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Abstract We detected a controlled release of CO2 (g) with pH eddy covariance. We quantified CO2 emission using measurements of water velocity and pH in the plume of aqueous CO2 generated by the bubble streams, and using model predictions of vertical CO2 dissolution and its dispersion downstream. CO2 (g) was injected 3 m below the floor of the North Sea at rates of 5.7–143 kg d − 1. Instruments were 2.6 m from the center of the bubble streams. In the absence of injected CO2, pH eddy covariance quantified the proton flux due to naturally-occurring benthic organic matter mineralization (equivalent to a dissolved inorganic carbon flux of 7.6 ± 3.3 mmol m − 2 d − 1, s.e., n = 33). At the lowest injection rate, the proton flux due to CO2 dissolution was 20-fold greater than this. To accurately quantify emission, the kinetics of the carbonate system had to be accounted for. At the peak injection rate, 73 ± 13% (s.d.) of the injected CO2 was emitted, but when kinetics were neglected, the calculated CO2 emission was one-fifth of this. Our results demonstrate that geochemical techniques can detect and quantify very small seafloor sources of CO2 and attribute them to natural or abiotic origins.

In this work, the wastewater obtained from the hydrothermal liquefaction of black liquor was treated and valorized for hydrogen production by supercritical water gasification (SCWG). The influence of the main process parameters on the conversion yield was studied. The experiments were conducted at three different temperatures (below and above the critical point of water): 350 °C, 450 °C and 600 °C. The results showed that by increasing the temperature from 350 °C to 600 °C, the total gas yield was highly improved (from 1.9 mol gas/kg of dried feedstock to 13.1 mol gas/kg of dried feedstock). The H2 composition was higher than that of CH4 and CO2 at 600 °C, and the HHV of the obtained gas was 61.2 MJ/kg. The total organic carbon (TOC) removal efficiency was also improved by increasing the temperature, indicating that the SCWG process could be used for both applications: (i) for wastewater treatment; (ii) for producing a high calorific gas. The experiments with the Raney-nickel catalyst were performed in order to study the catalyst’s influence on the conversion yield. The results indicated that the catalyst enhances carbon conversion and gas production from mild to higher temperatures. The maximum total gas yield obtained with this catalyst was 32.4 mol gas/kg of dried feedstock at 600 °C, which is 2.5 times higher than that obtained at the same operating conditions without a catalyst. The H2 yield and the HHV of the obtained gas with the catalyst were 20.98 mol gas/kg dried feedstock and 80.2 MJ/kg, respectively. However, the major contribution of the catalytic SCWG process was the improvement of the total gas yield at mild operating temperatures (450 °C), and the obtained performance was even higher than that obtained at 600 °C without catalyst (17.81 mol gas/kg dried feedstock and 13.1 mol gas/kg dried feedstock, respectively). This is a sustainable approach for treating wastewater at mild temperatures by catalytic SCWG.

Abstract Sub-seabed geological CO2 storage is discussed as a climate mitigation strategy, but the impact of any leakage of stored CO2 into the marine environment is not well known. In this study, leakage from a CO2 storage reservoir through near-surface sediments was mimicked for low leakage rates in the North Sea. Field data were combined with laboratory experiments and transport-reaction modelling to estimate CO2 and mineral dissolution rates, and to assess the mobilization of metals in contact with CO2-rich fluids and their potential impact on the environment. We found that carbonate and silicate minerals reacted quickly with the dissolved CO2, increasing porewater alkalinity and neutralizing about 5% of the injected CO2. The release of Ca, Sr, Ba and Mn was mainly controlled by carbonate dissolution, while Fe, Li, B, Mg, and Si were released from silicate minerals, mainly from deeper sediment layers. No toxic metals were released from the sediments and overall the injected CO2 was only detected up to 1 m away from seabed CO2 bubble streams. Our results suggest that low leakage rates of CO2 over short timescales have minimal impact on the benthic environment. However, porewater composition and temperature are effective indicators for leakage detection, even at low CO2 leakage rates.

Abstract To inform cost-effective monitoring of offshore geological storage of carbon dioxide (CO2), a unique field experiment, designed to simulate leakage of CO2 from a sub-seafloor storage reservoir, was carried out in the central North Sea. A total of 675 kg of CO2 were released into the shallow sediments (∼3 m below seafloor) for 11 days at flow rates between 6 and 143 kg d-1. A set of natural, inherent tracers (13C, 18O) of injected CO2 and added, non-toxic tracer gases (octafluoropropane, sulfur hexafluoride, krypton, methane) were used to test their applicability for CO2 leakage attribution and quantification in the marine environment. All tracers except 18O were capable of attributing the CO2 source. Tracer analyses indicate that CO2 dissolution in sediment pore waters ranged from 35 % at the lowest injection rate to 41% at the highest injection rate. Direct measurements of gas released from the sediment into the water column suggest that 22 % to 48 % of the injected CO2 exited the seafloor at, respectively, the lowest and the highest injection rate. The remainder of injected CO2 accumulated in gas pockets in the sediment. The methodologies can be used to rapidly confirm the source of leaking CO2 once seabed samples are retrieved.

Since the implementation of the sulfur cap legislation in 2020, marine very-low-sulfur fuel oil, often known as VLSFO, has become a crucial source of fuel for the contemporary shipping industry. However, both the production and utilization processes of VLSFO are plagued by the poor miscibility of the cutter fraction and the residual fraction, which can result in the precipitation of asphaltene. In this study, biodiesel was chosen as a cutter fraction to improve the stability and compatibility of asphaltene in VLSFO because of its environmental benefit and strong solubility. The average chemical structure of asphaltene derived from the marine low-sulfur fuel oil sample was analyzed using element analysis, FTIR, 1HNMR, and time-flight spectroscopy. The composition of biodiesel was analyzed using GC-MS. It was found that the asphaltene had a feature of a short side chain, low H/C ratio, high aromaticity, and a high proportion of heteroatoms. Both laboratory experiments and molecular dynamic simulations were applied to investigate the dispersion effect and mechanism compared with other dispersants. The dispersion effect of biodiesel was studied using measurements of the initial precipitation point (IPP), dispersion improvement rate, and morphology of asphaltene in the model oil. Experimental results revealed that biodiesel was fully compatible with heavy fuel oil and that it can postpone the IPP from 46% to 54% and increase the dispersion improvement rate to 35%. Molecular dynamics (MDs) simulation results show that biodiesel can form strong interactions with the fused aromatics structures and heteroatoms in the asphaltene; such interactions can increase the solubility of asphaltene and acts as a “connection bridge” to promote the dispersion effect of asphaltene molecules.

The paper presents the survey of ethanol application as the fuel for diesel engines which is added to diesel fuel or injected to the inlet manifold. The paper describes unsteady flow simulation in the inlet manifold of a 4 cylinder diesel engine with injected ethanol (Martin Diesel UR IV). The calculation of mixing rates is based on transient spray-plume-growth with concentration and temperature profile applying the CFD code (software of Fluent Inc. USA). The calculation of combustion was performed using a RNG kε (renormalization group) turbulent model, standard wall function and a PDF model for chemical equilibrium of gas composition and kinetics in the combustion chamber.

The QICS controlled release experiment demonstrates that leaks of carbon dioxide (CO2) gas can be detected by monitoring acoustic, geochemical and biological parameters within a given marine system. However the natural complexity and variability of marine system responses to (artificial) leakage strongly suggests that there are no absolute indicators of leakage or impact that can unequivocally and universally be used for all potential future storage sites. We suggest a multivariate, hierarchical approach to monitoring, escalating from anomaly detection to attribution, quantification and then impact assessment, as required. Given the spatial heterogeneity of many marine ecosystems it is essential that environmental monitoring programmes are supported by a temporally (tidal, seasonal and annual) and spatially resolved baseline of data from which changes can be accurately identified. In this paper we outline and discuss the options for monitoring methodologies and identify the components of an appropriate baseline survey.