Environmental and Potential Health Effects of Growing Leafy Vegetables on Soil Irrigated Using Sewage Sludge and Effluent: A Case of Zn and Cu

Abstract

The use of sewage sludge and effluent as a source of nutrients and water for crop production is increasing worldwide. A study was conducted in 2001 at Pension farm (near Harare) to determine the effect of long term (>30 yrs) application of sewage sludge and effluent on Zn and Cu accumulation in top soil, uptake of these metals by lettuce (Lactuca sativa L.) and mustard rape (Brassica juncea L.), and dry matter yield. Application of sewage sludge/effluent significantly (p < 0.001) increased total Zn (13.7–1563.9 mg kg^?1) and Cu (2.5–133.3 mg kg^?1) in the top soil (0–20 cm depth) compared to the control. Sewage sludge/effluent addition significantly (p < 0.001) increased Zn uptake by both test crops, while Cu uptake was significant in the first crop of lettuce and the second crop of mustard rape. Based on the dietary patterns of poor urban households in Zimbabwe, the maximum possible intake of Cu will only constitute 40% the Maximum Daily Intake (MDI). The toxicological implications for Zn will however be more severe, exceeding the MDI by 77% through exposure by lettuce consumption and by 251% consumption of mustard rape. It was concluded that long-term addition of sewage sludge/effluent to soil at Pension farm had increased the concentration of Zn and Cu in top soil to levels that pose environmental concern. The consumption of leafy vegetables produced on these soils pose a health risk to poor communities that reside around the study site, especially children, through possible Zn toxicity.     

Influence of sewage culvert cover plate thickness on dynamic response and damage of the cover plate under gas explosion

In order to address the risk of combustible gas explosions in sewage culverts, a numerical model was established using ANSYS/LS-DYNA software. The model consisted of a culvert and a cover plate, and was used to study the effect of cover plate thickness (ranging from 0.08 m to 0.12 m) on the dynamic response and damage of the structure under explosive loads. The results indicated that, during the loading negative pressure stage, the equivalent stress peak value of the central monitoring unit of the cover plate first increased and then decreased with increasing cover plate thickness. Additionally, the maximum principal stress peak value first decreased and then increased, while the maximum shear stress peak value first increased and then decreased. During the loading positive pressure stage, the maximum principal strain peak value of the monitoring unit decreased overall with increasing cover plate thickness. However, the equivalent plastic strain peak value initially increased and then decreased gradually. The equivalent strain indicated that plastic damage occurred in the cover plate. Beyond a thickness of 0.11 m, increasing the cover thickness did not appear to enhance its resistance to plastic damage. The damage analysis revealed that as cover plate thickness increased, the peak displacement and velocity of the monitoring unit continued to decrease, while the overall stability and explosive resistance of the cover plate increased. Additionally, the number of damaged fragments decreased. However, once the cover plate thickness reached 0.11 m, the bonding performance of the reinforced concrete structure had been fully developed, increasing the thickness of the cover plate no longer had a significant impact on the explosive resistance of the cover plate.     

Nonylphenol in the environment: a critical review on occurrence, fate, toxicity and treatment in wastewaters

Nonylphenol is a toxic xenobiotic compound classified as an endocrine disrupter capable of interfering with the hormonal system of numerous organisms. It originates principally from the degradation of nonylphenol ethoxylates which are widely used as industrial surfactants. Nonylphenol ethoxylates reach sewage treatment works in substantial quantities where they biodegrade into several by-products including nonylphenol. Due to its physical-chemical characteristics, such as low solubility and high hydrophobicity, nonylphenol accumulates in environmental compartments that are characterised by high organic content, typically sewage sludge and river sediments, where it persists. The occurrence of nonylphenol in the environment is clearly correlated with anthropogenic activities such as wastewater treatment, landfilling and sewage sludge recycling. Nonylphenol is found often in matrices such as sewage sludge, effluents from sewage treatment works, river water and sediments, soil and groundwater. The impacts of nonylphenol in the environment include feminization of aquatic organisms, decrease in male fertility and the survival of juveniles at concentrations as low as 8.2 mug/l. Due to the harmful effects of the degradation products of nonylphenol ethoxylates in the environment, the use and production of such compounds have been banned in EU countries and strictly monitored in many other countries such as Canada and Japan. Although it has been shown that the concentration of nonylphenol in the environment is decreasing, it is still found at concentrations of 4.1 mug/l in river waters and 1 mg/kg in sediments. Nonylphenol has been referred to in the list of priority substances in the Water Frame Directive and in the 3rd draft Working Document on Sludge of the EU. Consequently there is currently a concern within some industries about the possibility of future regulations that may impose the removal of trace contaminants from contaminated effluents. The significance of upgrading sewage treatment works with advanced treatment technologies for removal of trace contaminants is discussed.     

Watershed factors affecting stream acidification in the White Mountains of New Hampshire,USA

The streams tributary to acidic Cone Pond, pH 4.5–4.8, and circumneutral Black Pond, pH 5.3–6.4, in the White Mountains of New Hampshire, USA, were monitored for a year. The watersheds of these two ponds were characterized in terms of geology and stream hydrology. Chemical gradients and patterns in rock weathering and groundwater discharge explain many of the differences in mineral content and acidity of the streams. The rocks of Black watershed produced an average of ten times the equivalent of basic cations as rocks from Cone watershed. This is on the same order as the difference in acidity of the two streams. Down-stream changes in stream chemistry follow differing patterns, but reflect the same principle of residence time and water path length controlling chemical evolution of streamwater. Watershed and aquatic managers may use these parameters in an inexpensive and simple assessment of the susceptibility of individual streams and ponds to acidification. A method is recommended to determine quickly the potential influence of bedrock type to aquatic chemistry.     

Reusability of sewage sludge in clay bricks

Bricks produced from sewage sludge in different compositions were investigated. Results of the tests indicated that the sludge proportion is a key factor in determining the brick quality. Increasing the sludge content results in a decrease in brick shrinkage, bulk density, and compressive strength. Brick weight loss on ignition was mainly due to the contribution of the contained organic matter from the sludge being burnt off during the firing process, as well as inorganic substances found in both clay and sludge. The physical, mechanical, and chemical properties of the bricks that were supplemented with various proportions of dried sludge from 10 to 40wt% and generally complied with the General Specification for Brick as per the Malaysian Standard MS 7.6:1972, which dictates the requirements for clay bricks used in walling in general. A standard leaching test method also showed that the leaching of metals from the bricks is very low.     

城市污水污泥堆肥化技术的研究进展

本文介绍了堆肥化技术发展的历史，以及国内外污泥堆肥化技术的研究进展，并介绍了国内的生产实例，可供大家初步了解污泥堆肥化技术。     

基于农村生活污水生态处理工艺研究

伴随我国经济发展的进步,虽然农村的生活水平得到一定的改善,但是并没有根据实际情况将相关生态处理技术应用,导致农村污水处理的效率无法有效的提升,严重影响农村的发展。基于此,本文主要分析了农村生活污水处理的方式,以及污水处理不当对人们的危害与影响,并阐述了农村污水处理的主要对策与方案,笔者根据自身经验提出相应的建议与意见。     

厌氧降解两种苯二甲酸酯的试验研究

以邻苯二甲酸二[2-乙基己]酯(DEHP)和邻苯二甲酸二丁酯(DBP)为研究对象,以废水污泥和填埋场沥出液为接种物,在严格厌氧环境下,进行了苯二甲酸酯生物降解的研究试验。结果表明,DBP有较好的可降解性,去除率大于95％;而DEHP在填埋场沥出液培养样中去除率小于30％;但当接种物为消化污泥时,DEHP的去除率为89．7％。产甲烷的微生物群在邻苯二甲酸二酯的降解过程中起着非常重要的作用。     

PCDDs and PCDFs in sewage sludges from two wastewater treatment plants in Beijing, China

The levels of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) were analyzed by an isotope-dilution high-resolution mass spectrometric in 16 sewage sludges, sampled from 2004 to 2009, from two municipal wastewater treatment plants (WWTPs) in Beijing. Total toxicity equivalent (TEQ) values were evaluated using the toxicity equivalent factors proposed by International for PCDD/Fs. The I-TEQs for these sewage sludges were from 0.97 to 15.0 pg g⁻¹ dry weight (dw) with a mean value 4.43 pg g⁻¹ dw, indicating that all I-TEQs were below Chinese legislation limit value regulated for agricultural use in soils.The results from limited samples (16 samples) showed that the levels of PCDD/Fs might be correlated with the sludge age. Meanwhile, the temporal trends of PCD/Fs suggested that the I-TEQs may correlate with rainfall in the present study.     

某动车段污水处理调试方案设计

采用"MBBR+高效沉淀池"的工艺流程,对动车段内的生活污水和集便污水进行处理.为获得系统最佳运行参数,制定调试方案,分别进行单机调试、单元调试和系统调试,以生化池的单元调试为重点.通过工程的实施,为今后生活污水+集便污水处理工艺调试提供参考.