Evaluation of Trickle Bed Air Biofilter Performance as a Function of Inlet VOC Concentration and Loading,and Biomass Control

ABSTRACT

The 1990 Amendments to the Clean Air Act have stimulated strong interest in the use of biofiltration for the economical, engineered control of volatile organic compounds (VOCs) in effluent air streams. Trickle bed air biofilters (TBABs) are especially applicable for treating VOCs at high loadings. For long-term, stable operation of highly loaded TBABs, removal of excess accumulated bio-mass is essential. Our previous research demonstrated that suitable biomass control for TBABs was achievable by periodic backwashing of the biofilter medium. Backwashing was performed by fluidizing the pelletized biological attachment medium with warm water to about a 40% bed expansion. This paper presents an evaluation of the impact of backwashing on the performance of four such TBABs highly loaded with toluene. The inlet VOC concentrations studied were 250 and 500 ppmv toluene, and the loadings were 4.1 and 6.2 kg COD/m³ day (55 and 83 g toluene/m³ hr). Loading is defined as kg of chemical oxygen demand per cubic meter of medium per day. Performance deterioration at the higher loading was apparently due to a reduction of the specific surface of the attached biofilm resulting from the accumulation of excess biomass. For a toluene loading of 4.1 kg COD/m³ day, it was demonstrated that the long-term performance of biofilters with either inlet concentration could be maintained at over 99.9% VOC removal by employing a backwashing strategy consisting of a frequency of every other day and a duration of 1 hr.     

Thermal Exploitation of Wastes with Lignite for Energy Production

Abstract

The thermal exploitation of wastewood with Greek lignite was investigated by performing tests in a laboratory-scale fluidized bed reactor, a 1-MW_th semi-industrial circulating fluidized bed combustor, and an industrial boiler.

Blends of natural wood, demolition wood, railroad sleepers, medium-density fiberboard residues, and power poles with lignite were used, and the co-combustion efficiency and the effect of wastewood addition on the emitted pollutants were investigated. Carbon monoxide, sulfur dioxide, and oxides of nitrogen emissions were continuously monitored, and, during the industrial-scale tests, the toxic emissions (polychlorinated dibenzodioxins and dibenzofurans and heavy metals) were determined. Ash samples were analyzed for heavy metals in an inductively coupled plasma-atomic emission spectroscopy spectrophotometer.

Problems were observed during the preparation of wastewood, because species embedded with different compounds, such as railway sleepers and demolition wood, were not easily treated. All wastewood blends were proven good fuels; co-combustion proceeded smoothly and homogeneous temperature and pressure profiles were obtained. Although some fluctuations were observed, low emissions of gaseous pollutants were obtained for all fuel blends. The metal element emissions (in the flue gases and the solid residues) were lower than the legislative limits. Therefore, wastewood co-combustion with lignite can be realized, provided that the fuel handling and preparation can be practically performed in large-scale installations.     

Airborne Emissions of Mercury from Municipal Solid Waste. II: Potential Losses of Airborne Mercury before Landfill

Abstract

Waste distribution and compaction at the working face of municipal waste landfills releases mercury vapor (Hg⁰) to the atmosphere, as does the flaring of landfill gas. Waste storage and processing before its addition to the landfill also has the potential to release Hg⁰ to the air if it is initially present or formed by chemical reduction of Hg^II to Hg⁰ within collected waste. We measured the release of Hg vapor to the atmosphere during dumpster and transfer station activities and waste storage before landfilling at a municipal landfill operation in central Florida. We also quantified the potential contribution of specific Hg-bearing wastes, including mercury (Hg) thermometers and fluorescent bulbs, and searched for primary Hg sources in sorted wastes at three different landfills. Surprisingly large fluxes were estimated for Hg losses at transfer facilities (～100 mg/hr) and from dumpsters in the field (～30 mg/hr for 1,000 dumpsters), suggesting that Hg emissions occurring before landfilling may constitute a significant fraction of the total emission from the disposal/landfill cycle and a need for more measurements on these sources. Reducing conditions of landfill burial were obviously not needed to generate strong Hg⁰ signals, indicating that much of the Hg was already present in a metallic (Hg⁰) form. Attempts to identify specific Hg sources in excavated and sorted waste indicated few readily identifiable sources; because of effective mixing and diffusion of Hg⁰, the entire waste mass acts as a source. Broken fluorescent bulbs and thermometers in dumpsters emitted Hg⁰ at 10 to >100 μg/hr and continued to act as near constant sources for several days.     

Remote Sensing Tools Assist in Environmental Forensics. Part I: Traditional Methods

This is part one of a two-part discussion, in which we will provide an overview of the use of aerial photography, topographic mapping and photogrammetry in environmental enforcement actions. The visualization of spatial relationships of natural and man-made features can focus the scope of environmental investigation, and provide a simple, yet quantitative, historical record of changes in conditions on a site. Aerial photography has been used in environmental remote sensing since the early part of the 20th century. Aerial photos are valuable tools for environmental assessment because they provide objective, detailed documentation of surface conditions at a specific time. Furthermore, they can generally be obtained even in cases where access on the ground is denied to investigators. From aerial photos, precise quantitative information can be collected using photogrammetry. Such measurement and positional data can be produced in digital format for input into a Geographic Information System (GIS) for computerized analysis and display. Other information derived from aerial photographs requires specialized photointerpretive skills and experience. These include the recognition of vegetation mortality, oil-spill damage, and the ecological quality of water bodies. The location, extent and historical change of hazardous waste sites can be documented on topographic maps. These maps are often created from aerial photographs, and display the extent and location of real-world features by symbolizing them. The major advantage of maps over aerial photos is that maps can show things that are not visible from the air, while omitting unnecessary and distracting information. Because maps are derived products, they may contain bias in content and presentation, and they must be backed up by careful documentation and quality assurance protocols.     

Ion Composition Elucidation (ICE): an Investigative Tool for Characterization and Identification of Compounds of Regulatory Importance

Ion composition elucidation (ICE) often leads to identification of compounds and provides high-quality evidence for tracking compounds to their sources. Mass spectra for most organic compounds are not found in mass spectral libraries used to tentatively identify analytes. In addition, multiple matches are common. Ion Composition Elucidation provides the numbers of atoms of each element in the ions in the mass spectrum, greatly limiting the number of possible compounds that could produce the mass spectrum. Review of chemical and commercial literature then limits the number of possible compounds to one or a few that can be purchased to confirm tentative compound identifications by comparison of mass spectra and chromatographic retention times. Ion composition elucidation is conceptually simple relative to other analytical techniques and more easily explained to a judge or jury. It is based on sums of the exact masses of atoms and their isotopic abundances. Several applications of ICE are demonstrated for ultra-trace-level compounds in an extract of the e.uent from a tertiary sewage treatment plant including: (1) measurement of five values to determine an ion's composition and to generate evidence for the compound's identity, (2) rejection of incorrect library matches, (3) rapid screening for a target compound in an extract, and (4) a strategy for tracking unidentified compounds to their sources.     

Urban Transitions: On Urban Resilience and Human-Dominated Ecosystems

Urbanization is a global multidimensional process paired with increasing uncertainty due to climate change, migration of people, and changes in the capacity to sustain ecosystem services. This article lays a foundation for discussing transitions in urban governance, which enable cities to navigate change, build capacity to withstand shocks, and use experimentation and innovation in face of uncertainty. Using the three concrete case cities—New Orleans, Cape Town, and Phoenix—the article analyzes thresholds and cross-scale interactions, and expands the scale at which urban resilience has been discussed by integrating the idea from geography that cities form part of “system of cities” (i.e., they cannot be seen as single entities). Based on this, the article argues that urban governance need to harness social networks of urban innovation to sustain ecosystem services, while nurturing discourses that situate the city as part of regional ecosystems. The article broadens the discussion on urban resilience while challenging resilience theory when addressing human-dominated ecosystems. Practical examples of harnessing urban innovation are presented, paired with an agenda for research and policy.     

离子交换树脂处理二甲胺废水的研究

通过ZGSPC106型树脂对水中二甲胺(DMA)的静态吸附、动态吸附和解吸试验,探讨了溶液pH、初始浓度、温度和流速等对树脂吸附DMA的影响以及合适的再生条件。结果表明,该树脂对DMA有较强的吸附能力,293K下树脂的静态饱和吸附量为138.89mg/g;动态吸附试验表明,进液流速为20mL/min较为适宜;以2mol/L的HCl溶液为洗脱剂,在洗脱流速为10mL/min条件下,4倍树脂体积的HCl溶液对饱和树脂的洗脱率达90%以上;该树脂具有良好的稳定性,可多次重复利用。     

Responses of future air quality to emission controls over North Carolina,Part II: Analyses of future-year predictions and their policy implications

The MM5/CMAQ system evaluated in Part I paper is applied to study the impact of emission control on future air quality over North Carolina (NC). Simulations are conducted at a 4-km horizontal grid resolution for four one-month periods, i.e., January, June, July, and August 2009 and 2018. Simulated PM_2.5 in 2009 and 2018 show distribution patterns similar to those in 2002. PM_2.5 concentrations over the whole domain in January and July reduced by 5.8% and 23.3% in 2009 and 12.0% and 35.6% in 2018, respectively, indicating that the planned emission control strategy has noticeable effects on PM_2.5 reduction in this region, particularly in summer. More than 10% and 20% of 1-h and 8-h O₃ mixing ratios are reduced in July 2009 and 2018, respectively, demonstrating the effectiveness of emission control for O₃ reduction in summer. However, O₃ mixing ratios in January 2009 and 2018 increase by more than 5% because O₃ chemistry is VOC-limited in winter and the effect of NO_x reduction dominates over that of VOC reduction under such a condition. The projected emission control simulated at 4-km will reduce the number of sites in non-attainment for max 8-h O₃ from 49 to 23 in 2009 and to 1 in 2018 and for 24-h average PM_2.5 from 1 to 0 in 2009 and 2018 based on the latest 2008 O₃ and 2006 PM_2.5 standards. The variability in model predictions at different grid resolutions contributes to 1–3.8 ppb and 1–7.9 μg m^?3 differences in the projected future-year design values for max 8-h O₃ and 24-h average PM_2.5, respectively.