The main aim of this study was to examine the influence of sewage sludge (SS) and stabilized SS application on Olsen-P and DTPA-extractable Cu and Zn in relation to soil type, sewage source, mixing rate and incubation time. Two different SS were mixed with amendments by mixing rates 10 and 25%. These amendments include coal fly ash (CFA), bentonite (B), sugar beet factory lime (SBFL), calcium carbonate, rice straw (RS), water hyacinth (WH), and cotton stalks (CS). Treated and untreated SS had been applied to fluvial and calcareous soil with application rate 2.5% and incubated for one and two month. After incubation, soil samples were analyzed for Olsen-P and DTPA-extractable Cu and Zn. Application of SS increased significantly Olsen-P and DTPA extractable Cu and Zn compared to control. Application of stabilized SS increased significantly Olsen-P, with high increasing rate with SBFL and WH-stabilized SS. Stabilized-SS decreased significantly Cu and Zn availability compared to mono SS treatment. Bentonite-, SBFL and CFA-stabilized SS were the highest among inorganic treatments for reducing available Cu and Zn either in fluvial or calcareous soil, while WH and RS-stabilized SS treatment were the most suitable organic ones for reducing DTPA-extractable Cu and Zn.
Waste management is recognized as an important issue in modern societies, and waste recycling is encouraged as an alternative to stockpiling and incineration. The application of sewage sludge or composts of several origins as amendments to agricultural soils is an economically attractive waste management strategy promoted by scientists and regulating organisms and is a common practice since many years [
Recently, increased attention was paid to the sludge stabilization/immobilization process aiming to minimize the mobility of trace elements by using various additives, due to compliance to more stringent regulations issue in USA and European Union. Stabilization/immobilization refers to techniques that chemically reduce the hazardous potential of a waste by converting the contaminants into less soluble, mobile, or toxic forms. Sewage sludge can be treated in a matrix of different organic and inorganic materials [
Among the different macronutrients contained in sludge phosphorus is an essential element for plant metabolism since it is present in numerous molecules such as phospholipids or nucleotides. For this reason P is often considered one of the most limiting nutrients for plant productivity. Comparable quantities of sludge cakes are commonly applied to degraded soils in the Mediterranean areas. These rates, however, exceed crop nutrients requirements and may cause undesirable changes in soil chemical properties, leading to environmental contamination. Such effects include accumulation of P which can impact water bodies through surface run-off leaching which in turn may threaten surface and ground waters through eutrophication [
Copper and zinc are essential elements for higher plants but at the same time potentially environmental contaminants. Copper and zinc may enter the soil through fertilizer, organic wastes, and pesticides applications. Sewage sludge usually contains significant amounts of Cu and Zn and can be a source of these two metals in the soil [
The availability of P and trace elements present in the sewage sludge depends on many factors such as the nature and amount of element, degree of element association in the sludge, sewage source, application rate, soil type, plant characteristics, and weather conditions [
Although several studies have dealt with the possible increase of available P and trace elements arising through land application of SS [
Surface (0–30 cm) soil samples of cultivated Entisols (Typic Torrifluvents) developed on fluvial sediments and Aridisols (Typic Calcorthids) developed on calcareous sediments [
Two anaerobic digested sewage sludge samples were used; the first one (SS1) was collected from Kafr EL-Zayate wastewater treatment plant, which received sludge from both domestic and industrial sources. The second one (SS2) was collected from Messer wastewater treatment plant, Kafr el-Sheikh, which received sludge from both domestic and industrial sources with dominance of domestic. The sewage sludge samples were air-dried and passed through a 2 mm sieve.
Fly ash samples (CFA) collected from the electrostatic precipitator of a lignite-fired electric power plant in Northern Greece. Sugar beet factory lime (SBFL) was obtained from the sugar beet factory of the city of El Hamoul, Kafr el-Sheikh Governorate. Bentonite (B) is a calcium saturated clay mineral with a high sorption capacity was used in this study. Calcium carbonate (CaCO3) is a chemical reagent with 90% purity. Rice straw (RS) is dried and grinded rice residual plants. Cotton sticks (CS) are residuals of cotton plants, dried and grinded. Water hyacinth (WH) is a vascular floating aquatic plant, fast growing with a well-developed fibrous root system and large biomass. These plants were collected from fresh water pathway, dried, and grinded.
The influence of SS and the stabilized SS on soil properties, Olsen P and DTPA-extractable amounts of Cu and Zn in relation to soil types, sewage source, mixing rate, and incubation period was investigated in an incubation experiment in which alkaline fluvial and calcareous soils were used. An incubation experiment was conducted using the studied soils and sewage at room temperature and field capacity moisture content for 30 and 60 days as follows.
Stabilized sewage sludge was prepared by mixing the sludge with the amendments at two rates (10% and 25%) as shown in Table
Treatments of sewage sludge with the studied stabilized agents.
Codes | Treatments | Mixing rate | |
---|---|---|---|
10% | 25% | ||
SS | Sewage sludge | 100 g | 100 g |
SS + B | Sewage sludge + bentonite | 90 g SS + 10 g B | 75 g SS + 25 g B |
SS + SBFL | Sewage sludge + sugar beet factory lime | 90 g SS + 10 g SBFL | 75 g SS + 25 g SBFL |
SS + CFA | Sewage sludge + coal fly ash | 90 g SS + 10 g CFA | 75 g SS + 25 g CFA |
SS + CaCO3 | Sewage sludge + calcium carbonate | 90 g SS + 10 g CaCO3 | 75 g SS + 25 g CaCO3 |
SS + RS | Sewage sludge + rice straw | 90 g SS + 10 g RS | 75 g SS + 25 g RS |
SS + WH | Sewage sludge + water hyacinths | 90 g SS + 10 g WH | 75 g SS + 25 g WH |
SS + CS | Sewage sludge + cotton stalks | 90 g SS + 10 g CS | 75 g SS + 25 g CS |
The following chemical properties were determined in sieved samples: pH in deionized water in soil solution ratio of 1 : 1 for soil and inorganic amendments and 1 : 5 for sewage sludge and organic amendments according to [
All results were analyzed statistically using one-way ANOVA to compare the means of different treatments. The individual means were compared by Duncan’s test to a level of 5% using SPSS version 10.01. The results were subjected to multifactorial analysis. The considered variables were soil, sewage sludge, incubation period, maxing rate, and organic and inorganic amendments where
Both studied soils showed a neutral pH. The soils exhibited quite different physical and chemical properties (Table
Selected characteristics and metal concentrations in the studied soils and sewage sludge.
Soil classification | ||||
---|---|---|---|---|
Tested characteristics | Calcareous soil | Fluvial soil | Sewage sludge (SS1) | Sewage sludge (SS2) |
Typic Torrifluvents | Typic Calcorthids | |||
Tested basic characteristics | ||||
pH | 7.82 | 7.71 | 6.28 | 5.86 |
EC, dSm−1 | 0.94 | 0.55 | 3.90 | 3.80 |
OM, g kg−1 | 14.90 | 22.20 | 144.50 | 149.20 |
CEC, cmol(+)/kg | 12.63 | 34.10 | 35.80 | 36.30 |
CaCO3, % | 28.50 | 5.30 | 15.20 | 9.88 |
Olsen-P, mg kg−1 | 8.70 | 7.70 | 53.90 | 57.30 |
| ||||
Particle size distribution, % | ||||
Sand | 53.58 | 18.52 | — | — |
Silt | 28.72 | 56.30 | — | — |
Clay | 17.70 | 25.18 | — | — |
Texture class | Sandy clay loam | Silty loam | — | — |
| ||||
DTPA-extracted elements, mg kg−1 | ||||
Zn | 2.18 | 1.21 | — | — |
Cu | 3.10 | 4.26 | — | — |
Pb | 1.25 | 2.18 | — | — |
Ni | 0.24 | 0.45 | — | — |
Cd | 0.02 | 0.02 | — | — |
| ||||
Aqua-regia-extracted elements, mg kg−1 | ||||
Fe | 18250.50 | 55724.00 | 30260.00 | 39907.50 |
Mn | 331.50 | 779.00 | 723.00 | 251.00 |
Zn | 57.20 | 111.80 | 1437.20 | 1218.10 |
Cu | 24.50 | 56.10 | 158.80 | 148.90 |
Cd | 1.50 | 1.15 | 1.45 | 1.40 |
Ni | 23.10 | 60.00 | 34.10 | 41.90 |
Pb | 46.50 | 63.50 | 193.00 | 120.50 |
EC: electric conductivity (dSm−1); OM: organic matter; CEC: cation exchange capacity (cmol(+)/kg); (—): not measured; DTPA: diethylenetriaminepenta-acetic acid.
Kafr El-Ziat sludge (SS1) contains high amounts of all the studied metals except for Fe and Ni compared to Kafr el-Sheikh sludge (SS2). So, metal concentrations in sludge varied depending on several factors such as sludge origin, sludge pretreatment processes, organic matter content, and digestion process [
The pH of the organic amendments was lower than the inorganic amendments. Coal fly ash (CFA) and sugar beet factory lime (SBFL) recorded the highest pH values, that is, 12.50 and 12.59, respectively. Coal fly ash is an alkaline residue produced during the burning of coal for electricity generation usually containing appreciable amounts of ferroaluminum silicate minerals with Al, Ca, Mg, Fe, K, Na, and Si as predominant elements [
Selected characteristics and metal concentrations in the studied amendments.
Properties | Organic amendments | Inorganic amendments | ||||||
---|---|---|---|---|---|---|---|---|
WH | RS | CS | BFA | CFA | B | SBFL | CaCO3 | |
pH | 6.18 | 7.60 | 5.62 | 9.68 | 12.5 | 9.24 | 12.59 | 8.81 |
EC, dSm−1 | 6.91 | 2.83 | 2.01 | 0.98 | 4.48 | 1.13 | 1.55 | 0.17 |
OM, % | 75.25 | 52.7 | 97.49 | — | — | — | — | — |
CaCO3, % | — | — | — | — | 12.4 | — | 81.6 | — |
Total elements, mg kg−1 | ||||||||
Fe | — | — | — | 7590.0 | 21228.0 | 59750.0 | 651.5 | — |
Mn | — | — | — | 78.35 | 202.9 | 618.5 | 18.9 | — |
Zn | 111.4 | 28.6 | 65.0 | 5.55 | 55.1 | 108.25 | 26.40 | 37.0 |
Cu | 60.8 | 98.6 | 47.1 | 4.30 | 30.1 | 33.70 | 9.70 | 41.1 |
Cd | nd | nd | nd | nd | 2.15 | 1.35 | 3.45 | nd |
Ni | — | — | — | 8.8 | 170.9 | 50.35 | 13.10 | — |
Pb | 8.6 | 68.4 | — | 16.0 | 62.5 | 34.5 | 57.00 | — |
CFA: coal fly ash, B: bentonite, SBFL: sugar beet factory lime, RS: rice straw, WH: water hyacinth, CS: cotton stalks, nd: not detected, —: not measured.
Sewage sludge application increased significantly Olsen-P concentrations from 7.7 to 21.0 mg kg−1 in fluvial soil and from 8.8 to 25.7 mg kg−1 in calcareous soil (Table
Effect of SS and stabilized SS on Olsen-P in relation to soil type, sewage source, mixing rate, and incubation period.
Treatments | Fluvial soil | Calcareous soil | ||||||
---|---|---|---|---|---|---|---|---|
SS1 | SS2 | SS1 | SS2 | |||||
30 day | 60 day | 30 day | 60 day | 30 day | 60 day | 30 day | 60 day | |
Mixing rate, 10% | ||||||||
| ||||||||
C | 7.7f | 7.7d | 7.7e | 7.6c | 8.8e | 8.8e | 8.8e | 8.8f |
SS | 19.4c | 20.7b | 20.7b | 21.0a | 25.2b | 25.7b | 24.1abc | 24.9c |
SS + CFA | 17.0d | 17.8c | 18.6c | 19.9a | 20.4d | 18.1d | 24.5ab | 27.2b |
SS + B | 21.8a | 18.0c | 23.6a | 22.1a | 22.1c | 25.2b | 26.1a | 25.9c |
SS + SBFL | 21.2ab | 19.3bc | 21.2b | 20.8a | 31.3a | 28.3a | 21.9bcd | 29.2a |
SS + CaCO3 | 20.0bc | 18.7bc | 17.3cd | 15.3b | 26.1b | 27.3ab | 22.8abcd | 21.3d |
SS + WH | 18.8c | 23.4a | 16.9cd | 15.5b | 20.7d | 22.5c | 20.7cd | 21.6d |
SS + RS | 15.2e | 17.6c | 15.6d | 20.7a | 21.0cd | 20.0cd | 21.0bcd | 19.3e |
SS + CS | 16.9d | 18.7bc | 16.1d | 19.1ab | 19.9d | 20.2cd | 19.8d | 22.3d |
| ||||||||
Mixing rate, 25% | ||||||||
| ||||||||
C | 7.7c | 7.6f | 7.7f | 7.6d | 8.8h | 8.8e | 8.8f | 8.8f |
SS | 19.4a | 20.7ab | 20.7b | 21.0a | 25.2b | 25.7a | 24.1b | 24.9c |
SS + CFA | 16.6b | 16.3de | 19.8bc | 21.8a | 19.9ef | 20.9bc | 22.5bc | 25.4bc |
SS + B | 21.2a | 18.6abcd | 23.3a | 21.2a | 21.8de | 22.6b | 24.5b | 29.7a |
SS + SBFL | 19.7a | 21.0a | 18.2cd | 20.7a | 27.9a | 26.6a | 28.0a | 27.6ab |
SS + CaCO3 | 16.9b | 18.1bcd | 17.0de | 16.9c | 24.3bc | 25.8a | 21.8cd | 21.6d |
SS + WH | 19.4a | 17.8cde | 16.3e | 16.5c | 18.5fg | 20.4c | 19.8de | 21.9d |
SS + RS | 14.8b | 15.3e | 16.2e | 16.9c | 18.1g | 17.4d | 18.8e | 19.1e |
SS + CS | 19.5a | 19.3abc | 19.5bc | 19.1b | 22.7cd | 21.3bc | 22.6bc | 21.9d |
Values accompanied by different letters are significantly different within column (
C: control (un amended soil), SS: sewage sludge, CFA: coal fly ash, B: bentonite, SBFL: sugar beet factory lime, RS: rice straw, WH: water hyacinth, CS: cotton stalks, nd: not detected, —: not measured.
Multifactor analysis of statistical differences in P, Cu, and Zn concentrations as affected by soil types, sewage source, mixing rate, and incubation time.
Source | Soils | Sewages | Rates | Incubation periods | Amendments | Soils*sewages*rates*incubation periods*amendments | |
---|---|---|---|---|---|---|---|
P | DF | 1 | 1 | 1 | 1 | 8 | 8 |
|
949.08 | 8.23 | 3.79 | 10.37 | 620.57 | 3.39 | |
Prob > |
<0.01* | 0.04* | 0.05 | 0.01* | <0.01* | 0.01* | |
| |||||||
Zn | DF | 1 | 1 | 1 | 1 | 8 | 8 |
|
278.49 | 90.99 | 3.49 | 216.33 | 894.80 | 1.15 | |
Prob > |
<0.01* | <0.01* | 0.06 | <0.01* | <0.01* | 0.32 | |
| |||||||
Cu | DF | 1 | 1 | 1 | 1 | 8 | 8 |
|
1.23 | 1.01 | 1.01 | 0.96 | 0.99 | 0.99 | |
Prob > |
0.26 | 0.31 | 0.31 | 0.32 | 0.43 | 0.43 |
Our results were in consistency with [
The application of SS increased significantly DTPA extractable Zn compared to untreated soil from 1.20 to 9.57 mg kg−1 with increasing percent 684% and from 2.16 to 10.50 mg kg−1 with increasing percent 367% in fluvial and calcareous soil, respectively. This increase could be explained by the following possible reasons: high content of Zn in sewage sludge (1437 mg kg−1, Table
Also, data indicated that the increasing rate was high with SS2 compared to SS1 in fluvial soil especially after the first incubation period. However, the opposite trend was recorded in calcareous soil, where SS1 application increased available Zn compared to SS2 especially in the first incubation period. Additionally, fluvial soil showed increasing rate higher than calcareous soil. Lower increase rate of DTPA-extractable Zn in calcareous soil compared to fluvial one after application of SS may be due to the precipitation and/or sorption of biosolid-born released Zn with calcium carbonate. Increasing Zn sorption in soils rich in CaCO3 may be due to the formation of ZnCO3 and/or Zn sorption by calcium and magnesium carbonate. In this respect, [
The data showed that mixing SS with the studied amendments decreased significantly the amounts of DTPA-extractable Zn in both fluvial and calcareous soil with SS1 and SS2 and after both mixing rates and incubation periods except for CS-stabilized SS in some cases (Table
Effect of sewage sludge and stabilized sewage sludge on the DTPA-extractable zinc in relation to soil type, sewage source, mixing rate, and incubation period.
Treatments | Fluvial soil | Calcareous soil | ||||||
---|---|---|---|---|---|---|---|---|
SS1 | SS2 | SS1 | SS2 | |||||
30 day | 60 day | 30 day | 60 day | 30 day | 60 day | 30 day | 60 day | |
Mixing rate, 10% | ||||||||
| ||||||||
C | 1.21f | 1.20e | 1.21d | 1.20e | 2.18e | 2.16e | 2.18f | 2.16e |
SS | 8.46ab | 8.11a | 9.57a | 7.80b | 10.50a | 8.84a | 10.10a | 9.15a |
SS + CFA | 7.77bcd | 6.40c | 7.46bc | 6.39cd | 9.02b | 6.51cd | 9.46bc | 7.79b |
SS + B | 7.49cde | 7.36ab | 7.56bc | 7.46b | 6.24a | 7.13bc | 8.63d | 7.60bc |
SS + SBFL | 8.15abc | 6.49c | 7.59bc | 6.68cd | 7.57c | 8.10a | 8.78d | 7.81b |
SS + CaCO3 | 7.19de | 6.63bc | 7.57bc | 6.85c | 7.76c | 7.32b | 8.89cd | 6.72cd |
SS + WH | 7.15de | 6.18c | 7.37c | 6.07d | 7.22c | 6.69bcd | 6.87e | 6.49d |
SS + RS | 6.78e | 5.35d | 8.14b | 7.72b | 7.54c | 6.01d | 9.04bcd | 7.96b |
SS + CS | 8.89a | 7.33ab | 7.85bc | 8.60a | 8.62b | 8.19a | 9.66ab | 9.70a |
| ||||||||
Mixing rate, 25% | ||||||||
| ||||||||
C | 1.21c | 1.20e | 1.21e | 1.20f | 2.18e | 2.16f | 2.18d | 2.16 g |
SS | 8.46a | 8.11a | 9.57a | 7.80a | 10.5a | 8.84b | 10.10a | 9.15a |
SS + CFA | 7.24ab | 5.77cd | 7.50bc | 7.14bc | 8.36bc | 7.24d | 7.92bc | 7.39de |
SS + B | 6.86ab | 5.64cd | 7.28c | 7.31b | 7.72bcd | 7.99c | 8.75b | 7.87bcd |
SS + SBFL | 7.33ab | 6.70b | 8.00b | 7.34b | 7.12cd | 8.22c | 7.98bc | 7.54cde |
SS + CaCO3 | 6.12b | 8.00a | 7.37bc | 6.28d | 8.17bc | 7.34d | 8.64b | 6.00f |
SS + WH | 6.66b | 6.29bc | 5.99d | 5.80e | 6.52d | 5.73e | 7.20c | 6.90e |
SS + RS | 6.66b | 4.83d | 9.17a | 7.49ab | 7.17cd | 6.25e | 9.74a | 8.33abc |
SS + CS | 7.56ab | 7.88a | 8.92a | 6.88c | 8.71b | 9.64a | 9.95a | 8.73ab |
Values accompanied by different letters are significantly different within column (
Regarding the efficacy of tested amendments in reducing the Zn availability in biosolid amended soil, they differed widely depending on soil type and sewage source. In fluvial soil, in the case of SS1 and mixing rate 25% after 60-day incubation period, B- and CFA-stabilized SS treatment showed the highest decreasing rate of available Zn compared to the mono-SS treatment between the inorganic amendments and RS-stabilized SS between the organic ones. On the other hand, in calcareous soil and in the case of SS1 and mixing rate 25% after 60-day incubation period, B-stabilized SS treatment showed the highest decreasing percent of available Zn compared to the mono-SS treatment (9.6% reduction), while WH-stabilized SS treatment showed the highest decreasing percent between the organic amendments (35.2% reduction). These trends indicate that B was the best inorganic amendment for reducing DTPA-extractable Zn either in fluvial or calcareous soil. This result indicates that B has the ability to take up a significant concentration of Zn associated with the mobile forms. The fact that the bentonite binds the available element form had been reported before by [
One-way ANOVA showed a significant difference in Zn concentration as affected by sewage, soils, sewages, incubation periods, or amendments at the same significance level in each one of them (
The efficiency of CFA in reducing the availability of Zn in biosolid-amended soils may be due to its high alkalinity (pH = 12.5 Table
Also, data in Table
The results indicated that the decreasing rate of available Zn in stabilized SS treatments increased with increasing the mixing rate from 10 to 25% and with increasing the incubation period from 30 to 60 days. The 25% application rate was the best rate in reducing DTPA-extractable Zn either in the first or in the second incubation period. Also, data showed that the DTPA-extractable Zn decreased over incubation time. This result was in accordance with [
In regards to the effect of soil types, results indicated that the fluvial showed the best response for the effect of the tested amendments in decreasing DTPA-extractable Zn compared to calcareous soil in both incubation periods. The differences between the studied soils were highly significant. With respect to sewage sources, SS1 showed a positive significance response for all the studied amendments in reducing DTPA-Zn compared to SS2.
In fluvial soil the DTPA-extractable Cu increased from 3.86 to 7.01 and 6.95 mg kg−1 with SS1 and SS2, respectively. In calcareous soil, the DTPA-extractable Cu increased from 3.10 to 6.17 and 4.39 mg kg−1 with SS1 and SS2, respectively (Table
Effect of sewage sludge and stabilized sewage sludge on the DTPA-extractable copper in relation to soil type, sewage source, mixing rate, and incubation period.
Treatments | Fluvial soil | Calcareous soil | ||||||
---|---|---|---|---|---|---|---|---|
SS1 | SS2 | SS1 | SS2 | |||||
30 day | 60 day | 30 day | 60 day | 30 day | 60 day | 30 day | 60 day | |
Mixing rate, 10% | ||||||||
| ||||||||
C | 3.86d | 3.88d | 3.86d | 3.88b | 3.11d | 3.10d | 3.11b | 3.10a |
SS | 7.01a | 6.98a | 6.95a | 6.90a | 6.17a | 4.68a | 4.39a | 3.64a |
SS + CFA | 6.70a | 6.03b | 6.62ab | 6.62a | 4.11c | 3.19d | 3.39b | 3.29a |
SS + B | 6.22b | 6.85a | 6.21bc | 5.98a | 2.88e | 3.57cd | 3.36b | 2.77a |
SS + SBFL | 6.40ab | 6.80a | 6.90ab | 6.55a | 3.66c | 3.88bc | 4.25a | 3.62a |
SS + CaCO3 | 6.99a | 6.94a | 6.80ab | 6.30a | 3.96c | 4.35ab | 4.32a | 3.36a |
SS + WH | 6.73a | 5.79b | 5.88c | 4.20b | 3.81c | 3.33d | 3.12b | 3.18a |
SS + RS | 5.27c | 4.63c | 6.55ab | 6.89a | 3.89c | 3.36d | 4.34a | 3.55a |
SS + CS | 6.69a | 6.95a | 6.71ab | 5.97a | 4.87b | 3.33d | 4.12a | 3.39a |
| ||||||||
Mixing rate, 25% | ||||||||
| ||||||||
C | 3.86c | 3.88e | 3.86d | 3.88e | 3.11d | 3.10cd | 3.11c | 3.10bc |
SS | 7.01ab | 6.98a | 6.95ab | 6.90a | 6.17a | 4.68a | 4.39a | 3.64a |
SS + CFA | 6.46ab | 5.18cd | 5.92c | 5.53b | 3.26d | 2.88d | 2.63d | 2.97cd |
SS + B | 5.80ab | 5.59bcd | 5.72c | 5.25bc | 3.27d | 3.39bc | 3.88b | 2.62d |
SS + SBFL | 6.37ab | 6.50ab | 6.89ab | 6.59a | 3.52cd | 3.60b | 3.78b | 3.50a |
SS + CaCO3 | 7.21a | 7.11a | 7.28a | 6.77a | 4.05bc | 4.59a | 4.47a | 3.44ab |
SS + WH | 6.40ab | 5.98abc | 6.00bc | 4.02de | 3.54cd | 2.81d | 2.75cd | 2.99cd |
SS + RS | 5.22bc | 4.59de | 6.51abc | 6.64a | 3.67bcd | 2.70d | 3.85b | 2.74cd |
SS + CS | 6.31ab | 6.39ab | 6.12bc | 4.73cd | 4.32b | 3.67b | 4.19ab | 2.84cd |
Values accompanied by different letters are significantly different within column (
Also, data indicated that the increasing rate of DTPA-extractable Cu was high with SS1 compared to SS2 either in fluvial or calcareous soil. Additionally, fluvial soil showed increasing rate higher than calcareous soil. Decreasing rate of DTPA-extractable Cu in calcareous soil compared to fluvial one after application of SS may be due to the precipitation and/or sorption of biosolid-born released Cu with calcium carbonate. In this respect, [
Mixing SS with the studied amendments changed significantly the amounts of DTPA-extractable Cu depending on type of amendments, soils, mixing rate, incubation period, and SS source (Table
Regarding the efficacy of tested amendments in reducing the Cu availability in biosolid-amended soil, they differed widely depending on soil type and sewage source. In fluvial soil, in the case of SS1, B-, SBFL-, and CFA-stabilized SS treatment showed the highest significant decreasing rate of available Cu compared to the mono-SS treatment between the inorganic amendments and RS- and WH-stabilized SS between the organic ones. On the other hand, in calcareous soil, and also in the case of SS1, B, SBFL-, and CFA-stabilized SS treatment showed the highest significant decreasing rate of available Cu compared to the mono-SS treatment, while WH-stabilized SS treatment showed the highest decreasing percent between the organic amendments.
These trends indicate that B, SBFL, and CFA were the best inorganic amendments in reducing DTPA-extractable Cu either in fluvial or calcareous soil. Bentonite-stabilized SS treatments showed a relatively high reduction of available Cu in both of the tested soils. This reduction may be due to the adsorption of Cu on the surface of bentonite or fixation of Cu as a result of precipitation, physical entrapment in clay lattice wedge zones, or strong adsorption at the exchange sites. The same conclusions are reported by Kabata-Pendias [
The high ability of CFA in sorption of Cu in biosolid-amended soil was studied by [
Regarding the effect of incubation time, DTPA-extractable Cu decreased with increasing the incubation time. This trend was in agreement with [
The present study investigated the influence of sewage sludge and stabilized sewage sludge application on phosphorus availability and DTPA-extractable copper and zinc in relation to soil type, sewage source, mixing rate, and incubation time. Application of SS increased significantly Olsen-P compared to control. The increasing rates were higher in the case of domestic SS (SS2) compared to the industrial one (SS1), in the second incubation period (60 day) compared to the first one (30 day), and in calcareous soil compared to fluvial soil. Mixing SS with the studied amendments increased Olsen-P especially SBFL- and WH-stabilized SS treatments.
Application of SS increased significantly DTPA-extractable Zn compared to control. Fluvial soil showed increasing rate higher than calcareous soil. Stabilization of SS by all the studied amendments reduced Zn availability except for cotton stalks treatment. Bentonite-, CFA- and RS-stabilized SS showed the highest decreasing rate of available Zn. The highest application rate (i.e., %25) was the best in reducing DTPA-extractable Zn either in the first or in the second incubation period. DTPA-extractable Zn decreased over incubation time. Fluvial soil showed the best response for the effect of the tested amendments on decreasing DTPA-extractable Zn compared to calcareous soil in both incubation periods.
Application of SS increased significantly DTPA-Cu rate with the industrial SS compared to the domestic one. Fluvial soil showed higher increasing rate than calcareous soil. Bentonite-, SBFL-, CFA RS, and WH-stabilized SS treatment showed the highest decreasing rate of available Cu in relation to SS. Stabilized sludge products reduced the availability of sludge trace elements, that is, copper and zinc, compared to the mono-SS treatments. Nevertheless, the long-term accumulation of trace elements following the application of stabilized sludge warrants further studies.