Sediment pollution characteristics and in situ control in a deep drinking water reservoir

Sediment pollution characteristics, in situ sediment release potential, and in situ inhibition of sediment release were investigated in a drinking water reservoir. Results showed that organic carbon（OC）, total nitrogen（TN）, and total phosphorus（TP） in sediments increased from the reservoir mouth to the main reservoir. Fraction analysis indicated that nitrogen in ion exchangeable form and Na OH-extractable P（Fe/Al-P） accounted for 43% and 26% of TN and TP in sediments of the main reservoir. The Risk Assessment Code for metal elements showed that Fe and Mn posed high to very high risk. The results of the in situ reactor experiment in the main reservoir showed the same trends as those observed in the natural state of the reservoir in 2011 and 2012; the maximum concentrations of total OC, TN, TP, Fe,and Mn reached 4.42 mg/L, 3.33 mg/L, 0.22 mg/L, 2.56 mg/L, and 0.61 mg/L, respectively. An in situ sediment release inhibition technology, the water-lifting aerator, was utilized in the reservoir. The results of operating the water-lifting aerator indicated that sediment release was successfully inhibited and that OC, TN, TP, Fe, and Mn in surface sediment could be reduced by 13.25%, 15.23%, 14.10%, 5.32%, and 3.94%, respectively.

Fractionation of heavy metals in shallow marine sediments from Jinzhou Bay,China

This work investigated the distribution and speciation of Cd, Cu, Pb, Fe and Mn in the shallow sediments of Jinzhou Bay, Northeast China, which has been heavily contaminated by nonferrous smelting activities. The concentrations of Cd, Cu and Pb in sediments were found to be 100, 13 and 7 times, respectively, being higher than the national guideline （GB 18668-2002）. Sequential extraction test showed that 39%-61% of Cd were exchangeable fractions, indicating that Cd in the sediments posed a high risk to local environments. While Cu and Pb were at moderate risk levels. According to the relationships between percentage of metal speciation and total metal concentration, it was concluded that the distributions of Cd, Cu and Pb in some geochemical fractions were dynamic in the process of pollutants migration and the stability of metals in sediments of Jinzhou Bay decreased in the order of Pb 〉 Cu 〉 Cd.

Relationship of Morpho-Sedimentological Variations to the Fate of Hg-and Zn-Polluted Sediments in the Contaminated Site of Porto Marghera,Lagoon of Venice,Italy

New data collected from twenty-six sites during 2008 inthe contaminated Site of National Interest (SIN) of Porto Marghera within the Lagoon of Venice (Italy), which has been affected by the presence of an industrial zone for the last 80 years, were compared with data from a campaign performed in the same site 30 years before (1976-1978). The SIN was found to be heavily polluted in the earlier study, and several tons of Hg and Zn are still stored in soils and industrial channel sediments, potentially affecting the lagoon part of the SIN. Bathymetric variations, grain-size, Hg and Zn content in sediments were analysed. The severe contamination of the late 1970s (Hg 1.7 μg/g;Zn 754 μg/g) had fallen by the late 2000s (Hg 0.9 μg/g;Zn 225 μg/g). The fall in Hg and Zn contamination over the 30-year period was mainly linked to the patterns of geomorphological change inside the SIN that affected two distinct sub-areas: 1) a stable-depositional (SD) area in the Northern part, which exerted a “dilution” effect on contaminants, with significant deposition (~11%) of coarse-grained sediments (63 - 8 μm), and 2) an area characterised by moderate-to-severe-erosion (MSE) to the South, which saw the loss (~13%) of pollutant-bearing fine-grained sediments (sion if hydrodynamic conditions change in the future. This study provides useful support to decision-making systems by helping to select hot-spots for remediation measures.

Clean-up and disposal process of polluted sediments from urban rivers

In this paper, the discussion is concentrated on the properties of the polluted sediments and the combination of clean-up and disposal process for the upper layer heavily polluted sediments with good flowability. Based on the systematic analyses of various clean-up processes, a suitable engineering process has been evaluated and recommended. The process has been applied to the river reclamation in Yangpu District of Shanghai City, China. An improved centrifuge is used for dewatering the dredged sludge, which plays an important role in the combination of clean-up and disposal process. The assessment of the engineering process shows its environmental and technical economy feasibility, which is much better than that of traditional dredging-disposal processes.

Dynamic release process of pollutants during suspended sediment transport in aquatic system

Pollutants release is highly consistent with suspended sediment concentration （SSC） in water column, especially during re-suspension and transport events. The present research focuses on pollutant dynamic release from re-suspended sediment, especially the vertical distribution relationship between them. The sediment erosion experiments on a series of uniform flow are conducted in a circulate flume. Reactive tracer （phosphorus） is used as the contaminant in fine-grained sediments to identify the release characteristic length and time. Experimental results show that the flow condition near-bed depends on the sediment surface roughness. The region with high turbulent intensities corresponds to a high concentration sediment layer. In addition, the SSC decreases with the distance, water depth, and particle grain size. The sediment in a smaller grain size takes much more time to reach equilibrium concentration. Total phosphorus （TP） concentration changes along the water depth as SSC in the initial re-suspension stage, appearing in two obvious concentration regimes： the upper low-concentration layer and the high-concentration near-bottom layer. This layered phenomenon remains for about 3 hours until SSC distri- bution tends to be uniform. Longitudinal desorption plays an important role in long-way transport to reduce the amount of suspended sediment in water column.

Interaction effect of micro-and macro-organic on the biogeochemical function of the sediment and aquatic interface

Constructed stormwater infiltration basins have been broad applied in urban areas in terms of stormwater disposal and compensation of reduced groundwater recharge. However, stormwater derived from sediments accumulating in infiltration beds may act as a source of dissolved contaminants for groundwater. Concentrations of DO, NO3-N, NO2^--N, NH4^＋-N and PO4^3--P were monitored at multiple depth with time. The results showed that the occurrence of denitrificarion was restrained by sediments in term of no invertebrates. Under the conditions of invertebrates inoculated, the concentrations of DO, NO^3--N, NO2^＋-N, NH4^＋-N and PO4^3＋-P varied respectively with time and the occurrence of nitrification and mobilizing nitrate in the sediment. It is concluded that there exist the invertebrate activities such as building tubes and galleries and excreting faecal pellet which may increase water dispersion and enhance accessibility of nutrient, and stimulate microbial process effected in the sediment. Besides, the natural death and rot of worms were also found to be important factors of the invertebrate activities.

Sedimentation in the Submarine Outfall and in the Mixing Zones （Avoiding, Diagnosis and Remediation）

Some practical design tips and important recommendations are given to minimize the negative effect of discharge of wastewater laden with solid particles via submarine outfall. This study emphasizes the role of respecting the hydraulic conditions in the outfall to prevent sedimentation in the outfall or their accumulation in adjacent areas; also it includes the ways used to improve the outfall hydraulic capacity that decreases with time. The diagnostics and remediation procedures of mixing zones are discussed, especially in the case of previous toxic discharge that results in toxic sediments at the bed load. A literature review of techniques used to assess sediment quality near discharge points and locate effluent-affected sediment deposit is presented that include using acoustic profiles and images, chemical analysis, toxicity tests and multivariate indicators.

Risk Assessment of Heavy Metal Pollution in Sediments of the Fenghe River by the Fuzzy Synthetic Evaluation Model and Multivariate Statistical Methods

Concentrations of heavy metals in 74 sediment samples from the Fenghe River, which originates from the north of the Qinling Mountains and flows through Xi'an, Shaanxi Province, China, were characterized by employing geographic information system(GIS)mapping, fuzzy synthetic assessment, and multivariate statistical analysis to determine the enrichment characteristics of heavy metals as well as their potential risks of pollution to sediments. Al, Cd, and Co were the major pollutants, with a high enrichment factor(EF) value. Heavy metal concentrations from samples near the paper plant were maintained at a high level. Significant enrichment of Al, Ba, Cr, Ni, Pb, and Co was found in the midstream and downstream, while high concentration of Cu occurred in the headwater stream. Based on the cluster and principal component analyses, sediment metals mainly came from the paper plants, agronomic practices, natural sources, and tourism, with a contribution of 51.59%, 23.01%, 14.21%, and 9.88%, respectively. Sediment pollution assessment explored using fuzzy theory based on the entropy method and toxicity coefficient showed that 26, 32, and 11 sites fell into Class III(slightly polluted), Class IV(moderately polluted), and Class V(heavily polluted), respectively, and their scores of membership degree in the polluted level were on the rise, suggesting a relatively high degree of sediment metal pollution in the study area. Closely related to the excessive industrial and agricultural applications, metal pollution in sediment is necessary to be addressed in the Fenghe River.

Effects of sediment physical properties on the phosphorus release in aquatic environment

Particle size, porosity, and the initial phosphorus concentration in sediments are the main factors affecting phosphorus release flux through the sediment-water interface. Sediments can be physically divided to muddy and sandy matters, and the adsorption-desorption capacity of sediment with phosphorus depends on particle size. According to phosphorus adsorption-desorption experiments, phosphorus sorption capacity of the sediment decreases with the increase of particle dimension. But among the size-similar particles, sediment with a bigger particle size has the larger initial phosphorus release rate. In terms of muddy and sandy sediments, there are inversely proportional relationships between the release rate and the flux. Due to the contact of surface sediment and the overlying water, the release flux from the sediment is either from direct desorption of surface sediment layer or from the diffusion of pore water in the sediment layer, which is mainly determined by sediment particle size and porosity. Generally, static phosphorus release process may include two stages: the first is the initial release. As for coarse particles, phosphorus is desorbed from surface sediment. And for fine particles, phosphorus concentration in water often decreases, mainly from pore water by the molecular diffusion. During the second stage, pore water flows faster in coarse sediment, and phosphorus is easy to desorb from the surface of the particles as diffusion dominates. For the smaller liquid-solid ratio of fine particles and the larger amount of phosphorus adsorption, the release flux from pore water due to diffusion is very small with longer sorption duration.

Rapid control of black and odorous substances from heavilypolluted sediment by oxidation:Efficiency and effects

The control ofblack and odorous substances in sediments is of crucial importance to improve the urban ecological landscape and to restore water environments accordingly.In this study,chemical oxidation by the oxidants NaClO,H2O2,and KMnO4 was proposed to achieve rapid control of black and odorous substances in heavily-polluted sediments.Results indicate that NaClO and KMnO4 are effective at removing Fe(II)and acid volatile sulfides.The removal efficiencies of Fe(II)and AVS were determined to be 45.2%,94.1%,and 93.7%,89.5%after 24-h exposure to NaClO and KMnO4 at 0.2 mmol/g,respectively.Additionally,rapid oxidation might accelerate the release of pollutants from sediment.The release of organic matters and phosphorus with the maximum ratios of 22.1%and 51.2%was observed upon NaClO oxidation at 0.4 mmol/g.Moreover,the introduction of oxidants contributed to changes in the microbial community composition in sediment.After oxidation by NaClO and KMnO4 at 0.4 mmol/g,the Shannon index decreased from 6.72 to 5.19 and 4.95,whereas the OTU numbers decreased from 2904 to 1677 and 1553,respectively.Comparatively,H2O2 showed a lower effect on the removal of black and odorous substances,pollutant release,and changes in sediment microorganisms.This study illustrates the effects of oxidant addition on the characteristics of heavily polluted sediments and shows that chemical oxidants may be an option to achieve rapid control of black and odorous substances prior to remediation of water environments.

Distribution and assessment of heavy metals in the surface sediment of Yellow River, China

Large amounts of heavy metals discharged by industrial cities that are located along the middle reach of Yellow River, China have detrimental impacts on both the ecological environment and human health. In this study, fourteen surface sediment samples were taken in the middle reach of the Yellow River. Contents of Zn, Pb, Ni, Cu, Cr, Cd, As were measured, and the pollution status was assessed using three widely used pollution assessment methods, including the single factor index method, Nemerow pollution index method and potential ecological risk index. The concentrations of the studied heavy metals followed the order： Zn 〉 Cr 〉 Cu 〉 Ni 〉 Pb 〉 As 〉 Cd. Nearly 50% of sites had Cu and Cr accumulation. The concentration of Cu at the Yiluo River exceeded the secondary standard value of the Environmental quality standard for soils. Comparison of heavy metal concentrations between this study and other selected rivers indicated that Cu and Cr may be the major pollutants in our case. The single factor index indicated that many samples were at high levels of pollution for Cu and Cd; the Nemerow pollution index indicated that the Yihe River, Luohe River, Yiluo River and Huayuankou were polluted. According to the results of potential ecological risk assessment, Cd in the tributaries of Luo River, Yihe River,and Yiluo River showed high risk toward the ecosystem and human health, Cd in Huanyuankou and Cu in Yiluo River showed a middle level of risk and other samples were at a low level of risk.

STUDY ON THE EFFECT OF SEDIMENT MOTION ON TRANSPORT TRANSFORMATION OF HEAVY METAL POLLUTANTS

By combining laboratorial experiments,theoretical analysis and mathematical model,theeffect of sediment motion on transport-transformation of heavy-metal pollutants is studied. (1)Previous studies on adsorption-desorption of heavy-metal pollutants by sedimentparticles are systematically summarized.Based on this summary,subjects that need to be furtherstudied are put forward. In rivers most heavy-metal pollutants concentrate on sediment particles.In order tocontrolling water pollution aused by heavy-metal pollutants following topics should beemphasized:studies on the effect of suspended matter and deposit on transport-transformation of