Search Results (34)

Sewage sludge management remains a critical environmental and economic challenge due to high volumes, transport requirements, and landfill restrictions. Pyrolysis offers a promising alternative by reducing sludge mass and producing biochar with potential for soil fertility enhancement and long-term carbon sequestration. This study integrates physicochemical characterization of Portuguese wastewater treatment plant sludges with experimental drying data and literature-based pyrolysis yields to estimate mass reduction, energy requirements, and carbon retention. A simplified life cycle comparison highlights potential reductions in greenhouse gas emissions, human toxicity, and land use, while also suggesting significant economic savings from avoided transport and landfill disposal. Full article

The rising demand for sustainable agriculture and circular resource management has intensified interest in converting wastewater sludge into value-added products. This review explores the transformation of sewage sludge into slow- and controlled-release fertilizers (CRFs), with a focus on biochar production and encapsulation technologies. Sewage sludge is rich in essential macronutrients (N, P, K), micronutrients, and organic matter, making it a promising feedstock for agricultural applications. However, its use is constrained by challenges including compositional variability, presence of heavy metals, pathogens, and emerging contaminants such as microplastics and PFAS (Per- and Polyfluoroalkyl Substances). The manuscript discusses a range of stabilization and conversion techniques, such as composting, anaerobic digestion, pyrolysis, hydrothermal carbonization, and nutrient recovery from incinerated sludge ash. Special emphasis is placed on coating and encapsulation technologies that regulate nutrient release, improve fertilizer efficiency, and reduce environmental losses. The role of natural, synthetic, and biodegradable polymers in enhancing release mechanisms is analyzed in the context of agricultural performance and soil health. While these technologies offer environmental and agronomic benefits, large-scale adoption is hindered by technical, economic, and regulatory barriers. The review highlights key challenges and outlines future perspectives, including the need for advanced coating materials, improved contaminant mitigation strategies, harmonized regulations, and field-scale validation of CRFs. Overall, the valorisation of sewage sludge into CRFs presents a viable strategy for nutrient recovery, waste minimization, and sustainable food production. With continued innovation and policy support, sludge-based fertilizers can become a critical component of the green transition in agriculture. Full article

Municipal wastewater treatment relies primarily on biological methods, yet effective disposal of residual sludge remains a major challenge. Converting sludge into biochar via oxygen-limited pyrolysis presents a novel approach for waste resource recovery. This study prepared sludge-based biochar (SBC) through one-step pyrolysis of sewage sludge and applied it to activate peroxymonosulfate (PMS) for degrading diverse contaminants. Characterization (SEM, XPS, FTIR) revealed abundant pore structures and diverse surface functional groups on SBC. Using Acid Orange 7 (AO7) as the target pollutant, SBC effectively degraded AO7 across pH 3.0–9.0 and catalyst dosages (0.2–2.0 g·L⁻¹), achieving a maximum observed rate constant (k_obs) of 0.3108 min^–1. Salinity and common anions showed negligible inhibition on AO7 degradation. SBC maintained 95% degradation efficiency after four reuse cycles and effectively degraded sulfamethoxazole, sulfamethazine, and rhodamine B besides AO7. Mechanistic studies (chemical quenching and ESR) identified singlet oxygen (¹O₂) and superoxide radicals (O₂^•− ) as the dominant reactive oxygen species for AO7 degradation. XPS indicated a 39% reduction in surface carbonyl group content after cycling, contributing to activity decline. LC-MS identified five intermediates, suggesting a potential degradation pathway driven by SBC/PMS system. ECOSAR model predictions indicated significantly reduced biotoxicity of the degradation products compared to AO7. This work provides a strategy for preparing sludge-derived catalysts for PMS activation and pollutant degradation, enabling effective solid waste resource utilization. Full article

The pyrolysis of sewage sludge into biochar, enhanced by incorporating agriculture waste rich in inorganic minerals and lignocellulosic compounds, provides an effective approach for achieving sludge-harmless treatment and resourceful utilization. In this study, sewage sludge and maize straw-based biochar (SMB) was prepared using the co-pyrolysis method, and the effects of different application ratios (0%, 1%, 3%, and 5%, w/w) of SMB on soil properties, ryegrass growth, microbial community structure, and Pb content and speciation in the contaminated soil of constructed wetlands were investigated. The results showed that SMB had a high carbon content (28.58%) and was rich in functional groups (e.g., -C-O, -C-N). The results indicated that increasing SMB dosage (0–5% w/w) in Pb-contaminated soil elevated soil pH from 6.40 to 7.93, cation-exchange capacity (CEC) from 30.59 to 79.03 cmol/kg (+158%), and organic carbon content by 65% (from 176.79 mg/kg to 107.3 mg/kg), while reducing available phosphorus and potassium by 20% and 30%, respectively, resulting in a 6% decline in ryegrass leaf length. SMB application enriched Pb-resistant bacteria (e.g., Sphingomonas abundance increased from 10.3% to 11.2%) and enhanced Pb immobilization. After 55 days, the total soil Pb increased by 33%, and the residual fraction Pb significantly increased by 7.3% to 21.7%, driven by functional group complexation, ion exchange, pH, and CEC improvements. Full article

The pyrolysis process of residues has emerged as a sustainable method for managing organic waste, producing biochars that offer significant benefits for agriculture and the environment. These benefits depend on the properties of the raw biomass and the pyrolysis conditions, such as washing and drying. This study investigated biochar production through slow pyrolysis at 300 °C, using eight biomass types, four being plant residues (PBR)—sugarcane bagasse, filter cake, sawdust, and stranded algae—and four non-plant-based residues (NPBR)—poultry litter, sheep manure, layer chicken manure, and sewage sludge. The physicochemical properties assessed included yield, carbon (C) and nitrogen (N) content, electrical conductivity, pH, macro- and micronutrients, and potentially toxic metals. Pyrolysis generally increased pH and concentrated C, N, phosphorus (P), and other nutrients while reducing electrical conductivity, C/N ratio, potassium (K), and sulfur (S) contents. The increases in the pH of the biochars in relation to the respective biomasses were between 0.3 and 1.9, with the greatest differences observed for the NPBR biochars. Biochars from sugarcane bagasse and sawdust exhibited high C content (74.57–77.67%), highlighting their potential use for C sequestration. Filter cake biochar excelled in P (14.28 g kg⁻¹) and micronutrients, while algae biochar showed elevated N, calcium (Ca), and boron (B) levels. NPBR biochars were rich in N (2.28–3.67%) and P (20.7–43.4 g kg⁻¹), making them ideal fertilizers. Although sewage sludge biochar contained higher levels of potentially toxic metals, these remained within regulatory limits. This research highlights variations in the composition of biochars depending on the characteristics of the original biomass and the pyrolysis process, to contribute to the production of customized biochars for the purposes of their application in the soil. Biochars derived from exclusively plant biomasses showed important aspects related to the recovery of carbon from biomass and can be preferred as biochar used to sequester carbon in the soil. On the other hand, biochars obtained from residues with some animal contributions are more enriched in nutrients and should be directed to the management of soil fertility. Full article

The present study highlights the possibility of using sewage sludge-derived compost (SSC) or biochar (SSB) as valuable organic amendments. Such utilization of sewage sludge fulfills the principles of a carbon farming and nature-based solution strategy (NBS). This study focused on a detailed analysis of quantitative and qualitative changes in soil C compounds (total carbon—TC, total organic carbon—TOC, humic substances—CHS, labile carbon—LC, and water extractable organic carbon—WEOC), which resulted from the application of SSC or SSB; an assessment of variability in total and available forms of N and S as biogenic components that are integrally related to the organic matter of the amendments used in the experiment; and an indication of the possible relationships between C compounds and available nutrients. The experiment was conducted under greenhouse conditions with terra rosa soil amended with SSC or SSB at different application rates (25, 50, 75, 100% by mass). Soil samples were analyzed for the abovementioned parameters using appropriate analytical methods. Regardless of the organic amendment, the values of tested parameters increased with the applied dose, with the differences being significantly greater in relation to the contents determined for the control soil. In general, the application of SSC was more favorable than SSB, which was manifested by 12–49-fold higher TOC, 6–24-fold higher total N, and 10–41-fold higher total S levels. An exception was found for the content of available sulfur, which was significantly higher in the soil fertilized with biochar. In addition, SSC contributed more humic acid carbon (12.5–24.15 g∙kg⁻¹) and labile carbon (10.34–27.37 g∙kg⁻¹). On the other hand, SSB had a greater effect on fulvic acid carbon levels (2.18–2.75 g∙kg⁻¹), which were comparable to the levels of LC (3.44–6.86 g∙kg⁻¹) and WEOC (2.56–6.28 g∙kg⁻¹). The research results highlighted the validity of processing SS into compost or biochar for further use for agricultural/reclamation purposes. Despite their different impacts on the studied soil properties, both organic amendments are important for maintaining soil health and can play a significant role in carbon farming as NBS practices. The findings allow us to conclude that the strategy of increasing the amount of C through SSC or SSB fertilization is the advisable direction in sustainable soil management. Full article

Approximately 10 million megagrams of sewage sludge is produced each year in the European Union alone. To date, options to utilize sewage sludge are limited. Local regulations and sludge characteristics strictly determine waste management options. Thermal disposal methods are recommended for highly contaminated sludge. Pyrolyzed sewage sludge generates biochar that can be used as a value-added agricultural product or as an alternative fuel. The biochar production itself carries the risk of emitting harmful compounds. Unfortunately, these important safety considerations are rarely addressed in the literature. This research investigates the mechanistic effects of the storage headspace-to-biochar volume ratio and stored biochar headspace ventilation on hazardous gas emissions. Five hazardous organic compounds were emitted by biochar. However, based on this initial proof-of-the-concept research, we could not derive conclusive trends for the effects of the headspace-to-biochar volume ratio or air exchanges in the biochar headspace. Further research, which is broader in scope (feedstock type, pyrolysis conditions), should be carried out. Nevertheless, caution should be exercised when designing biochar storage, aiming to lower the risk of occupational exposure to hazardous gas emissions. Monitoring air pollutants, tracking the highest permissible concentrations and workers’ exposure, and using personal protective equipment are recommended. Full article

The remediation of dredged sediments (DS) as a major waste generation field has become an urgent environmental issue. In response to the limited strategies to restore DS, the current study aimed to investigate the suitability of Paulownia tomentosa (Thunb.) Steud as a tool for decontamination of DS, both independently and in combination with a sewage sludge-based biochar. The experimental design included unamended and biochar-supplemented DS with the application rates of 2.5, 5.0, and 10.0%, in which vegetation of P. tomentosa was monitored. The results confirmed that the incorporation of biochar enriched DS with the essential plant nutrients (P, Ca, and S), stimulated biomass yield and improved the plant’s photosynthetic performance by up to 3.36 and 80.0 times, respectively; the observed effects were correlated with the application rates. In addition, biochar enhanced the phytostabilisation of organic contaminants and shifted the primary accumulation of potentially toxic elements from the aboveground biomass to the roots. In spite of the inspiring results, further research has to concentrate on the investigation of the mechanisms of improvement the plant’s development depending on biochar’s properties and application rate and studying the biochar’s mitigation effects in the explored DS research system. Full article

Sewage sludge biochar (SSB) exhibits higher phosphorus (P) concentrations than the original sewage sludge (SS) and can be used as a P fertilizer. However, SSB-associated P is strongly retained in chemical compounds, which hinders its release and subsequent plant uptake. The use of organic acids facilitates P solubilization from SSB. Herein, we evaluated the effect of oxalic acid on P release from SSB applied to soil over time. Biochar was produced at 300 °C (SSB300) and 500 °C (SSB500). P release from SSB increased with an increasing concentration of oxalic acid in the SSB incubation solution and in SSB-treated soil. P speciation in SSB showed that P was predominantly inorganic (P_i), which represented 81% and 92% of the total P in SSB300 and SSB500, respectively. P_i in SSB consisted mainly of non-apatite P, accounting for 91% and 96% of all P_i in SSB300 and SSB500, respectively. Because SSB is predominantly insoluble in water, oxalic acid is crucial for the release of P from SSB. Oxalic acid increased P release from SSB300 and SSB500 by 103- and 600-fold, respectively, compared to the control, from which P was extracted with water. Oxalic acid enhancement of P release from SSB increases the possibility of using SSB as a sustainable source of P for agriculture. Full article

Co-application of sewage sludge (SS) with biochar in landscape/forestry soil is a common strategy for enhancing soil fertility and reducing the bioavailability of potential toxic elements (PTEs) derived from SS, such as Cd, Pb, Cu, Zn, and Ni. However, due to variability of biochar quality and uncertainties in responses of different plant species, whether the co-application benefits the landscape/forestry plant system remains elusive. Here, we tested the effectiveness of three types of biochar (SS-derived biochar (SB), rice straw-derived biochar (RB), and litter-derived biochar (LB)), which were added to soil amended with SS at 50% (w/w) at rates of 1.5%, 3%, and 4.5% as growth media for the landscape plant Aglaonema modestum (A. modestum). We analyzed the substrate’s physicochemical properties and assessed the alleviation of phytotoxicity by biochar application. A significant increase in the fertility index of substrate was observed in all the treatments with biochar addition. The addition of biochar reduced the potential mobility of PTEs while increasing their residual fraction in media. Nonetheless, it has been found that the addition of biochar has ineffective or even negative effects on A. modestum growth (height, biomass, root length) and nutrient absorption. Importantly, the reduction in root biomass and the increased activity of root antioxidant enzymes (SOD, POD, CAT, and MDA) indicate contamination stress of biochar on the roots of A. modestum. Toxic elements of concern—namely Cu, Cd, and Pb—were not significantly higher in tissues of A. modestum saplings planted in biochar-SS-amended soil. However, elevated levels of other elements that may pose toxicity concerns, such as Ni and Zn, increased in tissues at high biochar dosages. Based on the Entropy–Weight TOPSIS method, it was further confirmed that compared to the treatment without biochar, all treatments except for 3.0% LB application resulted in poorer A. modestum comprehensive growth. Our results emphasize the need for detailed research on the response of specific plants to biochar in specific environments, including plant adaptability and the unexplored toxicity of biochar, to understand the large variations and mechanisms behind these ineffective or negative effects before the large-scale co-utilization of SS and biochar in landscape/forestry soils. Full article

Pyrolysis is a recognized alternative for the sustainable management of contaminated organic waste, as it yields energy-rich gas, oil, and a carbon-rich biochar product. Low-volatility compounds, however, such as heavy metals (HMs; As, Cd, Cu, Cr, Ni, Pb, and Zn) typically accumulate in biochars, limiting their application potential, especially for soil improvement. The distribution of HMs in pyrolysis products is influenced by treatment temperature and the properties of both the HMs and the feedstock. There is a significant knowledge gap in our understanding of the mass balances of HMs in full-scale industrial pyrolysis systems. Therefore, the fate of HMs during full-scale relevant pyrolysis (500–800 °C) of seven contaminated feedstocks and a clean wood feedstock were investigated for the first time. Most of the HMs accumulated in the biochar (fixation rates (FR) >70%), but As, Cd, Pb, and Zn partly partitioned into the flue gas at temperatures ≥ 600 °C, as demonstrated by FRs of <30% for some of the feedstocks. Emission factors (EFs, mg per tonne biochar produced) for particle-bound HMs (<0.45 µm) were 0.04–7.7 for As, 0.002–0.41 for Cd, 0.01–208 for Pb, and 0.09–342 for Zn. Only minor fractions of the HMs were found in the condensate (0–11.5%). To investigate the mobility of HMs accumulated in the biochars, a novel leaching test for sustained pH drop (at pH 4, 5.5 and 7) was developed. It was revealed that increasing pyrolysis temperature led to stronger incorporation of HMs in the sludge-based biochar matrix: after pyrolysis at 800 °C, at pH 4, <1% of total Cr, Cu, Ni, and Pb and < 10% of total As and Zn contents in the biochars were leached. Most interestingly, the high HM mobility observed in wood-based biochars compared to sewage-sludge-based biochars indicates the need to develop specific environmental-management thresholds for soil application of sewage-sludge biochars. Accordingly, more research is needed to better understand what governs the mobility of HMs in sewage-sludge biochars to provide a sound basis for future policy-making. Full article

In this study, biochar derived from sewage sludge was applied to remediate Cu and Cd co-polluted soil in semi-arid areas for the first time, in which the effects of biochar on the improvement of soil physicochemical and biological properties as well as the immobilization of Cu and Cd were investigated. Soil water holding capacity increased by 0.22–2.74%, soil CEC increased by 0.52–4.06 units, soil SOM content increased by 1.41–5.97 times, and urease and catalase activities increased by 0.012–0.032 mg·g⁻¹·24 h⁻¹, 0.18–2.95 mg H₂O₂·g⁻¹, but soil pH increased only slightly by 0.69 units after biochar application. In addition, although the total content of these two metals in the soil increased with the use of biochar, the content of DTPA-Cu and Cd decreased by −0.128–0.291 mg/kg, 0–0.037 mg/kg, with the increase in biochar application, and the content of acid-soluble Cu in the soil decreased from 27.42 mg/kg to 3.76 mg/kg, the mobility and bioavailability of these two metals in the soil decreased. Finally, the complexation of organic functional groups with the soil dominates the immobilization process of metals, especially Cu. These findings suggest that biochar from sewage sludge can effectively improve soil quality and remediate heavy metal-contaminated soils in semi-arid regions. Meanwhile, the use of sludge-based biochar for the remediation of contaminated soils also provides a new method for the safe disposal of sewage sludge and a new way for sustainable development. In subsequent studies, methods such as modification are recommended to improve the efficiency of sludge-based biochar for the removal of Cu and Cd. Full article

Utilizing waste, such as sewage sludge, into biochar fits the circular economy concept. It maximizes the reuse and recycling of waste materials in the wastewater treatment plant. The experiments were conducted to assess: (1) the impact of the temperature on the properties of biochar from sewage sludge (400 °C, 500 °C, 600 °C, 700 °C); (2) how the physical activation (CO₂, hot water) or chemical modification using (MgCl₂, KOH) could affect the removal of ammonia nitrogen and phosphorus from filtrate collected from sludge dewatering filter belts or synthetic solution, wherein the concentration of ammonium nitrogen and phosphorus were similar to the filtrate. Based on the Brunner–Emmett–Teller (BET) surface and the type and concentration of surface functional groups for the second stage, biochar was selected and produced at 500 °C. The modification of biochar had a statistically significant effect on removing nitrogen and phosphorus from the media. The best results were obtained for biochar modified with potassium hydroxide. For this trial, 15%/17% (filtrate/synthetic model solution) and 72%/86% nitrogen and phosphorus removal, respectively, were achieved. Full article

Modified sludge biochar, recognized for its notable economic and environmental benefits, demonstrates potential as an effective catalyst for peroxydisulfate (PDS) activation. Nevertheless, the specific mechanisms underlying its catalytic performance require more comprehensive investigation. In this study, a modified biochar (TSBC) doped with oxygen (O) and nitrogen (N) atoms was synthesized from sewage sludge and tannin extract, which significantly enhanced the activation of PDS for the degradation of sulfamethoxazole (SMX). The TSBC/PDS system demonstrated robust performance for SMX degradation, achieving over 90% efficiency over a wide pH range (3–10). Subsequent quenching experiments demonstrated that TSBC predominantly catalyzed PDS to generate $\mathrm{O}_2^1$, which effectively degraded SMX via a non-radical pathway. The O- and N-containing functional groups in TSBC were identified as the primary catalytic sites. Besides, density functional theory (DFT) calculations revealed that the incorporation of graphitic N significantly improved the adsorption capacity of PDS on the TSBC surface. Furthermore, based on the identification of intermediates and theoretical calculations, SMX was degraded mainly by two different pathways: S-N cleavage and $\mathrm{O}_2^1$ oxidation. This study offers a foundational framework for the targeted modification of sludge biochar, thereby expanding its applications. Full article

Using sewage sludge to produce biochar-based adsorbents to remove phosphate (P) from water can be a sustainable and cost-effective method of waste management. However, the adsorption efficiency of sewage sludge biochar is not high. In this study, lanthanum-modified sludge-based biochar (La-SBBC) was synthesized by combining lanthanum nitrate with dewatered sludge. La-SBBC exhibited the highest removal efficiency of 99.06% for an initial P concentration of 15 mg/L at pH 3.0 with a dosage of 1.3 g/L. The maximum adsorption capacity of La-SBBC for P was 152.77 mg/g at 35 °C. The adsorption process followed the pseudo-second-order kinetic model (R² ≥ 0.973) and the Freundlich isothermal adsorption model (R² ≥ 0.928). Multilayer chemisorption was identified as the controlling process. The primary mechanisms of P adsorption by La-SBBC involved electrostatic interactions, precipitation, and inner sphere complexation. Thermodynamic analysis revealed that the adsorption process of La-SBBC was a spontaneous endothermic reaction. The fixed-bed experiment demonstrated that La-SBBC had significant practical utility. La-SBBC maintained 76.6% of the original P removal efficiency after six cycles. Therefore, La-SBBC can be used as a promising adsorbent for P in practical applications. Full article