent (\(V_{i}\)), were determined accordingly. The graphical representation (Figure 4) of these operating parameters will allow to determine the optimal volume (\(V_{opt}\)) of treated effluent which passes through the fixed/packed bed of immobilised residual biosorbent until imposed norms for the residual dye concentration in the treated effluent (M.A.C.). The optimal volume of treated effluent passing through the immobilized biosorbent mass (\(V_{opt}\)) was found to be 11.248 mL/g or 11.248\(\cdot\)10\({}^{3}\) m\({}^{3}\)/kg. In addition, the bulk density of immobilized residual biomass was considered to be of 576.65 kg/m\({}^{3}\). The sizes of the biosorption (column) reactors were calculated using the relations from Table 1, considering the uniformity distribution coefficient of biosorbent in packed/fixed bed of \(\beta\) = 1.5 and the free space above the packed bed of \(\lambda\) = 2. The sizes determined for biosorption reactors working in the static or dynamic regimes are feasible and are able to be applied to a large-scale setup in the biosorption treatment step of industrial dye-containing effluents resulting from textile finishing processes, or different chemicals synthesis industries with good removal results, thus the legal requirements of the final effluent discharges can be well controlled and respected. The relationships from Table 1 ensure an appropriate design of the biosorption (column) reactor according to the effluent flow rate to be treated and also the imposed constructive and experimental characteristics and operational restrictions. Thus, for a regular industrial effluent flow rate (i.e., textile effluent of a textile fabrics manufacturing company) of 50 m\({}^{3}\)/day (or 2.083 m\({}^{3}\)/h), the sizes of a biosorption (column) reactor working in a dynamic regime and of a static biosorption tank have been determined for comparison, taking into account a biosorption time of at least one day, and these data correspond to the values mentioned below: