Co-pyrolysis Of Sewage Sludge Research Articles

Co-pyrolysis of sewage sludge and poplar sawdust under controlled low-oxygen conditions: Biochar properties and heavy metals behavior

Biochar production by pyrolysis of sewage sludge (SS) is one of effective ways to realize resource recovery and harmless treatment of SS. However, biochar prepared by direct pyrolysis of SS has a lower specific surface area and higher heavy metal content. This study was aimed to evaluate the effect of low-oxygen and addition of poplar sawdust (PS) on sludge-derived biochar. The properties of biochar and heavy metals behavior were systematically characterized. The presence of 10% O2 during SS pyrolysis had a significant effect on the specific surface area of the pyrolytic biochar and the chemical species of heavy metals. In comparison with the pyrolytic biochar under N2 atmosphere, the yield of co-pyrolytic biochar from 10% O2 decreased by 6.7% at 350 °C and 8.3% at 650 °C, while it had the highest fixed carbon content of 19.6%. Moreover, the addition of PS also increased the specific surface area of pyrolysis biochar to 26.8 m2 g−1 at 650 °C. With the increase of pyrolysis temperature, heavy metals including Zn, Cr, and Cu in SS were transformed from the exchangeable and reducible states to oxidizable states and residue states. Especially, the presence of 10% O2 can also promote the formation of oxidizable states of heavy metals in biochar. Based on risk assessment code analysis, the ecotoxicity of heavy metals in biochar with the presence of O2 was evidently lowered. Therefore, a low oxygen atmosphere and co-pyrolysis of sludge and biomass could be effective ways to improve the quality of sludge-based biochar.

Co-pyrolysis of sewage sludge as additive with phytoremediation residue on the fate of heavy metals and the carbon sequestration potential of derived biochar

Considering the characteristics of municipal sewage sludge (MS) and Sedum alfreddi L. (SA, a hyperaccumulator plant), we attempted to use MS to enhance the enrichment and stability of heavy metals (HMs) in pyrolysis residue during SA pyrolysis. The effects of pyrolysis temperature (400–800 °C) and co-pyrolysis on migration behavior, chemical speciation, long-term leaching toxicity of HMs, and the environmental risk and carbon sequestration potential of biochar were systematically investigated. Besides, thermodynamic equilibrium simulations were performed to study the transformation of HM compounds during pyrolysis. When the pyrolysis temperature increased from 400 °C to 800 °C, the unstable fractions (F1+F2) of Cd, Pb, Cu, and Cr in MS1SA3 800 had decreased to less than 6% and Zn to 20.4%, and long-term leachability of HMs decreased continuously. Meanwhile, biochar's ecological risk was reduced to a low level, while its carbon sequestration potential improved with little released HMs. Compared with SA pyrolysis alone, adding MS increased the relative residue content of Cd and Zn in biochar, whereas no apparent effect on Pb, Cu, and Cr, and the proportion of stable fractions (F3+F4) increased. Co-pyrolysis enhanced the carbon sequestration potential of biochar, attributed to the inherent minerals of MS. Equilibrium calculations showed that the influence of MS on the fate of HMs during SA pyrolysis is mainly attributed to its high sulfur content, while Si and Al preferentially combine with alkali metal (K)/alkaline earth metal (Ca) and then interact with Zn. The findings in this paper suggest that co-pyrolysis of MS as an additive with hyperaccumulator plants is a feasible proposal, and the co-pyrolysis biochar obtained at suitable temperatures has the potential for safe application.

Immobilization effect of heavy metals in biochar via the copyrolysis of sewage sludge and apple branches

The excess sludge produced by sewage treatment plants can be recycled into energy through pyrolysis, and the byproduct biochar can be used for soil remediation. However, the heavy metals in sludge are retained in biochar after pyrolysis and may cause secondary pollution during its soil application. Herein, a fast copyrolysis method of activated sludge (AS) and apple branches (AT) was proposed to immobilize heavy metals while improving bio-oil yield. The results showed that the heavy metal release from the copyrolyzed biochar was markedly reduced compared with that from the biochar produced through the pyrolysis of AS alone (78% for Cr and 28% for Pb). The kinetic behavior of ion release from different biochars could be described by a first-order kinetic model. The excellent fixation of heavy metals was attributed to complexation by abundant oxygen-containing surface functional groups (–O–, =O, and –CHO) that were mainly donated by AT. Furthermore, high-temperature pyrolysis was conducive to the fixation of metals, and the release of Pb2+ and Cr3+ from the biochar pyrolyzed at 600 °C was approximately 2/3 and 1/10 of that from the biochar pyrolyzed at 400 °C, respectively. A growth experiment on Staphylococcus aureus and Escherichia coli revealed that the toxicity of the copyrolyzed biochar was greatly reduced. This work can provide a method for heavy metal fixation and simultaneous resource recovery from organic wastes.

Comparative life cycle assessment of co-pyrolysing sewage sludge and wastewater-grown microalgae for biofuel production

Using available data, we analysed the biofuel production via pyrolysis of sewage sludge (SS) and microalgae grown in wastewater, either alone or at mass ratios of 1:1, 1:2, and 2:1. The life cycle assessment (LCA), global warming potential (GWP), energy recovery, and economic feasibility were compared. GWP was 36–44% lower for the co-pyrolysis scenarios than for SS alone. For energy recovery from pyrolysis gases, a gas turbine was more effective than gas heating, compensating for up to 28% of the pyrolysis energy requirement for all five scenarios. The drying process accounted for 69−88% of the total energy consumption, indicating that the dewatering process should be improved to maximise sustainability and profitability. All scenarios were profitable; the 1:1 mixture gave the highest net profit (9% more than that of SS). To conclude, co-pyrolysis of SS and microalgae is environmentally and financially viable for biowaste management in municipal wastewater treatment plants.

Co-pyrolysis of sewage sludge with polyvinyl chloride (PVC)/CaO: Effects on heavy metals behavior and ecological risk

As an attractive method to recover energy and reduce heavy metals in the resultant biochar, co-pyrolysis of sewage sludge with polyvinyl chloride (PVC) plastics may increase the ecological risk of heavy metals. Considering the sound performance of CaO in dechlorination and immobilization of heavy metals, pyrolysis experiments were performed on four feedstocks and combined with the analysis of heavy metals to investigate the effects of temperature and added PVC/CaO on the behavior of As, Cr, Cu, Ni, Pb, and Zn. The results indicated that, increased temperature and added PVC could reduce the content of As, Pb, and Zn in biochar while CaO had the opposite effect, and the temperature set here had limited effect on the volatilization of Cr, Cu, and Ni with more than 90% of them remaining in biochar. Besides, compared with untreated sewage sludge, higher temperature and extra CaO could reduce the ecological risk of heavy metals in biochar by transforming them into more stable forms while the added PVC inhibited the transformation. When both PVC and CaO were present in pyrolysis system, although the ecological risk of heavy metals in biochar caused by PVC could be partially offset by increasing temperature and introducing CaO, it was still higher than that of other biochar. This study provides valuable insights for the treatment of heavy metals during sludge pyrolysis.

Renewable nitrogen-containing products by Maillard reaction of sewage sludge and glucose. Part I. Analysis of nitrogen composition and protein model based on AlphaFold2

• Composition, content, and structure of protein-N in sludge were investigated. • Distribution and relative content of Maillard reaction-related functional groups. • Trace the origin of protein by microbial community and protein function analysis. • Sludge protein model is predicted by Alphafold2. • Crucial factors of sludge protein model for Maillard reaction are proposed. In order to better understand the nitrogen transformation in Maillard reaction during the co-pyrolysis of sewage sludge (SS) and glucose, analysis of Maillard reaction-related nitrogen-containing compounds (NCCs) and the protein model of SS is proposed. The composition, content, and structure of NCCs, especially protein in SS, are critical for the investigation of nitrogen transformation in Maillard reaction. The distribution and relative content of Maillard reaction-related functional groups, NCCs, and amino acids in SS were studied. Genomes by DNA sequencing are further applied in building a database search for metaproteomic studies, which provide valuable information and insight into the origin of SS protein, such as the taxonomic composition of the underlying microbial community, inferred protein functions, and their relationship with the transformation of NCCs. SS protein model was constructed by Alphafold2, and key factors determining the selection of SS protein model were revealed.

Biofuel production by co-pyrolysis of sewage sludge and other materials: a review

Biofuel production by co-pyrolysis of sewage sludge and other materials: a review

Co-pyrolysis of sewage sludge and lignocellulosic biomass: Synergistic effects on products characteristics and kinetics

Co-pyrolysis of sewage sludge (SS) and corn stalk (CS) was conducted, followed by various online and offline analyses of pyrolysis products and reaction kinetics. Significant synergistic effects were found with the addition of CS to SS: the char yield decreased while the bio-oil yield increased significantly, and CO and CH4 yields increased. The sequential response order of functional groups in bio-oil to CS percentage is: alcohols → ketones → alkanes. The interaction of SS and CS significantly promoted the production of phenols and furans while inhibited the production of oxygen heterocycles and nitrogen compounds, which was beneficial for the subsequent utilization of bio-oil. The addition of CS to SS significantly increased the carbon content while reduced the sulfur content in the char. Activation energy (Ea) of the mixture was assessed by two iso-conversional methods, and Flynn-Wall-Ozawa (FWO) always had a higher correlation to the reaction than Kissinger-Akahira-Sunose (KAS). Average Ea of SS (604.42 and 631.76 kJ/mol) was higher than that of CS (251.18 and 258.05 kJ/mol), which implied that the addition of biomass was beneficial for SS pyrolysis. The pre-exponential factor was ≥1010 s−1, suggesting that the reactions occurring in co-pyrolysis were the loose junctional complex (simple complex) in nature. The co-pyrolysis of SS and CS followed the power law model reaction mechanism (P3). The synergistic effects were mainly caused by the radicals (e.g., H, HO, CH3, OCH3) formed from the devolatilization of CS and the metallic elements (e.g., Al, Fe, Ca, Mg, K) present in SS. The research findings provided practical and new insights into a cleaner and more efficient co-pyrolysis strategy.

Co-pyrolysis of sewage sludge and sodium lignosulfonate: Kinetic study and methylene blue adsorption properties of the biochar

Co-pyrolysis of sewage sludge (SS) and lignin is a promising method to dispose of SS and obtain valuable biochar, however, the synergy effect has been rarely reported. In this paper, lignin of sodium lignosulfonate (SL) was blended with SS for co-pyrolysis. Thermogravimetric analyzer/differential scanning calorimetry (TGA/DSC) was used to investigate the reaction kinetics during co-pyrolysis. And the adsorption performance of co-pyrolysis biochar on methylene blue (MB) was determined. Results showed that the SS decomposition was promoted with SL addition. Kinetic analysis using the Coats-Redfern method indicated the reaction order model to be the primary pyrolysis kinetic mechanism. The synergistic effect of promotion was caused by catalytic metals, and inhibition was caused by ash and tar adhesion. The specific surface area of biochar was improved during co-pyrolysis from 62.53 to 243.22 m2 g−1, while SL ratio of 80% achieved the maximum specific surface area. Co-pyrolysis showed an inhibition effect on porosity formation when SL ratio was below 60%, while a promotion effect was found when SL ratio exceeded 60%. Co-pyrolysis elevated the MB adsorption capacity of SS-derived biochars from 12.48 to 154.06 mg g−1, and was indicated as a promising method for adsorbents production.

Co-pyrolysis biochar derived from sewage sludge and lignin: Synergetic effect and adsorption properties

Co-pyrolysis of sewage sludge (SS) and biomass is expected to improve the biochar quality. Lignin as a major component of biomass was selected for co-pyrolysis with SS. The characteristics and kinetics of co-pyrolysis were studied by thermogravimetric analyzer/differential scanning calorimetry (TGA/DSC) and Coats-Redfern method; the effects of pyrolysis temperature and mixing proportion on the biochar yield were investigated via muffle furnace experiment, and the porosity and methylene blue (MB) adsorption capacity of the obtained co-pyrolysis biochar were evaluated. The results showed that co-pyrolysis promoted the decomposition of mixture and reduced the reaction temperature. The reaction order model was the primary mechanism model for co-pyrolysis, and both promotion and inhibition effects were observed based on the obtained activation energy. At 400 ℃ and 600 ℃, the co-pyrolysis synergetic effect on biochar yield was weak, and synergy effect of inhibition on the porosity of biochar was caused by tar and ash adhesion. When temperature was elevated to 800 ℃, catalytic effect of alkali and alkaline earth metals (AAEMs) dominated the synergetic effect, promoted char decomposition, meanwhile, pores were dramatically developed. Co-pyrolysis of SS and lignin improved MB adsorption capacity of SS biochar from 14.04 mg g−1 to 180.36 mg g−1, indicating it to be a prospective method for waste to valuable biochar production.

Ecotoxicity of sewage sludge- or sewage sludge/willow-derived biochar-amended soil

Co-pyrolysis of sewage sludge (SL) with plant biomass gains attention as a way to minimize SL-derived biochar drawbacks, such as high amount of toxic substances, low specific surface area and carbon content. The toxicity of soil amended with SL- (BCSL) or SL/biomass (BCSLW)-derived biochar was evaluated in long-term pot experiment (180 days). The results were compared to SL-amended soil. Biochars produced at 500, 600, or 700 °C were added to the soil (podzolic loamy sand) at a 2% (w/w) dose. Samples were collected at four different time points (at the beginning, after 30, 90 and 180 days) to assess the potential toxicity of SL-, BCSL- or BCSLW-amended soil. The bacteria Aliivibrio fischeri (luminescence inhibition – Microtox), the plant Lepidium sativum (root growth and germination inhibition test – Phytotoxkit F), and the invertebrate Folsomia candida (mortality and reproduction inhibition test – Collembolan test) were used as the test organisms. Depending on the organism tested and the sample collection time point variable results were observed. In general, SL-amended soil was more toxic than soil with biochars. The leachates from BCSLW-amended soil were more toxic to A. fischeri than leachate from BCSL-amended soil. A different tendency was observed in the case of phytotoxicity. Leachate from BCSL-amended soil was more toxic to L. sativum compared to BCSLW-amended soil. The effect of biochars on F. candida was very diversified, which did not allow a clear trend to be observed. The toxic effect of SL-, BCSL- or BCSW-amended soil to particular organisms was observed in different time, point's periods, which may suggest the different factors affecting this toxicity.

Co-pyrolysis of sewage sludge and metal-free/metal-loaded polyvinyl chloride (PVC) microplastics improved biochar properties and reduced environmental risk of heavy metals

Co-pyrolysis of sewage sludge and plastics have been utilized for producing biochars as a strategy to fix plastic pollution. However, comparative studies on the characteristics and environmental risk of heavy metals in biochars obtained by the co-pyrolysis of sludge and microplastic with/without metal additives are seldom. Here we demonstrated the effects of simulated co-pyrolysis (at 400 °C) of sewage sludge and metal-free or metal-loaded polyvinyl chloride (PVC) microplastics at different mass ratios (1:0, 19:1, 3:1, 1:3, sewage sludge: PVC (w/w)) respectively. Results revealed that co-pyrolysis of metal-loaded PVC and sewage sludge resulted in higher electrical conductivity, ash content, and an acidic pH of biochars as compared to the co-pyrolysis of metal-free PVC and sewage sludge. Addition of metal-loaded PVC increased total concentrations of calcium (Ca), magnesium (Mg), cadmium (Cd), and lead (Pb) in biochars, but reduced the bioavailability of Cd, chromium (Cr), nickel (Ni), and zinc (Zn) in biochars. Analysis of chemical speciation showed that heavy metals (except Pb) in biochars derived from co-pyrolysis of sewage sludge and metal-loaded PVC had higher percentage of more stable fraction (residual fraction) and lower potential ecological risk index (RI) value. S1AP3 (sludge: metal-loaded PVC = 1:3) biochar had the lowest environmental risk based on RI value (14.41). To sum up the present study suggests that the addition of metal-loaded PVC microplastic in sewage sludge had a positive impact on the immobilization of heavy metals during co-pyrolysis process.

Co-Pyrolysis of Sewage Sludge and Wetland Biomass Waste for Biochar Production: Behaviors of Phosphorus and Heavy Metals.

Large amounts of sewage sludge (SS) and wetland plant wastes are generated in the wastewater treatment system worldwide. The conversion of these solid wastes into biochar through co-pyrolysis could be a promising resource utilization scheme. In this study, biochar was prepared by co-pyrolysis of SS and reed (Phragmites australis, RD) using a modified muffle furnace device under different temperatures (300, 500, and 700 °C) and with different mixing ratios (25, 50, and 75 wt.% RD). The physicochemical properties of biochar and the transformation behaviors of phosphorus (P) and heavy metals during the co-pyrolysis process were studied. Compared with single SS pyrolysis, the biochar derived from SS-RD co-pyrolysis had lower yield and ash content, higher pH, C content, and aromatic structure. The addition of RD could reduce the total P content of biochar and promote the transformation from non-apatite inorganic phosphorus (NAIP) to apatite phosphorus (AP). In addition, co-pyrolysis also reduced the content and toxicity of heavy metals in biochar. Therefore, co-pyrolysis could be a promising strategy to achieve the simultaneous treatment of SS and RD, as well as the production of value-added biochar.

Co-pyrolysis of sewage sludge and food waste digestate to synergistically improve biochar characteristics and heavy metals immobilization

Food waste digestate (FWD) is a desirable additive in sewage sludge (SS)-based biochar preparation owing to its high contents of intrinsic inorganic minerals and lignocellulosic compounds. In this study, we investigated the co-pyrolysis of SS with FWD at different mixing ratios (4:0, 3:1, 2:2, 1:3, and 0:4; SS:FWD w/w) at 550 °C to synergistically improve the biochar characteristics and immobilize the heavy metals in the SS. The results showed that co-pyrolysis of SS with FWD greatly increased the aromaticity and pH (by 13.22–26.56%) of the blended biochar, and significantly reduced the contents of total and bioavailable heavy metals. The addition of FWD effectively enhanced the conversion of heavy metals from less stable fractions to more stable forms, but led to the transformation of Cr from the residual fraction (F4) to the oxidizable fraction (F3) when the FWD:SS ratio was ≥ 3:1. Overall, the formation of co-crystal compounds, stable kaolinite, and metal oxides together with the enhancement of biochar characteristics during co-pyrolysis significantly reduced the heavy metal-associated ecological risk (potential ecological risk index lower than 15.51) and phytotoxicity (germination index higher than 139.41%) of the blended biochar. These findings suggest that high levels of mineral components in FWD greatly immobilize more heavy metals in biochar.

Co-pyrolysis of sewage sludge and Ca(H2PO4)2: heavy metal stabilization, mechanism, and toxic leaching

The presence of unstable heavy metals in sewage sludge (SS) restricts its resource utilization. In this study, Ca(H2PO4)2 and SS were co-pyrolyzed to produce biochar, which contained relatively stable heavy metals. X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, and inductively coupled plasma atomic emission techniques were used to analyze the physical and chemical properties and heavy metal content of the biochar. The results indicated that co-pyrolysis of SS with Ca(H2PO4)2 resulted in the production of more stable heavy metals in the SS. The optimal co-pyrolysis conditions were a blended ratio of 15% Ca(H2PO4)2, 650 °C final temperature, 15 °C min−1, and 60 min retention time. The potential stabilization mechanisms of heavy metals were as follows: (1) organic decomposition and moisture (sourced from Ca(H2PO4)2 decomposition) evaporation resulted in greater biochar surface porosity; (2) phosphorous substances were complexed with heavy metals to form metal phosphates; and (3) the mixture reactions among inorganic substances, pyrolysis products of organics, and heavy metals resulted in the formation of highly aromatic metallic compounds. Additionally, the potential environmental risks posed by the heavy metals decreased from 65.73 (in SS) to 4.39 (in biochar derived from co-pyrolysis of SS and 15% of Ca(H2PO4)2). This study reports on a good approach for the disposal of SS and the reduction of its environmental risk.

Co-pyrolysis of sewage sludge and grape dreg to produce efficient and low-cost biochar for methylene blue removal: adsorption performance and characteristics

Co-pyrolysis of sewage sludge and grape dreg to produce efficient and low-cost biochar for methylene blue removal: adsorption performance and characteristics

Immobilization Effect of Heavy Metals in Biochar Via the Copyrolysis of Sewage Sludge and Apple Branches

Immobilization Effect of Heavy Metals in Biochar Via the Copyrolysis of Sewage Sludge and Apple Branches

Co-pyrolysis of sewage sludge/cotton stalks with K2CO3 for biochar production: Improved biochar porosity and reduced heavy metal leaching.

The co-pyrolysis of sewage sludge and biomass is considered a promising technique for reducing the volume of sewage sludge, adding value, and decreasing the risk associated with this waste. In this study, sewage sludge and cotton stalks were pyrolyzed together with different amounts of K2CO3 to evaluate the potential of chemical activation using K2CO3 for improving the porosity of the biochar formed and immobilizing the heavy metals present in it. It was found that K2CO3 activation effectively improved the pore structure and increased the aromaticity of the biochar. Moreover, K2CO3 activation transformed the heavy metals (Cu, Zn, Pb, Ni, Cr, and Cd) into more stable forms (oxidizable and residual fractions). The activation effect became more pronounced with increasing amount of added K2CO3, eventually resulting in a significant reduction in the mobility and bioavailability of the heavy metals in the biochar. Further analysis revealed that, during the co-pyrolysis process, K2CO3 activation resulted in a reductive atmosphere, increased the alkalinity of the biochar, and led to the formation CaO, CaCO3, and aluminosilicates, which aided the immobilization of the heavy metals. K2CO3 activation also effectively reduced the leachability, and thus, the environmental risks of the heavy metals. Thus, K2CO3 activation can improve the porosity of the biochar derived from sewage sludge/cotton stalks and aid the immobilization of the heavy metals in it.

Enhanced bioavailability of phosphorus in sewage sludge through pyrolysis aided by calcined clam shell powder

Phosphorus is an indispensable element, while the existing phosphate rock resources are not enough to maintain the long-term demand of modern agricultural development. To ensure the sustainability of economic and social, it is necessary and urgent to seek the alternative phosphorus source of phosphate rock. In this study, calcined clam shell powder (CSP) was firstly used as a modifier and mixed with sewage sludge (SS) for co-pyrolysis to obtain sludge-derived pyrochars containing a large amount of bioavailable phosphorus. The effect of different temperatures (500, 600, 700, 800 °C) and dosages (0%, 10%, 20%, 30%) on the change in the form of phosphorus during the pyrolysis process were investigated. With the increase of temperature and the addition of CSP, the orthophosphate (Ortho-P) increased from 63.69% in the original SS to nearly 100%. Furthermore, the main phase of inorganic phosphorus (IP) changed, mainly in the form of apatite phosphorus (hydroxyapatite increased from 8.88% to 35.97%), and the concentration of easy-to-lose phosphorus reduced to 0.11 mg/g. After co-pyrolysis of SS with CSP, the passivation situation of heavy metals (HMs), such as Zn, Mn, Cr, Cu, Cd and Pb was significantly improved, thus reducing the potential environmental risk. The planting experiment proved that the sludge-derived pyrochars obtained by adding 20% CSP at 800 °C promoted the germination of seeds and the growth of seedlings. Consequently, the product of SS co-pyrolysis with CSP could be used as an excellently bioavailable and environmentally friendly phosphate fertilizer for agricultural production.

Co-pyrolysis of sewage sludge and pinewood sawdust: the synergistic effect and bio-oil characteristics

Co-pyrolysis of sewage sludge and pinewood sawdust: the synergistic effect and bio-oil characteristics