Co-cropping for phyto-separation of zinc and potassium from sewage sludge

The use of sewage sludge as a fertilizer and soil amendment has resulted in high concentrations of heavy metals in the soil limiting its use. The present study was carried out to find the possibility of phyto-separating toxic and beneficial elements from the sludge using suitable plants. Of the five plants tested the hyperaccumulator Sedum alfredii H achieved the greatest removal of Zn, while shoots of Alocasia marorrhiza accumulated high content of K. Co-cropping these two plants on the sludge verified the previous observations on A. marorrhiza and the shoots of this plant could accumulate more than 120 g K kg(-1) dry matter in the median growth stage. Zn hyperaccumulated in Sedum's shoots to an extent more than 10 g kg(-1) dry matter; K concentrated five to ten times in the Alocasia's shoots which could be used as a good organic-K-fertilizer. Hence, the two elements were simultaneously phytoseparated and could be recycled. Furthermore, cultivation of plants in the sludge resulted in significant decreases in total Zn but kept the favorable agronomic characteristics of the sludge material, such as pH, organic matter content, and NPK concentrations and ameliorated its biological stability. These results suggest that simultaneous phyto-separation of toxic and beneficial elements from sewage sludge are possible by co-cropping using specific plants without the input of any chemicals.     

Occurrence of organic contaminants in sewage sludges from eleven wastewater treatment plants, China

This study presents the occurrence of 43 semi-volatile organic compounds (SVOCs) listed as priority pollutants by both China and the United States Environmental Protection Agency, in sewage sludges collected from eleven wastewater treatment plants (WWTPs) of mainland and Hong Kong, China. Thirty-six SVOCs were detected by gas chromatography coupled with mass spectrometer (GC-MS) and at least 14 in each sample. The most abundant compounds were phthalic acid esters (PAEs) and polycyclic aromatic hydrocarbons (PAHs) with total concentrations ranging from 10 to 114mgkg(-1) dry weight (d.w.) (with a mean of 30mgkg(-1) d.w.) and from 1.4 to 33mgkg(-1)d.w. (with a mean of 16mgkg(-1) d.w.), respectively, followed by chlorobenzenes, nitroaromatics, haloethers and halogenated hydrocarbons which occurred generally at concentrations lower than 10mgkg(-1) d.w. Large variations were observed between the concentrations of individual compounds as well as their total concentrations in sludge samples from different WWTPs. The highest values of sum concentration of 16 PAHs and of 6 PAEs were found in sewage sludge from Beijing. The mean total concentration of each class of SVOCs in sewage sludge from mainland was remarkably higher than that from Hong Kong. The concentrations of di(2-ethylhexyl) phthalate in 91% sludge samples met the limit (100mgkg(-1)d.w.) proposed by the Europe Union for land application, whereas the PAH concentrations of 64% sludge samples exceeded the maximum permissible concentration (6.0mgkg(-1)d.w.). The occurrence of SVOCs in this study are compared with other studies and their sources are discussed.     

邻苯二甲酸二丁酯在不同品种菜心-土壤系统的累积

在邻苯二甲酸二丁酯(DBP)污染的水稻土中盆栽不同品种菜心,采用GC/MS研究了菜心-土壤系统中DBP的分布特征.结果表明,不同品种菜心茎叶和根系对DBP的吸收累积存在明显差异;不同品种菜心茎叶中DBP含量与其叶面积大小之间存在一定的正相关关系.不同品种菜心-土壤系统中DBP的分布特征明显不同,新选45天油菜心表现为茎叶和根系中DBP含量较低,盆栽后土壤中DBP含量也较低;特青60天菜心和新选油青四九菜心表现为茎叶和根系中DBP含量较低,但盆栽后土壤中DBP含量较高;油青60天菜心表现为茎叶和根系中DBP含量较高,盆栽后土壤中DBP含量也较高.     

Plants grown on sewage sludge in South China and its relevance to sludge stabilization and metal removal

The production of sewage sludge in China has been increasing sharply in order to treat 40% of the municipal sewage in 2005 as planned by central government. The main sludge disposal method is landfill owing to heavy metal contamination, but it presents an attractive potential for agricultural land application. Experiments were carried out to study the simultaneous metal removal and sludge stabilization byplants. The sludge samples were collected from Datansha Wastewater Treatment Plant of Guangzhou, it contained excessive Cu and Zn comparedwith the Chinese National Standard for Agricultural Use of Sewage Sludge. Plants growing on sludge beds were investigated to follow their growthand metal uptake. 30 sludge plants were identified during 1 year‘s observation. A Zn high-accumulating and high growth rate plant( A/ocas/amacrorrhiza) was selected and grown on sludge beds in plots. The water, organic matter, heavy metals and nutrients contents, the E. colinumber and the cress seed germination index were monitored for the slu,ge samples collected monthly. The plant growth pparameters and its heavy metals contents were also determined. The sewage sludge treated by plants could be stabilized at about 5 months, the E. coli numberwas significantly decreased and the cress seed germination index attained 100%. Crop on sludge could ameliorate the sludge drying. Theexperiments are continuing to find out the appropriate plant combination for simultaneous sludge stabilization and metal removal for an acceptableperiod. Comparisons between the proposed processes and other methods for treating produced sludge such as composting, chemical and bacterial.     

Combining potassium chloride leaching with vertical electrokinetics to remediate cadmium-contaminated soils

This study evaluated the feasibility of combining potassium chloride (KCl) leaching and electrokinetic (EK) treatment for the remediation of cadmium (Cd) and other metals from contaminated soils. KCl leaching was compared at three concentrations (0.2%, 0.5%, and 1% KCl). EK treatment was conducted separately to migrate the metals in the topsoil to the subsoil. The combined approach using KCl leaching before or after EK treatment was compared. For the single vertical EK treatment, the removal of Cd, lead (Pb), copper (Cu) and zinc (Zn) from the topsoil (0–20 cm) was 9.38%, 4.80%, 0.95%, and 10.81%, respectively. KCl leaching at 1% KCl removed 84.06% Cd, 9.95% Pb, 4.34% Cu, and 19.93% Zn from the topsoil, with higher removal efficiency than that of the 0.2% and 0.5% KCl leaching treatments. By combining the KCl leaching and EK treatment, the removal efficiency of heavy metals improved, in particular for the 1% KCl + EK treatment, where the removal rate of Cd, Pb, Cu, and Zn from the upper surface soil reached 97.79%, 17.69%, 14.37%, and 41.96%, respectively. Correspondingly, the soil Cd content decreased from 4 to 0.21 mg/kg, and was below the Chinese standard limit of 0.3 mg/kg soil. These results indicate that 1% KCl + EK treatment is a good combination technique to mitigate Cd pollution from contaminated soils used for growing rice and leafy vegetables.

     

Occurrence and assessment of polycyclic aromatic hydrocarbons in soils from vegetable fields of the Pearl River Delta, South China

Surface soil (0-20 cm) samples from nine representative vegetable fields located in Guangzhou, Shenzhen, Zengcheng and Huadu within the Pearl River Delta, South China were collected and analyzed for 16 USEPA priority polycyclic aromatic hydrocarbons (PAHs) using gas chromatography coupled to mass spectrometry (GC-MS). Total concentrations of 16 PAHs (Sigma(PAHs)) ranged from 160 to 3700 microg kg(-1). Large variations were observed also between concentrations of individual PAHs from different vegetable fields and within the site as well. Acenapthylene, benzo[b]fluoranthene, fluoranthene, benzo[a]pyrene and benzo[k]fluoranthene were consistently the most prevalent individual PAHs. The values of PAH isomer ratios [anthracene/(anthracene+phenanthrene) and fluoranthene/(fluoranthene+pyrene)] indicate that combustion processes are the major sources of PAHs. Concentrations of PAHs were poorly correlated with organic carbon concentrations of soils, suggesting different sources and also indicating that the PAH pollution of this area is recent. The same outcome is confirmed by the predominance of PAHs with fewer rings (相似文献   

土壤改良剂联合间套种技术修复重金属污染土壤:田间试验

在田间条件下,验证通过盆栽试验初步筛选出的几种改良剂在玉米和东南景天间套种修复重金属污染土壤的大田实际应用效果.研究结果表明,施用改良剂蘑菇渣肥、云母和沸石能有效降低玉米籽粒和茎叶中的Cd和Pb,玉米籽粒Cd和Pb含量均达到食用标准.蘑菇渣肥显著增加了东南景天对Cd的提取量,腐植酸显著促进了东南景天对Pb的吸收,因此,蘑菇渣和腐植酸可以应用于玉米和东南景天套种系统.施用云母和沸石可以显著提高土壤pH值,降低土壤可交换态Cd/Pb含量,从而降低二种植物对Cd/Pb的吸收;然而,施用蘑菇渣肥和腐植酸却增加土壤可交换/吸附态Cd/Pb含量.植物根系吸收Cd的稳定常数显示该有机吸附态Cd难于被玉米根系吸收.