Underground hydrogen storage: The techno-economic perspective.

The changes in the energy sector after the Paris agreement and the establishment of the Green Deal, pressed the governments to embrace new measures to reduce greenhouse gas emissions. Among them, is the replacement of fossil fuels by renewable energy sources or carbon-neutral alternative means, such as green hydrogen. As the European Commission approved green hydrogen as a clean fuel, the interest in investments and dedicated action plans related to its production and storage has significantly increased. Hydrogen storage is feasible in aboveground infrastructures as well as in underground constructions. Proper geological environments for underground hydrogen storage are porous media and rock cavities. Porous media are classified into depleted hydrocarbon reservoirs and aquifers, while rock cavities are subdivided into hard rock caverns, salt caverns, and abandoned mines. Depending on the storage option, various technological requirements are mandatory, influencing the required capital cost. Although the selection of the optimum storage technology is site depending, the techno-economical appraisal of the available underground storage options featured the porous media as the most economically attractive option. Depleted hydrocarbon reservoirs were of high interest as site characterisation and cavern mining are omitted due to pre-existing infrastructure, followed by aquifers, where hydrogen storage requires a much simpler construction. Research on data analytics and machine learning tools will open avenues for consolidated knowledge of geological storage technologies.

Towards a Sustainable Future: Advancing an Integrated Approach for the Recycling and Valorization of Agricultural Plastics.

Plastic pollution has become a pressing environmental issue. The agricultural sector, in particular, is a significant contributor to this problem, given the widespread use of plastics in farming practices and a lack of and/or use of inefficient approaches for the recycling and valorization of agricultural plastic waste. This has resulted in the accumulation of these residues in landfills and/or their improper disposal, which has exacerbated their environmental impact, leading to negative consequences on soil, water, and ecosystems. This work provides an overview on the current methodologies available to address the challenges associated with inadequate management of agricultural plastics and highlights the need for a comprehensive and systematic methodology, involving material development, polymer processing, waste collection, sorting, and valorization. It emphasizes the importance of collaboration between polymer producers, polymer manufacturers, farmers, policymakers, waste management companies, and recyclers to develop effective, technical, and economically viable recycling and valorization schemes. This paper addresses gaps and provides guidance on possible solutions, specifically polymer development, policy instruments, regulatory frameworks, collection schemes, and the technical approaches required for the adequate valorization of agricultural plastic waste. Furthermore, it highlights the associated barriers and benefits of the different presented approaches. It also aims to promote awareness on agricultural plastic waste and provide guidance on the best approaches to reduce its environmental impact.

Irrigation of soil with reclaimed wastewater acts as a buffer of microbial taxonomic and functional biodiversity.

The usage of reclaimed wastewater (RWW) for irrigation of agricultural soils is increasingly being acknowledged for reducing water consumption by promoting reuse of treated wastewater, and for the delivery of extant nutrients in the soil. The downside is that RWW may be a vector for contamination of soils with contaminants of emerging concern (CECs), if left uncontrolled. Its usage is anticipated to alter the soil properties, consequently also the soil microbial community. In the present study, soil microcosms were set to monitor how short periods (up to fourteen days) of RWW irrigation influence the soil ecosystem, namely its physicochemical properties, functioning, and colonising microbiota (differentiating fungi from bacteria). Two scenarios were studied: clean soil and soil contaminated (spiked) with 9 CECs, at conditions that limit any abiotic decay processes, monitoring along time fluctuations in the taxonomic and functional microbiota diversity. As shortly as fourteen days, the irrigation of either soil with RWW did not significantly (p > 0.05) alter its physicochemical properties and scarcely impacted the bioremediation processes of the CECs that showed decay levels ranging from 24% to 100%. Bacillus spp. dominance was enhanced along time in all the soil microcosms (reaching over 70% of the total abundance on the 7th day) but the RWW help to preserve, to some extent, high bacterial diversity. Besides, irrigation with RWW acted as a buffer of the soil mycobiota, limiting alterations in its composition caused either along time (to a minor degree) or due to contamination with CECs (to a great degree). This includes limiting the rise of Rhizopus sp. relative abundance. Collectively, our data support the utility of short-term periods of RWW irrigation for preserving the soil microbial diversity and functioning, especially when fungi are considered.

Electro-bioremediation of a mixture of structurally different contaminants of emerging concern: Uncovering electrokinetic contribution.

This study analyses the electrokinetic (EK) contribution to the removal from a clay soil of a mixture of 10 different contaminants of emerging concern (CECs; 17ß-estradiol, E2; sulfamethoxazole, SMX; bisphenol A, BPA; ibuprofen, IBU; 17α-ethinylestradiol, EE2; oxybenzone, OXY; diclofenac, DCF; triclosan, TCS; caffeine, CAF; carbamazepine, CBZ). After 4 days, the CECs natural attenuation was between 0% (CBZ) and 90% (E2) yet increasing with the application of EK (20 mA, 12 h ON/OFF) to 14% (CBZ) and 100% (E2). When EK was applied, the CECs more recalcitrant to biodegradation (i.e. ≤ 13% biotic decay) mostly underwent electro-chemical induced degradation (OXY, DCF, TCS, CAF, CBZ). Daily irrigation enhanced the rates of the electro-oxidation -osmosis and -migration, increasing the CECs decay. After 8 days of EK treatment, the CECs decay increased, surpassing the decay lag phase of some compounds (OXY, TCS, and CBZ). Yet after 16 days, most CECs showed similar removals with and without EK, with EK only acting positively on SMX, OXY, TCS and CBZ (ca. +10%). Our results support that EK application can improve the removal of CECs from soil, however, under the conditions tested, 16-day treatment lead to pH alterations that decreased the bioremediation efficiency and inhibited electro-degradation near the cathode.

Emerging organic contaminants in soil irrigated with effluent: electrochemical technology as a remediation strategy.

The effluent reuse for soil irrigation is foreseen as a possible strategy to mitigate the pressure on water resources. However, there is the risk of potential accumulation in soil of emerging organic contaminants (EOCs). In the present work the electrokinetic remediation (EKR) technology, use of direct current, was applied for the removal of EOCs from a soil irrigated with effluent. For this, a soil collected from a rice field (located in Portugal) was mixed with spiked effluent to simulate flood irrigation in one time-period. The experiments were carried out for 6 days applying a low current intensity of 2.5 mA. Different current strategies were tested: continuous mode, reversed electrode polarization (REP), On/Off time periods, and the combination of the last two. The target EOCs comprises a list of six pharmaceuticals and personal care products widely detected in treated wastewater. This study showed that once introduced in soil through effluent irrigation, 20-100% of the EOCs were still present in the soil after 6 days. EKR enhanced up to 20% of the EOCs removal when comparing with control (without current). The EOC removals showed to be related to the microcosm location (anode, central or cathode sections) and dependent of EOCs characteristics. Soil characteristics did not change when On/Off system was combined with REP as a current strategy, and a more homogenous removal of the studied EOCs was achieved in the tested conditions. EKR showed to be a promising technology to be applied in EOCs contaminated soils, not only for removal purposes, but also to avoid possible dispersion in the environment.

Electrokinetic remediation of contaminants of emergent concern in clay soil: Effect of operating parameters.

The potential of electrokinetic (EK) remediation to remove from soils one particular group of contaminants - contaminants of emergent concern (CECs), remains largely overlooked. The present study aimed to evaluate the efficiency of the EK process for the remediation of an agricultural clay soil containing CECs. The soil was spiked with four CECs - sulfamethoxazole, ibuprofen, triclosan and caffeine - and their status (i.e. residual amounts and spatial distribution) evaluated at the seventh day of EK treatment at a defined current intensity, directionality and duration of void period. The characterization of the soil physicochemical properties was also undertaken. The results showed similar degradation trends in all applied EK strategies, which were suchlike to that of the natural attenuation (biotic control): sulfamethoxazole > ibuprofen ≥ triclosan ≥ caffeine. The removal of the CECs was higher under a 10 mA constant current application than in the natural attenuation (up to 2.8 times higher; from 13 to 85%). Caffeine was the exception with its best removal efficiency being achieved when the ON/OFF switch mode with a void period duration of 12 h was used (36%). The use of electro-polarization reversal mode did not favour the remediation. The soil pH variations resulting from EK application were determinant for triclosan remediation, which increased with soil pH increase. The only EK condition that promoted the removal of all CECs was the ON/OFF switch mode of 12 h (removals between 36 and 72%), in which only minor physicochemical disturbances of the soil were observed. This is in accordance with a potential application of EK in-situ. The last is reinforced by the low estimated electrical cost of the best EK technology - 2.33 €/m3 for the 7 days. Overall the EK remediation processes are a promising technology to stimulate in situ the removal of CECs from agricultural soils.

Remediation potential of caffeine, oxybenzone, and triclosan by the salt marsh plants Spartina maritima and Halimione portulacoides.

Pharmaceuticals and personal care products (PPCPs) have attracted increasing concern during the last decade because of their widespread uses and continuous release to the aquatic environment. This work aimed to study the distribution of caffeine (CAF), oxybenzone (MBPh), and triclosan (TCS) when they arrive in salt marsh areas and to assess their remediation potential by two different species of salt marsh plants: Spartina maritima and Halimione portulacoides. Experiments were carried out in the laboratory either in hydroponics (sediment elutriate) or in sediment soaked in elutriate, for 10 days. Controls without plants were also carried out. CAF, MBPh, and TCS were added to the media. In unvegetated sediment soaked in elutriate, CAF was mainly in the liquid phase (83%), whereas MBPh and TCS were in the solid phase (90% and 56%, respectively); the highest remediation was achieved for TCS (40%) and mainly attributed to bioremediation. The presence of plants in sediment soaked in elutriate-enhanced PPCPs remediation, decreasing CAF and TCS levels between approximately 20-30% and MBPh by 40%.. Plant uptake, adsorption to plant roots/sediments, and bio/rhizoremediation are strong hypothesis to explain the decrease of contaminants either in water or sediment fractions, according to PPCPs characteristics.

Electrodialytic 2-compartment cells for emerging organic contaminants removal from effluent.

The present work discusses the efficiency of the electrodialytic (ED) process to remove emerging organic contaminants (EOCs) from effluent. The ED process was carried out in a cell of two-compartments (2 C-cell) with effluent in either the anode or cathode compartment, separated from the electrolyte compartment through an anion or a cation exchange membrane (AEM and CEM, respectively). As effluent destination might be soil irrigation, and having in mind the nutrient recycling, phosphorus was also monitored in the process. The ED removals showed to be dependent of EOCs characteristics and cell design. Removals were higher when using an AEM (60-72%) than a CEM (8-63%), except for caffeine when the effluent was placed in the cathode, that did not show any removal. When using an AEM with the effluent placed in the anode compartment, all the EOCs (including caffeine) were removed between 57-72%, mainly through electrodegradation phenomena. Regarding phosphorus, a polarity switch may be done to a 2 C-cell with a AEM, depending on the effluent final use. This technology is still in its first steps and, in both cases, further optimization of ED parameters is needed. Still, this technological innovation and cross-cutting research envisages the promotion of economic, social and environmental benefits.

Comparative assessment of LECA and Spartina maritima to remove emerging organic contaminants from wastewater.

The present work aimed to evaluate the capacity of constructed wetlands (CWs) to remove three emerging organic contaminants with different physicochemical properties: caffeine (CAF), oxybenzone (MBPh), and triclosan (TCS). The simulated CWs were set up with a matrix of light expanded clay aggregates (LECA) and planted with Spartina maritima, a salt marsh plant. Controlled experiments were carried out in microcosms using deionized water and wastewater collected at a wastewater treatment plant (WWTP), with different contaminant mass ranges, for 3, 7, and 14 days. The effects of variables were tested isolatedly and together (LECA and/or S. maritima). The presence of LECA and/or S. maritima has shown higher removal (around 61-97%) of lipophilic compounds (MBPh and TCS) than the hydrophilic compound (CAF; around 19-85%). This was attributed to the fact that hydrophilic compounds are dissolved in the water column, whereas the lipophilic ones suffer sorption processes promoting their removal by plant roots and/or LECA. In the control (only wastewater), a decrease in the three contaminant levels was observed. Adsorption and bio/rhizoremediation are the strongest hypothesis to explain the decrease in contaminants in the tested conditions.

Valorisation of ferric sewage sludge ashes: Potential as a phosphorus source.

Sewage sludge ashes (SSA), although a waste, contain elements with socio-economic and environmental potential that can be recovered. This is the case of phosphorus (P). SSA from two Danish incinerators were collected during two years and characterized. The sampling was done immediately after incineration (fresh SSA) or from an outdoor deposit (deposited SSA). Although morphology and mineral composition were similar, physico-chemical and metal concentration differences were found between incinerator plants and sampling periods. No differences were observed between deposited and fresh SSA, except for the parameters directly influenced by disposal conditions (e.g. moisture content). All the SSAs had high concentrations of P (up to 16wt%), but they all exceeded Danish EPA Cd and Ni thresholds for direct application at agricultural soil. Fresh and deposited SSA were acid washed aiming P extraction, achieving 50gP/kg (approx. 37% of total P), but metals were also co-extracted to the liquid phase. To avoid and/or minimize the metals pollution of the extracted P, selective P recovery from the SSA was tested, using the electrodialytic (ED) process. ED laboratory cells, with 3 compartments (3c) and 2 compartments (2c), and two acid concentrations (H2SO4, 0.08M and 0.19M) were used for 7days. The most concentrated acid solution increased P solubilization. The 2c-cell combined with the higher acid concentration resulted in higher P recoveries, 125g of P/kg of SSA in the anolyte. The obtained results showed that the ED process is a valuable tool for the SSA valorisation as it promotes simultaneous P recovery and metals extraction from the SSA.

Electrokinetic remediation of six emerging organic contaminants from soil.

Some organic contaminants can accumulate in organisms and cause irreversible damages in biological systems through direct or indirect toxic effects. In this study the feasibility of the electrokinetic (EK) process for the remediation of 17ß-oestradiol (E2), 17α-ethinyloestradiol (EE2), bisphenol A (BPA), nonylphenol (NP), octylphenol (OP) and triclosan (TCS) in soils was studied in a stationary laboratory cell. The experiments were conducted using a silty loam soil (S2) at 0, 10 and 20mA and a sandy soil (S3) at 0 and 10 mA. A pH control in the anolyte reservoir (pH>13) at 10 mA was carried out using S2, too. Photo and electrodegradation experiments were also fulfilled. Results showed that EK is a viable method for the remediation of these contaminants, both through mobilization by electroosmotic flow (EOF) and electrodegradation. As EOF is very sensible to soil pH, the control in the anolyte increased EOF rate, consequently enhancing contaminants mobilization towards the cathode end. The extent of the mobilization towards the electrode end was mainly dependent on compounds solubility and octanol-water partition coefficient. In the last 24h of experiments, BPA presented the highest mobilization rate (ca. 4 µg min(-1)) with NP not being detected in the catholyte. At the end of all experiments the percentage of contaminants that remained in the soil ranged between 17 and 50 for S2, and between 27 and 48 for S3, with no statistical differences between treatments. The mass balance performed showed that the amount of contaminant not detected in the cell is similar to the quantity that potentially may suffer photo and electrodegradation.

Phosphorus recovery from sewage sludge ash through an electrodialytic process.

The electrodialytic separation process (ED) was applied to sewage sludge ash (SSA) aiming at phosphorus (P) recovery. As the SSA may have high heavy metals contents, their removal was also assessed. Two SSA were sampled, one immediately after incineration (SA) and the other from an open deposit (SB). Both samples were ED treated as stirred suspensions in sulphuric acid for 3, 7 and 14 days. After 14 days, phosphorus was mainly mobilized towards the anode end (approx. 60% in the SA and 70% in the SB), whereas heavy metals mainly electromigrated towards the cathode end. The anolyte presented a composition of 98% of P, mainly as orthophosphate, and 2% of heavy metals. The highest heavy metal removal was achieved for Cu (ca. 80%) and the lowest for Pb and Fe (between 4% and 6%). The ED showed to be a viable method for phosphorus recovery from SSA, as it promotes the separation of P from the heavy metals.

Suitability of oil bioremediation in an Artic soil using surplus heating from an incineration facility.

A 168-day period field study, carried out in Sisimiut, Greenland, assessed the potential to enhance soil remediation with the surplus heating from an incineration facility. This approach searches a feasible ex situ remediation process that could be extended throughout the year with low costs. Individual and synergistic effects of biostimulation were also tested, in parallel. An interim evaluation at the end of the first 42 days showed that biostimulation and active heating, as separate treatments, enhanced petroleum hydrocarbon (PHC) removal compared to natural attenuation. The coupling of both technologies was even more effective, corroborating the benefits of both techniques in a remediation strategy. However, between day 42 and day 168, there was an opposite remediation trend with all treatments suggesting a stabilization except for natural attenuation, where PHC values continued to decrease. This enforces the "self-purification" capacity of the system, even at low temperatures. Coupling biostimulation with active heating was the best approach for PHC removal, namely for a short period of time (42 days). The proposed remediation scheme can be considered a reliable option for faster PHC removal with low maintenance and using "waste heating" from an incineration facility.