Negative emissions of carbon dioxide through chemical-looping combustion (CLC) and gasification (CLG) using oxygen carriers based on manganese and iron

Carbon capture and storage (CCS) is an economically attractive strategy for avoiding carbon dioxide (CO₂) emissions from, e.g., power plants to the atmosphere. The combination of CCS and biomass combustion would result in a reduction of atmospheric CO₂, or net negative emissions, as plant growth is a form of sequestration of atmospheric carbon. Carbon capture can be achieved in a variety of ways, one of which is chemical looping. Chemical-looping combustion (CLC) and chemical looping gasification (CLG) are two promising technologies for conversion of biomass to heat and power or syngas/methane with carbon capture. There have been significant advances made with respect to CLC in the last two decades for all types of fuel, with much less research on the gasification technology. CLG offers some interesting opportunities for production of biofuels together with carbon capture and may have several advantages with respect to the bench mark indirect gasification process or dual-bed fluidized bed (DFBG) in this respect. In CLG, an oxygen carrier is used as a bed material instead of sand, which is common in indirect gasification, and this could have several advantages: (i) all generated CO₂ is present together with the syngas or methane in the fuel reactor outlet stream, thus in a concentrated stream, viable for separation and capture; (ii) the air reactor (or combustion chamber) should largely be free from trace impurities, thus preventing corrosion and fouling in this reactor; and (iii) the highly oxidizing conditions in the fuel reactor together with solid oxide surfaces should be advantageous with respect to limiting formation of tar species. In this study, two manganese ores and an iron-based waste material, LD slag, were investigated with respect to performance in these chemical-looping technologies. The materials were also impregnated with alkali (K) in order to gauge possible catalytic effects and also to establish a better understanding of the general behavior of oxygen carriers with alkali, an important component in biomass and biomass waste streams and often a precursor for high-temperature corrosion. The viability of the oxygen carriers was investigated using a synthetic biogas in a batch fluidized bed reactor. The conversion of CO, H₂, CH₄, and C₂H₄ was investigated in the temperature interval 800–950 °C. The reactivity, or oxygen transfer rate, was highest for the manganese ores, followed by the LD slag. The conversion of C₂H₄ was generally high but could largely be attributed to thermal decomposition. The K-impregnated samples showed enhanced reactivity during combustion conditions, and the Mangagran-K sample was able to achieve full conversion of benzene. The interaction of the solid material with alkali showed widely different behavior. The two manganese ores retained almost all alkali after redox testing, albeit exhibiting different migration patterns inside the particles. LD slag lost most alkali to the gas phase during testing, although some remained, possibly explaining a small difference in reactivity. In summary, the CLC and CLG processes could clearly be interesting for production of heat, power, or biofuel with negative CO₂ emissions. Manganese ores are most promising from this study, as they could absorb alkali, giving a better conversion and perhaps also inhibiting or limiting corrosion mechanisms in a combustor or gasifier.

     

不同合成条件对ZnAl-LDHs覆膜改性生物陶粒除磷效果的影响

采用3种Zn~(2+)/Al~(.+)金属浓度比的ZnCl_2和AlCl_3溶液,在两个不同pH值条件下,利用水热-共沉淀法对生物陶粒基质进行层状双金属氢氧化物(LDHs)覆膜改性.将生成的不同类型ZnAl-LDHs覆膜改性基质与原始生物陶粒基质分别填充于实验柱中,构建模拟垂直流人工湿地小试系统;对改性前后的7种基质进行磷素净化效果、等温吸附实验和解吸附实验研究,通过实验数据结合主成分分析,探讨ZnAl-LDHs覆膜改性生物陶粒除磷效果提升的影响因素.结果表明,pH=11的ZnAl-LDHs改性方式对磷素净化效果具有更为明显的提升功能;其中ZnAl-LDHs(pH=11,1∶1)改性生物陶粒基质相比于原始基质,对TP、TDP、SRP平均去除率的增幅超过70%,其最大理论吸附量达到原始生物陶粒的3倍.合成ZnAl-LDHs时的pH值和Zn~(2+)/Al~(3+)金属浓度比对改性生物陶粒的结构形态与覆膜效果有着不同程度的影响,其中合成时的pH值是ZnAlLDHs覆膜改性生物陶粒除磷效果的主要影响因素.通过合理调控制备ZnAl-LDHs覆膜改性生物陶粒时的pH值及Zn~(2+)/Al~(3+)金属浓度比,可以达到有效提高ZnAl-LDHs覆膜改性生物陶粒除磷效果的目的.     

氧化木糖无色杆菌(Achromobacte rxylosoxidans)LAX2对Cu、Pb和Cd复合污染土壤的生物矿化修复研究

我国土壤重金属复合污染较为突出,是目前亟待解决的土壤环境问题之一.本文研究了一株氧化木糖无色杆菌LAX2对Cu、Pb和Cd共存体系的生物矿化作用及其复合污染土壤的矿化修复作用.结果表明,菌株LAX2的发酵液、无菌发酵液和菌体细胞对3种重金属的去除能力大小顺序均为Pb~(2+)Cd~(2+)Cu~(2+).X-射线衍射、扫描电镜、红外光谱和能谱分析表明,3种重金属共存时菌株LAX2发酵液可诱导形成PbCO_3和CdCO_3晶体,而Cu不能单独成矿,混合矿物晶体呈长杆状.菌株LAX2发酵液能够明显降低黑钙土和白浆土中Cu、Pb和Cd的有效态含量,矿化修复30 d后,黑钙土中Cu、Pb、Cd的有效态含量分别降低了48.0%、71.4%、62.8%,白浆土中Cu、Pb、Cd的有效态含量分别降低了42.0%、63.2%、53.6%;碳酸盐结合态和铁锰氧化物结合态含量明显增加,可交换态和有机物结合态含量明显降低.矿化修复后的土壤中重金属的浸出毒性随修复时间的增长而降低,黑钙土中Cu、Pb、Cd浸出量分别降低了90.3%、93.2%、92.8%,白浆土中Cu、Pb、Cd浸出量分别降低了82.5%、86.1%、84.3%.以上结果说明,菌株LAX2可通过碳酸盐矿化作用固定土壤中的复合重金属,且在相同条件下对黑钙土的修复效果好于白浆土.     

Managed grassland alters soil N dynamics and N2O emissions in temperate steppe

Reclamation of degraded grasslands as managed grasslands has been increasingly accelerated in recent years in China. Land use change affects soil nitrogen(N) dynamics and nitrous oxide(N_2O) emissions. However, it remains unclear how large-scale grassland reclamation will impact the grassland ecosystem as a whole. Here, we investigated the effects of the conversion from native to managed grasslands on soil N dynamics and N_2O emissions by field experiments in Hulunber in northern China. Soil(0–10 cm), nitrate(NO_3~-),ammonium(NH_4~+), and microbial N were measured in plots in a temperate steppe(Leymus chinensis grassland) and two managed grasslands(Medicago sativa and Bromus inermis grasslands) in 2011 and 2012. The results showed conversion of L. chinensis grassland to M.sativa or B. inermis grasslands decreased concentrations of NO_3~–-N, but did not change NH_4~–N . Soil microbial N was slightly decreased by the conversion of L. chinensis grassland to M.sativa, but increased by the conversion to B. inermis. The conversion of L. chinensis grassland to M. sativa(i.e., a legume grass) increased N_2O emissions by 26.2%, while the conversion to the B. inermis(i.e., a non-legume grass) reduced N_2O emissions by 33.1%. The conversion from native to managed grasslands caused large created variations in soil NO?3~-+–N and NH_4~–N concentrations. Net N mineralization rates did not change significantly in growing season or vegetation type, but to net nitrification rate. These results provide evidence on how reclamation may impact the grassland ecosystem in terms of N dynamics and N_2O emissions.     

Preparation and characterization of a novel hybrid chelating material for effective adsorption of Cu(Ⅱ) and Pb(Ⅱ)

The discharge of heavy metal ions such as Cu~2+and Pb~2+poses a severe threat to public health and the environment owing to their extreme toxicity and bioaccumulation through food chains Herein, we report a novel organic–inorganic hybrid adsorbent, Al(OH)_3-poly(acrylamide dimethyldiallylammonium chloride)-graft-dithiocarbamate(APD), for rapid and effectiv removal of Cu~2+and Pb~2+. In this adsorbent, the "star-like" structure of Al(OH)3 poly(acrylamide-dimethyldiallylammonium chloride) served as the support of dithiocarbamat(DTC) functional groups for easy access of heavy metal ions and assisted development of larg and compact floccules. The synthesized adsorbent was characterized by scanning electron microscopy(SEM), transmission electron microscopy(TEM), Fourier transform infrared spectroscopy(FTIR), and thermogravimetric analysis(TGA). APD was demonstrated to hav rapid adsorption kinetics with an initial rate of 267.379 and 2569.373 mg/(g·min) as well a superior adsorption capacities of 317.777 and 586.699 mg/g for Cu~2+and Pb~2+respectively. Th adsorption process was spontaneous and endothermic, involving intraparticle diffusion and chemical interaction between heavy metal ions and the functional groups of APD. To assess it versatility and wide applicability, APD was also used in turbid heavy metal wastewater, and performed well in removing suspended particles and heavy metal ions simultaneously through flocculation and chelation. The rapid, convenient and effective adsorption of Cu~2+and Pb~2+give APD great potential for heavy metal decontamination in industrial applications.     

Relating Cd2 + binding by humic acids to molecular weight: A modeling and spectroscopic study

Molecular weight(Mw) is a fundamental property of humic acids(HAs), which considerably affect the mobility and speciation of heavy metals in the environment. In this study, soil humic acid(HA) extracted from Jinyun Mountain, Chongqing was ultra-filtered into four fractions according to the molecular weight, and their properties were characterized.Complexation of cadmium was investigated by titration experiments. For the first time,Langmuir and non-ideal competitive adsorption-Donna(NICA-Donnan) models combined with fluorescence excitation-emission matrix(EEM) quenching were employed to elucidate the binding characteristics of individual Mw fractions of HA. The results showed that the concentration of acidic functional groups decreased with increasing Mw, especially the phenolic groups. The humification degree and aliphaticity increased with increasing Mw as indicated by elemental composition analysis and FT-IR spectra. The binding capacity of Cd~(2+) to Mw fractions of HA followed the order UF1( 5 kDa) UF2(5–10 kDa) UF4( 30 kDa) UF3(10–30 kDa). Moreover, the distribution of cadmium speciation indicated that the phenolic groups were responsible for the variations in binding of Cd~(2+) among different Mw fractions. The results of fluorescence quenching illustrated that the binding capacity of Cd~(2+) to Mw fractions was controlled by the content of functional groups, while the binding affinity was largely influenced by structural factors. The results provide a better understanding of the roles that different HA Mw fractions play in heavy metal binding,which has important implications in the control of heavy metal migration and bio-toxicity.     

Anaerobic digestion in mesophilic and room temperature conditions: Digestion performance and soil-borne pathogen survival

Tomato plant waste(TPW) was used as the feedstock of a batch anaerobic reactor to evaluate the effect of anaerobic digestion on Ralstonia solanacearum and Phytophthora capsici survival. Batch experiments were carried out for TS(total solid) concentrations of 2%, 4% and 6% respectively, at mesophilic(37 ± 1°C) and room(20–25°C) temperatures. Results showed that higher digestion performance was achieved under mesophilic digestion temperature and lower TS concentration conditions. The biogas production ranged from 71 to 416 L/kg VS(volatile solids). The inactivation of anaerobic digestion tended to increase as digestion performance improved. The maximum log copies reduction of R. solanacearum and P. capsici detected by quantitative PCR(polymerase chain reaction) were 3.80 and 4.08 respectively in reactors with 4% TS concentration at mesophilic temperatures. However, both in mesophilic and room temperature conditions, the lowest reduction of R. solanacearum was found in the reactors with 6% TS concentration, which possessed the highest VFA(volatile fatty acid) concentration. These findings indicated that simple accumulation of VFAs failed to restrain R. solanacearum effectively, although the VFAs were considered poisonous. P. capsici was nearly completely dead under all conditions. Based on the digestion performance and the pathogen survival rate, a model was established to evaluate the digestate biosafety.     

铸铁管输配再生水铁溶出颗粒物特征研究

针对输配水过程中产生的"红水"现象及铁颗粒物溶出对水质的影响,开展了初步的模拟管网中试研究.实验采用内径为100 mm的铸铁管搭建了120 m长管网中试模拟系统,并以北京某再生水厂生产的再生水为水源,进行了单向连续流动和密闭循环流动模拟管网输配实验,并对管网出水水质进行了的连续跟踪监测.中试结果表明,两种方式的实验都发生了"红水"现象;出水水质的p H、总溶解性固体(TDS)、电导率及总铁都有明显升高;实验过程中得到的两种不同颜色颗粒物,它们都包括α-Fe OOH、γ-Fe OOH、Fe CO3、Fe2O3、Fe3O4及Fe O等矿物质;颗粒物颜色可能与颗粒中羟基氧化铁与碳酸亚铁的含量有关;水流速度对于管网中颗粒物的沉积和释放要一定影响;不带内衬的铸铁管不适合作为输配腐蚀性极强水质再生水的管材.     

Polycyclic aromatic hydrocarbon concentrations, compositions, sources, and associated carcinogenic risks to humans in farmland soils and riverine sediments from Guiyu, China

The concentrations of 16 priority polycyclic aromatic hydrocarbons(PAHs) were measured in 23 farmland soil samples and 10 riverine sediment samples from Guiyu, China, and the carcinogenic risks associated with PAHs in the samples were evaluated. Guiyu is the largest electronic waste(EW) dismantling area globally, and has been well known for the primitive and crude manner in which EWs are disposed, such as by open burning and roasting. The total PAH concentrations were 56–567 ng/g in the soils and 181–3034 ng/g in the sediments.The Shanglian and Huamei districts were found to be more contaminated with PAHs than the north of Guiyu. The soils were relatively weakly contaminated but the sediments were more contaminated, and sediments in some river sections might cause carcinogenic risks to the groundwater system. The PAHs in the soils were derived from combustion sources,but the PAHs in the sediments were derived from both combustion and petroleum sources.     

Reducing the risk of rear-end collisions with infrastructure-to-vehicle (I2V) integration of variable speed limit control and adaptive cruise control system

Objective: Adaptive cruise control (ACC) has been investigated recently to explore ways to increase traffic capacity, stabilize traffic flow, and improve traffic safety. However, researchers seldom have studied the integration of ACC and roadside control methods such as the variable speed limit (VSL) to improve safety. The primary objective of this study was to develop an infrastructure-to-vehicle (I2V) integrated system that incorporated both ACC and VSL to reduce rear-end collision risks on freeways.

Methods: The intelligent driver model was firstly modified to simulate ACC behavior and then the VSL strategy used in this article was introduced. Next, the I2V system was proposed to integrate the 2 advanced techniques, ACC and VSL. Four scenarios of no control, VSL only, ACC only, and the I2V system were tested in simulation experiments. Time exposed time to collision (TET) and time integrated time to collision (TIT), 2 surrogate safety measures derived from time to collision (TTC), were used to evaluate safety issues associated with rear-end collisions. The total travel times of each scenario were also compared.

Results: The simulation results indicated that both the VSL-only and ACC-only methods had a positive impact on reducing the TET and TIT values (reduced by 53.0 and 58.6% and 59.0 and 65.3%, respectively). The I2V system combined the advantages of both ACC and VSL to achieve the most safety benefits (reduced by 71.5 and 77.3%, respectively). Sensitivity analysis of the TTC threshold also showed that the I2V system obtained the largest safety benefits with all of the TTC threshold values. The impact of different market penetration rates of ACC vehicles in I2V system indicated that safety benefits increase with an increase in ACC proportions.

Conclusions: Compared to VSL-only and ACC-only scenarios, this integrated I2V system is more effective in reducing rear-end collision risks. The findings of this study provide useful information for traffic agencies to implement novel techniques to improve safety on freeways.