Tracking variations in the abundance and composition of dissolved organic matter in solar ponds of oilfield-produced brine

Abstract

The quantity and quality of dissolved organic matter (DOM) in the brine of solar ponds influence the efficiency of mineral extraction and brine evaporation rates. Here we report a characterization study of DOM in solar ponds of oilfield-produced brines using different approaches. The results showed that the concentrations of dissolved organic carbon and total dissolved solids exhibited a 2–3 fold increase with exposure time in the ponds. Analyses with two-dimensional correlation spectroscopy of attenuated total reflectance Fourier transform infrared spectroscopy and proton nuclear magnetic resonance, indicated that the aromatic and carboxylic acid structures in the DOM, were more susceptible to degradation/transformation compared with aliphatics, while aliphatics exhibited a preferential decline with increasing exposure time in the solar ponds. The relative abundance of aliphatic compounds (including functionalized ones) gradually decreased by 17.1% (r = −0.94, P < 0.001), in the solar pond process, while the opposite was observed for carbohydrates, which increased by 88.7% (r = 0.93, P < 0.001). Pyrolysis–gas chromatography–mass spectrometry revealed that the DOM in oilfield-produced brine contained polymethylene chain, terpenoid-like, carbohydrate (or carbohydrate-like) and aromatic structures. Terpenoid-like compounds were depleted while isoprenoid and linear polymethylene chain compounds increased upon irradiation in solar ponds. Finally, the guidelines for removing DOM from brine, and their ecological impacts and consequences in the process of brine resource exploitation, were discussed.