Protozoan bioassays of soil amended with sewage sludge and heavy metals,using the common soil ciliate Colpoda steinii

The common soil protozoan Colpoda steinii was used to study the toxicity of sulphate solutions of Ni, Cd, Cu, and Zn. The growth of C. steinii was reduced by 50% in the presence of 0.10, 0.22, 0.25, and 0.85 mg litre^-1 of Ni, Cd, Cu and Zn, respectively, during 24 h of incubation at 25°C, as calculated from a regression analysis of probit-transformed data. The same growth assay was used to assess the toxicity of soil solution extracted by centrifugation from soil samples of field plots of a grass/clover ley on a sandy loam treated with sewage sludge spiked with additional Cd, Cu, Cr, Ni, Pb, or Zn at concentrations either equivalent to or twice the limits for heavy metals recommended in recent EC guidelines (Commission of European Communities directive 86/278/EEC). The toxicity of these soil solutions varied with the season of the year. None of the soil solutions extracted in winter (February 1991) inhibited the growth of C. steinii. In summer (July 1991), the growth was reduced in solutions extracted from plots that were amended with sludge plus additional Zn or Ni at twice the maxima recommended by the EC. The changes in toxicity to C. steinii of the soil solutions between February and July were positively correlated with increases in heavy metal concentrations of Zn and Ni between winter and summer. These preliminary results suggest that regular protozoan bioassays may be used to monitor the biological availability of heavy metals in soils, especially when combined with other microbial assays and with chemical analyses of soil solutions.     

Nitrogen mineralization in soil amended with sewage sludge and fly ash

Summary The effect of fly ash on N mineralization in sewage sludge was studied during a 5-week aerobic incubation of soil-waste mixtures at different loading rates under controlled conditions. Periodically, the mixtures were leached with distilled water and the inorganic N released was determined in the percolates. The data were tested by an analysis of variance with repeated measures. Significant differences were found among different incubation periods and also between different treatments. The net N mineralization, expressed as a percentage of organic N added in the sludge, was drastically reduced when higher rates (500 Mg ha^-1) of fly ash were added.     

Initial organic matter transformation of soil amended with composted sewage sludge

 An incubation experiment with composted sewage sludge (CSS) just added to the soil was conducted to determine its initial effects on C decomposition, N nitrification and the transformation of organic matter. CSS was mixed with a sandy loam soil from uncultivated ochric epipedon of a Typic Haploxeralf at rates of 0, 40 and 80 t ha^–1 (dry weight). The data obtained showed that with regard to the unamended soil, both the 40 and the 80 t ha^–1 treatments produced the same result in decreasing respiratory activity, but the addition of increasing amounts of CSS progressively delayed C decomposition. The nitrification index (NI), defined as the relation between nitrate-N and nitrate-N + ammonium-N, increased in correlation with the C mineralization coefficient. Total organic matter decreased after incubation whereas the humic substances increased in relation to the total C mineralized. Received: 28 October 1999     

Behaviour of cadmium and nickel in a soil amended with sewage sludge

Various urban and industrial sewage sludges were applied to a soil at two doses (50 and 100 t ha⁻¹ y⁻¹) during eight years in a field experiment. The soil was analysed at two depths (0–30 and 30–60 cm) for extractable cadmium and nickel. In general these trace metal increased with dosage. However, cadmium formed complexes with organic matter and nickel bound to iron and manganese oxides. Hence, the available fractions of these metals constituted a small proportion of the total content. The results obtained show a low risk of contamination due to the available fractions of these metals at sludges dosages of up to 100 t ha⁻¹. Copyright © 2001 John Wiley & Sons, Ltd.     

Soybean nodulation and nitrogen fixation on soil previously amended with sewage sludge

Summary A greenhouse study was conducted to examine the residual effects of sewage sludge on soybean Glycine max (L.) Merr., nodulation, and N fixation. Nodulating and nonnodulating isolines of Clark soybean were grown to the R2 stage in soils (Typic Paleudults) obtained from plots where heat-treated sludge had been applied in 1976 at rates equal to 0, 56,112, and 224 Mg ha^–1 high (7.0) and low (6.2) soil pH regimes were established by CaCO₃ additions. Sludge and soil pH treatments resulted in clearly defined differences in metal uptake by soybean shoots. Plant Zn, Cd, and Ni concentrations were greater on pH 6.2, sludge-amended soil than on the pH 7.0, amended soil. At low soil pH, soybean Zn and Cd concentrations, respectively, increased from 41 and 0.19 mg kg^–1 (control) to 120 and 0.58 mg kg^–1 at the 224 Mg hat sludge rate. At the high soil pH and 224 hg hat sludge rate, Zn and Cd concentrations were 45 and 0.15 mg kg^–1, respectively.Symbiotic N fixation provided 90% of the total N accumulation. Total N accumulation, shoot N concentration, dry matter, and N fixation by nodulating soybeans exhibited a significant linear increase with sludge rate. Total N accumulation, dry matter, and N fixation were significantly greater at high soil pH. For high and low soil pH, respectively, N fixation increased from 422 and 382 mg N per plant (control) to 614 and 518 mg N per plant at the 224 Mg ha^–1 sludge rate. While soybean nodulation also increased linearly on sludge-amended soil, a significant rate times pH interaction for nodule number indicated that nodulation was less strongly enhanced by sludge at low soil pH.     

Dynamics of phosphorus phytoavailability in soil amended with stabilized sewage sludge materials

Reducing the environmental risk of soluble P loss from sludge-amended soils is essential for increasing soils capacity to utilize sewage sludge beneficially. Fresh dewatered anaerobically digested sewage sludge (FSS), stabilized with ferrous sulphate (FeSul–SS), calcium oxide (CaO–SS) and aluminum sulphate (alum–SS), each at three chemical-to-FSS ratios, or by composting (BSC), was applied to alluvial soil at rates of 150 and 300 mg P kg^? 1 soil. Changes in P phytoavailability in comparison to KH₂PO₄-amended soil were probed during 100 days of incubation by a P-bioassay and were compared to the concentration of water-soluble P (WSP) and Olsen-P. P phytoavailability was notably linked to the incubation duration and the stabilization process. In general, P phytoavailability at equal P-addition rates was KH₂PO₄ > > alum–SS > BSC ≥ FSS > CaO–SS > > FeSul–SS; and it was positively related to the added P rates, although with quite different patterns among the various sludge products. The concentration of inorganic WSP (WSP_i) extracted from the soil increased following the application of FSS or BSC, and additional P mineralization further increased its concentration during incubation. In contrast, in most cases the chemically stabilized sludges, especially the FeSul–SS, showed considerably reduced inorganic WSP concentrations relative to the untreated soil. The total WSP, Olsen-P and organic WSP (WSP_o) positively correlated to P phytoavailability, indicating that WSP_o plays a role in plant P utilization in these soils. It is concluded that all the chemically stabilized sewage sludge studied effectively controlled WSP_i in soil while still supplying P to support plant growth.     

Carbon sequestration in a limestone quarry mine soil amended with sewage sludge

To reclaim a limestone quarry, 200 and 400 Mg/ha of municipal sewage sludge were mixed with an infertile calcareous substrate and spread as mine soil in 1992. Soil samples were taken 1 week later and again after 17 yr of mine soil rehabilitation so as to assess changes in the amount and persistence of soil organic carbon (SOC). Sludge application increased SOC as a function of the sludge rate at both sampling times. Seventeen years after the sludge amendments, the nonhydrolysable carbon was increased in the 400 Mg/ha of sludge treatment. The recalcitrance of SOC was less in sludge‐amended soils than in the control treatment at the initial sampling, but 17 yr later this trend had reversed, showing qualitative changes in soil organic carbon. The CO₂‐C production had not differed between treatments, yet the percentage of mineralized SOC was less in the high sludge dose. When the size of active (C_active) and slow (C_slow) potentially mineralizable C pools was calculated by curve fitting of a double‐exponential equation, the proportion of C_active was observed to be smaller in the 400 Mg/ha sludge treatment. Soil aggregate stability, represented by the mean weight diameter of water‐stable soil aggregates, was significantly greater in mine soil treated with the high dose of sludge (18.5%) and SOC tended to be concentrated in macro‐aggregates (5–2 mm). Results suggest that SOC content in sludge‐amended plots was preserved due by (i) replacement of the labile organic carbon of sludge by more stable compounds and (ii) protection of SOC in aggregates.     

Plant availability of heavy metals in a soil amended with a high dose of sewage sludge under drought conditions

The objective of this research was to study the effect of water deficit on soil heavy metal availability and metal uptake by ryegrass (Lolium multiflorum Lam.) plants grown in a soil amended with a high dose of rural sewage sludge. Three fertility treatments were applied: sewage sludge (SS), mineral fertilizer (M), and control (C); unamended). The levels of irrigation were: well-watered (W) and water deficit (D). Microbial respiration decreased the total organic C (TOC) in sludge-treated soils, but this did not enhance soil DTPA-extractable heavy metal concentrations. Indeed, Zn, Cu, Mn and Ni availability decreased during the experiment. C- and M-treated soils showed either no changes or increases of some trace element concentrations during the incubation. In the plant experiment, ryegrass dry matter (DM) yield, relative water content (RWC) and leaf water potential (_w) decreased in drought conditions. Sludge addition increased metal concentrations in plants. However, in some instances, SS-treated plants showed either similar or lower transfer coefficient (Tc) values than did plants in the C and M treatments. Water deficit decreased the concentration and the Tc of some metals in roots of M and SS plants. Results indicate that sludge-borne heavy metals were maintained in chemical forms of low availability. The lower metal uptake by SS and M plants under dry conditions cannot be attributed to a lower availability of these elements in soil.     

Labile and stable pools of organic matter in soil amended with sewage sludge biochar

One of the main advantages of using biochar for agricultural purposes is its ability to store carbon (C) in soil for a long-term. Studies of labile and stable fractions of soil organic matter (SOM) may be a good indicator of the dynamics of biochar in soils. This study evaluated the effects of applying sewage sludge biochar (SSB) in combination with mineral fertilizer on fractions of SOM. To conduct this evaluation, 15 Mg ha^?1 of SSB combined or not with mineral fertilizer (NPK) was applied to the soil in two cropping seasons. Apart from total organic C (TOC), the labile and stable fractions of SOM were also determined. The combined use of SSB and NPK resulted in higher TOC, a 22% to 40% increase compared to the control and to the NPK treatments, respectively. The SSB produced at a lower temperature increased the labile fractions of SOM, especially the microbial biomass C, showing its capacity to supply nutrients in the short-term. The stable pools of SOM are increased after adding SSB produced at a higher temperature. It was concluded that pyrolysis temperature is a key-factor that determines the potential of SSB to accumulate C in labile and stable fractions of SOM.     

Residual metal reactivity of humic acids extracted,from soil amended with sewage sludge

Copper, Fe, and Mn were used as probes to investigate residual metal reactivity for humic acid (HA) samples extracted from a loam soil, either non-amended or amended with anaerobically digested sewage sludge for 4, 5, 6, or 7 yr at 90 t ha^?1. yr^?1. Irrespective of their origin, the HA complexes significant amounts of metal, in forms stable against intense water-leaching, in the order Fe > Cl > Mn. Sludge-amended soil HA adsorbed and retained Fe in amounts greater than HA extracted fron non-amended soil. Metal adsorption occurred mainly by cation-exchange replacement of metals previousl: bound to HA. Water-stable Fe³⁺-HA complexes prepared in the laboratory were partially stable agains H⁺ and metal ion exchange reactions, whereas Cu²⁺ and Mn²⁺ in laboratory-prepared, water-stabl HA complexes were desorbed almost completely by these two reactions. Electron spin resonance spectra indicated that the laboratory-prepared metal-HA complexes had a chemical composition and molecula structure similar to that of indigenous metal-HA complexes, which were stable against all leachin, and cation-exchange treatments. Although the HA samples showed a maximal metal binding (i.e. saturation) as metal loading of the sludge-amended soil increased, they still exhibited a high residua binding capacity for the three metals used as probes.     

The transfer of heavy metals to barley plants from soils amended with sewage sludge with different heavy metal burdens

Purpose

Our main aim objective was to evaluate the transfer of Cd, Cr, Cu, Ni, Pb and Zn to barley (Hordeum vulgare) grown in various soils previously amended with two sewage sludges containing different concentrations of heavy metals. This allowed us to examine the transfer of heavv metals to barley roots and shoots and the occurrence of restriction mechanisms as function of soil type and for different heavy metal concentration scenarios.

Material and methods

A greenhouse experiment was performed to evaluate the transfer of heavy metals to barley grown in 36 agricultural soils from different parts of Spain previously amended with a single dose (equivalent to 50 t dry weight ha^?1) of two sewage sludges with contrasting levels of heavy metals (common and spiked sludge: CS and SS).

Results and discussion

In soils amended with CS, heavy metals were transferred to roots in the order (mean values of the bio-concentration ratio in roots, BCF_Roots, in brackets): Cu (2.4)?~?Ni (2.3)?>?Cd (2.1)?>?Zn (1.8)?>?Cr (0.7)?~?Pb (0.6); similar values were found for the soils amended with SS. The mean values of the soil-to-shoot ratio were: Cd (0.44)?~?Zn (0.39)?~?Cu (0.39)?>?Cr (0.20)?>?Ni (0.09)?>?Pb (0.01) for CS-amended soils; Zn (0.24)?>?Cu (0.15)?~?Cd (0.14)?>?Ni (0.05)?~?Cr (0.03)?>?Pb (0.006) for SS-amended soils. Heavy metals were transferred from roots to shoots in the following order (mean values of the ratio concentration of heavy metals in shoots to roots in brackets): Cr (0.33)?>?Zn (0.24)?~?Cd (0.22)?>?Cu (0.19)?>?Ni (0.04)?>?Pb (0.02) for CS-amended soils; Zn (0.14)?>?Cd (0.09)?~?Cu (0.08)?>?Cr (0.05)?>?Ni (0.02)?~?Pb (0.010) for SS-amended soils.

Conclusions

Soils weakly restricted the mobility of heavy metals to roots, plant physiology restricted the transfer of heavy metals from roots to shoots, observing further restriction at high heavy metal loadings, and the transfer of Cd, Cu and Zn from soils to shoots was greater than for Cr, Ni and Pb. Stepwise multiple linear regressions revealed that soils with high sand content allowed greater soil-plant transfer of Cr, Cu, Pb and Zn. For Cd and Ni, soils with low pH and soil organic C, respectively, posed the highest risk.     

Changes in biological properties and antioxidant capacity of an agricultural soil amended with sewage sludge

The effects of applying sewage sludge (SS) to agricultural soil (at low rate of 22.5, LRS, and at high rate of 45 t ha^?1 dry basis, HRS) were monitored over a 120-d experimental period. Total organic carbon (TOC), water-soluble organic carbon (WSOC), alkali-soluble phenols, basal respiration, specific enzyme activity, dehydrogenase activity (DH-ase), metabolic potential (MP) and FDA-hydrolytic activity (FDA) were strongly increased by both rates of SS applications. In the SS amended soil, about 70% of the organic C added with the material remained at the end of the experiment. Basal respiration increased with increasing SS doses. The specific enzyme activity and the MP indicate an increase in the enzyme activity in soil.

The addition of SS led to higher values than the control of all the tested parameters up to the end of the experimental period. The antioxidant capacity (trolox equivalent antioxidant capacity, TEAC) was influenced by SS addition only when applied at HRS. After 120 days only HRS value of TEAC (5.13 mM g^?1) was higher than control (4.09 mM g^?1). The pattern of TEAC did not enable any link to be established between antioxidant capacity and both alkali-soluble phenols and basal respiration in soil.     

生活污泥对白菜供磷和土壤磷状况的影响

采用好气培养和盆栽试验以探明污泥磷的肥效,降低污泥施用导致的土壤磷累积引起的环境风险。结果表明,单施污泥土壤有效磷含量和白菜吸磷量均显著低于施用磷酸一铵和鸡粪处理;施用污泥后有利于增加白菜生长后期土壤磷酸酶的活性和土壤Olsen-P含量。在白菜等产量条件下,单施污泥处理土壤中Olsen-P残留量显著高于污泥与化肥混施处理;在P2O5施用量为902~70 kg/hm2时,污泥堆肥磷的肥效为磷酸一铵的25%左右。     

Heavy metals in mine soils amended with sewage sludge

In order to reclaim a clay quarry, a topsoil material was mixed with gravelly spoil at different ratios and with various rates of sewage sludge. The influence of three spoil/topsoil ratios (1:1, 2:1 and 3:1) and three sludge rates (40, 80 and 120 t ha⁻¹) on chemical properties of the resulting material was investigated, with emphasis on heavy metal (Fe, Cu, Mn, Ni and Zn) contents. The mixtures topsoil/spoil/sludge were water saturated and incubated for 15 or 30 days in a chamber under controlled conditions. The incubated samples were analysed for pH, total carbon and nitrogen, and total, available, exchangeable and soluble heavy metals. The addition of spoil to the topsoil increased the volume of material available, by utilizing an inert material unsuitable by itself to grow plants. The addition of sewage sludge repaired the disadvantages of the spoil, increasing the pH and the organic matter contents. The total heavy metal contents in the mixtures followed the sequence Fe>>Mn>>Zn, Cu>Ni. All except Cu were within the ranges allowed for agricultural lands. The available heavy metals constituted a small fraction of total contents and decrease with time due to complexation and immobilization processes. The exchangeable and soluble fractions were almost negligible; only small amounts of Mn, Zn and Cu were detected. Therefore, the risk of contamination by heavy metals is insignificant in the conditions investigated. Copyright © 1999 John Wiley & Sons, Ltd.     

Mutagenic potential of municipal sewage sludge amended soils

This study was conducted to measure the mutagenic potential of municipal sewage sludge amended soil. Two separate sludge samples were collected from one municipal wastewater treatment plant and applied to undisturbed soil lysimeters over a 9 mo interval. Soil and sludge samples were collected for approximately 2 yr following sludge application. Samples were solvent extracted using methylene chloride and methanol, and the bacterial mutagenicity of the resulting residue determined using the Salmonella/microsome assay. The maximum specific activity of the sludge amended soil was 416 net revertants per 10 mg of residue induced by the methanol fraction extracted from the Weswood soil collected 154 d following the first sludge application. In the Padina sand, the maximum specific activity was 320 net revertants per 10 mg of residue induced by the methanol fraction extracted from the sample collected 154 d following the first sludge application. The specific activity of the sludge amended soil was observed to decrease slowly with time. For both the Padina and the Weswood soils, mutagenic organic chemicals were detected in soil samples collected 510 d following the second sludge application. For the Weswood soil, the mutagenic activity per unit weight of soil with metabolic activation of the samples collected 510 d after the final sludge application was decreased by 15 and 76% for the methylene chloride and methanol fractions, respectively, when compared to the maximum weighted activity observed 56 d after the final sludge application. The results indicate that municipal sewage sludges may contain organic mutagens which are persistent in the soil.     

Runoff and losses by erosion in soils amended with sewage sludge

In order to promote the transformation of a burnt Mediterranean forest area into a dehesa system, 10 t ha⁻¹ of dry matter of the same sewage sludge in three different forms: fresh, composted and thermally‐dried, were added superficially to field plots of loam and sandy soils located on a 16 per cent slope. This application is equivalent to 13ċ8 t ha⁻¹ of composted sludge, 50 t ha⁻¹ of fresh sludge and 11ċ3 t ha⁻¹ of thermally‐dried sludge. The surface addition of a single application of thermally‐dried sludge resulted in a decrease in runoff and erosion in both kinds of soil. Runoff in thermally‐dried sludge plots was lower than in the control treatment (32 per cent for the loam soil and 26 per cent for the sandy soil). The addition of any type of sludge to both soil types also reduces sediment production. Significant differences between the control and sludge treatments indicate that the rapid development of plant cover and the direct protective effect of sludge on the soil are the main agents that influence soil erosion rates. Results suggest that the surface application of thermally‐dried sludge is the most efficient way to enhance soil infiltration. Copyright © 2003 John Wiley & Sons, Ltd.     

Transport of zinc,copper, and lead in a sewage sludge amended calcareous soil

The application of sewage sludge on farmland is practised in many countries since sludge is rich in macro- and micro- nutrients. However, increasing use of sewage sludge on farmland has raised concerns about the potential transport of heavy metals into food chains and groundwater. This study determined for a calcareous soil the effects of sludge application on soil physical properties and transport of zinc (Zn), copper (Cu), and lead (Pb). Secondary anaerobic digested sewage sludge was applied at rates of 0, 25, 50, and 100 t/ha (on a dried weight basis) for four consecutive years and mixed in the top 20-cm of soil. Corn (Zea mays L.) was planted as a spring crop, followed by wheat (Triticum aestivum) as a winter crop. Sludge application increased the dissolved organic matter content and modified the soil structure, increased the soil infiltration rate, saturated hydraulic conductivity, and aggregate stability, and decreased the bulk density. Sludge application greatly increased DTPA (diethylenetriamine pentaacetic acid)-extractable soil metal concentrations to 50 cm depth and significantly to 1 m. In the plots that received four application of 100 t/ha sewage sludge, the mean concentrations of Zn, Cu, and Pb in subsoil increased by 1600, 7, and 4.5 times, respectively, compared with the control. The results indicate that a combination of enhanced soil physical properties, heavy and inefficient irrigation and high organic matter content with heavy metals cause significant metal mobility. High sludge applications pose risks of groundwater and food chain contamination and rates are best restricted to those reflecting the nutrient demand of crops (20 t/ha every 4 to 5 yr or an average of 4 to 5 t/ha/yr).     

Heavy metal uptake by blue grama growing in a degraded semiarid soil amended with sewage sludge

Sewage sludge application to semiarid grassland may represent a beneficial means of utilizing this waste product for restoration of degraded sites. Consequently, dried municipal sewage sludge was applied at three rates (22.5, 45, and 90 Mg ha^–1) to a degraded semiarid grassland soil in order to determine the effects of sludge amendments on forage productivity, soil heavy metal content, and metal uptake by blue grama (Bouteloua gracilis).Soil and plant properties in control and amended plots were measured after 1, 2, and 5 growing seasons.Soil nutrients increased linearly with increased sludge application in the first two growing seasons. Consequently, forage quality and total production of blue grama improved significantly over the unamended control as the tissue levels of N, P, K, and crude protein increased. Cadmium and Pb in the sludge-treated plots did not increase significantly over the control after 1 and 2 growing seasons. Levels of DTPA-extractable soil micronutrients (Cu, Fe, Mn, Zn) increased linearly with increased sludge application rate to soil concentrations recommended for adequate plant growth. Soil N, P, and K concentrations remained higher in the sludge-amended soils after 5 growing seasons, while Cu and Cd increased to slightly above desireable limits as the soil pH decreased to 7.4 and 7.0 in the 45 and 90 Mg ha^–1 treatments, respectively. However, with the exception of Mn which remained within desirable limits, metal concentrations (including Cu and Cd) in blue grama tissue were not significantly different from the control treatment after five growing seasons. Based on soil and plant tissue metal concentrations, it appears that sludge applied at rates between 22.5 and 45 Mg ha^–1 will maintain the most favorable nutrient levels coupled with significant improvements in forage production in this semiarid grassland environment.     

Comparison of biological and chemical methods to determine available nitrogen in sewage sludge amended soil

Summary Two biological and two chemical methods were tested to quantify the available N of two sewage sludges in two soils. Sewage sludges increased the quantified available N of soil according to the rate for any tested method. A significant correlation between available N determined by biological methods (leaching and non-leaching incubation procedures) was observed, while no significant correlation between chemical methods (acidic hydrolysis and 2 N KCl extraction) was reported. With the exclusion of the method based on acid hydrolysis, the other procedures were correlated significantly with the available N determined in field experiments. It is concluded that the method based on NH₄ ⁺-N released by KCl gives an easy and accurate estimation of the sewage sludge available N.[/ab]