Combining reverse osmosis and pulsed electrical current electrodialysis for improved recovery of dissolved organic matter from seawater

Abstract

Dissolved organic carbon (DOC) in the oceans is one of the largest dynamic reservoirs of carbon on earth, comparable in size to the atmospheric reservoir of carbon (as CO2) in the atmosphere, or to the amount of carbon in all terrestrial and aquatic biota. The concerted efforts of earth scientists, atmospheric scientists, and biologists who study global biogeochemical cycles and the earth's climate have yielded a rather detailed understanding of carbon in the atmosphere and in biota. Marine dissolved organic matter (DOM) is far less well characterized, principally because it exists as a highly diluted mixture of perhaps millions of organic compounds in a highly saline aqueous solution. Prior to 2007, only around ⅓ of marine DOM was typically recovered from seawater for research purposes, regardless of the method of isolation. In 2007, reverse osmosis (RO) and electrodialysis (ED) were coupled to achieve recoveries of 64% – 93% of marine DOM. The level of residual salts in the concentrated samples, however, still precluded the characterization of marine DOM by solid-state NMR, mass spectrometry, or even elemental analysis. This paper describes a major improvement to the RO/ED method, in which pulsed electrodialysis is used (at sea) to reach roughly 100-fold greater removal of salts compared to not pulsed ED while maintaining comparable recoveries of DOM.