Selection of an effective sludge dewatering system for a small wastewater treatment plant

The Jahra Plant was commissioned in 1981 as a secondary treatment plant employing the extended aeration process. The plant has been upgraded since that time by constructing additional tertiary filtration units to improve effluent quality. The plant has a design capacity of 66 000 m³/d. At present, the daily inflow to the plant is about 47 000 m³/d of domestic sewage. The sludge produced at the Jahra Plant can be classified as excess activated sludge which combines the primary and secondary solids. At present, there are 30 drying beds receiving about 100 m³ of sludge dally. Sewage-sludge production represents about 0.5% of the total flow treated at the plant and is increasing yearly with increases in population and water consumption. Present dewatering systems are not adequate to cope with expansion in sewage treatment. Increasing the capacity of the existing plant would require more drying beds that could exacerbate existing odor problems. Some dewatering systems, such as the belt filter press and the centrifuge, have been tested to determine the most effective one under local conditions. Appropriate polymer doses for thickening have been determined. This paper describes present sludge dewatering units and operating techniques which have been developed during the operation of this facility.     

基于测试数据的室内超宽带信道建模研究

基于室内超宽带信道测量研究建立了基于簇的时延抽头模型以及与距离和载频有关的新颖的路径损耗模型,建立了路径损耗同时与距离和频率的依赖关系.同时,研究发现视距和非视距接收信号幅度分别满足莱斯和瑞利分布.该模型对超宽带无线系统仿真和设计有重要的指导意义.     

Sequestration of toxic Pb（II） ions by chemically treated rubber （Hevea brasiliensis ） leaf powder

Rubber leaf powder (an agricultural waste) was treated with potassium permanganate followed by sodium carbonate and its performance in the removal of Pb(II) ions from aqueous solution was evaluated. The interactions between Pb(II) ions and functional groups on the adsorbent surface were confirmed by Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) coupled with X-ray energy dispersive spectroscopy (EDX). The effects of several important parameters which can affect adsorption capacity such as pH, adsorbent dosage, initial lead concentration and contact time were studied. The optimum pH range for lead adsorption was 4–5. Even at very low adsorbent dosage of 0.02 g, almost 100% of Pb(II) ions (23 mg/L) could be removed. The adsorption capacity was also dependent on lead concentration and contact time, and relatively a short period of time (60–90 min) was required to reach equilibrium. The equilibrium data were analyzed with Langmuir, Freundlich and Dubinin-Radushkevich isotherms. Based on Langmuir model, the maximum adsorption capacity of lead was 95.3 mg/g. Three kinetic models including pseudo first-order, pseudo second-order and Boyd were used to analyze the lead adsorption process, and the results showed that the pseudo second-order fitted well with correlation coefficients greater than 0.99.     

Crash data analysis: collective vs. individual crash level approach

INTRODUCTION: Traffic safety literature has traditionally focused on identification of location profiles where "more crashes are likely to occur" over a period of time. The analysis involves estimation of crash frequency and/or rate (i.e., frequency normalized based on some measure of exposure) with geometric design features (e.g., number of lanes) and traffic characteristics (e.g., Average Annual Daily Traffic [AADT]) of the roadway location. In the recent past, a new category of traffic safety studies has emerged, which attempts to identify locations where a "crash is more likely to occur." The distinction between the two groups of studies is that the latter group of locations would change based on the varying traffic patterns over the course of the day or even within the hour. METHOD: Hence, instead of estimation of crash frequency over a period of time, the objective becomes real-time estimation of crash likelihood. The estimation of real-time crash likelihood has a traffic management component as well. It is a proactive extension to the traditional approach of incident detection, which involves analysis of traffic data recorded immediately after the incident. The units of analysis used in these studies are individual crashes rather than counts of crashes. RESULTS: In this paper, crash data analysis based on the two approaches, collective and at individual crash level, is discussed along with the advantages and shortcomings of the two approaches.     

On-line CO, CO2 emissions evaluation and (benzene, toluene, xylene) determination from experimental burn of tropical biomass

Atmospheric pollution and global warming issues are increasingly becoming major environmental concerns. Fire is one of the significant sources of pollutant gases released into the atmosphere; and tropical biomass fires, which are of particular interest in this study, contribute greatly to the global budget of CO and CO₂. This pioneer research simulates the natural biomass burning strategy in Malaysia using an experimental burning facility. The investigation was conducted on the emissions (CO₂, CO, and Benzene, Toluene, Ethylbenzene, Xylenes (BTEX)) from ten tropical biomass species. The selected species represent the major tropical forests that are frequently subjected to dry forest fire incidents. An experimental burning facility equipped with an on-line gas analyzer was employed to determine the burning emissions. The major emission factors were found to vary among the species, and the specific results were as follows. The moisture content of a particular biomass greatly influenced its emission pattern. The smoke analysis results revealed the existence of BTEX, which were sampled from a combustion chamber by enrichment traps aided with a universal gas sampler. The BTEX were determined by organic solvent extraction followed by GC/MS quantification, the results of which suggested that the biomass burning emission factor contributed significant amounts of benzene, toluene, and m,p-xylene. The modified combustion efficiency (MCE) changed in response to changes in the sample moisture content. Therefore, this study concluded that the emission of some pollutants mainly depends on the burning phase and sample moisture content of the biomass.     

Chemical,physical and biological methods to convert lignocellulosic waste into value-added products. A review

Environmental Chemistry Letters - Actual agricultural practices produce about 998 million tonnes of agricultural waste per year. Therefore, converting lignocellulosic wastes into energy, chemicals,...     

Synthesis and preparation of acid capped CdSe nanocrystals as successful adsorbent and photocatalyst for the removal of dyes from water and its statistical physics analysis

Environmental Science and Pollution Research - In this study, mercaptosuccinic acid capped CdSe nanocrystals were successfully synthesized and used as photocatalyst for the effective removal of...     

Assessment of cobalt in wheat grains as affected by diverse fertilizers: implications for public health

Environmental Science and Pollution Research - Present study was conducted to check the heavy metal content in wheat treated with municipal solid waste, Although municipal solid waste was enriched...     

Efficient removal of the antibiotic Cefixime on Mg0.3Zn0.7O under solar light: kinetic and mechanism studies

Environmental Science and Pollution Research - The heterogeneous photocatalysis is known to provide significant degradation and mineralization of emerging contaminants including antibiotics. For...