Mechanistic insights into the (im)mobilization of arsenic, cadmium, lead, and zinc in a multi-contaminated soil treated with different biochars.

The effect and mechanistic evidence of biochar on the (im)mobilization of potentially toxic elements (PTEs) in multi-contaminated soils, with respect to the role of surface-functional groups and organic/inorganic compounds of biochar, are poorly understood. Herein, biochars produced from grass residues, rice straw, and wood were applied to a mining-soil contaminated with As, Cd, Pb, and Zn for 473-d. Biochars did not reduce the mobilization of Cd and Zn, whereas they simultaneously exhibited disparate effects on As and Pb mobilization. The phenolic hydroxyl and carboxylic groups on the wood biochar's surfaces promoted the conversion of Pb2+ into PbCO3/Pb(OH)2 and/or PbO, minimally by the rice and grass biochars. Rice and grass biochars led to the dissolution of scorodite and the formation of less stable forms of Fe-oxide-bound As (i.e., goethite and ferrihydrite); furthermore, it resulted in the reduction of As(V) to As(III). The PTEs mobilization and phytoavailability was mainly governed by the release of dissolved aliphatic- and aromatic-carbon, chloride, sulfur chemistry, phosphate competition, and the electrostatic repulsion in biochar-treated soils. In conclusion, pristine-biochar has a limited impact on the remediation of multi-contaminated soils, and the use of modified-biochar, possessing higher surface areas and functionality and active exchange sites, are preferred under such conditions.

Biochar-induced metal immobilization and soil biogeochemical process: An integrated mechanistic approach.

The nature of biochar-derived dissolved organic matter (DOM) has a crucial role in the interactions between biochar and metal immobilization, carbon dynamics, and microbial communities in soil. This study utilized excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC) modeling to provide mechanistic evidence of biochar-induced influences on main soil biogeochemical processes. Three biochars produced from rice straw, wood, and grass residues were added to sandy and sandy loam soils and incubated for 473 d. Microbial and terrestrial humic-like fluorescent components were identified in the soils after incubation. The sandy loam soil exhibited a higher DOM with microbial sources than did the sandy soil. All biochars reduced Pb bioavailability, whereas the rice straw biochar enhanced the As bioavailability in the sandy loam soil. The biochar-derived aliphatic-DOM positively correlated with As bioavailability (r = 0.82) in the sandy loam soil and enhanced the cumulative CO2-C (r = 0.59) in the sandy soil. The promoted cumulative CO2-C in the sandy soil with all biochars correlated with the enhanced microbial communities, in particular, gram-positive (r = 0.59) and gram-negative (r = 0.59) bacteria. Our results suggest that the integration of EEM-PARAFAC with spectroscopic indices could be useful for a comprehensive interpretation of the soil quality changes in response to the application of biochar.

Slow pyrolyzed biochars from crop residues for soil metal(loid) immobilization and microbial community abundance in contaminated agricultural soils.

This study evaluated the feasibility of using biochars produced from three types of crop residues for immobilizing Pb and As and their effects on the abundance of microbial community in contaminated lowland paddy (P-soil) and upland (U-soil) agricultural soils. Biochars were produced from umbrella tree [Maesopsis eminii] wood bark [WB], cocopeat [CP], and palm kernel shell [PKS] at 500 °C by slow pyrolysis at a heating rate of 10 °C min-1. Soils were incubated with 5% (w w-1) biochars at 25 °C and 70% water holding capacity for 45 d. The biochar effects on metal immobilization were evaluated by sequential extraction of the treated soil, and the microbial community was determined by microbial fatty acid profiles and dehydrogenase activity. The addition of WB caused the largest decrease in Pb in the exchangeable fraction (P-soil: 77.7%, U-soil: 91.5%), followed by CP (P-soil: 67.1%, U-soil: 81.1%) and PKS (P-soil: 9.1%, U-soil: 20.0%) compared to that by the control. In contrast, the additions of WB and CP increased the exchangeable As in U-soil by 84.6% and 14.8%, respectively. Alkalinity and high phosphorous content of biochars might be attributed to the Pb immobilization and As mobilization, respectively. The silicon content in biochars is also an influencing factor in increasing the As mobility. However, no considerable effects of biochars on the microbial community abundance and dehydrogenase activity were found in both soils.

Experimental study of fry-drying and melting system for industrial wastewater sludge.

In South Korea, ocean dumping of organic sludges has been prohibited by the London Convention and by Korean regulations. Therefore, the Government of South Korea has sought an alternative process for the disposal of organic sludges. Recently, the combined fry-drying and melting system has been recognized as an efficient way to utilize the energy content of organic industrial sludge. Three kinds of fry-dried industrial sludges (obtained from industrial sites DG, DJ and GM), which had average heating value of 20,470kJ/kg and less than 5% water content, were tested. Unlike sewage sludge, industrial sludge contains high concentrations of heavy metals and thus cannot be directly utilized as refuse-derived fuel. The dried sludges were melted in a furnace and then rapidly cooled to form vitrified slags; the vitrification of SiO2 securely encapsulates hazardous heavy metals within the crystalline structure of the slag. To evaluate the hazard of vitrified slag, the heavy metal elution concentration was analyzed. Following vitrification, Hg, Cd, Cr(+6), HCN and Pb concentrations were not detectable, whereas Cu concentration decreased from 26.78mg/L to 0.42mg/L in DJ sludge, from 27.10mg/L to 0.13mg/L in DG and from 49.47mg/L to 0.047mg/L in GM sludge.

Hydrodeoxygenation of Guaiacol Over Pt/Al-SBA-15 Catalysts.

Upgrading of bio-oil through catalytic hydrodeoxygenation (HDO) reaction was investigated for guaiacol as a model compound. A batch reactor was used for the reaction condition of 40 bar and 250 degrees C. The target product was cyclohexane. Pt/Al-SBA-15 with the Si/Al ratios of 20, 40, and 80 and Pt/HZSM-5 were used as the catalyst. The SBA-15 catalysts were characterized by N2 adsorption-desorption, X-ray diffraction analysis, and temperature programmed desorption of ammonia. The order of cyclohexane yield was Pt/Al-SBA-15 (Si/Al = 20) > Pt/Al-SBA-15(40) > Pt/Al-SBA-15 (80), indicating that the quantity of acid sites plays an important role in the HDO reaction. On the other hand, Pt/HZSM-5 led to a very low cyclohexane yield, in spite of its abundant strong acid sites, due to its small pore size.

Effect of steam activation of biochar produced from a giant Miscanthus on copper sorption and toxicity.

This study aims to evaluate the physiochemical properties, sorption characteristics, and toxicity effects of biochar (BC) produced from Miscanthus sacchariflorus via slow pyrolysis at 500°C and its steam activation product (ABC). Although BC has a much lower surface area than ABC (181 and 322m(2)g(-1), respectively), the Cu sorption capacities of BC and ABC are not significantly different (p>0.05). A two-compartment model successfully explains the sorption of BC and ABC as being dominated by fast and slow sorption processes, respectively. In addition, both BC and ABC efficiently eliminate the toxicity of Cu towards Daphnia magna. However, ABC itself induced acute toxicity to D. magna, which is possibly due to increased aromaticity upon steam activation. These findings suggest that activation of BC produced from M. sacchariflorus at a pyrolytic temperature of 500°C may not be appropriate in terms of Cu sorption and toxicity reduction.

Slow pyrolysis of rice straw: analysis of products properties, carbon and energy yields.

Among many uses of rice straw, application of its biochar from pyrolysis to the soil is receiving greater interest for increased crop productivity and sequestration of CO2. This study investigated slow pyrolysis of rice straw at 300-700°C to characterize the yields and detailed composition of the biochar, bio-oil and non-condensable gases. Biochar was analyzed for pH, microscopic surface area and pore volume distribution. Although the mass yield for the organic fraction was only about 25% above 500°C, biochar was the primary product of pyrolysis containing 40% of energy and 45% of carbon from the straw. The utilization of by-products (bio-oil and gases) as energy resources was essential, since the sum of energy yield was about 60%. The gases could be burned to produce the heat for an auto-thermal pyrolysis process, but the heat balance was significantly influenced by the moisture content of the raw material.

Highly stretchable piezoelectric-pyroelectric hybrid nanogenerator.

A highly stretchable hybrid nanogenerator has been developed using a micro-patterned piezoelectric polymer P(VDF-TrFE), PDMS-CNT composite, and graphene nanosheets. Mechanical and thermal energies are simultaneously harvested from a single cell of the device. The hybrid nanogenerator exhibits high robustness behavior even after 30% stretching and generates very stable piezoelectric and pyroelectric power outputs due to micro-pattern designing.

Comparison of biochar properties from biomass residues produced by slow pyrolysis at 500°C.

Application of biochar from biomass pyrolysis to soil is gaining greater interest; this can ameliorate the soil quality, reduce fertilizer consumption, and sequestrate carbon. This study compares the characteristics of biochar produced by slow pyrolysis at 500°C for agricultural residues: sugarcane bagasse, cocopeat, paddy straw, palm kernel shell (PKS) and umbrella tree. In the biochar yield, the influence of the inert and lignin contents was significant. The wood stem, bagasse and paddy straw had biochar yields of 24-28 wt.% from the organic fraction while cocopeat had 46 wt.%. The carbon content of biochar ranged from 84 wt.% to 89 wt.%, which corresponded to 43-63% of carbon in the biomass. The biochar from wood stem and bagasse had well-developed pores of various sizes with large surface areas. Although the surface area was significant, PKS biochar had dense matrix with few large pores. The elemental composition and pH of biochars were also compared.

Biodiesel production via the transesterification of soybean oil using waste starfish (Asterina pectinifera).

Calcined waste starfish was used as a base catalyst for the production of biodiesel from soybean oil for the first time. A batch reactor was used for the transesterification reaction. The thermal characteristics and crystal structures of the waste starfish were investigated by thermo-gravimetric analysis and X-ray diffraction. The biodiesel yield was determined by measuring the content of fatty acid methyl esters (FAME). The calcination temperature appeared to be a very important parameter affecting the catalytic activity. The starfish-derived catalyst calcined at 750 °C or higher exhibited high activity for the transesterification reaction. The FAME content increased with increasing catalyst dose and methanol-over-oil ratio.

Characterization of cadmium removal from aqueous solution by biochar produced from a giant Miscanthus at different pyrolytic temperatures.

The objective of this study was to investigate the feasibility of biochar for removing Cd from aqueous solution. Biochars were produced from a Miscanthus sacchariflorus via slow pyrolysis at 300, 400, 500 and 600°C. Higher pyrolytic temperature resulted in biochar with a higher aromatic structure and fewer polar functional groups. In particular, pH and surface area of biochar increased greatly at pyrolytic temperatures ≥ 500°C, which increased Cd sorption capacity up to 13.24 mgg(-1). The diffuse-controlled Cd removal was likely due to a surface sorption or a precipitation reaction depending on pH. A simulation with the visual MINTEQ program indicated that the precipitate was Cd(OH)2. In addition, biochar treatment significantly removed the acute toxicity of Cd toward Daphnia magna, resulting in increase of EC50 (50% effective concentration) value from 0.16 to 0.76 mgL(-1).

Characteristics of biochar produced from slow pyrolysis of Geodae-Uksae 1.

This study investigated producing biochar from Geodae-Uksae 1 for soil applications to sequestrate carbon from the atmosphere and improve the productivity of crops. Using a lab-scale packed bed reactor, pyrolysis products of Geodae-Uksae 1 were produced over a temperature range of 300-700°C with a heating rate of 10°C/min. Pyrolysis at 500°C was found appropriate for biochar production considering the properties of char and the amount of heat required. It yielded biochar of 27.2wt.% that contained approximately 48% carbon in the raw biomass. The surface area of the biochar rapidly increased to 181m(2)/g. Large cylindrical pores with diameters of 5-40µm developed within the biochar due to the vascular cell structure of the parent biomass. The byproducts (bio-oil and gases) were also analyzed for use as fuel.

The characteristics of bio-oil produced from the pyrolysis of three marine macroalgae.

The pyrolysis of two brown macroalgae (Undaria pinnatifida and Laminaria japonica) and one red macroalgae (Porphyra tenera) was investigated for the production of bio-oil within the temperature range of 300-600°C. Macroalgae differ from lignocellulosic land biomass in their constitutional compounds and high N, S and ash contents. The maximum production of bio-oil was achieved at 500°C, with yields between 37.5 and 47.4 wt.%. The main compounds in bio-oils vary between macroalgae and are greatly different from those of land biomass, especially in the presence of many nitrogen-containing compounds. Of the gaseous products, CO(2) was dominant, while C(1)-C(4) hydrocarbons gradually increasing at 400°C and above. The pretreatment of macroalgae by acid washing effectively reduced the ash content. The pyrolysis of macroalgae offers a new opportunity for feedstock production; however, the utilization of bio-oil as a fuel product needs further assessment.

Ash deposit characterisation in a large-scale municipal waste-to-energy incineration plant.

The deposition of ash - combustion residues - on superheaters and heat exchanger surfaces reduce their efficiency; this phenomenon was investigated for a large-scale waste-to-energy incineration facility. Over a period of six months, ash samples were collected from the plant, which included the bottom ash and deposits from the superheater, as well as flyash from the convective heat exchanger, the economiser and fabric filters. These were analysed for particle size, unburned carbon, elemental composition and surface morphology. Element partitioning was evident in the different combustion residues, as volatile metals, such as cadmium, antimony and arsenic, were found to be depleted in the bottom ash by the high combustion temperatures (1000+°C) and concentrated/enriched in the fabric filter ash (transferred by evaporation). Non-volatile elements by contrast were distributed equally in all locations (transported by particle entrainment). The heat exchanger deposits and fabric filter ash had elevated levels of alkali metals. 82% of flyash particles from the fabric filter were in the submicron range.

Potential of municipal solid waste for renewable energy production and reduction of greenhouse gas emissions in South Korea.

Energy from waste (EfW) for nonrecyclable wastes is a suitable method of waste management and is important for renewable energy production. South Korea currently recycles 57% of household waste and landfills 26%. The remaining 17% is incinerated, mainly for heat production. In this study, the potential for energy production and reduction of corresponding greenhouse gas (GHG) emissions from municipal solid waste (MSW) in Korea was estimated without accounting for the lifecycle impact of waste management. The properties of the MSW were established from data available in national-scale waste surveys and reports. The potential of EfW for GHG emission reduction was calculated considering (1) the direct release of anthropogenic carbon, nitrous oxide (N2O), and methane (CH4); and (2) the reduction in indirect GHG emissions by fossil fuel displacement. CH4 emissions from landfilling were also estimated from biogenic carbon in waste. Applying the resulting emission factors to various EfW cases suggests that the current level of GHG emissions is significant but can be substantially reduced by increased use of EfW. A net reduction in GHG emissions can be achieved only by EfW with combined heat and power (CHP).

Influence of operation variables on fast pyrolysis of Miscanthus sinensis var. purpurascens.

Fast pyrolysis of Miscanthus was investigated in a bench-scale fluidized bed reactor for production of bio-oil. Process conditions were varied for temperature (350-550 degrees C), particle size (0.3-1.3mm), feed rate and gas flow rate. Pyrolysis temperature was the most influential parameter upon the yield and properties of bio-oil. The highest bio-oil yield of 69.2wt.% was observed at a temperature of 450 degrees C which corresponded to the end of the thermal composition of hemicellulose and cellulose. In the bio-oil, the water content was 34.5wt.%, and the main compounds in the organic fraction were phenolics and oxygenates. With increasing temperature, the amount of oxygenates in the bio-oil decreased gradually while that of water and aromatics increased rapidly. The bio-oil yield was not significantly affected by particle sizes or feed rates. The use of product gases as a fluidizing medium aided in increasing bio-oil yield.

Bio-oil production from fast pyrolysis of waste furniture sawdust in a fluidized bed.

The amount of waste furniture generated in Korea was over 2.4 million tons in the past 3 years, which can be used for renewable energy or fuel feedstock production. Fast pyrolysis is available for thermo-chemical conversion of the waste wood mostly into bio-oil. In this work, fast pyrolysis of waste furniture sawdust was investigated under various reaction conditions (pyrolysis temperature, particle size, feed rate and flow rate of fluidizing medium) in a fluidized-bed reactor. The optimal pyrolysis temperature for increased yields of bio-oil was 450 degrees C. Excessively smaller or larger feed size negatively affected the production of bio-oil. Higher flow and feeding rates were more effective for the production of bio-oil, but did not greatly affect the bio-oil yields within the tested ranges. The use of product gas as the fluidizing medium had a potential for increased bio-oil yields.

Clean bio-oil production from fast pyrolysis of sewage sludge: effects of reaction conditions and metal oxide catalysts.

Fast pyrolysis of sewage sludge was carried out under different reaction conditions, and its effects on bio-oil characteristics were studied. The effect of metal oxide catalysts on the removal of chlorine in the bio-oil was also investigated for four types of catalysts. The optimal pyrolysis temperature for bio-oil production was found to be 450 degrees C, while much smaller and larger feed sizes adversely influenced production. Higher flow and feeding rates were more effective but did not greatly affect bio-oil yields. The use of the product gas as the fluidizing medium gave an increased bio-oil yield. Metal oxide catalysts (CaO and La2O3) contributed to a slight decrease in bio-oil yield and an increase in water content but were significantly effective in removal of chlorine from the bio-oil. The fixed catalyst bed system exhibited a higher removal rate than when metal oxide-supported alumina was used as the fluidized bed material.

The reuse of spent mushroom compost and coal tailings for energy recovery: comparison of thermal treatment technologies.

Thermal treatment technologies were compared to determine an appropriate method of recovering energy from two wastes - spent mushroom compost and coal tailings. The raw compost and pellets of these wastes were combusted in a fluidised-bed and a packed-bed, and contrasted to pyrolysis and gasification. Quantitative combustion parameters were compared to assess the differences in efficiency between the technologies. Fluidised-bed combustion was more efficient than the packed-bed in both instances and pellet combustion was superior to that of the compost alone. Acid gas emissions (NO(x), SO(x) and HCl) were minimal for the fluidised-bed, thus little gas cleaning would be required. The fuels' high ash content (34%) also suggests fluidised-bed combustion would be preferred. The Alkali Index of the ash indicates the possibility of fouling/slagging within the system, caused by the presence of alkali metal oxides. Pyrolysis produced a range of low-calorific value-products, while gasification was not successful.

Ignition and burning rates of segregated waste combustion in packed beds.

Recent developments in national recycling and re-use programmes for municipal waste have led to segregation of an increasing proportion of waste to enhance material recovery. Several of the segregated streams contain materials that can not viably be re-used or recycled but can be used for energy recovery. In this study, the combustion of cardboard and waste wood was investigated in a small-scale packed bed reactor in order to provide fundamental data for the design/operation of moving bed furnaces. Key parameters of combustion including the ignition and burning rates were evaluated for various air flowrates and compared to the modelling results. Two successive stages of combustion were identified for both samples: the propagation of ignition front into the bed and combustion of the fuel above the ignition front. The burning rate of cardboard reached a peak of about 300 kg/m(2)h at the air flowrate of 936 kg/m(2)h and decreased at higher air flowrates. For waste wood, both the ignition and burning rates increased in the tested range of the air flowrate up to 702 kg/m(2)h, of which the values were very close to those for the cardboard. The model prediction was in good agreement with the test results for waste wood. However, the burning rate for cardboard was under-predicted due to strongly irregular shapes of the fuel.