Metal concentrations in lime stabilised, thermally dried and anaerobically digested sewage sludges

Nutrient management: as a panacea to improve the caryopsis quality and yield potential of durum wheat (Triticum turgidum L.) under the changing climatic conditions

The increasing human population and the changing climate, which have given rise to frequent drought spells, pose a serious threat to global food security, while identification of high-yielding drought-tolerant genotypes coupled with nutrient management remains a proficient approach to cope with these challenges. An increase in seasonal temperature, recurring drought stress, and elevated atmospheric CO2 are alarmingly affecting durum wheat production, productivity, grain quality, and the human systems it supports. An increase in atmospheric carbon dioxide can improve wheat grain yield in a certain amount, but the right amount of nutrients, water, and other required conditions should be met to realize this benefit. Nutrients including nitrogen, silicon, and sulfur supply could alleviate the adverse effects of abiotic stress by enhancing antioxidant defense and improving nitrogen assimilation, although the effects on plant tolerance to drought stress varied with nitrogen ionic forms. The application of sewage sludge to durum wheat also positively impacts its drought stress tolerance by triggering high accumulation of osmoregulators, improving water retention capacity in the soil, and promoting root growth. These beneficial effect of nutrients contribute to durum wheat ability to withstand and recover from abiotic stress conditions, ultimately enhance its productivity and resilience. While these nutrients can provide benefits when applied in appropriate amounts, their excessive use can lead to adverse environmental consequences. Advanced technologies such as precision nutrient management, unmanned aerial vehicle-based spraying, and anaerobic digestion play significant roles in reducing the negative effects associated with nutrients like sewage sludge, zinc, nanoparticles and silicon fertilizers. Hence, nutrient management practices offer significant potential to enhance the caryopsis quality and yield potential of durum wheat. Through implementing tailored nutrient management strategies, farmers, breeders, and agronomists can contribute to sustainable durum wheat production, ensuring food security and maintaining the economic viability of the crop under the changing climatic conditions.

Photochemical transformation mechanisms of dissolved organic matters (DOM) derived from different bio-stabilization sludge

Bio-stabilization sludge contains numerous dissolved organic matter (DOM) that could enter aquatic environments by soil leaching after sludge land use, but a clear understanding of their photochemical behavior is still lacking. In this study, we systematically investigated the photoactivity and photochemical transformation of aerobic composting sludge-derived DOM (DOM_ACS) and anaerobic digestion sludge-derived DOM (DOM_ADS) by using multispectral analysis coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The results indicated that DOM_ACS and DOM_ADS have a higher proportion of highly unsaturated and phenolic compounds (HuPh)with high DBE_wa, but the different polyphenols (Polyph) abundance of them, causing the different photoactivity between them. DOM_ACS had much higher apparent quantum yields (AQY) for triplet states of dissolved natural organic matter (³DOM*) and hydroxyl radical (•OH) but slightly lower AQY for singlet oxygen (¹O₂) than DOM_ADS under simulated sunlight conditions. As the irradiation time increased, HuPh and Polyph (associated with humic-like substances) contained in DOM_ACS (DOM_ADS) decreased by 12.0% (14.1%) and 3.0% (0.2%), respectively, with concurrent decrease in average molecular weight and aromaticity moieties, resulting in more generation of aliphatic compounds. Furthermore, based on 27 types of photochemical transformation reactions, DOM_ACS containing higher fractions of O_10-15 and N_1-3O_y class preferred dealkyl group and carboxylic acid reactions, whereas DOM_ADS composed of more N₄O_y and S₂O_y fragments preferred oxygen addition and anmine reactions. Consequently, photochemical transformations reduced the Cd (II) ion activity in the presence of DOM_ACS (DOM_ADS). This study is believed to unveil the photochemical transformation of bio-stabilization sludge-derived DOM and its impact on pollutants' fate in the aquatic environment.

Portable X-ray Fluorescence Analysis of Organic Amendments: A Review

Portable XRF spectrometry (pXRF) has recently undergone significant technological improvements and is being applied in a wide range of studies. Despite pXRF advantages, this technique has rarely been used to characterize organic amendments and residues. This article reviews those studies undertaken to date in which pXRF is used to characterize these products. Published studies show that pXRF correctly measures elements such as Fe, Pb, Zn, Mn, Ca, and K but gives conflicting results for elements such as Cr, Ni, and As. Among the reasons that may cause the low performance of the technique with certain elements or under certain measurement conditions would be the inadequacy of the analytical comparison procedures used (i.e., digestion with aqua regia), the lack of knowledge of the interfering effects of organic matter, and sample moisture on the XRF signals and the need for a standardized protocol for performing the measurements. However, the speed and low cost of the procedure forecast a greater future use of this technique, especially in cooperation with other fast spectroscopic techniques based on near-infrared (NIRS) or mid-infrared (MIR) spectroscopies. Chemometric procedures based on one or more of these techniques will allow the prediction of elements below the detection limit of pXRF instruments (Cd, Hg), or other properties of organic amendments (organic matter, N, electrical conductivity, cation exchange capacity).

Human health risk assessment of lead (Pb) through the environmental-food pathway

Drinking water and farm-to-fork pathways have been identified as the predominant environmental pathways associated with human exposure (HE) to Pb. This study integrates a GIS-based survey of metal concentrations in soil and a probabilistic quantitative risk assessment of Pb through the food chain. The case study area was selected in the east of Ireland. A step-wise exposure assessment collated the data for Pb concentration in soil and water media, bioaccumulation of Pb in unprocessed food products, such as potatoes, carrots, green vegetables, and salad vegetables. The daily mean HE to Pb through selected food products was found to be 0.073 mg day^-1, where a mean weekly exposure was estimated as 0.0065 mg kg body weight^-1 week^-1. Multiple risk estimates were used. Hazard Quotient (HQ), Daily Dietary Index (DDI), Daily Intake of Metal (DIM), Health Risk Index (HRI), Target Hazard Quotient (THQ) and Cancer Risk (CR) were found as 0.234 to 0.669, 0.002, 0.0002, 0.020 to 0.057, 0.234 to 0.669, and 0.00001, respectively which signify a low to moderate risk. A sensitivity analysis revealed that intake of potato is the most sensitive parameter of the model, which is positively correlated (coeff. + 0.66) followed by concentration of Pb in the arable soil (+0.49), bioaccumulation in tubers (+0.37), consumption of salad vegetables (+0.20), and consumption of green vegetables (+0.13) (top 5). A back-calculated limit of Pb in the soil (51 mg kg^-1) justifies the lower threshold limit of Pb (50-300 mg kg^-1) in agricultural soil set by the European Union to mitigate potential bio-transfer into food products. The study concludes there is a low to moderate risk posed by Pb, within the system boundary of the probabilistic model, and highlights the significance of limiting Pb concentrations in the vegetable producing agricultural soil.

Risk factors and assessment strategies for the evaluation of human or environmental risk from metal(loid)s - A focus on Ireland

Elevated human exposure to metals and metalloids (metal(loid)s) may lead to acute sickness and pose a severe threat to human health. The human body is exposed to metal(loid)s principally through food, water, supplements, and (occasionally) air. There are inherent background levels of many metal(loid)s in regional soils as a consequence of geological sources. Baseline levels coupled with anthropogenic sources such as regional application of biosolids may lead to increased levels of certain metal(loid)s in soil, leading to potential transfer to water sources and potential uptake by plants. The latter could potentially transfer into the feed-to-food chain, viz. grazing animals, and bio-transfer to food products resulting in human exposure. This study addresses health concerns due to excessive intake of metal(loid)s by conducting a traditional review of peer-reviewed journals between 2015 and 2019, secondary references and relevant websites. The review identified the most researched metal(loid)s as Cu, Zn, Pb, Cd, Ni, Cr, As, Hg, Mn, Fe in the environment. The potential uptake of metal(loid)s by plants (phytoavailability) is a function of the mobility/retainability of metal(loid)s in the soil, influenced by soil geochemistry. The most critical parameters (including soil pH, soil organic matter, clay content, cation exchange capacity, the capability of decomposition of organic matter by microbes, redox potential, ionic strength) influencing metal(loid)s in soil are reviewed and used as a foundation to build a framework model for ranking metal(loid)s of concern. A robust quantitative risk assessment model is recommended for evaluating risk from individual metal(loid)s based on health-based indices (Daily Dietary Index (DDI), No Observed Adverse Effect Level (NOAEL), and Lowest Observed Adverse Effect Level (LOAEL)). This research proposes a risk assessment framework for potentially harmful metal(loid)s in the environment and highlights where regulation and intervention may be required.

Analysis of the levels of metal(loid)s in environmental compartments in Ireland towards a screening measure for potential relative risk using open-source datasets

Several metals and metalloids (metal(loid)s) have been identified as potential pollutants. Naturally occurring background levels and anthropogenic sources (direct or indirect) contribute to the baseline concentration of metal(loid)s in the environment. Recorded metal(loid)s in various environmental media (soil, water, sediment) were evaluated from existing databases. The first database is the national soil database or Soil Geochemical Atlas of Ireland (SGAI). The second one is a higher resolution Tellus project database created by the Geological Survey Ireland. This study focussed on 16 metal(loid)s: As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Sb, Sn, U, V, and Zn. A Risk Quotient (RQ) and Integrated Risk Quotient (IRQ) were used to analyse individual and combined effects of selected metal(loid)s due to the potential ingestion by humans through the food chain. The results revealed that in a few locations of Ireland, the predicted environmental concentration (PEC) of As, Cd, Pb and Zn in the soil was higher than the threshold values resulting in an RQ exceedance of 1. The RQ values of metal(loid)s corresponding to the water, and sediment samples suggest minimal exceedance of threshold values. The exceedance of the IRQ values (>2) for the soil, water, and sediment samples is 32.3 %, 14.8 %, and 1.3 %, respectively. Regions along the East coast of Ireland may pose a higher potential relative risk compared to other parts of Ireland. This research suggests the need for in-depth risk assessment studies on Cd, As and Pb, which showed elevated levels. Furthermore, it is essential to understand the fate of metal(loid)s and their risk assessment to inform regulations around metal(loid)s where intervention may be required.

Agricultural and non-agricultural directions of bio-based sewage sludge valorization by chemical conditioning

This literature review outlines the most important-agricultural and non-agricultural-types of sewage sludge management. The potential of waste sludge protein hydrolysates obtained by chemical sludge conditioning was reported. The discussed areas include acidic and alkaline hydrolysis, lime conditioning, polyelectrolyte dewatering and other supporting techniques such as ultrasounds, microwave or thermal methods. The legislative aspects related to the indication of the development method and admission to various applications based on specified criteria were discussed. Particular attention was devoted to the legally regulated content of toxic elements: cadmium, lead, nickel, mercury, chromium and microelements that may be toxic: copper and zinc. Various methods of extracting valuable proteins from sewage sludge have been proposed: chemical, physical and enzymatic. While developing the process concept, you need to consider extraction efficiency (time, temperature, humidity, pH), drainage efficiency of post-extraction residues and directions of their management. The final process optimization is crucial. Despite the development of assumptions for various technologies, excess sewage sludge remains a big problem for sewage treatment plants. The high costs of enzymatic hydrolysis, thermal hydrolysis and ultrasonic methods and the need for a neutralizing agent in acid solubilization limit the rapid implementation of these processes in industrial practice.

Solid waste: An overlooked source of microplastics to the environment

Microplastics pollution is one of the most pressing environmental problems of the 21st century. While microplastics are pervasive throughout various environmental compartments, research to date has primarily focused on marine systems. Land-based microplastics sources (e.g., solid waste) have received comparatively little attention, although they account for the main flow of microplastics into aquatic environments. Solid waste microplastics sources primarily include landfill refuse, sludge, and food waste. Microplastics in these waste streams can be associated with various micropollutants that can have deleterious impacts on ecosystem health as they enter the food chain. Thus, understanding the occurrence, fate, and degradation pathways of solid waste microplastics is essential to develop comprehensive control and mitigation strategies. This study critically reviewed these key aspects of microplastics in municipal solid waste landfill refuse, sewage sludge, and food waste, and identified the interconnections of these components in the proliferation of microplastics to the environment. Additionally, microplastics related laws and regulations and their relevance to solid waste microplastics mitigation are discussed.

An ecotoxicological approach to microplastics on terrestrial and aquatic organisms: A systematic review in assessment, monitoring and biological impact

Marine and land plastic debris biodegrades at micro- and nanoscales through progressive fragmentation. Oceanographic model studies confirm the presence of up to ∼2.41 million tons of microplastics across the Atlantic, Pacific, and Indian subtropical gyres. Microplastics distribute from primary (e.g., exfoliating cleansers) and secondary (e.g., chemical deterioration) sources in the environment. This anthropogenic phenomenon poses a threat to the flora and fauna of terrestrial and aquatic ecosystems as ingestion and entanglement cases increase over time. This review focuses on the impact of microplastics across taxa at suggested environmentally relevant concentrations, and advances the groundwork for future ecotoxicological-based research on microplastics including the main points: (i) adhesion of chemical pollutants (e.g., PCBs); (ii) biological effects (e.g., bioaccumulation, biomagnification, biotransportation) in terrestrial and aquatic organisms; (iii) physico-chemical properties (e.g., polybrominated diphenyl ethers) and biodegradation pathways in the environment (e.g., chemical stress, heat stress); and (iv) an ecotoxicological prospect for optimized impact assessments.

Prediction of As, Cd, Cr, Hg, Ni, and Se Concentrations in Organic Amendments Using Portable X-ray Fluorescence and Multivariate Modeling

Portable X-ray fluorescence (pXRF) has been a widely used technique in various applications. However, its use for the analysis of organic amendments (composts, sewage sludges, organic fertilizers) is scarce. In these matrices, concentrations of some elements are below their detection limit. The objective of this work was to find multiple linear regression equations that were able to predict the aqua-regia-soluble concentrations of the elements As, Cd, Cr, Hg, Ni, and Se using the pXRF readings of other measurable elements as predictor variables. For this, a set of 30 samples of organic amendments (composts, sewage sludges, and organic fertilizers) from the Manure and Refuse Sample Exchange Programme of the Wageningen Evaluating Programs for Analytical Laboratories (MARSEP-WEPAL) was used. Several amendment type-dependent single or multiple linear functions were found based on 1, 2, or 3 predictors. The predictor readings corresponded to the concentration of elements of geogenic (Fe, Si, Ti, Cl, Zr Al, Ca, S, Mn, and Ba), anthropogenic (Zn and Pb), and agricultural (P and K) origin. The regression coefficients of these functions were r = 0.90–0.99; therefore, they allowed for the quantitative determination of the target elements. These results will allow for fast and reliable analysis of organic amendments using pXRF that is valid for quality control in treatment plants.

Flow and fate of silver nanoparticles in small French catchments under different land-uses: The first one-year study

This study focused on surface waters from three small creeks, within the Seine River watershed, which are characterized by different land-uses, namely forested, agricultural and urban. Silver nanoparticles (Ag-NPs) in these waters were detected and quantified by single-particle ICPMS during one-year of monthly sampling. Their temporal and spatial variations were investigated. Ag-NPs, in the three types of surface water, were found to range from 1.5 × 10⁷ to 2.3 × 10⁹ particles L^-1 and from 0.4 to 28.3 ng L^-1 at number and mass concentrations, respectively. These values are in consistent with the very few previous studies. In addition, the role of factors driving process and potential sources are discussed with correlations between Ag-NPs concentrations and biogeochemical parameters, like dissolved organic carbon concentration and divalent cations concentrations. For the forested watershed NOM controls the stability (number and mass) of the Ag-NPs as recently observed in the field in lake water in Germany. In the case of the agricultural and urban watersheds major cations such as Ca would control the number and mass of Ag-NPs. Dilution processes are rejected as conductivity and Cl^- ions do not show significant correlations with Ag-NPs or other major geochemical parameters. The specific exportation rates of Ag-NPs for artificial, agricultural and forested areas were calculated based on the monthly data for the full year and are equal to 5.5 ± 3.0, 0.5 ± 0.3 and 0.2 ± 0.2 gy^-1km^-2, respectively. These data suggest a constant release of Ag-NPs from consumer products into freshwaters in artificial areas, for instance, from textiles, washing machines, domestic tap-water filters, outdoor paints. These first data of Ag-NPs fluxes in surface waters of France enlarge the very limited database of field measurements. Moreover, for the first time, the influence of time, land-use and aquatic geochemistry parameters on Ag-NPs in real natural water samples is reported. It is also helpful to further understand the fate and the process of Ag-NPs in natural waters, as well as to the ecotoxicity studies in real-world environment.

Successive sewage sludge fertilization: Recycling for sustainable agriculture

Sewage sludge (SS) is widely used in agriculture in several countries around the world. However, the impact of successive applications of SS on soil and the risks of nutrient leaching are often neglected. In this study, corn was grown on a constructed wetland for four crop cycles (two years), in which the wetland was subjected to successive SS applications. The objective of this study was to evaluate how the successive applications of SS affect the availability and leaching of nutrients in the soil profile, after two years of cultivation. Experiments were performed using a randomized block design with repeated measurements in time, that is, soil was sampled in each harvest. Six treatments were tested: four fertilizations based on sewage sludge, resulting from biological and anaerobic treatment, calculated to provide 25 (SS25), 50 (SS50), 75 (SS75), and 100% (SS100), of the N required for corn production (140 kg ha^-1); a mineral fertilization (NPK) (140 kg ha^-1 N, 70 kg ha^-1 of P₂O₅ and 40 kg ha^-1 of K₂O) and a control (without fertilization). The results showed that four consecutive applications of SS100 for two years caused significant accumulation of nutrients and organic matter in the superficial layers of the soil. The electrical conductivity and the concentration of NO₃^- in the soil solution were higher than those permitted by Brazilian legislation. The adoption of domestic SS in Brazilian agriculture can be a viable alternative in the search for an environment-friendly and economically feasible method for SS disposal.

Thermal dehydration of urban biosolids with green liquor dregs from pulp and paper mill

This study aims to investigate the sewage sludge (SS) drying process by incorporating a by-product formed in the pulp and paper industry (green liquor dregs - GLD) as drying adjuvant. Through an innovative approach, the drying kinetics was modelled, and the final dried product was tested for soil applications. After the characterization phase, small cylinders of SS without and with 0.15 g GLD g SS^-1_wb (SS_GLD) were dried in isothermal conditions at 70, 100, and 130 °C. The experimental data were fitted by Fick's second law and thin-layer models, and good results were achieved in both cases (R² > 0.98 and RMSE <0.05). Although only a slight improvement was observed, the best conditions for drying biosolids were found with the addition of GLD at 130 °C, where the drying rate was 30.88 gH₂O kg^-1 SS_wb min^-1. In this condition, a decrease of 8% in the energy required for moisture evaporation was observed. Regarding the phytotoxicity tests with Lepidium sativum L. (garden cress), 60% improvement in EC₅₀ was noticed for the sample with GLD when compared to the raw SS. The dried product SS_GLD complied with the regulations for soil applications regarding the potentially toxic metals (Cr, Ni, Cu, Pb, Zn, and Cd), and promoted an increase in soil organic matter and pH. However, further and in-depth studies should be conducted to assess the potential of SS_GLD application in agricultural soil.

Feasibility and Carbon Footprint Analysis of Lime-Dried Sludge for Cement Production

Cement manufacturing and the treatment of sludge are considered both energy-intensive industries and major greenhouse gas (GHG) emitters. However, there are still few studies on comprehensive carbon footprint analysis for adding municipal sludge in the cement production. In this study, the lime-dried sludge blended with calcium oxide at the mass mixing ratio of 10% was utilized as raw material for the preparation of Portland cement. The chemical and physical properties of sludge were analyzed. A set of carbon footprint calculation methods of lime-drying treatment of sludge and reuse in cement kilns was then established to explore the feasibility of coprocessing lime-dried sludge in cement kilns. The results showed lime-dried sludge containing CaO, SiO2, Al2O3, and Fe2O3 was ideal for cement production as raw material. However, the water content of lime-dried sludge should be strictly limited. The lime-drying process presented the biggest carbon emission (962.1 kg CO2-eq/t sludge), accounting for 89.0% of total emissions. In the clinker-production phase, the lime-dried sludge as raw material substitute and energy source gained carbon credit of 578.8 and 214.2 kg CO2-eq/t sludge, respectively. The sludge used for producing cement clinker could reduce carbon emissions by 38.5% to 51.7%. The addition ratio of lime and stacking time in the sludge lime-drying process could greatly affect the carbon footprint of coprocessing lime-dried sludge in cement kiln.

Quick Analysis of Organic Amendments via Portable X-ray Fluorescence Spectrometry

The determination of heavy metals in soils and organic amendments, such as compost, manure, biofertilizer, and sludge, generally involves the digestion of samples with aqua regia, and the determination of those in the solution using various techniques. Portable X-ray fluorescence (PXRF) has many advantages in relation to traditional analytical techniques. However, PXRF determines the total elemental content and, until now, its use for the analysis of organic amendments has been limited. The objective of this work is the calibration of a PXRF instrument to determine the aqua regia-soluble elemental contents directly in solid samples of organic amendments. Our proposal will avoid the digestion step and the use of other laboratory techniques. Using a training set of samples, calibration functions were obtained that allow the determination of the aqua regia-soluble contents from the PXRF readings of total contents. The calibration functions (obtained by multiple linear regression) allowed the quantitative determination of the aqua regia-soluble contents of Fe, K, P, S, Zn, Cu, Pb, Sr, Cr, and Mn, as well as the organic matter content and a semi-quantitative assessment of Al, Ca, V, Ba, Ni, and As contents. The readings of Si, Fe, Al, Ca, K, or S were used as correction factors, indicating that the calibrations functions found are truly based on the chemical composition of the sample matrix. This study will allow a fast, cheap, and reliable field analysis of organic amendments and of other biomass-based materials.

Analysis of potentially toxic metal constraints to apply sewage sludge in Portuguese agricultural soils

The application of sewage sludge (SS) in the soil can be a valuable way to increase its content of organic matter. However, the concentration of potentially toxic metal (PTM) in both SS and soil can hinder this route of management. Thus, the main objective of this work was to evaluate the compliance with the restrictions related to PTM contained in SS from wastewater treatment plants (WWTP) for agricultural land application. The regulatory constraints associated with SS and soil in respect to PTM (Cd, Cr, Cu, Ni, Pb, and Zn) were analyzed. These metals showed a deleterious effect on germination of Lepidium sativum seeds, and their phytotoxicity may be ranked as Cd > Cu > Cr(VI) > Cr(III) ~ Zn ~ Ni > Pb. Portuguese SS samples from different WWTP, from a national sludge management operator, and from the literature were considered. The results revealed that the content of these metals, in general, complies with the regulatory threshold values. The content of PTM in the soil is not restrictive to receive SS in at least 90% of the national territory. The assessment of ecological risk based on the geoaccumulation index (I_geo), pollution index (PI), and potential ecological risk index (PERI) showed low risk for all metals. The exception was I_geo of Cd, Cu, and Zn, which presented moderate to high level of pollution. According to the state of the art, no significant negative impacts have been detected on human health and the environment due to SS applications in the soil. Thus, in a country with low carbon content in the land and whenever compliance with regulations is achieved, the main route for SS management may be agricultural soil.

Distribution trend of trace elements in digestate exposed to air: Laboratory-scale investigations using DGT-based fractionation

The use of digestate as amendment for agricultural soils has already been proposed as an alternative to mineral fertilizers or undigested organic matter. However, little information is available concerning the effect of digestate atmospheric exposure on trace elements speciation and, consequently, on their mobility and bio-accessibility when digestate is stored in open tanks or handled before land spreading. In this study, we investigated at laboratory-scale the effect of digestate aeration on the distribution of Al, As, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sb, Se and W using the diffusive gradients in thin films technique (DGT)-based fractionation. For this purpose, experiments were performed to assess the variation in distribution between the labile, soluble and particulate fractions over time in digested sewage sludge during passive and forced aeration. Results showed that aeration promoted a dissolution of Al, As, Co, Cr, Cu, Fe, Mn, Mo and Pb, suggesting a possible increase in their mobility that may likely occur during storage in open tanks or handling before land spreading. Labile elements' fraction increased only during forced aeration (except for Fe and Mn), suggesting that their short-term bio-accessibility can increase only after significant aeration as the one assumed to occur when land spreading takes place.

Municipal solid waste (MSW): Strategies to improve salt affected soil sustainability: A review

Salt-induced soil degradation is a serious threat to global agriculture which is responsible for diminished productivity of agro-ecosystems. Irrigation with poor quality water and indiscriminate use of chemical fertilizers to increase crop productivity creates salt accumulation in soil profile thereby reducing crop sustainability. High concentration of salts in soil inhibits plant growth due to low osmotic potential of the soil solution, ion toxicity and imbalance reduces nutrient uptake, crop yields. Low productivity of saline soils is not only due to salt toxicity or excess amounts of soluble salts but also lack of available mineral nutrients especially nitrogen, phosphorus, potassium and soil organic matter. Hence, sustainable management of salt-affected soils are paramount importance to meet the demands of food grain production for an ever-rising population in the world. Recently, municipal solid waste has gained importance as an organic amendment for restoring soil fertility and finally contributing to productivity of salt-affected soils. This paper compares extant waste generation, their properties and standards pertinent to municipal solid waste in different countries and explores the unique recent history in some countries that shows high environmental regard and rapid changes and also suggests policy experiencing from high environmental regard and rapid changes from other countries, so that policy makers can propose new or revise current municipal solid waste standards for salt affected soils. Municipal solid waste compost improves soil biological, physical and chemical properties because of high soil organic matter and lower concentration of pollutants. Therefore, the use of municipal solid waste in salt-affected soils could be an alternative to costly chemical amendments as well as reduce the reliance on chemical fertilizers for increasing productivity of salt-affected soil. The municipal solid wastes significantly improve crop yields. However, further long-term experimental investigations are needed to re-validate the application of municipal solid waste compost in improving physical, chemical and biological properties and to step up organic fertilization use in a wide range of both saline and sodic soils. In future, research should be directed to address these issues globally to minimise ecological disturbances and to set environmental standards, and evaluate the feasibility of the policies in different countries and their impact on socio-economic conditions of local people.

Sanitary and environmental aspects of sewage sludge management

Currently, sewage sludge management is a huge challenge in the field of environmental engineering. New effective solutions for the treatment of wastewater led to an improvement of the quality of the final effluent but considerably increased the volume of produced sewage sludge, which increases each year. Two points of view conflict regarding the recycling of those “wastes.” Primarily, dehydrated sewage sludge is considered a reservoir of nutrients and organic matter that can be used as a fertilizer in agriculture or as an organic amendment in the remediation of contaminated sites or to build “anthroposoils.” On the other hand, recycled sewage sludge is seen as a potential source of soil contamination by organic and inorganic pollutants and pathogens; potentially toxic elements (such as zinc, copper, cadmium, lead, silver, etc.); polycyclic aromatic hydrocarbons (PAH); polychlorobiphenyls (PCB); biocides and phytopharmaceuticals; pharmaceuticals, personal care products (PPCP), and residuals; synthetic hormones; microplastics; nanotechnology life cycle end products; and microorganisms such as Escherichia coli O157:H7 or Salmonella typhimurium.

This chapter will focus on these aspects, highlighting the health and ecotoxicological risks associated with the presence of such contaminants in sludge. The environmental dangers of sludge spreading on soils will be presented as well as their possible treatment scenarios to propose an acceptable reuse of sewage sludge in a circular economy.

Activated charcoal as a capture material for silver nanoparticles in environmental water samples

Silver nanoparticles (AgNPs), due to their antibacterial activity, have been incorporated into numerous consumer products. Their environmental impact however, is currently unclear. Uncertainties surround the concentration, fate, and effects of AgNPs in aquatic environments. This study examined the suitability of activated charcoal as a capture material for AgNPs from water. Samples of 100 ppb AgNPs were initially generated and exposed to activated charcoal for 24 h to examine the ability of charcoal to capture AgNPs. The decrease in Ag concentration was measured using ICP-MS. Following initial investigations, the surface area of the charcoal was increased firstly with a pestle and mortar and secondly by milling the charcoal using a ball mill. The increased surface area of the milled charcoal increased the capture of the AgNPs from 11.9% to 63.6% for the 100 ppb samples. Further investigations were carried out examining the effect on the capture of AgNP concentration (with concentration ranging from 10 to 100 ppb), particle coating and the effect of exposure time to the activated charcoal. The capture of AgNP increased with decreasing concentration. A hydrochloric acid (HCl) leaching procedure was also developed which successfully removed the captured silver allowing the fraction captured by the charcoal to be quantified with an average of 94.8% recovery. The results show that milled activated charcoal, can successfully capture AgNPs from water samples, and that therefore, activated charcoal may prove to be a cost effective material for the remediation of waters impacted by AgNP or other nano-wastes.

Monitoring metal pollution in soils using portable-XRF and conventional laboratory-based techniques: Evaluation of the performance and limitations according to metal properties and sources

Large variability in the spatial distribution and content of metals is generally recognised in anthropogenically-polluted soils, hence, a detailed site investigation implying the collection and analysis of a large number of soil samples is often necessary. To this regard, the selection of a rapid, cost-effective and accurate analytical technique to assess the concentration of metals in soil is of paramount importance. The overall objective of this work was to evaluate the possibility of assessing the aqua regia-extractable (AR) content of metals in soil from the multi-element profile of the soil obtained by a portable X-ray fluorescence analyser (pXRF). To this objective, we attempted: (i) to establish, by simple linear regressions, the relations occurring between the metal contents measured by pXRF and AR in laboratory setting on air-dried and 2 mm-sieved soil samples from two case studies (A-agricultural and B-industrial sites); (ii) to define metal-based linear models predicting metal AR contents from pXRF measurements; (iii) to assess the influence of metal properties and sources on relations found between the two analytical methods. Very satisfying correlations (R² > 0.90) were observed between the AR and pXRF contents of Ca, Cu, Cr, Ni, Pb and Zn in the site A, and of Cd, Cu, Pb and Zn in the site B. For the majority of metals, lower AR than pXRF contents were measured, as result of the AR incomplete dissolution of metal-bearing silicates. This was not observed when metals - of anthropogenic origin - occurred in soil in very high concentrations (i.e., Cr for A and Pb for B). In both sites, the comparison among different regression parameters revealed a strong metal-dependence. Moreover, for most of the metals, the parameters of each metal-regression line significantly differed between the two case studies, indicating site-dependence of regression fits.

Structural characterization and evaluation of municipal wastewater sludge (biosolids) from two rural wastewater treatment plants in East Texas, USA

Wastewater sludge (or) biosolids collected from two rural wastewater treatment plants (NWWTP, LWWTP) in East Texas, USA were characterized and evaluated via inductively coupled plasma optical emission spectrometry, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), thermogravimetric analysis, X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), and ion chromatography. The proximate organic and inorganic compositions and spectroscopic characteristics of sewage sludge were determined. The results show that the concentrations of toxic metals Cd, Cr, Cu, Mo, Ni, Pb, Hg, and Zn meet USEPA guideline recommendations for land applications. Notably, metals concentrations in biosolids from NWWTP (Mn (700 ± 83) > Zn (422.5 ± 35.4 ppm) > Ba (319.5 ± 87 ppm) > Cu (240 ± 27 ppm) > B (107 ± 14 ppm) > V (24 ± 3.3 ppm) > Cr (20 ± 3.3 ppm) > Ni (16.7 ± 2.0 ppm) > Pb (16.8 ± 1.1 ppm) > As (11.99 ± 1.27 ppm) > Co (7.6 ± 0.7 ppm) > Mo (6.4 ± 1.4 ppm) > Hg (0.55 ± 0.24 ppm) > Cd (0.130 ± 0.109 ppm)) and LWWTP follow similar trends. Macro-elements concentrations in LWWTP follow the trend P (19,648 ± 169) > Fe (22,688 ± 2110) > Ca (9372 ± 163) > S (9010 ± 1009) > Al (12,538 ± 2116) > K (3514 ± 550) > Mg (33,370 ± 502) > Na (1511 ± 472). The Br^-, NO₃^-, NO₂^-, F^-, Cl^-, and SO₄^2- concentrations meet USEPA guidelines. Whereas biosolid particle sizes were in the range ~20 μm to 500 μm mineralogical results show quartz and vermiculite to be major constituents with abundancies 12.94%, and 10.87% w/wt, respectively.

Extractability and crop transfer of potentially toxic elements from mediterranean agricultural soils following long-term sewage sludge applications as a fertilizer replacement to barley and maize crops

Sewage sludge is used as a fertilizer replacement in agricultural soils for its chemical properties, such as organic matter content, and for its capability to improve physical soil characteristics like porosity. This is also an appealing disposal option for residue whose production is increasing worldwide. However, there is some concern about the presence of potentially toxic elements (PTEs) that can accumulate in soils and become available for crops. In this work, a study was conducted to evaluate the extractability and crops transfer of thirteen PTEs from soils that had been amended with biosolids each year for 15 years as a regular agricultural practice. The study was conducted with barley (winter cereal) and maize (spring cereal) crops. After this long period, an increase in the amount of Pb, Hg, Zn and Ag in soils amended by biosolids was confirmed. However, it is important to emphasize that the PTE total content in croplands was still far below the thresholds established by US and European regulations. Statistically significant differences were also found between the soils fertilized with biosolids and other treatments compared with the potential phytoavailable amount of Cu, Se, Sb and especially for As and Zn, by a DTPA leaching test. Despite these results, the concentration of PTEs in the barley and maize grains grown in fields repeatedly amended with biosolids was not statistically different from those grown with chemical fertilization, except for As in barley grains. In this case, a significant correlation was found between the DTPA-extractable As content in soils and the total content in grains (r = 0.83).

The presence of contaminations in sewage sludge - The current situation

Sewage sludge/biosolids are by-wastes of municipal and industrial wastewater treatment. As sources of nutrients (C, N, P) they are widely used in intensive farming where large supplementation of organic matter to maintain fertility and enhance crop yields is needed. However, according to the report of European Commission published in 2010, only 39% of produced sewage sludge is recycled into agriculture in the European Union. This situation occurs mainly due to the fact, that the sewage sludge may contain a dangerous volume of different contaminants. For over decades, a great deal of attention has been focused on total concentration of few heavy metals and pathogenic bacteria Salmonella and Escherichia coli. The Sewage Sludge Directive (86/278/EEC) regulates the allowable limits of Zn, Cu, Ni, Pb, Cd, Cr and Hg and pathogens and allows for recovery of sludge on land under defined sanitary and environmentally sound conditions. In this paper, a review on quality of sewage sludge based on the publications after 2010 has been presented. Nowadays there are several papers focusing on new serious threats to human health and ecosystem occurring in sewage sludge - both chemicals (such as toxic trace elements - Se, Ag, Ti; nanoparticles; polyaromatic hydrocarbons; polychlorinated biphenyl; perfluorinated surfactants, polycyclic musks, siloxanes, pesticides, phenols, sweeteners, personal care products, pharmaceuticals, benzotriazoles) and biological traits (Legionella, Yersinia, Escherichia coli O157:H7).

Bioaccumulation of metals in juvenile rainbow trout (oncorhynchus mykiss) via dietary exposure to blue mussels

The potential for metals to bioaccumulate in aquatic species, such as fish, via trophic level transfer was investigated. An in vivo experiment was set up in a flow-through system in which juvenile rainbow trout were fed blue mussels collected from a Class A pristine site and an effluent-impacted river estuary, over a period of 28 days. Selected elements (As, Cd, Cr, Co, Cu, Fe, Pb, Mn, Mo, Ni, Se, Sn, V, Zn) were determined in the mussels and fish tissues (muscle and skin) collected at 0, 14 and 28 days. This study reveals the occurrence of metals in mussels sampled in the Irish marine environment and highlights the bioaccumulation potential of metals in fish tissues via trophic transfer. All 14 monitored metals were determined in the mussels collected from both sites and mussels collected from the effluent-impacted site contained three times more Co, Mo, Sn and V than the mussels collected from the Class A site. Following a 28-day dietary exposure, concentrations of As and Se (fish muscle), and Pb, Se and Zn (fish skin), were significantly greater in fish feeding on contaminated mussels compared to those with a regular fish feed diet. The significance of metal detection and bioaccumulation in the mussel and fish tissues, highlights the potential for metal exposure to humans through the food chain. As fish are recommended as a healthy and nutritious food source, it is important to fully understand metal bioaccumulation in commercially important aquatic species and ensure the safety of human consumers.

Quantification of Element Fluxes in Wastewaters: A Nationwide Survey in Switzerland

The number and quantities of trace elements used in industry, (high-tech) consumer products, and medicine are rapidly increasing, but the resulting emissions and waste streams are largely unknown. We assessed the concentrations of 69 elements in digested sewage sludge and effluent samples from 64 municipal wastewater treatment plants as well as in major rivers in Switzerland. This data set, representative of an entire industrialized country, presents a reference point for current element concentrations, average per-capita fluxes, loads discharged to surface waters, and economic waste-stream values. The spatial distribution of many individual elements could be attributed either to predominant geogenic or to anthropogenic inputs. Per-capita element fluxes ranged from <10 μg day^-1 (e.g., Au, In, and Lu) to >1 mg day^-1 (e.g., Zn, Sc, Y, Nb, and Gd) and >1 g day^-1 (e.g., for P, Fe, and S). Effluent loads of some elements contributed significantly to riverine budgets (e.g., 24% for Zn, 50% for P, and 83% for Gd), indicating large anthropogenic inputs via the wastewater stream. At various locations, precious metal concentrations in sludge were similar to those in profitable mining ores, with total flux values of up to 6.8 USD per capita per year or 15 USD per metric ton of dry sludge.

Antimicrobial compounds (triclosan and triclocarban) in sewage sludges, and their presence in runoff following land application

The reuse of treated municipal sewage ('biosolids') on land is an effective method to divert waste away from landfill and to use an alternative, low cost method of fertilisation. While legislation has mainly focused on the control of nutrient and metal application rates to land, other potentially harmful emerging contaminants (ECs) may be present in biosolids. Up to 80% of municipal sewage sludge is reused in agriculture in Ireland, which is currently the highest rate of reuse in Europe. However, unlike other countries, no study has been conducted on the presence of ECs across a range of wastewater treatment plants (WWTPs) in this country. This study evaluated the concentrations of two ECs in sewage sludge, the antimicrobials triclosan (TCS) and triclocarban (TCC), and their presence in surface runoff following land application in controlled rainfall simulation studies. In 16 WWTPs, concentrations of TCS and TCC were 0.61 and 0.08µgg^-1, which is at the lower end of concentrations measured in other countries. The concentrations in runoff post land application were also mainly below the limits of detection (90ngL^-1 for TCS, 6ngL^-1 for TCC), indicating that runoff is not a significant pathway of entry into the environment.

Agricultural utilization of biosolids: A review on potential effects on soil and plant grown

Environmental and economic implications linked with the proper ecofriendly disposal of modern day wastes, has made it essential to come up with alternative waste management practices that reduce the environmental pressures resulting from unwise disposal of such wastes. Urban wastes like biosolids are loaded with essential plant nutrients. In this view, agricultural use of biosolids would enable recycling of these nutrients and could be a sustainable approach towards management of this hugely generated waste. Therefore biosolids i.e. sewage sludge can serve as an important resource for agricultural utilization. Biosolids are characterized by the occurrence of beneficial plant nutrients (essential elements and micro and macronutrients) which can make help them to work as an effective soil amendment, thereby minimizing the reliance on chemical fertilizers. However, biosolids might contain toxic heavy metals that may limit its usage in the cropland. Heavy metals at higher concentration than the permissible limits may lead to food chain contamination and have fatal consequences. Biosolids amendment in soil can improve physical and nutrient property of soil depending on the quantity and portion of the mixture. Hence, biosolids can be a promising soil ameliorating supplement to increase plant productivity, reduce bioavailability of heavy metals and also lead to effective waste management.

Microplastics in Sewage Sludge: Effects of Treatment

Waste water treatment plants (WWTPs) are receptors for the cumulative loading of microplastics (MPs) derived from industry, landfill, domestic wastewater and stormwater. The partitioning of MPs through the settlement processes of wastewater treatment results in the majority becoming entrained in the sewage sludge. This study characterized MPs in sludge samples from seven WWTPs in Ireland which use anaerobic digestion (AD), thermal drying (TD), or lime stabilization (LS) treatment processes. Abundances ranged from 4196 to 15 385 particles kg^-1 (dry weight). Results of a general linear mixed model (GLMM) showed significantly higher abundances of MPs in smaller size classes in the LS samples, suggesting that the treatment process of LS shears MP particles. In contrast, lower abundances of MPs found in the AD samples suggests that this process may reduce MP abundances. Surface morphologies examined using scanning electron microscopy (SEM) showed characteristics of melting and blistering of TD MPs and shredding and flaking of LS MPs. This study highlights the potential for sewage sludge treatment processes to affect the risk of MP pollution prior to land spreading and may have implications for legislation governing the application of biosolids to agricultural land.

Linking toxicity profiles to pollutants in sludge and sediments

Obtaining a complex picture of how pollutants synergistically influence toxicity of a system requires statistical correlation of chemical and ecotoxicological data. In this study, we determined concentrations of eight potentially toxic metals (PTMs) and four groups of organic pollutants in 15 sewage sludge and 12 river sediment samples, then linked measured contaminant concentrations to the toxicity of each matrix through constrained correspondence analysis (CCA). In sludge samples, Hg, As, hexachlorohexane (HCH), polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecane (HBCD) influenced the toxicity profiles, with the first four having significant effects and HBCD being marginally significant. In sediment samples, Hg, As, PBDEs, hexachlorobenzene (HCB), dichlorodiphenyltrichloroethane (DDT), HBCD, HCH and polycyclic aromatic hydrocarbons (PAHs) were found to explain toxicity profiles with Hg, As, PBDEs, HCB, DDT, HBCD, and HCH having significant effects and PAHs being marginally significant. Interestingly, HCH was present in small amounts yet proved to have a significant impact on toxicity. To the contrary, PAHs were often present in high amounts, yet proved to be only marginally significant for sediment toxicity. These results indicate that statistical correlation of chemical and ecotoxicological data can provide more detailed understanding of the role played by specific pollutants in shaping toxicity of sludge and sediments.

Bioaccumulation of metals in ryegrass (Lolium perenne L.) following the application of lime stabilised, thermally dried and anaerobically digested sewage sludge

The uptake and accumulation of metals in plants is a potential pathway for the transfer of environmental contaminants in the food chain, and poses potential health and environmental risks. In light of increased population growth and urbanisation, the safe disposal of sewage sludge, which can contain significant levels of toxic contaminants, remains an environmental challenge globally. The aims of this experiment were to apply municipal sludge, having undergone treatment by thermal drying, anaerobic digestion, and lime stabilisation, to permanent grassland in order to assess the bioaccumulation of metals (B, Al, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, As, Nb, Mo, Sb, Ba, W, Pb, Fe, Cd) by perennial ryegrass over a period of up to 18 weeks after application. The legislation currently prohibits use of grassland for fodder or grazing for at least three weeks after application of treated sewage sludge (biosolids). Five treatments were used: thermally dried (TD), anaerobically digested (AD) and lime stabilised (LS) sludge all from one wastewater treatment plant (WWTP), AD sludge from another WWTP, and a study control (grassland only, without application of biosolids). In general, there was no significant difference in metal content of the ryegrass between micro-plots that received treated municipal sludge and the control over the study duration. The metal content of the ryegrass was below the levels at which phytotoxicity occurs and below the maximum levels specified for animal feeds.