The correct answer is (a) Membranes need to be replaced at regular intervals
Explanation: Advantages of membrane reactors are as follows:
* These may be used in either batch or continuous mode.
* These reactors allow easy removal of enzyme from the product.
* These reactors avoid the costs and problems associated with other methods of immobilization.
Membrane reactor system may be established. Hence, they may be used for production of enzymes on small scale, especially where multienzyme pathway is involved or regeneration of co-enzyme is needed. The cost of the membranes and their replacement at regular intervals are the major disadvantages of membrane reactor.