Preparation and characterization of bio-oils from internally circulating fluidized-bed pyrolyses of municipal, livestock, and wood waste

Remediation of heavy metals polluted soil environment: A critical review on biological approaches

Heavy metals (HMs) pollution is a globally emerging concern. It is difficult to cost-effectively combat such HMs polluted soil environments. The efficient remediation of HMs polluted soil is crucial to protect human health and ecological security that could be carried out by several methods. Amidst, biological remediation is the most affordable and ecological. This review focused on the principles, mechanisms, performances, and influential factors in bioremediation of HMs polluted soil. In microbial remediation, microbes can alter metallic compounds in soils. They transform these compounds into their metabolism through biosorption and bioprecipitation. The secreted microbial enzymes act as transformers and assist in HMs immobilization. The synergistic microbial effect can further improve HMs removal. In bioleaching, the microbial activity can simultaneously produce H2SO4 or organic acids and leach HMs. The production of acids and the metabolism of bacteria and fungi transform metallic compounds to soluble and extractable form. The key bioleaching mechanisms are acidolysis, complexolysis, redoxolysis and bioaccumulation. In phytoremediation, hyperaccumulator plants and their rhizospheric microbes absorb HMs by roots through absorption, cation exchange, filtration, and chemical changes. Then they exert different detoxification mechanisms. The detoxified HMs are then transferred and accumulated in their harvestable tissues. Plant growth-promoting bacteria can promote phytoremediation efficiency; however, use of chelants have adverse effects. There are some other biological methods for the remediation of HMs polluted soil environment that are not extensively practiced. Finally, the findings of this review will assist the practitioners and researchers to select the appropriate bioremediation approach for a specific soil environment.

Transformation pathways of the carbon-containing group compounds during municipal sludge pyrolysis treatment

Municipal sludge contains abundant amounts of carbon, with contents ranging from 14 % to 38 %. The various carbon-containing group compounds can be converted into beneficial products, but pollutants and greenhouse gases are also released through the municipal sludge pyrolysis process. Ascertaining the pathways by which carbon-containing group compounds is converted and transformed is crucial for addressing pollution concerns and promoting recycling. This study explored the transformation pathways of carbon-containing group compounds during the pyrolysis process of municipal sludge. The results showed that the three major carbon-containing group compounds including protein (61 %), cellulose (9 %), and hemicellulose (7 %), had significantly different pyrolysis temperature of 600 °C, 400 °C and 300 °C. In terms of gas pollution, most carbon was fully pyrolyzed into CO2. While the temperature raised up to 500 °C, a part of the CO2 converted into CO. Meanwhile, the various carbon-containing compounds exhibited distinct effects on gas production, which CH4 was produced more with cellulose and protein presenting in the sludge. When temperature increased to 700 °C, the 60 % of the carbon-containing group compounds were transformed into liquid and solid. The pyrolysis liquid in the low-temperature stage (30-300 °C) contained a relatively high aliphatics content and lower organooxygen species (OOSs) content (at 200 °C), suggesting a potential for resource utilization. The yield of CO in the gas rapidly increased as the temperature increased in the high-temperature stage (500-700 °C). The insights from this study hold practical implications for enhancing municipal sludge pyrolysis efficiency, reducing pollution, and facilitating more sustainable and resource-efficient practices.

Pyrolysis of food waste and food waste solid digestate: A comparative investigation

The effects of anaerobic digestion (AD) on pyrolysis were elaborated by comparing the pyrolysis performance of food waste (FW) and food waste solid digestate (FWSD). The pyrolysis mechanisms of FW and FWSD were revealed by experimental and kinetic analysis. The properties and potential applications of pyrolytic products from FW and FWSD were discussed. The results showed that part of organic matters of FW were consumed during AD, which altered the pyrolysis performance of FWSD. The pyrolytic gas from FW had better quality due to its higher lower heating value (LHV) (20.52 kJ/Nm³). The pyrolytic oil and biochar derived from FWSD showed better qualities as oil fuel and carbon-based absorbent. Pyrolysis of FWSD produced less nitrogen-containing pollutants (NCPs) indicated that AD coupled with pyrolysis is more environmental-friendly to treat FW. This study provides potential approach and theoretical guidance for the treatment and resource utilization of FW and FWSD.

Liquefaction of Cellulose for Production of Advanced Porous Carbon Materials

Cellulose is a renewable resource for the production of advanced carbonaceous materials for various applications. In addition to direct carbonization, attention has recently been paid to the preparation of porous carbons from liquid cellulose-based precursors. Possible pathways of cellulose conversion to a liquid state suitable for the preparation of porous carbons are summarized in this review. Hydrothermal liquefaction leading to liquid mixtures of low-molecular-weight organics is described in detail together with less common decomposition techniques (microwave or ultrasound assisted liquefaction, decomposition in a strong gravitation field). We also focus on dissolution of cellulose without decomposition, with special attention paid to dissolution of nonderivatized cellulose. For this purpose, cold alkalines, hot acids, ionic liquids, or alcohols are commonly used.

Progress of the Pyrolyzer Reactors and Advanced Technologies for Biomass Pyrolysis Processing

In the future, renewable energy technologies will have a significant role in catering to energy security concerns and a safe environment. Among the various renewable energy sources available, biomass has high accessibility and is considered a carbon-neutral source. Pyrolysis technology is a thermo-chemical route for converting biomass to many useful products (biochar, bio-oil, and combustible pyrolysis gases). The composition and relative product yield depend on the pyrolysis technology adopted. The present review paper evaluates various types of biomass pyrolysis. Fast pyrolysis, slow pyrolysis, and advanced pyrolysis techniques concerning different pyrolyzer reactors have been reviewed from the literature and are presented to broaden the scope of its selection and application for future studies and research. Slow pyrolysis can deliver superior ecological welfare because it provides additional bio-char yield using auger and rotary kiln reactors. Fast pyrolysis can produce bio-oil, primarily via bubbling and circulating fluidized bed reactors. Advanced pyrolysis processes have good potential to provide high prosperity for specific applications. The success of pyrolysis depends strongly on the selection of a specific reactor as a pyrolyzer based on the desired product and feedstock specifications.

Influence of Phenethyl Acetate and Naphthalene Addition before and after Pyrolysis on the Quantitative Analysis of Bio-Oil

The condensation-collection and quantitative analysis of bio-oil limit its component investigation and utilization. In order to find a convenient method for the analysis of bio-oil, the present study conducted an attempt for bio-oil quantitative analysis with the addition of internal standards before pyrolysis. Based on their good thermal stability, phenethyl acetate and naphthalene were selected as standards in the study and experiments were carried out to compare the effects of two added modes (adding into the biowaste before pyrolysis or adding into bio-oil after pyrolysis) on the bio-oil analysis. The results showed that both phenethyl acetate and naphthalene were mainly volatilized under testing conditions, which could be transferred into the oil with the volatile matters during biowaste pyrolysis. Through the co-pyrolysis experiments of the internal standards with lignin and cellulose, almost no interactions were found between the internal standards and such components. Furthermore, adding these standards before pyrolysis hardly affected the properties of noncondensable gas and biochar from the used biowaste samples (tobacco and sawdust waste). Compared with the bio-oil analysis results via traditional methods by adding standards into the bio-oil after pyrolysis, the results regarding the component distribution characteristics of the bio-oil were similar using the proposed method through the addition of standards before pyrolysis. Considering adequate mixing of the added standards (before pyrolysis) in the generated bio-oil, the proposed method could partly help to avoid inaccurate analysis of bio-oil components caused by incomplete collection of the pyrolytic volatiles.

Comparative study for fluidized bed pyrolysis of textile dyeing sludge and municipal sewage sludge

A comparative research was performed to evaluate the products yields and chars properties for pyrolysis of textile dyeing sludge (TDS) and municipal sewage sludge (MSS). The high fixed carbon (19.36 wt%) and low volatile (23.66 wt%) contents of TDS resulted in higher char yields and lower condensate yields. TDS char (TC) had a higher sulfur (S) retention efficiency than MSS char (MC) and CaO exhibited a great S retention effect in MC. More alkali and alkaline earth metals (e.g. Na, K, Mg and Ca) in MSS contributed to enhanced catalytic pyrolysis. In comparison to non-catalytic pyrolysis, chars from catalytic pyrolysis had lower iodine number and higher methylene blue (MB) adsorption value. MB adsorption values of MC (212.28-414.20 mg/g) were much higher than those of TC (84.32-156.07 mg/g). In contrast, heavy metals risk degrees of MC (4.20-7.56) were lower than those of TC (7.55-12.87), and heavy metals in TC and MC showed slight risks to environment.

Co-pyrolysis of sewage sludge and manure

The management and valorization of residual organic matter, such as sewage sludge and manure, is gaining interest because of the increasing volume of these residues, their localized generation and the related problems. The anaerobic digestion of mixtures of sewage sludge and manure could be performed due to the similarities between both residues. The purpose of this study is to evaluate the feasibility of the co-pyrolysis of sewage sludge (SS) and digested manure (DM) as a potential management technology for these residues. Pyrolysis of a sewage sludge/manure blend (50:50%) was performed at 525°C in a stirred batch reactor under N₂ atmosphere. The product yields and some characteristics of the product were analyzed and compared to the results obtained in the pyrolysis of pure residues. Potential synergetic and antagonist effects during the co-pyrolysis process were evaluated. Although sewage sludge and manure seem similar in nature, there are differences in their pyrolysis product properties and distribution due to their distinct ash and organic matter composition. For the co-pyrolysis of SS and DM, the product yields did not show noticeable synergistic effects with the exception of the yields of organic compounds, being slightly higher than the predicted average, and the H₂ yield, being lower than expected. Co-pyrolysis of SS and DM could be a feasible management alternative for these residues in locations where both residues are generated, since the benefits and the drawbacks of the co-pyrolysis are similar to those of the pyrolysis of each residue.

The effect of bioleaching on sewage sludge pyrolysis

The effects of bioleaching on sewage sludge pyrolysis were studied. Sewage sludge was treated by bioleaching with solid concentrations of 6% (w/v), 8% (w/v), 10% (w/v). Results showed that bioleaching treatment could modify the physicochemical properties of sewage sludge and enhance the metals removal. The optimum removal efficiencies of heavy metals were achieved with solid concentration of 6% (w/v) bioleaching treatment: Cu, 73.08%; Zn, 78.67%; Pb, 24.65%; Cd, 79.46%. The characterization results of thermogravimetric analysis (TGA) showed that the bioleached sewage sludge with a 6% (w/v) solid concentration treatment was the easiest to decompose. Pyrolytic experiments of bioleached sewage sludge were performed in a laboratory-scale fixed bed reactor. Results indicated that bioleaching treatment greatly influenced the product yields and gas composition.

Bio-oil production from eight selected green landscaping wastes through hydrothermal liquefaction

This study investigated the potential of eight types of green landscaping waste as feedstock to produce bio-oil through hydrothermal liquefaction (HTL).

Pyrolysis of mangaba seed: production and characterization of bio-oil

The aim of this study was to evaluate the potential of Hancornia speciosa GOMES (mangaba) seeds as a novel matrix for the production of bio-oil. The study was divided into three steps: (i) characterization of the biomass (through elemental analysis (CHN), infrared spectroscopy (FTIR-ATR), thermogravimetry (TG), and determination of biomass composition; (ii) pyrolysis of mangaba seed to obtain the bio-oil; and (iii) characterization of the bio-oil (thermogravimetry and gas chromatography/mass spectrometry-GC/qMS). The TG of the sample showed a mass loss of around 90% in 450°C. In the pyrolysis experiments the variables included temperature (450 and 600°C), sample mass (5 and 11g) and prior heating (with or without), with the best conditions of 600°C, 11g of seeds and prior heating of the furnace. The GC/qMS analysis identified carboxylic acids and hydrocarbons as the major components, besides the presence of other compounds such as furanes, phenols, nitriles, aldehydes, ketones, and amides.

Comprehensive utilization of the pyrolysis products from sewage sludge

Bio-oils were produced from pyrolysis of sewage sludge in a horizontal tubular furnace under the anoxic or anaerobic conditions, by varying operating parameters and moisture content (MC) of the feedstock. Physicochemical properties of the obtained bio-oil (such as density, acid value, kinematical viscosity, high heating value and flash point) were analysed and compared with Chinese fuel standards. Tend, RT and β were found critical to control the yield and physico-chemical properties of bio-oil products. The relative importance of various parameters such as Tend, RT, β and MC was determined and the optimum values for the lowest kinematic viscosity and acid value and the highest yield of the bio-oil were achieved using the orthogonal matrix method. The parameters 550°C, 45 min, 5°C min(-1) and MC of 10% were found effective in producing the bio-oils with most of the desirable physico-chemical properties and yield. Benefit analysis was conducted to further optimize the operating parameters, considering pyrolysis treatment, comprehensive utilization of the pyrolysis products and final disposal of sewage sludge; the results showed the best economy of the pyrolysis parameters 450°C, 75 min, 3°C min(-1) and MC of 10%. The char obtained under this condition may serve as a microporous liquid adsorbent, while the bio-oil may serve as a low grade fuel oil after upgrading it with conventional fuel oil and deacidification. Pyrolysis products may become economically competitive in addition to being environment friendly.

Characterization of top phase oil obtained from co-pyrolysis of sewage sludge and poplar sawdust

To research the impact of adding sawdust on top phase oil, a sewage sludge and poplar sawdust co-pyrolysis experiment was performed in a fixed bed. Gas chromatography (GC)/mass spectrometry (MS) was used to analyze the component distribution of top phase oil. Higher heating value, viscosity, water content, and pH of the top phase oil product were determined. The highest top phase oil yield (5.13 wt%) was obtained from the mixture containing 15% poplar sawdust, while the highest oil yield (16.51 wt%) was obtained from 20% poplar sawdust. Top phase oil collected from the 15% mixture also has the largest amount of aliphatics and the highest higher heating value (28.6 MJ/kg). Possible reaction pathways were proposed to explain the increase in the types of phenols present in the top phase oil as the proportion of poplar sawdust used in the mixture increased. It can be concluded that synergetic reactions occurred during co-pyrolysis of sewage sludge and poplar sawdust. The results indicate that the high ash content of the sewage sludge may be responsible for the characteristic change in the top phase oil obtained from the mixtures containing different proportions of sewage sludge and poplar sawdust. Consequently, co-pyrolysis of the mixture containing 15 % poplar sawdust can increase the yield and the higher heating value of top phase oil.

Babassu nut residues: potential for bioenergy use in the North and Northeast of Brazil

Babassu is considered the largest native oil resource worldwide and occurs naturally in Brazil. The purpose of this study was to evaluate the potential of babassu nut residues (epicarp, mesocarp and endocarp) for bioenergy use, especially for direct combustion and charcoal production. The material was collected in the rural area of the municipality of Sítio Novo do Tocantins, in the state of Tocantins, Brazil. Analyses were performed considering jointly the three layers that make up the babassu nut shell. The following chemical characterizations were performed: molecular (lignin, total extractives and holocellulose), elemental (C, H, N, S and O), immediate (fixed carbon, volatiles and ash), energy (higher heating value and lower heating value), physical (basic density and energy density) and thermal (thermogravimetry and differential thermal analysis), besides the morphological characterization by scanning electron microscopy. Babassu nut residues showed a high bioenergy potential, mainly due to their high energy density. The use of this biomass as a bioenergy source can be highly feasible, given their chemical and thermal characteristics, combined with a low ash content. Babassu nut shell showed a high basic density and a suitable lignin content for the sustainable production of bioenergy and charcoal, capable of replacing coke in Brazilian steel plants.

Understanding the stability of pyrolysis tars from biomass in a view point of free radicals

Fast pyrolysis of biomass has attracted increasing attention worldwide to produce bio-tars that can be upgraded into liquid fuels and chemicals. However, the bio-tars are usually poor in quality and stability and are difficult to be upgraded. To better understand the nature of the bio-tars, this work reveals radical concentration of tars derived from pyrolysis of two kinds of biomass. The tars were obtained by condensing the pyrolysis volatiles in 3s. It shows that the tars contain large amounts of radicals, at a level of 10(16)spins/g, and are able to generate more radicals at temperatures of 573K or higher, reaching a level of 10(19)spins/g at 673K in less than 30min. The radical generation in the tar samples is attributed to the formation of THF insoluble matters (coke), which also contain radicals. The radical concentrations of the aqueous liquids obtained in pyrolysis are also studied.

Pyrolysis of high-ash sewage sludge in a circulating fluidized bed reactor for production of liquids rich in heterocyclic nitrogenated compounds

A circulating fluidized bed reactor was used for pyrolyzing sewage sludge with a high ash content to produce liquids rich in heterocyclic nitrogenated compounds. GC/MS and FTIR analyses showed that heterocyclic nitrogenated compounds and hydrocarbons made up 38.5-61.21% and 2.24-17.48% of the pyrolysis liquids, respectively. A fluidized gas velocity of 1.13 m/s, a sludge feed rate of 10.78 kg/h and a particle size of 1-2mm promoted heterocyclic nitrogenated compound production. Utilizing heterocyclic nitrogenated compounds as chemical feedstock could be a way for offsetting the cost of sewage sludge treatment.

Fractions composition study of the pyrolysis oil obtained from sewage sludge treatment plant

In this work the parameters of Low Temperature Conversion--LTC were applied in a centrifuged sludge from a sewage treatment plant located in Rio de Janeiro, Brazil. Before the conversion, the sludge was dried and analyzed by TGA to observe its behavior with increasing temperature. The chemical composition of the crude pyrolysis oil was analyzed by FTIR, 1H NMR and GC-MS. The results showed that the oil is a mixture of hydrocarbons, oxygenated and nitrogenated compounds. Using a catalytic treatment it was possible to fractionate the oil where the predominant constituents were hydrocarbons showing that the cracking was effective. An important result was the difference between the calorific value of dry sludge (10 MJ kg(-1)), the pyrolysis oil (36 MJ kg(-1)) and one of the fractions separated by catalytic cracking (40 MJ kg(-1)) when compared with commercial diesel (45 MJ kg(-1)).