Concise review on ethanol production from food waste: development and sustainability

Cost-Benefit Analysis of Enzymatic Hydrolysis Alternatives for Food Waste Management

In this study, we aimed to evaluate the economic, environmental, and social viability of the enzymatic hydrolysis process for food waste valorization by applying cost-benefit analysi (CBA). Our research was based on the investigation of three scenarios/alternatives for the final product of the enzymatic hydrolysis process and the production of bioethanol, bioactive peptides, and organic acids. Key economic indicators, such as cost/benefit ratios, net present value (NPV), and internal rate of return (IRR), were used to evaluate financial performance. At the end of the CBA, a sensitivity analysis was conducted to highlight the performance of each scenario under varying conditions, including fluctuating costs, benefits, and discount rates. These results indicate that enzymatic hydrolysis offers a significant opportunity for reducing food waste and its environmental impacts and promotes sustainability. Bioactive peptide production was found to be the most environmentally viable option, offering the highest cost-benefit efficiency. In both the optimistic and pessimistic scenarios of the sensitivity analysis, the results revealed that bioactive peptide production is economically viable, while the other alternatives, such as bioethanol and organic acid production, are more sensitive to economic and operational changes. This study revealed that enzymatic hydrolysis, as evaluated through CBA, offers a viable and impactful method for food waste management. It reduces environmental impacts, enhances sustainability, and aligns with the principles of a circular economy. The adoption of such innovative waste management strategies is considered essential for building a more sustainable and resource-efficient food system.

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.

Whether biorefinery is a promising way to support waste source separation? From the life cycle perspective

Since the implementation of the waste separation policy, the disposal of source-separated food waste (FW) has been more strictly required. Traditional source-separated FW treatment technologies, such as anaerobic digestion (AD) and aerobic composting (AC), suffer from low resource utilization efficiency and poor economic benefits. It is one of the main limiting factors for the promotion of waste separation. Life cycle assessment (LCA) was conducted for five municipal solid waste (MSW) treatment technologies, compared their environmental impacts, and analyzed the impact of waste separation ratios to determine whether biorefinery is a promising way to support waste source separation. The results showed that black soldier fly (BSF) treatment had the lowest net global warming potential (GWP) of all technologies, reduced by 40.8 % relative to the non-source-separated treatment. Ethanol production had the second-lowest net environmental impact potential because bioethanol replaces fossil fuel to avoid the emission of pollutants from its combustion. When two biorefinery technologies with excellent efficiency to avoid environmental impact are used to treat source-separated FW, the increase in the percentage of waste separation will help reduce the environmental impact of MSW treatment. The application of biorefinery technologies is considered a viable option for source-separated FW treatment. AC should not be widely promoted because it showed the worst net environmental benefits, and waste separation will elevate the environmental impact of its treatment process.

Potential and Restrictions of Food-Waste Valorization through Fermentation Processes

Food losses (FL) and waste (FW) occur throughout the food supply chain. These residues are disposed of on landfills producing environmental issues due to pollutants released into the air, water, and soil. Several research efforts have focused on upgrading FL and FW in a portfolio of added-value products and energy vectors. Among the most relevant research advances, biotechnological upgrading of these residues via fermentation has been demonstrated to be a potential valorization alternative. Despite the multiple investigations performed on the conversion of FL and FW, a lack of comprehensive and systematic literature reviews evaluating the potential of fermentative processes to upgrade different food residues has been identified. Therefore, this article reviews the use of FL and FW in fermentative processes considering the composition, operating conditions, platforms, fermentation product application, and restrictions. This review provides the framework of food residue fermentation based on reported applications, experimental, and theoretical data. Moreover, this review provides future research ideas based on the analyzed information. Thus, potential applications and restrictions of the FL and FW used for fermentative processes are highlighted. In the end, food residues fermentation must be considered a mandatory step toward waste minimization, a circular economy, and the development of more sustainable production and consumption patterns.

Moving towards the Application of Biocatalysis in Food Waste Biorefinery

Waste valorization is an important strategy to reduce environmental pollution and dependency on petroleum-based fuels. In this regard, utilization of food waste as a versatile and low-cost resource is important. Several advanced catalytic methods for the valorization of food waste have been widely investigated for the production of liquid biofuels. Along this line, chemical catalysts have been explored for the synthesis of liquid biofuels. Chemo-catalysis is mainly metal based, which requires harsh process conditions. Alternatively, biocatalysts are currently being investigated as a result of several advantages such as mild reaction conditions, recyclability, selectivity and biodegradability. In this work, recent biocatalytic technologies for the preparation of liquid biofuels through food waste valorization are discussed thoroughly. Lipases are employed for the synthesis of biodiesel and the upgradation of bio-oil, whereas methane mono-oxygenases could be explored for the production of methanol via the oxidation of methane generated from food wastes. Industrial production of ethanol from food waste using bioconversion technologies is a success story. To date, there has been no specific report on the use of food waste for propanol preparation using enzymes. The ABE process (Acetone–Butanol–Ethanol) (using suitable microorganisms) is used for butanol preparation, where the vacuum stripping system is integrated to remove butanol from the broth and circumvent inhibition. The synthesis of hydrocarbon fuels from fatty acids and triglycerides can be carried out using enzymes, such as carboxylic acid reductase and fatty acid photodecarboxylase (an algal photoenzyme). Both carboxylic acid reductase and fatty acid photodecarboxylase have not yet been applied in the direct valorization of food wastes. Furthermore, limitations of the reported methods, societal and economic aspects and a fresh perspective on the subject, along with important examples, are described.

Valorization of Fourth-Range Wastes: Evaluating Pyrolytic Behavior of Fresh and Digested Wastes

Changes in daily habits and a stressful lifestyle create modifications in consumer preferences and open opportunities to new market products. This is the case of fourth-range products in which the industrial sector generates a waste stream of high quality. Valorization of this type of waste as a single stream is desirable to avoid lowering quality with other low-grade materials. Anaerobic digestion of fourth-range wastes was studied under discontinuous and semi-continuous conditions. A high carbon content characterizes the organic material composed of fruit and vegetable wastes. The fast degradation of the substrate indicated no limitations associated with the hydrolysis stage, as observed from kinetic parameters estimated from batch assays. However, the easiness of degradation did not translate into short hydraulic retention times when operating under semi-continuous conditions. Additionally, the insufficient amount of nutrients prevented the development of a well-balanced digestion process. Specific methane production was 325 mL CH4/g VS added at a hydraulic retention time of 30 days. However, solid accumulation was observed at the end of the experiment, indicating that conditions established did not allow for the complete conversion of the organic material. Digestate evaluation using thermal analysis under inert conditions showed a thermal profile evidencing the presence of complex components and a high tendency to char formation.

A comprehensive review on the advances of bioproducts from biomass towards meeting net zero carbon emissions (NZCE)

This review investigates the development of bioproducts from biomass and their contribution towards net zero carbon emissions. The promising future of biomasses conversion techniques to produce bioproducts was reviewed. The advances in anaerobic digestion as a biochemical conversion technique have been critically studied and contribute towards carbon emissions mitigation. Different applications of microalgae biomass towards carbon neutrality were comprehensively discussed, and several research findings have been tabulated in this review. The carbon footprints of wastewater treatment plants were studied, and bioenergy utilisation from sludge production was shown to mitigate carbon footprints. The carbon-sinking capability of microalgae has also been outlined. Furthermore, integrated conversion processes have shown to enhance bioproducts generation yield and quality. The anaerobic digestion/pyrolysis integrated process was promising, and potential substrates have been suggested for future research. Lastly, challenges and future perspectives of bioproducts were outlined for a contribution towards meeting carbon neutrality.

Optimization of consolidated bioprocessing by response surface methodology in the conversion of corn stover to bioethanol by thermophilic Geobacillus thermoglucosidasius

The swift depletion of fossil fuels and their associated environment and economic impact has led the world to explore the sustainable alternate fuels. Amidst the available alternatives lignocellulosic bioethanol provides the edge over the exhausting fossil fuels. In this current study, Response surface methodology, a mathematical and statistical tool was used to optimize the fermentation conditions in consolidated bioprocessing of corn stover by Geobacillus thermoglucosidasius. The impact of inoculum concentration, temperature, pH, agitation speed and time in bioethanol fermentation were screened with Plackett-Burman design and it was farther optimized with central composite design. The analysis by PBD confirmed the significant impact of fermentation time, inoculum concentration, and temperature of the fermentation process. Further, it was optimized with CCD. This showed that 15% v/v of Inoculum concentration, 50 °C of temperature and fermentation time of 72 h increased the bioethanol concentration to a maximum of 9.04 g/L with 0.45 g/g significant yield and a conversion efficiency of 88%. Thus, the CCD showed a satisfactory result in consolidated bioprocessing of bioethanol from corn stover. Thus, in the future, this approach of optimization will yield a good base for consistent production of bioethanol.

Production of bioethanol from food waste: Status and perspectives

There is an immediate global requirement for an ingenious strategy for food waste conversion to biofuels in order to replace fossil fuels with renewable resources. Food waste conversion to bioethanol could lead to a sustainable process having the dual advantage of resolving the issue of food waste disposal as well as meeting the energy requirements of the increasing population. Food waste is increasing at the rate of 1.3 billion tonnes per year, considered to be one-third of global food production. According to LCA studies discarding these wastes is detritus to the environment, therefore; it is beneficial to convert the food waste into bioethanol. The CO₂ emission in this process offers zero impact on the environment as it is biogenic. Among several pretreatment strategies, hydrothermal pretreatment could be a better approach for pretreating food waste because it solubilizes organic solids, resulting in an increased recovery of fermentable sugars to produce bioenergy.

Green Recycling Methods to Treat Lithium-Ion Batteries E-Waste: A Circular Approach to Sustainability

E-waste generated from end-of-life spent lithium-ion batteries (LIBs) is increasing at a rapid rate owing to the increasing consumption of these batteries in portable electronics, electric vehicles, and renewable energy storage worldwide. On the one hand, landfilling and incinerating LIBs e-waste poses environmental and safety concerns owing to their constituent materials. On the other hand, scarcity of metal resources used in manufacturing LIBs and potential value creation through the recovery of these metal resources from spent LIBs has triggered increased interest in recycling spent LIBs from e-waste. State of the art recycling of spent LIBs involving pyrometallurgy and hydrometallurgy processes generates considerable unwanted environmental concerns. Hence, alternative innovative approaches toward the green recycling process of spent LIBs are essential to tackle large volumes of spent LIBs in an environmentally friendly way. Such evolving techniques for spent LIBs recycling based on green approaches, including bioleaching, waste for waste approach, and electrodeposition, are discussed here. Furthermore, the ways to regenerate strategic metals post leaching, efficiently reprocess extracted high-value materials, and reuse them in applications including electrode materials for new LIBs. The concept of "circular economy" is highlighted through closed-loop recycling of spent LIBs achieved through green-sustainable approaches.

Enhanced Energy Recovery from Food Waste by Co-Production of Bioethanol and Biomethane Process

The primary objective of this research is to study ways to increase the potential of energy production from food waste by co-production of bioethanol and biomethane. In the first step, the food waste was hydrolysed with an enzyme at different concentrations. By increasing the concentration of enzyme, the amount of reducing sugar produced increased, reaching a maximum amount of 0.49 g/g food waste. After 120 h of fermentation with Saccharomyces cerevisiae, nearly all reducing sugars in the hydrolysate were converted to ethanol, yielding 0.43–0.50 g ethanol/g reducing sugar, or 84.3–99.6% of theoretical yield. The solid residue from fermentation was subsequently subjected to anaerobic digestion, allowing the production of biomethane, which reached a maximum yield of 264.53 ± 2.3 mL/g VS. This results in a gross energy output of 9.57 GJ, which is considered a nearly 58% increase in total energy obtained, compared to ethanol production alone. This study shows that food waste is a raw material with high energy production potential that could be further developed into a promising energy source. Not only does this benefit energy production, but it also lowers the cost of food waste disposal, reduces greenhouse gas emissions, and is a sustainable energy production approach.

Sustainable processing of food waste for production of bio-based products for circular bioeconomy

Sustainable development of circular bioeconomy concept is only possible upon adopting potential advanced technologies for food waste valorization. This approach can simultaneously answer resources and environmental challenges incurred due to capital loss and greenhouse gases accumulation. Food waste valorization opens new horizons of economical growth, bringing waste as an opportunity feedstock for bio processes to synthesize biobased products from biological source in a circular loop. Advanced technologies like Ultrasound assisted extraction, Microwave assisted extraction, bioreactors, enzyme immobilization assisted extraction and their combination mitigates the global concern caused due to mismanagement of food waste. Food waste decomposition to sub-zero level using advanced techniques fabricates food waste into bio-based products like bioactive compounds (antioxidants, pigments, polysaccharides, polyphenols, etc.); biofuels (biodiesel, biomethane, biohydrogen); and bioplastics. This review abridges merits and demerits of various advanced techniques extended for food waste valorization and contribution of food waste in revenue generation as value added products.

Effect of honeycomb, granular, and powder activated carbon additives on continuous lactic acid fermentation of complex food waste with mixed inoculation

To accelerate and stabilize lactic acid fermentation from food waste, three types of activated carbon, including honeycomb activated carbon, granular activated carbon, and powder activated carbon, were tested as additives in continuous food waste fermentation processes. The results showed that carbohydrate was the primary substrate for lactic acid production, but its conversion reached a high, stable level after a long period of microbial acclimation in the control system. Activated carbon, especially honeycomb activated carbon accelerated the stabilization of lactic acid fermentation and enhanced the tolerance of fermentation systems to a hostile and fluctuating environment. The addition of activated carbon increased the oxidation-reduction potential to approximately 100 mV and altered the microbial communities. Homolactic fermentation bacteria were dominant in all the systems, and the honeycomb activated carbon addition stimulated the growth of unclassified Lactobacillus and immobilized Lactobacillus panis with strong carbohydrate metabolism. In addition, powder activated carbon enhanced the degradation of protein due to the multiplying Pseudomonas. At the stable stage, the organic conversion rates were close in the control system and the systems with the activated carbon addition, and the lactic acid concentrations in these systems remained at 8000-10,000 mg/L. Considering the cost of the additives, honeycomb activated carbon is a good choice to stabilize lactic acid production from food waste.

Organic waste streams as feedstock for the production of high volume-low value products

Valorisation of organic wastes to produce industrially relevant commodity products is a sustainable, cost-effective and viable alternative providing a green platform for chemical production while simultaneously leading to waste disposal management. In the present study, organic wastes such as agricultural residue-derived sugars, oilseed meals, poultry waste and molasses were used for substituting expensive organic fermentation medium components. Moorella thermoacetica and Aurantiochytrium limacinum were adapted on these waste-derived hydrolysates to produce high volume-low value products such as bio-acetic acid (80% theoretical yields) and oil-rich fish/animal feed (more than 85% dry cell weight as compared with conventional nutrient sources) respectively. Use of these waste-derived nutrients led to ~ 75% and ~ 90% reduction in media cost for acetic acid and oil-rich biomass production respectively as compared with that of traditionally used high-priced medium components. The strategy will assist in the cost reduction for high volume-low value products while also ensuring waste recovery.

Direct Conversion of Food Waste Extract into Caproate: Metagenomics Assessment of Chain Elongation Process

In a circular economy strategy, waste resources can be used for the biological production of high added-value substances, such as medium chain fatty acids (MCFAs), thus minimising waste and favouring a sustainable process. This study investigates single-stage fermentation processes for the production of MCFAs in a semi-continuous reactor treating the extract of real food waste (FW), without the addition of external electron donors. Two sequential acidogenic fermentation tests were carried out at an organic loading rate (OLR) of 5 and 15 gCOD L⁻¹d⁻¹ with a hydraulic retention time of 4 days and pH controlled at 6 ± 0.2. The highest level of caproate (4.8 g L⁻¹) was observed at OLR of 15 gCOD L⁻¹d⁻¹ with a microbiome mainly composed by lactate-producing Actinomyces, Atopobium, and Olsenella species and caproate-producing Pseudoramibacter. Metagenomic analysis revealed the presence of key enzymes for the production of lactate, such as lactate dehydrogenase and pyruvate ferredoxin oxidoreductase, as well as several enzymes involved in the reverse β-oxidation pathway, thus suggesting the occurrence of a lactate-based chain elongation process.

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.

Nano iron materials enhance food waste fermentation

Anaerobic fermentation can produce valuable chemicals from food waste, such as butyric acid, lactic acid, and ethanol. Three nano iron materials, i.e. zero-valence iron (nZVI), ferric oxide (nFO), and magnetite (nM), were tested to improve food waste fermentation with mixed inoculation. nZVI and nFO enhanced the dissolution and conversion of carbohydrate to lactate, dependent on different mechanisms, while nM had almost no effects due to its aggregation at high doses. nZVI alleviated the drop of pH, kept the ORP at an anaerobic level, increased functional enzymes, and resulted in a high hydrolysis rate of 45% and lactic acid yield of 0.16 g/g VS_fed at the dose of 500 mg/(L_fed·d). nFO increased the ORP to 100 mV, stimulated the enrichment of Pseudomonas, and increased the abundance of Lactobacillus_panis, leading to hydrolysis rate of 47% and lactic acid yield of 0.19 g/gVS_fed at the dose of 200 mg/(L_fed·d).

Estimation and analysis of municipal food waste and resource utilization potential in China

With rapid urbanization, municipal food waste (MFW), which is an important part of municipal solid waste, has attracted considerable attention owing to its environmental impact and polluting nature. There has been little research on the quantity and distribution of food waste (FW) produced in China. This study focused on a systematic estimation and analysis of MFW produced in administrative divisions at the prefecture-level and above in China for the first time. From the national level to the prefectural level, with the shrinking of the research units, more intuitive support was obtained for relevant decisions. On the basis of the estimated results, suggestions are provided for proper FW treatment technologies and operational scale of the facilities, and the resource utilization potential has also been estimated. The distribution results indicated that FW characteristics have great variability in the different economic regions of China. Furthermore, it was found that the available FW has a resource utilization potential that is equivalent to 4669.1 million m³ of biogas, 3.6 million tons of biodiesel, and 1.5 million tons of organic fertilizer (dry weight). It is worth mentioning that this amount of biogas can replace 7.5 million tons of standard coal. However, only a small part of the generated MFW can be treated in the existing treatment plants in China. Finally, current key bottlenecks of FW treatment in China have been discussed, and detailed suggestions are presented for further improvement of MFW management.

Oriented Fermentation of Food Waste towards High-Value Products: A Review

Food waste has a great potential for resource recovery due to its huge yield and high organic content. Oriented fermentation is a promising method with strong application prospects due to high efficiency, strong robustness, and high-value products. Different fermentation types lead to different products, which can be shifted by adjusting fermentation conditions such as inoculum, pH, oxidation-reduction potential (ORP), organic loading rate (OLR), and nutrients. Compared with other types, lactic acid fermentation has the lowest reliance on artificial intervention. Lactic acid and volatile fatty acids are the common products, and high yield and high purity are the main targets of food waste fermentation. In addition to operational parameters, reactors and processes should be paid more attention to for industrial application. Currently, continuously stirred tank reactors and one-stage processes are used principally for scale-up continuous fermentation of food waste. Electro-fermentation and iron-based or carbon-based additives can improve food waste fermentation, but their mechanisms and application need further investigation. After fermentation, the recovery of target products is a key problem due to the lack of green and economic methods. Precipitation, distillation, extraction, adsorption, and membrane separation can be considered, but the recovery step is still the most expensive in the entire treatment chain. It is expected to develop more efficient fermentation processes and recovery strategies based on food waste composition and market demand.

Effect of yeast addition on the biogas production performance of a food waste anaerobic digestion system

Food waste contains numerous easily degradable components, and anaerobic digestion is prone to acidification and instability. This work aimed to investigate the effect of adding yeast on biogas production performance, when substrate is added after biogas production is reduced. The results showed that the daily biogas production increased 520 and 550 ml by adding 2.0% (volatile solids; VS) of activated yeast on the 12th and 37th day of anaerobic digestion, respectively, and the gas production was relatively stable. In the control group without yeast, the increase of gas production was significantly reduced. After the second addition of substrate and yeast, biogas production only increased 60 ml compared with that before the addition. After fermentation, the biogas production of yeast group also increased by 33.2% compared with the control group. Results of the analysis of indicators, such as volatile organic acids, alkalinity and propionic acid, showed that the stability of the anaerobic digestion system of the yeast group was higher. Thus, the yeast group is highly likely to recover normal gas production when the biogas production is reduced, and substrate is added. The results provide a reference for experiments on the industrialization of continuous anaerobic digestion to take tolerable measures when the organic load of the feed fluctuates dramatically.

Enhanced hydrogen production from food waste dark fermentation by potassium ferrate pretreatment

Hydrogen generation from food waste anaerobic dark fermentation is identified as a promising strategy for resource recovery. In this work, an innovative strategy of using potassium ferrate (PF), a strong oxidant, to promote anaerobic dark fermentation of food waste to produce hydrogen has been reported. The experimental results revealed that PF enhanced the hydrogen production from food waste, the maximal hydrogen yield was 173.5 mL/g, and the optimal PF dosage was 0.4 g/g total suspended solids. PF shortened the lag phase for hydrogen generation from 120 to 96 h. Mechanisms investigation revealed that PF accelerated the disintegration of organic compounds and increased the soluble organic matter in the liquid phase. The strong oxidation of PF inhibited the processes of hydrolysis, acidification, acetogenesis, homoacetogenesis, and methanogenesis by using synthetic wastewater in the fermentation process. The inhibition of PF on these processes was further verified by the enzyme activity analysis. Economic analysis indicated that 0.1 g/g PF was the optimal dosage. PF treatment is a promising strategy to enhance the production of hydrogen from food waste dark fermentation.

Non-thermal plasma and ultrasound-assisted open lactic acid fermentation of distillery stillage

Stillage is the main by-product of bioethanol production and the cost of its treatment significantly affects the economy of bioethanol production. A process of thermal sterilization before lactic acid fermentation (LAF) is energy demanding and is causing deterioration of valuable compounds in stillage. In this study, ultrasound (UT) and plasma (PT) treatments were used for microbial inactivation, and a significant reduction in the number of viable microorganisms in the stillage after PT and UT was observed. After application of treatment, LAF by Lactobacillus rhamnosus ATCC 7469 was initiated. The concentration of LA is used to quantify the efficiency of the stillage revalorization. The highest LA productivity of 1.21 g/Lh and yield of 0.82 g/g were obtained after PT, while UT of 10 min provided productivity of 1.02 g/Lh and LA yield of 0.69 g/g. The results were benchmarked against closed LAF. Around 20% better revalorization of stillage by PT was achieved when compared with conventional sterilization. In addition, an excellent L (+) LA stereoselectivity of 95.5% was attained after PT. From the aspect of energy efficiency, that of PT was three times lower than UT and almost ten times lower than thermal sterilization, but it is the most expensive due to the high consumption of gas which could reduce application of closed Ar atmosphere on larger scales. This way, a simpler and energy efficient process for LA production on stillage was accomplished by "open" fermentation.

Sustainability

This review on Sustainability covers selected 2018 publications on the focus of sustainability. It is divided into the following sections: (a) Water quantity; (b) Water quality; (c) Climate change and resilience; (d) Planning and ecosystem evaluation; (e) Life cycle assessment (LCA) applications; (f) Sustainable management; (g) Sustainability and asset management; (h) Sustainability in wastewater treatment; (i) Sustainable water and wastewater utilities; (j) Sustainable water resource management.

Improvement of bioethanol production from pomegranate peels via acidic pretreatment and enzymatic hydrolysis

The aim of this study was to improve the ethanol production from pomegranate peels (PPs). Therefore, the effect of enzymatic hydrolysis and different pretreatments on ethanol production by yeasts was examined. There were three different enzyme concentrations (3.6, 7.2, 14.4 FPU/g substrate) tested for enzymatic hydrolysis, and four different PP media, such as WSPP (whole slurry of PP), LFPP (liquid fraction of PP), WSFPP (washed solid fraction of PP) and N-WSFPP (non-washed solid fraction of PP), were prepared. Bioethanol production was monitored for 96 h. Maximum ethanol concentrations were obtained at WSPP medium as 12.69 g/L, 14.35 g/L and 4.23 g/L in Saccharomyces cerevisiae, Kluyveromyces marxianus and Pichia stipitis, respectively. On the other hand, the washing step of biomass increased the kinetic parameters dramatically and the highest theoretical ethanol yields and Y_P/S values were obtained from WSFPP medium in all tested yeasts. Theoretical ethanol yields were 97.8%, 98.7% and 35.5% for S. cerevisiae, K. marxianus and P. stipitis, respectively. Q_p values were observed as 0.98 g/L h, 0.99 g/L h and 0.04 g/L h for the same yeasts. The highest Y_P/S values were detected as 0.50 g/g for S. cerevisiae, 0.50 g/g for K. marxianus and 0.30 g/g for P. stipitis in the washed pomegranate peel biomass.