Desalination and enrichment of phosphorus-containing wastewater via cyclopentane hydrate

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 K 3 PO 4 from effluents. It was found via the in situ optical microscopy that the reaction temperature and the concentration of feeding K 3 PO 4 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 K 3 PO 4 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 °C to 3 °C; 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 K 3 PO 4 concentration during the reaction processes. The desalination efficiency shows an inverted volcanic shape with the increased concentration of feeding K 3 PO 4 solution. The pre-melting effect plays a critical role in improving desalination efficiency at high K 3 PO 4 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.