Comparative assessments of VOC emission rates and associated health risks from wastewater treatment processes

With the growing concern regarding emission of volatile organic compounds (VOCs) from wastewater treatment plants (WWTPs), the relationship between the VOC emission rates and the associated public health risks has been rarely discussed. The objective of this study was to examine and compare the VOC emission rates and cancer and non-cancer risks by inhalation intake, using a municipal WWTP in China as an example, with respect to the effects of treatment technologies, VOC species, and seasonal variation. Given the treatment technology considered, the emission rates of VOCs in this study were estimated by means of mass balance or calculated on the molecular level. From the viewpoints of both emission rates and cancer and non-cancer risks, sedimentation was the treatment technology with the highest health risks to the workers. Slightly lower VOC emission rates and health risks than those for sedimentation were observed in anaerobic treatment. Although the aeration significantly enhanced the VOC emission rates in the aerobic treatment process, the associated health risks were limited due to the low VOC concentrations in the gas phase, which were likely attributed to the strong mixing and dilution with fresh air by aeration. Amongst the VOCs investigated, benzene was the VOC with both a relatively high emission rate and health risk, while trichloroethylene possessed a high emission rate but the lowest health risk. Without strong interfacial aeration and turbulence between the water and atmosphere, the effects of treatment technology and seasonal variation on the health risks might be connected to the VOC emission rates, while the effect of VOC species depended considerably on the respective cancer slope factors and reference concentrations; the employment of aeration provided a different conclusion in which the emission rates were enhanced without a significant increase in the related cancer risks. These findings can provide insight into future health risk management and reduction strategies for workers in WWTPs.     

Estimation of phosphorus flux in rivers during flooding

Reservoirs in Taiwan are inundated with nutrients that result in algal growth, and thus also reservoir eutrophication. Controlling the phosphorus load has always been the most crucial issue for maintaining reservoir water quality. Numerous agricultural activities, especially the production of tea in riparian areas, are conducted in watersheds in Taiwan. Nutrients from such activities, including phosphorus, are typically flushed into rivers during flooding, when over 90 % of the yearly total amount of phosphorous enters reservoirs. Excessive or enhanced soil erosion from rainstorms can dramatically increase the river sediment load and the amount of particulate phosphorus flushed into rivers. When flow rates are high, particulate phosphorus is the dominant form of phosphorus, but sediment and discharge measurements are difficult during flooding, which makes estimating phosphorus flux in rivers difficult. This study determines total amounts of phosphorus transport by measuring flood discharge and phosphorous levels during flooding. Changes in particulate phosphorus, dissolved phosphorus, and their adsorption behavior during a 24-h period are analyzed owing to the fact that the time for particulate phosphorus adsorption and desorption approaching equilibrium is about 16 h. Erosion of the reservoir watershed was caused by adsorption and desorption of suspended solids in the river, a process which can be summarily described using the Lagmuir isotherm. A method for estimating the phosphorus flux in the Daiyujay Creek during Typhoon Bilis in 2006 is presented in this study. Both sediment and phosphorus are affected by the drastic discharge during flooding. Water quality data were collected during two flood events, flood in June 9, 2006 and Typhoon Bilis, to show the concentrations of suspended solids and total phosphorus during floods are much higher than normal stages. Therefore, the drastic changes of total phosphorus, particulate phosphorus, and dissolved phosphorus in rivers during flooding should be monitored to evaluate the loading of phosphorus more precisely. The results show that monitoring and controlling phosphorus transport during flooding can help prevent the eutrophication of a reservoir.     

The concentrations, distribution and sources of PAHs in agricultural soils and vegetables from Shunde, Guangdong, China

The concentrations, distribution and sources of 16 polycyclic aromatic hydrocarbons (PAHs) were determined in 30 agricultural soil and 16 vegetable samples collected from subtropical Shunde area, an important manufacturing center in China. The total PAHs ranged from 33.7 to 350 μg/kg in soils, and 82 to 1,258 μg/kg in vegetables. The most abundant individual PAHs are phenanthrene, fluoranthene, chrysene, pyrene and benzo(b)fluoranthene for soil samples, and anthracene, naphthalene, phenanthrene, pyrene and chrysene for vegetable samples. Average vegetable–soil ratios of total PAHs were 2.20 for leafy vegetables and 1.27 for fruity vegetables. Total PAHs in vegetable samples are not significantly correlated to those in corresponding soil samples. Principal component analyses were conducted to distinguish samples on basis of their distribution in each town, soil type and vegetable specie. Relatively abundant soil PAHs were found in town Jun’an, Beijiao, Chencun, Lecong and Ronggui, while abundant vegetable PAHs were observed in town Jun’an, Lecong, Xingtan, Daliang and Chenchun. The highest level of total PAHs were found in vegetable soil, followed by pond sediment and “stacked soil” on pond banks. The PAHs contents in leafy vegetables are higher than those in fruity vegetables. Some PAH compound ratios suggest the PAHs derived from incomplete combustion of petroleum, coal and refuse from power generation and ceramic manufacturing, and paint spraying on furniture, as well as sewage irrigation from textile industries. Soil PAHs contents have significant logarithmic correlation with total organic carbon, which demonstrates the importance of soil organic matter as sorbent to prevent losses of PAHs.     

Characteristics of particulate matter pollution in the Pearl River Delta region, China: an observational-based analysis of two monitoring sites

Two-year monitoring data (2006 and 2009), collected at the sub-urban site (WQS) and the background site (TH), were used to study the characteristics of Particulate Matter (PM) pollution in the Pearl River Delta region, China. Similar levels of PM(2.5) concentration measured at both sites seem to confirm that the fine particles have emerged as a major regional pollution issue. The seasonal variation of PM(2.5) concentration is associated with the regional monsoon circulations while the diurnal variation is related to land-sea breeze, traffic emissions and boundary layer development. Negative correlation was found in PM(2.5)-wind speed and PM(2.5)-humidity. Analysis of radiation, temperature and ozone suggests the existence of secondary aerosol formation. Transport effect may be another contributing factor to high PM pollution in the region, such as occasional long-distance dust intrusion and trans-boundary effects from upwind areas.     

化学物质的土壤化学行为与环境污染研究展望

本文讨论了化学物质的土壤化学行为的研究趋向。认为重金属离子和多价含氧酸根在土壤中的主要化学过程是吸附和解吸、成络和解络以及沉淀和溶解。为了明确土壤对这些离子的缓冲能力和容量,以及进入食物链的数量和速率,当前则宜侧重于上述离子在土壤中的形态及其转化条件的研究。对于有机化学物质,土壤同时具有缓冲性和自净能力,展望趋势,则宜以有机化学物质在土壤中的降解历程包括降解速率和中间产物及其对作物-土壤-地下水系统的环境效应为主。     

生物法处理NOx废气的研究进展

氮氧化物 (NOx)是主要的大气污染物之一 ,是治理大气污染的一大难题。对当前国内外生物处理NOx 的研究现状进行了系统的论述 ,介绍了生物过滤法处理氮氧化物的基本原理 ,分析了生物过滤法处理氮氧化物存在的问题 ,并预测该技术的未来发展趋势     

长江流域土地资源情势及其发展战略对策

土地资源对国民经济和社会发展十分重要,在一些地区已成为制约因素。本文着重对长江流域土地资源情势进行分析,指出该流域的特点是:土地资源绝对量大,人均占有量少;土地资源态势优劣并存;土地资源形势喜忧相伴。同时提出如下几个战略对策:1.实行开源与节流并重的方针,走节约型农业发展道路;2.增加农业投资,改土治水,集约经营;3.统一规划,优势互补,联合协作,共同发展;4.完善土地法制建设,健全土地资源预测预报工作。     

我国人口增长方式的转变与可持续发展

本文探讨了人口增长的不同方式对可持续发展的影响,分析了我国可持续发展中存在的人口障碍,并提出建议以促进我国人口增长方式向有利于可持续发展方向转变。