Membrane distillation (MD) has been attracting more attention from research and engineering professionals. This article explores the developed multi-effect vacuum membrane distillation (MEVMD), designed with clean- and dry-in-place system and membrane wetting channels, in two industrial projects – zero liquid discharge (ZLD) of chloride containing wastewater, and recycling of spent acid wastewater.
BY GAO YONGGANG, SHI ZHIWEI, LI CONG AND SU CHENGLONG
Membrane distillation technology, combined with the advantages of membrane and evaporation technologies, has been developed for half a century. Basic membrane distillation (MD) configuration includes direct contact MD (DCMD), vacuum MD (VMD), air gap MD (AGMD), and sweeping gas MD (SGMD). DCMD, the simplest configuration with high flux, is the most popular in research publications and is convenient for lab-scale research work, but it is rarely applied in industrial projects due to high conductive heat loss from feed side to permeate side.
However, VMD, AGMD, and vacuum-assisted AGMD are often adopted in commercial companies such as Memsys, Solarspring, Aquastill, Memsift, because the heat recovery system for the three configurations can be designed and the membrane wetting risk is low.
In the initial phase, MD was mainly used for seawater desalination, but with the advancement of reverse osmosis (RO) technology, it was not economically feasible. In the recent decade, its application is transitioning from seawater desalination to high strength wastewater treatment to partly replace the function of metallic evaporator – for instance multi-effect distillation (MED) and mechanical vapour recompression (MVR) to optimise the surplus heat in the plant area, and reduce the operation cost of evaporating concentration.
This effectively address the corrosion issues faced by metallic evaporators in the field of acidic wastewater treatment due to full plastic construction materials. In recent years, zero liquid discharge (ZLD) or minimum liquid discharge (MLD) has become increasingly adopted due to water scarcity and environmental issues caused by wastewater discharge, especially in developing countries.
Gao Yonggang, Shi Zhiwei, Li Cong and Su Chenglong are from Beijing CSRE Technology.
The full article is published on the latest edition of Water & Wastewater Asia May/Jun 2021 issue. To continue reading the article, click here.