• Energy Research

The paper presents the MEFLO ranking method and the Simple Integrated System Management (SISMan) concept for assessing the feasibility of integrated energy and Waste Management System (WMS) alternatives. The MEFLO method is based on dividing the decision-making process into five modules, including mass, energy and financial flows, legislative criteria (e.g., environmental restrictions and target values) and other decision support criteria, such as the local political guidelines. The utilisation of the MEFLO method is presented by comparing five system alternatives, including energy recovery from household waste. The calculations needed in the MEFLO assessment were performed with the SISMan spreadsheet calculation model developed at the Lappeenranta University of Technology. The MEFLO method and the SISMan concept contribute to the design and assessment of different integrated management systems. Any of the appropriate available tools can be used in the model forming and assessment processes, according to the proposed methods.

Sustainable biomass production based on efficient carbon and nutrient recycling is crucial in materially efficient, sustainable biobased production. A circular bioeconomy model of the replacement of mineral fertilizers with recycled nutrients from pulp and paper mill sludge is tested here within a hypothetical case from Indonesia, Southeast Asia. First, the financial feasibility of the use of recycled nutrients originating from pulp and paper processes was analyzed in fast-growing pulpwood production. Secondly, the comprehensive social and environmental benefits of the practice were analyzed through qualitative sustainability analysis. The availability of the basic material of all required parameters referring to Indonesia limited the analysis period to be from 1996 to 2013. The establishment costs of a pulpwood plantation were adjusted according to a reference study, while the other data were compiled from various sources. The financial profitability of the circular model was analysed by using two indicators, net present value (NPV) and internal rate on return (IRR). The application of sludge-based recycled nutrients slightly increased the establishment costs in some circumstances but had no direct impact on the financial profitability, as the financial profitability was not sensitive to the establishment costs. The results showed that the financial profitability of biomass production is not sensitive to the plantation establishment and management costs. The profitability depends on the mean annual increment and product price. The qualitative analysis showed a holistic value of the practice that goes beyond the direct benefits. The use of sludge-based recycled nutrients in the production of pulpwood closed the economic loop, which is illustrative of the circular bioeconomy within the integrated pulp and paper sector including the raw material source, forest plantation.

This study focused on identifying various system boundaries and evaluating methods of estimating energy performance of biogas production. First, the output-input ratio method used for evaluating energy performance from the system boundaries was reviewed. Secondly, ways to assess the efficiency of biogas use and parasitic energy demand were investigated. Thirdly, an approach for comparing biogas production to other energy production methods was evaluated. Data from an existing biogas plant, located in Finland, was used for the evaluation of the methods. The results indicate that calculating and comparing the output-input ratios (Rpr1, Rpr2, Rut, Rpl and Rsy) can be used in evaluating the performance of biogas production system. In addition, the parasitic energy demand calculations (w) and the efficiency of utilizing produced biogas (η) provide detailed information on energy performance of the biogas plant. Furthermore, Rf and energy output in relation to total solid mass of feedstock (FO/TS) are useful in comparing biogas production with other energy recovery technologies. As a conclusion it is essential for the comparability of biogas plants that their energy performance would be calculated in a more consistent manner in the future.

The aim of the study was to explore the currently unexploited potential of agrifood waste and by-product biomasses for energy recovery and nutrient recycling, to mitigate climate change and eutrophication. The technical potential was assessed in two different case regions in Finland using two contrasting processing technologies, one oriented to recycle carbon and the other one to maximise replacement of fossil energy. The reduction in nutrient surplus through efficient recycling of biomass and consequent decline in fertiliser use was calculated. The reduction in GHG emissions was estimated based on the replacement of fossil energy and the diminished fertiliser manufacture. It was established that the full potential of use of the biomass to reduce GHG emissions can only be exploited in biorefineries that both produce energy and efficiently recycle nutrients. Such biorefineries have the potential to significantly mitigate climate change and prevent eutrophication. The potential reduction in GHG emissions corresponded to a third of agricultural emissions, and the reduction in fertiliser manufacture contributed with an additional fifth of that. The energy recovery corresponded to 5–10% of the fossil energy used in the regions, and the reduction in energy use for manufacture of fertilisers represented an additional 14–20% in comparison with that. The potential for nutrient recycling corresponded to 99–120% of P and 45–72% of N in the yields harvested in the regions. The choice of technology had a more pronounced impact on energy recovery, GHG emissions and C budget than on nutrient recycling.

The COVID-19 pandemic has imposed a global emergency and also has raised issues with waste management practices. This study emphasized the challenges of increased waste disposal during the COVID-19 crisis and its response practices. Data obtained from the scientific research papers, publications from the governments and multilateral organizations, and media reports were used to quantify the effect of the pandemic towards waste generation. A huge increase in the amount of used personal protective equipments (facemasks, gloves, and other protective stuffs) and wide distribution of infectious wastes from hospitals, health care facilities, and quarantined households was found. The amount of food and plastic waste also increased during the pandemic. These factors caused waste treatment facilities to be overwhelmed, forcing emergency treatment and disposals (e.g., co-disposal in a municipal solid waste incinerator, cement kilns, industrial furnaces, and deep burial) to ramp up processing capacity. This paper discussed the ways the operation of those facilities must be improved to cope with the challenge of handling medical waste, as well as working around the restrictions imposed due to COVID-19. The study also highlights the need for short, mid, and longer-term responses towards waste management during the pandemic. Furthermore, the practices discussed in this paper may provide an option for alternative approaches and development of sustainable strategies for mitigating similar pandemics in the future.

Recovering and recycling nitrogen available in waste streams would reduce the demand for conventional fossil-based fertilizers and contribute toward food security. Based on life cycle assessment (LCA), this study aimed to evaluate the environmental performance of nitrogen recovery for fertilizer purposes from sewage sludge treatment in a municipal wastewater treatment plant (WWTP). Utilizing either air stripping or pyrolysis-derived biochar adsorbent, nitrogen was recovered from ammonium-rich reject streams generated during mechanical dewatering and thermal drying of anaerobically digested sewage sludge. A wide range of results was obtained between different scenarios and different impact categories. Biochar-based nitrogen recovery showed the lowest global warming potential with net negative GHG (greenhouse gas) emissions of −22.5 kt CO2,eq/FU (functional unit). Ammonia capture through air stripping caused a total GHG emission of 2 kt CO2,eq/FU; while in the base case scenario without nitrogen recovery, a slightly lower GHG emission of 0.2 kt CO2,eq/FU was obtained. This study contributes an analysis promoting the multifunctional nature of wastewater systems with integrated resource recovery for potential environmental and health benefits.

The speed of the propagation of the ignition front downwards against the air flow in a fixed bed of burning wooden particles has been studied. The ignition speed reaches a steady state soon after ignition at the surface, if the inlet air temperature is the same as the initial temperature of the fixed bed. Modeling of the quasi-steady-state speed of propagation of the ignition front is considered. The effects of the flow rate of air, moisture, particle size, density, and wood species on the velocity of the ignition front and on the maximum temperature in the bed are studied experimentally and interpreted by modeling. A maximum speed of propagation was observed with a specific air rate. Correlations for estimating the velocity of the ignition front and maximum temperature in the bed are presented.

The European Union is currently in the process of transformation toward a circular economy model in which different areas of activity should be integrated for more efficient management of raw materials and waste. The wastewater sector has a great potential in this regard and therefore is an important element of the transformation process to the circular economy model. The targets of the circular economy policy framework such as resource recovery are tightly connected with the wastewater treatment processes and sewage sludge management. With this in view, the present study aims to review existing indicators on resource recovery that can enable efficient monitoring of the sustainable and circular solutions implemented in the wastewater sector. Within the reviewed indicators, most of them were focused on technological aspects of resource recovery processes such as nutrient removal efficiency, sewage sludge processing methods and environmental aspects as the pollutant share in the sewage sludge or its ashes. Moreover, other wide-scope indicators such as the wastewater service coverage or the production of bio-based fertilizers and hydrochar within the wastewater sector were analyzed. The results were used for the development of recommendations for improving the resources recovery monitoring framework in the wastewater sector and a proposal of a circularity indicator for a wastewater treatment plant highlighting new challenges for further researches and wastewater professionals.