Modeling and multi-objective optimization of vacuum membrane distillation for enhancement of water productivity and thermal efficiency in desalination

Abstract

Water productivity and thermal efficiency in membrane distillation (MD) have been the main research targets for the aims of commercial application in desalination. The comprehensive understanding of the influence of module configuration parameters, operating conditions and their interaction on MD performance is the key for MD commercialization. In this paper, the multi-objective modeling and optimization in the vacuum membrane distillation were performed by response surface methodology and desirability function approach. A series of PVDF hollow fiber modules of different scale were used to provide the essential data and to verify the modeling program. The multi-objectives including water permeate flux (J), water productivity per unit volume of module (Pv), gained output ratio (GOR), and a comprehensive index (Dm) assessing the desired MD performances were predicted and experimentally verified. The influence of operating parameters (temperature, velocity, and concentration of feed) and membrane module parameters (membrane packing density and length–diameter ratio of module) and their binary interactions on the multi-objectives were investigated. It is found that among the investigated factors, feed inlet temperature and its interaction effect with module parameters play dominant roles on MD performance. Under the multi-objective optimum conditions, 4.85×103kg/(m3h) of Pv and 0.91 of GOR were achieved within the investigated range. Water productivity and thermal efficiency can be simultaneously enhanced by optimizing operating and module conditions with the approach developed in this study.