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Research on wastewater treatment processes in Maluti-a-Phofung Municipality (South Africa) has revealed that substandard wastewater management in this region contributes to terrestrial and aquatic pollution. Because this pollution poses a threat to the environment, there is a pressing need to reduce the environmental impact of poorly managed sewage sludge in the region. Biochar has been regarded as a cost-effective way of reducing chemical toxicity in terrestrial environments. In the present study, we aimed to investigate the effectiveness of biochar in the remediation of the toxicity of sewage sludge using the earthworm Eisenia fetida. Sewage sludge was collected from a local wastewater treatment plant and E. fetida were exposed to 0, 25, 50, and 100% non-amended and 10% biochar-amended sludge. After 28 days, survival, biomass and reproduction were assessed. Separately, in clean artificial soil, E. fetida was exposed to 5, 10 and 15% biochar amendment for 96 hours to determine if biochar amendment alone could be harmful to E. fetida. The results showed no significant differences in all parameters between the worms exposed to non-amended sludge and 10% biochar-amended sludge. Assessment of acetylcholinesterase and catalase activities in the earthworms that were exposed to biochar via clean soil revealed that 10% and 15% biochar amendment rates caused the worms to experience significant levels of neurotoxic and oxidative stress (p < 0.05). These findings reveal that biochar alone is likely to have adverse effects on soil organisms, and amendment rates higher or equal to 10% are not suitable to alleviate the toxic effects of sewage sludge. Significance: This study can be used as a reference in the usage of biochar as a toxicity remediator. Different biochar rates (≥ 10%) can have different effects on soil-dwelling organisms. Policymakers can use this study when constructing laws regarding the disposal of sewage sludge by wastewater treatment plants. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel combination of X-ray tomography with elemental and crystalline composition. • 3D view of microstructure and phosphate distribution based on the X-ray attenuation. • Phosphates comprised 7–17 vol% of slag particle volume. • Porosity of 15–35 vol% for slag particles from combustion of sewage sludge mixtures. The purpose of this study was to provide detailed knowledge of the morphological properties of ash particles, including the volumetric fractions and 3D distributions of phosphates that lay within them. The ash particles came from digested sewage sludge co-combusted with K- and Si-rich wheat straw or K-rich sunflower husks. X-ray micro-tomography were combined with elemental composition and crystalline phase information to analyse the ash particles in 3D. Analyses of differences in the X-ray attenuation enabled calculation of 3D phosphate distributions that showed high heterogeneity in the slag particles. This is underscored by a distinct absence of phosphates in iron-rich and silicon-rich parts. The slag from silicate-based wheat straw mixtures had lower average attenuation than that from sunflower husks mixtures, which contained more calcium. Calculated shares of phosphates between 7 and 17 vol% were obtained, where the highest value for a single assigned phosphate was observed in hard slag from wheat straw with 10 % sewage sludge. The porosity was notably higher for particles from pure wheat straw combustion (62 vol%), compared to the other samples (15–35 vol%). A high open pore volume fraction (60–97 vol%) indicates that a large part of the pores can be accessed by the surroundings. For all samples, more than 60 % of the discrete (closed) pores had an equivalent diameter < 30 μm, while the largest volume fraction consisted of pores with an equivalent diameter > 75 μm. Slag from sunflower husk mixtures had larger pore volumes and a greater relative number of discrete pores >75 µm compared to wheat straw mixtures. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons (PAHs) are widely present in the environment, causing increasing concern because of their impact on soil health, food safety and potential health risks. Four bioremediation strategies were examined to assess the dissipation of PAHs in agricultural soil amended with sewage sludge over a period of 120 days: soil-sludge natural attenuation (SS); phytoremediation using maize (Zea mays L.) (PSS); mycoremediation (MR) separately using three white-rot fungi (Pleurotus ostreatus , Phanerochaete chrysosporium and Irpex lacteus) ; and plant-assisted mycoremediation (PMR) using a combination of maize and fungi. In the time frame of the experiment, mycoremediation using P. chrysosporium (MR-PH) exhibited a significantly higher (P < 0.05) degradation of total PAHs compared to the SS and PSS treatments, achieving a degradation rate of 52 %. Both the SS and PSS treatments demonstrated a lower degradation rate of total PAHs, with removal rates of 18 % and 32 %, respectively. The PMR treatments showed the highest removal rates of total PAHs at the end of the study, with degradation rates of 48–60 %. In the shoots of maize, only low- and medium-molecular-weight PAHs were found in both the PSS and PMR treatments. The calculated translocation and bioconversion factors always showed values < 1. The analysed enzymatic activities were higher in the PMR treatments compared to other treatments, which can be positively related to the higher degradation of PAHs in the soil. [ABSTRACT FROM AUTHOR]

To reduce the operating cost of wastewater treatment plants and in situ treatment of sewage sludge and domestic food waste, the current investigation of anaerobic codigestion of domestic food waste and primary bioflocculated sewage sludge was conducted in an anaerobic reactor coupled with a decentralized domestic wastewater treatment plant. The performance of the anaerobic reactor and wastewater treatment system was tested for 30 days. The anaerobic digester was placed after the flocculation chamber in the wastewater treatment plant to transfer the primary bioflocculated sludge using gravity. The 0.5 kg Day−1 of domestic food waste and 29 L Day−1 of bioflocculated sewage sludge were used as feedstock for an anaerobic codigestion and supernatant collected in the flocculation chamber were passed to the water treatment stages. The bioflocculated sludge was collected by adding flocculant in domestic raw wastewater and fed in a digester whereas food waste was added using the separate port in the digester on daily basis. The anaerobic digester was operated in continuous mode at mesophilic temperature conditions at a hydraulic retention time of 7 days. The physiochemical parameters for controlling the anaerobic digester were examined periodically which showed the maximum volatile fatty acid accumulation of 6,500 mg L−1 on the 12th day with the highest biomethane production of 0.35 L CH4 g−1 VSconsumed. The highest energy production potential of biogas was estimated as 0.35 kWh unit. The physical, chemical, organic, inorganic, and biological characteristics of treated water were tested to quantify the treatment efficiency of the process for the reuse of treated water. Results indicated that more than 90% of effluent was collected at the outlet of treatment units and the tested parameters were fulfilling the guidelines set by the different agencies for the reuse of effluent for various purposes. Practical Applications: This paper investigates the performance of anaerobic codigestion of food waste and bioflocculated sewage sludge coupled with a decentralized wastewater treatment plant for the ease of substrate availability. Biomethane production was used to analyze the energy generation potential of domestic sewage sludge and food waste to reduce the operating cost of wastewater treatment systems. The feeding ratio used for operating the anaerobic reactor was decided based on food waste and sewage sludge availability from typical households. The limiting values of VFA with codigestion of food waste and bioflocculated sewage sludge have been reported in the current study and compared with literature values. This work provides insights to make possible the in situ treatment of domestic wastewater along with energy generation from food waste and bioflocculated sewage sludge in an integrated system which is unavailable in the literature. [ABSTRACT FROM AUTHOR]

The continuous tightening of legislation regulating the agricultural usage of sewage sludge in the province of Catalonia (Spain) leads us to propose its gasification to produce hydrogen-rich syngas. A thermodynamic equilibrium model was developed using Aspen Plus® to simulate the air and steam gasification of sewage sludge from a wastewater treatment plant in Catalonia. The syngas generated is analyzed in terms of composition and lower heating value (LHV), as a function of equivalence ratio (ER), gasification temperature (Tgas), steam-to-biomass ratio (SBR), and moisture content (MC). Results show that air-blown gasification finds the highest LHV of 7.48 MJ/m3 at 1200 °C, ER of 0.2, and MC of 5%. Using steam as the gasifying agent, an LHV of 10.30 MJ/m3 is obtained at SBR of 0.2, MC of 5%, and 1200 °C. A maximum of 69.7% hydrogen molar fraction is obtained at 600 °C, MC of 25%, and SBR of 1.2. This study suggests using steam as a gasifying agent instead of air since it provides a higher LHV of the syngas as well as a hydrogen-richer syngas for the implementation of gasification as an alternative method to sewage sludge treatment in the region of Catalonia. Since the economic aspect should also be considered, in this regard, our sensitivity analysis provided important data demonstrating that it is possible to reduce the gasification temperature without significantly decreasing the LHV. [ABSTRACT FROM AUTHOR]

The valorisation of sewage sludge for sustainable agricultural use and biofuel production proposes an effective and beneficial management of sewage sludge in a closed-loop cycle. The management of sewage sludge biowaste is a rising problem due to increasing waste storage expenses. In this sense, the use of circular economy principles in sewage sludge management creates opportunities to develop new technologies for processing. The biorefinery model allows the application of wasteless technologies via sewage sludge valorisation in terms of agricultural use and biofuel production, especially with the hydrothermal carbonisation method. Applying hydrothermal carbonisation in the treatment of biosolid sewage sludge has numerous benefits due to processing highly hydrated organic waste into carbon hydro char, a high-quality solid biofuel. The direct use of sewage sludge in the soil does not allow for full use of its functional properties. However, the hydrothermal carbonisation of sewage sludge results in biocarbon pellets, making it a viable approach. This work also discusses the barriers (legal, chemical, biological, and technical) and possibilities related to sewage sludge biorefining processes. [ABSTRACT FROM AUTHOR]

Soil application of treated sewage sludge is considered a beneficial management option for agriculture and environment. Sludge treated with clay minerals or biochar was evaluated as soil amendment, in comparison with limed or untreated sludge. Bentonite, vermiculite, biochar or lime was added to dewatered sewage sludge at 0 and 15% rates, in three replications and air-dried. Then, the treated and untreated sludge were added to two soils, one acid and one alkaline, at 0 (control), 1 and 3% rates, in three replications. The results showed that the pH of acid soil significantly increased compared to control upon addition of treated and untreated sludge at both rates, but remained acidic (<6.0) in all cases except for limed sludge. Upon addition of 3% treated or untreated sludge to both soils, organic carbon (OC) significantly increased compared to control. The same stands for soil available ammonium nitrogen (NH4-N), phosphorus (P), potassium (K), copper (Cu), zinc (Zn) and boron (B) for both soils and rates. Soil total heavy metals, which regulate sludge's agronomic use, were below the legislative limits. However, the 3% addition rate of all kinds of sludge, especially of untreated, to both soils increased the electrical conductivity of saturation extract (ECse >2 dS m−1) at unacceptable levels for sensitive crops and available P, B and Zn 2–3, 2–4 and 6–12 times above the initial, respectively. Consequently, sewage sludge treated with bentonite, vermiculite or biochar could be used as a soil amendment but at rates lower than 3% (≈120 Mg ha−1). [ABSTRACT FROM AUTHOR]

This article is devoted to the search for effective ways of neutralizing sewage sludge to obtain sludge-based reclamation material. It was necessary to solve the problems of deodorizing the sludge and fixing the mobile forms of heavy metals in its composition. The composition, effective for solving the assigned problems, was experimentally determined; it included quicklime, sodium hypochlorite and peat. In the presence of sodium hypochlorite in the sludge-based composition, oxidation processes occur with the chemical transformation of ammonia and hydrogen sulfide into non-toxic and odorless compounds. Lime combined with peat promotes the humification of sewage sludge and the binding of heavy metals. Based on the composition that showed the best results, a technology has been developed for the chemical treatment of sewage sludge in situ to produce reclamation material. [ABSTRACT FROM AUTHOR]

Effectively managing sewage sludge from Fenton reactions in an eco-friendly way is vital for Fenton technology's viability in pollution treatment. This study focuses on sewage sludge across various treatment stages, including generation, concentration, dehydration, and landfill, and employs chemical composite MoS2 to facilitate green resource utilization of all types of sludge. MoS2, with exposed Mo4+ and low-coordination sulfur, enhances iron cycling and creates an acidic microenvironment on the sludge surface. The MoS2-modified iron sludge exhibits outstanding (>95%) phenol and pollutant degradation in hydrogen peroxide and peroxymonosulfate-based Fenton systems, unlike unmodified sludge. This modified sludge maintains excellent Fenton activity in various water conditions and with multiple anions, allowing extended phenol degradation for over 14 d. Notably, the generated chemical oxygen demand (COD) in sludge modification process can be efficiently eliminated through the Fenton reaction, ensuring effluent COD compliance and enabling eco-friendly sewage sludge resource utilization. [ABSTRACT FROM AUTHOR]

An innovative process layout for sludge waste management based on chemical looping combustion and flue gas methanation is analyzed in this work. The technical performance of the system was assessed by considering that the flue gas is first purified and then mixed with a pure hydrogen stream sourced from an array of electrolysis cells to produce methane. The life cycle assessment (LCA) and life cycle cost (LCC) methodologies were applied to quantify the environmental and economic performances of the proposed process, and a hotspot analysis was carried out to recognize its most critical steps. The proposed system was then compared with a reference system that includes both the conventional waste management pathways for the Italian context and methane production. Finally, to account for the variability in the future economic climate, the effects of changes in landfill storage costs on sewage end-of-life costs for both the proposed and reference systems were evaluated. With respect to 1 kg/h of sewage sludge with 10%wt of humidity, the analysis shows that the proposed system (i) reduces landfill wastes by about 68%, (ii) has an end-of-life cost of 1.75 EUR × kg−1, and (iii) is environmentally preferable to conventional sewage sludge treatment technologies with respect to several impact categories. [ABSTRACT FROM AUTHOR]

Sewage sludge treatment and disposal remains a challenging problem. Composting of sewage sludges is gaining increasing attention due to its cost-effectiveness, operation convenience, advantages in lifecycle management, and low greenhouse gas emissions. Disadvantages, such as long reaction time, significant land area occupation requirement, potential risks of residual heavy metals, and emerging contaminants, have restricted wider application. Here we review applications of hyperthermophiles in composting , focusing on the unique improvements provided by hyperthermophiles in composing temperatures, product safety, nitrogen preservation and humification. Inoculation of hyperthermophiles allows temperature of composting to reach over 80°C. Specific metabolic strategies are critical in hyperthermophiles-inoculated composting. High-temperature resistance in the metabolism of hyperthermophiles and their roles in temperature rising during composting is often overlooked. This review discusses both aspects, allowing for a deeper understanding of the functions and influences of hyperthermophiles in sludge composting. Additionally, this review highlights the policy challenges associated with the hyperthermophiles-inoculated sludge composing technique and provides potential directions for future research in this field. [ABSTRACT FROM AUTHOR]

• Microalgae and sewage sludge were converted into hydrochars at three temperatures. • High addition of sewage sludge affected formation and composition of secondary char. • Less sewage sludge led to higher C retainment and fixed C in hydrochars. • Presence of toxic compounds in microalgae may limit potential utilization. The role of microalgae cultivation in wastewater treatment and reclamation has been studied extensively, as has the potential utility of the resulting algal biomass. Most methods for processing such biomass generate solid residues that must be properly managed to comply with current sustainable resource utilization requirements. Hydrothermal carbonization (HTC) can be used to process both individual wet feedstocks and mixed feedstocks (i.e., co-HTC). Here, we investigate co-HTC using microalgae and digested sewage sludge as feedstocks. The objectives were to (i) study the material's partitioning into solid and liquid products, and (ii) characterize the products' physicochemical properties. Co-HTC experiments were conducted at 180–250°C using mixed microalgae/sewage sludge feedstocks with the proportion of sewage sludge ranging from 0 to 100 %. Analyses of the hydrochar composition and the formation and composition of secondary char revealed that the content of carbonized material in the product decreased as the proportion of sewage sludge in the feedstock increased under fixed carbonization conditions. The properties of the hydrochars and the partitioning of material between the liquid phase and the hydrochar correlated linearly with the proportion of microalgae in mixed feedstocks, indicating that adding sewage sludge to microalgae had weak or non-existent synergistic effects on co-HTC outcomes. However, the proportion of sewage sludge in the feedstock did affect the secondary char. For example, adding sewage sludge reduced the abundance of carboxylic acids and ketones as well as the concentrations of higher molecular weight cholesterols. Such changes may alter the viable applications of the hydrochar. [ABSTRACT FROM AUTHOR]

Miscanthus yields well on raw subsoil where organic matter and nutrients are supplied by sewage sludge; the yield is directly dependent on the amount of sludge applied; the greatest productivity (12.9t/ha) was achieved by adding 60t/ha of flocculated sludge. Among the macronutrients, nitrogen is most actively absorbed, the intensity of biomass accumulation of phosphorus and potassium is much lower; other essential elements can be ranked as Fe → Zn → Mn → Cu. Cobalt, nickel and cadmium do not accumulate in biomass but chromium does. The introduction of sewage sludge affects the thermal characteristics of the miscanthus biomass. The proportion of incombustible residue increases when sludge is applied at high doses. Application of 20t/ha flocculated sludge appears to be optimal for ensuring environmental safety and suitability as a fuel. [ABSTRACT FROM AUTHOR]

Sewage sludge as a byproduct of industrial and municipal wastewaters treatment is produced worldwide at large quantities. This organic waste contains nutrients, pathogens, heavy metals, organic pollutants and other toxic substances. In recent years, the significant increase in the amount of sludge as an important environmental issue, which is considered both a threat and an opportunity, has highlighted the issue of its proper management. In recent decades, various methods have been used to manage and energy recovery from sewage sludge, including pyrolysis, incineration, gasification, anaerobic digestion, aerobic digestion, landfill, composting, lime and microbial fuel cell. Nowadays bioenergy production from sewage sludge attracted the attention of environmentalists due to environmental and economic considerations. In this regard, microbial fuel cells (MFCs) have gained a great importance as an alternative energy conversion method for bioenergy production. This system converts the chemical energy in the organic substance directly into valuable electrical energy by the catalytic reaction of microorganisms. The effectiveness of the system depends on the reactor configuration, operational and environmental parameters. Identifying and optimizing these parameters are important to increase the system efficiency. In this paper, we reviewed and discussed the effects of different parameters on the treatment and electricity generation from waste activated sludge (WAS) using MFC system such as nature of electrode materials, oxygen flow rate, reactor design, substrates and pH. Furthermore, a better understanding of the MFCs performance for bio-fuel generation from WAS, as well as solving concerns associated to the abilities of this technology in real application is aims of this review. [Display omitted] • To power generation and sewage sludge stabilization, simultaneously. • Impact of configurations and operation of MFC on sewage sludge stabilization. • To study the factors influencing the sewage sludge treatment and power generation by MFC. [ABSTRACT FROM AUTHOR]

A reasonable strategy for the development of sludge conditioning methods prior to dewatering appears to be the use of substances that allow the safe management of dewatered sludge. It is also justified to use mineral or organic conditioners instead of synthetic chemicals, e.g., polyelectrolytes, or to try to use other substances, e.g., waste. The properties of iron coagulant (PIX 113) combined with perlite and cellulose can be an environmentally safe method of sludge conditioning. The tests were carried out in accordance with European standards on the efficiency of mechanical dewatering of sewage sludge. The most advantageous method of sludge conditioning was the dosing of the iron coagulant PIX 113. The use of at least a coagulant dose of 0.40 g/g DS enabled the achievement of minimum sludge dewatering parameters, i.e., specific resistance of filtration (SRF) < 5.0 E12 m/kg and final hydration of filtration cake (FH) < 80%. The use of cellulose and perlite as stand-alone conditioners or in combination with PIX 113 resulted in a deterioration of the sludge dewaterability and the quality of the filtrate. It is assumed that the further development of environmentally friendly conditioning methods requires the use of easy-to-use, non-toxic and biodegradable substances. It is important to select conditioners which, in practically acceptable doses, can improve the conditioning effect or show a synergistic effect in combination with previously used conditioners. [ABSTRACT FROM AUTHOR]

Due to the amendment of sewage sludge ordinance in Germany, phosphorus must be recovered from sewage sludge in the future. Previously developed phosphorus recycling processes are not economically viable due to high material and energetic expenditures. Gasification of dried sewage sludge enables the energetic utilization of sewage sludge and provides the energy for phosphorus recovery. The present paper focuses on thermodynamic modeling of the gasification system to demonstrate the potential for holistic utilization of dried sewage sludge as phosphorus fertilizer. The results shows that an energy self‐sufficient, optimized process can be realized for recovery of phosphorus by gasification and subsequent thermo‐chemical treatment of dried sewage sludge. [ABSTRACT FROM AUTHOR]

Disposal of sewage sludge (SS) is one of the problems in treatment plants; however, SS has a high-water volume and lacks some compounds and can be mixed with other biomass. The present study analyzed co-hydrothermal carbonization of sewage sludge with sawdust and corn stalk. This research aimed to optimize the process parameters, the temperature in the range of 180–300 °C, the reaction time in the range of 30–60 min, and pH in the range of 5–9 on the mass yield, energy yield, and high heat value (HHV) to increase the quality of hydrochar, and to analyze the effect of hydrothermal carbonization (HTC) on the characteristics of raw materials and hydrochar. The response surface method and Benken's box model were conducted using Design Expert 10 software. The optimal conditions for HHV, mass yield, and energy yield were 15.802 MJ/kg, 63.754%, and 67.415% respectively which occurred in the 205.358 °C, 30 min reaction time, and pH of 5. The temperature was the most influential parameter. The morphological, physicochemical, thermal, and crystalline properties of the hydrochar with the maximum HHV, mass yield and energy yield were evaluated as well. These results demonstrate that HTC is a suitable process to produce hydrochar, which can be used as a direct solid fuel. Highlights : • Hydrothermal carbonization of sewage sludge with sawdust and cornstalk was investigated. • Response surface optimization hydrothermal carbonization process was studied. • The morphological, physicochemical, thermal, and crystalline properties of the hydrochar are reported. • The optimal HHV was 15.802 MJ/kg. • The process can produce hydrochar which can be used for direct combustion or activated carbon. [ABSTRACT FROM AUTHOR]

In the wake of economic and population growth, increased wastewater production poses a challenge related to sewage sludge treatment, which is problematic given its high moisture content, amount, and hazardous characteristics. This study focuses on the hydrothermal carbonization of sewage sludge to produce carbonous material–hydrochar, which may be an alternative to fossil fuels. The effect of process parameters, namely, temperature (180, 240, 300 °C) and duration time (30, 90, 180 min), on hydrochar properties (proximate and ultimate analysis, heating values) and process performance were studied. Obtained results indicate and confirm that hydrothermal carbonization, especially temperature increase, improves the fuel properties of carbonized sewage sludge. The highest low heating value was obtained for hydrochar derived at 300 °C in 180 min (~23 MJ × kg−1). The highest energy gain was noted for hydrochar derived at 240 °C in 180 min (~23%). As well as relatively high mass and energy yield in comparison to other hydrochars, these parameters are considered the most favorable for sewage sludge hydrothermal carbonization. However, high energy consumption (over 1300 kJ × g−1) suggests that more research on the process's economical efficacy is required. [ABSTRACT FROM AUTHOR]

[Display omitted] • Slow pyrolysis of sewage sludge (SS) was conducted at an industrial pilot scale. • The effect of pyrolysis on 161 organic contaminants in SSs was studied. • Pyrolysis temperature of >500 °C is advised for organic contaminant removal. • Pyrolysis is suitable for SSs with moderate inorganic contaminant levels. • Industrial scale results were mostly in line with published laboratory scale data. Pyrolysis has been gaining global interest as a viable option for reducing organic contaminant levels in waste materials such as sewage sludge (SS) for their subsequent use as a soil amendment. However, publicly available knowledge on the capacity of pyrolysis to reduce the levels in SSs is mostly based on laboratory or bench scale studies. The aim of this study was to examine the effects of industrial pilot scale slow pyrolysis at two temperatures and retention times (450 °C, 1 h and 500 °C, 1.5 h) on a wide range of organic and inorganic contaminants in SSs. Pyrolysis at 500 °C decreased the concentrations of the detected per- and polyfluoroalkyl substances (PFASs, by 30–93 %), brominated diphenyl ethers (BDEs; by 97–98 %) and most endocrine disrupting compounds (EDCs, by 82–96 %) more efficiently than pyrolysis at 450 °C. Estrone and pharmaceuticals, with the exception of paracetamol, were removed to below quantification limits. Non-volatile inorganic contaminants concentrated to the chars (22–46 % increase). These results confirm that slow pyrolysis has the capacity to significantly reduce organic contaminant levels in SSs at an industrial scale, while content of inorganic contaminants depends mainly on the feedstock properties. Pyrolysis temperature of over 500 °C is advised to secure efficient removal of organic contaminants. However, it is anticipated that reactor design with good heat transfer and volatile removal could further improve the removal of organic contaminants from SSs. The results are especially valuable for sludge management operators planning to procure a pyrolysis plant. [ABSTRACT FROM AUTHOR]

This study was conducted to investigate the effects of anaerobically stabilized sewage sludge (SS) converted into 90% dryness granules at different doses of control, 3% SS, 6% SS, and 9% SS on elemental composition of Festuca arundinacea Schreb. and physicochemical properties of soil. Color measurements were made with the CIE L* a* b* method unit; the highest color (4.10) and the highest coating score (5.7) were calculated for the 6% SS treatment. The highest biomass (9.11 g) was obtained from the 3% SS and the lowest (7.67 g) from the 9% SS dose. Plant height measurements were listed as follows: 3% SS (9.5 cm) > 6% SS (8.8 cm) > control (8.7 cm) > 9% SS (8.1 cm). Average bioaccumulation factor for the present heavy metals were ordered as: Cd (0.542) > Hg (0.452) > Cr (0.448) > Ni (0.246) > Pb (0.076). The lowest geoaccumulation index (Igeo) was obtained in Cr (-1.35) and the highest value in Cd (1.69). Available P, K, Ca, Mg were analyzed with ammonium acetate extraction method, and Fe, Zn, Cu, and Mn in the soil extracted with DTPA were determined. In the soil samples, total N (0.180%) and available elements (mg kg-1) P (101.393), Ca (6502.570), Mg (609.433), Na (259.44), Fe (13.61), Cu (4.05), Zn (17.76), and B (1.00) were determined at high values in the 9% SS application. Heavy metals (mg kg-1) were extracted with aqua regia. Nickel (48.87), Pb (26.83), Cd (0.97), and Hg (153.12 µg kg-1) were determined at high values in the 9% SS application. Plant nutrients in the plant samples were extracted from acid digestion, and N (3.93%), P (0.51%), Mg (0.59%), Ca (1.77%), Zn (127 mg kg-1), and B (15 mg kg-1) were determined at high values in the 9% SS application. Heavy metals' (Ni, Cd, Cr, Pb, and Hg) content toxic effects were not observed in the plants. [ABSTRACT FROM AUTHOR]

In recent years, promising developments in the hydrothermal carbonization (HTC) of sewage sludge, as well as the potential to reclaim phosphorus and nitrogen, have emerged. In this study, the HTC of digested sewage sludge (DSS) was investigated for the downstream production of heavy metal (HM)-free fertilizer and the use of freeze concentration (FC) as a novel technology for process water treatment. To obtain clean fertilizer, phosphatic acid extracts were first treated with ion-exchange resins to remove dissolved HM, as well as phosphorus precipitating agents (i.e., aluminum and iron). Over 98% of the aluminum (Al) and 97% of the iron (Fe) could be removed in a single treatment step. The purified extract was then used for the precipitation of HM-free struvite crystals, with P-recovery rates exceeding 89%. Process water (PW) makes up the largest share of the two main HTC-products (i.e., hydrochar and PW) and is very rich in organic compounds. Compared to evaporation or membrane separation, FC is a promising technology for concentrating solutes from PW. Separation experiments resulted in the recovery of over 90% of the dissolved compounds in the concentrate. In our study, the concentrate was later utilized as an ammonium source for struvite precipitation, and the subsequent aerobic digestion of the remaining ice water resulted in an 85% reduction in chemical oxygen demand (COD) in 15 days. [ABSTRACT FROM AUTHOR]

Sewage sludge, also referred to as biosolids, consists of the by-products of wastewater treatment, which are a mixture of the water and organic and inorganic materials eliminated from wastewater sourced from domestic sewage industries during physical, biological, and/or chemical treatments. Biosolids are nutrient-rich organic materials resulting from the treatment of domestic wastewater in treatment plants. Sewage sludge can be considered a significant biological resource for sustainable agriculture. A new composite has been made consisting of soil, sewage sludge collected from the Galati Wastewater Treatment Plant, and slag from the Galati Steel Plant. This study aimed to investigate the structural, morphological, and chemical parameters of this composite through FTIR, SEM-EDX analysis, and XRF analysis. The samples had values of potential toxic elements that were within normal limits according to Directive 86/278/CEE, and, in terms of the iron-to-calcium ratio (I/C), all samples were of a low grade. This is the first time that slag has been added in a sewage sludge–soil combination, which can be an effective fertilizer replacement. Sewage sludge contains substantial amounts of organic matter, and slag reduces the contents of potentially toxic elements. In addition to these attributes, they may provide an opportunity for the beneficial re-use of sewage sludge and slag as resources in agriculture. [ABSTRACT FROM AUTHOR]

• Techno-economic analysis of adding HTC in existing sewage sludge treatment plants. • Co-combustion of hydrochar and sludge improves investment opportunities for HTC. • High sewage sludge gate fee stimulates investment in HTC. • Wet oxidation of process water improves heat output but decreases electricity output. • Energy advantage of HTC over thermal dryer is often insufficient for profitability. Hydrothermal carbonization (HTC) can mitigate the disposal costs of sewage sludge in a wastewater treatment plant. This study analyzes the impact of integrating HTC with anaerobic digestion (AD) and combustion from a combined energy and economic performance perspective. Net energy balance and investment opportunity are investigated for a number of technical scenarios considering i) different combinations of the technologies: AD + HTC, AD + thermal dryer + combustion, and AD + HTC + combustion, ii) different options for HTC process water treatment: wet oxidation (WO) + AD, and direct return to AD, and iii) different products: heat-only, heat and electricity, hydrochar, and phosphorus. The results show trade-offs between investment cost, self-supplement of heat, and output electricity when WO is used. In AD + HTC, net heat output decreases compared to the reference plant, but avoided disposal costs and hydrochar revenue result in profitable investment when the process water is directly returned to the AD. Although HTC has a lower heat demand than the thermal dryer, replacing the thermal dryer with HTC is only possible when AD, HTC, and combustion are connected, or when WO covers HTC's heat demand. HTC may impair the electricity production because of the necessity for a high-temperature heat source, whereas the thermal dryer can utilize a low-temperature heat source. In conclusion, energy advantages of HTC in AD + HTC + combustion are insufficient to provide a promising investment opportunity due to high investment costs of HTC. The investment opportunity improves by co-combustion of hydrochar and external sludge. [ABSTRACT FROM AUTHOR]

Efficient utilization of natural resources and possible valorization of solid waste materials such as sewage sludge into secondary materials via thermal conversion and simultaneously recovering energy is vital for sustainable development. The continuous increase in metropolises leads to an enormous production of wet sewage sludge, which creates major environmental and technical issues. In this paper, the samples of sewage sludge from Astana's waste water treatment plant are analyzed for their thermochemical properties, followed by thermogravimetric and kinetic analysis using the Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose methods. Overall, the calorific value of sewage sludge sample was 18.87 MJ/kg and was comparable to that of the bituminous coal samples. The activation energy varied from 140 to 410 kJ/mol with changing conversion from 0.1 to 0.7. Further, mono-combustion and co-combustion experiments of the sewage sludge with high ash bituminous coal were conducted using the laboratory scale bubbling fluidized bed rig, respectively. The difference in NOx emissions between mono-combustion of sewage sludge and co-combustion with coal were at around 150 ppm, while this value for SO2 was similar in average, but fluctuates between 150 and 350 ppm. Overall, the findings of this study will be useful in developing a co-combustion technology for a sustainable disposal of municipal sewage sludge. [ABSTRACT FROM AUTHOR]

• Fate of nine tri-OPFRs in sludge was studied in a WWTP in Beijing, China. • Sludge contained high concentrations of tri-OPFRs (971.48–1,702.22 ng/g). • Mass flow of tri-OPFRs showed seasonal decreases. • The dehydration unit removed the most tri-OPFRs during sludge treatment. • Ecological risk of OPFRs in treated sludge was reduced. Organophosphate flame retardants (OPFRs) are emerging environmental pollutants that cause endocrine disruption, neurotoxicity, and reproductive toxicity. Sewage sludge is an important source of tri-OPFRs that are released into the environment. The occurrence, distribution, and ecological risk of OPFRs in the full-scale "Cambi® thermal hydrolysis (TH) + advanced anaerobic digestion (AAD) + plate-frame pressure filtration" sludge treatment process is closely related to the application of sewage sludge. We tested sludge samples from a wastewater treatment plant in Beijing, China. Nine tri-OPFRs were detected in the sludge samples collected at different treatment units during four seasons. The ΣOPFRs decreased from 1,742.65–2,579.68 ng/g to 971.48–1,702.22 ng/g. The mass flow of tri-OPFRs in treated sludge decreased by 61.4%, 48.9%, 42.4%, and 63.9% in spring, summer, autumn and winter, respectively, effectively reducing the corresponding ecological risk. The ecological risk of tri-OPFRs in sludge in forestland utilization mainly lies in chlorinated tri-OPFRs, especially TCPP and TCEP. No >42.20 t/hm2 of sludge could be used continuously for one year to prevent tri-OPFRs from exceeding the low ecological risk level, indicating that the current commonly applied proportion of sludge (1.6–30 t/hm2) will likely not raise the ecological risk of tri-OPFRs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effects of inherent moisture on sludge-derived biochar (SDB) properties were studied. • Inherent moisture promoted both micropore and mesopore formation in SDB at 400 °C. • The total pore volume of SDB (600 °C) is proportional to sludge moisture content. • Moisture induces SDB equipped with more functional groups and defective structures. • Absorption capacity of SDB for tetracycline is improved by inherent moisture. Understanding the impact of abundant inherent moisture in sewage sludge on the physicochemical properties and adsorption applications of sludge-derived biochar (SDB) contributed significantly to promoting economical sludge reuse. The moisture (0–80%) contributed to the development of micropore and mesopore in SDB at 400 °C, resulting in a maximum increase in specific surface area (SSA) and total pore volume (TPV) of SDB by 38.47% (84.811–117.437 m2/g) and 92.60% (0.0905–0.1743 m3/g), respectively. At 600/800 °C, moisture only facilitated mesopore formation, while was exacerbated with increasing moisture content. Despite reduction in SSA during this stage, TPV increased by a maximum of 20.47% (0.1700–0.2048 m3/g). The presence of moisture during pyrolysis led to an increase in the formation of 3–5 thickened benzene rings and defective structures in SDB, along with more C=O, O–C=O/–OH, pyrrole N, pyridine N, and thiophene. As a result, moisture (40%/80%) increased the maximum adsorption capacity (76.2694–88.0448/90.1190 mg/g) of SDB (600 °C) for tetracycline, mainly due to enhanced pore filling effect and hydrogen bonding induced by improved physicochemical properties. This study offered a novel approach for optimizing the performance of SDB adsorption applications by manipulating the sludge moisture, which is critical for practical sludge management. [ABSTRACT FROM AUTHOR]

The global production of fecal wastes is envisioned to reach a very high tonnage by 2030. Perilous handling and consequential exposition of human and animal fecal matter are inextricably linked with stunted growth, enteric diseases, inadequate cognitive skills, and zoonoses. Sludge treatment from sewage and water treatment processes accounts for a very high proportion of overall operational expenditure. Straightforward carbonization of sludges to generate biochar adsorbents or catalysts fosters a circular economy, curtailing sludge processing outlay. Biochars, carbonaceous substances synthesized via the thermochemical transformation of biomass, possess very high porosity, cation exchange capacity, specific surface area, and active functional sorption sites making them very effective as multifaceted adsorbents, promoting a negative carbon emission technology. By customizing the processing parameters and biomass feedstock, engineered biochars possess discrete physicochemical characteristics that engender greater efficaciousness for adsorbing various contaminants. This review provides explicit insight into the characteristics, environmental impact considerations, and SWOT analysis of different sludges (drinking water, fecal, and raw sewage sludge) and the contemporary biochar production, modification, characterization techniques, and physicochemical characteristics, factors influencing the properties of biochars derived from the aforestated sludges, along with the designing of chemical reactors involved in biochar production. This paper also manifests a state-of-the-art discussion of the utilization of sludge-derived biochars for the eviction of toxic metal ions, organic compounds, microplastics, toxic gases, vermicomposting approaches, and soil amelioration with an emphasis on biochar recyclability, reutilization, and toxicity. The practicability of scaling up biochar generation with multifaceted, application-accustomed functionalities should be explored to aggrandize socio-economic merits. [ABSTRACT FROM AUTHOR]

A widespread method of sewage sludge disposal is still simple storage in sludge lagoons. Subsequent thermal utilization is hardly possible because sludge properties change over time and energy content is reduced. Use as a soil conditioner in agriculture or landscaping is usually not possible due to high heavy metal contents. This paper describes a method in which a 10-year-old accumulated sewage sludge can be utilized as technical soil by mixing it with pyrolized fresh sewage sludge. For this purpose, physicochemical and toxicological characteristics of sewage sludge of different storage periods were identified, processes of thermal destruction of sewage sludge analyzed, toxicological characteristics of solid products of thermal sludge treatment determined, and the possibility of using the sewage sludge–pyrolysate mixture as technical soil was assessed. Results show that the gross calorific value of fresh and one-year stored sewage sludge is with approx. 15,000 kJ/kg dry basis sufficient to produce pyrolysate autothermally. It is also shown that when the pyrolysis residue is mixed with fresh or 1-year old sewage sludge, heavy metals can be immobilized and thus the leaching of heavy metals significantly reduced by up to 75%. The method described can thus be a possible option for recycling accumulated sewage sludge. [ABSTRACT FROM AUTHOR]

Soil pollution caused by heavy metals has emerged as one of the most significant environmental problems in the world. In soils, specific plant species are able to grow, adapt and absorb heavy metals. Phytoremediation is an emerging technology in which higher plants are used to reclaim the contaminated environment. In this study, the possibilities of removing the pollution caused by Zn, which is applied to the loamy soil together with and without sewage sludge at increasing levels (0, 75, 150, 300, 600 and 1200 μg g-1), has been researched with certain hyperaccumulator plants such as Brassica juncea, Raphanus sativus and Silene vulgaris grown in Bafra ecological conditions. In order to clean Zn added to the soil at increasing levels with or without sewage sludge by using phytoremediation technology, Silene vulgaris was found to remove the highest amount of Zn in the soil by producing the greatest amount of biomass in the ecological conditions of the region compared to Brassica juncea and Raphanus sativus, and other hyperaccumulator plants grown in the plots. Significant differences were determined in the development of plants and Zn removal between the sludge treated and untreated plots. Water-soluble Zn, which was found at high levels in the cultivation of plants at 600 and 1200 μg g-1 Zn application doses in the sewage sludge treated plots, was determined at lower levels at the end of the harvest of the plants. In the application of increasing levels of Zn with sewage sludge, the lowest organic bound Zn was determined in the plots where Silene vulgaris was grown. The highest exchangeable Zn concentration was determined in soil samples taken after the harvest of the Raphanus sativus plant among the hyperaccumulator plants grown at all Zn application doses in the trials with and without sewage sludge application. [ABSTRACT FROM AUTHOR]

The current global concern is how to replace polluting fossil fuels with sustainable green fuels. On this basis, in this study, a characterization protocol for sewage sludge in Algeria was carried out. Their objective was to study the process of anaerobic digestion for biogas production by analogy to experiments that have already been made in the literature. The performance of the proposed models has been validated with experimental data from the scientific literature. Biodegradable organic matter levels are high (160–500 mg L−1) giving an acceptable yield for biogas production. The modeling of cumulative biogas production was carried out by Gompertz and models were proposed for different products. It has been observed that there is a better agreement of the models proposed with the experimental data with a maximum value of r2 = 0.9996. The modeling of the degradation of organic matter was carried out by the first order‐model, and dimensionless models were proposed. The latter gave a good agreement with the experimental data better than the model in the literature, with a maximum value of r2 = 0.9985. The proposed models to study the anaerobic digestion process of organic matter, as well as those related to the process of cumulative biogas production, are universal (without units of measurement), which will help producers in this field to improve production, as well as reduce the investment cost through preliminary simulations. [ABSTRACT FROM AUTHOR]

Effects of pressure, dewatering time, and sludge cake thickness on the dewatering of wastewater sludge by the hydraulic dehydrator under the condition of adding CaO and FeSO4 were analyzed using the response surface method (RSM). It was found that when the parameters of pressure, dewatering time, and sludge cake thickness were changed, the trends of dewatering papermaking sludge and municipal sludge were similar under the condition of raw sludge with 3% CaO and 3% FeSO4. Specifically, the increase of pressure and dewatering time promotes the dewatering effect of wastewater sludge, and the thinner the sludge cake is, the better the dewatering effect. The water content can be affected by the change of pressure, dewatering time, and sludge cake thickness. In response surface analysis, the model F-value and coefficient of determination (R²) were 541.43 and 0.9986, respectively, indicating high significance and good correlation. In the model, the change of pressure, dewatering time, and sludge cake thickness affected the water content of paper sludge. Particularly, the increase of pressure and compression time enhanced the dewatering efficiency. The thinner the sludge cake was, the better the dewatering effect of paper sludge was. [ABSTRACT FROM AUTHOR]

Aqueous phase byproduct from hydrothermal carbonization of sludge (named AHT) has high COD and TOC, supercritical water gasification (SCWG)can efficiently convert AHT into rich-H 2 syngas. This study investigated the effect of temperature on syngas production, elements distribution and pollutants decomposition during the HTC of sewage sludge and SCWG of AHT. Compared to traditional directly SCWG of sludge, the combined method could produce syngas with higher H 2 proportion and lower gaseous sulfur concentration. The maximum H 2 proportion and carbon conversion efficiency (CE) in syngas could reach 59% and 30.40%. Meanwhile, higher SCWG temperature can reduce the sulfur concentration of syngas. SCWG effectively reduce the COD and TOC in AHT. With HTC and SCWG temperature increased, the concentration of total nitrogen (TN) gradually decreased but NH 4 + ions concentration (NH 4 +-N) increased in aqueous phase product. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Phosphorus (P) recovery was investigated in a multi-stage process. • Hydrothermal carbonization (HTC) and thermochemical treatment were considered. • A pretreatment with an HTC can improve thermochemical process. • MgCl 2 as additive can increase P retention rate and reduce heavy metal content. Phosphorus (P) is a non-regenerative and finite raw material. Due to its decreasing availability, and to protect the environment, recycling methods are needed. With the focus on closing nutrient cycles, sewage sludge (SS) is a potential source for P recovery. The objective of this study was to produce a mineral P-reach fertilizer. For this purpose, the treatment of SS in a multi-stage process, consisting of a hydrothermal carbonization (HTC) and thermochemical post-treatment was examined and compared with a direct thermochemical treatment. The focus was on the transformation of P and the migration of the heavy metals during the processes. In addition, the role of MgCl 2 as an additive was examined. During the HTC, most of the P remained in the HTC-char, so that the P content increased in the HTC-char compared with the SS. The addition of MgCl 2 to the process resulted in lower transportation rates of P in the liquid phase and higher P solubilities in water, citric acid, and alkalic ammonium citrate out of the solid phase. The thermochemical treatment of SS and the HTC-chars further concentrated P in the ash. Retention rates of >97% were achieved, and P 2 O 5 contents in the ash were as high as ∼16 wt-%. The presence of the additive resulted in (i) higher retention rates of P in the ashes (ii) higher P-solubility and (iii) higher removal rates of easily volatile heavy metals such as Pb and Zn, and the treatment of HTC-char favored these effects compared with the direct treatment of SS. [ABSTRACT FROM AUTHOR]

Real-time measurement of sewage sludge moisture content renders it possible to optimize the consumption of auxiliary fuel and the thermal treatment. Thus, we explored whether a dielectric soil moisture sensor could be used to measure real-time changes in sludge moisture content. This was possible with the aid of a unified calibration curve. The explanatory variable was the third-order sensor output voltage. The calibration curve well-fitted the data; the mean measurement error was 6.14 wt.%. The use of individual calibration curves for each sludge batch reduced the mean measurement error to 3.09 wt.%. The mean measurement error improves when multiple sensors are simultaneously used. The sensor operates very well when the moisture content is low; the results are minimally affected by the bulk density and Fe level. Considering feed-back to the process, it is ideal to measure sludge moisture content near the outlet of the thermal treatment. [ABSTRACT FROM AUTHOR]

• Quantitative analysis of GHGs emission in mainstream sludge treatment was studied. • Incineration and bio-stabilization technologies have high GHGs reduction potential. • The LCA method needs to be improved and unified in GWP of sludge treatment. • Resource recovery coupled with N 2 O and CH 4 reduction are the key points. • Novel anaerobic digestion pathways have considerable GHGs reduction potential. This study aims to comprehensively analyze the Greenhouse Gases (GHGs) emissions from current sewage sludge treatment and disposal technologies (building material, landfill, land spreading, anaerobic digestion, and thermochemical processes) based on the database of Science Citation Index (SCI) and Social Science Citation Index (SSCI) from 1998 to 2020. The general patterns, spatial distribution, and hotspots were provided by bibliometric analysis. A comparative quantitative analysis based on life cycle assessment (LCA) put forward the current emission situation and the key influencing factors of different technologies. The effective GHG emissions reduction methods were proposed to mitigate climate change. Results showed that incineration or building materials manufacturing of highly dewatered sludge, and land spreading after anaerobic digestion have the best GHG emissions reduction benefits. Biological treatment technologies and thermochemical processes have great potential for reducing GHGs. Enhancement of pretreatment effect, co-digestion, and new technologies (e.g., injection of carbon dioxide, directional acidification) are major approaches to facilitate substitution emissions in sludge anaerobic digestion. The relationship between the quality and efficiency of secondary energy in thermochemical process and GHGs emission still needs further study. Solid sludge products generated by bio-stabilization or thermochemical processes are considered to have a certain carbon sequestration value and can improve the soil environment to control GHG emissions. The findings are useful for future development and processes selection of sludge treatment and disposal facing carbon footprint reduction. Graphical Abstract. [Display omitted] [ABSTRACT FROM AUTHOR]

The thermal–chemical conversion method has significant potential for the recovery of organic matter present in sewage sludge (abbreviated as SS), offering broad market prospects. In this study, a novel approach is proposed for the preparation of a composite adsorbent, named SS-EP, derived from the co-pyrolysis residue of sewage sludge and Enteromorpha prolifera. An orthogonal experiment was designed to investigate the performance of the adsorbent, and the results revealed that the optimal conditions were achieved when the SS proportion was 40%, the concentration of zinc chloride was 0.1 mol/l, the pyrolysis temperature was 500 °C, and the pyrolysis time was 30 min. Notably, the SS-EP composite adsorbent exhibited pronounced efficacy in the removal of Cr(VI) under both acidic and neutral conditions, achieving a removal rate exceeding 97%. Furthermore, the concentration of heavy metals in the leaching solution of the adsorbent was found to be significantly lower than the limit specified in the GB5085.3-2007 standard. Regeneration experiments demonstrated that even after the third regeneration, the SS-EP composite adsorbent maintained a removal rate of 70% for Cr(VI). [ABSTRACT FROM AUTHOR]

The huge amounts of sewage sludge produced by municipal wastewater treatment plants induce major environmental and economical issues, calling for advanced disposal methods. Traditional methods for sewage sludge disposal increase greenhouse gas emissions and pollution. Moreover, biochar created from sewage sludge often cannot be used directly in soil applications due to elevated levels of heavy metals and other toxic compounds, which alter soil biota and earthworms. This has limited the application of sewage sludge-derived biochar as a fertilizer. Here, we review biomass and sewage sludge co-pyrolysis with a focus on the stabilization of heavy metals and toxicity reduction of the sludge-derived biochar. We observed that co-pyrolyzing sewage sludge with biomass materials reduced heavy metal concentrations and decreased the environmental risk of sludge-derived biochar by up to 93%. Biochar produced from sewage sludge and biomass co-pyrolysis could enhance the reproduction stimulation of soil biota by 20‒98%. Heavy metals immobilization and transformation are controlled by the co-feed material mixing ratio, pyrolysis temperature, and pyrolysis atmosphere. [ABSTRACT FROM AUTHOR]

Polymer flocculants are used to promote solid–liquid separation processes in wastewater treatment technologies, and bio-based flocculants possess many advantages over conventional synthetic polymers. Potato starch microgranules were chemically modified and mechanically sheared to produce modified starch flocculants. The effectiveness of produced cationic starch (CS) and cross-linked cationic starch (CCS) flocculants in the thickening and dewatering of surplus activated sewage sludge was evaluated and compared with that of synthetic cationic flocculants (SCFs) The flocculation efficiency of SCF, CS, and CCS in sludge thickening was determined by measuring the filtration rate of treated surplus activated sludge. Comparing the optimal dose of SCFs and CCS flocculants needed for thickening, the CCS dose was more than 10 times higher, but a wide flocculation window was determined. The impact of used flocculants on the dewatering performance of surplus activated sludge at optimal dose conditions was investigated by measuring capillary suction time. The filtration efficiencies (dewaterability) of surplus activated sludge using SCF, CS, and CCS were 69, 67, and 72%, respectively. The study results imply that mechanically processed cross-linked cationic starch has a great potential to be used as an alternative green flocculant in surplus activated sludge thickening and dewatering operations in municipal sewage sludge treatment processes. [ABSTRACT FROM AUTHOR]

In this study, the potential use of sewage sludge (SS) as a fertilizer source for cultivated Dhaincha (Sesbania bispinosa (Jacq.) W.Wight) crops was investigated. Field experiments were conducted using different doses of SS such as 0% (T0), 5% (T1), 10% (T2), and 15% (T3) to amend the soil (w/w). The findings showed that soil amended with SS significantly (p < 0.05) improved the response parameters of S. bispinosa with an increase in the dose of SS from 0% to 15%. In particular, the T3 treatment gave the best results (mean values) for plant growth and yield parameters such as plant height (380.59 cm), fresh weight (1.47 kg/plant), dry weight (0.27 kg/plant), base diameter (3.19 cm), seed yield (44.71 g/plant), total chlorophyll (3.15 mg/g fwt), carotenoids (0.88 mg/g fwt), carbohydrates (9.40 mg/g), and phenol (0.13 mg/g) contents. Moreover, the selected proximate and fiber characteristics of the S. bispinosa crop were significantly (p < 0.05) improved by the same treatment (T3); such as ash (7.25%), crude fiber (32.70%), crude protein (15.94%), lignin (24.60%), cellulose (37.25%), fiber weight (3.06 g/plant), stick weight (32.08 g/plant), fiber: stick ratio (0.10), fiber diameter (26.97 µm), ultimate tensile strength (855.98 MPa), strength (58.92 g/tex), density (1.54 g/cm3), and luster (45.65%) compared with the control treatment (T0). The bioaccumulation factor (BAF) studies showed that the S. bispinosa plant was capable of accumulating selected heavy metals from the soil following the order: Fe > Mn > Zn > Cu > Cd > Cr. The study suggested a sustainable approach for efficient soil fertilization and high-quality S. bispinosa fiber production that could minimize the environmental pollution caused by the unsafe disposal of SS. [ABSTRACT FROM AUTHOR]

• Management of sewage sludge is a critical issue in the European sustainability plan. • WtE technologies need to be assessed from an integrated sustainability perspective. • A sustainability assessment is conducted using real data from Spanish WWT plants. • The gasification is the best performing technology for the location study. The management of sewage sludge still represents a challenge in the EU sustainability plan for biowaste. Although there are consolidated alternatives for the valorization of sewage sludge (incineration, pyrolysis and gasification), technical issues related to heavy metals and other pollutants are not sufficiently understood considering the whole waste-to-energy process. In addition, societal-economic and environmental aspects are usually not included in the evaluation of these conversion technologies. In this study, we propose an integrated assessment from a sustainability perspective to evaluate the valorization of sewage sludge by thermal conversion, comparing different alternatives based on existing Waste-to-energy (WtE) technologies. The results provide an insightful vision on the challenges to manage the sewage sludge disposal and to transform the obtained waste into new raw materials with added value. In addition, the evaluation of the WtE alternatives shows that they face important challenges preventing their application, being the gasification the best performing technology according to the sustainability assessment. Finally, a decentralized scheme based on sewage sludge gasification is further evaluated using real data from wastewater treatment plants in Andalusia. [ABSTRACT FROM AUTHOR]

In the face of material shortages, growing environmental awareness, and technical advancement, incinerated waste materials are being considered secondary resources. Especially incinerated sewage sludge ash is of interest due to its massive and increasing production and relatively stable composition with a satisfying concentration of elements of value. This paper revises the basic methods for recovery of valuable components from incineration sewage sludge and simultaneous removal or stabilization of elements that may negatively influence the environment with further ash usage or storage. The presented work focuses on collating and analysing the efficiency of currently used approaches as well as their limitations and perspectives for future development. Chemical methods analysed include acidic and alkaline leaching, chelating, and sequential leaching. Due to scarce examples from literature, the exploration of a microbiological approach focuses on the mechanisms and potential for application of different microorganisms for element extraction. The methods described are relatively efficient and affordable, yet still need further development. Specifically, microbiological approaches are rarely used for incineration sewage sludge treatment regardless of their potential advantages over other approaches. Constant mineral and chemical composition within one incineration plant can vary among plants due to many factors, so a well-established range of techniques and an individual approach are important. [ABSTRACT FROM AUTHOR]

[Display omitted] • The oxidation effect in Fe(II)/CaO 2 system is influenced by DOM composition. • Hydrophobic acid/neutrals facilitate the oxidation of organic carbon. • The C N group is more favorable on DOC removal than C O and C O group. • Maillard and cyclization products exhibit negative effects on DOC removal. • The oxidation products are mainly acids and phenols. The Fe(II)/CaO 2 system with a stable oxidant and a low-cost homogeneous activating agent has been considered as a prospective process for the disposal of wastewater. The system was constructed to treat sewage sludge hydrothermal carbonization aqueous phase (HTC-AP) in this study. As the hydrothermal temperature increased, the organics in the HTC-AP were first decomposed and then cyclized, while the Maillard reaction occurs throughout the stage. The oxidation efficiency of the Fe(II)/CaO 2 system was related to the composition of organics in HTC-AP, and the removal of dissolved organic carbon (DOC) by the system was 38.56 % in the HTC-AP obtained by hydrothermal treatment at 220 °C. Redundancy analysis showed that the low molecular weight organics, hydrophobic acids, and hydrophobic neutral components were beneficial to DOC removal, while Maillard products and cyclization products were hard to be oxidized to CO 2 and H 2 O. The C N functional group of the protein facilitated DOC removal, and some organics in HTC-AP were oxidized to acids and phenols. The energy input to remove DOC in Fe(II)/CaO 2 system was 27.74 MJ per kg carbon. This study provides a low-energy consumption Fe(II)/CaO 2 system for the post-treatment of HTC-APs and explores the applicability of the system. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) is an attractive, green technology for the management of sewage sludge. In this study, low-value secondary sewage sludge was subjected to an HTC treatment in a 1 L batch hydrothermal reactor and transformed into a high-energy-density hydrochar under varying HTC conditions (temperature of 150–300 °C, carbonization time of 30–150 min and a solid loading of 10–30%). The resulting hydrochar fuel characteristics were analyzed for ultimate and proximate analyses, functional group composition and energetic parameters. It was found that the hydrochar yield decreased with the increasing HTC temperature and reaction time, primarily due to the loss of organic volatile matter and functional groups. Under the optimum conditions of 150 °C, 30 min of carbonization time and 30% solid loading, 80.56% of the hydrochar was recovered, providing a maximum energy yield of 90.32% and a high heating value of 18.49 MJ/kg. Compared to the raw sewage sludge (H/C ratio of 2.67 and O/C ratio of 0.51), the hydrochar also had lower H/C and O/C atomic ratios of 1.42 and 0.18, respectively. The results suggest that significant dehydration and decarboxylation during the HTC treatment of sewage sludge have resulted in the formation of carbonaceous hydrochar with energetic properties close to the sub-bituminous coals. [ABSTRACT FROM AUTHOR]

The large and growing volume of tire waste and sewage sludge requires disposal, for which thermochemical processes such as gasification can be used. Co-gasification of these two waste products allows the tire char to be used as a charge stabilizer and the sewage sludge to improve reactivity and efficiency. The purpose of this study was to evaluate the effect of the composition of a waste tire char and sewage sludge fuel blend on the gasification process, using steam as the gasification agent. Tests were carried out for tire char, municipal sewage sludge, and blends of the two in ratios of 90:10 and 67:33. An analysis of the materials used was carried out (ultimate and proximate analysis as well as ash composition), and isothermal measurements of steam gasification were taken using the thermal volumetric method for temperatures of 800, 850, and 900 °C at an elevated pressure of 1 MPa. On the basis of the results, the formation curves of the main gasification products (H2, CO, CO2, and CH4) were created, the curves for the degree of carbon conversion were plotted, the reactivity indexes were determined for different degrees of conversion (0.25, 0.5, and 0.75), and the quantity and composition of the resulting gas were analyzed. Using the grain model, the kinetic parameters (activation energy and pre-exponential factor) of the gasification reaction were calculated. The addition of municipal sewage sludge had a positive effect on the reactivity of tire char and increased the efficiency of gasification, because it contained components that act as catalysts in the gasification process. There was a favorable effect from the addition and higher amount of sewage sludge on lowering both the activation energy (49.5 kJ/mol and 89.2 kJ/mol for 90:10 and 67:33 blends, respectively) and the pre-exponential factor. A significant improvement in reactivity, with a high degree of conversion and the best gas composition, was obtained for a 90:10 blend at 900 °C. [ABSTRACT FROM AUTHOR]

As a result of growing interest in the thermal treatment of sewage sludge with methods such as combustion, gasification or pyrolysis, and also in processes that aim to recover precious components such as phosphorus from this waste, a growing demand has been observed for Computational Fluid Dynamics (CFD) models that provide solutions rapidly and accurately for efficient application in research and development. This study was carried out to develop a computationally inexpensive modelling approach for the combustion of pulverized sewage sludge in entrained flow furnaces. Sewage sludge is a very volatile-rich fuel. Therefore, the Steady Diffusion Flamelet model (SFM), in combination with a validated skeletal reaction mechanism, was applied to consider the pulverized firing of sewage sludge. It was possible to represent the complex composition of volatiles emitted from the sludge particles by releasing surrogate fuels. In addition, the influence of limestone additive (calcination reaction) and varying water content (water–gas shift reaction) was investigated experimentally and modelled via CFD. The simulation results confirm that the surrogate fuel approach is valid and can be used to describe pulverized sewage sludge effectively. The temperature and species concentration results, including the influence of the additive and different levels of water content, were confirmed by experimental data, which is usually hard to obtain due to the tendency of PSS to form agglomerates in entrained flow combustion furnaces. The model yields plausible and experimentally validated results for the combustion of sewage sludge powder across a wide range of operating conditions. [ABSTRACT FROM AUTHOR]

The unsustainable management of sewage sludge induces environmental and economic issues, yet sewage sludge is a promising feedstock for the production of biofuels by pyrolysis. Actual challenges include poor chemical stability, high water content, high viscosity, high concentrations of nitrogen, and the presence of oxygen in the produced biofuels. Moreover the produced biochars contain elevated amounts of toxic metals and, as a consequence, may not be used in agricultural soils. Here we review the co-pyrolysis of sewage sludge with other materials to enhance bio-oil quality. Several studies show that co-pyrolysis of sewage sludge with non-biomass materials reduces water, oxygen and nitrogen contents, activation energy, and enthalpy; and increases the calorific value. [ABSTRACT FROM AUTHOR]

The problem of sludge management in wastewater treatment plants remains a current issue. The characteristics of the sludge depend on the degree of pollution and the nature of the pollutants in the wastewater undergoing purification and on the sludge treatment methods. Before utilization or disposal, the sludge must be treated, with the aim of reducing the water content, fermentation properties and the presence of pathogens. Treated sludge can be used or disposed of, most commonly, in three ways: agricultural use, incineration or landfilling, depending on the properties of the sludge, as well as the option of the treatment plant operator. Other disposal and recovery methods exists, but they are less used. Researchers are looking for new ways to utilize this type of waste in order to minimize the negative impact both on the environment and on the operators of treatment plants. The article presents a way of handling for this waste - the use of sludge for the manufacture of construction materials. Agricultural waste can also be incorporated into building materials. [ABSTRACT FROM AUTHOR]

• Inventory data of biological treatment of sludge address all inputs and outputs. • Biogas production varies considerably in the 64 datasets on anaerobic digestion. • Very few data are available on digestate or energy in anaerobic digestion of sludge. • VS degradation in composting is hard to estimate due to the added bulking materials. • Data on emissions into the air are currently scarce for sludge composting processes. The biological treatment of municipal sewage sludge, including anaerobic digestion and composting, was reviewed with the purpose of establishing inventory data to address all the inputs and outputs related to sludge treatment. We identified 193 scientific papers, resulting in 64 datasets on anaerobic digestion and 35 datasets on composting. For anaerobic digestion, biogas production varied significantly (up to a factor of four) depending on the sludge. A useful correlation was identified between the amount of methane produced and the degradation of volatile solids. According to statistical tests, no significant differences were found in biogas production for mesophilic and thermophilic digesters. In addition, methane content varied significantly, and very few data were available for digestate composition or for energy consumption and recovery. For composting, accurate estimates relating to the degradation of sewage sludge could not be made, since organic bulking materials were part of the final composted product. Data on emissions to air are currently scarce, which points to the need for more published information. The inventory data evaluated herein are useful in the feasibility assessment of the biological treatment of sewage sludge, for comparing technologies, for example in LCA studies and as a basis for evaluating the performance of a specific biological sludge treatment plant. However, a great deal of the reviewed data originated from laboratory and pilot-scale studies, and so there is a need for more complete datasets on the performance of full-scale technologies, in order to establish full inventories and identify differences in technologies and operational conditions. [ABSTRACT FROM AUTHOR]