Modeling the reaction kinetics of Fenton's process on the removal of atrazine

The degradation of pesticide, atrazine (ATZ), 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine, by Fenton's reagent (FR) was investigated as a function of reagents' concentrations and ratios in a batch reactor. The degradation of ATZ was effectively achieved by hydroxyl radicals, which were generated in the FR process. The decay rates of ATZ and the oxidation capacities of FR were found to depend on the concentrations of hydrogen peroxide and ferrous ion. The removal kinetics of ATZ are initiated by a rapid decay and then followed by a much slower one. After an extended reaction time (5-10 min), the reactions ceased because the Fe(II) and H(2)O(2) were consumed and would be deactivated in the process. A mathematical model was successfully developed to describe the two-stage reaction kinetics by using two simple but critical parameters: the initial ATZ decay rate and the final oxidation capacity of Fenton's process. In general, higher [Fe(II)] or H(2)O(2) concentrations result in faster initial decay rate and higher oxidation capacity. However, the oxidation capacity is more sensitive to the initial [Fe(II)] due to the presence of side reactions as discussed in the paper.     

Anaerobic digestion of polyelectrolyte flocculated waste activated sludge

This work examined how adding one of three polyelectrolyte flocculants (T3052: cationic, T2000: non-ionic, and T1052: anionic) affected the anaerobic digestion of wastewater sludge. Methane production, floc characteristics (morphology and zeta-potential) and process parameters (soluble chemical oxygen demands (SCODs) and reductive potentials) were monitored along the digestion tests. The digestion rates of T2000- and T1052-conditioned sludge resembled that for original sludge. The T3052-flocculated sludge generated methane at a higher rate during the first 6 days of digestion than did the original one. In the following stage, the digestion rate of sludge flocculated with T3052 at dosage exceeding 15 g/kg dried solids declined. For example, at 40 days of digestion the methane production amounts for original, 15 g/kg DS flocculated, and 40 g/kg flocculated sludge were of 136, 105, and 85 g/kg DS, respectively. The role of flocculants could change in different stages of digestion.The dosed polymers had no apparent toxicity to the inoculum used. The changes in SCOD, adenosintriphosphate concentrations, oxidative and reductive potential, and zeta-potentials did not correlate with the noted hindered digestion for T3052-conditioned sludge. Microphotographic observation revealed that the flocs of T3052-conditioned sludge were not only of a large size, but also were resistant to structural deterioration during digestion. Therefore, mass transfer resistance was proposed to account for the hindered digestion efficiency observed for T3052-conditioned sludge.     

An unconventional approach to studying the reaction kinetics of the Fenton's oxidation of 2,4-dichlorophenoxyacetic acid

The Fenton's oxidation kinetics of herbicide 2,4-D at various [Fe(II)] and [H(2)O(2)] combinations was investigated and modelled through an unconventional approach. The reaction kinetics of 2,4-D degradation demonstrated a two-stage pattern of decay, where a very fast reactive stage was followed by a retardation stage due to the depletion of oxidants and to the competitive side-reactions of the intermediates (including 2,4-dichlorophenol, chlorohydroquinone and 2,6-dichlororesorcinol). A model characterized by two newly established constants, the initial decay rate and the maximum oxidative capacity, was proposed and proven capable of describing the two-stage process, which cannot easily be described by conventional first- or second-order kinetics approaches.     

新型聚合铝硅混凝剂处理洗浴废水的试验研究

针对常规铝盐、铁盐去除洗浴废水中阴离子洗涤剂 (LAS)效果不理想的状况 ,采用高碱化度钙型聚合铝硅混凝剂 (CPASC)进行了试验研究 ,同时与聚合氯化铝 (PAC)作了比较。结果表明 ,该混凝剂对洗浴废水中COD、LAS、SS及浊度都有较高的去除率 ,特别对LAS、COD的去除率分别比PAC高 10 %和 8%以上。当投加量为 6 0mg/L时 ,出水各项指标均达到生活杂用水水质标准 (GJ2 5 .1 89)。     

The study of fine and coarse particles, and metallic elements for the daytime and night-time in a suburban area of central Taiwan, Taichung

Daily average concentrations of fine and coarse particulates, and TSP samples have been measured simultaneously at daytime and night-time periods by using Universal and PS-1 sampler in a suburban area of central Taiwan from June to August 1998. The samples were analyzed by atomic absorption spectrometry to determine the fine and coarse particulate concentrations of metallic elements (Ca, Fe, Mn, Pb, Cu, Zn and Cr). The concentration of PM2.5 and TSP showed a decreased trend for the daytime period. The fine particle concentrations were about two times as that of coarse particulate concentrations. The averaged fine particulate concentrations at daytime are higher than at night-time. Ca and Fe were mostly in the coarse particulate mode. The correlation coefficients were 0.63 and 0.69 for elements Ca and Fe in the coarse particle mode for day and night periods. Pb showed a similar distribution ratio with Mn for the fine to coarse particle ratios at both day and night period. Pb and Mn are highly correlated for the day (R = 0.78) and night period (R = 0.61) at particle size <2.5 microm. Cu and Zn were mainly in fine particles at both day and night period. Fe and Ca consist of the major parts of all the elements. Elemental Mn is the lowest among the rest of the heavy metals.     

Toxicological response and its reversibility in rats fed Lake Ontario or Pacific coho salmon for 13 weeks

Lake Ontario coho salmon were known to contain a mixture of chemical contaminants. A previous study demonstrated that rats fed the Lake Ontario fish-supplemented diet for 28 days exhibited mild biochemical and histological changes. The purpose of the present study was to determine the effects due to a longer term of exposure and the reversibility of these effects. Growth rate and food consumption were not affected by feeding the animals with Lake Ontario or Pacific fish-supplemented diets for 13 weeks. No deaths were observed. Decreased spleen weights were observed in groups of males fed 1.45%, 5.8% Lake Ontario and 2.9% Pacific diet. After a 13 week recovery the spleen weights returned to normal. Decreased serum potassium was observed in male rats fed 2.9% Lake Ontario diet, and all levels of Pacific diet for 13 weeks, and was not evident following maintenance on normal diet. Serum glucose was not affected by the 13-week period of treatment, however; a reduction in this parameter occurred in male rats fed the two highest doses of Lake Ontario diet and all doses of Pacific diet following the 13-week recovery period. Minor hematological changes occurred only in the male rats fed either Lake Ontario or Pacific diet following a 13 week recovery period and included reduced marrow myeloid cells and myeloid/erythroid ratio. Hepatic microsomal ethoxyresorufin deethylase activity was significantly increased in rats ingesting Lake Ontario diet. Mild histological changes occurred in the liver and thyroid of the treated males, and in the liver and kidney of the treated females. These changes were attributed to the chemical residues and/or the fish diet. Data presented here indicated that the Lake Ontario fish-supplemented diet can cause mild biochemical, hematological and histological changes but most of these were reversible when exposure was terminated.     

工厂的氟污染对蔬菜含氟量的影响

上海某厂生产氟利昂和氢氟酸等化工产品,排放的废水、废气中含有大量氟化物。该厂排放的废气中氟化氢的量相当于全市氟化氢总排放量的50％左右。     

Assessment of Potential Capability of Water Bamboo Leaves on the Adsorption Removal Efficiency of Cationic Dye from Aqueous Solutions

Removal of toxic pollutants from water and wastewater is becoming an important process with the increase of industrial activities. The present study focused on assessing the suitability and efficiency of water bamboo leaves (WBL) for the removal of cationic dye from aqueous solutions. The effect of different variables in the batch method including solution pH (2–12), initial dye concentration (50–250 mg L^?1), adsorbent dose (0.05–0.30 g), contact time (5–180 min) and temperature (283–333 K) on the dye removal was investigated. The adsorption kinetics was discussed in view of four kinetics models. The results showed that the pseudo-second-order kinetics model described dye adsorption on WBL very well. The experimental equilibrium data were also tested by four isotherm models. It was found that adsorption of dye on WBL fitted well with the Langmuir isotherm model, implying the binding energy on the whole surface of the adsorbent was uniform and the dye molecules onto the surface of the adsorbent were monolayer coverage. Calculation of various thermodynamic parameters of the adsorption process indicated feasibility and exothermic nature of dye adsorption.     

谈春节期间燃放烟花爆竹对空气质量的影响

"爆竹声中一岁除",在春节期间燃放烟花爆竹这一传统习俗在我国有着悠久历史,可是,在春节期间大量集中燃放烟花爆竹会对空气质量造成严重的影响。本文对河源市2018年春节期间监测数据进行分析,探究燃放烟花爆竹对空气质量的影响,为春节期间烟花爆竹燃放管控提供技术参考。     

Effectiveness of terrestrial protected areas for conservation of lake fish communities

Freshwater protected areas are rare even though freshwater ecosystems are among the most imperiled in the world. Conservation actions within terrestrial protected areas (TPAs) such as development or resource extraction regulations may spill over to benefit freshwater ecosystems within their boundaries. Using data from 175 lakes across Ontario, Canada, we compared common indicators of fish‐assemblage status (i.e., species richness, Shannon diversity index, catch per unit effort, and normalized‐length size spectrum slopes) to evaluate whether TPAs benefit lake fish assemblages. Nearest neighbor cluster analysis was used to generate pairs of lakes: inside versus outside, inside versus bordering, and bordering versus outside TPAs based on lake characteristics. The diversity and abundance indicators did not differ significantly across comparisons, but normalized‐length size spectrum slopes (NLSS) were significantly steeper in lakes outside parks. The latter indicated assemblage differences (greater abundances of small‐bodied species) and less‐efficient energy transfer through the trophic levels of assemblages outside parks. Although not significantly different, pollution‐ and turbidity‐tolerant species were more abundant outside parks, whereas 3 of the 4 pollution‐intolerant species were more abundant within parks. Twenty‐one percent of the difference in slopes was related to higher total dissolved solids concentrations and angling pressure. Our results support the hypothesis that TPAs benefit lake fish assemblages and suggest that NLSS slopes are informative indicators for aquatic protected area evaluations because they represent compositional and functional aspects of communities.