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.

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

A transition to a low carbon energy system is needed to respond to global challenge of climate change mitigation. Aquifer Thermal Energy Storage (ATES) is a technology with worldwide potential to provide sustainable space heating and cooling by (seasonal) storage and recovery of heat in the subsurface. However, adoption of ATES varies strongly across Europe, because of both technical as well as organizational barriers, e.g. differences in climatic and subsurface conditions and legislation respectively. After identification of all these barriers in a Climate-KIC research project, six ATES pilot systems have been installed in five different EU-countries aiming to show how such barriers can be overcome. This paper presents the results of the barrier analysis and of the pilot plants. The barriers are categorized in general barriers, and barriers for mature and immature markets. Two pilots show how ATES can be successfully used to re-develop contaminated sites by combining ATES with soil remediation. Two other pilots show the added value of ATES because its storage capacity enables the utilization of solar heat in combination with solar power production. Finally, two pilots are realized in countries with legal barriers where ATES systems have not previously been applied at all.

Extraction of sediment-associated polycyclic aromatic hydrocarbons with granular activated carbon.

Addition of activated carbon (AC) to sediments has been proposed as a method to reduce ecotoxicological risks of sediment-bound contaminants. The present study explores the effectiveness of granular AC (GAC) in extracting polycyclic aromatic hydrocarbon (PAH) from highly contaminated sediments. Four candidate GAC materials were screened in terms of PAH extraction efficiency using single-step 24-h GAC extractions, with traditional 24-h Tenax extraction as a reference. Subsequently, sorption of native PAHs to the best performing GAC 1240W (0.45-1.70 mm) was studied for sediment only and for GAC-sediment mixtures at different GAC-sediment weight ratios, using 76-µm polyoxymethylene (POM) passive samplers. Granular AC sorption parameters for PAHs were determined by subtracting the contribution of PAH sorption to sediment from PAH sorption to the GAC-sediment mixture. It appears that the binding of PAHs and the effectiveness of GAC to reduce sediment porewater concentrations were highly dependent on the GAC-sediment mixing ratio and hydrophobicity of the PAH. Despite the considerable fouling of GAC by organic matter and oil, 50 to 90% of the most available PAH was extracted by the GAC during a 28-d contact time, at a dose as low as 4%, which also is a feasible dose in field-scale applications aimed at cleaning the sediment by GAC addition and removal.

In situ remediation of contaminated sediments using carbonaceous materials.

Carbonaceous materials (CM), such as activated carbons or biochars, have been shown to significantly reduce porewater concentrations and risks by binding hydrophobic organic compounds (HOCs) present in aquatic sediments. In the present study, the authors review the current state-of-the-art use of CM as an extensive method for sediment remediation, covering both technical and ecological angles. The review addresses how factors such as CM type, particle size and dosage, sediment characteristics, and properties of contaminants affect the effectiveness of CM amendment to immobilize HOCs in aquatic sediments. The authors also review the extent to which CM may reduce bioaccumulation and toxicity of HOCs and whether CM itself has negative effects on benthic species and communities. The review is based on literature and datasets from laboratory as well as field trials with CM amendments. The presence of phases such as natural black carbon, oil, or organic matter in the sediment reduces the effectiveness of CM amendments. Carbonaceous material additions appear to improve the habitat quality for benthic organisms by reducing bioavailable HOC concentrations and toxicity in sediment. The negative effects of CM itself on benthic species, if any, have been shown to be mild. The beneficial effects of reducing toxicity at low CM concentrations most probably outweigh the mild negative effects observed at higher CM concentrations.

Enhancement of PAH biodegradation in soil by physicochemical pretreatment.

The effects were studied of short-term heating of contaminated soil and its soaking in an organic solvent on the subsequent biodegradation of PAHs. In a clayey dredged sludge with a high organic-matter content (12%), heating at 120 degrees C for one hour increased the degree of degradation after 21 days of an aged PAH contamination from 9.5 +/- 0.7% to 27 +/- 5%. Lower temperatures resulted in smaller increases. The observed increase in biodegradation is caused by either transfer of PAHs from sorption sites with low desorption rates to those with high ones or transformation of slow-sorption sites into fast-sorption ones. Soaking of the above sludge in a 4:1 (v/v) acetone-water mixture increased the degree of degradation from 9.5 +/- 0.7% to 20.4 +/- 1.4%, probably as a result of dissolution of the PAHs in the pore liquid during soaking. Thermal pretreatment of a contaminated sandy soil with a low organic-matter content showed no significant effect on the degradation of aged PAHs. Soaking of the sandy soil increased the degradation of only PAHs of high molecular weight, namely from 24 +/- 5% to 48 +/- 7%.

Super-optimal CO2 reduces seed yield but not vegetative growth in wheat.

Although terrestrial atmospheric CO2 levels will not reach 1000 micromoles mol-1 (0.1%) for decades, CO2 levels in growth chambers and greenhouses routinely exceed that concentration. CO2 levels in life support systems in space can exceed 10000 micromoles mol-1(1%). Numerous studies have examined CO2 effects up to 1000 micromoles mol-1, but biochemical measurements indicate that the beneficial effects of CO2 can continue beyond this concentration. We studied the effects of near-optimal (approximately 1200 micromoles mol-1) and super-optimal CO2 levels (2400 micromoles mol-1) on yield of two cultivars of hydroponically grown wheat (Triticum aestivum L.) in 12 trials in growth chambers. Increasing CO2 from sub-optimal to near-optimal (350-1200 micromoles mol-1) increased vegetative growth by 25% and seed yield by 15% in both cultivars. Yield increases were primarily the result of an increased number of heads per square meter. Further elevation of CO2 to 2500 micromoles mol-1 reduced seed yield by 22% (P < 0.001) in cv. Veery-10 and by 15% (P < 0.001) in cv. USU-Apogee. Super-optimal CO2 did not decrease the number of heads per square meter, but reduced seeds per head by 10% and mass per seed by 11%. The toxic effect of CO2 was similar over a range of light levels from half to full sunlight. Subsequent trials revealed that super-optimal CO2 during the interval between 2 wk before and after anthesis mimicked the effect of constant super-optimal CO2. Furthermore, near-optimal CO2 during the same interval mimicked the effect of constant near-optimal CO2. Nutrient concentration of leaves and heads was not affected by CO2. These results suggest that super-optimal CO2 inhibits some process that occurs near the time of seed set resulting in decreased seed set, seed mass, and yield.

Super-optimal CO2 reduces wheat yield in growth chamber and greenhouse environments.

Seven growth chamber trials (six replicate trials using 0.035, 0.12, and 0.25% CO2 in air and one trial using 0.12, 0.80, and 2.0% CO2 in air) and three replicate greenhouse trials (0.035, 0.10, 0.18, 0.26, 0.50, and 1.0% CO2 in air) compare the effects of super-optimal CO2 on the seed yield, harvest index, and vegetative growth rate of wheat (Triticum aestivum L. cvs. USU-Apogee and Veery-10). Plants in the growth chamber trials were grown hydroponically under fluorescent lamps, while the greenhouse trials were grown under sunlight and high pressure sodium lamps and in soilless media. Plants in the greenhouse trials responded similarly to those in the growth chamber trials; maximum yields occurred near 0.10 and 0.12% CO2 and decreased significantly thereafter. This research indicates that the toxic effects of elevated CO2 are not specific to only one environment and has important implications for the design of bio-regenerative life support systems in space, and for the future of terrestrial agriculture.