Determining C/N ratios for typical organic wastes using biodegradable fractions

It is well established that an optimal aerobic and anaerobic microbial metabolism is achieved with a C/N ratio between 20 and 30. Most studies are currently based on chemically-measured carbon and nitrogen contents. However, some organic wastes can be composed of recalcitrant carbon fractions that are not bioavailable. To know the biodegradable C/N ratio, two different methods to determine the aerobic and anaerobic biodegradable organic carbon (BOC_AE and BOC_AN) are proposed and used to analyze a wide variety of different organic samples. In general, raw wastes and digested products have more amount of BOC_AE. On the contrast, the samples collected after an aerobic treatment have higher content of BOC_AN. In any case, all the BOC fractions are lower than the total organic carbon (TOC). Therefore, the C/N ratios based on BOC are always lower than the total C/N ratio based on the TOC measure. The knowledge of the real bioavailable C/N ratio is crucial for the biological treatments of organic materials. To reduce the test time necessary for BOC determination, the values of BOC for all the samples obtained at different times were compared and correlated with the final BOC. A method that allows for the determination of BOC_AE in 4 d is proposed. In relation to the anaerobic assay, the biogas potential calculated after 21 and 50 d was positively correlated with the final potential defined after 100 d of assay.     

Estimating Greenhouse Gas Emission Reduction Potential: An Assessment of Models and Methods for the Power Sector

The success of the Clean Development Mechanism of the Kyoto Protocol to reduce global greenhouse gas emissions requires that there are scientifically sound and usable measurement methods for the emission baseline. Three different methods are investigated in the context of China’s electrical sector: simulation with dispatch analysis, decomposition analysis, and operating and build margin analysis. It is found that dispatch analysis is the best method available as it is able to consider important regional and temporal dimensions, while decomposition analysis can help quantify the potential effects of different energy and environment policy choices.     

General plume dispersion model (GPDM) for point source emission

Gaussian-based dispersion models are widely used to estimate local pollution levels. The accuracy of such models depends on stability classification schemes as well as plume rise equations. A general plume dispersion model (GPDM) for a point source emission, based on Gaussian plume dispersion equation, was developed. The program complex was developed using Java and Visual basic tools. It has the flexibility of using five kinds of stability classification schemes, i.e., Lapse Rate, Pasquill–Gifford (PG), Turner, σ–θ and Richardson number. It also has the option of using two types of plume rise formulations – Briggs and Holland’s. The model, applicable for both rural and urban roughness conditions, uses meteorological and emission data as its input parameters, and calculates concentrations of pollutant at the center of each cell in a predefined grid area with respect to the given source location. Its performance was tested by comparing with 4-h average field data of continuous releases of SO₂ from Dadri thermal power plant (Uttar Pradesh, India). Results showed that the Turner scheme used with Holland’s equation gives the best outcome having a degree of agreement (d) of 0.522.     

城市生态环境质量评价初探

以新疆乌鲁木齐市、石河子市、克拉玛依市为例,依据城市生态学理论,对城市的生产位、生态位、环境位进行评估,并对评价结果进行综合分析,以确定城市生态环境质量的优劣,以此反映城市经济发展、人类各种活动和环境保护之间的适应程度.     

Exposure of an anoxic and contaminated canal sediment: Mobility of metal(loid)s

A derelict canal contains an estimated 9800 tonnes of anoxic sediment with highly elevated concentrations of trace elements. Lack of maintenance, reduced water levels and vegetation colonization threaten the stability of pollutants by removing existing waterlogged reduced conditions. A column leaching study of the sediment under increasingly oxidized conditions showed reductions in As mobility but increased heavy metal concentrations. In a reduced state, As mobility was higher (as a consequence of enhanced Fe and organic carbon solubility) whilst heavy metal concentrations in leachates were lower (due to markedly higher pH). Over 10 contiguous wetting and drying cycles, the consequences were profound; all trace elements were continuously leached with enhanced flushing of Fe, As, Zn and Cu. This raises concern over possible mobilization of pollutants to the wider environment, including groundwater. Options for management to stabilize contaminants are discussed that point to the importance of limiting water flow through the sediment.     

One-electron standard reduction potentials of nitroaromatic and cyclic nitramine explosives

Extensive studies have been conducted in the past decades to predict the environmental abiotic and biotic redox fate of nitroaromatic and nitramine explosives. However, surprisingly little information is available on one-electron standard reduction potentials (E^o(R-NO₂/R-NO₂⁻)). The E^o(R-NO₂/R-NO₂⁻) is an essential thermodynamic parameter for predicting the rate and extent of reductive transformation for energetic residues. In this study, experimental (linear free energy relationships) and theoretical (ab initio calculation) approaches were employed to determine E^o(R-NO₂/R-NO₂⁻) for nitroaromatic, (caged) cyclic nitramine, and nitroimino explosives that are found in military installations or are emerging contaminants. The results indicate a close agreement between experimental and theoretical E^o(R-NO₂/R-NO₂⁻) and suggest a key trend: E^o(R-NO₂/R-NO₂⁻) value decreases from di- and tri-nitroaromatic (e.g., 2,4-dinitroanisole) to nitramine (e.g., RDX) to nitroimino compound (e.g., nitroguanidine). The observed trend in E^o(R-NO₂/R-NO₂⁻) agrees with reported rate trends for reductive degradation, suggesting a thermodynamic control on the reduction rate under anoxic/suboxic conditions.     

初始pH值对泔脚发酵产氢余物甲烷化的强化研究

以城市生活垃圾厌氧消化污泥为接种物,考察了初始pH值为5、6、7和8时对泔脚发酵产氢余物中温（36℃）批式厌氧消化的影响。结果表明,当初始pH值低于7时,随着初始pH值的增大,产氢余物的产甲烷能力也随之增大;而当初始pH值高于7时,体系的产沼能力却受到了极大的抑制。结合Gompertz模型拟合结果,初始pH值为7为泔脚发酵产氢余物沼气化的最佳初始pH值,其沼气化的延迟时间λ、产甲烷率、生物气中甲烷的最高体积含量分别为： 4.02 d,379.28 mL/g VS,82.2％。厌氧消化结束后,除初始pH值为5的以外,厌氧消化余物的pH值在 6.8～6.9之间,这为沼气中甲烷的高体积含量（高于常规厌氧消化的最高甲烷体积含量75%）提供了证据。     

施肥及秸秆还田处理下玉米季温室气体的排放

以华北地区冬小麦-夏玉米轮作农田为研究对象,在玉米整个生长季,运用静态箱法针对正常施肥及正常施肥结合秸秆还田处理进行了为期3年N2O排放通量的连续观测,并开展了1季CO2和CH4交换通量的研究.在玉米整个生长过程中施肥阶段N2O的排放量占到了总排放量的83%—96%,表明现有化肥的使用明显导致了农田N2O排放增加.与控制地相比,施肥和耕种可导致玉米田CO2排放明显增加,且正常施肥及秸秆还田样地CO2排放主要集中在苗期至吐丝期.控制地、正常施肥样地及施肥结合秸秆还田样地CH4的累积排放量均为负值,说明旱地土壤是CH4的一个汇.秸秆还田在一定程度上增加了玉米季N2O和CO2的排放量,但对CH4的吸收有所抑制.正常施肥样地和秸秆还田样地全球净增温潜势分别为-1392.8 kg C.hm-2和-179.2 kg C.hm-2,表明华北农田在现有耕作方式下是大气温室气体的一种重要汇.