Path analysis of factors influencing household solid waste generation: a case study of Xiamen Island,China

Comprehensive study of the factors influencing household solid waste (HSW) generation is crucial and fundamental for exploring the generation mechanism and forecasting future dynamics of HSW. A case study of Xiamen Island, China was employed to reveal the direct and indirect effects of demographic/socioeconomic factors on solid waste generation at the urban household scale. Based on a face-to-face questionnaire and two-stage survey of solid waste generation, a path analysis model was built. Results showed that the proposed path model exhibited good fit indices. Family size and dinning-at-home rate (DR), whose coefficients were ?0.40 and 0.43, respectively, were the two major factors influencing HSW directly. Moreover, family size, education level, employment rate and age structure played different degrees of indirect effects on HSW generation through respective paths, which should not be ignored. In terms of total effects, coefficients of family size, DR and employment rate were ?0.46, 0.43 and ?0.37, respectively, which were three most dominant factors influencing HSW generation. As for waste composition, organic waste was the most representative of HSW dynamics, and was the most sensitive to impact by the factors studied. Quantitative results of this study have important policy implications for sustainable municipal solid waste management.     

Recycling of combined coal-biomass ash from electric power plant waste as a cementitious material: characteristics and improvement

Combined coal-biomass ash has an enormous impact on environmental quality near electric power plants. This paper describes an alternative to disposal in which the ash is used to produce cementitious materials. Ash was obtained from combustion of coal and biomass containing four mass ratios of anthracite, bitumen, rice husks, and eucalyptus bark. The cement-forming properties were systematically characterized including compressive strength development, durability, and expansion in water. The ash samples were ground to increase the specific surface area, and then used to partially replace ASTM Type I Portland cement in mixtures containing 15, 30, or 45 % ash by mass. The water-binder material's (Portland cement with or without combined coal-biomass ash) ratios (w/c) were held constant at 45, 55, or 65 % by mass. Types A, B, and D ash behaved similarly, while the properties of type C ash were slightly different. Increasing the ash fraction in Portland cement mixtures increased the water requirement and resulted in lower compressive strength. Thorough mechanical grinding reduced the porosity and significantly enhanced the material properties.     

Recycling of cathode ray tube panel glasses as aggregates of concrete blocks and clay bricks

While the cathode ray tube (CRT) funnel containing lead could be transported to a smelting facility to recover lead, which could be an available option in domestic, a proper technology to recycle a CRT panel must be developed. Thus, it was suggested that CRT panel glass be used as aggregates of concrete blocks and clay bricks. Samples of blocks and bricks were fabricated with CRT powders and tested to measure their strength and absorption rate to determine their qualities, and environmental soundness was determined by measuring the leaching rate of hazardous metals. For concrete blocks, CRT panel glass powders incorporated as aggregates up to 40 % replacing stone powder was proposed as the proper condition for manufacturing blocks. Around 2 % of CRT panel incorporated into clay brick to substitute Kaoline was suggested to fabricate the best quality of clay brick. Results of leaching test met the criteria with much less concentration of hazardous metals, even lead compound containing in the CRT funnel. To conclude, the use of CRT panel powder after crushing it to the proper size as an aggregate of concrete blocks or clay bricks could be one of the appropriate alternatives to recycle for CRT glass waste being generated drastically in a short term.     

The application and evaluation research of coffee residue ash into mortar

Coffee residue is usually regarded as a kind of agriculture waste; as its quantity increases the treatment of coffee residue will become an environmental problem. This research is innovative in that it derives the possibility of recycle application using coffee residue ash for cement replacement. In this research, coffee residue is burned in an electronic oven to three kinds of coffee residue ash at 500, 600 and 700 °C, and then appropriate apparatus is used to check the chemical and physical properties of these three types of coffee residue ash. After a general comparison, this study selected 500 and 600 °C coffee residue ashes with 2, 3, 5, 10 and 15 % cement replacements to make 5 cm³ cube mortar specimen to test different curing ages’ compressive strength. Through measurement and experiment, this research found that the compressive strength decreased by adding 500 or 600 °C coffee residue ash into the mortar. By considering waste reduction and practice application, this research derives that using the 600 °C coffee residue ash with 10 % replacement is better than others application, such using result also can get valuable efficiencies of financial and CO₂ reduction.     

Heavy metal mobility and potential availability in animal manure: using a sequential extraction procedure

In this study, dairy cow manure, goat manure, and chicken manure were collected from three farms and analyzed to find out the concentration of Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn. The concentration and potential of mobility and availability of heavy metals were studied in the animal manure samples. BCR Sequential extraction procedure was used to determine the binding forms of the metals. In this study, pseudo total concentrations of Mn and Zn were found out to be predominant in all the types of animal manure samples. According to the results, it was traced that Cr, Cu, and Ni were observed to be at the second highest level while Cd, Co, and Pb were seen at the lowest level in all the manure samples. When extractable amounts of heavy metals are taken into consideration, it is seen that the amount of the mobile fractions of heavy metals except for Cr and Ni are higher in comparison with that of immobile fraction in all the animal manure samples. It was also viewed that Mn, Cd, and Zn are more available in dairy cow manure and chicken manure whereas Cd, Co, and Mn are more available in goat manure.     

Rare earth element recovery potentials from end-of-life hybrid electric vehicle components in 2010–2030

Increasing attention is currently given to the management of end-of-life (EoL) hybrid electric vehicles (HEVs), because approximately two decades have passed since they were first introduced to the market. A HEV would be one of the largest consumers of rare earth elements (REEs), and hence represents the greatest potential for REE recovery in the future. The purpose of this study is to clarify the present and future recovery potential of REEs that are disposed of as EoL HEVs. This study first estimated the numbers of EoL HEVs during fiscal years (FYs) 2010–2030, and then clarified the potential for recovery of REEs from two HEV-specific components—the hybrid transmission and NiMH battery unit. The results suggest that 0.51–0.65 million HEVs will reach the EoL stage in FY2030, compared with only 11,000 HEVs in FY2010. As of FY2030, REE recovery potentials will increase to 220 tons and 2900 tons for EoL hybrid transmission and NiMH battery units, respectively. A total of 49,000 tons of REEs will be contained within HEV-specific components of HEVs still in use. Moreover, the potential for recovery of REEs from EoL hybrid transmissions and NiMH battery units is estimated to equal 35.4 and 92.1 % of respective demand.     

Carbon dioxide utilization with carbonation using industrial waste-desulfurization gypsum and waste concrete

In this study, we propose a process making calcium carbonate and calcium sulfate and recovering absorbent using ammonia absorbent, carbon dioxide, and industrial waste. The main objective of this study is to confirm the possibility of carbon capture and utilization based on waste materials. We assumed desulfurization gypsum and construction waste (ready mixed concrete washing water, waste concrete, etc.) are CaSO₄, Ca(OH)₂, respectively. And concentration of simulated carbon dioxide gas was 15 vol% similar to flue gas. Calcium carbonate was produced by combination reaction between ionic CO₂ in absorbent and metal ion in the solid waste. Experiments were conducted at normal temperature and pressure. Furthermore, the generated products were characterized by X-ray diffraction, and scanning electron microscope.     

A dynamic simulation of methane fermentation process receiving heterogeneous food wastes and modelling acidic failure

Microbial response on volatile fatty acids (VFAs) is a key for methane fermentation processes since accumulation of VFAs often causes an acidic failure, especially treating such organics as food wastes composed of mostly readily biodegradable materials. To evaluate the impact of VFA accumulation, a lab-scale continuous experiment was performed for 110 days with sequential feeding of heterogeneous food wastes. When the volumetric loading rate was increased from 6 to 8 kg-COD/m³/day, a sudden decrease of methane production was observed with an accumulation of acetate and propionate in the fermenter. After discontinuation of feeding for 10 days, the digestate in the fermenter was centrifuged and washed with tap water to reduce the VFAs to be acceptable concentration below 1000 mg-COD/L. Nevertheless, no recovery of methane production was observed and VFA concentrations consistently increased. To model the event, a modification of ADM1 was made assuming the methanogens in the fermenter were irreversibly inactivated under very high VFA. Also considering the different nature of the fed food wastes over 11 samples, decomposition kinetics of individual food wastes were manipulated. The modified ADM1 with methanogenic activity decay reasonably reproduced the responses for soluble material concentrations and methane gas production rate over the experimental period.     

Potential methane yield of food waste/food waste leachate from the biogasification facilities in South Korea

This study was to find out potential of methane yield on food waste and food waste leachate as biomass in Korea. The seven biogasification facilities were selected for comparison of theoretical methane yield and actual methane yield. The theoretical methane yield was calculated based on organic constituents (carbohydrate, protein, fat) and based on element analysis. The actual methane yield was investigated based on volatile solids and CODcr. Theoretical methane yields by organic constituents were 0.52 Sm³CH₄/kg VS and 0.35 Sm³CH₄/kg CODcr and these by element analysis were 0.53 Sm³CH₄/kg VS and 0.36 Sm³CH₄/kg CODcr. Actual methane yields were 0.36 Sm³CH₄/kg VS_in and 0.26 Sm³CH₄/kg CODcr_in. Considering the average removal efficiency of organic materials of seven FWL biogasification facilities, actual methane yields were 0.48 Sm³CH₄/kg VS_rem and 0.33 Sm³CH₄/kg CODcr_rem. Methane yield by organic constituents is very similar to that by element analysis and actual methane yields of volatile solids and CODcr were similar to theoretical value. The actual methane yield in this study showed approximated boundary values with previous other references which conducted in lab-scale or biochemical methane potential (BMP) tests. In conclusion, Korean food waste and food waste leachate have sufficient potential of methane yield in the ongoing biogasification facilities.     

Study of nitrogen oxide absorption in the calcium sulfite slurry

Experiments were conducted using a bubbling reactor to investigate nitrogen oxide absorption in the calcium sulfite slurry. The effects of CaSO₃ concentration, NO₂/NO mole ratio and O₂ concentrations on NO₂ and SO₂ absorption efficiencies were investigated. Five types of additives, including MgSO₄, Na₂SO₄, FeSO₄, MgSO₄/Na₂SO₄ and FeSO₄/Na₂SO₄, had been evaluated for enhancing NO₂ absorption in CaSO₃ slurry. Results showed that CaSO₃ concentration had significant impact on NO₂ and SO₂ absorption efficiencies, and the highest absorption efficiencies of SO₂ and NO₂ could reach about 99.5 and 75.0 %, respectively. Furthermore, the NO₂ absorption was closely related to the NO₂/NO mole ratio, and the existence of NO₂ in flue gas may promote NO absorption. The presence of O₂ in simulated flue gas was disadvantage for NO _x removal because it can oxidize sulfite to sulfate. It was worth pointing out that FeSO₄/Na₂SO₄ was the best additive among those investigated additives, as the NO₂ removal efficiency was significantly increased from 74.8 to 95.0 %. IC and in situ FTIR results suggest that the main products were NO₃ ^? and NO₂ ^? in liquid phase and N₂O, N₂O₅ and HNO₃ in gas phase during the CaSO₃ absorption process.