Sewage Sludge Research Articles

Dynamic interaction of antibiotic resistance between plant microbiome and organic fertilizers: sources, dissemination, and health risks.

Antibiotic resistance is a global health problem driven by the irrational use of antibiotics in different areas (such as agriculture, animal farming, and human healthcare). Sub-lethal concentrations of antibiotic residues impose selective pressure on environmental, plant-associated, and human microbiome leading to the emergence of antibiotic-resistant bacteria (ARB). This review summarizes all sources of antibiotic resistance in agricultural soils (including manure, sewage sludge, wastewater, hospitals/pharmaceutical industry, and bioinoculants). The factors (such as the physicochemical properties of soil, root exudates, concentration of antibiotic exposure, and heavy metals) that facilitate the transmission of resistance in plant microbiomes are discussed. Potential solutions for effective measures and control of antibiotic resistance in the environment are also hypothesized. Manure exhibits the highest antibiotics load, followed by hospital and municipal WW. Chlortetracycline, tetracycline, and sulfadiazine have the highest concentrations in the manure. Antibiotic resistance from organic fertilizers is transmitted to the plant microbiome via horizontal gene transfer (HGT). Plant microbiomes serve as transmission routes of ARB and ARGS to humans. The ingestion of ARB leads to human health risks (such as ineffectiveness of medication, increased morbidity, and mortality).

Recent Advances in Hydrothermal Oxidation Technology for Sludge Treatment

With the rapid development of urbanization and the widespread adoption of wastewater treatment facilities, the volume of sludge produced has steadily increased. Hydrothermal oxidation (HTO) technology offers an effective solution for sludge reduction, harmless disposal, and resource recovery, making it a highly promising method for sludge treatment. In recent years, HTO has attracted significant attention due to its efficiency and environmental benefits. This paper provides a detailed explanation of the fundamental principles of HTO in sludge treatment, with a focus on the removal of organic pollutants, nitrogen transformation, and phosphorus recovery. The influence of key operational parameters, such as reaction temperature, time, initial oxygen pressure, and pH, on the performance of HTO treatment is also explored. In addition, the research status of HTO sludge treatment and an example of product recovery after treatment are also discussed. It examines the challenges associated with scaling up HTO for large-scale sludge treatment, along with potential research directions for future work. Special attention is given to the innovation of catalysts, with the goal of achieving self-catalysis in sludge treatment. Moreover, considering that ammonia nitrogen (NH3-N) is a major intermediate product in HTO, its removal, as well as the prediction and planning of other unintended products, remains a key issue. Further areas of interest include improving sludge dewatering performance and enhancing the production of valuable single carboxylic acids, which can boost resource recovery efficiency. This paper also highlights the diversification of sludge applications after HTO treatment. By providing insights into future development trends, this review offers valuable references for further research and practical applications. The ultimate goal is to support the development of HTO as a sustainable and efficient solution for sludge treatment, addressing environmental concerns while maximizing resource recovery opportunities.

Research of batch and fixed-bed column adsorption for phosphorus removal from wastewater using sewage sludge biochar

Wastewater treatment and the efficient use of sewage sludge biochar are critical in addressing the needs of ever-increasing population in the world. Recently, phosphorus (P) removal from wastewater has become highly relevant and important, primarily to reduce eutrophication in surface waters. Using sewage sludge biochar as an adsorbent for phosphate removal from wastewater offers an opportunity to reuse sewage sludge (SS) and return phosphorus to the biogeochemical cycle. In this study, the efficiency of two phosphate removal methods - batch adsorption and fixed-bed column process – was investigated using pyrolyzed sewage sludge biochar (PSSB) produced at different temperatures (300 °C, 400 °C, 500 °C, 600 °C). In the batch adsorption experiment, direct mixing of 600 °C pyrolyzed sewage sludge biochar with wastewater resulted in a relatively low phosphate removal efficiency (only about 18 %) at an initial phosphate concentration of 100 mg/l. In contrast, the fixed-bed column process, using PSSB as a filter for phosphate adsorption, showed significantly better results. The highest phosphate removal efficiency (up to 90%) was achieved after 30 min of filtration, using an initial phosphate concentration of 30 mg/l initial and biochar pyrolyzed at 600 °C.

Impact of calcination temperature, organic additive percentages, and testing temperature on the rheological behaviour of dried sewage sludge

Abstract The main objective of the present work is to evaluate the influence of calcination pretreatment (600–1,000°C), organic additive incorporation (4% methocel, 4% amijel, and 8% starch), and testing temperature (20–60°C) on the rheological flow behaviour of dried sewage sludge and sewage sludge ashes. Besides, the dependency of sludge systems rheology on total solid content (4–15%) and methocel percentage (3–6%) was also evaluated. Furthermore, characterization techniques such as thermal gravimetric analysis-differential scanning calorimetry, X-ray fluorescence, X-ray diffraction, Brunauer–Emmett–Teller, and scanning electron microscopy were employed to investigate, respectively, the thermal decomposition, the chemical composition, the structural variations, the specific surface area, the surface morphology, and microstructure of sludges. The analysis of rheological characteristics according to best-fitting rheological models such as Herschel–Bulkley, Ostwald–de Waele, Cross, and Carreau models revealed that the yield stress (τ 0) and infinite apparent viscosity (η ∞) increase with an increase in TS or methocel percentage and decrease with increasing calcination or testing temperature. The strong impact of testing temperature concerning the reduction of the viscosity involves high activation energy (E a). This last criterion was used to compare the inter-particle strength of sludge systems.

Electro-dewatering of activated sludge of sewage treatment plants, Ternopol

The sewage sludge formed at wastewater treatment plants constitutes a small percentage of the volume of treated wastewater. However, the costs associated with sludge treatment and disposal account for the lion's share of the operational expenses of wastewater treatment plants. The sludge contains harmful and toxic substances. On the other hand, sludge is a source of carbon, nutrients, and trace elements, meaning it can be effectively utilized. An important stage in sludge disposal is its dewatering, particularly with the use of electric current. The study investigated the electro-dewatering of activated sludge with a moisture content of 98% from secondary clarifiers at the Ternopil wastewater treatment plant using direct electric current. Experiments were conducted on a laboratory setup with a U-shaped glass tube and carbon rod anode and cathode. The effect of the electric field was observed during the fading period, when, after a significant amount of water had been separated from the sludge, the electro-dewatering process slowed down. The obtained results were compared with those from the electro-dewatering of activated sludge with a moisture content of 98% from secondary clarifiers at the Ternopil wastewater treatment plant on a setup with a graphite rod anode and a flat cathode, as reported by other researchers. Electro-dewatering of activated sludge on both setups produced practically the same effect. It was confirmed that sludge dewatering using direct electric current can be applied on sludge drying beds at wastewater treatment plants.

Frequent Irrigation Under Increasing Doses of Stabilized Sewage Sludge in The Soil Increases the Yield and Quality of Silage Maize

Achieving higher efficiency and better quality production with appropriate irrigation regimes in silage maize cultivation in soils mixed with urban sludge is a requirement of sustainable agriculture. Therefore, a two-year field study was carried out with three replicates with four different sewage sludge doses (D0: 0 t/ha, D1: 30 t/ha, D2: 60 t/ha, and D3: 90 t/ha), and three different irrigation regimes (S1, S2, and S3). In the S1, S2 and S3 regimes, when the sum of (Reference evapotranspiration - Effective rainfall) was 25 mm, 50 mm and 75 mm, respectively, irrigation was carried out and the soil moisture deficit was completed to the field capacity. Considering the two-year average, increasing sewage sludge dose and frequent irrigation significantly increased fresh and dry biomass yields and crude protein, while decreasing acid detergent fiber (ADF) and neutral detergent fiber (NDF). The fresh biomass yield in D3 treatment was 12.4%, 20.6%, and 42.1% higher than D2, D1, and D0, respectively. ADF in D3 was 5.6%, 2.1% and 1.7% lower than D0, D1 and D2, respectively, while NDF was 4.4%, 3.7% and 2.1% lower. D3 treatment increased the crude protein value by 27.3%, 15.5% and 7.7% compared to D0, D1 and D2 treatments, respectively. S1 provided 12.9% and 28.3% higher fresh biomass yield compared to S2 and S3. ADF value in S1 was 0.69% and 2.4% lower than S2 and S3, respectively, and NDF value was 0.86% lower compared to S3. There was a positive linear relationship with a high correlation between fresh and dry biomass yields. It could be concluded that D3-S1 treatment is the most effective practice for higher and quality yields, and followed by D3-S2 treatment.

The Effect of the Mixing Ratio of Sewage Sludge and Organic Fraction of Municipals Solid Waste on Biogas Production in Anaerobic Digestion Process

Anaerobic digestion was the best way to treat organic waste biologically. It uses microorganisms to biodegrade biosolids without oxygen, producing biogas and compost. The study involved conducting batch experiments to investigate biogas and fertilizer production. Three digestive systems (A, B, and C) with three different mixing ratios were operated simultaneously and had a retention time of thirty-five days. The organic fraction of municipal solid waste, sewage sludge, and bacteria were employed in the experiments. The Al-Rustamiyah wastewater treatment plant was the source of the sewage sludge. The organic municipal solid waste fraction was utilized as materials, including fruit peels, rotten fruits, vegetable peels, eggshells, rotten vegetables, and garden leaves. The bacterial strain used in this research was E. coli, isolated directly from the local sewage sample and selected as an eco-friendly bacteria after conducting many tests. The digester's initial temperature was 30 °C, and it reached a high of 42 °C on the 16th day. Three digesters had initial pH values (6.7, 6.3, 6) and final values (7.3, 7.1, 7). The results showed good anaerobic digestion performance. The digester (C) achieved the highest biogas production, with a maximum cumulative biogas production value of 0.0549 m3. It also demonstrated removal efficiencies of 78.30% for TS, 89.13% for VS, 86.36% for BOD5, and 80.5% for COD. Additionally, the moisture content was measured at 43.30%. The anaerobic digestion’s final product was used as a high-quality fertilizer.

Comparison of Oxytetracycline and Sulfamethazine Effects Over Root Elongation in Selected Wild and Crop Plants Commonly Present in the Mediterranean Cropland and Pasture Scenarios.

Fertilization with animal manure and sewage sludge, and the use of sewage water for irrigation, can lead to high antimicrobial concentrations in agricultural soils. Once in soil, antimicrobials can exert direct and indirect toxic effects on plants by misbalancing plant-microbe symbiotic relationships. We performed germination tests to determine the optimum germination conditions of 24 plant species (10 crop and 14 wild species). Subsequently, we analyzed the differences in oxytetracycline and sulfamethazine phytotoxicity in 19 plant species for which optimum germination conditions could be established. The root elongation of the majority of wild species was inhibited in the presence of oxytetracycline and sulfamethazine, whereas crops were mainly affected by oxytetracycline. There were no differences in sensitivity to oxytetracycline between crop and wild plant species, whereas wild plants were significantly more susceptible to sulfamethazine than crop species. Thus, to cover both productivity and biodiversity protection goals, we recommend pharmaceuticals' predicted no-effect concentration (PNEC) values based on crop and wild plant species phytotoxicity data.

Innovative Approach to Sustainable Fertilizer Production: Leveraging Electrically Assisted Conversion of Sewage Sludge for Nutrient Recovery

Innovative Approach to Sustainable Fertilizer Production: Leveraging Electrically Assisted Conversion of Sewage Sludge for Nutrient Recovery

Isolation and characterization of novel bacterial strain from sewage sludge and exploring its potential for hydrogen production.

Hydrogen (H2) energy has garnered significant attention due to its numerous advantages. Nonetheless, for future commercialization, it is imperative to screen and identify strains with enhanced H2-producing capacities. In order to attain a high and consistent production performance, the conversion of biomass sources into H2 requires careful selection of the most appropriate H2-producing bacteria. This study aimed to isolate and identify a highly effective H2 producing bacteria from local sewage sludge and assess its fermentability for H2 production. The isolate was first identified by means of morphological, phenotypic, biological, and 16S rRNA investigations. A facultative anaerobe that produces H2 and is gram-negative was identified as Alcaligenes ammonioxydans strain SRAM. For the purpose of determining whether the isolate could produce H2 using glucose as the substrate, its fermentability was evaluated in 500 mL serum bottles. This strain demonstrated the ability to produce H2 from glucose under anaerobic environment, achieving a maximum H2 yield of 2.9mol H₂/mol of glucose. The highest rate of H2 production, 9.261 mmol H₂/ g dry cell weight per hr, was attained at 37°C and an initial pH of 6.8. This work effectively illustrated the use of a novel locally isolated strain in the biotechnological conversion of glucose to H2. This strategy offers an effective remedy for the world's energy instability in addition to addressing environmental issues related to industrial operations.

Designing low-carbon ultra-high performance concrete with co-combustion ash of sewage sludge and rice husk

Designing low-carbon ultra-high performance concrete with co-combustion ash of sewage sludge and rice husk

Enhancement of medium-chain fatty acids production from sewage sludge fermentation by zero-valent iron.

The effect of zero-valent iron (ZVI) dosage on medium-chain fatty acids (MCFAs) production from sewage sludge fermentation was explored. ZVI within a dosage of 2-20 g/L favored MCFAs production. Adding 20 g/L ZVI (ZVI20) increased the MCFAs and long-chain alcohols (LCAs) production to 4079.0 mg/L and 93.1 mg/L, the electron transfer efficiency of MCFAs and MCFAs selectivity were also increased by over 40% and 25% than the control. This may be due to the enriched MCFAs-producing genera, like Romboutsia and Paraclostridium. 2 g/L ZVI favorably strengthened the RBO pathway and facilitated intracellular electron generation. Moreover, ZVI facilitated the extracellular electron transfer, and cytochrome C was most enriched by ZVI20. The low MCFAs production in the ZVI50 group might be due to the inhibition of acetyl-CoA and ATP synthesis. These results provided a deep insight into the effects of ZVI dosage on MCFAs production and the specific mechanisms.

The Impact of Exogenous Organic Matter on the Properties of Humus Compounds of Soils Developing on a Reclaimed Fly Ash Landfill

Fly ash does not contain organic matter to initiate soil-forming processes and the proper development of plant cover. Therefore, in the reclamation of fly ash landfills, an integrated approach is required, including the introduction of exogenous organic matter into the top layer of ash. This study assessed changes in the content and quality of organic matter in soils developing on a reclaimed fly ash landfill. This study included reclaimed areas without the introduction of EOM (RV_1—the direct introduction of plants) and with the introduction of EOM (RV_2—surface humus and RV_3—sewage sludge). In samples taken 15 years after reclamation, the contents of total organic carbon (TOC) and total nitrogen (TN), the fractional composition of organic matter, the susceptibility of organic matter to oxidation, and soil carbon management indices (carbon pool index (CPI), C lability (L), lability index (LI), and carbon management index (CMI)) were determined. The study results showed that the use of EOM in the reclamation of the ash dump significantly increased the content and improved the quality parameters of organic matter and thus influenced the initiation of the process of organic matter accumulation. In RV_1 soil, the accumulation of carbon resources was only found in the topsoil. An increase in carbon resources in the 15–40 cm layer was only noted in the variants in which EOM was introduced (RV_2 and RV_3). Carbon management indices showed that organic matter transformations covered only the top layers of these soils and were closely related to the EOM inflow. The interdependence of the CPI and L was most beneficial in the soil reclaimed with sewage sludge. In the soil of this reclaiming variant, the CMI had a value above 100, which indicates the initiation of the soil-forming process. Significant differences between the assessed reclamation variants were confirmed by means of PCA based on organic matter quality indicators. The organic matter content and quality indicators were the most favorable in the soil of variant RV_3. The obtained results confirmed that the introduction of EOM into the top layer of fly ash has a beneficial effect on the accumulation and quality indicators of organic matter and thus on the development of the soil-forming process in Technosols developing on a reclaimed fly ash landfill.

Exploration of Agronomic Efficacy and Drought Amelioration Ability of Municipal Solid-Waste-Derived Co-Compost on Lettuce and Maize

Organic soil amendments, such as composts, mitigate the negative impacts on the environment that are caused by poor waste management practices. However, in the sub-Saharan African region, and Malawi in particular, studies investigating the agronomical efficacy and their ability to ameliorate drought stress when used as a soil amendment are minimal. This study aimed to evaluate the efficacy of sewage sludge and municipal solid waste (MSW) co-compost to ameliorate drought stress and improve crop productivity. Three experiments were conducted (i) to determine optimal application rate for co-compost, (ii) to evaluate yield response of maize and lettuce to co-compost application under contrasting soils, and (iii) to assess the effect of co-compost under water-limited conditions. Our results indicate that an application rate of 350 g co-compost per station was the most effective. This rate is 50% and 37% lower than the currently recommended rate for applying conventional compost to green vegetables and maize, respectively. In addition, under drought conditions, the co-compost application enhanced growth in lettuce, with less wilting, increased biomass and yield, approximately 130% greater leaf yield, and a 138% improvement in root growth. Furthermore, the relative root mass ratio (RRMR) was enhanced with the co-compost application by 103% under drought stress. This suggests that the co-compost amendment resulted in a greater allocation of biomass to the roots, which is a crucial morphological attribute for adapting to drought conditions. The concentration of K in the leaves and roots of plants treated with co-compost was significantly increased by 44% and 61%, respectively, under drought conditions, which may have contributed to osmotic adjustment, resulting in a significant increase in leaf relative water content (RWC) by a magnitude of 11 times. Therefore, in light of the rising inorganic fertilizer costs and the limited availability of water resources, these results demonstrate the potential of MSW and sludge co-composting in ameliorating the drastic effects of water- and nutrient-deficient conditions and optimizing growth and yield under these constraining environments.

Technical–Economic Analyses of Electric Energy Generation by Biogas from Anaerobic Digestion of Sewage Sludge from an Aerobic Reactor with the Addition of Charcoal

This study aimed to obtain the energy recovery potential of the biogas produced from anaerobic digestion (AD) of the sludge from a wastewater treatment plant (WWTP), including the use of biochar as an additive for substrate co-digestion and catalyst for methane production. We carried out the following steps: chemical–physical laboratory analyses of sludge samples; the building, operation, and monitoring of an experimental prototype of a batch bioreactor of 2.5 L for the AD of the sludge (with and without the addition of charcoal); qualitative measurements of biogas; the study of charcoal morphology; and the projection of useful energy generation from the AD sludge after treatment. A study on the economic viability and avoided greenhouse gas (GHG) emissions was performed based on the experimental results. The substrate showed alterations in all the physicochemical parameters evaluated after AD, such as a reduction of 35% in the biochemical oxygen demand (BOD) analysis; the experiment carried out using biochar showed positive results regarding the speed of CH4 production and a greater potential for energy recovery. Enterprises from 2000 kW onwards would present an internal rate of return (IRR) equal to or higher than the minimum attractiveness rate (MAR) of 15%. The USD 95.28/MWh tariff presented economic feasibility for the studied scenarios. WWTPs that produce enough sludge to generate power of 2000 kW would need to process the waste of 117,200 inhabitants with charcoal addition and 136,000 without charcoal. It would be possible to avoid the emission of 2307.97 tCO2/year (2000 kW). According to the results obtained, this study revealed that using alternative energies based on anaerobic digestion and biochar can generate positive results regarding methane production, and its application as an energy source in a WWTP proved to be economically viable at a specific level of power production.

Efficient Removal of Lipophilic Compounds from Sewage Sludge: Comparative Evaluation of Solvent Extraction Techniques

Municipal sewage sludge, a by-product of wastewater treatment plants, presents environmental challenges due to its complex composition. Particular concern is the lipophilic and aliphatic compounds that pose risks to the environment and human health. This study focuses on the efficient removal of those compounds from sewage sludge using several organic solvents (hexane, toluene, chloroform, dichloromethane, acetone, hexane-methanol mixture, ethanol, and methanol) and ionic liquids (ILs) like tetrakis(hydroxymethyl)phosphonium chloride and 1-ethyl-3-methylimidazolium acetate by solvent extraction techniques. To determine optimal conditions, various factors such as solvent types, contact time, and temperature were examined. The results reveal that solvent polarity significantly impacts extract composition, with non-polar solvents like hexane and toluene yielding profiles characteristic of lipid-type compounds. An in-depth analysis of contaminants present in the sewage sludge was studied by Fourier-transform infrared spectroscopy (FTIR). Additionally, nuclear magnetic resonance (NMR) was used to identify the extracted compounds, including triglycerides, aliphatic esters, aliphatic alcohols, and free carboxylic acids. NMR provides data on the composition of the sewage sludge and indicates that among all the solvents used, tetrakis(hydroxymethyl) phosphonium chloride was the most suitable solvent for removing lipophilic and aliphatic compounds. Regeneration potential and reusability of the IL were conducted and verified by NMR. The results showed that tetrakis(hydroxymethyl) phosphonium chloride ionic liquid could be used for several extraction cycles. Identifying these compounds in the extracted mixture demonstrates that it adds value and potential for various applications. Towards environmental sustainability and circular economy, this effort develops strategies for the safe management, disposal, and recyclability of sewage sludge and, the reduction in environmental and health hazards associated with organic compounds.

Influence of coal slime on migration behavior and ecological risk of heavy metals during hydrothermal carbonation of sewage sludge

The heavy metals (HMs) presented in sewage sludge (SS) limit the application of SS hydrochar. Compare to SS, coal slime (CS) contains higher carbon, silicates and aluminates. Addition of CS during the hydrothermal carbonization (HTC) of SS can improve the quality of hydrochar, and facilitates better solidification of HMs. In this paper, the influence of CS on migration behavior and ecological risk of HMs during HTC of SS was investigated, and the environmental risks associated with HMs in co-hydrochar was assessed. The results showed that adding CS during SS HTC could lower the content of HMs in co-hydrochar, and compared to the total content of Cd, Cr, Cu and Zn in SS-240-1, the total contents of these HMs in S5C5-240-1 decreased by approximately 43.8, 51.6, 36.5, 42.8%, respectively. The addition of CS also could facilitate the transformation of HMs from bioavailable fractions to relatively stable fractions. The leaching concentration and bioavailability of HMs in hydrochar decreased substantially with the increase of reaction temperature and residence time, and the leaching concentration of Ni in S5C5-280-1 decreased by 83.7%, and the bioavailability concentration decreased by 89.5%. Interestingly, the results also showed that co-HTC of CS and SS could effectively reduce the ecological risk and the potential contamination level associated with HMs in hydrochar, and then reduced the potential environmental risk. The results of this study may provide theoretical basis for the solidification of HMs in hydrochar, as well as for clean and efficient utilization of SS and CS.

PFAS, PCBs, PCDD/Fs, PAHs and extractable organic fluorine in bio-based fertilizers, amended soils and plants: Exposure assessment and temporal trends

Bio-based fertilizers (BBFs) produced from organic waste contribute to closed-loop nutrient cycles and circular agriculture. However, persistent organic contaminants, such as per- and poly-fluoroalkyl substances (PFAS), polychlorobiphenyls (PCBs), polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), as well as polyaromatic hydrocarbons (PAHs) can be present in organic waste or be formed during valorization processes. Consequently, these hazardous substances may be introduced into agricultural soils and the food chain via BBFs. This study assessed the exposure of 84 target substances and extractable organic fluorine (EOF) in 19 BBFs produced from different types of waste, including agricultural and food industrial waste, sewage sludge, and biowaste, and through various types of valorization methods, including hygienization at low temperatures (<150 °C) as well as pyrolysis and incineration at elevated temperatures (150–900 °C). The concentrations in BBFs (ΣPFOS & PFOA: <30 μg kg−1, Σ6PCBs: <15 μg kg−1, Σ11PAHs: <3 mg kg−1, Σ17PCDD/Fs: <4 ng TEQ kg−1) were found to be below the strictest thresholds used in individual EU countries, with only one exception (pyrolyzed sewage sludge, Σ11PAHs: 5.9 mg kg−1). Five BBFs produced from sewage sludge or chicken manure contained high concentrations of EOF (>140 μg kg−1), so monitoring of more PFAS is recommended. The calculated expected concentrations in soils after one BBF application (e.g. PFOS: <0.05 μg kg−1) fell below background contamination levels (PFOS: 2.7 μg kg−1) elsewhere in the literature. This was confirmed by the analysis of BBF-amended soils from field experiments (Finland and Austria). Studies on target legacy contaminants in sewage sludge were reviewed, indicating a general decreasing trend in concentration with an apparent half-life ranging from 4 (PFOS) to 9 (PCDD/Fs) years. Modelled cumulative concentrations of the target contaminants in agricultural soils indicated low long-term risks. Concentrations estimated and analyzed in edible plant part were low, indicating that exposure by plant consumption is well below tolerable daily intakes.

Enhanced phosphorus bioavailability of biochar derived from sewage sludge co-pyrolyzed with K, Ca-rich biomass ash

Sewage sludge has great potential for phosphorus (P) recovery. However, sewage sludge-derived biochar suffers from low P bioavailability in land application. K, Ca-rich biomass ash was used to co-pyrolyze with sewage sludge to enhance P bioavailability of synthesized biochar. Phase transformation mechanism of P during the co-pyrolysis process was studied. When sunflower straw ash (SSA) was used as an additive (50 wt%) for co-pyrolysis with sludge at 600°C, the ratio of bioavailable P (Bio-P, determined by 2 wt% citric acid) to total P (TP) of the co-pyrolyzed biochar could achieve 92.1 wt%, which was remarkably higher than that of biochar pyrolyzed by sludge alone (9.5 wt%). The K and Ca elements in SSA significantly contributed to the conversion of the Fe-phosphate phase (FePO4) in sludge into K, Ca-phosphates (KCaPO4, K2CaP2O7 and K2CaP2O7·4H2O) and Ca-phosphate (Ca5(PO4)3OH) phases, therefore enhancing the Bio-P content in the co-pyrolyzed biochar. Model compound pyrolysis results indicate that KCl/K2CO3 and CaCO3 phases in SSA play a synergistic role in enhancing the P bioavailability of co-pyrolyzed biochar. Based on the DFT calculations, the absolute value of the adsorption energy (|ΔEads|) of CH3COO- presented an order: K2CaP2O7 (2.43 eV) > KCaPO4 (1.70 eV) > Ca5(PO4)3OH (1.64 eV)> FePO4 (1.08 eV), indicating that K2CaP2O7, KCaPO4, and Ca5(PO4)3OH are more likely to interact with organic acid and have higher bioavailability than FePO4. Furthermore, the co-pyrolyzed biochar reaches the release rate standard for P, K-slow-release fertilizer. This study proposes a promising and sustainable solution to simultaneously realize sludge utilization and P resource recycling.

Behavior and flow of microplastics during sludge treatment in Japan.

Microplastic (MP) pollution is a growing public and scientific concern. In urban environments, wastewater treatment plants (WWTPs) are major sources of MPs. This study sampled sludge and separated water from each sludge treatment unit in two WWTPs in Osaka, Japan. Analyzing method for MPs in sewage sludge was optimized, ultrasonic pretreatment and double digestion were introduced into the analyzing method of MPs in sewage sludge, recovering test of standard MPs proved its high efficiency. Then MPs larger than 100 μm were extracted and analyzed, their size and type were recorded, the MP concentration was calculated, and the MP flow in the sludge treatment system was estimated. MPs were detected at every step of the sludge treatment process, and 13 types of MPs were identified. The MP concentration in sludge ranged from 81 ± 48 to 6470 ± 1490 particles/kg dry sludge (DS). In the separated water, MP concentrations were much lower, ranging from 0 to 1740 ± 794 particles/kg DS. During the thickening and dewatering processes, nearly all MPs were transferred into thickened or dewatered sludge; only 5-10 % of MPs returned to the primary sedimentation pond with the separated water. The most common types of MPs were PMMA, PE, and PS. No significant differences in MP type distributions were observed among sampling batches; however, significant differences in a few types of MPs were detected between treatment units, which requires further investigation. All detected MPs were smaller than 1000 μm; larger MPs might have been removed in the grit chamber before reaching the primary or secondary sedimentation ponds. Overall, the particle size distribution did not substantially change during sludge treatment.