Desalination and enrichment of phosphorus-containing wastewater via cyclopentane hydrate

Abstract With the rapid development of agriculture, controlling phosphorus emissions is a pressing challenge for preventing water eutrophication. A graphite-promoted cyclopentane (CP) hydrate-based desalination was proposed to remove K3PO4 from effluents. It was found via the in situ optical microscopy that the reaction temperature and the concentration of feeding K3PO4 solution significantly affect the morphologies and amount of the as-produced CP hydrate crystals. The lower reaction temperature produces more crystals with irregular shapes, while fewer crystals formed in K3PO4 solution with higher concentration. The reaction temperature, time and feeding concentration-dependent desalination and salt enrichment performances were studied. It was found that desalination efficiency linearly increases with the elevated reaction temperature ranging from -2 oC to 3 oC; however, water recovery declines with temperature. The temperature-dependent water recovery is due to the strong driving force for hydrate formation at low temperatures. The time-dependent water recovery shows a three-stage feature, including exponential growth, linear increase, and stable stages, owing to the interaction between the driving force of supercooling and the increasing K3PO4 concentration during the reaction processes. The desalination efficiency shows an inverted volcanic shape with the increased concentration of feeding K3PO4 solution. The pre-melting effect plays a critical role in improving desalination efficiency at high K3PO4 concentrations. A maximum desalination efficiency of 85.0% was reached for treating an artificial solution with salinity as high as 42452 mg/L. Both desalted water and concentrated phosphorus-containing solution can be recovered by this method, which is attractive for producing freshwater with potential for recovery of resources.