Food waste as nutrient source in heterotrophic microalgae cultivation

Sustainable and biotechnological production of docosahexaenoic acid from marine protists and slaughterhouse waste

Docosahexaenoic acid (DHA, 22:6n-3) is an essential omega-3 polyunsaturated fatty acid, abundant in the brain and eyes. DHA is crucial for maintaining the structural integrity and physiological functions of these vital organs. Within the brain, DHA is concentrated in the gray matter, synaptic membranes, and hippocampus. Likewise, in the eyes, substantial quantities can be found in the retina, with lower levels in the cornea and lens. Previous studies have outlined the potential for culturing marine heterotrophic protists in ways that provide cost-effective and sustainable DHA biosynthesis. Similarly, our previous work on repurposing slaughterhouse waste has highlighted this underutilized source of brain and ocular tissue, which can support the extraction of valuable nutrients such as DHA. In this review, we will examine the current state of the art related to DHA production from these two sources, explore potential applications, and outline the possible benefits that may be generated from our approaches, with an emphasis on ocular diseases.

Efficient Production of Bacterial Cellulose Using Komagataeibacter sucrofermentans on Sustainable Feedstocks

The production of bacterial cellulose (BC) has indeed garnered global attention due to its versatile properties and applications. Despite potential benefits, the challenges like low productivity, high fermentation costs, and expensive culture media hinder its industrialization. Utilizing low-cost substrates, especially waste streams, can help address the challenges. In this study, waste feedstocks such as restaurant leftovers, oranges, and grapefruit from canteens and supermarkets were valorized for BC production by Komagataeibacter sucrofermentans. Orange juice is a fascinating substrate with a highest concentration of 20.6 g/L and productivity of 2.05 g/L/d. Using HS medium with supplementary ions, organic acids, ethanol, and various carbon sources is a strategic approach for enhancing BC production. The study reveals that the addition of organic acids or ethanol moderately increased BC production, while ions inhibit BC synthesis, highlighting the complex interplay between various cultivation medium components. Additionally, fermentation with K. sucrofermentans using single and mixed carbon sources was conducted to elucidate the potential metabolic mechanism of BC production. Through alkaline treatment and drying in a 30 °C incubator, we produced the highest quality BC with 92.09 % crystallinity. Overall, the study enhances BC production knowledge and provides green and sustainable strategies for fermentative BC production.

Food waste generation and its industrial utilization: An overview

Food waste is produced for intended human consumption and is normally lost, discharged, contaminated, or finally degraded. The rising problem of food waste is increasing rapidly, so every sector is involved in minimizing food waste generation as well as waste management from collection to disposal, and scientists are developing the best eco-friendly and sustainable solutions for all sectors in the food supply chain, from the agricultural sector to the industrial sector and even up to the retailer to human consumption. Sustainable management is needed for the food wastes in the agricultural and industrial sectors, which are a major burning headache for environmentalists, health departments, and the government all over the earth. Various strategies can be employed to effectively control food waste, and these strategies can be ranked in a manner similar to the waste management hierarchy. The most desirable options involve the act of avoiding and donating edible portions to social agencies. Food waste is utilized in industrial operations to produce biofuels or biopolymers. The next stages involve the retrieval of nutrients and the sequestration of carbon through composting. The government implements appropriate management practices, laws, and orders to minimize food waste generation. Different contemporary methods are utilized to produce biofuel utilizing various types of food waste. In order for composting techniques to recover nutrients and fix carbon, food waste must be processed. Both the management of food waste and the creation of outgrowths utilizing biomaterials require additional study. This review aims to present a comprehensive analysis of the ongoing discourse surrounding the definitions of food waste, the production and implementation of methods to reduce it, the emergence of conversion technologies, and the most recent trends.

Composition of carbohydrate, protein and lipid derived from microalgae using thermally pretreated solid waste

Microalgae are widely recognized for their capacity to generate value-added products in a variety of sectors, including the pharmaceutical and food industries, bioenergy industries and wastewater industries. The quality of a microalga is significantly influenced by its proliferation. Along with growth, the biochemical profile may also vary based on the nutrient that is supplemented. The majority of the supplemented nutrients utilized are not in a functional state, as they are typically extracted in liquid form or pretreated prior to use. Parallel to numerous commonly applied pretreatment processes, including chemical, mechanical and biological, thermal pretreatment appears to receive less attention. Hence it is crucial to comprehend the potential for thermal pretreatment as well as its mechanism in militating the solid waste to release additional nutrients in order to enhance the biochemical profile of microalgae. The current review takes a closer look at the impact of various thermal pretreatments on solid waste on influencing microalgal performance in terms of their overall biochemical profiles such as carbohydrates, proteins and lipids. This approach is likely to enhance the circular economy by utilizing waste products and effectively closing the loop on waste. © 2024 Society of Chemical Industry.

Upcycling food waste as a low-cost cultivation medium for Chlorella sp. microalgae

BACKGROUND

Global food loss and waste have raised environmental concerns regarding the generation of greenhouse gases (e.g., carbon dioxide and methane gas), which directly contribute to climate change. To address these concerns, the present research aims to upcycle food waste into an alternative culture medium for the cultivation of microalgae. Various parameters including pretreatment of food waste (i.e., autoclave and non-autoclave), concentration of food waste culture medium (i.e., 10%, 30%, 50%, 70%, 90% and 100%), harvesting efficiency and biochemical compounds of Chlorella sp. microalgae were carried out.

RESULTS

Based on the preliminary findings, the highest biomass concentration obtained from 10% food waste culture medium in the autoclave for Chlorella sp., including strains FSP-E, ESP-31 and CY-1, were 2.869 ± 0.022, 2.385 ± 0.018 and 0.985 ± 0.0026 g L-1, respectively. Since Chlorella vulgaris FSP-E exhibited the highest biomass concentration, this microalgal strain was selected to examine the subsequent parameters. Cultivation of C. vulgaris FSP-E in 100FW achieves a biomass concentration of 4.465 ± 0.008 g L-1 with biochemical compounds of 6.94 ± 1.396, 248.24 ± 0.976 and 406.23 ± 0.593 mg g-1 for lipids, carbohydrates and proteins, respectively.

CONCLUSION

This study shows that using food waste as an alternative culture medium for C. vulgaris FSP-E can achieve substantial biomass productivity and biochemical content. This research work would contribute to the concept of net zero emission and transitioning toward a circular bioeconomy by upcycling food waste as an alternative culture medium for the cultivation of microalgae. © 2024 Society of Chemical Industry.

From waste to resource: Effects of digested rotten potato supernatant on the growth, total biomass and nutrient composition of Chlorella vulgaris

A study was carried out to evaluate the growth performance of Chlorella vulgaris, a green microalga, in three different concentrations of digested rotten potato supernatant (DRPS) for 16 days. C. vulgaris was grown in 20 % (T1), 40 % (T2), and 60 % (T3) of the DRPS and at the same time in Bold Basal Medium (BBM) as a control (T4). A significantly highest cell density of C. vulgaris was found in T1 (192.83 ± 1.75 × 105 cells mL-1) in comparison to T2 (136.83 ± 5.58 × 105 cells mL-1), and T3 (99.11 ± 5.38 × 105 cells mL-1) (p < 0.001 for all comparisons) while the cell density at T1 (192.83 ± 1.75 × 105 cells mL-1) and T4 (180.907 ± 4.58 × 105 cells mL-1) did not differ significantly (p = 0.227). Moreover, the mean daily division rate of C. vulgaris was significantly higher in T1 (0.340 ± 0.001 divisions day-1) in comparison to other concentrations of DRPS (p < 0.001 for all comparisons). The maximum value of total biomass (1.07 ± 0.10 g L-1) was found in T1 which was statistically similar to those in T4 and T2. In addition, there was no significant difference between the mean maximum values of chlorophyll-a content and optical density of C. vulgaris in T1 and T4. The highest protein content of 42.67 ± 0.57 % was observed in T4 which was significantly higher than T1 (39.43 ± 1.67 %) (p = 0.027). It is also worth mentioning that there was no significant difference in the crude lipid content of the microalgae grown in T1 (10.06 ± 0.17 %) and T4 (9.88 ± 0.14 %) (p = 0.616). Hence, 20 % DRPS can be used as an alternative culture media of BBM for C. vulgaris with a broad aim to accelerate the sustainable advancement of microalgal production.

Turning food waste to microbial lipid towards a superb economic and environmental sustainability: An innovative integrated biological route

With the drastic growth of the economic and population, the global energy requirement is on the rise, and massive human and material resources have been put into the development of alternative and renewable energy sources. Biodiesel has been recognized as a green and sustainable alternative energy, but the raw materials-associated source and cost makes it difficult to achieve large-scale commercial production. Microbial lipids (ML) produced by oleaginous microbes have attracted more and more topics as feedstocks for biodiesel production because of their unique advantages (fast growth cycle, small footprint and so on). However, there are still many problems and challenges ahead towards commercialization of ML-based biodiesel, especially the cost of feedstock for ML production. Food waste (FW) rich in organic matters and nutrients is an excellent and almost zero-cost feedstock for ML production. However, current biological routes of FW-based ML production have some defects, which make it impossible to achieve full industrialization at present. Therefore, this review intends to provide a critical and comprehensive analysis of current biological routes of FW-based ML production with the focus on the challenges and solutions forward. The biological routes towards future FW-based ML production must be able to concurrently achieve economic feasibility and environmental sustainability. On this condition, an innovative integrated biological route for FW-based ML production has thus been put forward, which is also elucidated on its economic and environmental sustainability. Moreover, the prospective advantages, limitations and challenges for future scale-up of FW-based ML production have also been outlined, together with the perspectives and directions forward.

Valorization of food waste: A comprehensive review of individual technologies for producing bio-based products

BACKGROUND

The escalating global concerns about food waste and the imperative need for sustainable practices have fuelled a burgeoning interest in the valorization of food waste. This comprehensive review delves into various technologies employed for converting food waste into valuable bio-based products. The article surveys individual technologies, ranging from traditional to cutting-edge methods, highlighting their respective mechanisms, advantages, and challenges.

SCOPE AND APPROACH

The exploration encompasses enzymatic processes, microbial fermentation, anaerobic digestion, and emerging technologies such as pyrolysis and hydrothermal processing. Each technology's efficacy in transforming food waste into bio-based products such as biofuels, enzymes, organic acids, prebiotics, and biopolymers is critically assessed. The review also considers the environmental and economic implications of these technologies, shedding light on their sustainability and scalability. The article discusses the role of technological integration and synergies in creating holistic approaches for maximizing the valorization potential of food waste. Key finding and conclusion: This review consolidates current knowledge on the valorization of food waste, offering a comprehensive understanding of individual technologies and their contributions to the sustainable production of bio-based products. The synthesis of information presented here aims to guide researchers, policymakers, and industry stakeholders in making informed decisions to address the global challenge of food waste while fostering a circular and eco-friendly economy.

Innovation in precision fermentation for food ingredients

A transformation in our food production system is being enabled by the convergence of advances in genome-based technologies and traditional fermentation. Science at the intersection of synthetic biology, fermentation, downstream processing for product recovery, and food science is needed to support technology development for the production of fermentation-derived food ingredients. The business and markets for fermentation-derived ingredients, including policy and regulations are discussed. A patent landscape of fermentation for the production of alternative proteins, lipids and carbohydrates for the food industry is provided. The science relating to strain engineering, fermentation, downstream processing, and food ingredient functionality that underpins developments in precision fermentation for the production of proteins, fats and oligosaccharides is examined. The production of sustainably-produced precision fermentation-derived ingredients and their introduction into the market require a transdisciplinary approach with multistakeholder engagement. Successful innovation in fermentation-derived ingredients will help feed the world more sustainably.

A Holistic Approach to Circular Bioeconomy Through the Sustainable Utilization of Microalgal Biomass for Biofuel and Other Value-Added Products

Emissions from transportation and industry primarily cause global warming, leading to floods, glacier melt, and rising seas. Widespread greenhouse gas emissions and resulting global warming pose significant risks to the environment, economy, and society. The need for alternative fuels drives the development of third-generation feedstocks: microalgae, seaweed, and cyanobacteria. These microalgae offer traits like rapid growth, high lipid content, non-competition with human food, and growth on non-arable land using brackish or waste water, making them promising for biofuel. These unique phototrophic organisms use sunlight, water, and carbon dioxide (CO2) to produce biofuels, biochemicals, and more. This review delves into the realm of microalgal biofuels, exploring contemporary methodologies employed for lipid extraction, significant value-added products, and the challenges inherent in their commercial-scale production. While the cost of microalgae bioproducts remains high, utilizing wastewater nutrients for cultivation could substantially cut production costs. Furthermore, this review summarizes the significance of biocircular economy approaches, which encompass the utilization of microalgal biomass as a feed supplement and biofertilizer, and biosorption of heavy metals and dyes. Besides, the discussion extends to the in-depth analysis and future prospects on the commercial potential of biofuel within the context of sustainable development. An economically efficient microalgae biorefinery should prioritize affordable nutrient inputs, efficient harvesting techniques, and the generation of valuable by-products.

Comparison of Different Pretreatment Processes Envisaging the Potential Use of Food Waste as Microalgae Substrate

A significant fraction of the food produced worldwide is currently lost or wasted throughout the supply chain, squandering natural and economic resources. Food waste valorization will be an important necessity in the coming years. This work investigates the ability of food waste to serve as a viable nutritional substrate for the heterotrophic growth of Chlorella vulgaris. The impact of different pretreatments on the elemental composition and microbial contamination of seven retail food waste mixtures was evaluated. Among the pretreatment methods applied to the food waste formulations, autoclaving was able to eliminate all microbial contamination and increase the availability of reducing sugars by 30%. Ohmic heating was also able to eliminate most of the contaminations in the food wastes in shorter time periods than autoclave. However, it has reduced the availability of reducing sugars, making it less preferable for microalgae heterotrophic cultivation. The direct utilization of food waste containing essential nutrients from fruits, vegetables, dairy and bakery products, and meat on the heterotrophic growth of microalgae allowed a biomass concentration of 2.2 × 108 cells·mL-1, being the culture able to consume more than 42% of the reducing sugars present in the substrate, thus demonstrating the economic and environmental potential of these wastes.

Dairy, Plant, and Novel Proteins: Scientific and Technological Aspects

Alternative proteins have gained popularity as consumers look for foods that are healthy, nutritious, and sustainable. Plant proteins, precision fermentation-derived proteins, cell-cultured proteins, algal proteins, and mycoproteins are the major types of alternative proteins that have emerged in recent years. This review addresses the major alternative-protein categories and reviews their definitions, current market statuses, production methods, and regulations in different countries, safety assessments, nutrition statuses, functionalities and applications, and, finally, sensory properties and consumer perception. Knowledge relative to traditional dairy proteins is also addressed. Opportunities and challenges associated with these proteins are also discussed. Future research directions are proposed to better understand these technologies and to develop consumer-acceptable final products.

Fruit residues as substrates for single-cell oil production by Rhodococcus species: physiology and genomics of carbohydrate catabolism

Strains belonging to R. opacus, R. jostii, R. fascians, R. erythropolis and R. equi exhibited differential ability to grow and produce lipids from fruit residues (grape marc and apple pomace), as well as single carbohydrates, such as glucose, gluconate, fructose and sucrose. The oleaginous species, R. opacus (strains PD630 and MR22) and R. jostii RHA1, produced higher yields of biomass (5.1-5.6 g L-1) and lipids (38-44% of CDW) from apple juice wastes, in comparison to R. erythropolis DSM43060, R. fascians F7 and R. equi ATCC6939 (4.1-4.3 g L-1 and less than 10% CDW of lipids). The production of cellular biomass and lipids were also higher in R. opacus and R. jostii (6.8-7.2 g L-1 and 33.9-36.5% of CDW of lipids) compared to R. erythropolis, R. fascians, and R. equi (3.0-3.6 g L-1 and less than 10% CDW of lipids), during cultivation of cells on wine grape waste. A genome-wide bioinformatic analysis of rhodococci indicated that oleaginous species possess a complete set of genes/proteins necessary for the efficient utilization of carbohydrates, whereas genomes from non-oleaginous rhodococcal strains lack relevant genes coding for transporters and/or enzymes for the uptake, catabolism and assimilation of carbohydrates, such as gntP, glcP, edd, eda, among others. Results of this study highlight the potential use of the oleaginous rhodococcal species to convert sugar-rich agro-industrial wastes, such as apple pomace and grape marc, into single-cell oils.

Biodiesel production and properties estimation from food waste and domestic wastewater by Rhodosporidium toruloides

Producing biodiesel from food waste (FW) would benefit both environment and economy. Current study investigated biodiesel production from food waste and domestic wastewater by utilizing the oleaginous yeast Rhodosporidium toruloides under non-sterile condition. The potential of biolipid production from the mixture of effluents of existing local FW treatment facilities and domestic wastewater was firstly evaluated. Then, to increase the nutrient recovery efficiency, FW hydrolysis process by crude enzymes produced from solid FWs by Aspergillus oryzae was introduced and the conditions were further optimized. The optimized hydrolysis process resulted in reducing sugar (RS) yield of 251.81 ± 8.09 mg gdryFW-1 and free amino nitrogen (FAN) yield of 7.70 ± 0.74 mg gdryFW-1 while waste oil with the RS yield of 93.54 ± 0.01 mg gdryFW-1 was easily separated without solvent usage. Compared to the hydrolysate only used, when mixed with domestic wastewater, the results showed obvious enhancement on biomass yield, biolipid yield, and wastewater treatment efficiency. The maximum biolipid yield was 29.80 ± 0.50 mg gdryFW-1 and the estimated quality of biodiesel produced from the biolipid met both EN 14214 and ASTM D6751 standards.

Lipid Production of Schizochytrium sp. HBW10 Isolated from Coastal Waters of Northern China Cultivated in Food Waste Hydrolysate

Marine oleaginous thraustochytrids have attracted increasing attention for their great potential in producing high-value active metabolites using various industrial and agricultural waste. Food waste containing abundant nutrients is considered as an excellent feedstock for microbial fermentation. In this study, a thraustochytrid strain Schizochytrium sp. HBW10 was isolated from a water column in Bohai Bay in Northern China for the first time. Further lipid production characteristics of S. sp. HBW10 were investigated utilizing sulfuric acid hydrolysate of food waste (FWH) from two different restaurants (FWH1 and FWH2) with the initial pH value adjusted by NaOH or NaHCO3. Results showed that the highest concentration of total fatty acids (TFAs) was observed in FWH2 medium with the 50% content level on the fifth day, reaching up to 0.34 g/L. A higher initial pH promoted the growth and saturated fatty acid (SFA) accumulation of S. sp. HBW10, achieving nearly 100% of the sum of saturated and monounsaturated fatty acids (SMUFAs) in TFAs with initial pH7 and pH8 in FWH1 medium. This work demonstrates a possible way for lipid production by thraustochytrids using food waste hydrolysate with a higher initial pH (pH7~pH8) adjusted by NaHCO3.

Oscillatoria sancta Cultivation Using Fruit and Vegetable Waste Formulated Media and Its Potential as a Functional Food: Assessment of Cultivation Optimization

The most cost-effective technique to cultivate microalgae is with low-cost resources, like fruit and vegetable peels. This study examined the viability of culturing microalgae (Oscillatoria sancta PCC 7515) isolated from a waterlogged region of Punjab, India, in a low-cost medium (fruit and vegetable waste peels) for pharmaceutical use. 16S rRNA sequencing discovered O. sancta PCC 7515. Fruit and vegetable peels were mineralized and chemically analyzed. At a 5% Bacillus flexus concentration, fruit and vegetable peels were liquefied at room temperature for 24 h. Response Surface Methodology (RSM) was used to assess and improve important cultural variables. The RSM predicted the best results at 10 pH, 30 days of incubation, 5% inoculum concentration, and 5% fruit and vegetable waste liquid leachate. The optimum conditions yielded more biomass than the basal conditions (0.8001 g/L). O. sancta PCC 7515 produced more lipids, proteins, Chl a, and Chl b in a formulated alternate medium than standard media. This study shows that O. sancta PCC 7515 may thrive on fruit and vegetable peel media. Fruit and vegetable waste (FVW) media assure low-cost microalgae-based functional foods.

Employing salt-tolerant bacteria Serratia marcescens subsp. SLS for biodegradation of oily kitchen waste

The high oil and salt content of kitchen waste (KW) inhibit bioconversion and humus production. To efficiently degrade oily kitchen waste (OKW), a halotolerant bacterial strain, Serratia marcescens subsp. SLS which could transform various animal fats and vegetable oils, was isolated from KW compost. Its identification, phylogenetic analysis, lipase activity assays, and oil degradation in liquid medium were assessed, and then it was employed to carry out a simulated OKW composting experiment. In liquid medium, the 24 h degradation rate of mixed oils (soybean oil: peanut oil: olive oil: lard = 1:1:1:1, v/v/v/v) was up to 87.37% at 30 °C, pH 7.0, 280 rpm, 2% oil concentration and 3% NaCl concentration. The ultra-performance liquid chromatography/tandem mass spectrometry (UPLC-MS) method demonstrated that the mechanism of SLS strain metabolizing long-chain triglycerides (TAGs) (C53-C60), especially the biodegradation of TAG (C18:3/C18:3/C18:3) by the strain can reach more than 90%. Degradation of 5, 10, 15% concentrations of total mixed oil were also calculated to be 64.57, 71.25, 67.99% respectively after a simulated composting duration of 15 days. The results suggest that the isolated strain of S. marcescens subsp. SLS is suitable for OKW bioremediation in high NaCl concentration within a reasonably short period of time. The findings introduced a salt-tolerant and oil-degrading bacteria, providing insights into the mechanism of oil biodegradation and offering new avenues of study for OKW compost and oily wastewater treatment.

Valorization of environmental-burden waste towards microalgal metabolites production

The present study develops a novel concept of using waste media as an algal nutrient resource compared to the usual growth media with the aid of growth kinetics study and metabolite production abilities. Food- and agri-compost wastes are compact structures with elemental compounds for microbial media. As a part of the study, environ-burden wastes (3:1) as a food source for photosynthetic algae as a substitute for the costly nutrient media were proposed. The environment-burden waste was also envisaged for macromolecule production, i.e., 99200 μg/ml lipid, 112.5 μg/ml protein, and 8.75 μg/ml carbohydrate with different dilutions of agri-waste, bold basal media (BBM), and Food waste, respectively. The fabricated growth kinetics and dynamics showcased the unstructured models of different photosynthetic algal growth phases and the depiction of productivity and kinetic parameters. The theoretical maximum biomass concentration (Xp) was found to be more (0.871) with diluted agricompost media than the usual BBM (0.697). The X_Lim values were found to be 0.362, 0.323 and 0.209 for BBM, diluted agri-compost media and diluted food waste media, respectively. Overall, the study proposes a cleaner approach of utilizing the wastes as growth media through a circular economy approach which eventually reduces the growth media cost with integrated macromolecule production capabilities.

Value Addition Employing Waste Bio-Materials in Environmental Remedies and Food Sector

Overall, combating food waste necessitates a multifaceted approach that includes education, infrastructure, and policy change. By working together to implement these strategies, we can help reduce the negative impacts of food waste and create a more sustainable and equitable food system. The sustained supply of nutrient-rich agrifood commodities is seriously threatened by inefficiencies caused by agricultural losses, which must be addressed. As per the statistical data given by the Food and Agriculture Organisation (FAO) of the United Nations, nearly 33.33% of the food that is produced for utilization is wasted and frittered away on a global level, which can be estimated as a loss of 1.3 billion metric tons per annum, which includes 30% cereals, 20% dairy products 35% seafood and fish, 45% fruits and vegetables, and 20% of meat. This review summarizes the various types of waste originating from various segments of the food industry, such as fruits and vegetables, dairy, marine, and brewery, also focusing on their potential for developing commercially available value-added products such as bioplastics, bio-fertilizers, food additives, antioxidants, antibiotics, biochar, organic acids, and enzymes. The paramount highlights include food waste valorization, which is a sustainable yet profitable alternative to waste management, and harnessing Machine Learning and Artificial Intelligence technology to minimize food waste. Detail of sustainability and feasibility of food waste-derived metabolic chemical compounds, along with the market outlook and recycling of food wastes, have been elucidated in this review.

Bioconversion of Cheese Whey and Food By-Products by Phaeodactylum tricornutum into Fucoxanthin and n-3 Lc-PUFA through a Biorefinery Approach

This study investigates the potential of utilizing three food wastes: cheese whey (CW), beet molasses (BM), and corn steep liquor (CSL) as alternative nutrient sources for the cultivation of the diatom Phaeodactylum tricornutum, a promising source of polyunsaturated eicosapentaenoic acid (EPA) and the carotenoid fucoxanthin. The CW media tested did not significantly impact the growth rate of P. tricornutum; however, CW hydrolysate significantly enhances cell growth. BM in cultivation medium enhances biomass production and fucoxanthin yield. The optimization of the new food waste medium was conducted through the application of a response surface methodology (RSM) using hydrolyzed CW, BM, and CSL as factors. The results showed a significant positive impact of these factors (p < 0.005), with an optimized biomass yield of 2.35 g L^-1 and a fucoxanthin yield of 3.64 mg L^-1 using a medium composed of 33 mL L^-1 of CW, 2.3 g L^-1 of BM, and 2.24 g L^-1 of CSL. The experimental results reported in this study showed that some food by-products from a biorefinery perspective could be utilized for the efficient production of fucoxanthin and other high-added-value products such as eicosapentaenoic acid (EPA).

Succinic Production from Source-Separated Kitchen Biowaste in a Biorefinery Concept: Focusing on Alternative Carbon Dioxide Source for Fermentation Processes

This study presents sustainable succinic acid production from the organic fraction of household kitchen wastes, i.e., the organic fraction of household kitchen waste (OFHKW), pretreated with enzymatic hydrolysis (100% cocktail dosage: 62.5% Cellic® CTec2, 31%% β-Glucanase and 6.5% Cellic ® HTec2, cellulase activity of 12.5 FPU/g-glucan). For fermentation, A. succinogenes was used, which consumes CO2 during the process. OFHKW at biomass loading > 20% (dry matter) resulted in a final concentration of fermentable sugars 81–85 g/L and can be treated as a promising feedstock for succinic production. Obtained results state that simultaneous addition of gaseous CO2 and MgCO3 (>20 g/dm3) resulted in the highest sugar conversion (79–81%) and succinic yields (74–75%). Additionally, CH4 content in biogas, used as a CO2 source, increased by 21–22% and reached 91–92% vol. Liquid fraction of source-separated kitchen biowaste and the residue after succinic fermentation were successfully converted into biogas. Results obtained in this study clearly document the possibility of integrated valuable compounds (succinic acid) and energy (biogas) production from the organic fraction of household kitchen wastes (OFHKW).

Okara Waste as a Substrate for the Microalgae Phaeodactylum tricornutum Enhances the Production of Algal Biomass, Fucoxanthin, and Polyunsaturated Fatty Acids

Despite the rich nutritional content of okara, the majority remains underutilized and discarded as food waste. In this study, solid-state fermentation of okara with food-grade fungi was performed to extract and solubilize any remnant nutrients locked within the lignocellulosic matrix to produce a nutrient-rich okara fermentate. Fermented okara media (FOM) was used as the sole nutrient source for growing marine diatom, Phaeodactylum tricornutum. Results have shown a two-fold increase in biomass production when grown on FOM (0.52 g L−1) as compared with conventional Guillard’s F/2 media (0.25 g L−1). Furthermore, cellular fucoxanthin content was enhanced significantly by two-fold to reach a final concentration of 15.3 mg g−1 compared to 7.3 mg g−1. Additionally, a significantly higher amount of polyunsaturated fatty acid (PUFA) was produced, particularly eicosapentaenoic acid (EPA) which yield has increased by nearly three-fold. Metabolomics analysis of intracellular contents in fermented okara culture revealed a significantly enhanced accumulation of nitrogenous metabolites, alongside the decrease in sugar metabolites as compared to F/2 culture, thus indicating metabolic flux towards pathways involved in cellular growth. This study demonstrated an innovative and low-cost strategy of using fermented okara as a nutritious substrate for achieving a sustainable media replacement for high density algal growth with a simultaneous enhancement of production in highly valued nutraceuticals, including fucoxanthin and EPA.

Cultivation of microalgae on food waste: Recent advances and way forward

Microalgae are photosynthetic microbes that can synthesize compounds of therapeutic potential with wide applications in the food, bioprocessing and pharmaceutical sector. Recent research advances have therefore, focused on finding suitable economic substrates for the sustainable cultivation of microalgae. Among such substrates, food derived waste specifically from the starch, meat, dairy, brewery, oil and fruit and vegetable processing industries has gained popularity but poses numerous challenges. Pretreatment, dilution of waste water supernatants, mixing of different food waste streams, utilizing two-stage cultivation and other biorefinery approaches have been intensively explored for multifold improvement in microalgal biomass recovery from food waste. This review discusses the advances and challenges associated with cultivation of microalgae on food waste. The review suggests that there is a need to standardize different waste substrates in terms of general composition, genetically engineered microalgal strains, tackling process scalability issues, controlling wastewater toxicity and establishing a waste transportation chain.

Functional bioplastics from food residual: Potentiality and safety issues

Plastic pollution and food waste are two global issues with much in common. Plastic containers were introduced as a practical and easy remedy to improve food preservation and reduce the risk of creating waste, but ironically, to address one problem, another has been made worse. The spread of single-use containers has dramatically increased the amount of plastic that has to be discarded, and the most urgent task is now to find a solution to what has become part of the problem. An innovative way around it consists of promoting the valorization of food residues by turning them into novel materials for packaging. Although the results are promising, the aim of completely replacing plastics with biodegradable materials still seems far from being achieved. This review illustrates the main strategies adopted thus far to produce new bioplastic materials and composites from waste resources and focuses on the pros and cons of the food recovery process to look for the aspects that represent an obstacle to the development of the circular food economy on an industrial scale.

A cheap two-step cultivation of Phaeodactylum tricornutum for increased TAG production and differential expression of TAG biosynthesis associated genes

A cheap cultivation of microalgae greatly reduces the biodiesel production cost. Subsequently in this study, citric acid and effluents from sugar and tannery industries were used as the nutritional supplements for the improvement of biomass and TAG production in Phaeodactylum tricornutum using two-step cultivation. When compared to control (media without supplementation), a considerable increase in biomass and chlorophyll a was obtained with citric acid (CA) and sugar industry effluent (SIE) supplemented media. In the two-step cultivation method, biomass raised from CA (100mg·L^-1) and SIE (1.5mL·L^-1) supplementations in the first step, viz. biomass production (BP) step was allowed for lipid accumulation in the second step, viz. lipid production (LP) step, and thus yielded enhanced lipids of 11.5 ± 0.7mg·L^-1·day^-1 and 13.5 ± 1.9mg·L^-1·day^-1 respectively, with improved TAG synthesis. Further, differential expression analysis of TAG biosynthetic genes of P. tricornutum under single-step and two-step cultivation modes were performed, and the gene expression patterns were studied.

Biorefinery Processing of Waste to Supply Cost-Effective and Sustainable Inputs for Two-Stage Microalgal Cultivation

Overcoming obstacles to commercialization of algal-based processes for biofuels and co-products requires not just piecemeal incremental improvements, but rather a comprehensive and fundamental re-consideration starting with the selected algae and its associated cultivation, harvesting, biomass conversion, and refinement. A novel two-stage process designed to address challenges of mass outdoor microalgal cultivation for biofuels and co-products was previously demonstrated using an oleaginous, haloalkaline-tolerant, and multi-trophic green Chlorella vulgaris. ALP2 from a soda lake. This involved cultivating the microalgae in a fermenter heterotrophically or photobioreactor mixotrophically (first-stage) to rapidly obtain high cell densities and inoculate an open-pond phototrophic culture (second-stage) featuring high levels of NaHCO3, pH, and salinity. An improved two-stage cultivation that instead sustainably used as more cheap and sustainable inputs the organic carbon, nitrogen, and phosphorous from fractionation of waste was here demonstrated in a small-scale biorefinery process. The first cultivation stage consisted of two simultaneous batch flask cultures featuring (1) mixotrophic cell productivity of 7.25 × 107 cells mL−1 day−1 on BG-110 medium supplemented with 1.587 g L−1 urea and an enzymatic hydrolysate of pre-treated (torrefaction + grinding + ozonolysis + soaking ammonia) wheat-straw that corresponded to 10 g L−1 glucose, and (2) mixotrophic cell productivity of 2.25 × 107 cells mL−1 day−1 on BG-110 medium supplemented with 1.587 g L−1 urea and a purified and de-toxified condensate of pre-treated (torrefaction + grinding) wheat straw that corresponded to 0.350 g L−1 of potassium acetate. The second cultivation stage featured 1H NMR-determined phototrophic lipid productivity of 0.045 g triacylglycerides (TAG) L−1 day−1 on BG-110 medium supplemented with 16.8 g L−1 NaHCO3 and fed batch-added 22% (v/v) anaerobically digested food waste effluent at HCl-mediated pH 9.

Food waste bioconversion into new food: A mini-review on nutrients circularity in the production of mushrooms, microalgae and insects

The global challenge of feeding an ever-increasing world population is leading scientists' attention towards nutritious and sustainable foods whose production should have low impacts on environment, economy and society. In case the input feedstock can be waste nutrients, the label of such productions becomes even greener. Nutrients circularity is nowadays an important circular economy practice. This mini-review focuses on the valorisation of food waste as precious biomass to grow new food and feed. In particular, three functional edibles are discussed in the present paper: mushrooms, microalgae and insects. These foods are part of people diets since ages in certain areas of the world and the original aspect of their cultivation and breeding found on waste nutrients recovery is here reviewed. Proofs of such food waste biorefinery viability are already given by several researches featuring the main traits of a suitable growing medium: optimal pool of nutrients and optimal pH. However, lot of work still needs to be done in order to assess the optimal growth and cultivation conditions and the health security of the harvested/bred edibles. A SWOT factors analysis was performed.

Microalgal transformation of food processing byproducts into functional food ingredients

Large amounts of food processing byproducts (FPBs) are generated from food manufacturing industries, the second-largest portion of food waste generation. FPBs may require additional cost for post-treatment otherwise cause environmental contamination. Valorization of FPBs into food ingredients by microalgae cultivation can save a high cost for organic carbon sources and nutrients from medium cost. This study reviews FPBs generation categorized by industry and traditional disposal. In contrast with the low-value production, FPBs utilization as the nutrient-abundant medium for microalgae can lead to high-value production. Due to the complex composition in FPBs, various pretreatment methods have been applied to extract the desired compounds and medium preparation. Using the FPB-based medium resulted in cost reduction and a productivity enhancement in previous literature. Although there are still challenges to overcome to achieve economic viability and environmental sustainability, the microalgal transformation of FPBs is attractive for functional food ingredients production.

Formulation of New Media from Dairy and Brewery Wastes for a Sustainable Production of DHA-Rich Oil by Aurantiochytrium mangrovei

Mozzarella stretching water (MSW) is a dairy effluent generated from mozzarella cheese production that does not have a real use and is destined to disposal, causing environmental problems and representing a high disposal cost for dairy producers. Spent brewery yeast (SBY) is another promising food waste produced after brewery manufacturing that could be recycled in new biotechnological processes. Aurantiochytrium mangrovei is an aquatic protist known as producer of bioactive lipids such as omega 3 long chain polyunsaturated fatty acids (ω3 LC-PUFA), in particular docosahexaenoic acid (DHA). In this work MSW and SBY have been used to formulate new sustainable growth media for A. mangrovei cultivation and production of DHA in an attempt to valorize these effluents. MSW required an enzymatic hydrolysis to enhance the biomass production. The new media obtained from hydrolysed MSW was also optimized using response surface methodologies, obtaining 10.14 g L^-1 of biomass in optimized medium, with a DHA content of 1.21 g L^-1.

Cultivation of Chlorella vulgaris on dairy waste using vision imaging for biomass growth monitoring

Continuous automation of conventional industrial operations with smart technology have drawn significant attention. Firstly, the study investigates on optimizing the proportion of industrial biscuit processing waste powder, (B) substituted into BG-11 as a source of cultivation medium for the growth of C. vulgaris. Various percentages of industrial biscuit processing waste powder, (B) were substituted in the inorganic medium to analyse the algal growth and biochemical composition. The use of 40B combination was found to yield highest biomass concentration (4.11 g/L), lipid (260.44 mg/g), protein (263.93 mg/g), and carbohydrate (418.99 mg/g) content compared with all the other culture ratio combination. Secondly, the exploitation of colour acquisition was performed onto C. vulgaris growth phases, and a novel photo-to-biomass concentration estimation was conducted via image processing for three different colour model pixels. Based on linear regression analysis the red, green, blue (RGB) colour model can interpret its colour variance precisely.

Advances in production of bioplastics by microalgae using food waste hydrolysate and wastewater: A review

Microalgae have emerged as an effective dual strategy for bio-valorisation of food processing wastewater and food waste hydrolysate which favours microalgae cultivation into producing value-added by products mainly lipids, carbohydrates, and proteins to the advantages of bioplastic production. Moreover, various microalgae have successfully removed high amount of organic pollutants from food processing wastewater prior discharging into the environment. Innovation of microalgae cultivating in food processing wastewater greatly reduced the cost of wastewater treatment compared to conventional approach in terms of lower carbon emissions, energy consumption, and chemical usage while producing microalgae biomass which can benefit low-cost fertilizer and bioplastic applications. The study on several microalgae species has all successfully grown on food waste hydrolysates showing high exponential growth rate and biomass production rich in proteins, lipids, carbohydrates, and fatty acids. Multiple techniques have been implemented for the extraction of food wastes to be incorporate into the bioplastic production.

Valorization of lipidic food waste for enhanced biodiesel recovery through two-step conversion: A novel microalgae-integrated approach

The present study designed an innovative route for two-step biodiesel recovery from lipidic food waste followed by microalgae cultivation. Optimization of oil conversion showed the highest fatty acid methyl esters (FAMEs) recovery of 92.6% (lipid basis). Microalgal lipid accumulation enhanced by the increased lipid-free waste hydrolysate ratio in the medium, where the maximum lipid content of 26.2 dw% was recorded using 50% hydrolysate. Application of 30% hydrolysate ratio resulted in the maximum recorded lipid productivity, which was 99.4% higher than that of the control and insignificant with 40% hydrolysate. Waste oil-derived FAMEs showed 69.0% higher saturated fatty acids (SFAs) proportion than that of algal lipids. In contrast, the highest polyunsaturated fatty acids (PUFAs) proportion (48.8% of total fatty acids) was recorded in microalgal lipids. The study concluded that mixing microalgal lipids with waste oil (1:1, w/w) provides a desirable practical route for enhanced biodiesel production complying with the international standards.

Role of Microalgae in Global CO2 Sequestration: Physiological Mechanism, Recent Development, Challenges, and Future Prospective

The rising concentration of global atmospheric carbon dioxide (CO2) has severely affected our planet’s homeostasis. Efforts are being made worldwide to curb carbon dioxide emissions, but there is still no strategy or technology available to date that is widely accepted. Two basic strategies are employed for reducing CO2 emissions, viz. (i) a decrease in fossil fuel use, and increased use of renewable energy sources; and (ii) carbon sequestration by various biological, chemical, or physical methods. This review has explored microalgae’s role in carbon sequestration, the physiological apparatus, with special emphasis on the carbon concentration mechanism (CCM). A CCM is a specialized mechanism of microalgae. In this process, a sub-cellular organelle known as pyrenoid, containing a high concentration of Ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco), helps in the fixation of CO2. One type of carbon concentration mechanism in Chlamydomonas reinhardtii and the association of pyrenoid tubules with thylakoids membrane is represented through a typical graphical model. Various environmental factors influencing carbon sequestration in microalgae and associated techno-economic challenges are analyzed critically.

Cultivation of the heterotrophic microalga Galdieria sulphuraria on food waste: A Life Cycle Assessment

The aim of this study was to perform a Life Cycle Assessment of a production process of 1 kg dry algal biomass powder (Galdieria sulphuraria) with 27 % (w/w) protein content for human consumption for optimizing the production regarding global warming potential and resource efficiency in combination with food waste utilization. It was investigated, underpinned by a comparison of the use of conventional glucose, whether and to what extent the environmental impact/global warming potential can be reduced by changing to food waste hydrolysate and how this can lead to a more sustainable use of resources and a sustainable development. Overall, the results showed that hydrolysis, along with freeze-drying, caused most of the overall impact. The carbon footprint associated with the use of hydrolyzed food waste was 11% higher than using conventional glucose and supplementary nutrients mainly driven by the high demand of energy for hydrolysis.

Heterotrophic cultivation of Galdieria sulphuraria under non-sterile conditions in digestate and hydrolyzed straw

Non-sterile heterotrophic cultivation of Galdieria sulphuraria in presence of digestate as well as straw after hydrolysis was investigated. G. sulphuraria can be grown in pure digestate at rates of 0.9 day^-1 with glucose. However, a proteolytic treatment of digestate resulted in increased growth rates (1.2 day^-1) and doubled cell concentrations. Furthermore, G. sulphuraria can utilize glucose obtained after straw hydrolysis. Biomass yields in glucose limited cultures were around 0.9 g per g glucose, while only 0.2 g biomass was formed per g glucose in glucose sufficient cultures. Biomass composition (w/w) of G. sulphuraria grown in digestate supplemented with straw hydrolysate consisted of 20% carbohydrates, 37% proteins and 3% lipids. This study revealed the potential to utilize agricultural waste streams to form algal biomass rich in proteins and may pave the way to novel utilization strategies to be implemented in rural areas.

Bioproducts generation from carboxylate platforms by the non-conventional yeast Yarrowia lipolytica

In recent years, there has been a growing interest in the use of renewable sources for bio-based production aiming at developing sustainable and feasible approaches towards a circular economy. Among these renewable sources, organic wastes (OWs) can be anaerobically digested to generate carboxylates like volatile fatty acids (VFAs), lactic acid, and longer-chain fatty acids that are regarded as novel building blocks for the synthesis of value-added compounds by yeasts. This review discusses on the processes that can be used to create valuable molecules from OW-derived VFAs; the pathways employed by the oleaginous yeast Yarrowia lipolytica to directly metabolize such molecules; and the relationship between OW composition, anaerobic digestion, and VFA profiles. The review also summarizes the current knowledge about VFA toxicity, the pathways by which VFAs are metabolized and the metabolic engineering strategies that can be employed in Y. lipolytica to produce value-added biobased compounds from VFAs.

Assortment of Native Microalgae for Improved Biomass and Lipid Production on Employing Vegetable Waste as a Frugal Cultivation Approach for Biodiesel Application

Enhanced biofuel production strategies from microalgae by employing affordable bio-waste usage are fetching significance, nowadays. This study examines the effect of VWE for enhanced biomass from new indigenous microalgal isolates, Asterarcys sp. SPC, Scenedesmus sp. KT-U, Scenedesmus sp. KTWL-A, Coelastrum sp. T-E, and Chlorella sp. TWL-B. The growth of microalgae in VWE-treated growth media showed considerable increase (1.14-2.3 folds) than control medium (without VWE). Further, two effective native microalgae were selected based on growth in VWE treatment, biomass productivity, and TAG accumulation through statistical clustering analysis. Mixotrophic batch cultivation of Scenedesmus sp. KT-U and Asterarcys sp. SPC cultivated using VWE treatment in the optimum concentration had produced significant average increase in BP (1.8 and 1.4 folds, respectively) than control (without VWE). Whereas in the lipid production phase, there was a noticeable increase in lipid yield in VWE-treated cells of lipid phase (231.8 ± 17.9 mg/L and 243.5 ± 25 mg/L) in Scenedesmus sp. KT-U and Asterarcys sp. SPC, respectively, than in control (140.5 ± 28 mg/L and 166.4 ± 23 mg/L) with considerable TAG accumulation. Thus, this study imparts strain selection process of native microalgae based on vegetable waste usage for improved yield of biomass and lipid amenable for cost-effective biodiesel production.

High-value utilization of the waste hydrolysate of Dioscorea zingiberensis for docosahexaenoic acid production in Schizochytrium sp

The starch saccharification liquid of Dioscorea zingiberensis tubers (SSLD) is a glucose-rich agro-industrial waste. Herein, SSLD was used as a novel potential carbon source for the biosynthesis of docosahexaenoic acid (DHA) in Schizochytrium sp. to achieve waste recycling and high-value utilization. Component analysis showed that SSLD contains abundant nutrients, such as glucose, amino acids, phenolics and flavonoids. When the total sugar concentration in SSLD was optimized to 90 g/L, the biomass and DHA yield reached 44.85 and 6.60 g/L, respectively, which were 32.1% and 36.92% higher than that at pure glucose culture condition. Fermentation characteristics and gene expression analysis showed that SSLD could remarkably improve cell antioxidant capacity, which is beneficial to scavenge intracellular reactive oxygen species and increase the gene expression of antioxidant enzymes in Schizochytrium sp. Hence, SSLD is an effective and economic carbon source for DHA production in Schizochytrium sp.

COVID-19 mask waste to energy via thermochemical pathway: Effect of Co-Feeding food waste

In this study, co-pyrolysis of single-use face mask (for the protection against COVID-19) and food waste was investigated for the purpose of energy and resource valorization of the waste materials. To this end, disposable face mask (a piece of personal protective equipment) was pyrolyzed to produce fuel-range chemicals. The pyrolytic gas evolved from the pyrolysis of the single-use face mask consisted primarily of non-condensable permanent hydrocarbons such as CH₄, C₂H₄, C₂H₆, C₃H₆, and C₃H₈. An increase in pyrolysis temperature enhanced the non-condensable hydrocarbon yields. The pyrolytic gas had a HHV of >40 MJ kg^-1. In addition, hydrocarbons with wider carbon number ranges (e.g., gasoline-, jet fuel-, diesel-, and motor oil-range hydrocarbons) were produced in the pyrolysis of the disposable face mask. The yields of the gasoline-, jet fuel-, and diesel-range hydrocarbons obtained from the single-use mask were highest at 973 K. The pyrolysis of the single-use face mask yielded 14.7 wt% gasoline-, 18.4 wt% jet fuel-, 34.1 wt% diesel-, and 18.1 wt% motor oil-range hydrocarbons. No solid char was produced via the pyrolysis of the disposable face mask. The addition of food waste to the pyrolysis feedstock led to the formation of char, but the presence of the single-use face mask did not affect the properties and energy content of the char. More H₂ and less hydrocarbons were produced by co-feeding food waste in the pyrolysis of the disposable face mask. The results of this study can contribute to thermochemical management and utilization of everyday waste as a source of energy.

Minimizing hazardous impact of food waste in a circular economy - Advances in resource recovery through green strategies

Recent trends in food waste and its management have increasingly started to focus on treating it as a reusable resource. The hazardous impact of food waste such as the release of greenhouse gases, deterioration of water quality and contamination of land areas are a major threat posed by food waste. Under the circular economy principles, food waste can be used as a sustainable supply of high-value energy, fuel, and nutrients through green techniques such as anaerobic digestion, co-digestion, composting, enzymatic treatment, ultrasonic, hydrothermal carbonization. Recent advances made in anaerobic co-digestion are helping in tackling dual or even multiple waste streams at once with better product yields. Integrated approaches that employ pre-processing the food waste to remove obstacles such as volatile fractions, oils and other inhibitory components from the feedstock to enhance their bioconversion to reduce sugars. Research efforts are also progressing in optimizing the operational parameters such as temperature, pressure, pH and residence time to enhance further the output of products such as methane, hydrogen and other platform chemicals such as lactic acid, succinic acid and formic acid. This review brings together some of the recent progress made in the green strategies towards food waste valorization.

Biodiesel Production From Lignocellulosic Biomass Using Oleaginous Microbes: Prospects for Integrated Biofuel Production

Biodiesel is an eco-friendly, renewable, and potential liquid biofuel mitigating greenhouse gas emissions. Biodiesel has been produced initially from vegetable oils, non-edible oils, and waste oils. However, these feedstocks have several disadvantages such as requirement of land and labor and remain expensive. Similarly, in reference to waste oils, the feedstock content is succinct in supply and unable to meet the demand. Recent studies demonstrated utilization of lignocellulosic substrates for biodiesel production using oleaginous microorganisms. These microbes accumulate higher lipid content under stress conditions, whose lipid composition is similar to vegetable oils. In this paper, feedstocks used for biodiesel production such as vegetable oils, non-edible oils, oleaginous microalgae, fungi, yeast, and bacteria have been illustrated. Thereafter, steps enumerated in biodiesel production from lignocellulosic substrates through pretreatment, saccharification and oleaginous microbe-mediated fermentation, lipid extraction, transesterification, and purification of biodiesel are discussed. Besides, the importance of metabolic engineering in ensuring biofuels and biorefinery and a brief note on integration of liquid biofuels have been included that have significant importance in terms of circular economy aspects.

The Role of Heterotrophic Microalgae in Waste Conversion to Biofuels and Bioproducts

In the last few decades, microalgae have attracted attention from the scientific community worldwide, being considered a promising feedstock for renewable energy production, as well as for a wide range of high value-added products such as pigments and poly-unsaturated fatty acids for pharmaceutical, nutraceutical, food, and cosmetic markets. Despite the investments in microalgae biotechnology to date, the major obstacle to its wide commercialization is the high cost of microalgal biomass production and expensive product extraction steps. One way to reduce the microalgae production costs is the use of low-cost feedstock for microalgae production. Some wastes contain organic and inorganic components that may serve as nutrients for algal growth, decreasing the culture media cost and, thus, the overall process costs. Most of the research studies on microalgae waste treatment use autotrophic and mixotrophic microalgae growth. Research on heterotrophic microalgae to treat wastes is still scarce, although this cultivation mode shows several benefits over the others, such as higher organic carbon load tolerance, intracellular products production, and stability in production all year round, regardless of the location and climate. In this review article, the use of heterotrophic microalgae to simultaneously treat wastes and produce high value-added bioproducts and biofuels will be discussed, critically analyzing the most recent research done in this area so far and envisioning the use of this approach to a commercial scale in the near future.

Increasing 2 -Bio- (H2 and CH4) production from food waste by combining two-stage anaerobic digestion and electrodialysis for continuous volatile fatty acids removal

A novel approach of using two stage anaerobic digestion coupled with electrodialysis technology has been investigated. This approach was used to improving bio hydrogen and methane yields from food waste while simultaneously producing a green chemical feedstock. The first digester was used for hydrogen production and the second digester was used for methane production. The first digester was combined with continuous separation of volatile fatty acids using electrodialysis. The concentrations of carbohydrates, proteins and fats in the prepared food waste were 22.7%, 5.7% and 5.2% respectively. Continuous removal of volatile fatty acids during fermentation in the hydrogen digester not only increased hydrogen yields but also increased the production rate of volatile fatty acids. As a result of continuous VFA separation, hydrogen yields increased from 17.3 mL H₂/g VS _fermenter to 33.68 mL H₂/g VS _fermenter. Methane yields also increased from 28.94 mL CH₄/g VS _fermenter to 43.94 mL CH₄/g VS _fermenter. This represents a total increase in bio-energy yields of 77.1%. COD reduced by 73% after using two stage anaerobic digestion, however, this reduction increased to 86.7% after using electrodialysis technology for separation of volatile fatty acids. Electrodialysis technology coupled with anaerobic digestion improved substrate utilization, increased bioenergy yields and looks to be promising for treating complex wastes such as food waste.

Removal of sugars in wastewater from food production through heterotrophic growth of Galdieria sulphuraria

The unicellular extremophilic red alga Galdieria sulphuraria is capable of chemoheterotrophy and its growth has been investigated on some defined and undefined substrates. In this study, the removal of sugars in wastewater from fruit-salad production with G. sulphuraria strain SAG 21.92 was analyzed. Growth and sugar consumption were determined under variation of temperature, pH-value and concentration of a model substrate, containing sucrose, glucose and fructose. In shake flask cultivation maximum specific growth rate and specific substrate consumption rate of 1.53±0.09 day-1 and 2.41±0.14 gSub·gDW -1·day-1 were measured at pH 2 and 42°C. A scale-up of this process was conducted in a 3 L stirred tank reactor (STR). Wastewater from fruit-salad production was diluted to 15 g·L-1 total sugar concentration, supplemented with micronutrients and ammonia and pH was set to 3. Determined growth rate and substrate consumption were 1.21 day-1 and 1.88 gSub·gDW -1·day-1, respectively. It was demonstrated, that high sugar concentrations in wastewater streams from food production processes can be significantly reduced with G. sulphuraria SAG 21.92. This strain could achieve substrate consumption rates in wastewater, equal to the more common strain 074G, but at higher pH values. Generated biomass can be used for production of phycocyanin, a valuable nutraceutical.

Food waste valorization: Energy production using novel integrated systems

Management of food waste (FW) is a global challenge due to increasing population and economic activities. Presently, landfill and incineration are the keyways of FW management, while economical and environmental sustainability have been an issue. Therefore, the biological processes have been investigated for resource and energy recovery from FW. However, these biological approaches have certain drawbacks and cannot be a complete solution for FW management. Therefore, this review aims to offer a detailed and complete analysis of current available technologies to achieve environmental and economical sustainability. In this context, zero solid waste discharge for resource and energy recovery has been put into view. Corresponding to which several innovative technologies using integrated biological methods for resource and energy recovery from FW have been elucidated.