土霉素对厌氧发酵中酶活性和甲烷产量的影响

以猪粪为原料,小麦秸秆为调节物质,在小型厌氧发酵装置进行中温(37℃)厌氧发酵试验,研究了外源添加土霉素(OTC)对厌氧发酵过程中累积甲烷产量、脲酶活性和脱氢酶活性的影响以及土霉素的浓度变化情况.依据土霉素的添加量不同,试验共设置4个处理:CK处理,L处理(OTC质量分数60 mg·kg-1),M处理(OTC质量分数100 mg·kg-1),H处理(OTC质量分数140 mg·kg-1).结果表明:厌氧发酵初期,土霉素对甲烷累积产量有一定的促进作用,以后转变为抑制作用.厌氧发酵结束时,同对照相比,L至H处理甲烷累积产量依次减少了8.9%,4.6%,9.4%.厌氧发酵初期,土霉素对脲酶活性有一定的促进作用,随后转变为抑制作用;厌氧发酵前期,不同浓度土霉素对脱氢酶活性均表现为抑制作用,厌氧发酵后期,只有H处理的脱氢酶活性显著小于对照.土霉素含量在第10 d大幅度减少,30 d后土霉素含量基本维持不变.     

Aquatic arsenic: Toxicity,speciation, transformations,and remediation

This paper reviews the current knowledge on the toxicity, speciation and biogeochemistry of arsenic in aquatic environmental systems. The toxicity of arsenic is highly dependent on the chemical speciation. The effects of pH, E_h, adsorbing surfaces, biological mediation, organic matter, and key inorganic substances such as sulfide and phosphate combine in a complex and interwoven dynamic fashion to produce unique assemblages of arsenic species. The number of different arsenic species found in environmental samples and an understanding of the transformations between arsenic species has increased over the past few decades as a result of new and refined analytical methods. Changes in arsenic speciation and in total arsenic content of foods upon processing have suggested possible risks associated with processed and unprocessed food. Arsenic removal from water using adsorbents, chemical oxidation, photolysis and photocatalytic oxidation techniques is also reviewed.     

Development finance in the 1990s for Latin American resource exporting countries

As a result of the debt crisis, per capita income in Latin America in 1990 was 10% below its 1981 level. Many resource exporting countries in the region have undertaken wide and deep reforms in order, among other reasons, to attract and retain long-term capital to fuel growth prospects. One newly proposed long-term instrument for development finance and risk management is the commodity bond. Given the sovereign risk component, the costly premiums that must be paid to insure it and more efficient alternative instruments for both issuers and investors, commodity bonds are unlikely to generate the required long-term capital needed to enhance growth prospects. With the continuing globalization of the goods, factors and currency markets, long-term capital can be attracted and maintained in both developed and developing countries by an attractive investment environment characterized by a competitive microeconomy, a stable macroeconomy, strong global linkages, and a serious programme to improve physical and social infrastructure.     

Chile's resource sectors

Chilean economic reforms, introduced in the 1970s and early 1980s, discarded decades of state intervention in the economy, but were accompanied by considerable economic pain and social stress from domestic and international sources. In the 1990s, Chile, supported by a competitive micro-economy, a stable macro-economy, strong linkages with the world economy and the return to democratic government, is exploiting its world-class resource sectors to propel economic growth in order to address social problems. However, the prospects for raising living standards in Chile and other resource-exporting developing countries are critically dependent on a favourable external environment.     

Monitoring and modeling of disinfection by-products (DBPs)

In the United States, the newly promulgateddisinfectant/disinfection by-product (D/DBP) regulationsforce water treatment utilities to be more concerned withfinished and distributed water qualities. In this study,monitoring of DBP formation was conducted from three Frenchwater treatment plants trying to assess DBP variationsthrough time and space. Compared to the in-plant totaltrihalomethanes (TTHM) levels, TTHM levels in thedistribution system increased from less than 150% to morethan 300%. Significant variations for TTHM and bromate(BrO₃ ^-) levels throughout the seasons were alsoobserved; generally higher levels in the summer and lowerlevels in the winter. Combining chemical DBP models(empirical power functional models) and hydraulicsimulations, DBPs including TTHM and BrO₃ ^- weresuccessfully simulated from the full-scale monitoring data,indicating that empirical DBP model can be a potential toolto access DBP formation in actual plants. This study alsoprovides the protocols to assess DBP simulations in thewater treatment systems.     

Rapidly locating and characterizing pollutant releases in buildings

Releases of airborne contaminants in or near a building can lead to significant human exposures unless prompt response measures are taken. However, possible responses can include conflicting strategies, such as shutting the ventilation system off versus running it in a purge mode or having occupants evacuate versus sheltering in place. The proper choice depends in part on knowing the source locations, the amounts released, and the likely future dispersion routes of the pollutants. We present an approach that estimates this information in real time. It applies Bayesian statistics to interpret measurements of airborne pollutant concentrations from multiple sensors placed in the building and computes best estimates and uncertainties of the release conditions. The algorithm is fast, capable of continuously updating the estimates as measurements stream in from sensors. We demonstrate the approach using a hypothetical pollutant release in a five-room building. Unknowns to the interpretation algorithm include location, duration, and strength of the source, and some building and weather conditions. Two sensor sampling plans and three levels of data quality are examined. Data interpretation in all examples is rapid; however, locating and characterizing the source with high probability depends on the amount and quality of data and the sampling plan.     

Removal of toxic ions (chromate, arsenate, and perchlorate) using reverse osmosis, nanofiltration, and ultrafiltration membranes

Rejection characteristics of chromate, arsenate, and perchlorate were examined for one reverse osmosis (RO, LFC-1), two nanofiltration (NF, ESNA, and MX07), and one ultrafiltration (UF and GM) membranes that are commercially available. A bench-scale cross-flow flat-sheet filtration system was employed to determine the toxic ion rejection and the membrane flux. Both model and natural waters were used to prepare chromate, arsenate, and perchlorate solutions (approximately 100 μg L⁻¹ for each anion) in mixtures in the presence of other salts (KCl, K₂SO₄, and CaCl₂); and at varying pH conditions (4, 6, 8, and 10) and solution conductivities (30, 60, and 115 mS m⁻¹). The rejection of target ions by the membranes increases with increasing solution pH due to the increasingly negative membrane charge with synthetic model waters. Cr(VI), As(V), and rejection follows the order LFC-1 (>90%) > MX07 (25–95%)  ESNA (30–90%) > GM (3–47%) at all pH conditions. In contrast, the rejection of target ions by the membranes decreases with increasing solution conductivity due to the decreasingly negative membrane charge. Cr(VI), As(V), and rejection follows the order CaCl₂ < KCl  K₂SO₄ at constant pH and conductivity conditions for the NF and UF membranes tested. For natural waters the LFC-1 RO membrane with a small pore size (0.34 nm) had a significantly greater rejection for those target anions (>90%) excluding (71–74%) than the ESNA NF membrane (11–56%) with a relatively large pore size (0.44 nm), indicating that size exclusion is at least partially responsible for the rejection. The ratio of solute radius (r_i,s) to effective membrane pore radius (r_p) was employed to compare ion rejection. For all of the ions, the rejection is higher than 70% when the r_i,s/r_p ratio is greater than 0.4 for the LFC-1 membrane, while for di-valent ions (, , and ) the rejection (38–56%) is fairly proportional to the r_i,s/r_p ratio (0.32–0.62) for the ESNA membrane.     

Analysis of volatile organic compounds released during food decaying processes

A number of volatile organic compounds (VOCs) including acetone, methyl ethyl ketone, toluene, ethylbenzene, m,p-xylene, styrene, and o- xylene released during food decaying processes were measured from three types of decaying food samples (Kimchi (KC), fresh fish (FF), and salted fish (SF)). To begin with, all the food samples were contained in a 100-mL throwaway syringe. These samples were then analyzed sequentially for up to a 14-day period. The patterns of VOC release contrasted sharply between two types of fish (FF and SF) and KC samples. A comparison of data in terms of total VOC showed that the mean values for the two fish types were in the similar magnitude with 280 ± 579 (FF) and 504 ± 1,089 ppmC (SF), while that for KC was much lower with 16.4 ± 7.6 ppmC. There were strong variations in VOC emission patterns during the food decaying processes between fishes and KC that are characterized most sensitively by such component as styrene. The overall results of this study indicate that concentration levels of the VOCs differed significantly between the food types and with the extent of decaying levels through time.     

Rapidly Locating and Characterizing Pollutant Releases in Buildings

Abstract

Releases of airborne contaminants in or near a building can lead to significant human exposures unless prompt response measures are taken. However, possible responses can include conflicting strategies, such as shutting the ventilation system off versus running it in a purge mode or having occupants evacuate versus sheltering in place. The proper choice depends in part on knowing the source locations, the amounts released, and the likely future dispersion routes of the pollutants. We present an approach that estimates this information in real time. It applies Bayesian statistics to interpret measurements of airborne pollutant concentrations from multiple sensors placed in the building and computes best estimates and uncertainties of the release conditions. The algorithm is fast, capable of continuously updating the estimates as measurements stream in from sensors. We demonstrate the approach using a hypothetical pollutant release in a five-room building. Unknowns to the interpretation algorithm include location, duration, and strength of the source, and some building and weather conditions. Two sensor sampling plans and three levels of data quality are examined. Data interpretation in all examples is rapid; however, locating and characterizing the source with high probability depends on the amount and quality of data and the sampling plan.