[Characteristics of Municipal Solid Waste in Some Urban Agglomeration in the Past Five Years].

The treatment and disposal of municipal solid waste has increasingly become a common concern around the world, and the characteristics of municipal solid waste(MSW) are an important basis for the selection of terminal treatment methods. In this study, more than 400 MSW samples from over 30 cities across China were collected, and the basic physical and chemical properties, such as the physical composition, pollutant content, and calorific value, were analyzed. Shenzhen was taken as an example to analyze the influence of time and waste sorting measures on the physical and chemical characteristics of MSW. The correlation model between MSW composition and calorific value was established using partial least squares(PLS) regression, and the model was verified. The results showed that with per capita GDP increasing by 10,000 yuan, per capita MSW production and the low calorific value of MSW increased by 0.1 kg·(person·d)-1 and 373.8 kJ·kg-1, respectively. However, when per capita GDP was less than 60,000 yuan, the correlation between per capita GDP and per capita MSW production was relatively poor. Kitchen waste was still the most abundant component of MSW, and the content of most samples was between 40% and 60%. The combustible content of rubber/plastic and paper was relatively high, between 20%-30% and 10%-20%, respectively. The inorganic content did not usually exceed 5%, and the moisture content of the MSW was between 50% and 60%. After the implementation of waste classification in 2019, the content of kitchen waste in MSW had been significantly reduced, the content of rubber/plastic had increased, and other components had not changed much. Additionally, the calorific value of waste had been improved to a certain extent. The pollution element contents in MSW, S Cl, and N were all below 1%, and the average value was:N>Cl>S. The contents of Hg, As, Cr, Cd, and Pb in MSW samples did not change significantly with the composition and sampling time, and the content of Pb and Cr in MSW was affected by the environmental background value. The model analysis revealed that rubber/plastics and moisture content were the main variables that affected the calorific value of MSW. The deviation between the measured value and the predicted value was less than 20% for 85.96% of the samples. The model established in this study can meet the needs of the prediction of the calorific value of MSW.

Decentralized wastewater treatment in an urban setting: a pilot study of the circulating fluidized bed bioreactor treating septic tank effluent.

To meet the increasing wastewater treatment demand while minimizing the land footprint of the treatment systems and plants, more efficient and compact processes are needed. The circulating fluidized bed bioreactor (CFBBR) has been proven to achieve high levels of biological nutrient removal. Past studies at the lab and pilot scale achieved 94% COD removal and 80% nitrogen removal at HRT's of 2-4 h. A collaborative project between Western University and the Guangzhou Institute of Energy Conversion (GIEC), in Guangzhou, China, further explored the treatment of municipal wastewater with the CFBBR. A pilot CFBBR, with aerobic and anoxic columns for nitrification and denitrification, was constructed at the GIEC for in-situ treatment of septic tank effluent from a residential building. Due to high concentrations of ammonia (NH4-N), the wastewater had a COD/N ratio of 2-3. Thus, operating at a longer HRT and supplementing COD, in the form of glucose, was necessary to achieve a high nitrogen removal efficiency. The system was run both with and without supplemental COD at HRT's between 16 and 21 h, treating approximately 1000-1270 L/d. Overall, a COD removal efficiency of at least 92%, ammonia removal of 97%, and nitrogen removal of 82% was achieved. The CFBBR system achieved an effluent with BOD and NH4-N concentrations both below 5 mg/L, a NO3-N concentration below 15 mg/L, and a total nitrogen concentration below 25 mg/L. The compact design of this pilot-CFBBR, coupled with its high BNR performance make it an excellent option for decentralized treatment of urban wastewaters.

A molten carbonate shell modified perovskite redox catalyst for anaerobic oxidative dehydrogenation of ethane.

Acceptor-doped, redox-active perovskite oxides such as La0.8Sr0.2FeO3 (LSF) are active for ethane oxidation to CO x but show poor selectivity to ethylene. This article reports molten Li2CO3 as an effective "promoter" to modify LSF for chemical looping-oxidative dehydrogenation (CL-ODH) of ethane. Under the working state, the redox catalyst is composed of a molten Li2CO3 layer covering the solid LSF substrate. The molten layer facilitates the transport of active peroxide (O2 2-) species formed on LSF while blocking the nonselective sites. Spectroscopy measurements and density functional theory calculations indicate that Fe4+→Fe3+ transition is responsible for the peroxide formation, which results in both exothermic ODH and air reoxidation steps. With >90% ethylene selectivity, up to 59% ethylene yield, and favorable heat of reactions, the core-shell redox catalyst has an excellent potential to be effective for intensified ethane conversion. The mechanistic findings also provide a generalized approach for designing CL-ODH redox catalysts.

Impact of ball-milling and ionic liquid pretreatments on pyrolysis kinetics and behaviors of crystalline cellulose.

In this work, the kinetic mechanisms of pyrolysis of cellulose with different physical structures were illustrated. The crystalline cellulose showed better thermal stability and required higher energy for decomposition with more concentrated reactions due to the highly ordered structure. The crystallinity of the ball milling and ionic liquid pretreated cellulose decreased and the structure was relatively loose and disordered, thereby reducing the thermal stability, so the global activation energy of both samples decreased and the intensive reaction caused by the collapse of structure was alleviated. In fast pyrolysis, crystalline cellulose favored fast pyrolytic saccharification, and the highest levoglucosan yield reached 64.3 wt% at 400 °C. This research was helpful to deduce the influence of physical structure on the pyrolytic product distribution of cellulose, thereby providing useful information to promote the development of pyrolytic saccharification.

Controlling Deoxygenation Pathways in Catalytic Fast Pyrolysis of Biomass and Its Components by Using Metal-Oxide Nanocomposites.

Selectively breaking the C-O bonds within biomass during catalytic fast pyrolysis (CFP) is desired, but extremely challenging. Herein, we develop a series of metal-oxide nanocomposites composed of W, Mo, Zr, Ti, or Al. It is demonstrated that the nanocomposites of WO3-TiO2-Al2O3 exhibit the highest deoxygenation ability during CFP of lignin, which can compete with the commercial HZSM-5 catalyst. The nanocomposites can selectively cleave the C-O bonds within lignin-derived phenols to form aromatics by direct demethoxylation and subsequent dehydration. Moreover, the nanocomposites can also achieve the selective breaking of the C-O bonds within xylan and cellulose to form furans by dehydration. The Brønsted and Lewis acid sites on the nanocomposites can be responsible for the deoxygenation of lignin and polysaccharides, respectively. This study provides new insights for the rational design of multifunctional catalysts that are capable of simultaneously breaking the C-O bonds within lignin and polysaccharides.

Novel crude glycerol pretreatment for selective saccharification of sugarcane bagasse via fast pyrolysis.

Pretreatment is a vital process for efficient saccharification and utilization of lignocellulose. In this study, crude glycerol derived from biodiesel production was used for pretreatment to facilitate selective saccharification via fast pyrolysis. Due to the efficient removal of alkali and alkaline earth metals (>95.0%) and lignin (79.4%) by crude glycerol pretreatment, the yield of levoglucosan was evaluated to 25.2% as compared to those from pure glycerol pretreated (14.4%) and untreated sugarcane bagasse (8.4%). Meanwhile, the production of inhibitors (e.g. acetic acid, phenol) to biocatalysts was also obviously inhibited from crude glycerol pretreated biomass. Consequently, this work provided a cost-effective and eco-friendly pretreatment mode, which could not only make full utilization of crude glycerol, but also improve the fermentability of lignocellulosic pyrolysate.

A comparative investigation of fast pyrolysis with enzymatic hydrolysis for fermentable sugars production from cellulose.

In this study, ball milling and ionic liquid pretreatments were utilized to alter cellulose structure prior to fast pyrolysis and enzymatic hydrolysis. The variations in the products distribution of cellulose fast pyrolysis, and their dependence on the structure of cellulose, and the temperature of fast pyrolysis were illustrated. Fast pyrolysis of pretreated cellulose yielded more levoglucosan than crystalline cellulose (14.7%) at 300 °C. Nevertheless, the levoglucosan achieved higher yield (64.3%) from crystalline cellulose at 400 °C. At last, a comparison between fast pyrolysis and enzymatic hydrolysis for cellulose saccharifaction was made. Fast pyrolysis was a promising alternative to liberate levoglucosan from cellulose. Further investigation and development were required to maximize the levoglucosan production.

Highly abrasion resistant thermally fused olivine as in-situ catalysts for tar reduction in a circulating fluidized bed biomass gasifier.

Olivine synthesized by wetness impregnation (WI) and thermal fusion (TF) methods were investigated as in-situ catalysts to reduce the tar content during air-blown biomass gasification in a circulating fluidized bed (CFB). The results showed that the tar content decreases with the increase of reaction temperature. Raw-olivine reduced tar content by 40.6% compared to non-active bed material (silica sand) experiments; after calcination, the catalytic activities of olivine catalysts were further improved due to the migration of Fe from olivine grain to the surface. 1100-WI-olivine could reduce the tar content by up to 81.5% compared with that of raw-olivine because of the existence of Fe2O3, NiO and NiO-MgO. For 1400-TF-olivine, due to the formation of NiFe2O4, the tar content decreased to 0.77 g/Nm3, an 82.9% reduction compared to raw-olivine. Moreover, the TF-olivine had a stronger anti-attrition performance and was more suitable for using in a circulating fluidized bed.

Effect of Glycerol Pretreatment on Levoglucosan Production from Corncobs by Fast Pyrolysis.

In this manuscript, glycerol was used in corncobs' pretreatment to promote levoglucosan production by fast pyrolysis first and then was further utilized as raw material for chemicals production by microbial fermentation. The effects of glycerol pretreatment temperatures (220⁻240 °C), time (0.5⁻3 h) and solid-to-liquid ratios (5⁻20%) were investigated. Due to the accumulation of crystalline cellulose and the removal of minerals, the levoglucosan yield was as high as 35.8% from corncobs pretreated by glycerol at 240 for 3 h with a 5% solid-to-liquid ratio, which was obviously higher than that of the control (2.2%). After glycerol pretreatment, the fermentability of the recovered glycerol remaining in the liquid stream from glycerol pretreatment was evaluated by Klebsiella pneumoniae. The results showed that the recovered glycerol had no inhibitory effect on the growth and metabolism of the microbe, which was a promising substrate for fermentation. The value-added applications of glycerol could reduce the cost of biomass pretreatment. Correspondingly, this manuscript offers a green, sustainable, efficient and economic strategy for an integrated biorefinery process.

The integration of dilute acid hydrolysis of xylan and fast pyrolysis of glucan to obtain fermentable sugars.

BACKGROUND: Fermentable sugars are important intermediates in the biological conversion of biomass. Hemicellulose and amorphous cellulose are easily hydrolyzed to fermentable sugars in dilute acid, whereas crystalline cellulose is more difficult to be hydrolyzed. Cellulose fast pyrolysis is an alternative method to liberate valuable fermentable sugars from biomass. The amount of levoglucosan generated from lignocellulose by fast pyrolysis is usually lower than the theoretical yield based on the cellulose fraction. Pretreatment is a promising route to improve the yield of levoglucosan from lignocellulose. RESULTS: The integration of dilute sulfuric acid hydrolysis and fast pyrolysis to obtain fermentable sugars was evaluated in this study. Dilute sulfuric acid hydrolysis could remove more than 95.1 and 93.4 % of xylan (the main component of hemicellulose) from sugarcane bagasse and corncob with high yield of xylose. On the other hand, dilute sulfuric acid hydrolysis was also an effective pretreatment to enhance levoglucosan yield from lignocellulose. Dilute acid hydrolysis could accumulate glucan (the component of cellulose) and remove most of the alkali and alkaline earth metals which were powerful catalysts during fast pyrolysis. Further increase in dilute acid concentration (from 0 to 2 %) in pretreatment could promote the yield of levoglucosan in fast pyrolysis. The acid pretreated sugarcane bagasse and corncob gave levoglucosan yields of 43.8 and 35.2 % which were obvious higher than those of raw sugarcane bagasse (12.0 %) and corncob (7.0 %). CONCLUSIONS: Obtaining fermentable sugars by combination dilute acid hydrolysis of xylan and fast pyrolysis of glucan could make full utilization of biomass, and get fermentable sugars economically from biomass for bio-refinery.

The comparison of obtaining fermentable sugars from cellulose by enzymatic hydrolysis and fast pyrolysis.

Sugars are one of intermediates in the biological and chemical conversion of biomass. The objective of this study was to make comparison of obtaining fermentable sugars by enzymatic hydrolysis and fast pyrolysis of ball milling pretreated cellulose. After ball milling pretreatment for 0-18h, with the accumulation of alkali and alkali earth metals (from 50.8 to 276.4ppm) and decrease of the crystalline structure (from 89.8% to 10.1%), the hydrolysis yields increased from 23.6% to 56.0% in enzymatic saccharification, while the yields of levoglucosan diminished from 61.5% to 45.6% gradually in fast pyrolysis. Both enzymatic saccharification and fast pyrolysis had unique attractive features and unfavorable limitations. The present research provided a concept for considering choices among the technologies and feedstocks currently available.

Comprehensive utilization of glycerol from sugarcane bagasse pretreatment to fermentation.

In this study, the effects of glycerol pretreatment on subsequent glycerol fermentation and biomass fast pyrolysis were investigated. The liquid fraction from the pretreatment process was evaluated to be feasible for fermentation by Paenibacillus polymyxa and could be an economic substrate. The pretreated biomass was further utilized to obtain levoglucosan by fast pyrolysis. The pretreated sugarcane bagasse exhibited significantly higher levoglucosan yield (47.70%) than that of un-pretreated sample (11.25%). The promotion could likely be attributed to the effective removal of alkali and alkaline earth metals by glycerol pretreatment. This research developed an economically viable manufacturing paradigm to utilize glycerol comprehensively and enhance the formation of levoglucosan effectively from lignocellulose.

Obtaining fermentable sugars by dilute acid hydrolysis of hemicellulose and fast pyrolysis of cellulose.

The objective of this study was to get fermentable sugars by dilute acid hydrolysis of hemicellulose and fast pyrolysis of cellulose from sugarcane bagasse. Hemicellulose could be easily hydrolyzed by dilute acid as sugars. The remained solid residue of acid hydrolysis was utilized to get levoglucosan by fast pyrolysis economically. Levoglucosan yield from crystalline cellulose could be as high as 61.47%. Dilute acid hydrolysis was also a promising pretreatment for levoglucosan production from lignocellulose. The dilute acid pretreated sugarcane bagasse resulted in higher levoglucosan yield (40.50%) in fast pyrolysis by micropyrolyzer, which was more effective than water washed (29.10%) and un-pretreated (12.84%). It was mainly ascribed to the effective removal of alkali and alkaline earth metals and the accumulation of crystalline cellulose. This strategy seems a promising route to achieve inexpensive fermentable sugars from lignocellulose for biorefinery.

Comparison of the effect of wet and dry torrefaction on chemical structure and pyrolysis behavior of corncobs.

Wet and dry torrefaction of corncobs was conducted in high-pressure reactor and tube-type reactor, respectively. Effect of wet and dry torrefaction on chemical structure and pyrolysis behavior of corncobs was compared. The results showed that hemicellulose could be effectively removed from corncobs by torrefaction. However, dry torrefaction caused severe degradation of cellulose and the cross-linking and charring of corncobs. X-ray diffraction analysis revealed that crystallinity degree of corncobs was evidently enhanced during wet torrefaction, but reduced during dry torrefaction as raising treatment temperature. In thermogravimetric analysis, wet torrefied corncobs produced less carbonaceous residues than raw corncobs, while dry torrefied corncobs gave much more residues owing to increased content of acid insoluble lignin. Pyrolysis-gas chromatography/mass spectroscopy analysis indicated that wet torrefaction significantly promoted levoglucosan yield owing to the removal of alkali metals. Therefore, wet torrefaction can be considered as a more effective pretreatment method for fast pyrolysis of biomass.

Effect of hydrothermal pretreatment on properties of bio-oil produced from fast pyrolysis of eucalyptus wood in a fluidized bed reactor.

Eucalyptus wood powder was first subjected to hydrothermal pretreatment in a high-pressure reactor at 160-190°C, and subsequently fast pyrolyzed in a fluidized bed reactor at 500°C to obtain high quality bio-oil. This study focused on investigating effect of hydrothermal pretreatment on bio-oil properties. Hemicellulose and some metals were effectively removed from eucalyptus wood, while cellulose content was enhanced. No significant charring and carbonization of constituents was observed during hydrothermal pretreatment. Thus pretreated eucalyptus wood gave higher bio-oil yield than original eucalyptus wood. Chemical composition of bio-oil was examined by GC/MS and (13)C NMR analyses. Bio-oil produced from pretreated eucalyptus wood exhibited lower contents of ketones and acids, while much higher levoglucosan content than bio-oil produced from original eucalyptus wood, which would help to improve thermal stability of bio-oil and extract levoglucosan from bio-oil. Hydrothermal pretreatment also improved bio-oil fuel quality through lowering water content and enhancing heating value.

Effect of torrefaction on structure and fast pyrolysis behavior of corncobs.

Pretreatment of corncobs using torrefaction was conducted in an auger reactor at 250-300 °C and residence times of 10-60 min. The torrefied corncobs were fast pyrolyzed in a bubbling fluidized bed reactor at 470 °C to obtain high-quality bio-oil. The heating value and pH of the bio-oil improved when the torrefaction as pretreatment was applied; however, increasing bio-oil yield penalties were observed with increasing torrefaction severity. Fourier transform infrared Spectroscopy (FTIR) and quantitative solid (13)C nuclear magnetic resonance spectrometry (NMR) analysis of torrefied corncobs showed that the devolatilization, crosslinking and charring of corncobs during torrefaction could be responsible for the bio-oil yield penalties. Gas chromatography-mass spectrometry (GC-MS) analysis showed that the acetic acid and furfural contents of the bio-oil decreased with torrefaction temperature or residence time. The results showed that torrefaction is an effective method of pretreatment for improving bio-oil quality if the crosslinking and charring of biomass can be restricted.

[Leaching and stabilization of heavy metal in the fly ash of medical wastes].

Through the experiments of leaching and melting on the fly ash of medical wastes, the influence of leaching time, L/S, pH and grain size on the leaching characteristics of heavy metal and the effect of melting on the stabilization of fly ash are studied. Results show that, following the leaching time extending, the leaching concentrations of heavy metals and lixiviate toxicity of heavy metals increase in the fly ash. When the ratio of liquid and solid add, the leaching concentrations of heavy metals obviously become big, and the Cd's leaching concentration is the biggest, when the ratio of liquid and solid is 90, the Cd' s leaching ratio exceed the percent of 70. At the time pH is about 7, the leaching concentrations of heavy metals are the lowest. When the grain size is the bigger or little, the leaching concentrations of heavy metals are lower, however when the grain size is 250-900 microm, the concentrations are higher. After fly ash melt in the high temperature, the lixiviate toxicity of heavy metals greatly reduce, which explains that the effect of melting on heavy metals' stabilization is very good.