Guanghui Guo

Current status and developing trends of the contents of heavy metals in sewage sludges in China

It is essential to determine the heavy metal concentrations in sewage sludge to select appropriate disposal methods. We conducted a national survey of heavy metal concentrations of sewage sludge samples from 107 municipal sewage treatment plants located in 48 cities covering the 31 provinces and autonomous regions, as well as Hong Kong, Macao and Taiwan by Xinjiang Production and Construction Corps in 2006, and identified the temporal trends of heavy metal contents in sewage sludge by comparison with surveys conducted in 1994–2001. In 2006, the average concentrations of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn in sewage sludge were 20.2, 1.97, 93.1, 218.8, 2.13, 48.7, 72.3, and 1058 mg·kg−1, respectively. Because of the decreased discharge of heavy metals into industrial wastewater in China and the increasingly stringent regulations governing the content of industrial wastes entering sewers, the average concentrations of Cd, Cr, Cu, Hg, Ni, Pb, and Zn have decreased by 32.3%, 49.7%, 54.9%, 25.0%, 37.2%, 44.8%, and 27.0%, respectively, during the past 12 years. The concentrations of Cd, Cr, Cu, Ni, and Zn in the samples exceeded the heavy metal limits of the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant in China (GB 18918-2002) by 6.5%, 3.7%, 6.5%, 6.5%, and 11.2%, respectively. From these results, 85 of the 107 municipal sludges analyzed would be considered suitable for land application.

New isotopic evidence of lead contamination in wheat grain from atmospheric fallout

Crops could accumulate trace metals by soil-root transfer and foliar uptake from atmospheric fallout, and an accurate assessment of pollution sources is a prerequisite for preventing heavy metal pollution in agricultural products. In this study, we examined Pb isotope rates to trace the sources of Pb in wheat grain grown in suburbs. Results showed that, even in zones with scarcely any air pollution spots, atmospheric fallout was still a considerable source of Pb accumulation in wheat. The concentration of Pb in wheat grain has poor correlation with that in farm soil. The Pb concentration in wheat grains with dust in bran coat was significantly higher than that in wheat grains, which indicates that Pb may accumulate by foliar uptake. The Pb isotope rate has obvious differences between the soil and atmospheric fallout, and scatter ratio is significantly closer between the wheat grain and atmospheric fallout. Atmospheric fallout is a more significant source of Pb concentration in wheat grains than in soil. As far as we know, this is the first study on the main sources of lead in grain crop (wheat) samples with isotope. This study aims to improve our understanding of the translocation of foliar-absorbed metals to nonexposed parts of plants.

Reduction in greenhouse gas emissions from sludge biodrying instead of heat drying combined with mono-incineration in China

ABSTRACT Sludge is an important source of greenhouse gas (GHG) emissions, both in the form of direct process emissions and as a result of indirect carbon-derived energy consumption during processing. In this study, the carbon budgets of two sludge disposal processes at two well-known sludge disposal sites in China (for biodrying and heat-drying pretreatments, both followed by mono-incineration) were quantified and compared. Total GHG emissions from heat drying combined with mono-incineration was 0.1731 tCO2e t−1, while 0.0882 tCO2e t−1 was emitted from biodrying combined with mono-incineration. Based on these findings, a significant reduction (approximately 50%) in total GHG emissions was obtained by biodrying instead of heat drying prior to sludge incineration. Implications: Sludge treatment results in direct and indirect greenhouse gas (GHG) emissions. Moisture reduction followed by incineration is commonly used to dispose of sludge in China; however, few studies have compared the effects of different drying pretreatment options on GHG emissions during such processes. Therefore, in this study, the carbon budgets of sludge incineration were analyzed and compared following different pretreatment drying technologies (biodrying and heat drying). The results indicate that biodrying combined with incineration generated approximately half of the GHG emissions compared to heat drying followed by incineration. Accordingly, biodrying may represent a more environment-friendly sludge pretreatment prior to incineration.

Comparing ordinary kriging and inverse distance weighting for soil as pollution in Beijing

Spatial interpolation method is the basis of soil heavy metal pollution assessment and remediation. The existing evaluation index for interpolation accuracy did not combine with actual situation. The selection of interpolation methods needs to be based on specific research purposes and research object characteristics. In this paper, As pollution in soils of Beijing was taken as an example. The prediction accuracy of ordinary kriging (OK) and inverse distance weighted (IDW) were evaluated based on the cross validation results and spatial distribution characteristics of influencing factors. The results showed that, under the condition of specific spatial correlation, the cross validation results of OK and IDW for every soil point and the prediction accuracy of spatial distribution trend are similar. But the prediction accuracy of OK for the maximum and minimum is less than IDW, while the number of high pollution areas identified by OK are less than IDW. It is difficult to identify the high pollution areas fully by OK, which shows that the smoothing effect of OK is obvious. In addition, with increasing of the spatial correlation of As concentration, the cross validation error of OK and IDW decreases, and the high pollution area identified by OK is approaching the result of IDW, which can identify the high pollution areas more comprehensively. However, because the semivariogram constructed by OK interpolation method is more subjective and requires larger number of soil samples, IDW is more suitable for spatial prediction of heavy metal pollution in soils.

Element Case Studies: Arsenic

Arsenic contaminated soil is a major issue in PR China. The discovery of an As hyperaccumulator fern, Pteris vittata opens a door for phytoextraction of As-contaminated soils. In situ phytoextraction projects using P. vittata have been established that achieved high removal rates of As. The first phytoextraction project in the world was established in Chenzhou, Hunan Province. Subsequently, more phytoextraction projects were established in Guangxi Zhuang Autonomous Region, Yunnan Province, Henan Province and Beijing. During these field-based projects, the safe disposal and re-utilization of P. vittata biomass were considered essential processes. Incineration technologies for P. vittata biomass are well developed. Safe landfilling has been applied for the disposal of the burned ash of P. vittata when the amount of that ash is small. When the ash amount is large, a recycling method has to be applied. Agromining of Ni has been successfully achieved, but agromining of As is at present only an idea, owing to the low commercial value of As. Nevertheless, production of a biofuel resulting from the incineration process, together with the recycling of As, could be a potential opportunity for agromining of this metalloid.

Development of a model to simulate soil heavy metals lateral migration quantity based on SWAT in Huanjiang watershed, China

Lateral transportation of soil heavy metals in rainfall events could significantly increase the scope of pollution. Therefore, it is necessary to develop a model with high accuracy to simulate the migration quantity of heavy metals. A model for heavy metal migration simulation was developed based on the SWAT (Soil and Water Assessment Tool) model. This model took into consideration the influence of soil pH value, soil particle size, runoff volume, sediment amount, concentration of water-soluble heavy metals dissolved in runoff and insoluble absorbed to the soil particles. This model was reasonable in Huanjiang watershed, Guangxi Zhuang Autonomous Region, south China, covering an area of 273 km2. The optimal drainage area threshold was determined by analyzing the effects of watershed subdivision on the simulation results to ensure the simulation accuracy. The main conclusions of this paper were: (1) watershed subdivision could affect simulation migration quantity of heavy metals; (2) the quantity of heavy metals transported by sediment accounted for 97%-99% of the total migration quantity in the study watershed. Therefore, sediment played the most important role in heavy metal migration; (3) the optimal drainage area threshold percentage to ensure high simulation accuracy was determined to be 2.01% of the total watershed; (4) with the optimal threshold percentage, this model could simulate the migration quantity of As, Pb and Cd accurately at the total watershed and sub-watershed level. The results of this paper were useful for identifying the key regions with heavy metal migration.

Assessments of contamination and human health risks of heavy metals in the road dust from a mining county in Guangxi, China

ABSTRACT A total of 32 road dust samples were collected from mining areas and a control area in Nandan County, Guangxi, in order to investigate the contamination characteristics of heavy metals and associated health risks to local residents. The results indicated that elevated concentrations of As, Cd, Cu, Pb, Sb, and Zn were found in road dust in mining areas compared with control areas and background values. Pearsons correlation analysis and principal component analysis indicated that As, Cd, Cu, Pb, Sb, and Zn in road dust mainly originated from anthropogenic sources (e.g., vehicles emission, mining activities, and smelting activities), whereas Cr, Co, and Ni were associated with natural sources (e.g., soil weathering). Furthermore, noncarcinogenic hazards to both adults and children were found in mining areas, while noncarcinogenic health risks in the control area were negligible. The health hazard was mostly ascribed to the ingestion, followed by the dermal contact, and the inhalation. The cancer risks from As, Cd, Co, Cr, and Ni in all studied areas were within safe levels as the R values were below the threshold of 1 × 10−6.

Rare earth elements (REEs) in PM10 and associated health risk from the polymetallic mining region of Nandan County, China

ABSTRACT A total of 26 samples were collected from Dachang, Chehe and Liuzhai in Nandan County, China, in order to investigate the concentrations of rare earth elements (REEs) and associated health risk in particulate matter. The concentrations of REEs in Dachang (23.54 ng/m3), Chehe (20.29 ng/m3) were significantly higher than those in Liuzhai (8.1 ng/m3). The light rare earth elements (LREEs) account for 87.08%, 87.09%, and 86.17% of the total REE burden in PM10 at Dachang, Chehe, and Liuzhai, respectively, indicating that the distribution pattern of REEs in PM10 was characterized by the obvious fractionation of LREEs. Enrichment factor calculation indicated that EFs for La, Ce, Nd, Pr, and Nd in PM10 from Dachang and Chehe were greater than 2, indicating moderate enrichment. Source identification indicated that REEs in PM10 from Dacheng and Chehe originated from anthropogenic activities such as mining and smelting activities, while REEs in PM10 from Liuzhai were associated with natural sources, like soil erosion. Noncarcinogenic and carcinogenic risks associated with the exposure of REEs in PM10 were negligible based on the health risk assessment models. However, greater noncarcinogenic risk for children was found in studied areas compared with the adults.

Comparison among Soil Additives for Enhancing the Pteris vittata L.: Phytoremediation of As-contaminated Soil

Abstract Pot experiments were conducted to assess the effects of monoammonium phosphate (NH4H2PO4) and citric acid (CA) on the arsenic uptake of Chinese brake fern (Pteris vittata L. in two typical arsenic-contaminated soils i.e. fluvo-aquic and brown) from Jiyuan (JY) City and Baoding (BD) City in Northern China. NH4H2PO4 improved the biomass of P. vittata, whereas CA exerted no significant influence. NH4H2PO4 and CA both increased the arsenic uptake of P. vittata by 6.08 and 2.72 times, respectively, in fluvo-aquic soil and 4.20 and 2.52 times, respectively, in brown soil. Moreover, CA, but not NH4H2PO4, promoted the transfer of arsenic from the root to the frond. NH4H2PO4 and CA increased Olsens arsenic contents in the soils and promoted the transformation of residual arsenic and crystalline Fe/Al oxide-bound arsenic to nonspecifically and specifically sorbed arsenic. This study proved that P. vittata can be used in Northern China. Applying NH4H2PO4 and CA can enhance the effectiveness of P. vittata in the phytoremediation of arsenic-contaminated soils.