Cadmium adsorption by oxic sediment

To understand the strong pH dependency of cadmium adsorption by oxic sediment, we investigated the surface charge of sediment particles by potentiometric titration with acid and base. Metal adsorbed by sediment can occur by complexation of metal ions with weakly acidic functional groups or by ion exchange of metal ions. A multi-site binding model, which incorporates the effect of pH, has been applied to describe the adsorption of cadmium onto sediment. The model has been used to satisfactorily predict the extent of adsorption over the pH range of 4.5–7.0.     

Cadmium adsorption in freshwaters — a quantitative appraisal of the literature

Information from 33 studies of cadmium adsorption on amorphous and crystalline hydrous iron oxides, clays, silica, humic solids, manganese oxides and natural sediments has been collated. The results have been transferred to a unified data base using a surface complexion model, and are presented in terms of conditional adsorption constants as a function of pH. The adsorption constants for a given substrate at a fixed pH generally agree within an order of magnitude. This is reasonable given the wide range of experimental conditions employed. The affinity of the substrates (on a weight basis) for cadmium appears to follow the order Mn > Fe_am > chlorite (montmorillonite?) > Fe_cryst. = illite = humics > kaolinite > silica.Application of the experimental conditional adsorption constants for the individual substrates to a model suspended sediment predicts adsorption levels similar to those found in experiments with real sediments. The results confirm the potentially important role played by hydrous oxides of iron and manganese. They also emphasise that cadmium is in a very dynamic regime with respect to adsorption in many freshwaters. Deficiencies in our present information on cadmium adsorption are highlighted and suggestions made for future studies.     

Cadmium and lead adsorption by a natural polysaccharide in MF membrane reactor: experimental analysis and modelling

In the present work, Pb(2+) and Cd(2+) adsorption onto a natural polysaccharide has been studied in membrane reactors. The process involves a stirred semi-batch reactor for the adsorption step and a microfiltration (MF) process in order to confine the particles. Due to their lower affinity for the biosorbent, Cd(2+) ions were found to breakthrough the process faster than Pb(2+) cations. The experimental results showed the technical feasibility of the pilot. A mass balance model based on the Langmuir equilibrium isotherm was used to describe the adsorption process. This relation is able to predict experimental data under different operating conditions: the adsorbent and metal concentrations, and the permeate flow rate. Based on these results, it is demonstrated that the biosorbent studied represents an interesting low-cost solution for the treatment of metal ions polluted waters.     

Cadmium uptake by floating macrophytes.

Cd uptake capacity of a group of floating macrophytes (Salvinia herzogii, Pistia stratiotes, Hydromistia stolonifera and Eichhornia crassipes) was determined in outdoors experiments during the lowest temperature period of the year. Although all studied species were highly efficient in the Cd uptake, Pistia stratiotes was selected for further research because of its superior performance and its higher average relative growth rate. Cadmium% removal by Pistia stratiotes was greater in the first 24 h of the experiments (63, 65, 72 and 74% of the added Cd for 1, 2, 4 and 6 mg Cd 1(-1), respectively). After 31 days of growth, Pistia statiotes efficiently removed Cd at the studied concentrations. The macrophyte was able to keep its capacity for Cd removal even though some toxicity symptoms appeared at 4 and 6 mg Cd 1(-1). The greater the initial concentration, the greater Cd bioaccumulation rates. The increase of Cd concentration in plant tissues occurred especially in roots and was linearly related to the quantity of Cd added. Cd sorption by roots is faster than translocation to the plant aerial part and it occurs mainly during the first 24h.     

Cadmium adsorption on goethite-coated sand in the presence of humic acid

Heat was employed to coat crystalline goethite onto a quartz sand surface so that the adsorbent properties of the coating could be utilized. The adsorption characteristics of cadmium and humic acid onto goethite-coated sand were examined. Results show that the goethite-coated sand surface had a higher specific surface area and more mesopores than the uncoated sand. The adsorption of both cadmium and humic acid was highly pH-dependent: cadmium adsorption increased with pH, but humic acid adsorption decreased as pH increased. The presence of humic acid resulted in increasing cadmium adsorption in a specific pH range. The order of reacting humic acid with cadmium was found to have a noticeable effect on the final adsorption capacity. The adsorption capacity of cadmium for humic acid that is adsorbed onto goethite-coated sand before reacting with a cadmium system, exceeds that of humic acid that is mixed with cadmium ions before goethite-coated sand is added.     

Cadmium and zinc uptake by volunteer willow species and elder rooting in polluted dredged sediment disposal sites

Salix species and Sambucus nigra L. (elder) naturally invade dredged sediment landfills and are commonly encountered on substrates contaminated with heavy metals. Foliar concentrations of Cd and Zn in four Salix species and elder were explored in the field. Metal contents in dredged sediment derived soils were elevated compared to baseline concentration levels reported for Flanders. To evaluate foliar concentrations, reference data were compiled from observations in nurseries, young plantations and unpolluted sites with volunteer willow vegetation. Willows grown on polluted dredged sediment landfills showed elevated foliar Cd and Zn concentrations (>6.6 mg Cd/kg DW and >700 mg Zn/kg DW). This was not the case for elder. For willow, a significant relation was found between soil total Zn or Cd and foliar Zn or Cd, regardless of age, species, or clone. Willows proved to be useful bioindicators. Results indicated a possible threat in long-term habitat development of willow brushwood from transfer of Cd and Zn to the food web.     

Metal and sediment ingestion by dabbling ducks.

The chemical analysis of intestinal digesta from hunter-killed carcasses or of wildlife scat is a promising means of estimating the exposure of wildlife to those environmental contaminants that, like lead, are poorly absorbed in the digestive tract. When evaluating contaminants at a site, biologists may find the results of this non-destructive approach more straightforward to interpret in terms of exposure to wildlife than would be analyses of soils, sediments, water, or wildlife tissues. To illustrate the approach, we collected digesta from 47 waterfowl shot by hunters at Prime Hook National Wildlife Refuge, in Delaware, USA. The waterfowl digesta contained an average of approximately 2.4% sediment, estimated from the Al concentrations in the digesta, a marker for sediment. Al concentrations were significantly correlated with concentrations of Cr (Spearman's rank correlation coefficient, r = 0.57), V (r = 0.70), Ni (r = 0.31), and Pb (r = 0.55), and we concluded that these metals were ingested mainly with sediment. American widgeon (Anas americana) ingested sediment at a rate of about four times that of three other species of dabbling ducks (Anas crecca, A. acuta, A. rubripes) and had several times the exposure to the sediment-associated metals. The digesta of one American black duck contained a high concentration of lead (70 mg/kg, dry wt.), presumably from lead shot, but none of the other samples had notably elevated metal concentrations. We suggest that scat and digesta be analyzed more widely by biologists and resource managers seeking a simple, inexpensive assessment of contaminants in local wildlife habitat.     

Estimating sediment yield from a forest road network by using a sediment prediction model and GIS techniques

In forest lands, the stream channels receive the highest amount of sediment during road construction activities due to removal of vegetation cover from road surface, cut-slope, fill-slope, and ditch areas. Sediment delivered from a road section to streams causes serious damages on water resources and aquatic life. Performing revegetation in cut-slope and fill-slope reduce sediment yield from a road section; however, road surface and ditch continue to deliver considerable amount of sediment to the streams. Therefore, accurate prediction of sediment yield from existing road network can be very critical. In order to estimate average sediment yield, several sediment prediction models have been developed based on empirical relationships between various road erosion factors. In this study, average annual sediment yield from a road network to streams in a forest watershed was estimated by using the methodology of a GIS-based sediment prediction model, the SEDMODL model. GIS techniques were used to provide required data layers such as topography, streams, roads, geology, and average precipitation. The results indicated that the SEDMODL model integrated with GIS techniques can assist road managers to estimate total sediment yield quickly and effectively. Besides, critical road sections with high sediment yield potential can be identified and the efficiencies of various sediment control measures can be evaluated for these sections.     

沉淀池的三相流数值模拟

采用FLUENT中多相流Mixture模型对辐流式沉淀池内流场、悬浮物浓度场进行模拟,经分析认为不同粒径的颗粒可设置为不同的相,据此实现了对沉淀池的三相流数值模拟。     

Wastewater treatment in a deep aeration tank

Pilot-scale experiments were conducted to investigate the performance of a deep aeration tank (DAT) (10 m deep) treating a high-strength synthetic wastewater and the DAT biokinetics. At the mean cell residence of 2 days or at the food to microorganisms ratio of 1.41 and less, the DAT reactor, operating continuously as completely mixed and without cellular recycle, removed more than 95% of the chemical oxygen demand of the wastewater. The treatment kinetics were observed to follow the Lawrence and McCarty's models in which the values of the kinetic constants Y, k_d, k and K₃ for this particular operating condition were found to be 0.53, 0.085, 9.25 day^?1 and 259 mg 1^?1, respectively. The results of solid separation by flotation, using the hydrostatic pressure developed in the DAT reactor, were satisfactory. However, better flotation results can be expected with the proper design and operation of the flotation tank.     

南水北调中线工程京石段干渠底泥吸附铬研究

近些年水质重金属污染事件频发,南水北调中线工程京石段干渠沿程交叉建筑物较多,对突发意外事故可能产生的水质重金属铬迁移转化规律进行了实验室模拟研究.结果表明,在模拟水流振荡过程中,Cr（Ⅲ）、Cr （VI）之间难以相互转化.酸性条件下底泥对Cr（Ⅲ）的吸附去除效果较好,在pH=5时,底泥对Cr（Ⅲ）的吸附效率最高,为97％;且吸附速度很快,10 min吸附率可达97％左右.Cr（Ⅲ）浓度为1～20 mg/L时,底泥对Cr（Ⅲ）的吸附去除率随铬浓度升高而略有下降,但均在94％以上,底泥对Cr（Ⅲ）的最大吸附量为0.952 mg/g.底泥吸附去除Cr （VI）的效率较低,不同pH、振荡时间条件下,底泥对Cr（VI）的最大去除率为12.50％.不同有机物浓度、吸附时间条件下,底泥对Cr（VI）的最大去除率为20.96％.     

Phosphorus adsorption on natural sediments: modeling and effects of pH and sediment composition

The classic Langmuir isotherm equation was modified to describe phosphorus (P) adsorption on P-polluted sediments. The P adsorption characteristics of six sediment samples from Chinese Taihu Lake were studied by short-term isotherm batch experiments and related to sediment composition. The maximum P adsorption capacities (PAC) and P-binding energy constant (k) were obtained by nonlinearly fitting sorption data using the modified Langmuir isotherm model. Native adsorbed exchangeable phosphorus (NAP), the zero equilibrium P concentration value (EPC(0)), and partitioning coefficients (K(p)) were subsequently calculated by corresponding formulae. K(p) and PAC were linearly related to the contents of active Fe and Al in sediments by least squares regression analyses (R(2) approximately 0.9 for both). The effect of pH in a wide range on adsorption process was investigated and H2PO4- was presumed to be the preferential sorption species in overall sorption process. The fact that the amount of P sorbed and zeta potential of sediment particles have no necessary relationship reveals that a strong contribution to the P binding still comes from a ligand-exchange process on the Me-OH(2+) and Me-OH sites rather than electrostatic attraction. In addition, the influence of oxidation-reduction potential (ORP) was investigated and discussed and the dual nature of sediments as a pool or source of P in natural waters was evaluated in site T1-T4.     

Degradation of faecal sterols in urine for assessment of faecal cross-contamination in source-separated human urine and urine storage tank sediment

The degradation of the faecal sterol coprostanol and its precursor cholesterol, were determined in source-separated human urine and urine tank sediment. The aim was to assess their potential as biomarkers of faecal cross-contamination in source-separated waste systems since traditional microbial indicators have been shown not to be reliable in this context. Investigations were performed at 4 and 20°C in collected human urine and urine tank sediment to which human faeces and synthetic cholesterol and coprostanol were added. The individual degradation experiments were performed over periods of up to 118 days and represented a wide concentration range both for the urine and the urine tank sediment. Coprostanol showed no significant degradation in either the urine or urine tank sediment when faeces or synthetic coprostanol were added. Neither the normalised variance for the individual slopes, nor the combined regression analysis showed any significant difference from the common slope of zero. For cholesterol no significant degradation was found in the urine tank sediment, but based on pooled data, a moderate decrease occurred in the urine. This was most evident for endogenous cholesterol in the urine at low concentrations where 38 and 55% of the original amounts were lost at 4 and 20°C, respectively. The daily rate of loss of cholesterol based on the regression analysis was 0.73 μg l⁻¹ per day. It is concluded that amounts of coprostanol in urine collection tanks can be used as an indicator of faecal cross-contamination cumulatively occurring over the collection period. Together with die-off data of indicator organisms and pathogens, establishment of a baseline risk assessment would now be possible in relation to storage, handling and reuse of the urine.     

AO脱氮工艺中引入解偶联池的污泥减量化研究

在AO脱氮工艺的污泥回流系统中引入解偶联池,改造成为污泥减量系统.在主体反应区(缺氧区和好氧区)HRT为7.68 h,解偶联池HRT为6 h的工况下,获得了30.6%的污泥减量效果.在该工况下,解偶联池的引入对系统的COD去除效果、硝化效果没有影响,对反硝化效果有所影响,从而使得系统总的脱氮效果略有降低.     

Determination of carbohydrate in lake sediment by a modified phenol-sulfuric acid method

A spectrophotometric method for the assay of carbohydrates in lake sediments and soil is described that is based on the measurement of color development in phenol-sulfuric acid at 485 nm. The method is more sensitive than the previously used proximate method and consumes less time. The spectrophotometric procedure is therefore advantageous as only a minute quantity of sample (2–50 mg) is required for the carbohydrate determination.     

Fate and microbiological effects of furazolidone in a marine aquaculture sediment.

Furazolidone is used in the treatment of bacterial diseases in farmed fish. During application a large proportion of the administered drug reaches the environment directly or via feces. The persistence and metabolism of furazolidone in sediment from a Norwegian salmon farm is described. Furazolidone, in contrast to oxytetracycline and oxolinic acid, is actively metabolized by microorganisms in the sediment. The main metabolite is 3-(4-cyano-2-oxobutylidene-amino)-2-oxazolidone. This is a well known metabolite of the degradation of furazolidone in mammals, fish and Escherichia coli. 3-(4-Cyano-2-oxobutylideneamino)-2- oxazolidone had no detectable antibacterial activity. The half-life of furazolidone in the sediment at 4 degrees C was calculated to be 18 h.     

Cadmium uptake by freshwater bacterial communities

Microcosm experiments in chemostat incubated at 20°C showed that cadmium contamination does not greatly affect bacterial communities in cultures contaminated with up to 1 mg Cd l⁻¹.Bacterial productivity remains unchanged and cadmium-resistant strains arise quickly and in great number. The cadmium accumulation by bacteria depends on the bacterial productivity. The free bacteria can accumulate up to 1200 ppm cadmium whereas the adhering bacteria concentrate up to 6100 ppm. At a steady state, 11–29% cadmium is removed from the water phase of cultures.     

树根桩在储罐地基处理中的应用

基于树根桩复合地基承载力特点,结合树根桩加固储罐地基的工程实例,探讨了桩土分开计算的树根桩复合地基承载力计算方法.对施工过程中难以控制的注浆压力和注浆量等施工技术指标,提出了一些有益的工程经验.实践表明,用树根桩处理储罐地基是一种非常有效的途径.     

Investigation to replace the conventional sedimentation tank by a microstrainer in the rotating disc system

The function of the microstrainer in removing suspended solids from the effluent of the rotating disc system was studied. Furthermore the SS removal efficiency of the microstrainer was compared with that of the conventional sedimentation tank. It was found that in connection with the complete biological treatment in the rotating disc system, the microstrainer was more efficient in removing suspended solids than the conventional sedimentation tank, and that under the dry-weather-flow condition an effluent SS concentration of 10 mg 1⁻¹ could be obtained with the microstrainer at a surface loading rate of 10–15 m h⁻¹.     

Heavy metal removal in anaerobic semi-continuous stirred tank reactors by a consortium of sulfate-reducing bacteria

Removal of heavy metals by an enriched consortium of sulfate-reducing bacteria (SRB) was evaluated through the abundance of SRB, sulfate reduction, sulfide production and heavy metal precipitation. Five parallel anaerobic semi-continuous stirred tank reactors (CSTR, V = 2 L) (referred as R1-R5) were fed with synthetic wastewater containing mixtures of Cu²⁺, Zn²⁺, Ni²⁺, and Cr⁶⁺ in the concentrations of 30, 60, 90, 120, and 150 mg L⁻¹ of each metal and operated with a hydraulic retention time of 20 days for 12 weeks. The loading rates of each metal in R1-R5 were 1.5, 3, 4.5, 6, and 7.5 mg L⁻¹ d⁻¹, respectively. The results showed that there was no inhibition of SRB growth and that heavy metal removal efficiencies of 94-100% for Cu²⁺, Zn²⁺, Ni²⁺, and Cr⁶⁺ were achieved in R1-R3 throughout the experiment and in R4 during the first 8 weeks. The toxic effect of heavy metals on the SRB consortium was revealed in R5, in which no SRB could survive and almost no heavy metal precipitation was detected after four weeks of operation.