Study of the digestion process at a full-scale solid-state biogas plant by using ORWARE: Model modification and implementation.

The configuration of the reactor influences the digestion process and thus the product yields; other factors such as the rate of biogas production or biogas loss also affect the process specifically with high solid configuration. With these in mind, the ORganic WAste REsearch (ORWARE) anaerobic digestion sub-model was modified to be able to study solid-state anaerobic digestion (SS-AD) (using plug-flow reactor). The simulation results from the updated model agreed with the operational data with respect to methane yield, digestate yield and energy turnover. The model was found to be sensitive to changes in feedstock composition but to a lesser extent to changes in process temperature and retention time. By applying the model on several cases of liquid anaerobic digestion (L-AD), it was noticed that L-AD at mesophilic condition with 25 retention days seemed to be superior to other cases of L-AD with regard to energy turnover. However, even if similar methane production were observed for L-AD and SS-AD, the model suggested higher energy turnover for the case of SS-AD at thermophilic condition, being 10% more in average in comparison with cases of L-AD.

Life cycle assessment of upgrading options of a preliminary wastewater treatment plant including food waste addition.

Life cycle assessment (LCA) is a beneficial tool to evaluate the performance of wastewater treatment plants (WWTPs) and to compare different upgrading options. The main objective of this study is to investigate the environmental impact of upgrading options of a preliminary WWTP in Istanbul, Turkey. The preliminary plant currently consists of mechanical treatment units and various upgrading options including primary treatment and high-rate activated sludge system (HRAS) process as well as the addition of food waste to wastewater were compared. Results showed that the baseline scenario (S0) had worse performance than all future scenarios (S1-3) except for climate change. The scenario of adding food waste to wastewater (S3) has the best performance in climate change, terrestrial acidification, terrestrial ecotoxicity and fossil depletion. Increased addition of food waste was also tested in the sensitivity analysis, and major improvements were obtained especially in climate change and terrestrial ecotoxicity.

Horse manure as feedstock for anaerobic digestion.

Horse keeping is of great economic, social and environmental benefit for society, but causes environmental impacts throughout the whole chain from feed production to manure treatment. According to national statistics, the number of horses in Sweden is continually increasing and is currently approximately 360,000. This in turn leads to increasing amounts of horse manure that have to be managed and treated. Current practices could cause local and global environmental impacts due to poor performance or lack of proper management. Horse manure with its content of nutrients and organic material can however contribute to fertilisation of arable land and recovery of renewable energy following anaerobic digestion. At present anaerobic digestion of horse manure is not a common treatment. In this paper the potential for producing biogas and biofertiliser from horse manure is analysed based on a thorough literature review in combination with mathematical modelling and simulations. Anaerobic digestion was chosen as it has a high degree of resource conservation, both in terms of energy (biogas) and nutrients (digestate). Important factors regarding manure characteristics and operating factors in the biogas plant are identified. Two crucial factors are the type and amount of bedding material used, which has strong implications for feedstock characteristics, and the type of digestion method applied (dry or wet process). Straw and waste paper are identified as the best materials in an energy point of view. While the specific methane yield decreases with a high amount of bedding, the bedding material still makes a positive contribution to the energy balance. Thermophilic digestion increases the methane generation rate and yield, compared with mesophilic digestion, but the total effect is negligible.

Enhancement of biogas production from food waste and sewage sludge - Environmental and economic life cycle performance.

Management of municipal solid waste is an efficient method to increase resource efficiency, as well as to replace fossil fuels with renewable energy sources due to that (1) waste to a large extent is renewable as it consists of food waste, paper, wood etc. and (2) when energy and materials are recovered from waste treatment, fossil fuels can be substituted. In this paper results from a comprehensive system study of future biological treatment of readily degradable waste in two Swedish regions are presented. Different collection and separation systems for food waste in households have been applied as well as technical improvements of the biogas process as to reduce environmental impact. The results show that central sorting of a mixed fraction into recyclables, combustibles, biowaste and inert is a competitive option compared to source separation. Use of pellets is beneficial compared to direct spreading as fertiliser. Fuel pellets seem to be the most favourable option, which to a large extent depends on the circumstances in the energy system. Separation and utilisation of nitrogen in the wet part of the digestion residue is made possible with a number of technologies which decreases environmental impact drastically, however to a substantial cost in some cases.

Multiple system modelling of waste management.

Due to increased environmental awareness, planning and performance of waste management has become more and more complex. Therefore waste management has early been subject to different types of modelling. Another field with long experience of modelling and systems perspective is energy systems. The two modelling traditions have developed side by side, but so far there are very few attempts to combine them. Waste management systems can be linked together with energy systems through incineration plants. The models for waste management can be modelled on a quite detailed level whereas surrounding systems are modelled in a more simplistic way. This is a problem, as previous studies have shown that assumptions on the surrounding system often tend to be important for the conclusions. In this paper it is shown how two models, one for the district heating system (MARTES) and another one for the waste management system (ORWARE), can be linked together. The strengths and weaknesses with model linking are discussed when compared to simplistic assumptions on effects in the energy and waste management systems. It is concluded that the linking of models will provide a more complete, correct and credible picture of the consequences of different simultaneous changes in the systems. The linking procedure is easy to perform and also leads to activation of project partners. However, the simulation procedure is a bit more complicated and calls for the ability to run both models.

Models for waste life cycle assessment: review of technical assumptions.

A number of waste life cycle assessment (LCA) models have been gradually developed since the early 1990 s, in a number of countries, usually independently from each other. Large discrepancies in results have been observed among different waste LCA models, although it has also been shown that results from different LCA studies can be consistent. This paper is an attempt to identify, review and analyse methodologies and technical assumptions used in various parts of selected waste LCA models. Several criteria were identified, which could have significant impacts on the results, such as the functional unit, system boundaries, waste composition and energy modelling. The modelling assumptions of waste management processes, ranging from collection, transportation, intermediate facilities, recycling, thermal treatment, biological treatment, and landfilling, are obviously critical when comparing waste LCA models. This review infers that some of the differences in waste LCA models are inherent to the time they were developed. It is expected that models developed later, benefit from past modelling assumptions and knowledge and issues. Models developed in different countries furthermore rely on geographic specificities that have an impact on the results of waste LCA models. The review concludes that more effort should be employed to harmonise and validate non-geographic assumptions to strengthen waste LCA modelling.

Simulation of reflected light intensity changes during navigation and radio-frequency lesioning in the brain.

An electrode with adjacent optical fibers for measurements during navigation and radio frequency lesioning in the brain is modeled for Monte Carlo simulations of light transport in brain tissue. Relative reflected light intensity at 780 nm, I780, from this electrode and probes with identical fiber configuration are simulated using the intensity from native white matter as reference. Models are made of homogeneous native and coagulated gray, thalamus, and white matter as well as blood. Dual layer models, including models with a layer of cerebrospinal fluid between the fibers and the brain tissue, are also made. Simulated I780 was 0.16 for gray matter, 0.67 for coagulate gray matter, 0.36 for thalamus, 0.39 for coagulated thalamus, unity for white matter, 0.70 for coagulated white matter, and 0.24 for blood. Thalamic matter is also found to reflect more light than gray matter and less than white matter in clinical studies. In conclusion, the reflected light intensity can be used to differentiate between gray and white matter during navigation. Furthermore, coagulation of light gray tissue, such as the thalamus, might be difficult to detect using I780, but coagulation in darker gray tissue should result in a rapid increase of I780.

Combined diffuse light reflectance and electrical impedance measurements as a navigation aid in deep brain surgery.

AIM: The aim of this study is to assess reflected light intensity combined with impedance as a navigation aid during stereotactic neurosurgery. METHODS: During creation of 21 trajectories for stereotactic implantation of deep brain stimulation electrodes in the globus pallidus internus or subthalamus (zona incerta or subthalamic nucleus), impedance at 512 kHz and reflected light intensity at 780 nm were measured continuously and simultaneously with a radio frequency electrode containing optical fibres. The signals were compared with the anatomy, determined from pre- and post-operative MRI and CT. The measurements were performed within minutes, and signal analysis was done post-operatively. RESULTS: Reflected light intensity was low from the cortex, lateral ventricle, caudate nucleus and putamen; intermediate from the globus pallidus and thalamus; while it was high from the subcortical white matter, internal capsule and subthalamus. The electrical impedance was less consistent, but generally low in the cortex, intermediate in the subcortical white matter, putamen, globus pallidus and thalamus, and high in the internal capsule and subthalamus. CONCLUSION: Reflected light intensity and electrical impedance give complementary information about passed tissue, and the combination seems promising as a navigation aid during stereotactic neurosurgery.

Diffuse reflectance spectroscopy measurements for tissue-type discrimination during deep brain stimulation.

Diffuse reflectance spectroscopy as a method for improving intracerebral guidance during functional neurosurgery has been investigated. An optical probe was developed for measurements during stereotactic and functional neurosurgery in man. The aim of the study was to investigate the spectral differences between white and grey matter and between white matter and functional targets. Diffuse reflectance spectroscopy measurements in ten patients were recorded at incremental steps towards and in three different functional targets (STN, GPi and Zi). The recorded spectra along the trajectory were sorted into white or grey matter, based on preoperative MRI images or the recorded spectral shape and intensity. The difference between tissue types was calculated as a quotient. Significant intensity differences between white and grey matter were found to be at least 14% (p < 0.05) and 20% (p < 0.0001) for MRI and spectral-sorted data respectively. The reflectance difference between white matter and the functional targets of GPi was higher than for STN and Zi. The results indicate that diffuse reflectance spectroscopy has a potential to be developed to a suitable complement to other intracerebral guidance methods.

A laser Doppler system for intracerebral measurements during stereotactic neurosurgery.

A laser Doppler system for intracerebral measurements during stereotactic and functional neurosurgery is presented. The system comprises a laser Doppler perfusion monitor, an optical probe adapted for the Leksell Stereotactic System and a personal computer with software for acquisition, data analysis and presentation. The software makes it possible to present both the perfusion and the total backscattered light intensity (TLI) in real-time. During intracerebral measurements, the perfusion signal records the tissue's microcirculation whereas the TLI signal may be used to distinguish between grey and white matter. Evaluation of the system has been done during stereotactic neurosurgery in relation to implantation of deep brain stimulation electrodes. Measurements were made along trajectories towards targets in the deep brain structure as well as in pre-calculated target areas. The measurements show that the system has a potential to be used for intracerebral guidance but further evaluation of the technique is needed.

Intracerebral microvascular measurements during deep brain stimulation implantation using laser Doppler perfusion monitoring.

The aim of the study was to investigate if laser Doppler perfusion monitoring (LDPM) can be used in order to differentiate between gray and white matter and to what extent microvascular perfusion can be recorded in the deep brain structures during stereotactic neurosurgery. An optical probe constructed to fit in the Leksell Stereotactic System was used for measurements along the trajectory and in the targets (globus pallidus internus, subthalamic nucleus, zona incerta, thalamus) during the implantation of deep brain stimulation leads (n = 22). The total backscattered light intensity (TLI) reflecting the grayness of the tissue, and the microvascular perfusion were captured at 128 sites. Heartbeat-synchronized pulsations were found at all perfusion recordings. In 6 sites the perfusion was more than 6 times higher than the closest neighbor indicating a possible small vessel structure. TLI was significantly higher (p < 0.005) and the perfusion significantly lower (p < 0.005) in positions identified as white matter in the respective MRI batch. The measurements imply that LDPM has the potential to be used as an intracerebral guidance tool.

Flexible and robust strategies for waste management in Sweden.

Treatment of solid waste continues to be on the political agenda. Waste disposal issues are often viewed from an environmental perspective, but economic and social aspects also need to be considered when deciding on waste strategies and policy instruments. The aim of this paper is to suggest flexible and robust strategies for waste management in Sweden, and to discuss different policy instruments. Emphasis is on environmental aspects, but social and economic aspects are also considered. The results show that most waste treatment methods have a role to play in a robust and flexible integrated waste management system, and that the waste hierarchy is valid as a rule of thumb from an environmental perspective. A review of social aspects shows that there is a general willingness among people to source separate wastes. A package of policy instruments can include landfill tax, an incineration tax which is differentiated with respect to the content of fossil fuels and a weight based incineration tax, as well as support to the use of biogas and recycled materials.

What life-cycle assessment does and does not do in assessments of waste management.

In assessments of the environmental impacts of waste management, life-cycle assessment (LCA) helps expanding the perspective beyond the waste management system. This is important, since the indirect environmental impacts caused by surrounding systems, such as energy and material production, often override the direct impacts of the waste management system itself. However, the applicability of LCA for waste management planning and policy-making is restricted by certain limitations, some of which are characteristics inherent to LCA methodology as such, and some of which are relevant specifically in the context of waste management. Several of them are relevant also for other types of systems analysis. We have identified and discussed such characteristics with regard to how they may restrict the applicability of LCA in the context of waste management. Efforts to improve LCA with regard to these aspects are also described. We also identify what other tools are available for investigating issues that cannot be adequately dealt with by traditional LCA models, and discuss whether LCA methodology should be expanded rather than complemented by other tools to increase its scope and applicability.

Radio-frequency lesioning in brain tissue with coagulation-dependent thermal conductivity: modelling, simulation and analysis of parameter influence and interaction.

Radio-frequency brain lesioning is a method for reducing e.g. symptoms of movement disorders. A small electrode is used to thermally coagulate malfunctioning tissue. Influence on lesion size from thermal and electric conductivity of the tissue, microvascular perfusion and preset electrode temperature was investigated using a finite-element model. Perfusion was modelled as an increased thermal conductivity in non-coagulated tissue. The parameters were analysed using a 2(4)-factorial design (n=16) and quadratic regression analysis (n=47). Increased thermal conductivity of the tissue increased lesion volume, while increased perfusion decreased it since coagulation creates a thermally insulating layer due to the cessation of blood perfusion. These effects were strengthened with increased preset temperature. The electric conductivity had negligible effect. Simulations were found realistic compared to in vivo experimental lesions.

Optical measurements during experimental stereotactic radiofrequency lesioning.

The aim of this study was to evaluate in vivo a laser Doppler measurement system in porcine brain tissue during thermal lesioning. A 2-mm monopolar radiofrequency lesioning electrode was equipped with optical fibers in order to monitor the lesioning procedure. Laser Doppler and backscattered light intensity signals were measured along the electrode trajectory and during bilateral lesioning in the central gray (70, 80 and 90 degrees C, n = 14). The time course of the coagulation process could be followed by optical recordings. Two separate groups of tissue were identified from the intensity signals. The changes in the perfusion levels in both groups displayed significant changes (p < 0.05, n = 48) at all temperature settings, while backscattered light intensity was significant for only one group at the different temperatures (p < 0.05, n = 39). These results indicate that optical measurements correlate with lesion development in vivo. The study also indicates that it is possible to follow the lesioning process intra-operatively.

The effect of cystic cavities on deep brain stimulation in the basal ganglia: a simulation-based study.

Although the therapeutic effect of deep brain stimulation (DBS) is well recognized, a fundamental understanding of the mechanisms responsible is still not known. In this study finite element method (FEM) modelling and simulation was used in order to study relative changes of the electrical field extension surrounding a monopolar DBS electrode positioned in grey matter. Due to the frequently appearing cystic cavities in the DBS-target globus pallidus internus, a nucleus of grey matter with and without a cerebrospinal fluid filled cystic cavity was modelled. The position, size and shape of the cyst were altered in relation to the electrode. The simulations demonstrated an electrical field around the active element with decreasing values in the radial direction. A stepwise change was present at the edge between grey and white matters. The cyst increased the radial extension and changed the shape of the electrical field substantially. The position, size and shape of the cyst were the main influencing factors. We suggest that cystic cavities in the DBS-target may result in closely related unexpected structures or neural fibre bundles being stimulated and could be one of the reasons for suboptimal clinical effects or stimulation-induced side effects.

Radio frequency electrode system for optical lesion size estimation in functional neurosurgery.

Radiofrequency (RF) lesioning in the human brain is one possible surgical therapy for severe pain as well as movement disorders. One obstacle for a safer lesioning procedure is the lack of size monitoring. The aim of this study was to investigate if changes in laser Doppler or intensity signals could be used as markers for size estimation during experimental RF lesioning. A 2 mm in diameter monopolar RF electrode was equipped with optical fibers and connected to a digital laser Doppler system. The optical RF electrode's performance was equal to a standard RF electrode with the same dimensions. An albumin solution with scatterers was used to evaluate the intensity and laser Doppler signal changes during lesioning at 70, 80, and 90 degrees C. Significant signal changes were found for these three different clot sizes, represented by the temperatures (p<0.05, n=10). The volume, width, and length of the created coagulations were correlated to the intensity signal changes (r=0.88, n=30, p<0.0001) and to the perfusion signal changes (r=0.81, n=30, p<0.0001). Both static and Doppler-shifted light can be used to follow the lesioning procedure as well as being used for lesion size estimation during experimental RF lesioning.

How model-based systems analysis can be improved for waste management planning.

Waste management models have been developed worldwide since the late 1960s. The overall aim of the models is to assist decision makers who are facing a complex task in order to handle waste in a cost-efficient and environmentally sound way. International research publications regarding waste management models point out the major benefits to be their capacity to deal with complexity and uncertainty and of finding benefits of co-operation and handling different goals. Such models have been developed and used successfully in Swedish research projects since the beginning of the 1990s, but the current situation is that such models are rarely requested for waste management planning in the country. Based on case studies (with the waste management models MIMES/Waste and ORWARE) in the Swedish municipality of Jönköping and a follow-up study, the paper discusses and draws conclusions on how to improve and increase the use of models to better correspond to the needs of decision makers involved in waste management planning.

Experimental radiofrequency brain lesions: a volumetric study.

OBJECTIVE: This study describes the production, under strictly standardized and controlled conditions, of radiofrequency lesions with identical neurogenerator settings: in vitro in two different albumin solutions (nongelatinous and gelatinous) and in vivo in the thalamus of the pig. METHODS: The radiofrequency lesions were investigated in vitro by the use of a specially designed video system and in vivo by magnetic resonance imaging. Moreover, the size of the in vivo lesions was estimated with the use of histological sectioning. The statistical analysis included the calculation of a correlation coefficient for the length, width, and volume for each lesion estimation. RESULTS: A high correlation (R = 0.96, P < 0.005; n = 14) was found between clot sizes in the two albumin solutions. Albumin clots generated in gelatinous albumin showed systematically larger volumes. In the pig, two concentric zones were seen in all magnetic resonance images and all histological preparations. The width correlation of the completely coagulated brain tissue (inner zones) was R = 0.94, P < 0.005, and n = 7. The corresponding correlation between magnetic resonance images and gelatinous albumin was R = 0.93, P < 0.005, and n = 7. As a rule, the in vitro clots were smaller than the outer zone but larger than the inner zone of the magnetic resonance imaging-recorded lesions for all of the electrode and temperature combinations tested. In vivo lesions generated with the same electrode and parameter settings showed high reproducibility. CONCLUSION: The value of presurgical electrode tests to validate the electrode function and lesion size in vitro has become evident in this study, which shows a high correlation between the in vitro albumin clots and the in vivo lesions observed on magnetic resonance images.