The desalination industry, a critical source of potable water in many arid regions, generated more than $13 billion last year and is expected to double within a decade. Most desalination plants today use a process called reverse osmosis (RO), which forces water through huge rolls of membranes, leaving the salt behind. One of the most expensive operational challenges for such plants is the fouling of these membranes by microorganisms.<\/p>\n
Now, research from MIT suggests a different approach to reducing the rate of fouling and thus improving the efficiency of RO plants.<\/p>\n
The prevailing idea in the industry has been that the high pressure required by RO is responsible for the relatively high rate of fouling, compared to other systems such as forward osmosis. But the MIT study shows that this is not the case, a finding that opens up new approaches to reducing fouling in RO. The research, by Emily Tow \u201912, SM \u201914, PhD \u201917 and MIT Professor John H. Lienhard V, was recently published in the\u00a0Journal of Membrane Science\u00a0<\/em>and presented at the 2017 AMTA\/AWWA Membrane Technology Conference, where it received the Student Best Paper Award.<\/p>\n Many experts believe that the high pressure in an RO system compresses the microbial mats that grow on the membranes, and that this \u201ccompaction\u201d makes the growth much harder to remove. In contrast, in low-pressure forward osmosis (FO) systems, which are less energy-efficient but more fouling-resistant, the supposedly looser mat is thought to be easier to clean off.<\/p>\n However, these microbial mats are generally full of water, which does not compress under RO pressures, so \u201cthere is no good reason why high pressure should worsen fouling,\u201d Tow says. She compares the microbes to a scuba diver: \u201cThere\u2019s a lot of pressure at the bottom of the ocean, but it doesn\u2019t make you stick to the seafloor.\u201d But if pressure doesn\u2019t matter, and the flow rates through FO and RO systems are similar, what could account for the disparity in fouling resistance?<\/p>\n