Investigation of membrane de-clogging techniques in the Submerged Membrane Filtration Adsorption Hybrid System (SMFAHS)

Publication Type:
Journal Article
Citation:
Fluid - Particle Separations Journal, 2004, 16 (2), pp. 165 - 173
Issue Date:
2004-12-01
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Membrane clogging is a major obstacle to the successful operation of the membrane separation process. A submerged hollow fibre membrane with powdered activated carbon (PAC) adsorption (adsorption-membrane hybrid system) was used for the removal of organics from a synthetic wastewater representative of biologically treated sewage effluent. PAC usage successfully adsorbs the majority of the organics, and then the organic laden PAC is separated by the membrane reducing the direct organic loading to the membrane. However, membrane clogging still occurs. This study involved the development of an automation system and Supervisory Control and Data Acquisition (SCADA) system for performing an investigation and evaluation of three automated de-clogging techniques. The first de-clogging method involved the use of periodic relaxation, whereby permeate production for 12 minutes was periodically stopped for 3 minutes and the shear forces created by the aeration system and the absence of suction pressure during the relaxation period were used to de-clog the membrane. The second de-clogging method involved the use of a series of periodic back flush experiments with varied frequencies and durations to force permeate in the opposite direction out through the membrane pores. The optimal results in terms of de-clogging the membrane were achieved using a 15 second backflush after 15 minutes of permeate production. The third de-clogging method involved the application of an understanding of results of the periodic back flush series of experiments to design an automation system with a new approach to backflushing where an upper limit of a transmembrane pressure (TMP) increase each cycle was used to initiate the backflush. The transmembrane pressure represents the pressure measured across the membrane and it is a vital parameter indicating the degree of fouling of the membrane. A periodic backflush was found to be significantly more effective in terms of increasing the total quantity of wastewater treated than was achieved using periodic relaxation and was investigated in detail during the study. For the periodic backflush, an optimal frequency and duration was determined for treatment of wastewater with a fixed foulant concentration. The new approach to backflushing using more advances in the control system incorporating the TMP increase each cycle resulted in a 40% reduction in the number of backwashes required and was capable of self-optimising operating parameters under an unsteady foulant concentration of wastewater.
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