[Dataset] Influence of shallow geothermal energy on the behaviour of organic contaminants of emerging concern in urban aquifers

Urban aquifers are a valuable resource of freshwater for cities, however, their quality is degraded due to the presence of organic contaminants of emerging concern (CECs). The effects of organic CECs are largely unknown, but there is evidence that they pose a risk for human health, soil, plants and animals. Organic CECs are naturally degraded in aquifers and their degradation rates depend on the physico-chemical properties, i.e., redox conditions and groundwater temperature. Some anthropogenic activities, like low-enthalpy geothermal energy (LEGE), may modify subsurface physico-chemical conditions altering the behaviour of organic CECs. LEGE is a renewable and carbon-free energy that allows obtaining cooling and heating energy. The utilization of LEGE is currently growing and it is expected that in a near future the density of LEGE systems will increase. LEGE modifies the groundwater temperature and in some situations the redox state (i.e., if the dissolved oxygen increases when groundwater is returned to the aquifer as a result of a poorly design), thus, it is of paramount importance to determine the impact of LEGE related activities on the behaviour of organic CECs. The behaviour of organic CECs under the influence of LEGE is investigated by means of thermo-hydro-chemical numerical modelling. Simulation output shows that LEGE activities have the potential to modify the degradation rates of organic CECs, and thus, their concentrations in aquifers. In the simulated scenario, the concentration of the chosen CEC decreases by the 77 % at the downgradient boundary of the model. The results of this study have significant implications for predicting the behaviour of organic CECs in urban aquifers and suggest specific changes in the design of LEGE facilities aiming to improve the quality of urban groundwater by boosting in-situ attenuation mechanisms.

城市含水层是城市宝贵的淡水资源，但其水质因新兴关注有机污染物（Contaminants of Emerging Concern, CECs）的存在而退化。目前这类有机CECs的生态与健康影响尚未完全明晰，但已有证据表明，它们会对人类健康、土壤、动植物构成潜在风险。有机CECs可在含水层中发生自然降解，其降解速率取决于自身理化性质，即氧化还原条件与地下水温度。部分人为活动，例如低焓地热能源（Low-enthalpy Geothermal Energy, LEGE），可能改变地下理化环境，进而改变有机CECs的环境行为。LEGE是一种可再生无碳能源，可同时提供制冷与制热能量。当前LEGE的开发利用规模正持续增长，预计未来LEGE系统的布设密度将进一步提升。LEGE会改变地下水温度，在部分工况下还会改变含水层的氧化还原状态——例如，若回灌地下水至含水层时设计不当，会导致溶解氧含量升高，因此明确LEGE相关活动对有机CECs环境行为的影响至关重要。本研究通过热-水-化学数值模拟方法，探究了LEGE影响下有机CECs的环境行为。模拟结果显示，LEGE活动有可能改变有机CECs的降解速率，进而改变其在含水层中的浓度分布。在本次模拟场景中，所选CECs在模型下游边界处的浓度降低了77%。本研究结果对预测城市含水层中有机CECs的环境行为具有重要指导意义，并提出了优化LEGE设施设计的具体方向，以期通过强化原位衰减机制提升城市地下水水质。