Biofilm is communities of microorganisms attached to the surface and is capable to uptake and concentrate metal species within their cell structure. The purpose of this research was to produce Bacillus arsenicus MTCC 4380 biofilm on Sawdust/MnFe2O4 composite and estimate its capability for biosorption/bioaccumulation of As(III) and As(V) from wastewater. A laboratory-scale batch model was utilized for biosorption/bioaccumulation assay. The effect of pH, biosorbent dose, contact time, temperature and initial adsorbate concentration on the removal efficiency were studied. The minimum contact time to reach equilibrium is about 220 min at pH 7 at 30 °C temperature for both ions. FT–IR confirmed that there are some functional groups on the surface of biosorbent attached with biofilm that may interact with the metal ions. The pattern of biosorption/bioaccumulation fitted well with Khan isotherm model for As(III) and Brouers–Sotolongo and Fritz–Schlunder–V isotherm models for As(V). On the basis of $$\overline{{{\text{R}}^{{\text{2}}} }}$$ R 2 ¯ values the highest fitted model order among one and two parameter models is Langmuir model with a maximum adsorption capacity of 2584.6679 mg/g for As(III) and 2651.6749 mg/g for As(V). The effect of co-existing ions for example Cu2+, Zn2+, Bi3+, Cd2+, Fe3+, Pb2+, Co2+, Ni2+, Cr6+ and SO42− at different concentrations were inspected. Desorption study exhibited that over 83.568% of As(III) and 89.081 of As(V) could be desorbed from composite with 0.05 M NaOH solution.