Jens Aage Hansen

Energy production, nutrient recovery and greenhouse gas emission potentials from integrated pig manure management systems

Improper management of pig manure has resulted in environmental problems such as surface water eutrophication, ground water pollution, and greenhouse gas emissions. This study develops and compares 14 alternative manure management scenarios aiming at energy and nutrient extraction. The scenarios based on combinations of thermal pretreatment, anaerobic digestion, anaerobic co-digestion, liquid/solid separation, drying, incineration, and thermal gasification were compared with respect to their energy, nutrient and greenhouse gas balances. Both sole pig manure and pig manure mixed with other types of waste materials were considered. Data for the analyses were obtained from existing waste treatment facilities, experimental plants, laboratory measurements and literature. The assessment reveals that incineration combined with liquid/solid separation and drying of the solids is a promising management option yielding a high potential energy utilization rate and greenhouse gas savings. If maximum electricity production is desired, anaerobic digestion is advantageous as the biogas can be converted to electricity at high efficiency in a gas engine while allowing production of heat for operation of the digestion process. In conclusion, this study shows that the choice of technology has a strong influence on energy, nutrient and greenhouse gas balances. Thus, to get the most reliable results, it is important to consider the most representative (and up-to-date) technology combined with data representing the area or region in question.

Strategic environmental assessment of alternative sewage sludge management scenarios

Strategic environmental assessment (SEA) of sewage sludge management in a Danish municipality (Aalborg), with 160,000 inhabitants using alternative methods for aggregation of environmental impacts was performed. The purpose is to demonstrate the use of SEA in relation to sludge management and to improve SEA methodology. Six different scenarios for management of sewage sludge within the Aalborg municipality involving thermal treatment, composting and landfilling of sludge were evaluated. Environmental impact categories considered were global warming, non-renewable resources (nutrients and fossil fuels) and land use. Impact categories human health, ecotoxicity and soil quality were excluded as methodology for their assessment is not yet fully developed. Thermal sludge treatment with energy utilisation was shown to be a promising option for sewage sludge management in Aalborg. Sensitivity of the relative environmental impacts with respect to calculation methodology and input parameter values were evaluated to identify important parameters and calculation methods. The analysis showed that aggregation procedures, sludge biogas potential and sludge production were very important whereas sludge transport was not.

Assessing the impacts of changes in treatment technology on energy and greenhouse gas balances for organic waste and wastewater treatment using historical data

Historical data on organic waste and wastewater treatment during the period of 1970—2020 were used to assess the impact of treatment on energy and greenhouse gas (GHG) balances. The assessment included the waste fractions: Sewage sludge, food waste, yard waste and other organic waste (paper, plastic, etc.). Data were collected from Aalborg, a municipality located in Northern Denmark. During the period from 1970—2005, Aalborg Municipality has changed its waste treatment strategy from landfilling of all wastes toward composting of yard waste and incineration with combined heat and power production from the remaining organic municipal waste. Wastewater treatment has changed from direct discharge of untreated wastewater to full organic matter and nutrient (N, P) removal combined with anaerobic digestion of the sludge for biogas production with power and heat generation. These changes in treatment technology have resulted in the waste and wastewater treatment systems in Aalborg progressing from being net consumers of energy and net emitters of GHG, to becoming net producers of energy and net savers of GHG emissions (due to substitution of fossil fuels elsewhere). If it is assumed that the organic waste quantity and composition is the same in 1970 and 2005, the technology change over this time period has resulted in a progression from a net annual GHG emission of 200 kg CO 2-eq. capita—1 in 1970 to a net saving of 170 kg CO2-eq. capita—1 in 2005 for management of urban organic wastes.

REMOVING NUMERICALLY INDUCED DISPERSION FROM FINITE DIFFERENCE MODELS FOR SOLUTE AND WATER TRANSPORT IN UNSATURATED SOILS

Numerically induced dispersion is an important, but often ignored, source of calculation errors in transport simulations. General correction terms for removing numerical dispersion from the applied calculation schemes would be valuable in improving the accuracy of the simulation results before they are compared with measured soil data. In this study, a general transport equation for unsaturated water and solute transport is obtained by casting the one-dimensional Richards and convection-dispersion equations into general form. Correction terms for removing numerical dispersion from four commonly used finite difference (FD) calculation schemes used on the general transport equation are derived using Taylor series. The correction terms are given both in case of constant and variable depth increments. The derived terms are validated by method of moments analysis and tests against analytical solutions. The use of the correction terms in cases where the transport equations are extended with sink-/source terms is discussed. It is shown that a variable calculation grid should be chosen with care because the use of variable depth increments creates additional numerical dispersion and skewness and, in some cases, numerical oscillations in depth. The suggested procedure for deriving and validating correction terms for numerical dispersion can easily be extended to other FD schemes.

Linking landfill hydrology and leachate chemical composition at a controlled municipal landfill (Kåstrup, Denmark) using state-space analysis.

Leachate production and composition data for a municipal landfill measured over a 25-year period was used to investigate important processes and parameters. Long-term leachate production could be satisfactorily predicted from a simple top-layer landfill hydrology model while short-term predictions were less accurate, likely due to water storage in the waste. State-space and multiple regression modelling were used to identify relations between different parameters. State-space models proved most accurate in fitting measured data, likely because temporal correlation between measurements is accounted for unlike multiple regression. State-space modelling showed that temporal correlation in leachate production must be taken into account and confirmed that water storage inside the landfill is important. Temporal correlation is also important when predicting pH and chloride concentrations but less so for BOD5 and NH3/NH4 + concentrations. Leachate flow did in general not have a strong impact upon leachate composition, small effects were observed for Cl-, and NH3/NH4 +concentrations. It was also observed that the mass load of nitrogen from the landfill was strongly dependent upon leachate nitrogen (ammonia/ammonium) concentrations and to a lesser degree upon leachate flow rates. This study introduces state-space modelling in solid waste management as a powerful tool to identify governing parameters for hydrological and bio-chemical processes.

Cities as development drivers: from waste problems to energy recovery and climate change mitigation

There is a strong connection between economic growth and development of cities. Economic growth tends to stimulate city growth, and city economies have often shaped innovative environments that in turn support economic growth. Simultaneously, social and environmental problems related to city growth can be serious threats to the realization of the socio-economic contributions that cities can make. However, as a result of considerable diversity of competences combined with interactive learning and innovation, cities may also solve these problems. The ‘urban order’ may form a platform for innovative problem solving and potential spill-over effects, which may stimulate further economic growth and development. This paper discusses how waste problems of cities can be transformed to become part of new, more sustainable solutions. Two cases are explored: Aalborg in Denmark and Malmö in Sweden. It is shown that the cities have the potential to significantly contribute to a more sustainable development through increased material recycling and energy recovery. Waste prevention may increase this potential. For example, instead of constituting 3% of the total greenhouse gas emission problem, it seems possible for modern European cities to contribute to greenhouse gas emission reduction by 15% through up to date technology and integrated waste management systems for material and energy recovery. Going from being part of the problem to providing solutions; however, is not an easy endeavour. It requires political will and leadership, supportive regulatory frameworks, realistic timetables/roadmaps, and a diverse set of stakeholders that can provide the right creative and innovative mix to make it possible.

Integrated flux model for unsteady transport of trace organic chemicals in soils

Simple deterministic models are useful tools for evaluating the relative environmental impact of chemicals. Analytical solutions that assume all soil parameters to be constant in time and depth have been used for screening purposes. In this study, two recently presented numerical models, the moving mean slope method for solving the unsteady water flow equations and the moving concentration slope method for solving the convective dispersion equation, were combined to calculate unsteady one-dimensional transport and volatilization of toxic organic compounds in soils. An expression for the combined gaseous and liquid flux (fluid flux) of chemicals was derived by integrating the fluid flux equation with respect to soil depth. The resulting model for evaluating the relative impact of chemicals at transient state (RIOCATS) is numerically simple, easy to program, and accurate if given criteria for time and depth increments are observed. Typical variations of soil parameters with depth and time, such as soil-water content, organic matter, and zone of microbial activity, resulted in a significant change in the ranking of volatilization of 18 different chemicals in a clay soil compared with a screening based on constant, average parameters. Therefore, the RIOCATS model appears to offer advantages for predicting the relative fate of toxic chemicals in soils.

Universities in Capacity Building in Sustainable Development: Focus on Solid Waste Management and Technology.

This paper analyses some of the higher education and research capacity building experiences gained from 1998—2006 by Danish and Malaysian universities. The focus is on waste management, directly relating to both the environmental and socio-economic dimensions of sustainable development. Primary benefits, available as an educational legacy to universities, were obtained in terms of new and enhanced study curricula established on Problem-oriented Project-based Learning (POPBL) pedagogy, which strengthened academic environmental programmes at Malaysian and Danish universities. It involved more direct and mutually beneficial cooperation between academia and businesses in both countries. This kind of university reach-out is considered vital to development in all countries actively striving for global and sustainable development. Supplementary benefits were accrued for those involved directly in activities such as the 4 months of field studies, workshops, field courses and joint research projects. For students and academics, the gains have been new international dimensions in university curricula, enhanced career development and research collaboration based on real-world cases. It is suggested that the area of solid waste management offers opportunities for much needed capacity building in higher education and research, contributing to sustainable waste management on a global scale. Universities should be more actively involved in such educational, research and innovation programmes to make the necessary progress. ISWA can support capacity building activities by utilizing its resources — providing a lively platform for debate, securing dissemination of new knowledge, and furthering international networking beyond that which universities already do by themselves. A special challenge to ISWA may be to improve national and international professional networks between academia and business, thereby making education, research and innovation the key driving mechanisms in sustainable development in solid waste management.

Global recycling - waste trafficking in disguise?

Global recycling seems to be a growing market. We are witnessing an increasing share of waste from the rich countries being exported to poorer countries. Is this due to a better utilization of natural resources, or is it due to a lower cost of treatment or disposal of waste in the poor countries? In most cases, the latter is the answer! We have all seen pictures of child labour or others who, under poor working conditions, sort hazardous waste, demolish ships on the shore or in other ways treat waste under occupational health conditions that we would not accept in our own countries. We have also seen containers with electronic products on the way to ‘global recycling’ being stopped for sample control in transfer harbours. Inspections often reveal that the containers are filled with obsolete electronic products on their way to cheap disposal in poor countries rather than on their way to recycling. The situation in Denmark is that on almost every occasion when random inspections have been carried out in harbours, containers with contents classified as used equipment or secondary raw material are in reality full of waste, with some of it even hazardous. The extent of this kind of export has increased since the introduction of ‘producer’s responsibility’. In the past there was a high degree of sorting and pretreatment of electronic waste in the countries where the waste was produced. Today, waste is often collected nationally and exported without any pre-treatment. What happens to the waste that is classified as hazardous waste – is it processed to new raw material or dumped on shore as happened in the Ivory Coast? Will it ever be treated at facilities that are approved for hazardous waste? What happens to metal and plastic components – are they reused as new raw material? Does plastic from Europe really end up at facilities that reuse the plastic or would incineration with energy recovery in the home country be a better solution for the global environment? We are concerned that in most cases the waste ends up at facilities that do not satisfy the strict requirements that apply in the country where the waste was produced. On closer inspection it appears that a great deal of waste designated for recycling is in fact waste that ought to be treated at special treatment facilities under strict environmental control. Is it really the right solution to transport waste to the other end of the world, destined for recycling but often ending up in uncontrolled land-fills and with labour not protected by occupational health regulations? It is initially named global recycling, but in reality it is waste trafficking; that is, illegal waste transportation over borders. Should we therefore forbid global recycling and instead demand that waste be treated where it is produced? This would mean that the EU would have to treat own waste within the borders of the EU, the USA within the borders of the USA and so on. If you really think about it – why not? In practice, international trade agreements, which also cover waste for recycling, would not facilitate such prohibition. So what can be done to prevent waste trafficking in whichever disguise it takes place? The most serious problem is between the industrialized and the developing world; however, waste trafficking is a real problem whenever countries or continents have different regulations on waste management or are more or less strict in controlling their implementation. Different definitions, for example, of hazardous wastes, add to the complexity of this problem. Therefore, the focus should probably be shifted to stricter enforcement of existing regulation and good practice in sustainable or at least environmentally acceptable waste management in all countries. Given that, some overarching principles for avoiding waste trafficking are contained in the following suggestions.

Where science meets practice

What happens when science meets practice? As always the human factor is important, but positive symbiosis is definitely an option. Actually, when it happens there are many examples of inspirational new developments in terms of essential problems being identified and solutions devised. In the 1930s, cadmium was identified by medical science as an element that is toxic to humans if they are exposed to it through inhalation of air or intake by food or water. Its effects can be crippling with high doses or cause fatal kidney malfunction with lower doses over extended periods of time. Polluted water from cadmium mining and the irrigation of rice fields created the first crippled victims (itai-itai disease) in Japan in the early 1930s. Subsequently the use of cadmium in industrial production revealed occupational health problems as a result of direct inhalation by soldering workers. Environmental problems involving cadmium, such as food and animal feed contamination, were found to link directly to emissions from waste incinerators or the use of chemical fertilizers in agriculture. Studies between the 1950s and the 1970s which investigated cadmium pathways in the human body and in air, soil, water and plants, showed the way to limit cadmium pollution and use to an acceptable level. Furthermore, regulation made it possible to implement control programmes in practice. In very simple terms, medical and natural science met with bad cadmium practice in industry, waste management and agriculture, and that encounter created innovative thinking and a healthier practice for the management of cadmium in society and the environment. Lead has been known for centuries as a toxic element to humans, for example by causing brain damage if the intake (e.g. when drinking wine from leaded cups or tins) exceeds certain limits (detected centuries after the first incidents in the Roman Empire). Lead was used as an additive in petrol to improve engine performance and it is clear that lead had been spread efficiently over land due to atmospheric transportation and fall out (wet and dry). Other sources of lead emissions to the atmosphere were combustion plants burning, for example, household and industrial waste materials. Even in remote areas the atmospheric pollution fall out was significant. In the 1970s, when it was scientifically documented that the major lead pollution of food and feed came from atmospheric precipitation (and not from plant root uptake) it became clear that the practice of using leaded fuel needed to be abandoned. At the same time other sources of atmospheric lead emissions, for example, from incinerators, had to be limited as well. Again, scientists met with practitioners and innovative solutions to serious problems were developed. Phosphorus is an essential element for all life on planet Earth. It can also be a problematic pollutant if over-fertilizing of soils occurs or effluents are discharged into water-bodies that become eutrophic with excessive algae blooms, discolouring of the water and depletion of oxygen. Natural science can document the actual flows of phosphorus in natural systems and identify where imbalances are present or likely to occur. This knowledge can then be translated into new and more adequate engineering and practice, for example, in terms of sustainable fertilization in agriculture; new detergent products from industry; or new waste and wastewater treatment designs that prevent phosphorus pollution of land and water and at the same time reduce consumption of a limited natural phosphorus resource. Some of the contributions to these positive developments can be found in articles published in Waste Management & Research since 1983. In 1986 a special issue was published on incinerator emissions of particulates and heavy metals and in 1987 trace organics were the topic matter. Not that these articles solved the problems, but they definitely expressed the joint concerns of professionals in practice and science. Advanced sampling and chemical analysis methodologies produced research results that helped industry achieve better in-plant process controls and reduced the emission of pollutants so that today’s incineration technology is part of sustainable waste management. Similar experiences are available from later Waste Management & Research special issues, on topics such as health care waste, waste prevention, and waste and climate change. In general, articles in Waste Management & Research have a scientific touch that increases understanding of the problem in question and often provides concrete leads toward preventive or remedial action. It is worth mentioning that both natural and social sciences contribute, as do humanities when dealing with, for example, social justice and behavioural issues. But above all, the coupling of science and experience is the mix that produces the most interesting articles and thereby advances in sustainable development of resources and waste management on a global scale. The International Solid Waste Association (ISWA) decided to publish Waste Management & Research in 1982 and some of the professionals and scientists of the then Scientific and Technical Committee invested much time in getting a good start by pushing colleagues to publish work in progress as well as acting as authors themselves. The initiation of working groups added to this science–practice symbiosis and helped ISWA organize exciting specialized conferences, and Waste Management & Research to publish the results of research necessary to make progress on documented (not postulated) evidence. After some 30 years of Where science meets practice 455602WMR0010.1177/0734242X12455602Waste Management & ResearchEditorial 2012