Phytase an enzyme produced by Aspergillus niger can be adsorbed on microcrystalline cellulose powder (MCCP). The adsorption follows a Langmuir isotherm and the maximum concentration of the protein that can be obtained on the adsorbent is 70 mg cm^–3. At a concentration of 50mgl^–1 of protein in the solution the concentration of protein on the adsorbent reaches 35 mg cm^–3. It is desired to recover 90% of the addition of MCCP to the solution. The concentration of the protein adsorbed on the solid at equilibrium will be