This study examined how OECD countries treat municipal solid waste (MSW) and how their methods of recovering energy after waste incineration changed as leaders prepared to resource circulation and reduce greenhouse gas emissions. The results showed that Korea, with its per capita MSW of 350 kg and recycling rate of 59%, was the most efficient among the 14 countries studied in regards to waste management. In Korea, the rate of waste reclamation dropped from 71% in 1995 to 15.7% in 2014. However, the rate of waste incineration is expected to increase, allowing the rate of waste reclamation to decrease to less than 1%. In addition, the study showed that the average rate of waste incineration was 49.8% in the OECD-EU countries and Japan, where reclamation rates are relatively low, and this average rate was higher than Korea’s rate of 25.3%. Therefore, Korea needs to identify ways to increase the rate of waste incineration and recover more energy from existing and future incineration plants. Such measures, along with the 3Rs of municipal solid waste and energy recovery, would help Korea become a society of both low carbon and resource circulation.
Recycling standards and methods of steel slag are prescribed in the “Waste Control Act” and the “Act on the Promotion of Saving and Recycling of Resources”. However, the recycling purposes and methods for non-ferrous slag are permitted for lead, zinc, and aluminum slag, etc., and only small amounts are recycled. Most non-ferrous slags are treated by consigned treatment or landfill. In addition, some non-ferrous slag can cause environmental pollution when directly recycled in soils or result in high costs for disposal or storage due to high heavy metal concentrations. In this study, we investigated the characteristics of slag generated during non-ferrous metal processing or recycling, providing recycling purposes and methods including those for useful metal recovery based on the characteristics of slags, cement and cement additives, and alternatives to natural aggregates. Content analysis of non-ferrous slag showed the concentration of metals such as Al and Cu ranging from 1 to 27%, indicating the necessity to recover the secondary metals by properly grinding slags and using economical concentration technologies. Based on the leaching test result of non-ferrous slag, rainfall blocking facilities need to be installed to prevent rainfall from flowing into storage sites for slags so that alternative materials can be safely managed.
High temperature corrosion is a major issue in waste-to-energy (WTE) facilities because it effects running cost and energy utilization efficiency. Corrosion of heating surfaces in WTE boilers is a complex phenomenon. The purpose of this study was to analyze the high temperature corrosion characteristics of WTE boiler tubes and to determine the influences of high temperature corrosion on heat exchange. Heating surface corrosion samples for this research were obtained from a superheater tube in municipal solid refuse fuel-fired power plant. Surface morphology, microstructure and phase composition were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction analysis. The morphology of the heating surface was rough and had porous structures. The chlorine content of the surface was 7.4wt.% and the samples were mainly composed of hematite (Fe2O3) and magnetite (Fe3O4). The thermal conductivity of the corrosion samples was characterized using thermal conductivity measurements and was found to be 2.33 W/mK at 500℃. This result, which is 17 times less than that of boiler tube carbon steel (40.40 W/mK), indicates that corrosion of WTE boiler tubes is closely related to a decrease in boiler heat exchange efficiency.
About 4,800 soil drums were generated in the process of maintenance on KRR site (Korea Research Reactor) in Seoul. Most of the drums are processed by regulatory clearance in 2007-2008 and the remaining 1800 drums are currently stored in KAERI (Korea Atomic Energy Research Institute). To decide a treatment method of radioactive soil for final disposal, the soil is classified according to a particle size. Based on the results of the radioactivity concentration for the classified soil, methods such as regulatory clearance, decommissioning, and solidification were decided. Many papers show that radioactive soil is disposed of using a decontamination agent or other method. But it is difficult to decontaminate radioactive particles from fine soil particles because the adsorptive power of fine soil particles is too strong. This study was focused on finding a particle size distribution of radioactive soil that can be used as an operating range for cement solidification produced by a suitable ratio of radioactive soil for final disposal. Workability, free-standing water, compressive strength, immersion, and leaching tests were carried out to evaluate characteristics of the cement solidification. Cement solidification is the only method for final disposal because radioactive soil particle sizes below 500 μm exceed the regulatory clearance criteria (< 0.1 Bq/g). According to the test results for cement solidification, 0.4 water/cement and 0.5 soil/cement ratios are the most appropriate operating ranges.
Even though removal of fluoride in HF wastewater by crystallization using a fluidized bed reactor (FBR) has been widely studied as an efficient alternative to the chemical precipitation method using traditional stirred tank reactor, serious problems have been encountered for the optimum design of FBR together with the determination of proper operating conditions. One problem is the proper formation of the fluidization state of the seed as a function of seed particle characteristics such as particle size and density. Because dynamics in the reactor are governed by forces such as gravity, drag, and buoyancy as a function of particle size, particle density, relative velocity together with flow characteristics, this study carefully examines the effects of these factors on the formation of fluidization via theoretical analysis and numerical calculation in fluidized bed reactors in the range of practical design and operation condition. The results of this study show the overall trend of the motion of particle behavior in terms of particle size and flow condition.
The effect of mixed oil on the drying characteristics of sewage sludge in oil vacuum evaporation systems was studied. The experimental results showed that the drying rate with cooking oil was faster than that with refined oil due to the difference of thermal conductivity and composition of mixed oil. However, the heating value of all dried sludge was enhanced and the moisture content was below 1% due to penetration of oil into the microbial cells in sludge during the drying procedure. TGA analysis of sludge mixed with the refined oil, which had a higher volatility, showed the slope of the primary falling period was sharply declined. The result of DTA analysis also showed that the first peak was higher than the second peak and corresponded with the phenomena observed in the TGA analysis. In the DTA analysis, the temperature of the primary peak and the secondary peak of dried sludge were comparatively lower than those of raw sludge. Therefore, mixed oil could decrease the self-ignition temperature in an oil-sludge mixing system. In case of waste cooking oil, the TGA and DTA results showed similar results to those of raw sludge, but the DTA results showed that the secondary peaks of dried sludge were narrower and sharper than those of raw sludge. Overall, mixing oil could be a principal factor in controlling the drying efficiency and thermal properties of sludge-derived fuel in oil vacuum evaporation systems.
Due to the increasing sewage sludge generation from wastewater treatment facilities, sewage sludge has been reconsidered as a renewable energy source in various ways. Lipid extraction from sewage sludge is an applicable method for biodiesel production. Higher biodiesel production yields can be achieved through the improvement of lipid recovery efficiency. Although sewage sludge has different features due to its types and steps in treatment plants, lipid content of sewage sludge generally ranges from 10 to 15%. Among solvent extraction methods, the highest lipid recovery efficiencies were observed for chloroform-methanol extraction: 13.6-14.6% for primary sludge, 10.6-12.1% for waste-activated sludge, and 2.9-4.2% for digested sludge. The extraction residue of sludge can be used as biosolid refuse fuel (bio-SRF). After lipid extraction, the residue had decreased volatile matter and carbon content. Consequently, the calorific value of the residue decreased by 3,000 kcal/kg. The level of calorific value can be available to use bio-SRF.
This study investigated the compressive strength characteristics of concrete and mortar containing waste pottery fine powder. To identify the effects of waste pottery fine powder on the compressive strength of concrete and mortar, cement was replaced with waste pottery fine powder at 5, 10 and 15% rates and the variations in compressive strength were evaluated. For high strength concrete, compared with a control mix, 5% replacement resulted in the reduction of 3.4% in compressive strength at 7 days; however, at 28 days, the strength actually increased by 2.5%. For normal strength concrete, compared with a control mix, 5% replacement resulted in the reduction of 20.4% in compressive strength at 7 days, and 14% reduction at 28 days. As for the mortar, at 5% replacement, compared with a control mortar mix, compressive strength of mortar decreased by 3% at 7 days, while an increase of 5.9% was observed at 28 days. Therefore, the optimum replacement rate of cement with waste pottery fine powder appears to be 5%.
The chemical kinetics of steam reforming of polystyrene (PS) and polypropylene (PP) pyrolysis oil were studied using a ruthenium-based catalyst. The experiments were performed in a tubular flow reactor at temperatures of 530-680℃, Weight Hourly Space Velocities (WHSVs) of 0.453-7.916 h-1, and different steam and pyrolysis oil gas-phase concentrations. The activation energy of steam reforming of polypropylene oil and polystyrene oil is 136 and 142 kJ/mol, respectively. The reaction orders of polypropylene and polystyrene oils were 0.42 and 0.37, respectively. Conversions of polypropylene and polystyrene oils were 2.0-50.3 and 1.9-45.3%, respectively. Indeed, a Langmuir-Hinshelwood (LH) mechanism requiring the dissociative adsorption of pyrolysis oil and steam at two different sites on plastics appeared to be the most plausible pathway for the steam reforming reaction.
Solid refuse fuel (SRF), which is made of combustible waste, has to pass the government's rigid standards. The Korean government plans to enhance the ratio of biomass energy to total energy use from 3.17% in 2013 to 4.16% in 2020. In particular, the Korean government aims to raise the ratio of combustible waste converted into SRF from 16% in 2014 to 100% in 2020 by increasing the number of facilities manufacturing and utilizing SRF. We attempt to analyze the external benefits of the expansion using the data obtained from a survey of 1,000 randomly selected households. A choice experiment, an economic technique, is employed here. The attributes considered in the study are ‘improvement of energy security’, ‘reduction of greenhouse gases emissions’, ‘extension of landfill life expectancy’, ‘job creation’, and ‘price’ measured as an additional amount of monthly electricity and heating bills per household. The multinomial logit model, which requires the assumption of the ‘independence of irrelevant alternatives’, is applied. However, the assumption could not be satisfied in our data. Thus, we finally utilized a nested logit model that does not require the assumption. All the parameter estimates, except for ‘improvement of energy security’, in the utility function are statistically significant at the 5% level. The estimation results show that the marginal willingness to pay (MWTP) for one year increase in landfill life expectancy is estimated to be 218.8 won per household per year. MWTP for 100,000 tCO2 decrease in greenhouse gases emission is calculated to be 171.9 won per household per year. MWTP for the creation of a new job is computed to be 10.7 won per household per year.
Raw and secondary waste materials from recycling products have been used to produce cements. A total of 10 cements produced from recycling products were analyzed for chemical composition, such as Na2O, MgO, Al2O3, SiO2, SO3, Cl, K2O, CaO, TiO2, Cr2O3, MnO, Fe2O3, CuO, ZnO, and PbO, using the Korean standard leaching test. The total content of toxic substances, such as Pb, Cd, Cu, As, Hg, and Cr(VI), present in each cement was also measured. The corrosion characteristics of cement leachates were also determined by measuring their pH values using an ion selective electrode and measuring the corrosion rate of a circular steel plate in each leachate. The chemical composition of the cements was found to be 60-67% CaO, 18-23% SiO2, and 5-6% Al2O3. Based on the results of the leaching tests, the samples did not exceed the prescribed regulatory leaching levels. The total content of toxic substances in each cement did not exceed the voluntary agreement criteria of 20 mg/kg. In the case of the corrosion characteristics of the cement leachates, the pH of each leachate was greater than 12.5 and the corrosion rate of a circular steel plate in each leachate did not exceed 6.35 mm/yr. The correlation between pH and the corrosion rate of steel in the solid waste leachates was difficult to determine.
Waste generation has been increased worldwide. Waste is generally recycled, incinerated, or landfilled. Currently, waste is also used as an energy resource because of a lack of energy resources and landfill sites. In South Korea, landfill of waste has been prohibited and the “Switching Promotion Act of the Resource Recycling Society” has been established. Landfill of municipal solid waste in the European Union was 210.18 million tons in 2012. The municipal solid waste landfilled was 22.8%, and the amount of landfill was 416 kg/cap·year. The landfill rates in the Netherlands, Belgium, Denmark, Luxembourg, Austria, Sweden, and Germany have been found to be more than 10% because of different landfill criteria and fees established by these countries.