Aqueous release of heavy metals from two sewage sludges

Two anaerobically digested sewage sludges, one of relatively low and the other of relatively high heavy metal content, were extracted several times with water to determine the levels of Cu, Zn, and Cd that would be readily available for transport in the soil water if these sludges were applied to land. Generally, the quantity of metal released in the aqueous extracts was between 1 to 7% of the total content with Cu and Zn being released to a greater extent than Cd. The porportion of relatively mobile, non-cationic heavy metals in the aqueous extract differed in the two sludges and ranged from < 1% for Zn and Cd in one sludge to 56.2% for Cd in the other sludge.[/P ]     

Determination of heavy metals in municipal sewage plant sludges by neutron activation analysis

Research is presented which deals with the use of Neutron Activation Analysis (NAA) to scan sewage sludges for their trace metal content. Of special interest are the metals Hg, Se, Cr, Sb, Co and Fe which are highlighted in sludges from six North Carolina cities that represent the spectrum of rural to heavily industrialized pollution sources. Trace metal content variations and possible meanings for these variations are presented along with the precision and potential of NAA for trace metal scanning.     

Application of composted sewage sludges contaminated with heavy metals to an agricultural soil

To elucidate the mechanism of transfer of heavy metals into the food chain, an experiment was carried out with a calcareous soil, to which two different doses of a sewage sludge compost contaminated with either Cd or Zn, Cd, Cu, and Ni were applied. A crop of lettuce was then grown in the amended soils. The application of sewage sludge composts to a calcareous soil lowered the soil's pH, although the value was always around 8 at the end of the experiment. Electric conductivity rose with organic amendment. As anticipated, such an amendment improved the nutritional level of the soils, particularly Nand P, both total and available. Plant yields were negatively affected by organic amendments contaminated with heavy metals, the most dangerous in our experiment being Cd and Zn since this metals easily taken up by plants. As Ni and Cu form insoluble complexes with the organic matter of the sewage sludge composts they are not readily absorbed. Of the metals studied, Cd and Zn showed the highest bioavailability index.     

Total concentrations of heavy metals and occurrence of antibiotics in sewage sludges from cities throughout China

Purpose

A total of 58 dewatered sludge samples were collected from 58 sewage treatment plants (STPs) geographically located in 31 provincial cities of China; the concentrations of heavy metals and antibiotics were determined to monitor the pollutant levels on a large scale, and the pollutant concentrations in sludge samples from different sources of sewage sludge and different geographical regions were compared.

Materials and methods

All the samples were divided into two portions, one of which was air-dried for determination of heavy metals. The other portion was placed in a brown glass bottle and frozen at ?20 °C for antibiotics analysis. Total heavy metals were digested with aqua regia and determined by atomic absorption spectrophotometry (Varian SpectrAA 220FS and Varian SpectrAA 220Z). The antibiotics were extracted with EDTA-sodium phosphate buffer with acetonitrile/Mg(NO₃)₂-NH₃?H₂O, v/v, 3:1 and analysed by liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) and quantified by the isotope-labelled internal standard method.

Results and discussion

In all the sludge samples, zinc was the most abundant metal followed by copper, with relatively low concentrations of chromium, lead, nickel and cadmium. Only 20 % of samples exceeded the Chinese class A values of heavy metal standards for agricultural use (GJ/T309-2009). Sixteen different antibiotics were detected in all the sludge samples, and fluoroquinolones (FQs) and tetracyclines (TCs) were more abundant than sulfonamides (SAs). Concentrations of ∑FQs, ∑TCs and ∑SAs ranged from 1,569 to 23,825 μg kg^?1 (mean 8,274 μg kg^?1, dry weight), from 592 to 37,895 μg kg^?1 (mean 8,326 μg kg^?1, dry weight) and from 20.1 to 117 μg kg^?1 (mean 55.4 μg kg^?1, dry weight), respectively. Tetracyclines (except chlortetracycline) were significantly correlated with zinc and lead. No significant regional trends were observed in the concentrations of heavy metals and antibiotics in sludges.

Conclusions

Heavy metal concentrations are not the major factor restricting domestic and mixed flow sludge application, but the antibiotic concentrations in sludges are problematic; regulation of antibiotic use and establishment of standards to ensure safe handling of sludges are needed.     

Trace metals and chlorinated hydrocarbons in sewage sludges of Kuwait

Levels of trace metals and chlorinated hydrocarbons were determined in sludge produced at the three main wastewater treatment plants in Kuwait (Ardhiya, Jahra, and Reqqa). Over the 6 mo study period (October 1984 to March 1985) levels at the three plants showed the following ranges (μg g^?1 dry weight); Cd, 0.5 to 5.0; Cu, 90 to 270; Zn, 1100 to 3000; Pb, 80 to 300; Ni, 25 to 60; Hg, 1.8 to 3.6; Ag, 1 to 35; PCBs, 0.1 to 3.6; lindane, 0.4 to 7.4; EDDT (i.e., DDT + DDD + DDE), 0.07 to 0.20; aldrin, below detection to 0.07; endrin, below detection to 0.27; dieldrin, 0.005 to 0.04). Mean levels were generally close or lower than mean concentrations reported in the United Kingdom and the United States. They were also lower than suggested concentration limits for application of sludge on agricultural land, which is one of the most cost-effective and attractive techniques for sludge disposal. For Kuwait to adopt this application, however, the characteristics of the local soil and prevailing environmental conditions, notably the frequent occurrence of severe dust storms, should be considered.     

Concentrations and forms of heavy metals in Slovak soils

The risk assessment of heavy‐metal contamination in soils requires knowledge of the controls of metal concentrations and speciation. We tested the relationship between soil properties (pH, CEC, C_org, oxide concentrations, texture) and land use (forest, grassland, arable) and the partitioning of Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn among the seven fractions of a sequential extraction procedure in 146 A horizons from Slovakia. Using a cluster analysis, we identified 92 soils as representing background metal concentrations while the remaining 54 soils showed anthropogenic contamination. Among the background soils, forest soils had the lowest heavy‐metal concentrations except for Pb (highest), because of the shielding effect of the organic layer. Arable soils had the highest Cr, Cu, and Ni concentrations suggesting metal input with agrochemicals. Grassland soils had the highest Cd and Zn concentrations probably for geogenic reasons. Besides the parent material (highest metal concentrations in soils from carbonatic rock, lowest in quartz‐rich soils with sandy texture), pedogenic eluviation processes controlled metal concentrations with podzols showing depletion of most metals in E horizons. Partitioning among the seven fractions of the sequential extraction procedure was element‐specific. The pH was the overwhelming control of the contributions of the bioavailable fractions (fractions 1–4) of all metals and even influenced the contributions of Fe oxide‐associated metals (fractions 5 and 6) to total metal concentrations. For fractions 5 and 6, Fe concentrations in oxides were the most important control of contributions to total metal concentrations. After statistically separating the pH from land use, we found that the contributions of Cu in fractions 1–4 and of NH₄NO₃‐extractable Al, Cd, Pb, and Zn to total metal concentrations were significantly higher under forest than under grassland and in some cases arable use. Our results confirm that metal speciation in soils is mainly controlled by the pH. Furthermore, land use has a significant effect.     

Retention of heavy metals from blast-furnace dedusting sludges by a clayey subsoil

The suitability of a clay (Upper Liassic) as barrier for a heavy metal disposal site had been investigated by analysing the subsoil of an approximately 40 yr old blast-furnace dust dump on this clay. Concentration profiles show that the heavy metals (mainly Zn and Pb) have been retained by sorption processes in the upper 5 to 10 cm below the clay/waste interface. Heavy-metal migrated into the clay by pure diffusion with an effective diffusion coefficient of 1.5 × 10^–9 cm² s^–1, which corresponds to a retardation factor R between about 600 and 2100. It could be concluded that there is no potential risk of groundwater pollution because the subsoil, a 3 m thick plastic clay underlain by a 40 m thick clay rock, has a sorption capacity high enough to retain all heavy metals leachable from the dust dump.     

Determination of organic matter in sewage sludges

Abstract

Procedures for determining organic matter indirectly and directly in sludges are described. A good agreement between chromic acid oxidation and dry—combustion elemental analysis methods of determining organic‐C was observed. Sludge organic matter content was determined directly by loss‐on‐ignition by thermal analysis. An average C factor of 1.68 to estimate the organic matter from organic‐C, obtained by chromic acid oxidation method, was calculated for aerobically digested sludges.     

中国五个典型城市污水厂污泥中重金属的形态分布研究

Metal content and bioavailability are often the limiting factors for application of sewage sludge in agricultural fields. Sewage sludge samples were collected from five typical urban wastewater treatment plants in China to investigate their contents and distribution of various chemical fractions of Cu, Zn, Ni, Cr, Pb and Mo by using the BCR （Community Bureau of Reference） sequential extraction procedure. The sludges contained considerable amounts of organic matter （31.8%- 48.0%）, total N （16.3-26.4 g kg^-1） and total P （15.1-23.9 g kg^-1）, indicating high potential agricultural benefits of their practical applications. However, total Zn and Ni contents in the sludge exceeded the values permitted in China＇s control standards for pollutants in sludges from agricultural use （GB 4284-1984）. The residual fraction was the predominant fraction for Mo, Ni and Cr, the oxidizable fraction was the primary fraction for Cu and Pb, and the exchangeable and reducible fractions were principal for Zn. The distribution of different chemical fractions among the sludge samples refiected differences in their physicochemical properties, especially pH. The sludge pH was negatively correlated with the percentages of reducible fraction of Cu and exchangeable fraction of Zn. The sludges from these plants might not be suitable for agricultural applications due to their high contents of Zn, Ni and Cr, as well as high potential of mobility and bioavailability of Zn.     

Bio-indicators to assess impacts of heavy metals in land-applied sewage sludge

Soils from a pastoral farm that had received large amounts of heavy metal contaminated sewage sludge 6-10 years previously were investigated to determine the impact of heavy metals on Rhizobium. The 8 ha application area was originally divided into five different-sized blocks (blocks 1-5), which received sludge at different times between 1991 and 1994. The response of a lux biosensor based on R. leguminosarum bv. trifolii (Rhizotox-C), was compared with more traditional techniques for measuring the presence of effective strains of Rhizobium (MPN) and nitrogen fixation (δ¹⁵N natural abundance). Although population size (MPNs), nitrogen fixation and biosensor response varied between treatment blocks, linear regression analysis determined that this block effect could not be directly linked to soil heavy metal concentrations, but was probably due to biological, physical, chemical and environmental compounding factors at the site. In this type of uncontrolled field application, the lux bioassay may provide the most useful information as it measures toxicity to any microorganism exposed to the soil solution, for example, the free living rhizobia.     

The determination of heavy metals in domestic sewage treatment plant wastes

Atomic absorption spectroscopy procedures are outlined for the determination of some important heavy metals in sewage treatment plant solids and liquids. Problems associated with sample preparation and sample solution interferences are described. It is recommended that reference standards and internal laboratory control samples be used to allow some assessment of the validity of results. Sewage treatment plant products both liquid and solid were analyzed and results given for samples representing a wide range of sewage input patterns.     

Study of nickel sorption onto biological sludges. possibilities for heavy metals removal treatments

Nickel adsorption onto a sludge wasting from a biological aeration tank is described in this work. This procedure is planned as an alternative method for metal removal from industrial effluents containing heavy metals in low concentrations. Experimental results of equilibrium adsorption and laboratory equipment operation are reported. Equilibrium data of nickel adsorption were fitted to the Freundlich equation. On the basis of this equation, the effect of several parameters such us metal concentration, sludge concentration and metal dosing rate were tested. Nickel removal efficiency is about 80% in the most favourable cases. Aeration during metal-sludge contact was also tested but little enhancing in metal uptake was observed. This analysis can be used to define the best operation conditions in practical cases either for metal or organic matter removal.     

污泥和水溶性重金属盐的植物有效性比较研究

采用盆栽方法研究了污泥中重金属的植物有效性,并与等量重金属盐进行了比较。结果表明,施用污泥50 g/kg土和100 g/kg土能明显增加番茄和玉米苗期地上部Zn、Cu、As的含量,对Cr、Ni、Pb含量影响不大。施用污泥可以降低玉米苗期地上部Cd的含量。施用污泥与施用等量水溶性重金属盐比较,污泥重金属有效性低于水溶性重金属盐的有效性。在土壤污泥施用量为50 g/kg时,污泥重金属在番茄苗期的Zn、Cu有效系数分别为80.9%和54.8%;玉米苗期Zn、Cu的有效系数分别为53.4%和70.3%;污泥用量为100 g/kg土时,污泥重金属在玉米苗期的Zn、As有效系数分别为74.5%和64.4%。     

污泥土地施用研究I.施用污泥土壤中重金属的化学浸提性研究

本研究了施用污泥的太湖水稻土和江西第四纪红壤性水稻土中重金属的化学提取性。结果表明，随着污泥施用量的增加，土壤中Ｃｕ，Ｚｎ，Ｃｄ的醋酸，醋酸铵，ＥＤＴＡ３种提取形态的浓度都明显增加，有很好的相关性，各提取态浓度在各施用量之间存在显差异。污泥施用没有增加Ｐｂ含量，这可能与污泥本身含Ｐｂ量低有关。     

Bacterial leaching of heavy metals from sewage sludge for agricultural application

Bacterial leaching of heavy metals from sewage sludge was studied to assess the potential of agricultural application of the decontaminated sludge. Experiments were conducted in both batch processes (at 28 ?C) and continuous process (at 30 ?C) using a culture of Thiobacillus ferrooxidans and a mixted culture of Thiobacillus ferrooxidans and Thiobacillus thiooxidans. Reagent grade ferrous sulfate, spent ferrous sulfate and pyrite were used as the energy substrates. A first order kinetic model of Cu solubilization was proposed. It was shown that the processes in the continuously stirred tank reactor (CSTR) and the air lift reactor (ALR) with 20% cell recycling were more efficient than the others for metal solubilization due to a relatively large bacterial population.     

Leaching of heavy metals from sewage sludge through coastal plain soils

Abstract

Three types of sewage sludge are applied to the surface of soil columns of Coastal Plain soils and leached with distilled water. The Zn concentrations in leachate samples from a Sassafras loamy sand soil loaded with an industrial sludge increased with sludge loading rate. All leachate samples contained very low concentrations of Cd, Cr and Cu. Hazardous amounts of Cd, Cr, Cu and Zn would not be leached to the groundwater when recommended rates of the tested sludges are applied to Coastal Plain soils under most conditions.     

Bioleaching of heavy metals from sewage sludge using indigenous iron-oxidizing microorganisms

Purpose

The objective of this study was to investigate the bioleaching of Cr, Cu, Pb, and Zn from sewage sludge using iron-oxidizing microorganisms. These conditions include the solid concentration, initial pH, ferrous iron concentration, inoculum concentration as well as the kinetics of solubilization of metals from sewage sludge to determine whether they impact on bioleaching efficiency.

Materials and methods

The sludge sample containing bacteria used in this study was collected from Fuzhou Jingshan sewage treatment plant. Indigenous iron-oxidizing bacteria were enriched from the sludge. Conditions affecting the bioleaching and application were conducted using batch experiments. The analysis of Cr, Cu, Pb, and Zn was carried out with an atomic absorption spectrophotometer, and the pH and ORP were measured using pH meter and ORP meter.

Results and discussion

The data show that 88.5 % of Zn, 79.9 % of Cu, 50.1 % of Pb, and 33.2 % of Cr can be removed from the sludge after 12 days of bioleaching at 30 °C, while only 80.2 % of Zn, 21.8 % of Cu, 10.9 % of Pb, and 10.5 % of Cr were leached out in the control without iron-oxidizing microorganisms. The leaching kinetics study shows that the rate of metal solubilization in bioleaching using iron-oxidizing microorganisms was more effective compared to chemical leaching.

Conclusions

The results suggest that the leaching of metals from sludge can be attributed to two leaching approaches: firstly, chemical leaching; and secondly, bioleaching. However, their effectiveness depends on metal species because of their different bindings in sludge. For example, the leaching of Zn from the sludge was dominated by chemical leaching while the removal of Cu, Pb, and Cr was dominated by bioleaching.     

Influence of sewage sludge and heavy metals on nematodes in an arable soil

Summary The abundance of nematodes was investigated in agricultural plots treated in three different ways, the first with no treatment, the second with 300 m³ ha^-1 a^-1 raw sewage sludge and the third with 300 m³ ha^-1 a^-1 sewage sludge with the addition of heavy metals. The nematodes were determined down to the genus and were assigned to five feeding groups. Total nematode numbers were highest in the site treated with sewage sludge and heavy metals. The smallest total numbers were found in the control site. The plant-feeding nematode genera showed different patterns of abundance depending on the sludge treatment and heavy metal content. For the mycophagic and bacteriophagic nematodes, numbers increased with the amount of sludge, especially in the sites with a higher heavy metal content. The family Rhabditidae was the most numerous group in the sludge plus heavy metals treatment. In contrast to these findings, the omnivorous nematodes were very rare in the sludgetreated plots and were completely absent in plots treated with sludge plus heavy metals, whereas predatory nematodes were numerous only after the application of sludge alone.     

Particle size fractionation and metal distribution in sewage sludges

A sequential step filtration technique has been used to investigate the different particle size fractions of suspended solids in several raw, activated and digested sewage sludge samples. Liquid sludge was passed through filters with progressively smaller pore sizes, from 100 µm down to 0.2 µm. The concentrations of Cd, Cu, Ni, Pb, and Zn associated with each particle size fraction were also determined. The particle size distributions indicated that there was a greater proportion of larger particles in the raw and activated sludges than in the digested sludges. Generally in activated sludge the metals tended to be associated with the large particles of > 100 µm, whereas in raw and particularly digested sludges the metals were found in the smaller particle size fractions from 20 µm, down to 2.5 µm. Calculating specific associations in terms of mg kg^?1 the 8 to 20 µm range appears important in complexing metals. This was especially evident when comparing the sludges from the same treatment works. Generally distributions were more widespread when results were expressed as mg kg^?1 as opposed to mg L^?1.