Department of Civil and Environmental Engineering, University of Pittsburgh, Pittsburgh, PA, 15261, USA.
Department of Civil and Environmental Engineering, University of Pittsburgh, Pittsburgh, PA, 15261, USA.
Water Res. 2020 Jun 15;177:115765. doi: 10.1016/j.watres.2020.115765. Epub 2020 Apr 2.
Produced water (PW) generated during unconventional oil and gas extraction is characterized by very high total dissolved solids (TDS) that mainly consist of alkali and alkaline earth metals. Dominant PW management strategy (i.e., injection in Class II disposal wells) is scrutinized by regulatory agencies, and the public and PW treatment that enables high water and salt recovery (i.e., evaporation/crystallization) is being considered as an alternative. Produced water generated in the Marcellus Shale play also contains very high levels of Naturally Occurring Radioactive Material (NORM) in the form of Ra-226 and Ra-228, which is one of the key impediments for the recovery of high-quality salts. This study was designed to evaluate the efficiency of Ra-226 removal using co- and post-precipitation with barium sulfate to enable advanced PW treatment processes. High Sr/Ba molar ratios in PW lead to relatively low Ba and Ra removal, and Ba concentration adjustment is necessary to achieve required treatment standards (i.e., [Ba] < 10 mg/L and [Ra] < 50 pCi/L). Seeding the reactor with barium sulfate enhanced Ba and Ra removal through induced heterogeneous precipitation of barite. However, it was necessary to simultaneously adjust the Sr/Ba ratio and barite level to achieve treatment requirements while maintaining reasonable detention time in the reactor (i.e., <30 min) and minimizing sludge production. Experimental and modeling results revealed that low Ba and Ra effluent concentrations, with minimized sludge production, can be achieved only when the barium sulfate saturation index was above 4.7, Sr/Ba molar ratio was below 2 and there was at least 25 g/L of barite "seed" in the system. This study provides useful guidelines for centralized wastewater treatment facilities in shale plays and serves to optimize pretreatment of produced water to enable recovery of valuable resources (i.e., clean water and usable salts).
产自非常规油气开采过程中的产出水（PW）具有极高的总溶解固体（TDS），其主要由碱金属和碱土金属组成。监管机构对主导的 PW 管理策略（即注入 II 类处置井）进行了审查，人们正在考虑将能够实现高水和盐回收率（即蒸发/结晶）的 PW 处理作为替代方案。在马塞勒斯页岩层中产生的产出水还含有很高水平的天然放射性物质（NORM），形式为 Ra-226 和 Ra-228，这是回收高质量盐的关键障碍之一。本研究旨在评估使用硫酸钡共沉淀和后沉淀去除 Ra-226 的效率，以实现先进的 PW 处理工艺。PW 中高 Sr/Ba 摩尔比导致 Ba 和 Ra 的去除率相对较低，需要调整 Ba 浓度以达到所需的处理标准（即[Ba] <10mg/L 和[Ra] <50pCi/L）。在反应器中添加硫酸钡可以通过诱导重晶石的异相沉淀来增强 Ba 和 Ra 的去除。然而，为了在保持反应器内合理停留时间（即 <30 分钟）和最小化污泥产量的同时，达到处理要求，有必要同时调整 Sr/Ba 比和重晶石水平。实验和建模结果表明，只有当硫酸钡饱和度指数高于 4.7、Sr/Ba 摩尔比低于 2 且系统中至少有 25g/L 的重晶石“种子”时，才能实现低 Ba 和 Ra 出水中浓度，同时最小化污泥产量。本研究为页岩层集中式废水处理设施提供了有用的指导，并有助于优化产出水的预处理，以回收有价值的资源（即清洁水和可用盐）。
