Low carbon heating and cooling by combining various technologies with Aquifer Thermal Energy Storage

Potential of low-enthalpy geothermal energy to degrade organic contaminants of emerging concern in urban groundwater

Low-enthalpy geothermal energy (LEGE) is a carbon-free and renewable source to provide cooling and heating to infrastructures (e.g. buildings) by exchanging their temperature with that of the ground. The exchange of temperature modifies the groundwater temperature around LEGE installations, which may contribute to enhancing the capacity of aquifers to degrade organic contaminants of emerging concern (OCECs), whose presence is significantly increasing in urban aquifers. Here, we investigate the impact of LEGE on OCECs and their bioremediation potential through numerical modelling of synthetic and real-based cases. Simulation results demonstrate that: (i) LEGE facilities have the potential to noticeably modify the concentrations of OCECs; and (ii) the final impact depends on the design of the facility. This study suggests that optimized LEGE facility designs could contribute to the degradation of OCECs present in urban aquifers, thus improving groundwater quality and increasing its availability in urban areas.

Thermally enhanced bioremediation: A review of the fundamentals and applications in soil and groundwater remediation

Thermally enhanced bioremediation (TEB), a new concept proposed in recent years, explores the combination of thermal treatment and bioremediation to address the challenges of the low efficiency and long duration of bioremediation. This study presented a comprehensive review regarding the fundamentals of TEB and its applications in soil and groundwater remediation. The temperature effects on the bioremediation of contaminants were systematically reviewed. The thermal effects on the physical, chemical and biological characteristics of soil, and the corresponding changes of contaminants bioavailability and microbial metabolic activities were summarized. Specifically, the increase in temperature within a suitable range can proliferate enzymes enrichment, extracellular polysaccharides and biosurfactants production, and further enhancing bioremediation. Furthermore, a systematic evaluation of TEB applications by utilizing traditional in situ heating technologies, as well as renewable energy (e.g., stored aquifer thermal energy and solar energy), was provided. Additionally, TEB has been applied as a biological polishing technology post thermal treatment, which can be a cost-effective method to address the contaminants rebounds in groundwater remediation. However, there are still various challenges to be addressed in TEB, and future research perspectives to further improve the basic understanding and applications of TEB for the remediation of contaminated soil and groundwater are presented.

Geothermal heating: Is it a boon or a bane for bioremediation?

There has been a worldwide interest in renewable energy technologies, as a means of decreasing reliance on fossil fuels, minimizing climate change effects, and reducing greenhouse emissions. One such technology is geothermal heating where the constant subsurface temperature is used to cool or heat building interiors via heat pumps. In Canada, the use of geothermal heating has become a popular option for heating and cooling buildings, and it is anticipated that, in the near term, most large buildings will include geothermal heating as part of their climate control strategy. However, little is known about the environmental impacts of geothermal heating on the subsurface environment. The present review will examine the effect of geothermal heating on groundwater flow and remediation efforts, whereby the heat generated by geothermal systems may help with urban pollution. "Geothermal Remediation" could leverage the subsurface heating resulting from geothermal systems to accelerate biodegradation of certain petroleum-based pollutants at brown-field sites, while providing building(s) with sustainable heating and cooling. This idea coincides with the rising momentum towards sustainable and green remediation in Europe and the United States. To ensure that Geothermal Remediation is achievable, the effect of heat on bioremediation needs to be examined. This review provides an insight into what we know about heat effects on bioremediation activities and subsurface transport.

The impacts of different heating systems on the environment: A review

This paper presents a review of the environmental impacts of most heating systems drawing together published literature on the subject, not previously available. Here, a comparison between the different systems such as coal, wood, oil, natural gas, heat pump, geothermal and solar energy is provided in terms of their environmental impact. The most important parameters considered are the emission rate and toxicity. This places the coal-fired system as the worst among all heating systems regarding the impacts on the environment. On the other hand, renewable energy sources are the most preferred sources decreasing total emissions and air pollution. In order to make a comparison between the different systems, the emissions that must be taken into consideration are CO, CO₂, NO_x, SO₂, PMs, N₂O, CH₄, volatile organic compounds, polycyclic aromatic hydrocarbons and aldehydes.

Potential Sites for Underground Energy and CO2 Storage in Greece: A Geological and Petrological Approach

Underground geological energy and CO2 storage contribute to mitigation of anthropogenic greenhouse-gas emissions and climate change effects. The present study aims to present specific underground energy and CO2 storage sites in Greece. Thermal capacity calculations from twenty-two studied aquifers (4 × 10−4–25 × 10−3 MJ) indicate that those of Mesohellenic Trough (Northwest Greece), Western Thessaloniki basin and Botsara flysch (Northwestern Greece) exhibit the best performance. Heat capacity was investigated in fourteen aquifers (throughout North and South Greece) and three abandoned mines of Central Greece. Results indicate that aquifers present higher average total heat energy values (up to ~6.05 × 106 MWh(th)), whereas abandoned mines present significantly higher average area heat energy contents (up to ~5.44 × 106 MWh(th)). Estimations indicate that the Sappes, Serres and Komotini aquifers could cover the space heating energy consumption of East Macedonia-Thrace region. Underground gas storage was investigated in eight aquifers, four gas fields and three evaporite sites. Results indicate that Prinos and South Kavala gas fields (North Greece) could cover the electricity needs of households in East Macedonia and Thrace regions. Hydrogen storage capacity of Corfu and Kefalonia islands is 53,200 MWh(e). These values could cover the electricity needs of 6770 households in the Ionian islands. Petrographical and mineralogical studies of sandstone samples from the Mesohellenic Trough and Volos basalts (Central Greece) indicate that they could serve as potential sites for CO2 storage.

Aquifer Thermal Energy Storage (ATES) for District Heating and Cooling: A Novel Modeling Approach Applied in a Case Study of a Finnish Urban District

Aquifer thermal energy storage (ATES) combined with ground-source heat pumps (GSHP) offer an attractive technology to match supply and demand by efficiently recycling heating and cooling loads. This study analyses the integration of the ATES–GSHP system in both district heating and cooling networks of an urban district in southwestern Finland, in terms of technoeconomic feasibility, efficiency, and impact on the aquifer area. A novel mathematical modeling for GSHP operation and energy system management is proposed and demonstrated, using hourly data for heating and cooling demand. Hydrogeological and geographic data from different Finnish data sources is retrieved in order to calibrate and validate a groundwater model. Two different scenarios for ATES operation are investigated, limited by the maximum pumping flow rate of the groundwater area. The additional precooling exchanger in the second scenario resulted in an important advantage, since it increased the heating and cooling demand covered by ATES by 13% and 15%, respectively, and decreased the energy production cost by 5.2%. It is concluded that dispatching heating and cooling loads in a single operation, with annually balanced ATES management in terms of energy and pumping flows resulted in a low long-term environmental impact and is economically feasible (energy production cost below 30 €/MWh).

Increasing market opportunities for renewable energy technologies with innovations in aquifer thermal energy storage

Heating and cooling using aquifer thermal energy storage (ATES) has hardly been applied outside the Netherlands, even though it could make a valuable contribution to the energy transition. The Climate-KIC project "Europe-wide Use of Energy from aquifers" - E-USE(aq) - aimed to pave the way for Europe-wide application of ATES, through the realization and monitoring of six ATES pilot plants across five different EU countries. In a preceding paper, based on preliminary results of E-USE(aq), conclusions were already drawn, demonstrating how the barriers for this form of shallow geothermal energy can be overcome, and sometimes even leveraged as opportunities. Based on final pilot project results, key economic and environmental outcomes are now presented. This paper starts with the analysis of specific technological barriers: unfamiliarity with the subsurface, presumed limited compatibility with existing energy provision systems (especially district heating), energy imbalances and groundwater contamination. The paper then shows how these barriers have been tackled, using improved site investigation and monitoring technologies to map heterogeneous subsoils. In this way ATES can cost-efficiently be included in smart grids and combined with other sources of renewable (especially solar) energy, while at the same time achieving groundwater remediation. A comparative assessment of economic and environmental impacts of the pilots is included, to demonstrate the sustainability of ATES system with different renewables and renewable-based technologies. The paper concludes with an assessment of the market application potential of ATES, including in areas with water scarcity, and a review of climate beneficial impact.

Comparative Life-Cycle Assessment of Aquifer Thermal Energy Storage Integrated with in Situ Bioremediation of Chlorinated Volatile Organic Compounds

Due to the increasing need for sustainable energy and environmental quality in urban areas, the combination of aquifer thermal energy storage (ATES) and in situ bioremediation (ISB) has drawn much attention as it can deliver an integrated contribution to fulfill both demands. Yet, little is known about the overall environmental impacts of ATES-ISB. Hence, we applied a life-cycle assessment (LCA) to evaluate the environmental performance of ATES-ISB, which is also compared with the conventional heating and cooling system plus ISB alone (CHC + ISB). Energy supply via electricity is revealed as the primary cause of the environmental impacts, contributing 61.26% impacts of ATES-ISB and 72.91% impacts of CHC + ISB. Specifically, electricity is responsible for over 95% of water use, global warming potential, acidification potential, and respiratory inorganics, whereas the production of the biological medium for bioremediation causes more than 85% of the eco- and human toxicity impacts in both cases. The overall environmental impact of ATES-ISB is two times smaller than that of CHC + ISB. Sensitivity analysis confirms the importance of electricity consumption and electron donor production to the environmental impacts in both energy supply and bioremediation. Thus, future studies and practical applications seeking possible optimization of the environmental performances of ATES-ISB are recommended to focus more on these two essential elements, e.g., electricity and electron donor, and their related parameters. With the comprehensive LCA, insight is obtained for better characterizing the crucial factors as well as the relevant direction for future optimization research of the ATES-ISB system.

Investigations into the First Operational Aquifer Thermal Energy Storage System in Wallonia (Belgium): What Can Potentially Be Expected?

In the context of energy transition, new and renovated buildings often include heating and/or air conditioning energy-saving technologies based on sustainable energy sources, such as groundwater heat pumps with aquifer thermal energy storage. A new aquifer thermal energy storage system was designed and is under construction in the city of Liège, Belgium, along the Meuse River. This system will be the very first to operate in Wallonia (southern Belgium) and should serve as a reference for future shallow geothermal developments in the region. The targeted alluvial aquifer reservoir was thoroughly characterized using geophysics, pumping tests, and dye and heat tracer tests. A 3D groundwater flow heterogeneous numerical model coupled to heat transport was then developed, automatically calibrated with the state-of-the-art pilot points method, and used for simulating and assessing the future system efficiency. A transient simulation was run over a 25 year-period. The potential thermal impact on the aquifer, based on thermal needs from the future building, was simulated at its full capacity in continuous mode and quantified. While the results show some thermal feedback within the wells of the aquifer thermal energy storage system and heat loss to the aquifer, the thermal affected zone in the aquifer extends up to 980 m downstream of the building and the system efficiency seems suitable for long-term thermal energy production.

Potential impact of hydrodynamic shear force in aquifer thermal energy storage on dissolved organic matter releasement: A vigorous shaking batch study

The combination of bioremediation and aquifer thermal energy storage (ATES) has become attractive because of the possibility of solving environmental and energy problems simultaneously. While the impact of ATES on groundwater quality due to temperature change has received ample attention in literature, the effect of the greatly enhanced groundwater flow velocity on groundwater quality has not yet received sufficient scientific attention. To fill this gap in understanding, we conducted a simple yet straightforward experiment to illustrate the impact of hydrodynamic shear force due to the water flow by ATES on the release of dissolved organic matter, which can potentially be advantageous to bioremediation. Vigorous shaking conditions were applied to simulate the enhanced dynamics at the ATES well center and nearby. As the indicators of dissolved organic matter, COD and TOC concentrations were significantly impacted by shaking. COD increased from 5.4 mgO₂/L to 36.3 mgO₂/L during horizontal shaking. The maximum COD level was determined as 33.8 mgO₂/L during orbital shaking, while the TOC level was growing from 6.7 to 28.7 mg C/L. Meanwhile, redox potential (with initial level -100 mV) was decreasing to -450 mV synchronously with the elevating COD and TOC level. Temperature was also revealed as a significant factor in the organic matter releasement. Microbial iron reduction was deemed to occur, yet sulfate reduction was not initiated during the whole experiment. Eventually, the structure of the soil-water matrix has been changed due to the extensive hydraulic and particle collisions, resulting in blackish appearance and thicker layer of fine particles. Overall, the findings advance our understanding of the role of the ATES-induced water flow in the subsurface biogeochemistry and give insight into the perspective of the combination of bioremediation and ATES. In general, an increase in dissolved organic matter can be expected due to the increased shear force at high flow conditions in the ATES system.