Co-pyrolysis Of Sludge Research Articles

Competitive adsorption of polycyclic aromatic hydrocarbons on phosphorus tailing-modified sludge biochar provides mechanistic insights.

Biochar has been widely used to solve the wastewater pollution of polycyclic aromatic hydrocarbons (PAHs). However, the competition of PAHs with different benzene ring numbers (e.g., phenanthrene [Phe], pyrene [Pyr], and benzo[a]pyrene [BaP]) for adsorption sites on biochar has received little attention. In this study, biochar was produced by co-pyrolysis of sludge and phosphorus tailing at different temperatures (300, 500, or 800°C) to adsorb PAHs. The results show that phosphorus tailing increased the adsorption of PAH by increasing the biochar's BET surface area (SBET), micropore volume, hydrophobicity (at low temperatures) and aromaticity (at high temperatures). The maximum adsorption capacities were 29.90µmol/g for Phe, 25.58µmol/g for Pyr and 20.45µmol/g for BaP, respectively. Importantly, the types and functions of groups involved in the adsorption of various PAHs were discussed. Adsorption of Phe and Pyr on the biochar mainly involved C=O and C-O-C functional groups, and there was a certain degree of competition between these PAHs for those sites. In contrast, BaP mainly adsorbed at C-OH and C=C moieties, without competing with Phe or Pyr at C-OH sites. The competitive edge of BaP was also stronger than that of Phe and Pyr on C=C functional groups. The adsorption mechanisms involving pore filling, hydrophobic interactions, and π-π interactions governed the adsorption of the evaluated PAHs. Overall, the adsorption of PAHs on biochar followed a heterogeneous chemical adsorption process.

High performance of heterogeneous catalytic ozonation for tetracycline removal by a N-doped biochar derived from co-pyrolysis of sludge and water hyacinth

Enhancing the performance of heterogeneous catalytic ozonation (HCO) for contaminant removal using biochar that is both cost-effective and stable is of great significance. In this research, a novel nitrogen-doped biochar (HSBC) was synthesized through the co-pyrolysis of sludge and water hyacinth. The presence of pyrrolic N, pyridinic N and graphitic N in HSBC as well as the high-temperature co-pyrolysis process, conferred a high degree of graphitization to the biochar. The graphitic N species facilitated the generation of free radicals, while the graphitic structure enhanced electron transfer between the catalyst and tetracycline (TC). HSBC demonstrated exceptional efficiency in TC removal via HCO, achieving a 93% removal rate within just 130 minutes. Moreover, the biodegradability of actual printing and dyeing wastewater with a chemical oxygen demand (COD) of (9900 mg/L) was increased sevenfold after HCO treatment. This study offers new perspectives on the preparation of N-doped biochar and its practical application in the treatment of industrial wastewater through HCO processes.

Study on the properties and components of solid-liquid products by co-pyrolysis of sludge and cotton stalk

The effects of sludge content and pyrolysis temperature on the pyrolysis process and product properties were studied through the co-pyrolysis of sludge and cotton stalk. Multi-objective fuzzy hierarchical analysis was used to analyze the multiphase properties of pyrolysis products, and describe the internal relationship between pyrolysis conditions and product properties. It has been proved using kinetic calculation that the mass ratio of sludge and cotton stalk is higher than 1:2 required the lower pyrolysis activation energy. According to the comparison between experimental and theoretical results, the addition of sludge is beneficial to increase the bio-oil yield. In terms of product performance, the addition of sludge and increase of pyrolysis temperature both can improve the specific surface area, pore volume of biochar and the pH value of bio-oil, reduce the total acid content, increase the total phenol content and optimize calorific value of bio-oil. The specific surface area of biochar, calorific value of bio-oil, total phenol content and pH were evaluated by multi-objective decision analysis method, the optimum process condition of sludge: cotton stalk = 2:1 at 600 ℃. Under the conditions, the specific surface area of biochar is 57.40 m2/g, the pH of the bio-oil is 8.06, the total acid content is 5.94 mg/g, the calorific value is 27.18 KJ/g and the total phenol content is 47.32 mg/g, respectively. Compared to the pyrolysis product of cotton stalks, the specific surface area is increased almost 20 times, the calorific value is increased by 13 %, the total acid content is decreased by 95 %, and the total phenol content is similar. This study proposed a preparation process of bio-oil with high performance, and provided a theoretical basis for the subsequent co-pyrolysis research.

Co-pyrolysis of sewage sludge and sawdust: Synergistic effects of product yield and synthetic gas calorific value

Co-pyrolysis of sludge and sawdust, which are two renewable and abundant biomass resources, offers a promising environmental-friendly way to produce valuable energy products. In this study, the synergistic effect between sludge and sawdust was quantified by fixed bed reactor and thermogravimetric experiments. The product yield and product quality were also studied. The results showed that both temperature and sawdust addition significantly affected the distribution of co-pyrolysis products. Biochar yield decreased with increasing temperature, with the highest yield at 700 °C. With the addition of sawdust, the yield of biochar first increased and then decreased. The highest biochar yield was 58.1 wt% after adding 10 wt% sawdust. The yield of bio-oil initially decreases and then increases with temperature. With the addition of sawdust, the yield of bio-oil first decreased and then increased. The process condition of a temperature of 700 °C–800 °C and a sawdust addition ratio of less than 30 wt% is more favorable for the production of bio-oil. Increasing temperature and the addition of sawdust boosteded syngas production and calorific value. When the sawdust ratio was 10 wt%, it exhibited the most pronounced influence on gas yield and demonstrated less susceptibility to temperature variations. The most obvious increase in the calorific value of syngas was observed at 700 °C and 10 wt% sawdust ratio. Taking into account the product yield and product quality, the optimum conditions for co-pyrolysis were determined to be 750 °C and a sawdust ratio of 10 wt%.

Influence of low-density polyethylene addition on nitrogen transformation during sludge protein pyrolysis

Co-pyrolysis of sludge and waste plastics is a long-term strategic approach for producing valuable fuels. However, sludge is characterized by a high protein content, which serves as a significant source of nitrogenous components in bio-oil. To improve the quality of pyrolysis products, the present study investigated the effect of low-density polyethylene (LDPE) on nitrogen transformation during the pyrolysis of sludge protein (SP). The study findings indicated that LDPE addition reduced the amount of solid residue owing to the interaction between SP and H radicals generated by LDPE pyrolysis. The thermal weight loss difference consistently remained below 0 when the SP-to-LDPE mixing ratio was 7:3, indicating that LDPE promotes the pyrolysis of SP. For the analysis of nitrogen-containing products during pyrolysis, LDPE addition significantly reduced the levels of nitrogen-containing compounds in the bio-oils of glutamate (Glu), histidine (His), and tyrosine (Tyr). Specifically, at 600°C, Glu, His, and Tyr in the bio-oils decreased by 31.4%, 33.3%, and 34.38%, respectively. No significant changes were observed in the nitrogen content within the pyrolysis char of Glu and His. However, all three amino acids exhibited a significant increase in the formation of NOx precursors due to the attack on the nitrogen positions of the heterocyclic nitrogen species by the H radicals generated by LDPE. This study contributes to research on the impact of LDPE on nitrogen migration and conversion during the pyrolysis of SP, laying the foundation for subsequent studies on pollutant removal reactions.

Effect of co-pyrolysis of sewage sludge with different plastics on the nitrogen, sulfur, and chlorine releasing characteristics and the heavy metals ecological risk of biochar

The high calorific value, low ash content and high volatility of the plastic can compensate for the deficiencies of the single pyrolysis of sewage sludge (SS), and these properties can improve the quality of the pyrolysis product. However, secondary contaminants may be generated during the co-pyrolysis of sludge and plastics. Plastics contain polluting elements that may also enter sludge, so different plastics may affect the release of N, S, and Cl as well as the ecological risk of heavy metals. In this study, polypropylene (PP), polyamide 6 (PA6) and polyvinyl chloride (PVC) were added to sludge to analyze the release of N, S and Cl from sludge pyrolysis products by different plastics. An environmental risk assessment was also conducted to evaluate the various forms of heavy metals. The results showed that PP, PA6, and PVC increased the total mass losses of sludge by 16.88%, 6.82% and 9.46%, respectively, inhibiting the release of NH3, CH3Cl, H2S and SO2 harmful gases from sludge. PP and PA6 increased the calorific value of pyrolysis oil and released more aliphatic hydrocarbons and alcohols. However, PA6 and PVC will increase the release of HCN and HCl, respectively. The presence of plastics enhanced the carbon structure of biochar, with PP and PA6 particularly enriching the pore structure and surface properties of biochar. PA6 and PVC reduced the potential ecological risk of biochar. These results will provide new insights into the co-pyrolysis of sludge and plastics.

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.

Elucidation of synergistic effects in straw/sludge co-pyrolysis through gaseous product monitoring and biochar analysis

The environmental problems posed by the increasing global production of sludge highlight the need for efficient sludge treatment methods ideally affording value-added products, as exemplified by the co-pyrolysis of sludge and biomass. In this study, we aimed to investigate the effects of temperature (500, 600, 700, and 800 °C) and straw content (0, 25, 50, 75, and 100 wt%) on the properties of gaseous products and biochar during pyrolysis of sludge–straw mixtures in a fixed-bed reactor. Gas (e.g., CO2, CO, CH4, and H2) release increased with increasing temperature (up to 700 °C) and straw content, which was ascribed to the high content of volatiles in straw and its ability to act as a hydrogen source for sludge. The specific surface area and pore volume of biochar first decreased and then increased with increasing temperature, whereas the reverse was true for pore size. The synergy between sludge and straw, quantified as the difference between experimental and predicted biochar yields and specific surface areas, was maximized at a straw content of 75 wt% and was analyzed to design a pyrolysis product framework based on the circular economy concept. Thus, this study paves way for the effective utilization of sludge co-pyrolysis products and the preparation of mixed biochar, providing a reference for solid-waste treatment and efficient energy utilization.

Immobilization of heavy metals in biochar by co-pyrolysis of sludge and CaSiO3

Sludge pyrolysis has become an important method of sludge recycling. Stabilizing heavy metals in sludge is key to sludge recycling. Currently, research on the co-pyrolysis of sludge and industrial waste is limited. This study aims to explore the impact and mechanism of the co-pyrolysis of sludge and CaSiO3 (the main component of slag) and to achieve the concept of “treating waste with waste”. To this end, we added different proportions of CaSiO3 (0%, 3%, 6%, 9%, 12%, and 15%) for the co-pyrolysis with sludge, and varied the pyrolysis temperatures (300, 400, 500, 600, and 700 °C) and retention times (15, 30, 60, and 120 min) to study heavy-metal stabilization in sludge. Consequently, the optimum dosage of CaSiO3 required for the immobilization of different heavy metals was 9% (Cu, Zn, Pb, and Cr) and 15% (Ni). The contents of Cu, Zn, Pb, Cr, and Ni in the stable state (oxidized and residual states) were 92.73%, 79.23%, 99.55%, 92.43% and 90.33% respectively. At a pyrolysis temperature of 700 °C, the steady-state proportions of Cr, Pb, and Zn were 88.12%, 90.21%, and 77.21%, respectively. At a pyrolysis temperature of 400 °C, the stable-Cu and -Ni contents were 97.21% and 99.43%, respectively. The optimal dwelling time was 15 min. The results showed that the CaSiO3 addition weakened the O–H stretching vibration peak intensity, promoted the formation of aromatic and epoxy ring structures, and enhanced the heavy-metal immobilization. Furthermore, the CaSiO3 decomposition during co-pyrolysis produced SiO2, CaO, and Ca(OH)2, which helped stabilize heavy metals.

Experimental study on co-pyrolysis of sludge and biomass straw

In order to maximize the potential energy utilization of agricultural and forestry waste and sludge, the experimental research on co-pyrolysis was carried out for two kinds of sludge (urban industrial sludge, paper sludge) and a typical biomass straw. The results show that adding biomass can effectively improve sludge pyrolysis characteristics; biomass straw and sludge, there are complex interactive effects between components in the co-pyrolysis process, and the characteristic parameters show nonlinear changes. When industrial sludge is mixed with straw, with the increase of straw content, the initial temperature of pyrolysis gradually decreases, the termination temperature increases, the peak of pyrolysis reaction rate and the corresponding temperature gradually increase, and the pyrolysis index gradually increases; when paper sludge is mixed with straw, with the increase of straw content, the initial temperature of pyrolysis gradually decreases, the termination temperature increases, the peak of pyrolysis reaction rate gradually increases, while the peak corresponding temperature gradually decreases, and the pyrolysis index gradually decreases. Combined with characteristic parameters and reaction kinetics analysis, it is suggested that the straw mixing proportion should be controlled at about 25% during the co-pyrolysis of industrial sludge and straw. During the co-pyrolysis of paper sludge and straw, it is suggested to control the straw blending ratio at about 75%.

Characteristics of Pyrolysis and Copyrolysis Products Sewage Sludge in Different Temperature Ranges

Rapid modernization, population growth, and improvement in people’s quality of life have resulted in an increase in urban sewage sludge as the main solid waste. At present, pyrolysis is the main treatment method for sludge due to carbon-free effects and less air pollution compared with incineration. To enhance the energy utilization value of sludge, copyrolysis of sludge and biomass with varying effects has been reported. Herein, biomass and sludge were pyrolyzed and copyrolyzed using self-designed fixed-bed pyrolysis and condensation collection system. The pre-fixed-bed process parameters were optimized by orthogonal test, and it was found that the carrier gas flow rate (a) > bed thickness (b) > constant temperature time (c). The optimum process combinations were 250 mL/min carrier gas, 10 mm bed thickness, and 10 min constant temperature. Experiments show that the ultimate pyrolysis temperature affects the oil production of fixed-bed pyrolysis by up to 15%. Copyrolyzing Sargassum thunbergii and sludge boost oil output at first and then drops; the maximum value is at 20% sludge. When pine sawdust and sludge were copyrolyzed, oil output climbed marginally and subsequently fell fast; the highest value was at 20% sludge. Peanut shell and sludge copyrolysis yield the most oil at 40% sludge content, and the experimental value is smaller than the linear value at 80% sludge content.

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 industrial sludge and rice straw: Synergistic effects of biomass on reaction characteristics, biochar properties and heavy metals solidification

Co-pyrolysis of sludge and biomass was conducted to produce biochar with heavy metals solidification. The synergistic coupling mechanism and the surface functional groups and pore structure characteristics of co-pyrolytic biochar were studied. The solidification characteristics and mechanism of heavy metals were also investigated. Biomass composition in the co-pyrolysis system provided energy, solidified heavy metals and improved product quality. Compared with the weighted calculated value of two individual materials, the secondary decomposition process of co-pyrolysis was prolonged by approximately 80 °C and enhanced by 29%. OH bond, CH bond, and CO bond of co-pyrolytic biochar obtained at 500 °C increased significantly, and the carbon network structure and skeleton were enhanced, and the specific surface area increased by 102.8%, comparing with that of sludge biochar. The solidification effect of Cu and Cd in co-pyrolytic biochar was 29% and 50% higher than that in sludge biochar, respectively. The leaching rates of Cu and Cd in co-pyrolytic biochar were only 38.22% and 39.54% of that from sludge biochar. This study demonstrated that high-quality biochar with low heavy metal risk can be obtained by co-pyrolysis technology, which provides a potential way for the comprehensive utilization of industrial sludge and biomass.

Co-pyrolysis of sludge and kaolin/zeolite in a rotary kiln: Analysis of stabilizing heavy metals

Co-pyrolysis of sludge and kaolin/zeolite in a rotary kiln: Analysis of stabilizing heavy metals

Desorption characteristics of phosphate and ammonium from sludge-based biochar

ABSTRACT It is effective to adsorb phosphate and ammonium from water by sludge-based biochar, while the desorption performance has not been studied systematically. Biochar in this study was prepared through the co-pyrolysis of sludge and walnut shells to remove and from water. The desorption characteristics of and from the post-adsorption sludge-based biochar were investigated. The effects of the adsorption condition (concentration of adsorption solution) and desorption conditions (pH value of desorption solution and desorption temperature and time) on desorption performance were examined. Several techniques were performed to characterise the properties of the post-adsorption sludge-based biochar. The adsorption amount of the pure sewage sludge biochar (SBC) for and the biochar derived from the co-pyrolysis of sewage sludge and walnut shell with the mixing ratio of 3:1 (MBC3-1) for were 14.19/ 23.75 mg/g and 9.28/ 16.23 mg/g, respectively, when the concentrations of the adsorbates were 100 and 500 mg/L. The desorption experiments showed that the acidic condition (pH = 2) was beneficial for and desorption. The highest desorption ratio reached 7.58% for and 2.18% for . The desorption of was endothermic, whereas that of was exothermic. The desorption amounts of and decreased and increased, respectively, with the increase in desorption time. This study of the desorption characteristics of and in sludge-based biochar provides a theoretical basis for the subsequent utilisation of sludge-based biochar.

Optimized preparation of activated carbon from coconut shell and municipal sludge

A low-cost and well-developed type of activated carbon (AC) was synthesized from coconut shell and municipal sludge via two-stage co-pyrolysis. It not only reused disposed sewage sludge and agricultural waste, but also turned waste into a porous adsorbent. The optimization of operating variables during the synthetic process was carried out using a single factor experiment. Simultaneously, the preparation conditions and interactions between factors were further optimized with the Box-Behnken design (BBD) of response surface methodology (RSM). The optimal conditions were determined as: an activation temperature of 800 °C, an activation time of 60 min, an activator concentration of 2.5 mol/L, a 50% addition of coconut shell, a carbonization temperature of 500 °C, a carbonization time of 45 min, 2.5 mol/L KOH, an impregnation ratio of 1.5:1 and a time of 20 h, under which a iodine value of 698.37 mg/g was achieved. Activation temperature was found to be the most significant factor affecting the iodine value of AC, and there was an interaction between these some factors (activation temperature, activation time and activator concentration). Some characterizations (FT-IR, SEM, Boehm's titration and textural test) were also used to measure the physicochemical properties of optimized activated carbon (AC0). The FT-IR results indicated that abundant oxygen-containing functional groups (C–O, O–H and CO) were observed on the surface of AC0 with irregular and well-developed porosity. These functional groups may have stemmed from carboxylic groups (0.99 mmol/g), lactonic groups (0.45 mmol/g) and phenolic groups (0.79 mmol/g) after co-pyrolysis of sludge and coconut shell. The total surface area (680.34 m2/g) and volume (0.73 cm3/g) of AC0 were obviously higher than those of activated carbon from municipal sludge (MSAC). By comparing the adsorption performances, the iodine value of AC0 was found to be superior to that of other carbon adsorbents. These consequences demonstrated that the physicochemical properties of AC employed in the field of adsorbents were improved due to the addition of biomass. The waste disposal method satisfied the demand of the current market and environmental requirements.

Cumulative effects of bamboo sawdust addition on pyrolysis of sewage sludge: Biochar properties and environmental risk from metals

A novel type of biochar was produced by mixing bamboo sawdust with sewage sludge (1:1, w/w) via a co-pyrolysis process at 400–600°C. Changes in physico-chemical properties and the intrinsic speciation of metals were investigated before and after pyrolysis. Co-pyrolysis resulted in a lower biochar yield but a higher C content in the end product compared with use of sludge alone as the raw material. FT-IR analysis indicates that phosphine derivatives containing PH bonds were formed in the co-pyrolyzed biochars. In addition, co-pyrolysis of sludge with bamboo sawdust transformed the potentially toxic metals in the sludge into more stable fractions, leading to a considerable decrease in their direct toxicity and bioavailability in the co-pyrolyzed biochar. In conclusion, the co-pyrolysis technology provides a feasible method for the safe disposal of metal-contaminated sewage sludge in an attempt to minimize the environmental risk from potentially toxic metals after land application.

Effect of lignin on the co-pyrolysis of sludge and cellulose

ABSTRACTIn order to investigate the role of the lignin in the co-pyrolysis process of the sludge and the cellulose, the co-pyrolysis process was carried out in a thermogravimetry analyzer. The result shows that when the proportion of the sludge:cellulose:lignin was 1:1:0.4, the main co-pyrolysis temperature range was narrower, the ultimate pyrolysis weight loss was more, and the synergistic effect had a longer duration time. When the pyrolysis temperature was below 400°C, the addition of the lignin could promote the co-pyrolysis process of the cellulose and the sludge, such as the decrease of the activation energy E.

Self-heating co-pyrolysis of excessive activated sludge with waste biomass: Energy balance and sludge reduction

In this work, co-pyrolysis of sludge with sawdust or rice husk was investigated. The results showed that the co-pyrolysis technology could be used to dispose of the excessive activated sludge without external energy input. The results also demonstrated that no obvious synergistic effect occurred except for heat transfer in the co-pyrolysis if the co-feeding biomass and sludge had similar thermogravimetric characteristics. The experimental results combined with calculation showed that adding sawdust accounting for 49.6% of the total feedstock or rice husk accounting for 74.7% could produce bio-oil to keep the energy balance of the co-pyrolysis system and self-heat it. The sludge from solar drying bed can be further reduced by 38.6% and 35.1% by weight when co-pyrolyzed with rice husk and sawdust, respectively. This study indicates that sludge reduction without external heat supply through co-pyrolysis of sludge with waste biomass is practically feasible.