Porewater Geochemical Assessment of Seismic Indications for Gas Hydrate Presence and Absence: Mahia Slope, East of New Zealand’s North Island

We compare sediment vertical methane flux off the Mahia Peninsula, on the Hikurangi Margin, east of New Zealand’s North Island, with a combination of geochemical, multichannel seismic and sub-bottom profiler data. Stable carbon isotope data provided an overview of methane contributions to shallow sediment carbon pools. Methane varied considerably in concentration and vertical flux across stations in close proximities. At two Mahia transects, methane profiles correlated well with integrated seismic and TOPAS data for predicting vertical methane migration rates from deep to shallow sediment. However, at our “control site”, where no seismic blanking or indications of vertical gas migration were observed, geochemical data were similar to the two Mahia transect lines. This apparent mismatch between seismic and geochemistry data suggests a potential to underestimate gas hydrate volumes based on standard seismic data interpretations. To accurately assess global gas hydrate deposits, multiple approaches for initial assessment, e.g., seismic data interpretation, heatflow profiling and controlled-source electromagnetics, should be compared to geochemical sediment and porewater profiles. A more thorough data matrix will provide better accuracy in gas hydrate volume for modeling climate change and potential available energy content

Catalytic Ozonation of Recalcitrant Organic Chemicals in Water Using Vanadium Oxides Loaded ZSM-5 Zeolites

The discharge of wastewater having recalcitrant chemical compositions can have significant and adverse environmental effects. The present study investigates the application of a catalytic ozonation treatment for the removal of recalcitrant organic chemicals (ROCs) from the water. Novel catalytic materials using vanadium (V) oxides deposited onto the surface of NaZSM-5 zeolites (V/ZSM) were found to be highly efficient for this purpose. The highly-dispersed V oxides (V4+ and V5+) and Si-OH-Al framework structures were determined to promote the surface reaction and generation of hydroxyl radicals. The constructed V1/ZSM450 (0.7 wt% of V loading and 450°C of calcination) exhibited the highest activity among the developed catalyst compositions. The V1/ZSM450-COP increased the mineralization rate of nitrobenzene and benzoic acid by 50 and 41% in comparison to single ozonation. This study demonstrates the enhanced potential of V/ZSM catalysts used with catalytic ozonation process (COP) for the treatment of chemical wastewaters

Spatial Variation in Sediment Organic Carbon Distribution across the Alaskan Beaufort Sea Shelf

In September 2009, a series of sediment cores were collected across the Alaskan Beaufort Sea shelf-slope. Sediment and porewater organic carbon (OC) concentrations and stable carbon isotope ratios (δ13C) were measured to investigate spatial variations in sediment organic matter (OM) sources and distribution of these materials across the shelf. Cores were collected along three main nearshore (shelf) to offshore (slope) sampling lines (transects) from east-to-west along the North Slope of Alaska: Hammerhead (near Camden Bay), Thetis Island (near Prudhoe Bay), and Cape Halkett (towards Point Barrow). Measured sediment organic carbon (TOC) and porewater dissolved organic carbon (DOC) concentrations and their respective δ13C values were used to investigate the relative contribution of different OM sources to sediment OC pool cycled at each location. Sources of OM considered included: water column-sourced phytodetritus, deep sediment methane (CH4), and terrestrial, tundra/river-sourced OM. Results of these measurements, when coupled with results from previous research and additional analyses of sediment and porewater composition, show a pattern of spatial variation in sediment OC concentrations, OM source contributions, and OM cycled along the Alaskan Beaufort Sea shelf. In general, measured sediment total organic carbon (TOC) concentrations, δ13CTOC values, porewater DOC concentrations, and δ13CDOC values are consistent with an east-to-west transport of modern Holocene sediments with higher OC concentrations primarily sourced from relatively labile terrestrial, tundra OM sources and phytodetritus along the Alaskan Beaufort shelf. Sediment transport along the shelf results in the medium-to-long term accumulation and burial of sediment OM focused to the west which in turn results in higher biogenic CH4 production rates and higher upward CH4 diffusion through the sediments resulting in CH4−AMO-sourced contribution to sediment OC westward along the shelf. Understanding current OM sources and distributions along the Alaskan Beaufort shelf is important for enhancing models of carbon cycling in Arctic coastal shelf systems. This will help support the prediction of the climate response of the Arctic created in the face of future warming scenarios

Hydrolysis and acidification of activated sludge from a petroleum refinery

Abstract The cost-effective treatment of activated sludge that is generated by refining petroleum is a challenging industrial problem. In this study, semi-continuous stirred tank reactors (CSTRs) containing petroleum refinery excess activated sludge (PREAS) were used to comparatively investigate hydrolysis and acidification rates, after the addition of heneicosane (C21H44) (R1) and 1-phenylnaphthalene (C16H12) (R2) to different and individual reactors. Operation of the reactors using a sludge retention time (SRT) of 6 days and a pH of 5.0, resulted in the maintenance of stable biological activity as determined by soluble chemical oxygen demand (SCOD), volatile fatty acids (VFAs) production and oil removal efficiency. The optimum conditions for hydrogen production include a SRT of 8 days, at pH 6.5. Under these conditions, hydrogen production rates in the control containing only PREAS were 1567 mL/L (R0), compared with 1365 mL/L in R1 and 1454 mL/L-PREAS in R2. Coprothermobacter, Fervidobacterium, Caldisericum and Tepidiphilus were the dominant bacterial genera that have the potential to degrade petroleum compounds and generate VFAs. This study has shown that high concentrations of heneicosane and 1-phenylnaphthalene did not inhibit the hydrolytic acidification of PREAS

Dissolution Process Observation of Methane Bubbles in the Deep Ocean Simulator Facility

To investigate the temperature dependency of the methane bubble dissolution rate, buoyant single methane bubbles were held stationary in a countercurrent water flow at a pressure of 6.9 MPa and temperatures ranging from 288 K to 303 K. The 1 to 3 mm diameter bubbles were analyzed by observation through the pressure chamber viewport using a bi-telecentric CCD camera. The dissolution rate in artificial seawater was approximately two times smaller than that in pure water. Furthermore, it was observed that the methane bubble dissolution rate increased with temperature, suggesting that bubble dissolution is a thermal activation process (the activation energy is estimated to be 9.0 kJ/mol). The results were different from the expected values calculated using the governing equation for methane dissolution in water. The dissolution modeling of methane bubbles in the mid-to-shallow depth of seawater was revised based on the current results

Comparison of Efficiencies and Mechanisms of Catalytic Ozonation of Recalcitrant Petroleum Refinery Wastewater by Ce, Mg, and Ce-Mg Oxides Loaded Al2O3

The use of catalytic ozonation processes (COPs) for the advanced treatment of recalcitrant petroleum refinery wastewater (RPRW) is rapidly expanding. In this study, magnesium (Mg), cerium (Ce), and Mg-Ce oxide-loaded alumina (Al2O3) were developed as cost efficient catalysts for ozonation treatment of RPRW, having performance metrics that meet new discharge standards. Interactions between the metal oxides and the Al2O3 support influence the catalytic properties, as well as the efficiency and mechanism. Mg-Ce/Al2O3 (Mg-Ce/Al2O3-COP) reduced the chemical oxygen demand by 4.7%, 4.1%, 6.0%, and 17.5% relative to Mg/Al2O3-COP, Ce/Al2O3-COP, Al2O3-COP, and single ozonation, respectively. The loaded composite metal oxides significantly increased the hydroxyl radical-mediated oxidation. Surface hydroxyl groups (–OHs) are the dominant catalytic active sites on Al2O3. These active surface –OHs along with the deposited metal oxides (Mg2+ and/or Ce4+) increased the catalytic activity. The Mg-Ce/Al2O3 catalyst can be economically produced, has high efficiency, and is stable under acidic and alkaline conditions

Investigation of Catalytic Ozonation of Recalcitrant Organic Chemicals in Aqueous Solution over Various ZSM-5 Zeolites

Catalytic ozonation processes (COPs) are an emerging technology for wastewater treatments. NaZSM-5 zeolites in three different SiO2/Al2O3 ratios (31, 45, and 120) and their metallic oxides loaded samples were compared for COP of nitrobenzene solution. NaZSM-5(120) showed high total organic carbon (TOC) removals (70.2–74.0%) by adsorption relative to NaZSM-5(45) (0.4–0.6%) at various initial pH conditions. NaZSM-5(31) was obtained by NaOH treatment of NaZSM-5(45) and displayed 20.9–23.8% of TOC removals by adsorption. In COPs, the different ZSM-5 zeolites exhibited various TOC removals and different reaction pathways. COP-NaZSM-5(120) showed high TOC removals compared to COP-NaZSM-5(45) and COP-NaZSM-5(31). The repeated uses of zeolites in COPs were performed to understand the reaction pathways and contribution of adsorption versus ozonation (i.e., catalytic oxidation and/or direct ozonation). Both adsorption and direct ozonation in COP-NaZSM-5(120) contributed TOC removal for the first use, whereas direct ozonation and •OH mediated oxidation dominated the process for eight repeated uses. Direct ozonation and •OH-mediated oxidation controlled the COP-NaZSM-5(45) process for the first and eight repeated uses. Adsorption and direct ozonation governed the COP-NaZSM-5(31) process for the first use, whereas the direct ozonation dominated it for eight repeated uses. In COPs, NaZSM-5(120) and NaZSM-5(45) showed the catalytic activity, whereas NaZSM-5(31) displayed negligible catalytic activity. The high catalytic activity of NaZSM-5(120) may be due to more Si-O bonds on zeolite surfaces. The results revealed that loading of Mg oxide on ZSM-5 zeolites can increase catalytic activity in COPs. These results show the application potential of ZSM-5 zeolites in ozonation of recalcitrant chemical wastewaters

Efficient ozonation of reverse osmosis concentrates from petroleum refinery wastewater using composite metal oxide-loaded alumina

Abstract Novel Mn–Fe–Mg- and Mn–Fe–Ce-loaded alumina (Mn–Fe–Mg/Al2O3 and Mn–Fe–Ce/Al2O3) were developed to catalytically ozonate reverse osmosis concentrates generated from petroleum refinery wastewaters (PRW-ROC). Highly dispersed 100–300-nm deposits of composite multivalent metal oxides of Mn (Mn2+, Mn3+, and Mn4+), Fe (Fe2+ and Fe3+) and Mg (Mg2+), or Ce (Ce4+) were achieved on Al2O3 supports. The developed Mn–Fe–Mg/Al2O3 and Mn–Fe–Ce/Al2O3 exhibited higher catalytic activity during the ozonation of PRW-ROC than Mn–Fe/Al2O3, Mn/Al2O3, Fe/Al2O3, and Al2O3. Chemical oxygen demand removal by Mn–Fe–Mg/Al2O3- or Mn–Fe–Ce/Al2O3-catalyzed ozonation increased by 23.9% and 23.2%, respectively, in comparison with single ozonation. Mn–Fe–Mg/Al2O3 and Mn–Fe–Ce/Al2O3 notably promoted ·OH generation and ·OH-mediated oxidation. This study demonstrated the potential use of composite metal oxide-loaded Al2O3 in advanced treatment of bio-recalcitrant wastewaters