Search Results (184)

Sustainable phosphorus (P) management in agriculture requires a circular economy approach through the use of so-called bio-based fertilizers (BBFs). The properties of BBFs vary widely depending on raw materials and production processes. However, it is still unknown how these properties, and particularly the dominant P compounds determine not only the efficiency of BBFs in supplying P to crops, but also their effects on soil functioning and crop quality. This study aimed to evaluate the efficiency of a representative set of BBFs, and relate this efficiency to their composition and dominant P compounds. To this end, 14 BBFs were studied: four from water purification (struvite, vivianite, and sewage sludge with and without composting), four composts (municipal solid waste (MSW), vineyard residues, and two using olive husks), three vermicomposts (two homemade and one commercial), fish meal, digestate, and a commercial organic fertilizer. Phosphorus forms in BBFs were determined using ³¹P nuclear magnetic resonance spectroscopy (P-NMR). The BBFs were compared to a single superphosphate (SSP) in a pot experiment growing wheat in two different alkaline soils, one rich in iron (Fe) oxides and one rich in carbonates. The effects on critical elements in grain [magnesium, Fe, zinc (Zn), manganese, and copper] and enzyme activities related to soil functioning and P cycling were also assessed. The dominant P compound in the BBFs was orthophosphate (73.8–89.5% of the total P in the NaOH–EDTA extracts). The MSW had the highest polyphosphate content (4.1%), a complex inorganic P compound. The organic P content ranged from 9.2% (fish meal) to 25.5% (Moge). Sewage sludge and composted sludge contributed high levels of phosphonates (4.1 and 5.6% of extracted P). The most abundant organic P compound class was inositol hexakisphosphates (IHPs), and myo-IHP (phytate) was the dominant IHP stereoisomer (1.2–6.4%) followed by D-chiro-IHP and scyllo-IHP. Plant dry matter and grain yield with most BBFs were not significantly different from that of SSP in both soils, likely due to the high concentrations of phosphate in relatively soluble forms in most of the BBFs. Vivianite and sewage sludge resulted in significantly higher grain yield than SSP (43% and 40%, respectively) in the carbonate-rich soil, likely due to progressive phosphate dissolution, which decreased the precipitation rate of insoluble calcium (Ca) phosphates. The highest P recoveries were obtained with horse manure vermicompost (65% and 15% higher than SSP in the Fe oxide-rich and in the carbonate-rich soil, respectively), partially attributed to the decreased precipitation rate of insoluble Ca phosphates with the added organic matter. Some BBFs increased micronutrient concentrations in grains and most decreased the P-to-Zn ratio relative to SSP. Overall, phosphatase and β-glucosidase activities increased with carbon-rich BBFs. Most of the studied BBFs could effectively replace fertilizers from non-renewable sources, in some cases with better crop P recoveries. Furthermore, some BBFs could provide additional benefits to grain quality, in terms of micronutrient supply for humans, and soil functioning. Full article

Anaerobic digestion is crucial for safe treatment and energy recovery from municipal sludge. However, seasonal variations in sludge physicochemical properties challenge the continuous, stable operation of anaerobic digestion systems. To investigate the seasonal variations in characteristics of municipal sludge and their impact, this study collected sludge samples from a Beijing plant over a year, analyzed their properties and microbial communities, and evaluated their biogas potential through four-week batch anaerobic digestion tests. The results demonstrated that spring sludge exhibited the highest organic matter (68.7% of total solids, TS), including soluble proteins, sugars, and lipids, while the lignocellulose content peaked in autumn (17% TS). These fluctuations were primarily driven by variations in rainfall, temperature, and human activities. The microbial community shifted significantly: Proteiniclasticum and other hydrolytic bacteria were dominant in spring, whereas Candidatus_Microthrix was notably enriched in winter. Consequently, the biochemical methane potential (BMP) was highest in spring (342.5 mL/g volatile solids) and lowest in autumn (255.8 mL/g volatile solids). Spearman’s correlation analysis indicated a significant positive correlation between BMP and soluble protein content, and a weak negative correlation with cellulose content. These findings provide essential data support for seasonal regulation of sludge anaerobic digestion systems, facilitating strategies to achieve stable biogas production. Full article

Improving the effluent quality of municipal wastewater treatment plants (WWTPs) is essential for sustainable water management and water quality protection in the Yellow River Basin. Many existing WWTPs in northern China were constructed under earlier discharge requirements and now face dual challenges of stricter effluent standards and poor low-temperature performance in winter. In this study, a municipal WWTP with a design capacity of 5 × 10⁴ m³/d in northern China was upgraded to improve winter treatment performance and support stable compliance with the discharge requirements of the Yellow River Basin. The original anaerobic + oxidation ditch process suffered from unstable effluent quality, excessive sludge loading, and insufficient pollutant removal under low-temperature conditions. A land-saving retrofit strategy was therefore proposed, involving oxidation ditch wall-height raising to extend the hydraulic retention time (HRT) and membrane bioreactor (MBR) integration to increase the mixed liquor suspended solids (MLSS) concentration. After the retrofit, the total HRT increased to 19.82 h, and the average MLSS concentration reached 7050 mg/L. The relative abundances of key nitrogen-removing bacteria, including Nitrospiraceae, Nitrosomonadaceae, and Rhodocyclaceae, increased markedly. Meanwhile, denitrification sludge loading and BOD₅ sludge loading decreased to 0.030 and 0.033 kg/(kg·d), respectively. Under low-temperature conditions, the theoretical removal capacities of total nitrogen (TN) and BOD₅ reached 44.32 and 286.19 mg/L, respectively, enabling stable effluent compliance. The results show that this retrofit strategy can improve WWTP effluent quality while avoiding large-scale land expansion, providing a practical and sustainable solution for upgrading cold-region WWTPs along the Yellow River Basin. Full article

The chemical equilibria of metal ions between soil solution and solid phases govern the solubility of metals in soil. However, the identity of these controlling phases remains poorly understood in historically polluted environments. This study aimed to identify the dominant mineral phases regulating the activities of Zn²⁺, Cd²⁺, Pb²⁺, and Ni²⁺ in soils subjected to long-term contamination from sewage sludge, municipal solid waste, river water, and industrial effluents across India. The soil samples were collected from various locations historically polluted by sewage sludge, municipal solid waste, polluted river water and industrial effluents. The free ion activities of Zn²⁺ (pZn²⁺), Cd²⁺ (pCd²⁺), Pb²⁺ (pPb²⁺) and Ni²⁺ (pNi²⁺) in soil pore water were estimated using the geochemical speciation model WHAM-VII. The metal ion activities were higher in industrial effluents and solid waste-treated soils as compared to other contaminated soils. The solubility of Zn and Cd in soils contaminated with Zn-smelter effluents was controlled by franklinite (ZnFe₂O₄) in equilibrium with goethite (α-FeOOH) and otavite (CdCO₃), respectively. Identification of minerals further reveals that nickel ferrite (NiFe₂O₄) in equilibrium with lepidocrocite (γ-FeOOH) governs the activity of Ni²⁺ in cycle factory effluent-irrigated soils of Sonepat, Haryana. At the municipal solid waste-contaminated site, the Pb²⁺ activity was controlled by exchangeable Pb in soils, whereas Zn²⁺ activity was governed by willemite (Zn₂SiO₄) in equilibrium with quartz (SiO₂). These findings provide new insights into mineralogical controls on heavy metal solubility under diverse contamination scenarios. Formation of highly soluble minerals like otavite, willemite, and nickel ferrite suggested the potential ecological risk of Cd, Zn, and Ni, respectively, in polluted soils. Full article

In municipal wastewater treatment plants (WWTPs), anaerobic digestion of municipal mixed sludge (MMS) often yields low energy recovery and operational instability due to imbalances between primary and secondary sludges. Anaerobic co-digestion (AcoD) with readily biodegradable wastes, such as fruit and vegetable waste (FVW), can enhance process stability and biogas production. Life cycle assessment (LCA) methodology is used in this study to evaluate the environmental performance of implementing AcoD of MMS and FVW in a municipal WWTP, compared with a business-as-usual scenario combining mono-digestion of MMS and incineration of FVW. The LCA was modelled in openLCA 2.5 using the ecoinvent 3.9.1 database (cut-off allocation approach), and impacts were assessed with the ReCiPe 2016 Midpoint (H) method, focusing on climate change, terrestrial acidification, fossil fuel depletion, and marine eutrophication. Results indicate that AcoD reduces impacts across all environmental categories, mainly due to higher biogas yields that increase on-site electricity generation and decrease reliance on grid electricity. Improved total solids removal also lowers digestate production and composting-related burdens. Electricity consumption remains the main hotspot in both scenarios, highlighting the importance of energy efficiency and electricity mix. Sensitivity analysis on methane content (61–65% v/v) confirms the robustness of AcoD’s environmental benefits. Full article

This article presents the results of investigations into washed mineral waste (WMW) from grit chambers, fly ash generated during the thermal treatment of municipal sewage sludge (SSA), and their mixtures prepared in varying proportions. Their general physicochemical characteristics and heavy metal concentrations were presented. An experiment was conducted to assess the mobility of metals in the analyzed samples during extraction with distilled water and groundwater. The feasibility and safety of using the recovered materials in the ground environment, as soil backfills, and as materials for the construction of roads and flood embankments, were assessed. The feasibility of safely using materials in the indicated construction solutions was demonstrated for WMW and mixtures with a dominant WMW content. These results will be helpful in further research on solid waste applications. To the best of the authors’ knowledge, this study is the first to confirm the ecological safety of the analyzed wastes, as evidenced by assessments of heavy metal content and mobility. Furthermore, taking into account the laboratory and field costs associated with waste verification to obtain appropriate values for other physical and mechanical parameters (e.g., compaction index or shear strength), and the need to determine the level of waste contamination before practical application, the physicochemical tests carried out are economically justified. Full article

This study evaluated the performance of a pilot unit for the combined removal of microplastics and total suspended solids at the municipal wastewater treatment plant of Mykonos, Greece. The pilot unit was installed downstream of the two-stage conventional activated sludge line and operated in semi-continuous mode to demonstrate its function under real effluent conditions. Across five experimental loops, influent microplastics concentrations ranged from 633 to 5843 microplastics/L, while effluent values were reduced to 96–263 microplastics/L, corresponding to an average removal efficiency of 86 ± 8%. In parallel, total suspended solids decreased by 95 ± 3%, turbidity by 93 ± 7%, and chemical oxygen demand by 70 ± 20%, while pH and conductivity remained stable. Influent water showed pronounced variability in chemical oxygen demand, total suspended solids, and turbidity due to irregular wastewater deliveries, yet the pilot consistently stabilized the effluent quality. A correlation analysis revealed strong associations between turbidity, total suspended solids, and chemical oxygen demand in the influent, while effluent data indicated close links between microplastics removal and particulate reduction. These findings confirm the robustness of the organosilane-based agglomeration process and highlight its potential as an advanced treatment stage to reduce MP emissions, improve effluent stability, and mitigate environmental risks in receiving environments such as the Mediterranean Sea. Full article

This study investigates the sequential integration of hydrothermal liquefaction (HTL) and anaerobic digestion (AD) as a strategy for resource recovery from municipal wastewater (MW) and semiconductor packaging wastewater (SPW) sludges. The primary objective is to determine the influence of HTL pretreatment on conversion efficiencies, water quality metrics, and subsequent anaerobic biodegradability. Specifically, the research focuses on biogas generation, COD removal, and the potential to promote circular resource utilization. HTL was conducted under controlled temperature (150–374 °C) and pressure (10–25 MPa) conditions, followed by batch AD at 41 °C using hydrogen- and methane-producing inocula at various ratios, specifically 20%, 50%, and 80%. Key variables, including total solids (TS), suspended solids (SS), chemical oxygen demand (COD), pH, and electrical conductivity (EC), were monitored to assess degradation efficiency and resource recovery. Additionally, chemical modifications in HTL-processed sludge were characterized using Fourier Transform Infrared Spectroscopy (FTIR). Results indicate that MW sludge achieved significant reductions in TS (65.3%) and enhanced biogas production of 156.7 mL/g VS at 80% inoculum. These figures reflect high biodegradability and compatibility with AD. In contrast, SPW sludge demonstrated limited COD removal (26.6–85%) and lower biogas yields of 154.0 mL/g VS. These results are likely due to elevated salinity and compositional complexity. These findings suggest that while HTL pretreatment significantly improves MW sludge utilization, SPW sludge may require additional or alternative treatment strategies. Overall, this study clarifies key factors influencing the performance of integrated HTL-AD systems across distinct sludge types and lays a foundation for the further development of sustainable sludge management processes. Full article

The rising volume of sludge production poses significant environmental threats. Sludge has a high moisture content (MC), which increases its disposal and transport expenses. On the other hand, sludge has low dewaterability due to its high concentration of soluble organic compounds. To reduce sludge production, understanding and improving preconditioning and mechanical dewatering are crucial for breakthroughs in advanced sludge dewatering. The sludge samples used in this analysis were obtained from the Sarabium municipal wastewater treatment plant, with a moisture content of 97% and a specific filtration resistance (SRF) of 9.15463 × 10¹⁵ m/kg. Sludge dewatering was enhanced by treating the samples chemically with ferric chloride, aluminum sulfate, Moringa olifera, and cationic polyacrylamide CPAM and physically with wood chips, slag, rice husk, and wheat straw. The experiments examined the sludge’s initial characterization (specific resistance to filtration (SRF) and time to filtrate (TTF)). To verify the structural characteristics (density), elemental composition, and the presence of various functional groups, a characterization investigation was conducted using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and energy-dispersive X-ray spectroscopy (EDS). The results showed that chemical conditioning with ferric chloride is better than aluminum sulfate and Moringa. Wood chips also provide better results for physical conditioning than rice husk, wheat straw, and slag. The reaction occurred at the carbonyl group, where FTIR showed more activated sites during SEM analysis, as evidenced by the FTIR results. Still, when CPAM was added to conditioned sludge, there was no difference in sludge dewatering performance, and the activated sites remained unchanged. Hence, this research found that mechanical sludge dewatering was improved by conditioning with ferric chloride (pH of 6 and dose of 0.12 g/g of dry solid) and wood chips (dose of 1.5 g/g of dry solid), which reduced sludge volume after dewatering by 82.5% under low pressure, which in turn minimizes transportation, energy, and handling costs. This study supports SDG 3 and SDG 6 by improving sludge dewatering efficiency and promoting sustainable wastewater management using natural wood chips. Full article

Reducing nitrous oxide (N₂O) emissions from biological wastewater treatment is critical for achieving low-carbon environmental goals. In this study, a Chlamydomonas reinhardtii -driven algal–bacterial granular sludge system was successfully established in a photo-sequencing batch reactor to enhance nitrogen removal while suppressing N₂O generation. Compact granules formed within 48 days, exhibiting good settling ability (SVI₅/SVI₃₀ = 1.0), an average diameter of 0.5 mm, and a mixed-liquor suspended solid concentration of 2.1 g/L. Algal enrichment was confirmed by an increase in chlorophyll-a to 6.6 mg/g-VSS and substantial accumulation of protein-rich extracellular polymeric substances, which improved granule stability and mass transfer. The system achieved efficient pollutant removal when treating synthetic municipal wastewater, maintaining a chemical oxygen demand removal efficiency of approximately 90% and total nitrogen removal of up to 69.4%, with effluent NH₄⁺-N consistently below 1.6 mg/L. Notably, the N₂O emission factor decreased from 4.2 to 0.4 g N₂O-N/kg N-removed, which is lower than that of conventional activated sludge processes. These results demonstrate the potential of microalgae-driven granulation as a promising low-carbon biotechnology for sustainable wastewater treatment. Full article

This study examines magnesium potassium phosphate cements (MKPCs) modified with industrial wastes for extrusion-based 3D concrete printing, evaluating the rheological properties (workability, setting time), mechanical performance and printability of formulations incorporating secondary materials: Mg dross waste (up to 20 wt.%, replacing MgO), calcined sewage sludge (up to 10 wt.%, replacing KH₂PO₄), alternative fillers such as glass from municipal solid waste glass and from construction and demolition waste and ground blast furnace slag, benchmarked against volcanic ash. The baseline MKPC exhibited initial/final setting times of 34/109 min, good workability and compressive strengths of 29 MPa (1 day)/28 MPa (28 days). Optimal low-waste mixes (e.g., using municipal glass or 20 wt.% Mg dross) shortened the initial setting to 19–25 min (decreasing 24–42%), reduced the slump by 9–18% yet remained printable at laboratory-scale and achieved 1-day strengths >23 MPa/28-day >31 MPa (comparable or superior). Glass from municipal waste proved most promising, due to superior workability, lighter aesthetics and strength gains, supporting circular economy goals while substantially reducing material costs; higher waste levels compromised fluidity and buildability. Mineralogical analyses confirmed K-struvite formation alongside residual periclase, validating these formulations for upscaling sustainable 3D printing. Full article

Sludge management is one of the most costly and technically challenging components of municipal wastewater treatment, highlighting the need for sustainable and low-cost stabilization technologies. This study evaluated a pilot-scale vermifiltration system for municipal sewage sludge stabilization under varying hydraulic and organic loading conditions. Three vermifilter pilots incorporating Eisenia andrei earthworms were operated using lightweight expanded clay aggregate (LECA), high-density polyethylene (HDPE) plastic media, and mineral pumice. The systems were tested at hydraulic loading rates (HLRs) of 150, 300, and 450 L/m²·d. Performance was assessed using chemical oxygen demand (COD), total solids (TS), volatile solids (VS), VS/TS ratio, sludge volume index (SVI), and sludge dewaterability indicators, including specific resistance to filtration (SRF) and time to filtration (TTF). Optimal performance occurred at an HLR of 150 L/m²·d, achieving maximum reductions of 49% in COD, 30% in TS, and 40% in VS, along with an SVI reduction of up to 78%. Increasing HLR significantly reduced treatment efficiency due to shorter retention times and biofilm washout. A regression analysis showed the strongest association between COD removal and organic loading rate (R² = 0.63) under the coupled HLR–OLR conditions tested, while weaker correlations were observed for SVI and VS/TS. Dewaterability improved markedly after vermifiltration, particularly in the LECA-based system. Although filter media type did not significantly affect COD or SVI removal, pumice and plastic media provided greater hydraulic stability at higher loadings. These results demonstrate that vermifiltration is an effective and environmentally sustainable option for municipal sludge stabilization when operated under controlled hydraulic conditions. Full article

Thermochemical treatments such as pyrolysis and hydrothermal carbonization (HTC) are increasingly used to convert municipal sewage sludge into solid products, offering benefits in contaminant reduction, pathogen sanitization, and nutrient recovery. This study assesses the agronomic potential of pyrochars and hydrochars produced under varying temperatures and residence times. Pyrolysis was performed at 250–520 °C for 20 and 60 min, while HTC was conducted at 180–300 °C for 30–120 min. Proximate and ultimate analyses revealed that pyrochars exhibit higher thermal stability and fixed carbon content, whereas hydrochars contain less condensed aromatic structures, indicating greater chemical reactivity but lower long-term stability. Surface area measurements showed meso- and macropore development in both materials, with hydrochars ranging from 14.7 to 86.0 m²·g⁻¹ and pyrochars from 12.7 to 41.7 m²·g⁻¹. Pyrochars tend to have a near-neutral pH, while hydrochars are slightly acidic. Hydrochars also retain higher levels of available nutrients (N, P, and S), particularly at lower temperatures, making them promising for agricultural applications. Agronomic evaluation confirmed greater N-NH₄⁺ and phosphorus availability in hydrochars compared to pyrochars, suggesting their potential as soil amendments or fertilizer additives. However, the mobility of heavy metals requires further assessment to ensure environmental safety. Full article

Municipal wastewater (MWW) was treated using a microalgal–bacterial consortium without mechanical aeration. An inoculum for the reactor was prepared by acclimatizing Chlorella vulgaris to MWW and supplementing with a small amount of activated sludge. The hydraulic retention time (HRT) and solids retention time (SRT) were progressively reduced from 6.67 to 1.17 d and from 10 to 6.67 d, respectively, to test the process robustness under realistic MWW operation. The COD removal efficiency was 88% at 0.23 kg-COD/m³/d. Mass balance suggested the major nitrogen and phosphorus removal mechanism as assimilation. A high percentage (80%) of oxidized nitrogen indicated an efficient nitrification at all HRTs. Inorganic carbon (IC) balance calculation explained the observed IC dynamics. The chlorophyll a-to-mixed liquor volatile suspended solids (MLVSS) ratio and percentage of nitrite responded to IC limitation and supplementation. The mixed liquor exhibited excellent settleability (sludge volume index: 42 mL/g) with dense algal–bacterial flocs. An increased organic loading rate, however, reduced daytime dissolved oxygen, suggesting limitation under non-aerated conditions. These findings demonstrate the potential of microalgal–bacterial systems to achieve efficient COD removal and nitrification at realistic HRTs without aeration while emphasizing the importance of IC management. Full article

Pyrolysis, as an efficient thermochemical conversion technology, demonstrates substantial advantages in achieving reduction and resource recovery of landfill sludge (LS). This work systematically examined the effects of pyrolysis temperature, residence time, and sludge type on the yield and compositional transformation of pyrolysis gases, as well as the yield and structural characteristics of the derived biochar, using LS and four other types of sludge as subjects. The research results indicate that as the pyrolysis temperature increased from 300 to 900 °C, the total gas yield of the LS sample rose markedly from 11.0 to 139.8 L/kg. The biochar obtained at 600 °C possessed the highest specific surface area (26.327 m²/g), with pore sizes primarily concentrated in the range of 10–20 nm. Extending the residence time facilitated the continuous release of gaseous products but exerted minimal influence on the yield of the solid-phase products. The pyrolysis responses varied considerably among different sludge types. Municipal sludge (MS) exhibited the highest gas production yield (197.5 L/kg), whereas LS demonstrated a greater carbon retention rate (73.7%). This work, based on a systematic analysis of product conversion behaviors, elucidated the correlation mechanism between parameter regulation and product performance during the pyrolysis process, thereby offering theoretical foundations and data support for optimizing LS pyrolysis conditions and enhancing product utilization efficiency. Full article