Sludge Amendment Research Articles

Global soil microplastic assessment in different land-use systems is largely determined by the method of analysis: A meta-analysis

Although microplastics (1 μm - 5 mm, MP) are increasingly recognised as a novel entity of pollutants, we still lack a basic understanding of their prevalence in different terrestrial environments. Here, we aimed at performing comparisons of MP concentrations (items kg−1) in different agro-ecosystems, with specific focus on input pathways and land uses, while accounting for the plethora of method variations available, such as analysed MP sizes, sampling depths, density separation solutions, as well as removal of organic matter. We found that the current global means of MP loads, from 89 studies (553 sites), benchmarks 2900 ± 7600 MP items kg−1 soil, substantially more than the global median of 480 MP items kg−1. Roughly 81 % of the studies were conducted in Asia; hence, continent-wider comparisons are still hampered by low study numbers for most regions. Maximum MP numbers were found for soils under both greenhouses and plastic mulching (5200 ± 8300 items kg−1), followed by arable soils with sludge amendments (3700 ± 8800 items kg−1), surprisingly without evidence of elevated MP loads in horticultural fields relative to other agricultural management practices. Intriguingly, global MP loads significantly increased with decreasing levels of urbanisation, i.e., they were highest in rural areas. Yet, quantitative comparisons among sites are biased by the methodology selected for MP analyses. Apart from inconsistencies in sampling depth and size of screened MP particles, across all sites and treatments, largest MP loads were commonly found when using high-density solutions rather than low-density ones, and when soil organic matter removal was performed after and not before the density separation step.

Microplastic accumulation and transport in agricultural soils with long-term sewage sludge amendments

Land application of sewage sludge brings microplastic contamination to soil. However, studies regarding the occurrence and mobility of sludge-borne microplastics in soil are insufficient. In the present study, based on an experimental field, the effects of sludge application amount on the accumulation and migration of microplastics in 0–20 (upper) and 20–40cm (lower) soil layers were evaluated. After 16 years of continuous sludge application (36 t/ha per year), the microplastic content and migration ratio in upper soil reached 6,811 particles/kg and 148%, which was about 5 and 20 times, respectively, higher than that of the control soil without sludge. The microplastics in upper and lower soil layers, were mainly 0.2–0.5mm in size, mostly fibrous in shape, primarily transparent in color, and predominantly rayon in composition. Microplastic surfaces may persistently adsorb clay minerals and iron/titanium oxides from soil, posing potential environmental risks. Sludge application had a significant positive correlation with soil microplastic abundance, resulting in a good fit of predictive model constructed for microplastic accumulation in sludge-amended soils. These findings help to improve the knowledge on environmental behavior of microplastics in sludge-amended soil, and can provide a scientific basis for the regulation of microplastic pollution during sludge land application.

Accumulation and Translocation of Heavy Metals in Hibiscus cannabinus Grown in Tannery Sludge Amended Soil

Digested sludge wasted by tanneries is rich in nutrients and trace elements however, the presence of toxic metals restricts their use in agriculture. The present study explores the possible application of tannery sludge amendment for the cultivation of an energy crop, Hibiscus cannabinus. The toxicity of various sludge amendments (25, 50, 75, and 100%, w/w) was examined during early seedling growth, followed by metal accumulation potential by performing pot experiments. Chemical characterization revealed the presence of Cr (709.6), Cu (366.43), Ni (74.6), Cd (132.71), Pb (454.8) μg.g-1 in tannery sludge beside N (2.1%), P 3.8 & K 316.96 (kg.hec-1.) respectively. Germination of H. cannabinus exposed to sludge extracts ranged between 80 to 95%; Relative seed germination, 81.33 to 84.43%. Relative root growth, 0.9 to 1.16 cm; and germination index, 95 to 110%. It was found that sludge extracts have not caused adverse effects on seed germination and early seedling growth. Heavy metal accumulation was observed as follows: Ni (3.37, 2.38, 1.46 & 0.90 mg.kg-1) > Pb (10.59, 10.15, 5.26, & 2.84 mg.kg-1) > Cu (2.34, 2.24, 0.97 & 0.24 mg.kg-1) > Cd (2.31, 1.19, 1.33 & 1.12 mg.kg-1) > Cr (1458, 1136.12, 601.73 & 211.6 mg.kg-1) in 100, 75, 50, & 25% sludge amended soil, respectively. The bio-concentration pattern of metals was found to be in the order of root > leaf > stem. The findings of the present study give direction for the eco-friendly and cost-effective management of tannery sludge. Further, H. cannabinus can be used for the restoration of metal-contaminated agricultural land, however, results need to be corroborated with field trials.

Sewage sludge amendment of rice as a potential alternative to mineral fertilizer: Analyses of physiological, biochemical and molecular mechanisms of plant response

Sewage sludge (SS) disposal poses environmental concerns, yet its organic matter, macro- and micronutrients, make it potentially beneficial for enhancing soil quality and crop yield. This study focuses on three types of SS: “R10” (SS1), which is commonly used in agricultural practices, and two environmentally friendlier options (SS2 and SS3), as alternatives to mineral fertilizer (urea) for rice cultivation. A pot experiment was conducted to investigate the ecophysiological, biochemical, and molecular responses of rice at three different growth stages. SS application led to a significant increase in biomass production (particularly SS3), along with increased nitrogen (N) levels. Enhanced chlorophyll content was observed in SS-treated plants, especially during inflorescence emergence (with the highest content in SS3 plants). At the ecophysiological and biochemical levels, SS treatments did not adversely affect plant health, as evidenced by unchanged values of maximal PSII photochemical efficiency and malondialdehyde by-products. At biochemical and gene expression levels, antioxidant enzyme activities showed transient variations, likely related to physiological adjustments rather than oxidative stress. Ascorbic acid and glutathione did not significantly vary. This study concludes that the use of SS in soil can be a viable alternative fertilizer for rice plants, with positive effects on biomass, chlorophyll content, and no adverse effects on plant health. Among the tested SSs, SS3 showed the most positive effect, even compared to commercial fertilizer. These results suggest that SS application could improve rice yield while addressing environmental concerns surrounding SS disposal.

Enhancing the carbon content of coal gangue for composting through sludge amendment: A feasibility study

Cocomposting coal gangue and sludge eliminates the challenge of utilizing coal gangue. However, there is limited understanding about the feasibility of cocomposting sludge and coal gangue, as well as the composting indicators, functional microorganisms, and safety risks involved. Therefore, this study evaluated the feasibility of enhancing carbon composting in coal gangue by incorporating sludge along with sawdust as a conditioner. Three laboratory-scale reactors were designed and labeled as T1 (20 % coal gangue, 60 % sludge, and 20 % sawdust), T2 (40 % coal gangue, 40 % sludge, and 20 % sawdust), and T3 (60 % coal gangue, 20 % sludge, and 20 % sawdust). Seed germination and plant growth assessments were conducted to ensure compost stability and assess phytotoxicity to cabbage (Brassica rapa chinensis L.) in terms of growth and biomass. The results indicated that the temperature, pH, EC and ammonia nitrogen of all three reactor conditions met the requirements for product decomposition. Composting was successfully achieved when the sludge proportion was 20 % (T3). However, when the sludge proportion was markedly high (T1), the harmlessness of the compost was reduced. The germination indices of T1, T2, and T3 reached 95 %, 122 %, and 119 % at maturity, respectively. This confirmed that the harmless cycle, which involved promoting condensation and aromatization, enhancing decay, and reducing composting time, was shorter in T2 and T3 than in T1. Coal gangue can also serve as a beneficial habitat for microorganisms, promoting an increase in their population and activity. Potting experiments in sandy soil revealed that the mechanism of action of compost products in soil included not only the enhancement of soil nutrients but also the improvement of soil texture. The results of this study suggest that using coal gangue as a raw material for composting is an efficient and environmentally friendly approach for producing organic fertilizers.

Methodological choices in size and density fractionation of soil carbon reserves – A case study on wood fiber sludge amended soils

Soil organic carbon (SOC) is in the focus of research due to its central role in regulating climate and maintaining fertility and resilience of soils. Methodologically, shifting from whole soil C measurements to specific SOC fractions increases possibility to detect small changes in the vast SOC storage, and enhances estimation of SOC stability. However, SOC fractionation schemes are numerous and variable. In this study, deionized water and sodium hexametaphosphate (SHMP) were compared in soil dispersion by separating soils into coarse (0.25–2 mm), medium (0.063–0.25 mm) and fine (<0.063 mm) size fractions. The first two fractions were further separated by density (1.8 g cm−3) to obtain free particulate organic C (POC) and mineral associated organic C (MOC). The approach was applied to a clay and a silt loam soil with and without wood fiber sludge amendment to follow the added C. Aggregate disruption was enhanced with SHMP in comparison to water, but the effect was small and the use of SHMP decreased recovery of SOC, wherefore water was preferred. In both soils, 5–10 % of SOC occurred as coarse POC, 1–3% as coarse MOC, 5 % as medium POC, 10 % as medium MOC, and 70–85 % as fine MOC. The added C resided in the POC fractions with an indication of minor accumulation to the fine MOC in the clay soil. Longer time frame with repeated C additions would be needed to increase the stable MOC storages though saturation of the MOC reserve may hinder accumulation in the silt loam low in fines.

Accumulation and migration of microplastics and its influencing factors in coastal saline-alkali soils amended with sewage sludge

Coastal saline-alkali soil can be transformed to agricultural soil with sewage sludge amendment. However, sewage sludge contains a large number of microplastics (MPs), and the fate of MPs in sludge-treated saline-alkali soil needs to be studied. Therefore, we investigated the accumulation and migration of MPs, and their influencing factors in saline-alkali soil after one-time sewage sludge application (0, 25, 50, 100 and 200 t ha−1 SSA). The results indicated that sewage sludge input contributed to MP accumulation in soil, and the MP abundance in 20–40 cm soil was significantly lower than that in 0–20 cm soil. Fragments and fibers were the most abundant MPs in soil, and the proportions of fragments and 50–200 µm MPs in 20–40 cm soil were lower than those in 0–20 cm soil, while the < 50 µm MP proportion was higher than that in 0–20 cm soil. Correlation analysis showed that MP accumulation rate (0–40 cm) and migration rate (20–40 cm) were negatively correlated with soil organic matter (SOM) content and SSA, but positively correlated with soil pH. Stepwise regression analysis further showed that SOM and SSA were the main factors affecting MP accumulation rate, which explained 47.7% and 46% of its variation, respectively, while pH was the crucial factor affecting the migration rate of MPs, followed by EC and SSA. In conclusion, SSA caused MP accumulation in saline-alkali soil, and SSA primarily affected the MP abundance, while soil OM, pH and EC directly affected MP migration in soil.

Unlocking fertilization potential of anaerobically digested sewage sludge centrate for protein-rich rice cultivation with composted sludge amendment

The use of composted sewage sludge (CSS) and centrate as alternatives to synthetic fertilizers in rice cultivation holds great promise. This study aims to determine the effects of varying doses and timings of centrate derived from anaerobically digested sewage sludge on rice yield, nutrient quality, and soil fertility when applied as a topdressing to rice fields fertilized with CSS. At the panicle initiation (PI) stage, 100, 300, and 500 kg N ha−1 of centrate topdressing (CT100, CT300, and CT500, respectively) was applied. In addition, different topdressing timings at a total dose of 500 kg N ha−1 were evaluated, including a two-split application (40% at active tillering (AT) and 60% at PI; CT500S2) and a three-split application (40% at AT + 40% at PI + 20% at heading; CT500S3). At a rate of 160 kg N ha−1, CSS was used as a base fertilizer in all treatments. A control treatment received synthetic fertilizers at a rate of 160 kg N ha−1 as a base application and 100 kg N ha−1 as a topdressing. Results showed that CSS-treated rice plants exhibited a lower N status and leaf chlorophyll content during the vegetative growth stage; however, the split application of centrate topdressing improved plant N status, resulting in an increase in biomass and grain yield. Centrate and CSS tended to increase the mineral content of rice; nevertheless, a significant accumulation of As in grains raised concerns about food safety. Combining CSS and centrate has the potential to increase rice production, improve grain nutritional value, and decrease reliance on synthetic fertilizers. However, it is essential to optimize this fertilization, mitigate environmental risks, and ensure food safety by employing appropriate fertilization dosing and timing as well as appropriate field management strategies.

Persistent Organic Pollutants in Sewage Sludge: Occurrence, Temporal Concentration Variation and Risk Assessment for Sewage Sludge Amended Soils

In this study, the occurrences, temporal concentration variations and ecotoxicological risks were determined for 18 polycyclic aromatic hydrocarbons (PAHs); 7 congeners of polychlorinated biphenyls (PCBs), and 18 selected organochlorine pesticides (OCPs) in the anaerobically digested sewage sludge samples obtained from a conventional wastewater treatment plant (WWTP) in Konya, Turkey. Flowrate of the evaluated WWTP was 200,000 m3/day, with the production of 140 tons/day treated sewage sludge. Total 18 PAHs were in the range of 1,203 – 17,599 μg/kg of dry matter (dm); total PCBs were in the range of 51.26 – 561.37 μg/kg dm, and total OCPs were in the range of 4.90 – 13.11 μg/kg dm. The highest concentrations were determined for fluoranthene among PAHs, with 2445 μg/kg dm, PCB118 congener with 514 μg/kg dm, and δ-HCH among OCPs with 2.44 μg/kg dm. Considering the average daily production amounts of treated sludge, the highest mass loads were 1,785 g/day for total PAHs; 79 g/day for total PCBs; and 1 – 2 g/day for total OCPs, while the annual mass load was estimated to be approximately 7.3 kg. An ecotoxicological risk assessment was performed by estimation of risk quotients (RQs). High risk for soil ecosystem was identified due to PAHs and PCBs ingredient of sludge, while lower risk was determined for OCPs compounds. The highest RQ values were determined for pyrene (RQ: 1337) among PAHs, PCB118 congener (RQ: 7608), and γ-HCH (RQ: 5.23) among OCPs. Findings of this study show that sewage sludge can be an important source in the spread of persistent pollutants to the environment, and may pose a risk for soil ecosystem.

Improving coarse-textured mineral soils with pulp and paper mill sludges: Functional considerations at laboratory scale

Building up the organic matter content of coarse-textured soils with organic amendments seeks to ameliorate the productivity of these soils, which is limited by plant available water and nutrient supply. Wood fibre-based sludges from the pulp and paper industry have potential for soil conditioning. In this study, the effects of three different pulp and paper mill sludges at application rates of 10 and 20 vol-% on water retention, respiration, and nitrogen (N) dynamics were examined in a series of laboratory studies using coarse field soils. Water retention curves comprising 13 matric potentials revealed that the amendments increased total soil porosity and volumetric water content at matric potentials corresponding to macro- and mesopores size range with pore diameters of >30 μm and 30–0.2 μm, respectively. Volumetric water content at field capacity increased by c. 10–30%, depending on the type (fresh, lime-stabilised and fibre sludge) and application rate of the amendment, with no marked change in the water content at the permanent wilting point. This was reflected as a mean increase of 1.9–3.3 mm in the plant available water content relative to the non-amended soils (17 mm), which corresponds to 19–33 m3 per hectare. At most, an increase of 5.5 mm (55 m3 ha−1) in plant available water was achieved by the fibre sludge amendment at an application rate of 20 vol-%. During a 60-day laboratory incubation, c. 30–40% of the carbon (C) added to soil in the sludge materials was respired as carbon dioxide. Additional N accelerated decomposition without increasing total respired C. Decomposition of the amendments in the soil led to a net N immobilisation of roughly 5–10 mg min-N g−1 added C, which occurred mainly during the first two weeks after soil incorporation. Overall, pulp and paper mill sludge amendments may serve to alleviate water shortages during drought in coarse-textured soils, but may generate a transient plant-microbe competition in N uptake.

Coupling effect of DOM and microbe on arsenic speciation and bioavailability in tailings soil after the addition of different biologically stabilized sludges

Dissolved organic matter (DOM) and microbes co-mediate the transformation of heavy metals in soil. However, few previous studies have investigated the effects of interaction between DOM and microbes on the transformation and bioavailability of heavy metals in tailings soil at the molecular level after the addition of organic wastes. This study used co-occurrence network analysis based on Fourier-transform ion cyclone resonance mass spectrometry and high-throughput sequencing to investigate the molecular mechanisms of different bio-stabilized sludge addition on arsenic fraction transformation and bioavailability in tailings soil. It was found that sludge amendments decreased the arsenic bioavailable fraction from 3.62% to 1.74% and 1.68% and promoted humification of DOM in soil. The extra inorganic salt ions introduced with sludge desorb the adsorbed As(V) into soil solution. Specifically, bio-stabilized sludge increased the contents of labile compounds that provided nutrients for microbial metabolism and shaped the microbial community composition into a more copiotrophic state, which increased the abundance of As(V)-reducing bacteria and then converted the As(V) into As(III) and precipitated as As2S3. This work innovatively explores the transformation mechanisms of As fractions through the perspectives of microbial community and DOM molecular characterization, providing an important basis for the remediation of As-contaminated soil using biosolids.

Effect of Sewage Sludge Amendment on Non-enzymatic Antioxidants in Vetiver Plants (Vetiveria zizanioides L. Nash.)

Effect of Sewage Sludge Amendment on Non-enzymatic Antioxidants in Vetiver Plants (Vetiveria zizanioides L. Nash.)

Sustainable Use of Sewage Sludge for Marigold (Tagetes erecta L.) Cultivation: Experimental and Predictive Modeling Studies on Heavy Metal Accumulation

The present study aimed to investigate the impact of sewage sludge (SS) amendment on the growth, yield, and biochemical attributes of the marigold (Tagetes erecta L. var. Pusa Basanti Gainda) crop. For this purpose, marigold flowers were cultivated using three different treatments of SS, i.e., 0% (control with no SS), 5%, and 10%. Multiple linear regression (MLR) modeling was performed to develop prediction models for the impact of soil properties on heavy metals uptake by marigold plants. The results showed that the growth, yield, and biochemical attributes of marigold plants significantly (p &lt; 0.05) increased with an increase in SS dose from 0 to 10%. The most feasible SS treatment was found to be 10%, which achieved a maximum flower yield of 318.42 g/plant. On the other hand, the bioaccumulation factor (BAF) values (&gt;1) showed that the marigold plant was capable of uptaking significant contents of six heavy metals in the order of Cd &lt; Cr &lt; Cu &lt; Zn &lt; Mn &lt; Fe. The MLR-based predictive models were capable of precisely predicting the contents of most heavy metal uptake by marigold plants as indicated by the coefficient of determination (R2 &gt; 0.73), model efficiency (ME &gt; 0.49), root mean square error (RMSE &lt; 3.25), and analysis of variance (ANOVA; p &lt; 0.05) results. Overall, this study presented a novel approach to floriculture by sustainable management of SS while reducing public health and environmental impacts.

Alleviated environmental constraints and restructured fungal microbiome facilitate aggregate formation and stabilization in coastal mudflat saline soil amended by sewage sludge

AbstractSoil aggregates are important drivers of soil productivity. However, the relative importance of soil abiotic and biotic agents in driving aggregate formation and stabilization remain largely unexplored, especially in coastal mudflat saline soils. We amended saline soil with sewage sludge at rates of 0, 30, 75, and 150 t ha−1 to investigate the effects of sewage sludge on the particle size distribution and stability of soil aggregate and the underlying mechanisms induced by soil environmental factors and fungal community. Results revealed that the sewage sludge amendment significantly (p &lt; 0.05) increased the proportion of macroaggregates with sizes larger than 0.25 mm (R0.25) and enhanced aggregate stability. Moreover, alleviation of saline‐alkali stress and nutrient (C, N, and P) deficiency conditions were significantly (p &lt; 0.05) observed in sewage sludge‐amended soils. Additionally, restructured fungal communities in amended soils harbored significantly (p &lt; 0.05) distinguishable structures and core and unique microbiomes. Particularly, fungal species belonging to Moterella significantly (p &lt; 0.05) enriched in sludge reclaimed soils. Results derived from the random forest (RF) model accompanied by linear regression analysis revealed that soil pH, soil organic carbon, and fungal structural diversity were significantly (p &lt; 0.05) related to aggregate composition (R0.25) and stability (geometric average diameter, GMD). Furthermore, fungal consortia composed of 20 closely interconnected operational taxonomic units (OTUs) affiliated with Ascomycota, Basidiomycota, and Zygomycota explained 28.36% and 49.88% variance of R0.25 and GMD, respectively. Overall, our results revealed the effect of sewage sludge on soil aggregation improvement in coastal areas and highlighted the respective importance of soil chemical properties and fungal microbiome in predicting aggregation status.

Retention Behaviour of Heavy Metals from Industrial Sludge Amended with Admixtures to Use Them as Liners for Landfill Facilities

The solidification of contaminants within the soil/waste has proved to be a versatile technique to de-contaminate them and make them usable for several applications. In this method, the development of binder provisions leads to the conversion of the environmentally unstable condition of waste materials into a nearly stable material. Further, these materials pose a minimum threat that can be absorbed into the environment. Normally lime/cement and other pozzolanic materials are used as binder materials. In this work, it is proposed to use the efficiency of binding fly ash to improve the unconfined compressive strength (UCC) of soils, particularly during the curing period. This is because improvement in strength is a reflection of the improvement of bonding soil particles. Fly ash as the main source material, in addition to a minor proportion of cement and lime, is used to determine the strength. UCC test results revealed that as the percentage of fly ash increases there is an increase in compressive strength. It is also observed that with an increase in lime content and an increase in cement content, the UCC strength also increases. The strength in cement-stabilized compacted specimens is more compared to lime-stabilized mixtures. To confirm that the improvement in strength is related to the solidification of contaminated metals, particularly for soils containing copper and chromium, the stabilized mixture is tested for the leaching of these metals. Leaching tests were conducted on various stabilized mixtures at different curing periods. The leachate was examined for metal ion concentration using Atomic Absorption Spectrophotometer. The leaching behavior of heavy metals from different proportions of soil matrix revealed that with an increase in lime or cement percentage, a decrease in leachability is observed. It is found that the leaching of heavy metals from cement-stabilized soils was lower than in lime mixture combinations. However, minimum strength improves the solidification and retention of heavy metals effectively.

Assessment of Earthworm Viability and Soil Health after Two Years of Raw and Composted De-Inking Paper Sludge Amendment

The improvement of soil fertility properties is a priority for meeting sustainable development goals and world food security. One potential benefit of using paper sludge in agriculture is the reduction of waste and associated environmental impacts. By using paper sludge as a soil amendment, it is possible to divert away this material from landfills and instead use it to improve soil fertility and support the growth of crops. However, it is important to note that paper sludge may contain contaminants harmful to plants and soil health, of which earthworm viability serves as a key indicator. The present investigation aimed to evaluate changes in soil properties after the application of raw and composted de-inking paper sludge for two years. Accordingly, a field study was conducted in Manouba, a semi-arid region of Tunisia with a clay loam soil. The raw de-inking sludge (DS) and composted de-inking paper sludge (DSC) were applied at 30 and 60 t ha−1 and 20 and 40 t ha−1, respectively. Soil treatments were compared to unamended soils (C), to determine the optimal sludge treatment and rate for increasing the soil quality. Soil chemical (soil organic matter SOM, total carbon TC, and nitrogen TN, nutrient soil contents organic matter fractioned), physical (porosity and structural stability), and biological parameters (earthworms viability) were assessed. The results showed an increase of soil OM in the DS and DSC amended soils with the lowest rates (30 and 20 t ha−1). The humic fraction was found to be the dominant form. TC and TN were improved in the DS and DSC amended soils with the highest rates: 60 (DS2) and 40 t ha−1 (DSC2). Phosphorus and potassium were also increased in a dose-dependent manner. However, the soil porosity decreased in all treatments. The composted de-inking sludge was toxic for epigeic species, which could be explained by the use of litter while composting. Overall, the application of DS and DSC at low rates (30 and 20 t ha−1, respectively) might be a promising alternative for improving soil quality and at the same time ensuring the proper management of these wastes.

Ecotoxicological Assessment of Potentially Toxic Elements in Waterworks Sludge Amended Soils Using Bermudagrass Bioassay

Waterworks sludge has the potential to be used as a soil amendment, but the ecotoxicological risk of potentially toxic elements should not be underestimated. In this regard, this study determined the contents of nine potentially toxic elements (Cr, Ni, Cd, Cu, Pb, Zn, As, Mn, and Al) of bermudagrass [Cynodon dactylon (L.) Pers.] grown in waterworks sludge amended soils. Treatments involved different loading rates of waterworks sludge, soil types, and fertilization options that represented different scenarios of greening applications. The recommended metal levels in plant tissues and maximum tolerable levels for feeding cattle are adopted as benchmarks for gauging the ecotoxicological risk to the first and second trophic levels of the ecosystem, respectively. No recommended levels for potentially toxic elements are exceeded when sludge loading rate is not higher than 50% (wt/wt). When various fertilization treatments are applied to 25% (wt/wt) sludge amended soils, the accumulation of aluminum and zinc deserves our attention because a few samples exceed the recommended levels. They are mainly samples of below-ground biomass. Overall, using waterworks sludge as a soil amendment does not cause an obvious ecotoxicological risk. The findings can provide a valuable reference to other cities for the sustainable management of waterworks sludge.

Response of occurrence in microplastics and its adsorped cadmium capacity to simulated agricultural environmental scenarios in sludge-amended soil

Large amounts of microplastics (MPs) enter the soil along with the amendment of sludge to soil. However, it is still unclear about the response of MPs occurrence and the adsorption behaviors of cadmium (Cd)on MPs to typical agricultural environmental scenarios. In present work, three kinds of MPs (polyethylene, polypropylene, and polystyrene) were chosen to investigate that response in three agricultural environmental scenarios with sludge-amended soil, including dry-wet alteration (7 d, five cycles), microbial addition (Bacillus subtilis, 0.05 g/g soil), and Ultraviolet (UV) irradiation (340 nm, 4 × 15 W, 4 d). The results showed that there was the highest adsorption capacity of Cd on MPs (36.21, 45.15, 12.43 μg/g for PE, PP, PS, respectively) after UV irradiation exceeding those from MPs triggered by other two scenarios). UV irradiation caused an increase in the abundance of Streptomyces, an expansion in specific surface area, a significant change in surface morphologies, an improvement in crystallinity or the formation of new crystals, and an enhancement in C–O and CO content, and then resulted in the incremental adsorption capacity of Cd on MPs. The findings are important of significance for controlling the environmental risks from sludge MPs via carrying heavy metals in the soil-plant systems.

Implication of sewage sludge increased application rates on soil fertility and heavy metals contamination risk

This paper aims to assess soil fertility and risk contamination parameters in response to increased amendment rates of sewage sludge application, under semi-arid climatic conditions of Morocco, using two soil textures: soil A (clay-silty) and soil B (sandy-clay) over two years. To this end, sewage sludge and soils treatments physicochemical parameters, heavy metals content, degree of pollution and associated risks were evaluated and compared to controlled soils. The results showed that all studied parameters changed significantly (p < 0.05) in a dose-dependent manner for both soils compared to the untreated control soils. Indeed, there were significant increase in organic matter (OM), total organic carbon (TOC) and nutrients content (N, P and K) of both sols as a response to increased sewage sludge amendment rates. Overall, sewage sludge application showed a positive agronomic potential for both soil and plant. However, there were concern about some heavy metals contamination risks, the results showed a gradual increase of heavy metals concentration in this order: Cu > Pb > Zn > Ni > Cd > Cr. Nevertheless, their concentrations were below the critical values established by the European Union for the agronomic use of soil. The obtained results of assessed parameters indicating SS degree of pollution and associated risks showed a low to a moderate contamination risks of heavy metals. Accordingly, environmental risks of sewage sludge application will be related to increase of heavy metals mainly in a long-term agricultural reuse. Thus, optimal management of sewage sludge application is recommended to ensure sustainability and benefits at the same time to master the contamination risks.

Effect of Solid Phosphate Sludge Amendments on the Growth of Fruit and Forest Trees in the Nursery

Phosphorus deficiency is a major limiting factor in horticultural production. One potential solution can be restoring soil phosphorus from mineral resources, such as solid phosphate sludge (SPS) generated from phosphate treatment processes at mining sites in agriculture. This study explores the possibility of using this sludge in nurseries to produce fruit and forest plants. We tested six mixtures of SPS with the sandy soil of the Maamora forest on ten plant species. In the second experiment, we tested the same mixtures with sea sand. In addition, one concentration of four composts based on phosphate sludge was also tested on two citrus rootstocks and carob. The first experiment’s results showed significantly higher growth with the control mixture for pomegranate, acacia, and C. volkameriana plants. The relative growth was higher at SPS concentrations of 20% to 30% for the other plant species, although there was no significant difference between treatments. The estimations of AUGPC (area under the growth progress curve) showed no significant difference in most species. In the second experiment, the relative growth in the M4 (30% of SPS + 70% of sand) mixture was higher, and the AUGCP showed a significant difference compared to the M1 control mixture. The application of solid phosphate sludge positively affects and improves the growth of fruit and forest trees in the nurseries, especially when the concentration is between 20 and 30%. For this purpose, the phosphate sludge could have great potential to be used in nurseries and create a favourable soil condition as a cultivation substrate.