**2. Food Waste Valorization by Biofuel and Bioenergy Production**

Due to its richness in moisture, carbohydrate polymers, and other constituents, food waste has been used as an excellent feedstock for the production of biofuel and bioenergy via microbial conversion [22,23]. The production of bioenergy from food waste would not only solve the environmental hazards resulting from the incineration of plants and sanitary landfill sites but would also mitigate the emissions of greenhouse gases while replacing the usage of fossil fuels with bioenergy [5].

Biomass such as rice husk, one of the most important crop residues around the world, can be converted by biochemical and thermochemical methods into useful products, as described by Tsai et al. [24]. Among the several methods applicable, pyrolysis is one of the most commonly used thermochemical conversion processes that involves the decomposition of biomass in the absence of air or oxygen at an elevated temperature [25]. The resulting biochar can be further used as solid fuel, carbon material, soil amendment, environmental adsorbent (biosorbent), functional catalyst, or feedstock for chemicals, depending on its final applications [26]. The study pointed out that rice husk-based biochar could be used as a material in environmental applications for water conservation, wastewater treatment, and soil amendment [24].

Pandit et al. [16] reviewed the bioenergy production using various types of agroindustrial wastewaters and agricultural residues utilizing the microbial fuel cell (MFC), also highlighting the techno-economics and lifecycle assessment of MFC, its commercialization, along with challenges. The use of different agricultural wastes and wastewater containing different industrial-by products for bioelectricity production in MFC seems to be a promising and alternative source of renewable energy generation. Moreover, it has been shown that different varieties of agricultural wastes and wastewater can be utilized using several different MFCs to enhance bioenergy production; thus, the conversion of agro-waste into bioenergy can be carried out by both biochemical and thermochemical MFC routes [16].

Another important issue concerning food waste biovalorization for bioethanol production is the substrate composition and the nutrients available for the microorganisms employed. It is well known that ethanol production is mainly dependent on glucose concentration (the theoretical alcohol yield is about 0.5 g of ethanol per g of glucose) and the yeast inoculums concentration, but nutrient supplementation is also an important parameter to take into consideration, since an adequate amount of specific nutrients, such as trace elements, vitamins, and nitrogen, often poor in agricultural waste, can significantly improve yeast viability and resistance to the medium, stimulating ethanol production performances [21,27]. Therefore, alcoholic fermentation is a complex biological process involving various operating factors, and the use of the classical "one factor at a time" approach for enhancing the final yield, could be time-consuming due to the large number of experiments to perform. In this regard, to implement an efficient fermentation process using industrial by-products, a predictive tool was investigated by Beigbeder et al. [17] to optimize the production of ethanol from non-treated sugar beet molasses by designing and developing a central composite design coupled with response surface methodology (CCD-RSM) statistical approach to investigate the effect of three fermentation process parameters (initial sugar, yeast, and nutrient concentrations) on ethanol productivity while considering several operating parameters such as ethanol yield and sugar utilization rate. Moreover, the second-order mathematical model obtained through the CCD-RSM was tested to evaluate its ability to make accurate predictions based on specific desired process outputs. The application of the CCDRSM statistical approach allowed to maximise the production of ethanol from non-sterilised sugar beet molasses using *Saccharomyces cerevisiae* while scaling up the experimental results up to a 100 L bioreactor scale [17].
