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[Display omitted] • Food waste can be a promising bioethanol source. • First conversion of food waste to bioethanol using amylolytic yeast. • The higher food waste starch content was, the higher were the ethanol levels. • Co-fermentation of food waste and rice waste boosted bioethanol production. Organic fraction of municipal solid waste (OFMSW) has the potential to sustain large-scale biofuel production. So far, OFMSW is mainly converted into biogas by anaerobic digestion (AD), and limited research is available on its use to produce bioethanol. This paper reports, for the first time, the conversion of starch-rich OFMSW to bioethanol by using a novel yeast co-secreting both glucoamylase and alpha-amylase enzymes. As such, OFMSW can be converted to bioethanol without adding costly enzymes following a consolidated bioprocessing (CBP) approach. The OFMSW, sampled at an industrial AD plant, was processed to bioethanol with an outstanding yield, approaching 100 % of the theoretical maximum. Moreover, the co-conversion of OFSMW with starch-rice waste, namely discolored rice (DR) available in large quantities close to the AD plant, was performed to test the feasibility of valorizing different waste substrates simultaneously. The ethanol levels reached 60 g/L, indicating that both the developed process and yeast strain have important features towards ethanol production from organic waste streams. [ABSTRACT FROM AUTHOR]

Increased environmental concern over climate change due to higher oil usage has made human being to shift to cleaner and greener alternatives. The utilization of abundant agricultural waste streams as renewable feedstock for biofuels production can be a pivotal strategy. Among others, rice is one of the most largely grown crops, and more than 4.8% of the total production goes to waste. Although previous reviews are related to biofuels obtained from some rice waste, most of those are focused on lignocellulosic rice residues with much attention to thermo-chemical processes. The present paper, instead, reviews for the first time the biotechnological approaches to convert all rice wastes, like rice husk, rice straw, broken rice, discolored rice, unripe rice, into liquid (bioethanol, biobutanol, biodiesel), and gaseous (biogas, biohydrogen) biofuels through the use of pure or mixed microbial cultures. The global availability of each rice byproduct has been also investigated and the potential of rice waste as a 'fuel farm' has been estimated for bioethanol. The physical, chemical, enzymatic, or microbial pretreatments, which play a key role in making carbon available for hydrolysis and fermentation, are here discussed and evaluated. Despite the great promise of technologies so far developed, further research is still required for their up-scale and industrial commercialization. Moreover, future process integrations will open the landscape to biorefinery schemes where rice waste streams can be processed into biofuels and other added-value products, towards the full exploitation of the feedstocks and the economic and environmental sustainability of the overall process. [Display omitted] • Rice waste has the potential to produce many gigalitres of biofuels worldwide. • Selection of pretreatment is the key to obtain the highest biofuel production. • Different biotechnological approaches for biofuel production are elucidated. • Complete rice waste valorization using a biorefinery approach is underscored. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nutrient stresses were applied to Cupriavidus necator growing on carbon dioxide. • Nitrogen starvation induced a PHB accumulation of 54% of total cell dry weight. • The carbon conversion yield into PHB reached a maximum of 85% under nitrogen stress. • Single-stage starvation was more effective than double-stages for PHB production. • Gas transfer enhancement in the fed-batch mode could improve the polymer yield. Cupriavidus necator is a facultative chemolithoautotrophic bacterium able to convert carbon dioxide into poly-3-hydroxybutyrate. This is highly promising as the conversion process allows the production of sustainable and biodegradable plastics. Poly-3-hydroxybutyrate accumulation is known to be induced by nutrient starvation, but information regarding the optimal stress conditions controlling the process is still heterogeneous and fragmentary. This study presents a comprehensive comparison of the effects of nutrient stress conditions, namely nitrogen, hydrogen, phosphorus, oxygen, and magnesium deprivation, on poly-3-hydroxybutyrate accumulation in C. necator DSM545. Nitrogen starvation exhibited the highest poly-3-hydroxybutyrate accumulation, achieving 54% of total cell dry weight after four days of nutrient stress, and a carbon conversion efficiency of 85%. The gas consumption patterns indicated flexible physiological mechanisms underlying polymer accumulation and depolymerization. These findings provide insights into strategies for efficient carbon conversion into bioplastics, and highlight the key role of C. necator for future industrial-scale applications. [ABSTRACT FROM AUTHOR]

The exploitation of agri-food wastes is of great importance for environmental and economic reasons. Date wastes are attractive biomasses that could be used as a carbon source for the growth of microorganisms to obtain added-value products. In this work, spoilage date syrup, containing 102.01 and 101.00 g/L of glucose and fructose, respectively, was assessed as a feedstock for the production of bioethanol and polyhydroxyalkanoates (PHAs) by Saccharomyces cerevisiae MEL2 and Cupriavidus necator DSM 545, respectively. The waste date syrup was first evaluated as a carbon source for microbial growth and resulted to sustain the growth of both strains. 47.95 g/L of ethanol, corresponding to the 93.52% of the theoretical yield, were obtained from the fermentation of date syrup by S. cerevisia e MEL2, here adopted as a proficient bioethanol yeast strain. Furthermore, C. necator DSM 545, a well-known PHAs-producer, was able to accumulate up to 79.20 % (w/w on dry mass) of PHAs. This study demonstrates that bioethanol and PHAs can be obtained from date wastes, contributing to developing cost-effective exploitation of these residues with economic and environmental advantages. [Display omitted] • Spoilage dates are suitable substrate for bioethanol and PHAs production. • A simple hot water extraction allows to obtain a date syrup containing simple sugars. • Simple sugars in syrup were converted by Saccharomyces cerevisiae MEL2 into ethanol. • A one step fermentation mode appears efficient in terms of sugars to PHAs conversion. • Cupriavidus necator DSM 545 is an effective PHAs‐ accumulator from date syrup. [ABSTRACT FROM AUTHOR]