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Hydrothermal carbonization (HTC) of sweet potato waste was performed to investigate the effect of process parameters including reaction temperature (180–300 °C) and residence time (0–120 min) on the characteristics of hydrochars. The results showed that the increase of reaction temperature and residence time both decreased the yield of hydrochars. With the increase of reaction temperature and residence time, the carbon content of hydrochars increased, while the hydrogen and oxygen contents decreased. The lower H/C and O/C ratios indicated that dehydration and decarboxylation reactions occurred during HTC. The occurrence of aromatization reaction was found in FTIR spectra. Thus, the fixed carbon content, higher heating value, and energy density of hydrochars increased. SEM analysis indicated that HTC developed rough surface with crack on the hydrochars. The thermogravimetric experiments displayed the increase trend in combustion ignition temperature, burnout temperature and activation energy as reaction temperature and time increase, which showed better combustion characteristics.

In this work, five typical components were employed as representative pseudo-components to indirectly complete previous established simulation system during hydrothermal carbonization (HTC) of municipal solid waste. The fuel characteristics and combustion behavior of HTC-derived hydrochars were evaluated. Results clearly illustrated that the energy ranks of hydrochars were upgraded after HTC. For paper and wood, superior combustion performances of their hydrochars could achieve under suitable conditions. While for food, none positive enrichments on combustion loss rate were observed for hydrochars due to its high solubilization and decomposition under hot compressed water. It was noteworthy that a new weight loss peak was detected for paper and food, suggesting that new compounds were formed. For rubber, the HTC process made the properties of styrene butadiene rubber more close to natural rubber. Therefore, the first peak of hydrochars became significantly intense. While for plastic, only physical changes of polypropylene and polyethylene were observed.

The composition, cellulose degradability and biochemical methane potential (BMP) of M. sinensis, M. floridulus, Miscanthus × giganteus and M. lutarioriparius were investigated concomitantly at different growth/harvest times during their growing season. For all the four species, there was only a slight change in the compositional content. Meanwhile there was a huge change in the BMP values. At the growth time of 60 days the BMPs ranged from 247.1 to 266.5 ml g−1 VS. As growth time was prolonged, the BMPs decreased by 11–35%. For each species, the BMP was positively correlated to the cellulose degradability with the correlation coefficients (R2) ranging from 0.8055 to 0.9925. This suggests that besides the biomass yield, it is justifiable to consider cellulose degradability when selecting the suitable harvest time for biofuels production from Miscanthus, especially in tropical and subtropical regions where Miscanthus can be harvested twice or more within a year.

The denitrification of bio-oil remains an important challenge in bio-oil quality upgrading. Microalgae (MA) and sweet potato waste (SPW) were co-liquefied to investigate the denitrification of Mannich reaction. The influence of interaction reaction between MA and SPW on products qualities was explored. The results showed that the N contents of bio-oils from co-liquefaction (4.44–7.19%) were lower than that from microalgae (7.60%). Besides, the ester contents from MA&SPW (60.31–73.17%) were higher than that from MA (56.11%) and SPW (17.55%).The addition of SPW decreased the lubricating oil and fuel oil content. The experimental energy recovery efficiency (66.82–70.16%) was higher than the calculated energy recovery efficiency (65.68–66.69%) during co-liquefaction processes. Based on chemical compositions of products, a possible reaction pathway of Mannich reaction during co-liquefaction process was proposed. The current study suggested that co-liquefaction of microalgae and sweet potato waste was a feasibility way to improve the bio-oil quality and energy recovery efficiency.

Microalgae (MA) was co-liquefied with sweet potato waste (SPW) to improve bio-oil and bio-char qualities via Mannich reaction. The influence of Mannich reaction on combustion performances of bio-oil and bio-char were investigated. Results suggested that the addition of SPW decrease the ignition temperature of bio-oil from 186.6 °C to 165.0 °C. In addition, the denitrification effect of Mannich reaction can decrease the HCN and NO emission of bio-oil, contributing to reducing pollutant emission. As for bio-char, Mannich reaction improved the combustible material content in bio-char, which decreased the risk of slagging problem. The comprehensive combustion indexes of bio-oil (1.23 × 10−6 × min−2×°C−3) and bio-char (4.79 × 10−8 × min−2×°C−3) from co-liquefaction were higher than those from liquefaction of MA (0.91 × 10−6 × min−2×°C−3 for bio-oil and 1.24 × 10−8 × min−2×°C−3 for bio-char), indicating that the combustion performance was promoted by adding SPW. Overall, Mannich reaction can be applied to improve the combustion performance of bio-oil and bio-char.

Aqueous phase recirculation was investigated in hydrothermal carbonization of sweet potato waste at 220 °C for 60 min. The result showed that the aqueous phase reuse significantly increased the hydrochar yield. The lower H/C and O/C ratios indicated that decarboxylation reaction was promoted. The CC vibration of the benzene backbone became intense, suggesting the occurrence of aromatization and polymerization reactions. Thus, the carbon content and HHV were improved. After recirculation, hydrochar showed a decrease in combustion ignition temperature whereas an increase in pyrolysis initial decomposition temperature. The burnout temperatures in combustion and terminated temperature in pyrolysis both showed an increase trend. The hydrochars obtained from the recirculation step possessed lower emissions of NOX or SO2 than that from reference step. The pyrolysis emission result showed that more high thermal stability components were formed during recirculation step. Overall, aqueous phase recirculation was a feasible way to improve hydrothermal carbonization process.

The synergistic interaction and kinetics of microalgae, textile dyeing sludge and their blends were investigated under combustion condition by thermogravimetric analysis. The textile dyeing sludge was blended with microalgae in the range of 10-90wt.% to investigate their co-combustion behavior. Results showed that the synergistic interaction between microalgae and textile dyeing sludge improved the char catalytic effect and alkali metals melt-induced effect on the decomposition of textile dyeing sludge residue at high temperature of 530-800°C. As the heating rate increasing, the entire combustion process was delayed but the combustion intensity was enhanced. The lowest average activation energy was obtained when the percentage of microalgae was 60%, which was 227.1kJ/mol by OFW and 227.4kJ/mol by KAS, respectively.

The kinetic behavior and evolution characteristics of gaseous products during the combustion of biocrude oil from solvolysis liquefaction of Chlorella pyrenoidosa were investigated by thermogravimetry–Fourier transform infrared spectroscopy (TG–FTIR). The results indicated the biocrude oil obtained from different ethanol/water mixed ratio had obvious difference with each other. The ignition temperature of biocrude oil from ethanol–water co-solvent was lower than that from pure water solvent, which promoted the comprehensive combustion index. Especially, BO40 (biocrude oil obtained from 40% ethanol content) achieved the lowest ignition temperature (163.4 °C) and high comprehensive combustion index (1.24 × 10 −06 min −2 °C −3 ). C H, C O, C C, CO 2 , CO and HCN were the main gaseous products. Compared to other biocrude oil samples, BO40 had high first peak intensity of C H, C O and C C, and low peak intensity of CO, which performed better combustion characteristic.

Microsphaeropsis sp. was used to produce SCO in solid-state fermentation (SSF) from a substrate consisting of steam-exploded wheat straw (SEWS) and wheat bran (WB). The yield of SCO was 42 mg/g dry substrate (gds) without adding cellulase. To achieve a higher SCO yield, cellulase was added to the solid-state medium, resulting in an increase of SCO from 42 to 74 mg/gds with a cellulase loading of 10 FPU/gds. Other SSF parameters such as ratio of SEWS to WB of the dry substrate, initial moisture content, and incubation temperature were optimized under the condition of cellulase loading of 10 FPU/gds. So optimized, the SCO yield was 80 mg/gds, and the SCO content of the dry fermented mass was 10.2%. This research explored a novel method to produce SCO from the abundant and cheap agricultural residues - wheat straw and wheat bran.

Hydrolysis is usually the rate-limited step for methane production from lignocellulosic substrate. Two bioaugmentation strategies, using the cellulolytic anaerobic bacteria Clostridium cellulolyticum, were adopted to enhance the hydrolysis of wheat straw with the purpose of improving the biochemical methane potential (BMP). Namely, the 24-h-incubated seed (C24S) with cellobiose as carbon source and the 60-h-incubated seed (WS60S) with wheat straw as carbon source were respectively used as the bioaugmentation agents. As a result, the BMPs were respectively 342.5 and 326.3 ml g (1) VS of wheat straw, with an increase of 13.0% and 7.6% comparing to the no-bioaugmentation BMP of 303.3 ml g (1) VS. The result indicates that the anaerobic digestion efficiency can be improved by bioaugmentation, which therefore may be a promising method for improving methane production from lignocellulosic substrate. (C) 2013 Elsevier Ltd. All rights reserved.

Calibration model using near-infrared reflectance spectroscopy (NIRS) for estimation of SCO content in solid-state fermented mass was established. The NIRS calibration model was derived by partial least-squares (PLS) regression and prediction of SCO contents of independent solid-state fermented mass samples fermented by different oleaginous fungi showed the model to be rapid and accurate, giving R-2-value higher than 0.9552 and root mean standard error of prediction (RMSEP) value lower than 0.5772%. The established NIRS calibration model could be used to estimate the SCO contents of the solid-state fermented masses and will provide much convenience to the research of SCO production in solid-state fermentation. (C) 2008 Elsevier Ltd. All rights reserved.