Pyrolysis Of Municipal Sludge Research Articles

Nitrogen recycling characteristics in multiphase transformation during municipal sludge pyrolysis

The nitrogen content of municipal sludge is as high as 2.5～9.0 wt%, which has become an important problem in pollution control during pyrolysis. Recycling nitrogen from municipal sludge not only enables resource utilization, but also reduces the nitrogen-related pollution. In this study, the transformation pathways of nitrogen to resource material and typical pollutants during the municipal sludge pyrolysis process were analyzed. The results showed that the nitrogen species in municipal sludge were mainly protein-N (64.41%), pyridine-N (19.47%) and inorganic-N (16.13%). After pyrolysis at 300 °C, the peptide bond of protein-N was gradually broken down, resulting in the formation of three nitrogenous intermediates (amine-N, nitrile-N and heterocyclic-N) were produced. These intermediates can be transformed to NH3 for resource recovery or to HCN pollutants. Moreover, the full nitrogen transformation pathways of municipal sludge pyrolysis were constructed by the method of Spearman's correlation coefficient and experiment analysis. It was found that NH3 and HCN were mostly generated from the cracking of three nitrogenous intermediates at 600–800 °C. In addition, there was a prominent effect on the transformation of HCN to NH3 with co-presence of calcium minerals in raw sludge. By adding inorganic calcium minerals, NH3 as a recyclable component was prominently improved by 10.30% at 700 °C, while HCN yield was decreased by 53.02% accordingly under the inhibitory effect. The results systematically provided a theoretical support to the possibility of nitrogen recycling for utilization during municipal sludge pyrolysis, as well as to control the transformation of nitrogen elements into pollutants.

Study on pyrolysis behavior of municipal sludge based on TG-FTIR-MS

Sludge pyrolysis, as a new sludge disposal technology, can realize the reduction and resource utilization of municipal sludge. Based on TG-FTIR-MS technology, pyrolysis behaviors such as pyrolysis reaction kinetics, pyrolysis product composition and other pyrolysis behaviors of four common municipal sludges (SD, NJ, CS, TJ) at different pyrolysis rates were investigated in this paper, and the migration and transformation of nitrogen elements in municipal sludge were analyzed. The results showed that the pyrolysis of municipal sludge was mainly divided into three stages: dewatering (below 160 °C), volatile decomposition (160–550 °C), and carbonization stage (550–900 °C). The activation energies of the four sludge pyrolysis stages were 189.75 kJ/mol, 138.13 kJ/mol, 300.76 kJ/mol, and 237.83 kJ/mol, respectively. It was found that the sludge pyrolysis stage followed the stochastic nucleation and subsequent growth mechanism through the study of SD and CS sludge. The pyrolysis gaseous product content was affected by the rate of heating and pyrolysis temperature. Moderate temperatures (400–550 °C) favored complete sludge decomposition. Sludge is more likely to decompose in a narrow temperature range at higher heating rates, and increasing the heating rate accelerates sludge decomposition. The nitrogenous compounds in sludge are mainly pyrrole nitrogen, protein nitrogen, and pyridine nitrogen. During sludge pyrolysis, the nitrogenous compounds decompose and precipitate in the form of heterocyclic nitrogen (pyridine, pyrrole), and release small molecules of nitrogenous compounds (NH3, HCN, HCNO). The experimental results can provide a reference for the disposal of municipal sludge by pyrolysis.

The conversion and migration behavior of phosphorus speciation during pyrolysis of different sludges

<abstract> <p>The study was enforced to probe the conversion and migration behavior of phosphorus speciation in sludge and the biochar received from pyrolysis of municipal sludge (MS), town sludge (TS), and slaughterhouse sludge (SS). This study creatively used fractionation of soil phosphorus to further differentiate speciation of phosphorus in three sludges (MS, TS, and SS). According to the x-ray diffraction (XRD) analysis and sequential extraction, the study proved the dependence of P speciation conversion on pyrolysis temperature and different types of raw sludge. The results of P-fractionation indicated that Ca-bound IP (Ca-IP) content in all biochars significantly increased at pyrolysis temperature of 350–800 ℃, and the proportion of soluble and loosely bound IP (SL-IP), aluminum-bound IP (Al-IP), and Fe-bound IP (Fe-IP) of MS and SS decreased. The difference is that the Al-IP in the TS increased slightly as the pyrolysis temperature increased. Among the three kinds of sludge, the Olsen-P of TS is the lowest because the content of Olsen-P in sludge will decrease with the decrease of pH in the process of sewage treatment after acidification. In addition, XRD patterns of three sludges and biochar further confirmed the low crystallinity of AlPO<sub>4</sub> minerals. Through in-depth research on the environmental behavior of phosphorus, this study might additionally provide essential knowledge for the recovery and utilization of phosphorus in sludge.</p> </abstract>

Effect of different calcium salts on phosphorus availability and immobilization of heavy metals in municipal sludge derived biochar

Transforming municipal sludge (MS) into biochar via co-pyrolysis with calcium salts enhances phosphorus (P) recovery and reduces the risk of heavy metal contamination. In this study, the performance and mechanism of bioavailable P conversion and heavy metal stabilization were systematically compared under co-pyrolysis of MS with CaCO3, CaO, and CaCl2 at mass ratios of 2.5–10 % at 700 °C. The results showed that CaCl2 had the best ability to convert P from non-apatite inorganic P to apatite P, followed by CaO and then CaCO3. CaO and CaCO3 addition induced more Ca5(PO4)3OH formation, while CaCl2 induced more Ca2PO4Cl and Ca5(PO4)3Cl formation. The degree of stabilization of heavy metals (e.g., Cd, Cr, Cu, Ni, Pd, and Zn) was significantly improved after co-pyrolysis of MS with these salts, thus reducing the potential environmental risk. In particular, because of the dual action mechanism of chloride ions and calcium ions, co-pyrolysis with CaCl2 exhibited the lowest risk of heavy metal contamination compared with CaCO3 and CaO. These findings suggest that addition of 2.5 % CaCl2 can optimize the production of bioavailable P and the stabilization of heavy metals in biochar. This treatment is recommended for the safe utilization of P resources derived via MS pyrolysis.

Effects of volatile-char interaction on the product properties from municipal sludge pyrolysis

In order to realize the harmless treatment and resource utilization of municipal sludge, the effect of volatile-char interaction on the properties of sludge pyrolysis products was investigated using a two-stage pyrolysis reactor. The experimental results show that volatile-char interaction promotes the decomposition of organic compounds into small molecular gases, which increases the gas yield and reduces the liquid and oil yields. Under the experimental conditions, the volatile-char interaction increases the mass yields of H2, CO and CO2 to varying degrees, and the yield of H2 increases maximum by 55.7–114.5% compared to that without interaction. The effect of interaction on the composition of bio-oil occurs mainly at low temperature range of 400–600 ℃ by reducing the content of oxygen-containing compounds except for aldehydes/ketones. The physical and chemical structure of solid char changes dramatically with the interaction. The enhanced removal of O-containing groups occurs and the degree of aromaticity of the char is increased due to the strengthened dehydrogenation and polycondensation of hydrocarbons. Meanwhile, the transformation of non-hydroxyapatite phosphorus to hydroxyapatite phosphorus in solid phase products is greatly promoted at high temperature of 700–800 ℃, increasing the potential utilization of char as carbon-based phosphate fertilizer in agriculture.

Removal of Cr(VI) from aqueous solutions by nZVI-loaded sludge-derived biochar: performance and mechanism.

With the rapid development of highland railways in China, a large amount of heavy metal wastewater was inevitably generated during the manufacturing process of alloy materials required for railway construction. In this paper, pyrolysis of municipal sludge was followed by ball milling to obtain ball milling sludge-derived biochar(SDBC), and then nZVI-loaded SDBC materials (nZVI@SDBC) were prepared by liquid-phase reduction. The effects of different factors on the Cr(VI) removal were investigated. The maximum Cr(VI) adsorption capacity of nZVI@SDBC(2:1) was 178.05 mg/g. The Cr(VI) removal process could be fitted by the Langmuir isotherm and pseudo-second-order kinetic model. The Cr(VI) removal mechanism mainly included complexation, reduction, electrostatic interaction, and coprecipitation. The Cr(VI) removal by nZVI@SDBC(2:1) was maintained at over 90% after five replicate experiments. nZVI@SDBC(2:1) was capable of removing most of the Cr(VI) from real electroplating wastewater. The cost of using nZVI@SDBC(2:1) to remove 1 m3of actual wastewater is approximately325.7162 USD/m3.This workprovided a new ideafor thesolutionof Cr(VI)-containingwastewater from the production of railway materials.

Effects of Three Sludge Products from Co-Treatment of Wastewater on the Soil Properties and Plant Growth of Silty Loam

Currently, little is known about systematic comparisons of sludge products obtained from different sludge treatment processes in terms of land use. Moreover, it is worth evaluating whether the sludge produced from the co-treatment of industrial wastewater and domestic sewage can be applied to land use. In this study, three sludge products derived from the same municipal sludge—sludge biochar (SSB), dried sludge (DSS), and sludge compost (SSC)—were added to silty loam (SL) at a 20% mass ratio to assess their effects on soil structure, properties, and fertility. Chinese cabbage was planted as a model crop and its growth and physiological state were monitored. The experimental results showed that the water retention of the soil was significantly related to its porosity, and the moisture in the three sludge products-modified soil mainly existed in the form of free water. The addition of three sludge products increased the total porosity of SL. SSC enhanced the water retention of SL by increasing the capillary porosity, and SSB improved the gas permeability of SL by increasing the non-capillary porosity. The three sludge products all increased the content of large particles in the soil and improved the stability of the aggregates of SL. Among them, SSB and DSS had significant effects on improving the stability of the aggregates. Although the addition of the three sludge products improved the fertility of SL, compared with that of DSS and SSC, the addition of SSB made the growth indices of Chinese cabbage the best, indicating that SSB can effectively maintain soil nutrients. The heavy metal test results of Ni showed that SSB had a good stabilizing effect on heavy metals. Therefore, compared with drying and composting, pyrolysis of municipal sludge is more suitable for SL improvement.

Effects of Volatile-Char Interaction on the Product Properties from Municipal Sludge Pyrolysis

Effects of Volatile-Char Interaction on the Product Properties from Municipal Sludge Pyrolysis

Migration and Environmental Effects of Heavy Metals in the Pyrolysis of Municipal Sludge

Migration characteristics of the heavy metals Fe, Zn, Mn, and Ni during the preparation of biochar from municipal sludge were studied, and the optimal pyrolysis temperature for the preparation of biochar was determined based on potential environmental risks. Four heavy metals (Fe, Zn, Mn, and Ni) with high total contents in the biochar were selected to determine their species and content changes under different pyrolysis temperatures using the BCR extraction method. An environmental risk assessment for sludge-based biochar was also carried out using the potential ecological risk index (PERI) and risk assessment code (RAC). The results showed that the volatility of the four metals is ranked as follows:Zn>Mn>Fe>Ni. The distribution and transformation of the four metal species were different, but their migration paths shared similar characteristics. In the pyrolysis stage at low temperatures (<500℃), unstable fractions gradually changed into more stable species; under high temperatures (>500℃), some of the oxidizable and residual fractions were broken, which transformed into reducible fractions, and other fractions escaped into the atmosphere. In the environmental risk assessment, biochar prepared under high pyrolysis temperatures (>500℃) showed lower environmental risks, with the best outcomes at 500℃.

Sludge biochar as a green additive in cement-based composites: Mechanical properties and hydration kinetics

Biochar is a green material obtained from the thermochemical decomposition of biosolids under an anaerobic or oxygen-limited condition. Although sludge pyrolysis has been extensively studied in municipal sludge (MS) disposal, it is challenging to utilize the formed sludge biochar (SB) products. This study developed a novel and sustainable method for incorporating SB-derived biochar in cement-based composites, providing an economical and efficient way of recycling such wastes. A series of SB were prepared under different pyrolysis processes to replace 2% cement. Numerous mechanical, physical, microstructural and isothermal calorimetry analyses were used to study the performances of the SB incorporated cement composites. The results showed that the mobility of the composites declined slightly with the addition of SB. Pyrolysis regimes played a key role in influencing the strength, and the optimum performance was obtained at a pyrolysis regime of 500 °C and residual time of 60 min, which increased the 1 d and 28 d strengths by 29.3% and 5.8%, respectively. The addition of SB accelerated the formation of more hydration products, increased the hydration degree and led to a denser matrix. All these improvements were ascribed to the internal curing effect of sludge biochar and a decrease in the ratio of local water to cement. Thermal analysis by Krstulovic-Dabic Model indicated that the hydration mechanisms of biochar-cement composites belonged to nucleation and crystal growth (NG)- interactions at phase boundaries (I)-diffusion (D). The SB incorporated sample possessed more nucleation sites with a higher reaction rate constant at NG stage and shorter I stage. In addition, environmental risk assessment revealed that SB was a safe additive in cement-based composites. Therefore, pyrolysis of MS under appropriate temperature conditions has great potential to provide a green biochar in cement-based composites and thereby offers an alternative and viable way of disposal of MS.

Pyrolysis derived char from municipal and industrial sludge: Impact of organic decomposition and inorganic accumulation on the fuel characteristics of char

A comprehensive study was conducted to evaluate the fuel properties of the char produced from pyrolysis of municipal sludge (MS) and industrial sludge (IS) at different pyrolysis temperatures (500–700 °C). A detailed characterisation of the char was performed to investigate the impact of the decomposition and the accumulation of organic and inorganic compounds during pyrolysis on the fuel properties of the derived char. Increase in pyrolysis temperature increased the fuel ratios especially in the MS-derived char. On the other hand, ash accumulation resulted in decreased higher heating values (HHVs). Dehydration and decarboxylation were the main reactions, which caused the decomposition of the organic compounds in raw sludge during pyrolysis. Thermogravimetric analysis results showed that high temperature pyrolysis could improve the thermal stability of the derived char. The accumulation of catalytic inorganic compounds improved the combustion reactivity of both the IS and MS-derived char. The MS-derived char showed higher slagging and ash fouling indices compared to the IS-derived char despite the lower ash content. However, slagging and ash fouling indices of the char were comparable to that of raw sludge samples. The results indicate that the accumulation and physicochemical transformations of heavy metals during pyrolysis process would not be significantly affected during combustion of the char. For practical application in combustion, the MS-derived char has a greater potential due to considerable HHVs, improved thermal stability, efficient combustion characteristics, lower heavy metals leaching and comparable ash related issues.

Pilot-scale pyrolysis experiment of municipal sludge and operational effectiveness evaluation

ABSTRACTTo promote engineering application of municipal sludge pyrolysis technology, pilot-scale sludge pyrolysis device systems integrated were set up to study the effectiveness of sewage sludge pyrolysis. With the application of various operating conditions, the optimal conditions and products were obtained. And comparing the operational effectiveness of pilot-scale experiment with the bench experiment, the optimal operating conditions and product characteristics coincide with those of the bench experiment. Through energy balance analysis, energy produced from pyrolysis oil and gas together or just from sewage-char is almost sufficient to supply the energy required for sewage sludge pyrolysis.

Application of Bio-Char from Sewage Sludge Pyrolysis

To promote engineering application of municipal sludge pyrolysis technology and reduce economic cost of sludge pyrolysis operation, the paper discussed the feasibility of sludge-based char application in three aspects: sewage adsorbent, fuel and soil improving agent. Conclusion: the sludge-based char on SCOD adsorption time in the 30min reaches saturation, the SCOD removal rate above 30%; the removal rate of sludge-carbon on A/O reactor effluent COD have less effect, but there are certain effect on nitrogen removal; the sludge-based char can be burned at 400°C, release a lot of heat, it can be used as a low-grade fuel; the sludge-based char can promote plants growth, and has a good safety performance, may be used as a good soil improving agent.

Pyrolysis Characteristics and Kinetics of Municipal Sludge by Thermogravimetry-Fourier Transform Infrared Analysis (TG-FTIR)

To obtain the pyrolysis characteristics and kinetics during the pyrolysis of municipal sludge, the characteristic of mass loss and the pyrolysis gas products were analyzed by TG-FTIR and the kinetic parameters were calculated by the Coats-Redfem method. The results indicate that the pyrolysis process of municipal sludge in nitrogen can be divided into three stages including dehydration, degradation of organic matters, and decomposition of inorganic minerals and undecomposed organic matters when the heating rate is 15 °C/min. CO2, CO, CH4, some aldehydes and carboxylic acids are the major pyrolysis gas products. Among these gasses, CO2 accounts for a large proportion. The kinetic parameters are different in the different pyrolysis stages. The activation energies and pre-exponential factors are in the range of 59.58~150.30 kJ/mol and 1.64×107~6.03×1011 min-1, respectively.