Anaerobic Fermentation Of Food Waste Research Articles

Mechanism and Effect of Amino Acids on Lactic Acid Production in Acidic Fermentation of Food Waste

Amino acids, particularly the ones that cannot be synthesised during fermentation, are reportedly to be key nutrients for anaerobic fermentation processes, and some of the acids are also intermediate products of anaerobic fermentation of protein-rich waste. To date, particularly, there is a lack of research on the effects of some amino acids, such as cysteine, glycine, aspartic acid, and valine, on lactic production from the fermentation of food waste and also the mechanisms involved in the process. Thus, this study investigated the effects of the four different amino acids on lactic acid production during the acidic anaerobic fermentation of food waste. Firstly, batch experiments on synthetic food waste at different pHs (4.0, 5.0, and 6.0) were executed. The results harvested in this study showed that higher LA concentrations and yields could be obtained at pH 5.0 and pH 6.0, compared with those at pH 4.0. The yield of lactic acid was slightly lower at pH 5.0 than at pH 6.0. Furthermore, caustic consumption at pH 5.0 was much lower. Therefore, we conducted batch experiments with additions of different amino acids (cysteine, glycine, aspartic acid, and valine) under pH 5.0. The additions of the four different amino acids showed different or even opposite influences on LA production. Glycine and aspartic acids presented no noticeable effects on lactic acid production, but cysteine evidently enhanced the lactic acid yield of food waste by 13%. Cysteine addition increased α-glucosidase activity and hydrolysis rate and simultaneously enhanced the abundance of Lactobacillus at the acidification stage as well as lactate dehydrogenase, which also all favoured lactic acid production. However, the addition of valine evidently reduced lactic acid yield by 18%, and the results implied that valine seemingly inhibited the conversion of carbohydrate. In addition, the low abundance of Lactobacillus was observed in the tests with valine, which appeared to be detrimental to lactic acid production. Overall, this study provides a novel insight into the regulation of lactic acid production from anaerobic fermentation of food waste by adding amino acids under acidic fermentation conditions.

Enhanced production of biohydrogen and biomethane through a two-stage anaerobic fermentation of food waste mixed with conductive additives

This study was conducted to examine the effects of three different conductive materials (CMs) on H2 and CH4 production in a two-stage fermentation process (TSFP). This study also investigated the distinct roles played by the different types of CMs within the process. The study findings revealed that the combination of two or more CMs led to a significant improvement in production compared to using a single CM. Magnetite nanoparticle (MNP) played a crucial role in enhancing H2 productivity during the first stage of the TSFP. The TSFP with carbon nanotubes (CNT) + MNP demonstrated the highest H2 yield of 121 ± 7 mL/g·COD with the H2 production rate of 219 ± 18 mL/hr, followed by the TSFP with MNP alone yielded the second highest H2 of 81 ± 5 mL/g·COD with the H2 production rate of 169 ± 25 mL/hr. Both powdered activated carbon (PAC) alone (277 ± 17 mL/g·COD) and PAC + CNT (278 ± 15 mL/g·COD) showed the highest CH4 yield, indicating that PAC contributed to higher CH4 production in the second stage of the TSFP. The addition of PAC to the samples led to higher chemical oxygen demand (COD) removal efficiency in the TSFP, while the presence of MNP significantly increased the total energy production.

Effects of iron additives on the removal of antibiotics and antibiotic resistance genes in anaerobic fermentation of food waste

The presence of antibiotics and antibiotic resistance genes (ARGs) in food waste (FW) during anaerobic fermentation poses significant environmental and health risks. This study elucidated the potential of iron additives, specifically 500-nm and 50-nm zero-valent iron (ZVI) and magnetite, in mitigating these contaminants. These findings revealed that 500-nm magnetite significantly reduced tetracyclines by 81.04%, while 500-nm ZVI effectively reduced cefotaxime by 89.90%. Furthermore, both 500-nm and 50-nm ZVI were observed to decrease different types and abundance of heavy metal resistance and virulence genes. Interestingly, while 500-nm ZVI reduced the overall abundance of ARGs by 50%, 500-nm magnetite primarily reduced the diversity of ARGs without significantly impacting their abundance. These results elucidate the efficacy of iron additives in addressing antibiotic contamination and resistance during the anaerobic fermentation process of FW. The findings acquired from this study mitigate the development of innovative and environmentally sustainable technologies for FW treatment, emphasizing the reduction of environmental risks and enhancement of treatment efficiency.

Effects of zero-valent iron and magnetite on ethanol and lactic acid production in the anaerobic fermentation of food waste

With the increasing global concern about food waste management, finding efficient ways to convert it into valuable products is crucial. The addition of zero-valent iron and magnetite to enhance ethanol and lactic acid fermentation yields from food waste emerges as a potential solution. This study compared the effects of 50-nm and 500-nm particle sizes of zero-valent iron and magnetite on ethanol and lactic acid fermentation and analyzed the mechanism of action from the perspective of organic matter material transformation and microbiology. The experimental results showed that 500-nm particle size magnetite and zero-valent iron could promote the hydrolysis of polysaccharides and proteins. 500-nm particle size magnetite could increase ethanol production (1.4-fold of the control), while 500-nm particle size zero-valent iron could increase lactic acid production (2.8-fold of the control). Metagenomic analysis showed that 500-nm magnetite increased the abundance of genes for amino acid metabolic functions, while 500-nm zero-valent iron increased the abundance of glycoside hydrolase genes (1.3-fold of the control). It's worth noting that while these findings are promising, they are based on controlled experimental conditions, and real-world applications may vary. his research not only offers a novel approach to augmenting anaerobic fermentation yields but also contributes to sustainable food waste management practices, potentially reducing environmental impacts and creating valuable products.

Systematic metabolic pathway analysis of selective hydrolytic strains for anaerobic fermentation of food waste and identification of molecular markers during stress response

Food waste (FW) disposal has become a global social, environmental, and economic problem. Anaerobic digestion (AD) is a promising option to manage FW, and hydrolysis is an important rate-limiting step. In this study, metabolic pathway analysis of selective hydrolase-producing strains was carried out to investigate their hydrolytic capability. Based on metabolic pathway analysis of 10 strains, Bacillus licheniformis DSM13 was identified as the best potential strain for hydrolysis of model substrates. Further, studies were carried out on the protein–protein interactions of key enzymes involved, i.e., triacylglycerol lipase, β-glycosidase, α-amylase, and serine protease, in the metabolic pathway with other proteins in Bacillus licheniformisDSM13 that get activated undercertain stress conditions. Consequently, essential regulators were identified as molecular markers, and metabolic pathways of interacting proteins as a survival strategy under stress were explored. In conclusion, such studies are the key to designing effective strategies for enrichment of specific microbial groups existing in AD.

Volatile fatty acid production in anaerobic fermentation of food waste saccharified residue: Effect of substrate concentration

In this study, food waste saccharified residue was used to produce volatile fatty acids (VFAs), and the effects of substrate concentration on VFA production, VFA composition, acidogenic efficiency, microbial community, and carbon transfer were investigated. Interestingly, chain elongation from acetate to n-butyrate played an important role with a substrate concentration of 200 g/L in the acidogenesis process. Results showed that 200 g/L was a suitable substrate concentration for both VFA and n-butyrate production, the highest VFA production, and n-butyrate composition were 280.87 mg COD/g vS and more than 90.00 %, respectively, and VFA/SCOD reached 82.39 %. Microbial analysis showed that Clostridium_Sensu_Stricto_12 promoted n-butyrate production by chain elongation. Carbon transfer analysis indicated that chain elongation made a contribution of 43.93 % to n-butyrate production. Totally 38.47 % of organic matter in food waste saccharified residue was further utilized. This study provides a new way for n-butyrate production with waste recycling and low cost.

Performance and mechanisms of medium-chain fatty acid production by anaerobic fermentation of food waste without external electron donors

This study performed a long-term operation to achieve efficient medium-chain fatty acids (MCFAs) production by anaerobic fermentation of food waste without external electron donors. The results show that total MCFAs reached the highest concentration of 29,886.10 mg COD/L, and n-caproate was the primary product, reaching the current maximum concentration of 28,191.66 mg COD/L. Microbial composition analysis demonstrated Lactobacillus, Bifidobacterium, Sporanaerobacter, and Caproiciproducens constituted the core community throughout the process. Metagenomic analysis suggested that two pathways, reverse β-oxidization (RBO) and fatty acid biosynthesis (FAB), were observed, and the FAB pathway was the main CE pathway. Unclassified_f_Ruminococcaceae and Limosilactobacillus were the main participants in the FAB pathway. This study is expected to provide new insights into MCFAs production from organic waste.

Enhanced economic benefit of recycling Fe3O4 for promotion of volatile fatty acids production in anaerobic fermentation of food waste

Fe3O4 addition in anaerobic fermentation of food waste (FW) is promising for enhancing volatile fatty acids (VFAs) production. However, the large amount of Fe3O4 in the digestate fertilizer leads to the waste of resources and possible toxicity to organisms. Thus, this study investigated the feasibility of Fe3O4 recycling for VFAs enhancement in anaerobic fermentation of FW and performed the cost-benefit evaluation of this process. Results revealed that Fe3O4 could be successfully recycled twice with recovery rates of 71.5% and 65.5%, respectively. X-ray diffraction analysis revealed a slight change to the Fe2O3-like structure after 2-time recycling. The VFAs yields were enhanced by 17.2% and 17.0% in Cycles 1 and 2 owing to the enhanced activities of hydrolytic and acid-forming enzymes. The net income of the Fe3O4 recycling process was about 13-fold higher than that of the conventional treatment process, suggesting a promising and economically feasible strategy for enhancing VFAs production.

Fe3O4 enhanced efficiency of volatile fatty acids production in anaerobic fermentation of food waste at high loading

High treatment capacity for food waste (FW) is required due to the huge amount generated worldwide. Conversion of FW to volatile fatty acids (VFAs) via anaerobic fermentation is a promising technology; however, inhibition of VFAs production could easily occur at high loadings. In this study, Fe3O4 was used to enhance VFAs production in anaerobic fermentation of FW at high loading, and the mechanisms involved were revealed at microbial levels. Results showed that Fe3O4 significantly enhanced VFAs yield and VFAs productivity of microbes by 160% at high loading (substrate to inoculum (S/I) ratio of 3). The enhancement effect of Fe3O4 was mainly due to the accelerated hydrolysis of particulate/soluble organics, the enriched hydrolytic and acidogenic bacteria, and the reduced relative abundance of Lactobacillus. This study provides a new approach for the high-efficient treatment of FW at high loadings, while the performance and economic benefit should be further studied for practical application.

Effect of zero-valent iron on acidification and methane production using food waste under different food-to-microorganism ratios

During anaerobic fermentation of food waste (FW), acidification destabilizes the fermentation, and affects methane production. This study analyzed the anaerobic fermentation of FW to produce acid and gas under different food-to-microorganism (F/M) ratios after adding zero-valent iron (ZVI) to improve the performance of anaerobic fermentation. Results showed that when the F/M was 2, ZVI had a significant promoting effect on acetic acid, ethanol, and butyric acid production but significantly reduced propionic acid production. Moreover, optimal acid production was observed when 6 g L−1 ZVI powder was added. Furthermore, at ≥6 g L−1 ZVI, the biodegradation rate increased to >70%, and the cumulative methane production of the load increased to >440 mg L−1. Therefore, these results indicate that adding ZVI to FW digestion under different F/M ratios can increase methane production in an anaerobic fermentation system by promoting acetic acid production and reducing propionic acid production.

Fungal mash enzymatic pretreatment combined with pH adjusting approach facilitates volatile fatty acids yield via a short-term anaerobic fermentation of food waste

As an alternative for commercial enzyme, crude enzyme of fungal mash could promote food waste (FW) hydrolysis, but its specific effects coupled pH adjusting on the production of volatile fatty acids (VFAs) remains unknown. The crude enzyme produced from an Aspergillus awamori, named complex-amylase (CA), was added to short-term anaerobic system of FW fermentation. Results showed that adding CA significantly improved the solubility and degradability of biodegradable and non-biodegradable organics in FW, where the SCOD concentration with adding CA increased by 116.9% relative to the control but a marginal enhancement on VFAs yield. In contrast, adding CA combined with adjusting pH 8 markedly increased the VFAs production to 32.0 g COD/L, almost 10 times as much as the control. Besides, pH adjusting altered the metabolic pathway from lactate-type to butyrate-type. Adding CA coupled pH adjusting significant increase the component of butyrate compared with pH adjusting alone. Moreover, microbial community analysis indicated that adding CA reinforced proportion of the butyrate-producing bacteria (e.g., Dialister) under basic conditions, thus enhancing the butyrate metabolic pathways. This study demonstrated that fungal mash pretreatment coupled pH conditioning could be an economical way to enhance VFAs yield for FW valorization during anaerobic fermentation.

Insight to maturity during biogas residue from food waste composting in terms of multivariable interaction.

This study used biogas residue produced by anaerobic fermentation of food waste as the raw material in large-scale windrow composting. The effects of the addition of a microbial consortium on the physical and chemical properties and stability of composting of biogas residue were studied. The maturity of food waste biogas residue during composting was investigated by multivariate interaction of environmental, maturity, and nutrient parameters, using structural equation modeling (SEM). Results showed that the temperature of T2 compost with the microbial consortium increased more rapidly. The pH ranges of T1 (without the microbial consortium) and T2 were 8.75-9.15 and 8.42-9.27, respectively; the electrical conductivity (EC) ranges of T1 and T2 were 2.74-3.95 mS/cm and 2.81-3.85 mS/cm, respectively; the degradation rates of organic matter (OM) in T1 and T2 were 21.74% and 33.62%, respectively; and the total nitrogen (TN) ranges of T1 and T2 were 1.93-3.10% and 1.80-3.21%, respectively. By the end of composting, the germination indices (GI) of T1 and T2 were 20.57% and 64.24%, respectively. The total oxygen consumption after 4days (AT4) was 1.88mg-O2/g and 1.2mg-O2/g in T1 and T2, respectively. SEM of T1 showed that compost temperature and EC were important factors affecting compost maturity. These factors highly significantly affected OM, which in turn affected AT4 of the biogas residue composting. SEM of T2 showed that compost temperature, pH, and EC affected OM, which in turn affected compost maturity. Temperature affected compost maturity by affecting AT4 and GI. Principal component analysis (PCA) showed that the overall score of T2 was higher than that of T1, indicating that the addition of the microbial consortium was beneficial for industrial-scale composting of biogas residue produced by anaerobic digestion of food waste.

Recent advances on organic biofertilizer production from anaerobic fermentation of food waste: Overview

Massive utilizations of chemical fertilizer in agriculture sector to improve the farming productivity have created increasing possibility of environmental damages. Severe human health issues, global warming, poor fertility and high cost of soil maintenance are the major side effects of the utilizations of inorganic fertilizers and needs immediate attention. To overcome these issues, agriculture farming has been shifted towards the development of organic fertilizers using natural bio-resources. Organic fertilizers have several advantages like low-cost, being produced from the renewable resources and are highly efficient to improve the productivity of soil and agriculture product, rapidly. Additionally, bio-fertilizers not only increase the production, nutrients and organic matter but also neutralize the harmful impacts caused by the chemical fertilizers due to the potential combination of the microorganisms with organic wastes. Food wastes have tremendous potential to enhance the production of bio-fertilizers because these wastes are present in bio-degradable forms and may efficiently accelerate the activity of the microbial metabolic. Thus, the present review summarizes an overview of the production strategy of bio-fertilizers using the combination of food wastes and microorganisms. Further, in depth discussion have been done about the microbial digestion of food wastes to produce biofertilizer along with discussions about the possible mechanisms involved therein. Plant growth promoting microorganisms and their mechanisms have been also analyzed in the present review along with the existing limitations and sustainable future prospective.

Prevailing acid determines the efficiency of oleaginous fermentation from volatile fatty acids

Microbial lipids are envisaged as promising alternatives for sustainable production of chemicals and fuels. Although sugar-based substrates are the most conventional carbon sources employed for this purpose, the use of low-cost feedstock, such as organic wastes, is crucial for an economically-viable process. In this study, volatile fatty acids (VFAs) obtained during the anaerobic fermentation of food waste were used as carbon sources to produce lipids in Yarrowia lipolytica ACA DC 50109. Different total VFAs concentrations, acids profiles and carbon:nitrogen (C:N) ratios were used in both real digestates and synthetic media to establish the optimal culture conditions for lipid production. Y. lipolytica was able to grow in all cases despite of using concentrations as high as 15 g/L of total VFAs. The highest obtained lipid contents were 43.4% and 37.3% w/w using 15 g/L VFAs, 6:1 acetic:hexanoic ratio and C:N of 200:1 and 150:1, respectively. These lipids contents implied lipid yields of 0.33 g/g and 0.31 g/g, that were very close or even higher than lipid yields reported from sugars. This fact proves the suitability of using VFA derived from wastes as a low-cost carbon sources for the production of lipids and highlights the importance of paying attention to VFAs profile and C:N in the media for an efficient process.

A Novel and Green Method for Turning Food Waste into Environmentally-Friendly Organic Deicing Salts: Enhanced VFA Production through AnMBR

In order to improve the production efficiency of volatile fatty acids (VFAs) by anaerobic fermentation of food waste and reduce the cost for the production of organic deicing salt (ODS), ceramic microfiltration (MF) membrane separation was applied in the conventional food waste fermenter to build an anaerobic membrane bioreactor (AnMBR). Results showed that the maximum VFA concentration in AnMBR was up to 55.37 g/L. Due to the fact that the MF membrane could realize in situ separation of VFAs, the recovery of VFAs could reach 95.0%; 66.6% higher than that of traditional fermentation reactors. After the application of the MF membrane, more than 20.0% of soluble COD, 40.0% of proteins, and 50.0% of polysaccharides were retained and more than 90.0% of VFAs could be transferred in a timely fashion in the AnMBR system. In addition, the enrichment effect of the MF membrane enhanced enzymatic activities such as protease, α-Glucosidase and acetate kinase, and increased the abundance of some important bacteria for organic acid generation such as Amphibacter, Peptoniphilus and Halomonas, which made a significant contribution to the yield of VFAs. After concentration, evaporation and crystallization, the melting efficiency of obtained ODS can reach more than 90.0% in chloride salts, which was 112.0% of commercial calcium magnesium acetate (CMA). When compared to chloride salts and CMA, ODS was more environmentally-friendly as it can reduce the corrosion of carbon steel and concrete significantly. This study created a new way of converting food waste into a high-value organic deicing agent, realizing the resource utilization of solid waste and reducing the production cost of organic deicing agents.

Chain Elongation Significantly Contributes to N-Butyrate Production in Anaerobic Fermentation of Food Waste Saccharified Residue: Effect of Substrate Content

Chain Elongation Significantly Contributes to N-Butyrate Production in Anaerobic Fermentation of Food Waste Saccharified Residue: Effect of Substrate Content

Effects of organic loading rate and temperature fluctuation on the microbial community and performance of anaerobic digestion of food waste.

Semi-continuous anaerobic fermentation of food waste was carried out using a solar-assisted heat reactor to explore effects of temperature fluctuation and organic loading rate (OLR: 2.0, 4.0, 6.0, 7.0kg/(m3day)VS on the reactor performance and microbial community structure. The results showed that the best methane production was achieved when OLR was 6.0kg/(m3day)VS because the reactors did not operate stably at 7.0kg/(m3day)VS. Compared with fluctuation of fermentation temperature, methane production at stable fermentation temperature increased by 21.72%, but higher power consumption occured. The results of high-throughput sequencing showed that OLR played a decisive role in succession of microbial community structure, while temperature fluctuation was more likely to affect microbial activity. When OLR was lower than 4.0kg/(m3day)VS, aceticlastic methanogens Methanosaeta were the dominant bacteria, while at 6.0kg/(m3day)VS, relative abundance of hydrogenotrophic methanogens Methanoregula and Methanospirillum increased.

Upgrading of Biogas to Methane Based on Adsorption

Upgrading raw biogas to methane (CH4) is a vital prerequisite for the utilization of biogas as a vehicle fuel or the similar field as well. In this work, biogas yield from the anaerobic fermentation of food waste containing methane (CH4, 60.4%), carbon dioxide (CO2, 29.1%), hydrogen sulfide (H2S, 1.5%), nitrogen (N2, 7.35%) and oxygen (O2, 1.6%) was upgraded by dynamic adsorption. The hydrogen sulfide was removed from the biogas in advance by iron oxide (Fe2O3) because of its corrosion of the equipment. Commercial 13X zeolite and carbon molecular sieve (CMS) were used to remove the other impurity gases from wet or dry biogas. It was found that neither 13X zeolite nor CMS could effectively remove each of the impurities in the wet biogas for the effect of water vapor. However, 13X zeolite could effectively remove CO2 after the biogas was dried with silica and showed a CO2 adsorption capacity of 78 mg/g at the condition of 0.2 MPa and 25 °C. Additionally, 13X zeolite almost did not adsorb nitrogen (N2), so the CH4 was merely boosted to ac. 91% after the desulfurated dry biogas passed through 13X zeolite, nitrogen remaining in the biogas. CMS would exhibit superior N2 adsorption capacity and low CO2 adsorption capacity if some N2 was present in biogas, so CMS was able to remove all the nitrogen and fractional carbon dioxide from the desulfurated dry biogas in a period of time. Finally, when the desulfurated dry biogas passed through CMS and 13X zeolite in turn, the N2 and CO2 were sequentially removed, and then followed the high purity CH4 (≥96%).

Calcium peroxide eliminates grease inhibition and promotes short-chain fatty acids production during anaerobic fermentation of food waste

Deterioration of anaerobic fermentation can occur with the presence of grease in food waste, but little information on eliminating this deterioration is currently available. In this study, it was found that the presence of 10 g/L grease decreased SCFAs production from 16.97 to 13.32 g COD/L and prolonged the optimal fermentation time to 7 days, but could be respectively recovered to 39.10 g COD/L and 4 days with 0.02 mg/g VS (volatile solids) calcium peroxide addition. Mechanism investigations indicated that calcium peroxide facilitated biodegradable organics release and improved grease degradation, thereby providing enough nutrients and better growth environments to microbes for SCFAs-producing, which could be further supported by the elevated enzymes activities responding to hydrolysis and acidification process. Further investigations revealed that among the main derivates of calcium peroxide, OH– and Ca2+ played vital role in SCFAs production promotion, O2– and OH radicals were the main contributors to grease degradation.

Enhancement effect of ionizing radiation pretreatment on biogas production from anaerobic fermentation of food waste

Anaerobic digestion has become an important technology in the treatment of food waste and the acquisition of renewable energy. However, the physicochemical properties of the fermentation substrate have a great influence on the fermentation process. The present study examined the use of radiation technology for the anaerobic digestion pretreatment of food waste. Food waste was irradiated with different doses of radiation from a Co-60 gamma source and then subjected to anaerobic digestion to produce biogas. The effects of ionizing radiation pretreatment on the dissolution of organics were also investigated. The results revealed that, for food waste that had been subjected to 8.28-kGy irradiation pretreatment, the soluble chemical oxygen demand (SCOD) increased by 70.6% from 140.1 g/L to 239.1 g/L while the biogas yield was 504 ml/g VSadd, which was an increase of 14.3% over the non-irradiated pretreatment group. Therefore, radiation technology is a novel and efficient means of pretreatment for the anaerobic digestion of food waste.