Sewage Sludge Application Rates Research Articles

Short-term residual effect of municipal sewage sludge on the soil properties and potato yield

Sewage sludge (SS) is one of the significant wastes of modern city lifestyle with environmental consequences. This study was conducted to determine the effect of the municipal sewage sludge on the potato plant’s yield and nutrient elements and heavy metals content in a clay loam textured calcareous soil. The field treatment (corn-wheat-potato rotation) was implemented as fixed randomized blocks with 3 replications. The treatments were: control (without fertilizer), optimum fertilizer (OCF), 20, 40, 80, 100, and 120 ton ha-1 SS incorporation. The third-year results regarding the potato cultivation were presented. Results indicated that 4 ton ha-1 SS treatment resulted in a greater yield than the optimum fertilizer. The sewage sludge influenced the mineral nutrient composition of the leaves and the roots and the heavy metal concentrations in the plants were below the Turkish legal threshold values. Excessive application of SS had an inverse effect on the yield and reduced the essential nutrient concentrations of the leaves of the potato plants. This suggested that the residual effects of SS in the third year were considerable for either heavy metal concentrations or plant nutrients in the soil. Therefore, it can be concluded that a site-specific determination of the SS application rate is required to avoid potential deleterious effects of SS.

Information-logical model of the influence of the composition of soil structures of the newly created agricultural landscape on the yield and nutritional value of crops

The studies conducted on establishing the impact of introducing various norms of sewage sludge on the yield and nutritional value of agricultural crops when creating an agrolandscape of a reclaimed municipal solid waste landfill were carried out on such crops as triticale, festulolium, awnless brome. The amount of nutrients supplied to the experimental variants depended on the application rate of sewage sludge or soil. No further nutrients were added. The conducted information-logical analysis showed the presence of a direct close relationship between the yield of triticale, festulolium, awnless brome and variants of the field experiment. The share of the influence of the introduction of sewage sludge according to the variants of the experiment on the yield of festulolium was 31.64%. The share of the influence of the introduction of sewage sludge according to the variants of the experiment on the yield of triticale is 54.4%. The share of the influence of the introduction of WWS according to the variants of the experiment on the yield of awnless rump was 77.2%. Based on the result of the information-logical analysis, a model of the influence of the residual sewage sludge on crop yields was compiled.

Uptake and translocation of synthetic musk fragrances by pea plant grown in sewage sludge-amended soils

Sewage sludges are rich in organic matter and several essential nutrients for plant growth, making them very appealing for application in agricultural soils. However, they may also contain a wide range of emerging pollutants, which has raised concerns about the potential risks of this practice to crops, the environment, and public health - accumulation in soils and/or plant uptake and translocation of contaminants. Therefore, there is a need to study plant-soil interactions and assess the uptake potential of these contaminants by food crops to better understand these risks. The main aim of this work was to assess the possible drawbacks of sludge application to cropland, by observing the impact on the growth and yield of a model crop (pea plant - Pisum sativum) grown over an 86-day greenhouse experiment and by assessing the uptake potential of synthetic musk fragrances. Different sewage sludge application rates (4–30-ton ha−1) and initial concentrations of contaminants were tested. The application of sludge yielded benefits to the cultivated plants, finding improved crop productivity with an application rate of 30-ton ha−1. At the end of the experiment, soil samples and plants separated into sections were analysed using a QuEChERS extraction methodology followed by gas chromatography-mass spectrometry (GC-MS) quantification. Galaxolide (HHCB) and tonalide (AHTN) underwent uptake by the plant roots, having been detected in concentrations up to 346 ng g−1 on a dry weight basis (dw), but only HHCB was detected in above ground tissues. At the end, a decrease in the levels of synthetic musks in the amended soils (>80% in several instances) was observed. Assuming the worst-case scenario, no risk to human health was observed from the ingestion of peas grown on sewage sludge-amended soils. However, a soil hazard quotient analysis yielded worryingly high quotient values for AHTN in nearly all tested conditions.

Prediction models based on soil properties for evaluating the uptake of eight heavy metals by tomato plant (Lycopersicon esculentum Mill.) grown in agricultural soils amended with sewage sludge

The aim of this study is to design de novo prediction models in order to gauge the likely uptake of eight heavy metals (Al, Cr, Cu, Fe, Mn, Ni, Pb and Zn) by Lycopersicon esculentum, the tomato plant. Uptake was assessed within the plant’s root, stem, leaf and fruit tissues, respectively. The plant was cultivated in soil amended by different application rates of sewage sludge, i.e. 0, 10, 20, 30 and 40 g/kg. The roots exhibited markedly elevated heavy metal concentrations compared to the above-ground plant components, with the exception of the quantity of Ni in the leaves. Apart from Al, Fe and Mn, a bioconcentration factor >1 was identified for all heavy metals. Excluding Ni in the leaves, all tested heavy metals exhibited a translocation factor < 1. The regression models were deployed to predict the accretion of the heavy metals under investigation within the various parts of L. esculentum. These were founded on the parameters of the equivalent eight heavy metals within the soil, pH and organic matter content. Student’s unpaired t-tests revealed no differences between the actual and predicted heavy metal concentrations in the roots, stems, leaves or fruits of the tomato plant. These data suggest an excellent model goodness of fit in terms of its accuracy to forecast the degree of heavy metal uptake. The constructed models may therefore facilitate the safe propagation of L. esculentum in growing media amended with sewage sludge, and concurrently provide a risk assessment with respect to human well-being.

Evaluation of newly reclaimed areas in Saudi Arabia for cultivation of the leguminous crop Phaseolus vulgaris under sewage sludge amendment

Herein, the cultivation of Phaseolus vulgaris was evaluated in newly reclaimed areas in Abha City, Saudi Arabia, following amendment with different rates of sewage sludge (SS) collected from a nearby municipal wastewater treatment plant. A pot experiment was designed to assess the soil heavy metal (HM) pools, growth, yield and HM uptake by P. vulgaris plants cultivated under different SS amendment rates (0, 10, 20, 30, 40 and 50 g kg−1). SS application was found to significantly change all of the chemical properties of the reclaimed soil (except Fe and Mn). The application of SS caused a gradual significant elevation in the soil organic matter content. The application of SS also led to a meaningful increase in the soil electrical conductivity and the Cd, Co, Cr, Cu, Mo, Ni, Pb and Zn contents. However, the soil pH decreased in reaction to the treatments. However, the measured HMs (except Fe) in the soil mixtures in all treatments after harvesting P. vulgaris plants were below the maximum permissible limits in agricultural soil. Generally, SS application up to 20 g kg−1 caused a significant increase in most of the morphological parameters and biomass of P. vulgaris compared to the plants grown in the control soil, followed by a decreasing trend at SS application rates of 30, 40 and 50 g kg−1. P. vulgaris flower production decreased with an increase in the SS application rate, and fruiting was only successful at rates of 10 and 20 g kg−1. All the HM contents in different tissues of P. vulgaris were meaningfully higher for plants treated with different SS levels matched to those grown in control soil. The highest contents of all of the HMs were documented at 50 g kg−1 SS in all P. vulgaris tissues. However, all HM contents (excluding Fe and Mn in the roots) were within safe limits, with most of the absorbed HMs persisting in roots. The regression analysis showed that P. vulgaris plants have an increasing ability to absorb more HMs with an increase in the SS amendment rate. Calculations of bioaccumulation factor (BAF) showed that the BAF for most investigated HM was < 1. This means that P. vulgaris is an excluder for these HMs. In addition, calculations of the translocation factor (TF) indicated that the capacity of P. vulgaris to translocate HMs from roots to shoots or pods is < 1 for most of the investigated HMs, indicating that the amounts of HMs that persisted in roots were always higher than those that travelled to the stems, leaves or pods. Taken together, our findings suggest that soil application of SS up to 20 g kg−1 can provide a sustainable safe practice for SS disposal and improve P. vulgaris growth and yield, while exerting no environmental threats provided there is no accumulation of HMs to toxic levels in shoots of the grown P. vulgaris plants or in the amended soils.

Sewage sludge application enhances soil properties and rice growth in a salt-affected mudflat soil

The most important measures for salt-affected mudflat soil reclamation are to reduce salinity and to increase soil organic carbon (OC) content and thus soil fertility. Salinity reduction is often accomplished through costly freshwater irrigation by special engineering measures. Whether fertility enhancement only through one-off application of a great amount of OC can improve soil properties and promote plant growth in salt-affected mudflat soil remains unclear. Therefore, the objective of our indoor pot experiment was to study the effects of OC amendment at 0, 0.5%, 1.0%, 1.5%, and 2.5%, calculated from carbon content, by one-off application of sewage sludge on soil properties, rice yield, and root growth in salt-affected mudflat soil under waterlogged conditions. The results showed that the application of sewage sludge promoted soil fertility by reducing soil pH and increasing content of OC, nitrogen and phosphorus in salt-affected mudflat soil, while soil electric conductivity (EC) increased with increasing sewage sludge (SS) application rates under waterlogged conditions. In this study, the rice growth was not inhibited by the highest EC of 4.43 dS m−1 even at high doses of SS application. The SS application increased yield of rice, promoted root growth, enhanced root activity and root flux activity, and increased the soluble sugar and amino acid content in the bleeding sap of rice plants at the tillering, jointing, and maturity stages. In conclusion, fertility enhancement through organic carbon amendment can “offset” the adverse effects of increased salinity and promote plant growth in salt-affected mudflat soil under waterlogged conditions.

Soil microbial properties and functional diversity in response to sewage sludge amendments

ABSTRACT Soil organic matter has vital role in maintaining important soil functions. Consequently, using sewage sludge as soil organic amendment is considered one of the agricultural practices for improving soil fertility, which is also a safe approach for its disposal. The present research was carried out to analyze the different microbial activities and functional diversity of agricultural soil with regard to sewage sludge application. A laboratory experiment was set up by taking the agricultural soil from Haryana Agricultural University fields and amended with 5, 10, 20, 30 and 50 t ha−1 of sewage sludge. It was observed that soil microbial biomass increased upto 60% and potential activities of dehydrogenase, alkaline phosphatase and urease enzymes increased upto 50–55% with increasing application rates of sewage sludge. In addition the community-level physiological profiling technique (CLPP) based on carbon source utilization was used to determine the microbial functional diversity of soil. The results indicated higher functional diversity of microbial population capable of exploiting different carbon substrates with sewage sludge application. These results are imperative for improving the approach of sewage sludge application to the agricultural soil in consideration of increasing soil fertility with reducing the use of chemical fertilizers.

Heavy Metal Bioaccumulation, Growth Characteristics, and Yield of Pisum sativum L. Grown in Agricultural Soil-Sewage Sludge Mixtures.

The application of sewage sludge (SS) in agriculture is an alternative disposal method for wastewater recycling and soil fertilization. This study evaluated heavy metal bioaccumulation, growth, and yield of Pisum sativum (pea) grown in agricultural soil amended with SS at rates of 0, 10, 20, 30, and 40 g/kg. The results show that root, shoot, pod length, biomass, and number of leaves and pods increased with SS amendments of 10 and 20 g/kg, while rates declined at 30 and 40 g/kg. SS had greater salinity and organic content than the soil. Heavy metals in the postharvest soil samples increased for all SS application rates except Fe and Mo. The significant increase in Cd content started at the lowest amendment rate 10 g/kg; for Co, Mn, and Pb, the significant increase was detected at the highest amendment rate (40 g/kg). Generally, all heavy metals increased significantly in portions of P. sativum except Cd in the shoot. At an amendment rate of 10 g/kg, Co in the shoot and root, Cr in the fruit, Cu in the root, Fe in the fruit, Mn in the shoot and fruit, Mo in the fruit, Pb in the shoot, and Zn in the fruit were elevated significantly. In contrast, the concentrations of Cd in the fruit, Cr in the root, Cu in the shoot, Fe in the shoot and root, Ni in the fruit and root, Pb in the fruit and root, and Zn in the root significantly increased only at the highest rate of 40 g/kg. The highest regression R2 was 0.927 for Mn in pods and the lowest was 0.154 for Cd in shoots. Bioaccumulation and translocation factors were > 1 for Mo and the bioaccumulation of Pb was >1. SS could be used for pea fertilization but only at rates below 20 g/kg to avoid environmental and health hazards.

Monitoring the variation of soil quality with sewage sludge application rates in absence of rhizosphere effect

Agricultural soils in semi-arid regions have frequently been degraded due to adverse climatic conditions, organic matter depletion, and poor farming practices. To enhance soil quality, this study examines the reuse of sewage sludge (SS) as an available source of organic matter in a typical Mediterranean sandy-loam soil. Accordingly, we studied the cumulative effect of two annual applications of 40, 80 and 120 tons of sludge per ha on soil quality in absence of vegetation. The dose-dependent improvement of organic matter content was the most significant event that reflected sludge application rates, and consequently influenced other soil properties. Accordingly, soil structural stability increased by 13.3%, 28.8% and 59.4% for treatments SS-40, SS-80 and SS-120 respectively as compared to unamended control. Structural stability improvement was also confirmed by the dose-dependent variation of other edaphic factors including calcium content, the microbial quotient as well as Welt and C:N ratios. These parameters are involved in cementing soil aggregates by cation bridging, the formation of microbial mucilage, and clay-humic complexes. Soil magnetic susceptibility (SMS) was measured in situ as a possible rapid tool to evaluate soil condition. SMS showed significant correlation with sludge dose and stability amelioration testifying to the aggregation role that can play Al2O3 and particularly Fe2O3 minerals added by the hematite-rich sludge. Besides, analytical results and field observations revealed no trends of soil salinization or acidification by excessive sludge amounts. By avoiding the rhizosphere effect, outcomes could reflect the resilience and intrinsic capacity of the soil to cope with excessive sludge loads.

An integrated assessment of the long-term impact of municipal sewage sludge on the chemical and biological properties of soil

The aim of the study was to assess the long-term changes of chemical and biological properties of soil treated with various application rates of municipal sewage sludge (SS) under the condition of field and laboratory experiments. The experiment scheme included five treatments: 1 – the control; 2 – 10 t of SS dry matter per hectare; 3 – 20 t of SS dry matter per hectare; 4 – 40 t of SS dry matter per hectare and 5 – 60 t of SS dry matter per hectare. Considerable dose-dependent enhancement of carbon and nitrogen contents as well as enzyme activities were observed, particularly when high rates of sewage sludge were applied. It was proven that such rates allowing for longer durability of favorable changes in the soil and did not pose risks for its quality in the context of heavy metal and PAH concentrations as well as enzymatic activity. The presence of Phalaris arundinacea plants had a positive impact on the chemical properties and biological condition of soil, expressed in the lower content of heavy metals and PAHs and higher activity of soil enzymes. Significant correlations between all analyzed parameters in the field and laboratory experiment indicates that such studies allow a reliable assessment of the impact of SS application on the chemical and biological condition of soils within a given ecosystem.

EFFECTS OF THE DIFFERENT IMPLEMENTATION OF LEGISLATION RELATING TO SEWAGE SLUDGE DISPOSAL IN THE EU

The European Directive 86/278/EEC implemented in 1986 was a means adopted by the European Union to improve use of the valuables in sewage sludge by applying treated sludge on agricultural soils. To prevent an accumulation of pollutants, the Directive provided suggestions limiting concentrations of toxic elements in sewage sludge and agricultural soil. The Directive was implemented diversely throughout EU member states, with current national legislations only partly reflecting the initial intentions of the EU Directive from 30 years ago. This study demonstrates how the European Directive was implemented in three countries currently at different stages of replacing the agricultural application of sewage sludge with incineration (Netherlands, Germany and Sweden). Additionally, recent changes in the legislation with regards to the re-use and final disposal of sewage sludge in the three chosen member states are analysed. The aim was to investigate how each member state has solved the conflict between improvement of nutrient recovery from sludge and limitation of pollutants in agricultural soil. Based on this review, limit values are not necessarily reflected in application rates of sewage sludge in agriculture. Following changes in current legislation, phosphorus recovery will become a priority task. The recovery of other valuables from sewage sludge is currently not regulated in the legislation of the three member states investigated.

Environmental performances of production and land application of sludge-based phosphate fertilizers-a life cycle assessment case study.

Phosphorus (P) is a non-renewable resource extracted from phosphate rock to produce agricultural fertilizers. Since P is essential for life, it is important to preserve this resource and explore alternative sources of P to reduce its criticality. This study aimed to assess whether fertilizing with sludge-based phosphate fertilizers (SBPF) can be a suitable alternative to doing so with fertilizers produced from phosphate rock. Environmental impacts of production and land application of SBPF from four recovery processes were compared to those of two reference scenarios: triple super phosphate (TSP) and sewage sludge. To avoid bias when comparing scenarios, part of the environmental burden of wastewater treatment is allocated to sludge production. The CML-IA method was used to perform life cycle impact assessment. Results highlighted that production and land application of SBPF had higher environmental impacts than those of TSP due to the large amounts of energy and reactants needed to recover P, especially when sludge had a low P concentration. Certain environmental impacts of production and land application of sewage sludge were similar to those of SBPF. Sensitivity analysis conducted for cropping systems highlighted variability in potential application rates of sewage sludge or SBPF. Finally, because they contain lower contents of heavy metals than sewage sludge or TSP, SBPF are of great interest, but they require more mineral fertilizers to supplement their fertilization than sewage sludge. Thus, SBPF have advantages and disadvantages that need to be considered, since they may influence their use within fertilization practices.

Processed agrifood residues for phosphorus recycling in the field

Processing of organic residues may affect plant-availability of phosphorus (P) and thus the potential to recycle the nutrient, i.e., recyclability, but empirical evidence in the field is lacking. In field experiments in clay and silt loam soils with low available P, impact on P recyclability by cattle manure and sewage sludge processing methods (composting, anaerobic digestion, lime-stabilization, acid-oxidizer) and three application rates were assessed. Synthetic nitrogen (N) and potassium (K) fertilizers were supplied in surplus and NPK served as a reference. The differences in plant response were small at relevant application rates and not consistently explained by solubility of fertilizer P. Least P was required in composted manure for the same P uptake in silt loam, and composting was beneficial to plant response in clay as well. Lime-stabilization of sewage sludge had an adverse effect on P uptake in silt loam. Increasing application rates of sewage sludge hardly enhanced but did not lower P uptake or yield even at an excessive rate. Soil water-extractable P in the autumn liable to leaching was increased by NPK only. In clay soil, sewage sludges performed better than manures obviously due to anaerobic conditions caused by high precipitation, but in silt loam the contrary was the case. In conclusion, the availability of P in processed residues is more susceptible to weather and soil variables than in synthetic fertilizer. P fertilization benefits in cereal cropping in current north European conditions appear to be generally small.

Evaluation of the potential of sewage sludge as a valuable fertilizer for wheat (Triticum aestivum L.) crops.

A greenhouse experiment was performed to assess the soil heavy metal pools, growth, yield, and heavy metal uptake of wheat plants (Triticum aestivum L.) that are grown at different rates in soils supplemented with sewage sludge (SS). The experimental design was completely randomized, with six replicates per treatment. The application of SS significantly increased the soil organic matter content. Generally, most growth parameters, as well as the biomass of treated wheat, were significantly increased with the amendment of SS, up to the addition rate of 40gkg-1. The content of all heavy metals (except Cr in grains and Pb in spikes) significantly increased in different tissues of treated wheat with the increasing rate of SS application. However, all heavy metal concentrations (except for Al, Cr, Fe, and Mn in the roots) were normal and did not overcome the phytotoxic levels. The wheat was recognized by a bioaccumulation factor < 1.0 for most of the heavy metals. The translocation factor for all of the heavy metals was < 1.0. Therefore, the SS utilized in the present study could be used as a valuable organic fertilizer in wheat cultivation areas in Saudi Arabia and could also act as an eco-friendly method for the recycling of SS.

The effects of different sewage sludge amendment rates on the heavy metal bioaccumulation, growth and biomass of cucumbers (Cucumis sativus L.).

When sewage sludge is incorrectly applied, it may adversely impact agro-system productivity. Thus, this study addresses the reaction of Cucumis sativus L. (cucumber) to different amendment rates (0, 10, 20, 30, 40 and 50gkg-1) of sewage sludge in a greenhouse pot experiment, in which the plant growth, heavy metal uptake and biomass were evaluated. A randomized complete block design with six treatments and six replications was used as the experimental design. The soil electrical conductivity, organic matter and Cr, Fe, Zn and Ni concentrations increased, but the soil pH decreased in response to the sewage sludge applications. As approved by the Council of European Communities, all of the heavy metal concentrations in the sewage sludge were less than the permitted limit for applying sewage sludge to land. Generally, applications of sewage sludge of up to 40gkg-1 resulted in a considerable increase in all of the morphometric parameters and biomass of cucumbers in contrast to plants grown on the control soil. Nevertheless, the cucumber shoot height; root length; number of leaves, internodes and fruits; leaf area; absolute growth rate and biomass decreased in response to 50gkg-1 of sewage sludge. All of the heavy metal concentrations (except the Cu, Zn and Ni in the roots, Mn in the fruits and Pb in the stems) in different cucumber tissues increased with increasing sewage sludge application rates. However, all of the heavy metal concentrations (except the Cr and Fe in the roots, Fe in the leaves and Cu in the fruits) were within the normal range and did not reach phytotoxic levels. A characteristic of these cucumbers was that all of the heavy metals had a bioaccumulation factor <1.0. All of the heavy metals (except Cd, Cu and Zn) had translocation factors that were <1.0. As a result, the sewage sludge used in this study could be considered for use as a fertilizer in cucumber production systems in Saudi Arabia and can also serve as a substitute method of sewage sludge disposal. Graphical Abstract The effects of different sewage sludge amendment rates on the heavy metal bioaccumulation, growth and biomass of cucumbers.

Effects of sewage sludge on bio-accumulation of heavy metals in tomato seedlings

The proposal to use sewage sludge (SS) on agricultural fields as a sustainable way to dispose of the waste is based on its high organic and nutrients content. However, the presence of heavy metals (HMs) in sludge can contaminate crops and accumulate in the food chain. The aim of this study was to assess changes in soil fertility, biochemical responses of tomato (Solanum lycopersicum L. cv. Rio Grande) seedlings and the availability of HMs with increased rate application of SS (0, 2.5, 5 and 7.5%). Leaf chlorophyll content, nutritional status, proline, membrane peroxidation, stomatal conductance and HM accumulation were investigated. Results showed that the soil pH decreased, whereas soil salinity, organic carbon, total N, available P and exchangeable Na, Ca, K and HM content increased significantly with increasing application rates of SS. Among the three HMs (Zn, Cu and Cr), Zn had the highest capacity for transferring from soil into plants. Low metal translocation was observed from roots to leaves. The 7.5% SS dose decreased biomass production and caused a decline in chlorophyll content and stomatal conductance. However, lipid peroxidation and proline contents increased. Therefore, the use of 2.5 and 5% doses of sewage sludge in agriculture would be an efficient and cost-effective method to restore the fertility of soil and an environment-friendly solution for disposal problems.

Effects of Sewage Sludge Amendment on Some Soil Properties, Growth, Yield and Nutrient Content of Raspberry (Rubus idaeus L.)

This study was focused not only at the assessment of effects of different sewage sludge application rates on vegetative parameters and yield of raspberry (Rubus ideaus L.) but also heavy metal accumulation in the soil and raspberry leaves. A three-year field study was set up in a completely randomized block design with five sewage sludge application rates (0.0, 2.5, 5.0, 7.5 and 10.0 kg of dry matter per plant) and three replications. One-year-old, virus free ‘Heritage’ saplings were used for the experiment. The results of this study clearly indicated that the sewage sludge application is an effective mean for improvement of vegetative growth, yield, soil and plant chemical properties of raspberry in light textured soils. In addition to macro-element contents, sewage sludge application also caused significant changes in micro-element content of soils. No adverse effects of these increases were observed on plants throughout the experimental period. The most effective application rate was found as 7.5 kg per plant for this ecological condition. It can be concluded that when properly treated and applied to farmland sewage sludge is not only disposed economically but also improved vegetative growth and yield of raspberry.

Field study on the uptake, accumulation, translocation and risk assessment of PAHs in a soil-wheat system with amendments of sewage sludge

Field experiments were conducted to explore the uptake and translocation of polycyclic aromatic hydrocarbons (PAHs) by wheat plants following sewage sludge application. Two types of application methods (single or annual application) and four application rates (5, 10, 20, and 40t/ha/year) were investigated. The contents of 16 PAHs in soils, wheat roots and straws increased as the rate of sewage sludge application increased and were in the range of 20.7 to 241, 166 to 700, and 110 to 260ng/g dry weight (dw), respectively. Meanwhile, for the PAH contents in grains (81.2–95.2ng/g dw), no statistically significant differences were observed among different treatments. A single application of a large quantity of sewage sludge would likely increase the accumulation of PAHs in soil as well as their subsequent uptake and translocation by wheat. Profile analysis indicated that the transfer and accumulation of lower weight PAHs in wheat plants were greater. Regarding PAHs, sewage sludge application at 40t/ha/year for 6years did not significantly increase the risks of intake by wheat grain grown on sludge-amended soils.

Land spreading of sewage sludge in forest plantations: effects on the growth of the duckweed Lemna minor and trace metal bioaccumulation in the snail Cantareus aspersus.

Wastewater plants generated annually millions of tons of sewage sludge (SS). Large amounts of this organic residue are spread on agricultural lands as a fertilizer, although it is viewed as a major potential source of contamination, presenting a danger to the terrestrial and aquatic environments. This study was undertaken to evaluate the impact of this practice on the duckweed Lemna minor and the snail Cantareus aspersus. Sludge was applied to soil either at six different loading rates equal to 0, 0.4, 3, 10, 30, and 60tons dry matter (DM) ha(-1) for L. minor test or at three rates equal to 0, 30, and 60tons DMha(-1) for C. aspersus test. At the highest rate of SS application (60tons DMha(-1)), the eluates showed that an increase in pH (6.1) resulted in a decrease in Al levels. Thus, the high stimulation of L. minor growth observed after this high rate of SS application can be explained by (i) a reduction in Al toxicity after precipitation and (ii) macro- and micronutrient enrichment. At a rate of SS application of only 30tons DMha(-1), growth appeared to be slightly significant (p < 0.05), in spite of the significant increase in essential mineral elements. However, it is very difficult to discriminate between Al toxicity and pH effects. For the test with C. aspersus, the snail biomass was not affected by sludge application over the exposure period. Mortality was extremely low, with a rate of less than 4% at the last sampling date. Yet, Cu, Pb, and Cd accumulated significantly in the soft body of snails exposed to SS application, suggesting that the amount of metals excreted is lower than that absorbed. In contrast, Zn levels remain constant, inferring that absorption and elimination of Zn are balanced at the beginning of the experiment.

Effect Of Wood-Based Biochar And Sewage Sludge Amendments For Soil Phosphorus Availability

Abstract This study investigated the effects of two biochars (pyrolysed wood chips and garden clippings) on phosphorus (P) availability in a heavy-metal contaminated soil poor in phosphorus. Short-term 14-days incubation experiments were conducted to study how applications of biochars at different rates (1 and 5 %) in combination with (1:1) and without dried sewage sludge from a municipal waste water treatment plant (WWTP) affected the content of soil extractable P. For P-availability analyses deionized water, calcium acetate lactate (CAL), Mehlich 3 and Olsen extraction protocols were applied. In addition, the content of total and mobile forms of potentially toxic heavy metals (PTHM) was studied. Application of both biochars caused a significant decrease of PTHM available forms in sewage sludge amended soil samples. The concentration of total and available P increased with higher biochar and sewage sludge application rates.