Monitoring and control of TMP and feed flow rate pulsatile operations during ultrafiltration in a membrane module

The aim of this paper is the presentation of a novel system for continuous monitoring of the operating variables involved in ultrafiltration process. The proposed system is based on the utilization of a data acquisition set, consisting of field point units supplied by National Instruments, connected to a Personal Computer, thus allowing UF module performance monitoring. It is, therefore, possible to continuously measure permeate flux decay and to control membrane fouling by means of a device, controlled by the PC, that is able to generate pulses on both trans-membrane pressure and feed flow rate. This device, already patented by the authors [1], is comprised by a system of electric valves that, during a standard cross-flow operation, prime, without any plant stop or any flux inversion, a “cleansing” procedure for the membrane. The main advantages related to the utilization of this device are: the improvement of both performances and efficiency of membrane cross-flow operations, its simplicity and the economy of its installation, the reduction of the dead times due to plant stops and to traditional cleaning procedures. The application of the proposed system to the BSA ultrafiltration showed a significant increase of permeate fluxes with respect to a traditional cross-flow filtration plant.

The proposed device, in spite of its simplicity, is able to promote a mechanical removal of the polarized layer that accumulates on the membrane surface reducing permeate flux decay and increasing the whole process efficiency. With respect to a traditional UF plant, pulsating operations allow attaining performances improvement of about 250% under turbulent hydrodynamic conditions. This improvement is more and more significant at increasing operation times. Generally, membrane performances are better if higher feed flow rates are used. Moreover, an optimal value of low pressure step duration to high pressure phase duration has been individuated in terms of both a maximization of permeate flux and a minimization of additional resistance to permeation. The utilization of Labview allows either monitoring system performances continuously or implementing, without any particular effort, a control system that could automatically control solenoid valves operation as a function of the instantaneous UF efficiency and this will be a possible future development of the present work.