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Abstract Sugarcane is a major crop cultivated globally and the residue left over after the crop harvest and extraction of juice is a good biomass source that can be used for the production of several useful chemicals. The sugarcane bagasse is an excellent substrate for the production of various biochemicals and enzymes through fermentation. Now major interest is focused on the utilization of these residue for biofuel production. The sugarcane crop residue is rich in cellulose and hemicellulose, hence it can be used for the production of bioethanol and other liquid transportation fuels. The present review gives a detailed account of the availability of sugarcane residue and various commercially important products that can be produced from this residue. It also provides recent developments in R&D on the bioconversion of sugarcane crop residue for value added products.

Abstract Standardization of biogas technology is immensely important for the promotion of the biogas industry worldwide. China has built a complete biogas standard system, which is divided into common, household biogas, biogas engineering, biogas digester for domestic sewage treatment, output utilization, and service system standards. The problems and potential barriers for biogas standardization in China are analyzed and come down to sluggish standard, overlapped standard, government-dominated standard, and lagging international standard. Accordingly, all potential biogas standards should be evaluated and placed under the same department. China Biogas Society and China Association of Rural Energy Industry play leading roles in developing enterprise or group/association biogas standards and ISO biogas standards. The bio-natural gas standard system and experimental standardization should be developed as well to replenish biogas standard system. A paradigm shift in biogas standardization should be from government-dominated to market-oriented model. The lessons learned for other developing countries includes expanding standardization to multi-aspects to realize full lifecycle control and management, building rapid responding mechanism of standardization to adopt industry transformation, integrating outdated standards into new versions, and establishing market-based standard system.

Zinc oxide (ZnO) nanostar synthesized by simple and up-scalable microwave-assisted surfactant free hydrolysis method was applied as catalyst for biodiesel synthesis through one-step simultaneous esterification and transesterification from high free fatty acid (FFA) contaminated unrefined feedstock. It was found that ZnO nanostar catalyst was reacted with FFA to yield zinc oleate (ZnOl) as intermediate and finally became zinc glycerolate (ZnGly). With the re-deposition of ZnGly back to the ZnO nanostar catalyst at the end of the reaction, the catalyst can be easily recovered and stay active for five cycles. Furthermore, the rate of transesterification is highly promoted by the presence of FFA (6 wt.%) which makes it an efficient catalyst for low grade feedstock like waste cooking oil and crude plant oils.

Abstract Large volumes of polymeric waste, including natural biomass residues and synthetic waste, motivate the development of a general, robust and flexible process for mining the energy and resources contained in these wastes. By analyzing the positive and negative aspects of current, conventional technologies for the recovery of energy from polymeric waste, an integrated concept of a hybrid technology combining biochemical (anaerobic digestion, gas fermentation, carbon chain elongation) and thermochemical conversion processes (pyrolysis, gasification, hydrothermal carbonization) was proposed. The hybrid technology aims at simultaneously enhancing the efficiency and stability of biochemical conversion, controlling the gaseous and aqueous pollution from thermochemical conversion, and sequestering carbon. This paper presents a detailed review of state-of-the-art research relating to the principles, technical feasibility and practices involved in each technical link between the two conversion processes.

Abstract Soybean residue (SR) is a main solid waste produced during the extraction of soybean oil with bulk volume. In addition to the use as vegetable protein feed, SR could also be used as feedstock for producing biofuels and carbon materials via pyrolysis. In this study, the pyrolysis behaviors of SR at varied temperatures and heating rates were investigated. The results show that the pyrolysis of the organic components in SR could reach completion even at 500 °C, due to the lower thermal stability of the organic component than that in the typical biomass. This also leads to the bio-oil with little heavy organics and also low carbon content of the resulting biochar, as the organic components decomposed to a significant extent while the charring reactions were insignificant. This leads to the biochar with low heating value and low energy yield when compared with that in the pyrolysis of typical biomass. In addition, the high content of proteins, amino acids and other nitrogen-containing nutrients make the SR derived bio-oil nitrogen-rich and a significant portion of nitrogen could also be retained in the biochar. These specialties have to be considered during their applications as either biofuels or functional carbon materials.

Abstract Faced with fossil fuel depletion and increasing environmental concerns, the conversion of renewable biomass into fuels or chemicals is promising but extremely challenging due to the inertness and complexity of biomass. Therefore, in situ multistage condensation combined with the HDO of pyrolysis bio-oil was chosen to reduce the complexity and improve the quality of bio-oil. In addition, the activity and stability of the catalyst was enhanced. The bio-oil obtained via continuous pyrolysis was divided into four-stage depending on their boiling point via in situ multistage condensation. After HDO, the relative content of long-chain alkanes was over 80% for each stage bio-oil via mixed supported Ni/HZSM-5-γ-Al2O3 catalyst. Especially, the main components in the 3rd oil (aqueous phase) were n-heneicosane (31.60%), icosane (5.13%) and n-heptadecane (4.36%) based on the highest HDO ratio. Moreover, the reaction mechanism was discussed via the HDO of model bio-oil. The main reaction pathway consisted of hydrogenation and dehydration reactions (HYD pathway), and a side reaction was the direct deoxygenation route (DDO pathway). This work provides a general and efficient pathway for directly converting biomass into valuable long chain alkanes.

Abstract Lignocellulosic biomass is considered to be a potential raw material for production of renewable fuels like bioethanol and biodiesel. Cellulose and hemicelluloses constitute major portion of the lignocellulosic biomass. Cellulose can be converted to glucose by hydrolysis and subsequently to ethanol by fermentation. The hemicellulosic portion mostly contains pentose sugars which cannot be utilized by many microorganisms for ethanol production. Acid pretreatment results in separation of a pentose-rich fraction which can be utilized for the production of various high value chemicals. The present study evaluates the utilization of pentose sugars as co-substrate, along with biodiesel industry-generated crude glycerol, for the production of 1,3-propanediol (1,3-PDO). Bioconversion of these low value byproducts into a high value chemical would be an economically advantageous strategy in terms of waste disposal for biorefineries. In this study, the production of 1,3-propanediol from the acid pretreated liquor obtained from rice straw was evaluated using Klebsiella pneumonia. Different carbon sources like pure hexose and pentose sugars, mixed pentose sugar containing acid pretreated liquor (APL) from rice straw and different concentrations of pentose sugars and acid pretreated liquor were evaluated. There is 65% increase in titers from 9.55 g/L to 15.75 g/L using APL as co-substrate. With addition of 0.5% (v/v) APL, 1,3-propanediol production reached 20.88 g/L with 0.69 g/g yield and 0.87 g/L/h productivity. The study comprehensively explains the behavior of Klebsiella pneumoniae strain utilizing pentose rich APL and crude glycerol which enroute to an integrated biorefinery approach.

Abstract Biodiesel is a promising alternative diesel fuel which has increased worldwide public interest in a number of countries including China. But the high cost of producing biodiesel from feedstock, predominately food grade oils, limited its economic feasibility. An alternative of using grease extracted from restaurant waste to produce biodiesel is a potential low cost approach. However, this approach generates a significant large quantity of solid residual fraction which required proper disposal. This study was conducted to evaluate the potential of a secondary biodiesel production from the solid residual fraction of restaurant waste after typical grease extraction (SRF) employing a high fat containing insect, black soldier fly, Hermetia illucens. The SRF was sampled and fed to black soldier fly larvae. The resulting larval biomass was used for crude grease extraction by petroleum ether. The extracted crude grease was then converted into biodiesel by acid-catalyzed (1% H 2 SO 4 ) esterification and alkaline-catalyzed (0.8% NaOH) transesterification. About 23.6 g larval grease-based biodiesel was produced from approximately 1000 larvae grown on 1 kg of SRF. The weight of SRF was reduced by about 61.8% after being fed by the black soldier fly larvae for 7 days. The amount of biodiesel yield from restaurant waste was nearly doubled (original restaurant waste grease, 2.7%; larval grease, 2.4%). The major methyl ester components of the biodiesel derived from black soldier fly larvae fed on SRF were oleinic acid methyl ester (27.1%), lauric acid methyl ester (23.4%), and palmitic acid methyl ester (18.2%). Most of the properties of this biodiesel met the specifications of the standard EN 14214, including density (860 kg/m 3 ), viscosity (4.9 mm 2 /s), flash point (128 °C), cetane number (58) and ester contents (96.9%). These results indicated that black soldier fly larval biomass obtained from larvae reared on SRF could potentially be used as a non-food feedstock for biodiesel production. This approach not only enhances the efficiency of biodiesel production from restaurant waste, it also helps to better manage and significantly reduce the large quantity of solid residual fraction produced during the process of biodiesel production using restaurant waste.

Abstract Renewable energy plays an important role in the modern economic growth paradigm. As a perpetual source, solar-based renewable energy has the ability to reduce CO2 emissions, which has been neglected in prior empirical studies. We have analyzed the asymmetric association between solar energy consumption and CO2 emissions in the top ten solar energy-consuming countries (Australia, Germany, Japan, Spain, Italy, USA, South Korea, UK, France, and China). Using data from 1991 to 2018, a novel methodology, ‘Quantile-on-Quantile (QQ)’, is applied. The results explore the mode of how quantiles of solar energy consumption asymmetrically affect the quantiles of CO2 emissions by providing an adequate framework to comprehend the overall dependence structure. The empirical findings demonstrate that solar energy consumption reduces CO2 emissions at different quantiles for all selected countries except France. The overall relationship is stronger at higher quantiles of CO2 emissions for various countries. The outcomes suggest that the intensity of asymmetric relationship in solar energy-CO2 emissions nexus differs with countries that need individual caution and attention for governments in formulating the policies connected to solar energy and the environment. Our empirical evidence also emphasizes that solar energy should be integrated for sustainable growth and environmental quality.