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981.
Effects of carrier gas composition(N_2/air) on NH_3 production, energy efficiency regarding NH_3 production and byproducts formation from plasma-catalytic decomposition of urea were systematically investigated using an Al_2 O_3-packed dielectric barrier discharge(DBD) reactor at room temperature. Results show that the presence of O_2 in the carrier gas accelerates the conversion of urea but leads to less generation of NH_3. The final yield of NH_3 in the gas phase decreased from 70.5%, 78.7%, 66.6% and 67.2% to 54.1%, 51.7%, 49.6% and 53.4% for applied voltages of 17, 19, 21 and 23 kV, respectively when air was used as the carrier gas instead of N_2.From the viewpoint of energy savings, however, air carrier gas is better than N_2 due to reduced energy consumption and increased energy efficiency for decomposition of a fixed amount of urea. Carrier gas composition has little influence on the major decomposition pathways of urea under the synergetic effects of plasma and Al_2 O_3 catalyst to give NH_3 and CO_2 as the main products. Compared to a small amount of N_2 O formed with N_2 as the carrier gas, however,more byproducts including N_2O and NO_2 in the gas phase and NH_4 NO_3 in solid deposits were produced with air as the carrier gas, probably due to the unproductive consumption of NH_3, the possible intermediate HNCO and even urea by the abundant active oxygen species and nitrogen oxides generated in air-DBD plasma. 相似文献
982.
983.
Wastewater remediation using coal ash 总被引:2,自引:0,他引:2
D. W. Kirk C. Q. Jia J. Yan A. L. Torrenueva 《Journal of Material Cycles and Waste Management》2003,5(1):0005-0008
Small-scale domestic septic tanks discharge excess nutrients such as phosphorus and nitrogen, as well as pathogens, which
can degrade local water supplies. Unfortunately, traditional chemical and physical treatments are not practicable for single-home
dwellings. This work reports on a potentially attractive solution to protect local water supplies by using a low-cost industrial
waste, coal ash, for contaminant removal. Coal ash is produced as a consequence of electric power generation. The majority
of the ash is disposed of in landfills and surface impoundments, or stored on- or off-site, producing large hills or leveling
valleys. Only a small portion of the ash is ever utilized, mainly by cement industries and road construction. For example,
in Canada less than 25% is used. Therefore, if useful applications can be found, an opportunity exists to make better use
of this waste material. Bench-scale laboratory experiments and full-scale field tests show that coal ash has the capacity
to remove phosphorus from domestic waste water. The experimental and field data demonstrate that phosphate levels and calcium
levels can be correlated, although not in a simple manner. In addition, the ash in packed beds removed total suspended solid
(TSS), biological oxygen demand (BOD), ammonia nitrogen (NH3—N), total Kjeldahl nitrogen (TKN), and E. coli. The removal of E. coli was close 100% in the cases studied.
Received: May 20, 2002 / Accepted: October 5, 2002 相似文献
984.
电晕法处理挥发性有机化合物技术研究现状 总被引:1,自引:0,他引:1
本文介绍了挥发性有机物(VOCs)的特点及危害,综述了各种处理技术的基本原理、优势及存在的问题,并进行对比。重点介绍了电晕放电技术的原理以及研究现状,强调其相对于其他技术所独有的优越性,针对其存在的问题,预期了研究工作未来的发展方向。 相似文献
985.
986.
James F. Saunders William M. Lewis 《Journal of the American Water Resources Association》2003,39(1):33-45
ABSTRACT: The maximum concentration of a regulated substance that is allowed in a wastewater effluent usually is determined from the amount of dilution provided by the receiving water. Dilution flow is estimated from historical data by application of statistical criteria that define low flow conditions for regulatory purposes. Such use of historical data implies that the past is a good indicator of future conditions, at least for the duration of a discharge permit. Short records, however, introduce great uncertainty in the estimation of low flows because they are unlikely to capture events with recurrence frequencies of multiple years (e.g., ENSO events or droughts). We conducted an analysis of daily flows at several gages with long records in the South Platte River basin of Colorado. Low flows were calculated for successive time blocks of data (3‐, 5‐, 10‐, and 20‐years), and these were compared with low flows calculated for the entire period of record (> 70 years). In unregulated streams, time blocks of three or five years produce estimates of low flows that are highly variable and consistently greater than estimates derived from a longer period of record. Estimates of low flow from 10‐year blocks, although more stable, differ from the long term estimates by as much as a factor of two because of climate variation. In addition, the hydrographs of most streams in Colorado have been influenced by dams, diversions, or water transfers. These alterations to the natural flow regime shorten the record that is useful for analysis, but also tend to increase the calculated low flows. The presence of an upward trend in low flows caused by water use represents an unanticipated risk because it fails to incorporate societal response to severe drought conditions. Thus, climate variability poses a significant risk for water quality both directly, because it may not be represented adequately in the short periods of the hydrologic record that are typically used in permits, and indirectly, through its potential to cause altered use of water during time of scarcity. 相似文献
987.
988.
排污权交易目前在中国非常受重视,但其中也存在一些问题,主要是企业和政府尚没有处理好经济发展和环境保护的关系,也存在着制度设置不合理的问题。今后应重视排污权交易中的内部和外部条件的建设。内部条件主要有排污总量的确定和排污许可证的发放,外部条件主要包括政府加强环境执法力度和提供有效的排污信息。 相似文献
989.
990.
河流及污水处理厂全氟化合物排放估算 总被引:8,自引:7,他引:1
为了解全氟化合物(PFCs)的环境排放强度,利用通量计算的方法,综合国内现有PFCs监测数据,对我国部分主要流域的河流水体和部分主要城市的污水处理厂PFCs排放通量进行了估算研究.环渤海北部沿海区域主要河流水体中全氟辛烷磺酸(PFOS)和全氟辛酸(PFOA)排放总通量分别为122 kg/a和216 kg/a,其中大辽河和大凌河分别为该区域PFOS和PFOA排放的主要河流.珠江和长江是中国PFOS排放的主要河流,PFOS排放通量分别为4.47×103 kg/a和807 kg/a.长江和黄浦江为中国PFOA排放的主要河流,PFOA排放通量分别为3.92×104 kg/a和1.60×104 kg/a.天津市和北京市污水处理厂人均PFOS排放量分别为291 μg·(a·人)-1和221 μg·(a·人)-1,远低于瑞士和美国污水处理厂的人均PFOS排放量.城市污泥PFCs排放量较高区域多集中在PFCs相关生产厂家集中省份的工业较发达城市.研究结果可为进一步进行污染源识别以及控制和减少PFCs污染和排放提供科学依据. 相似文献