Negative emissions of carbon dioxide through chemical-looping combustion (CLC) and gasification (CLG) using oxygen carriers based on manganese and iron

Carbon capture and storage (CCS) is an economically attractive strategy for avoiding carbon dioxide (CO₂) emissions from, e.g., power plants to the atmosphere. The combination of CCS and biomass combustion would result in a reduction of atmospheric CO₂, or net negative emissions, as plant growth is a form of sequestration of atmospheric carbon. Carbon capture can be achieved in a variety of ways, one of which is chemical looping. Chemical-looping combustion (CLC) and chemical looping gasification (CLG) are two promising technologies for conversion of biomass to heat and power or syngas/methane with carbon capture. There have been significant advances made with respect to CLC in the last two decades for all types of fuel, with much less research on the gasification technology. CLG offers some interesting opportunities for production of biofuels together with carbon capture and may have several advantages with respect to the bench mark indirect gasification process or dual-bed fluidized bed (DFBG) in this respect. In CLG, an oxygen carrier is used as a bed material instead of sand, which is common in indirect gasification, and this could have several advantages: (i) all generated CO₂ is present together with the syngas or methane in the fuel reactor outlet stream, thus in a concentrated stream, viable for separation and capture; (ii) the air reactor (or combustion chamber) should largely be free from trace impurities, thus preventing corrosion and fouling in this reactor; and (iii) the highly oxidizing conditions in the fuel reactor together with solid oxide surfaces should be advantageous with respect to limiting formation of tar species. In this study, two manganese ores and an iron-based waste material, LD slag, were investigated with respect to performance in these chemical-looping technologies. The materials were also impregnated with alkali (K) in order to gauge possible catalytic effects and also to establish a better understanding of the general behavior of oxygen carriers with alkali, an important component in biomass and biomass waste streams and often a precursor for high-temperature corrosion. The viability of the oxygen carriers was investigated using a synthetic biogas in a batch fluidized bed reactor. The conversion of CO, H₂, CH₄, and C₂H₄ was investigated in the temperature interval 800–950 °C. The reactivity, or oxygen transfer rate, was highest for the manganese ores, followed by the LD slag. The conversion of C₂H₄ was generally high but could largely be attributed to thermal decomposition. The K-impregnated samples showed enhanced reactivity during combustion conditions, and the Mangagran-K sample was able to achieve full conversion of benzene. The interaction of the solid material with alkali showed widely different behavior. The two manganese ores retained almost all alkali after redox testing, albeit exhibiting different migration patterns inside the particles. LD slag lost most alkali to the gas phase during testing, although some remained, possibly explaining a small difference in reactivity. In summary, the CLC and CLG processes could clearly be interesting for production of heat, power, or biofuel with negative CO₂ emissions. Manganese ores are most promising from this study, as they could absorb alkali, giving a better conversion and perhaps also inhibiting or limiting corrosion mechanisms in a combustor or gasifier.

     

Utilisation of steel slags as neutralising agents in biooxidation of a refractory gold concentrate and their influence on the subsequent cyanidation

A study on the possibilities to utilise steel slag as neutralising agent in biooxidation of a refractory gold concentrate has been done with reference to commercial grade slaked lime. The idea has been to reduce the operating costs for neutralisation in the biooxidation plant, which is known to be the second largest operating cost. Other benefits would be savings in cost for landfilling of slag, possibilities to recycle elements present in the slag and savings of virgin limestone deposits. The slags used were an EAF slag and a slag from ladle refining; both originating from Swedish scrap based steel-making. Continuous biooxidation of the refractory gold concentrate was conducted in a single-stage 5 L reactor at a retention time of 56 h. The neutralisation capacity was determined by comparing the amount needed, per ton of feed concentrate added, to maintain the desired pH of 1.5 during steady state operation. Slaked lime had the highest neutralisation capacity with 110 kg/ton feed followed by ladle slag and EAF slag with values of 152 and 267 kg/ton feed, respectively. Sulphide mineral oxidation was similar and high in all cases although the ladle slag results were slightly better. Gold recoveries after cyanide leaching on the residues obtained were also similar and were in the range of 86-89%. However, the cyanide consumption expressed as kilogram cyanide per ton of concentrate fed to biooxidation, was double in the case of ladle slag and three times as much for the EAF slag compared to the slaked lime experiment. The increased cyanide consumption could not be explained only by the increased amount of elemental sulphur obtained in the slag experiments. The elemental sulphur formed had different reactivities as seen from the thiocyanate formation and cyanide losses due to thiocyanate formation were 16%, 32% and 40% for EAF slag, slaked lime and ladle slag, respectively. It is concluded that the ladle slag could be a possible replacement for limestone if they are mixed in proper proportions so that the microbial carbon dioxide demand is met whereas the EAF slag is less suitable due to the very fine reaction products obtained which gave operational problems with filtration and washing. To come further, experiments with the normal multi-stage biooxidation set-up with total retention time of 120 h should be performed which would increase the sulphur oxidation and eventually also reduce the cyanide consumption.     

Nonthermal GSM RF and ELF EMF effects upon rat BBB permeability

Since the late 1980s, our group has examined the effects of radiofrequency electromagnetic fields (RF-EMF), including pulse-modulated waves of the type emitted by mobile phones, upon the blood?Cbrain barrier. In more than 2,000 rats, we have repeatedly demonstrated a passage of the rats?? own albumin from the blood through the brain capillaries into the surrounding brain parenchyma at SAR values down to 0.1mW/kg. In most of these experiments, the animals were exposed in TEM-cells, ventilated by an external electrical fan at 50 Hz. In the present study, we examined whether the extremely low frequency (ELF) magnetic fields from the fan (50 Hz, 0.3?C1.5 ??T) might add to the RF effect. Sixty-four rats were divided into 4 groups: RF only, ELF only and RF + ELF exposure plus a sham group. The GSM-900 MHz RF exposure was at the very low, nonthermal, average whole-body SAR level 0.4 mW/kg. Demonstration of the normally occurring albumin extravasation in the basal hypothalamus is our inbuilt control proving that the staining is reliable. Two full series of staining of the whole material gave negative results for hypothalamus. Not until we changed to avidin, biotin, and antibodies from a third supplier, we received an acceptable staining. Twenty-five percent of the RF animals had a pathological albumin leakage, while the ELF and RF + ELF groups with three and two pathological findings, respectively, were not significantly different from the control group. We conclude that the use of external fans has had no major influence upon the result.     

The Anthropocene: From Global Change to Planetary Stewardship

Over the past century, the total material wealth of humanity has been enhanced. However, in the twenty-first century, we face scarcity in critical resources, the degradation of ecosystem services, and the erosion of the planet's capability to absorb our wastes. Equity issues remain stubbornly difficult to solve. This situation is novel in its speed, its global scale and its threat to the resilience of the Earth System. The advent of the Anthropence, the time interval in which human activities now rival global geophysical processes, suggests that we need to fundamentally alter our relationship with the planet we inhabit. Many approaches could be adopted, ranging from geoengineering solutions that purposefully manipulate parts of the Earth System to becoming active stewards of our own life support system. The Anthropocene is a reminder that the Holocene, during which complex human societies have developed, has been a stable, accommodating environment and is the only state of the Earth System that we know for sure can support contemporary society. The need to achieve effective planetary stewardship is urgent. As we go further into the Anthropocene, we risk driving the Earth System onto a trajectory toward more hostile states from which we cannot easily return.     

Native predators reduce harvest of reindeer by Sámi pastoralists

Contemporary efforts to protect biological diversity recognize the importance of sustaining traditional human livelihoods, particularly uses of the land that are compatible with intact landscapes and ecologically complete food webs. However, these efforts often confront conflicting goals. For example, conserving native predators may harm pastoralist economies because predators consume domestic livestock that sustain people. This potential conflict must be reconciled by policy, but such reconciliation requires a firm understanding of the effects of predators on the prey used by people. We used a long-term, large-scale database and Bayesian models to estimate the impacts of lynx (Lynx lynx), wolverine (Gulo gulo), and brown bear (Ursus arctos) on harvest of semi-domesticated reindeer (Rangifer tarandus) by Sami pastoralists in Sweden. The average annual harvest of reindeer averaged 25% of the population (95% credible interval = 19, 31). Annual harvest declined by 96.6 (31, 155) reindeer for each lynx family group (the surveyed segment of the lynx population) in a management unit and by 94.3 (20, 160) for each wolverine reproduction (the surveyed segment of the wolverine population). We failed to detect effects of predation by brown bear. The mechanism for effects of predation on harvest was reduced population growth rate. The rate of increase of reindeer populations declined with increasing abundance of lynx and wolverine. The density of reindeer, latitude, and weather indexed by the North Atlantic Oscillation also influenced reindeer population growth rate. We conclude that there is a biological basis for compensating the Sámi reindeer herders for predation on reindeer.     

Potential emissions from two mechanically-biologically pretreated (MBT) wastes

The interaction of parameters determining the potential emissions of two different mechanically-biologically pretreated municipal solid wastes (MBT wastes) is elucidated in this work. The origins of the wastes are Germany and Sweden. By means of lab-scale experiments, increased stabilisation through composting is preferably determined by a decrease in respiration activity. Concurrently, the stabilisation is verified for the leachates by a decrease in COD, DOC, and BOD(5). Total organic carbon content reflects stabilisation less accurately. FT-IR and thermal analytical methods add valuable information about the state of degradation, especially when several distinct thermal parameters are taken into account. Mobility of Cr, Ni, Pb, and Zn produced by a batch leaching test with deionized water is reduced by the pretreatment of both materials. Mobility of copper unambiguously increased. A principle component analysis (PCA) of membrane fractionated leachates indicates an affinity of Cu to mobile humic acids or dissolved organic carbon. High Cr, Zn, and Ni contents in the solid co-occur with high contents of solid humic acids. To a lesser extent, this is also true for solid Cd, Cu, and Pb contents. Due to differences in required landfilling conditions, actual emissions and after-care phase length will depend on whether each waste is landfilled in Germany or Sweden.     

Community Odours in the Vicinity of a Petrochemical Industrial Complex

Community odours in the vicinity of an oil refinery and petrochemical industrial area were studied by an observer network throughout an entire year. Odour episodes occurred during 0.86 percent of the time of the study. Odour reports increased closer to the refinery. Within a range of 12.5 km, more than 50 percent of the odours were estimated to originate from the refinery. The most typical odour was that of reduced sulphur compounds (35.2 percent of all observations). Odour episodes occurred during low wind velocities and high humidity. Odours were most frequent during January-April, and were usually reported early in the morning. The odours were evidently due to the general operation of the plants, as no single activity or in-plant factor could be identified as the source of the odours.     

Polychlorinated biphenyls in polysulfide sealants--occurrence and emission from a landfill station

Approximately 80,000 kg polysulfide sealant containing 10,000-18,000 kg polychlorinated biphenyls (PCB) was deposited at a Swedish municipal landfill station during 1965-1973. Investigations during 1994 showed that soil layers underneath the landfill had concentration of PCB not alarmingly high. The concentration of PCB congeners in ground water samples was elevated 4-750 times compared to a reference sample. Based on samples of ground water, leachate water, and flux chambers measuring evaporation of PCB from the landfill surface, the emission of PCB was estimated to be 1 g sigmaPCB/yr. This very low rate was attributed to the high sorptive capacity of the sealant. Compared to a reference site, the evaporation flux was elevated for the most volatile congeners, but factors 20-1400 lower than from another landfill which was contaminated with PCB in paper-pulp fibres.     

Animal community structure and energy budget calculations of a Daphnia magna (straus) population in relation to the rock pool environment

The fauna and environmental conditions in a freshwater rock pool ecosystem were followed by a weekly quantitative sampling program from April to August, 1974. The rock pool, situated on a small island in the northern Baltic Sea, was heavily eutrophicated by droppings from the surrounding colony of sea birds. The intermittent flushing of the pool with rainwater and the input of bird droppings, as well as the biological activity, contributed to the large seasonal variations in nutrients and organic matter that were observed. A dense algal bloom of flagellates occurred in April but vanished when the animal population started to increase in the middle of May. During the rest of the summer, most of the photosynthetic pigments were found in the bottom sediment, mostly as degraded phaeo-pigments due to intensive grazing by the animals in the pool. Very few animal taxa were found and the phyllopod Daphnia magna (Straus) dominated throughout the whole sampling period. D. magna contributed to more than 50% of the total biomass, except in late July when chironomid larvae were most abundant. The total biomass in the pool increased from about 15 mg (dry weight) l^?1 in May to a maximum of about 60 mg l^?1 at the end of June. There were few carnivores in the system, except during the spring when the water bug Deronectes griseostriatus (de Geer) was common.Analyses of size, age and sex structure and calculations of birth and death rates of the D. magna population showed large seasonal variations, correlated with the volume fluctuations and flushings of the pool which stimulated both the algal production and the growth and reproduction of Daphnia. Data from the extensive literature that exists on D. magna and other species of the same genus were used, together with field and experimental data from the rock pool population, in a numerical model describing the energy budget of this species. The model describes variations in weight-specific growth, reproduction, moulting, feeding and respiration rates in relation to temperatures and food concentrations. Energy budget relationships that maximise the chances for survival and utilisation of the available energy for a population exposed to varying food concentrations are predicted by the model. The energy budget model was also used to estimate the secondary production of the rock pool population of D. magna. The total production between April and August was 203 mg (dry weight) l^?1 and the average production per biomass ratio was 0.094 day^?1. The average net production efficiency was 42%, very close to other values reported for D. magna from other biotopes. The relative importance of different factors controlling the production was also analysed with the model. Production per biomass ratio was calculated, assuming a constant temperature and/or food concentration for the whole sampling period. The varying food concentrations in the rock pool had the most pronounced influence, greater than that of temperature and size structure variations in the population.     

Phosphorus in tributaries to Lake Mälaren, Sweden: analytical fractions, anthropogenic contribution and bioavailability

Riverine phosphorus (P) concentration and P-transport to Lake M?laren, the third largest lake in Sweden, has been monitored for 35 years in 12 major tributaries. During a period of 15 months, complementary assessments of particulate P, suspended matter and dissolved reactive P were made. Particulate P comprised 64%, dissolved unreactive P 23% and dissolved reactive P 13% as flow-weighted means, with high seasonal variability. "Background" or "reference" P-transports in the streams were estimated by different methods and the anthropogenic contribution to P-transport was shown to be reduced over time. Potential algal availability of particulate P showed a mean availability of c. 45% for water draining arable and forested land, while the availability was higher for sewage discharge particulate P and algal P. Calculated total bioavailable P in tributaries was shown to equal reactive P measured on coarsely filtered water and it was indicated that the proportion of bioavailable P was higher during the period with high anthropogenic P-contribution than with a lower contribution.