Behavior of PAHs from sewage sludge incinerators in Korea

Although production of sewage sludge increases every year, its proper treatment has only been recently raised as a new issue, as current landfill and ocean dumping arrangements are expected to become increasingly difficult to manage in the future. The Korean Ministry of Environment plans to diversify its processing facilities and expand its processing systems by 2011, with the purpose of processing all sludge produced in Korea. According to this plan, incineration (including incineration of municipal wastes) will process 30% of the entire sewage sludge throughout the country in 2011. This study reviews the characteristics of PAH, which is one of the organic substances found in sewage sludge during the incinerating process. The total amount of PAH produced from sewage sludge incineration was found to be 6.103 mg/kg on average, and investigation performed on 16 PAHs of inlets and outlets of the air control devices at five full-scale incineration facilities showed that concentrations of the PAHs on the inlet and on the outlet ranged from 3.926 to 925.748 microg/m(3) and from 1.153 to 189.449 microg/m(3), respectively. In the case of the incineration facility fed with municipal waste (95%) and sewage sludge (5%), the total of the PAH emissions concentration was higher than that found at the incineration facilities used exclusively to treat sewage. The combustion of waste vinyl and plastics contained in municipal waste fed into the facility might contribute to the high levels of PAHs in the stack gas. However more investigation is needed on the production mechanism of PAHs at different operating conditions of the incineration facilities, such as the types of waste, and other relevant factors.     

Efficiency analysis of reduction and stabilization of biodegradable waste using an aerobic stabilization system

The reduction and stabilization of biodegradable waste were studied using three operational stages in an aerobic stabilization system. The system used for mechanical/biological treatment utilized two-shaft screws in multiple box reactors. In the first operational stage, 50-kg batches of biodegradable waste were charged in each of the three reactors, with peat moss used as a bulking agent. Analysis revealed that peat moss can be used at this initial stage, based on the observed increase in temperature and carbon dioxide levels. The second stage of operation involved adding 100 kg/day of biodegradable waste to the first reactor. It was confirmed that a continuous reaction is possible by the addition of more waste. In the third stage of operation, 20 kg/day of the 100 kg/day of biodegradable waste feed was replaced with material fed back from the third reactor. At this stage, final product was also removed from the third reactor. The temperature was not controlled, and up to 8%–9% carbon dioxide was formed, enabling normal activation of decomposition. This three-stage operational test confirmed the expected decomposition of organic matter and biodegradable materials. The rate of mass reduction calculated for the final product compared with the input amount was 94.3%, which confirmed that this system would be a useful means for the reduction and stabilization of biodegradable waste. This study also measured the water content of the material in the reactors: the water content decreased as the reaction progressed. This indicated that the activation of microorganisms did not occur sufficiently in the second and third reactors. Future studies of methods to control the internal water content of each reactor should improve the decomposition efficiency.     

A comparative review for understanding elite interest and climate change policy in China

China’s climate change policy has rapidly evolved from one of neglect to necessity with sinologists drawing on a wide range of theories in trying to explain this shift. The rising influence of citizens' movements coupled with international pressure are often cited as significant drivers behind the government’s evolving climate change strategy. But can the influence of public pressure and international lobbying offer a complete explanation for the government’s dramatic policy changes? In this article, we advance theoretical pluralism where three contending schools of thought are made complementary to offer distinct explanations for understanding the mechanisms and rationale for Beijing’s elite-driven climate change policy. In brief, by bridging three separate theoretical streams including rational choice theory, authoritarian environmentalism and advocacy coalition framework, we show that the interests of elites in China’s upper political echelon are the driving force behind the country’s climate change policy.     

Effect of pH on surface characteristics of switchgrass-derived biochars produced by fast pyrolysis

Surface properties of switchgrass-derived biochars produced at fast pyrolysis temperatures of 450, 600 and 800 °C were characterized at different solution pHs in order to determine the structural and chemical changes of artificially-weathered biochars when incorporated into soil. As biochars were acidified from pH 7 to 3, crystalline minerals dissolved slowly releasing nutrients; however, residual minerals were still detected in biochars produced at higher pyrolysis temperatures after pH treatment. Moreover, the amount of exchangeable bases and other inorganic compounds released from the biochars increased when pH decreased. As minerals dissolved from the biochars, total surface area and pore volume were found to increase. Surface functional groups and water vapor adsorption capacity at 0.8 P/P_o also increased, whereas the potential CEC of biochars decreased due to the replacement of exchangeable sites by hydrogen ion. Therefore, during the aging process, it is predicted that soil-incorporated biochars will slowly release nutrients with changes in surface functionality and porosity, which are expected to enhance water holding capacity of soil and provide a beneficial habitat for microbial colonization.     

Enrichment of PCDDs/PCDFs in the cooling system of municipal solid waste incineration plants

This study measured the levels of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDDs/PCDFs), destroyed or formed in combustors and re-synthesized in cooling systems. For the proper control of PCDDs/PCDFs in municipal solid waste (MSW) incinerators, three grate-type MSW incinerators were selected, two of which had boilers, and one of which had a water spray tower (WST) as a cooling system. At the combustor outlets, dusts were in the range of 1640-4270 mg/Sm3 and PCDDs/PCDFs were in the range of 0.103-2.619 ng-TEQ/Sm3, showing the different values according to the grate structure of combustor and the flow direction of flue gas. After the flue gases passed through the cooling system, PCDDs/PCDFs at the waste heat boiler (WHB) outlets were enriched to levels that were 10.8-13.6 times higher than those at the furnace outlets, but PCDDs/PCDFs at the WST outlet was reduced to 5% of the level found at the furnace outlet. The emission patterns, such as the ratio of PCDFs to PCDDs, the ratio of gaseous-phase to particulate-phase PCDDs/PCDFs, and the compositional percentiles of each 2,3,7,8-substituted congener varied according to the types of air pollution control devices (APCDs). Reducing re-synthesis in the cooling system rather than enhancing the removal efficiencies of the APCDs seems to be more effective for lowering the levels of PCDDs/PCDFs in MSW incineration plants.     

Modeling binding equilibrium in a competitive estrogen receptor binding assay

Although the free concentration is more significant in the environmental chemistry and toxicology of receptor-mediated toxicants, few studies have been conducted to use it as a dose-metric. The relative binding affinity of three model endocrine disrupting compounds, diethylstilbestrol (DES), ethynylestradiol (EE2), and bisphenol A (BPA), were evaluated using a competitive ELISA with human estrogen receptor alpha. After measuring the available receptors and the dissociation constant for 17beta-estradiol, binding inhibition curves using the free concentration as the dose-metric were obtained by assuming species equilibrium in the ELISA system and compared with apparent inhibition curves generated using the nominal concentration as the dose-metric. Because ligand binding to estrogen receptors may reduce its free concentration in the assay system, the differences between the two curves for free and nominal concentrations are more significant for more strongly binding ligands. The ratio of a compound's nominal concentration causing 50% inhibition (IC50) to the IC50 of DES, the positive control, was strongly affected by specific assay conditions, while that estimated by modeling free concentration is independent of receptor concentration, indicating that the free concentration is a better dose-metric for a competitive binding assay.     

The Effects of Local Cooling on Thermophysiological Response in Participants Wearing Dust-Free Garments

This study was designed to find the effects of two kinds of dust-free garments with (A) and without (B) frozen gel strip (FGS), and half-naked clothing (brassiere and shorts; C) on thermophysiological parameters and on temperature and humidity within clothing. The heart rate, rectal, and skin temperatures as well as sweat rate and clothing microclimate were measured during 140 min in 9 healthy females. Inquiries were also made into the subjective rating of thermal, humidity, and comfort sensations. The main findings in our experiments are as follows: (a) Physiological parameters such as rectal and skin temperatures (chest and forehead), heart rate, and sweat rate were clearly lowest in garb C, intermediate in garb A, and highest in garb B throughout the experiment; (b) Temperature and humidity within clothing were lower in garb A than in garb B; (c) More than half of the 9 participants decreased thermal sensation by wearing garb A. These results suggest that the usage of FGS could improve the heat load in lightly working participants wearing dust-free garments.     

Performance of a full-scale biofilm system retrofitted with an upflow multilayer bioreactor as a preanoxic reactor for advanced wastewater treatment

To enhance nitrogen removal in an existing microbial contact oxidation (MCO) system with a treatment capacity of 900 m3/d, an upflow multilayer bioreactor (UMBR) was chosen as a preanoxic reactor for the removal of organic matter and nitrate. The removal performance of the retrofitted plant was evaluated during the startup phase at a low temperature in winter. The high removal (>80%) of organic matter and suspended solids in the UMBR provided stable nitrification conditions in the MCO system, as a result of the substantial reduction in organic matter and solids loaded onto the MCO system. This treatment system showed a stable nitrogen removal efficiency of 75.3%, even in the low temperature range 7 to 10 degrees C. Phosphorus was completely removed by chemical precipitation. Production rates of excess sludge, as a function of the loads of influent flowrate and biological oxygen demand (BOD), were 0.022 kg dry solid/m3 wastewater and 0.132 kg dry solid/kg BOD.     

Fuel cell system with sodium borohydride hydrogen generator for small unmanned aerial vehicles

A 100 W proton exchange membrane fuel cell (PEMFC) system with a sodium borohydride (NaBH₄) hydrogen generator was investigated for small unmanned aerial vehicles (UAVs). The performance of a cobalt–phosphorous/nickel foam catalyst was evaluated to determine the change in catalytic activity under real operating conditions. The response time increased owing to oxidation of the metals and accumulation of sodium; however, the catalyst remained active at high reaction temperatures. A NaBH₄ hydrogen generator with the catalyst was developed for a 100 W PEMFC system. The hydrogen generation rate was stable for 3 h, and the conversion efficiency was 97.8%. Finally, a 100 W PEMFC system with the NaBH₄ hydrogen generator was investigated for small UAVs. The maximum power and energy density of the PEMFC system were 95.96 W and 185.2 Wh/kg, respectively.     

In vivo evaluation and comparison of developmental toxicity and teratogenicity of perfluoroalkyl compounds using Xenopus embryos

Perfluoroalkyl compounds (PFCs) are environmental toxicants that persistently accumulate in human blood. Their widespread detection and accumulation in the environment raise concerns about whether these chemicals might be developmental toxicants and teratogens in ecosystem. We evaluated and compared the toxicity of PFCs of containing various numbers of carbon atoms (C8–11 carbons) on vertebrate embryogenesis. We assessed the developmental toxicity and teratogenicity of various PFCs. The toxic effects on Xenopus embryos were evaluated using different methods. We measured teratogenic indices (TIs), and investigated the mechanisms underlying developmental toxicity and teratogenicity by measuring the expression of organ-specific biomarkers such as xPTB (liver), Nkx2.5 (heart), and Cyl18 (intestine). All PFCs that we tested were found to be developmental toxicants and teratogens. Their toxic effects were strengthened with increasing length of the fluorinated carbon chain. Furthermore, we produced evidence showing that perfluorodecanoic acid (PFDA) and perfluoroundecanoic acid (PFuDA) are more potent developmental toxicants and teratogens in an animal model compared to the other PFCs we evaluated [perfluorooctanoic acid (PFOA) and perfluorononanoic acid (PFNA)]. In particular, severe defects resulting from PFDA and PFuDA exposure were observed in the liver and heart, respectively, using whole mount in situ hybridization, real-time PCR, pathologic analysis of the heart, and dissection of the liver. Our studies suggest that most PFCs are developmental toxicants and teratogens, however, compounds that have higher numbers of carbons (i.e., PFDA and PFuDA) exert more potent effects.