Enhancement of acidogenic fermentation for volatile fatty acid production from food waste: Effect of redox potential and inoculum

Volatile fatty acids production from saccharification residue from food waste ethanol fermentation: Effect of pH and microbial community

In this study, residue from saccharification and centrifugation of food waste ethanol fermentation was used as substrate to produce volatile fatty acids. The effects of different pH (5.5, 6.5, and uncontrolled) on the VFAs concentration, composition, acidogenic efficiency and microbial community distribution were investigated. The results showed that the highest concentration of VFAs was 267.8 ± 8.9 mg COD/g VS at pH of 6.5, and the highest percentage of butyric acid (79.8%) was followed by propionic acid and acetic acid at the end of the reaction. Microbial analysis showed that the contents of Vagococcus and Actinomyces increased, while the contents of Bacteroides and Fermentimonas decreased during anaerobic fermentation. The comparative high pH induced the accumulation of butyric acid. This study provides a new idea for the step anaerobic fermentation of food waste to produce alcohol and acid simultaneously.

Volatile fatty acids production via mixed culture fermentation: Revealing the link between pH, inoculum type and bacterial composition

The aim of the study was to investigate the effects of operational parameters, inoculum type and bacterial community on mixed culture fermentation to produce one dominant acid type in the mixture of volatile fatty acids (VFA). The study was performed using three different inocula (large&small granular and slurry) with glucose under various initial pH. The VFA production efficiency reached to 0,97 (gCOD/gSCOD) by granular sludge. VFA composition was changed by initial pH: in neutral conditions, acetic acid; in acidic conditions, acetic and butyric acids, in alkali conditions butyric acid were dominated, respectively. The VFA production was positively affected by the high relative abundance of Firmicutes. On the contrary, a negative correlation was seen between VFA production and the relative abundance of Chloroflexi. The results revealed the physical sludge structure of inoculum was the key factor for production efficiency, whereas, pH was the most important parameter to affect VFA composition.

Insights into redox mediator supplementation on enhanced volatile fatty acids production from waste activated sludge

Anaerobic fermentation of waste activated sludge (WAS) for recycling valuable volatile fatty acids (VFAs) is economically valuable. However, the fermentation of protein is the rate-limiting step of VFA production with WAS as a substrate. In this study, the effect of redox mediators (RMs, i.e., riboflavin and lawsone) on the enhanced production of VFAs from WAS was investigated. The results indicate that both RMs can promote protein-dependent fermentation, increasing maximum VFA accumulation by 43.9% and 42.5% respectively. In cultures supplemented with riboflavin and lawsone, VFA production was highly correlated with protease activities, but not with α-glucosidase activities. This implies that RMs affected the redox reaction of amino acids degradation, resulting in an increased release of ammonia. Sequencing results showed that RMs significantly increased the abundance of bacteria related to VFA fermentation and protein/amino acid degradation at the levels of phylum, class, order, family, and even genus.

Enhancing the anaerobic bioconversion of complex organics in food wastes for volatile fatty acids production by zero-valent iron and persulfate stimulation

The addition of zero-valent iron (ZVI) and ZVI & persulfate (PS) were efficient approaches to enhance the production of volatile fatty acids (VFAs), especially butyric acid, from food wastes (FW) during anaerobic fermentation. The maximal concentration of VFAs was increased from 1256 mg COD/L in the control reactor to 8245 mg COD/L with ZVI addition, and it was further improved to 9800 mg COD/L with the PS/ZVI treatment. An investigation of the mechanisms revealed that both the ZVI and PS/ZVI treatments improved the bioavailable substrates in FW and enhanced the bioconversion efficiency of fermentation substrates, especially proteins and lipids. The provision of a sufficient amount of bioavailable substrates was advantageous to the enrichment of the functional bacteria that are responsible for the production of VFAs. Additionally, the microbial activity and key metabolic enzymes involved in the biological VFAs generation processes were stimulated in the ZVI and PS/ZVI-added reactors, which jointly contributed to high-rate VFAs yields.

Performance of microaeration hydrolytic acidification process in the pretreatment of 2-butenal manufacture wastewater

The performance of the microaeration hydrolytic acidification (MAHA) process and microbial community were investigated under different organic loading rates (OLRs) for the pretreatment of 2-butenal manufacture wastewater (2-BMW). Results indicated that OLRs had different impact on the performance of MAHA process. More than 23.7 ± 2.3% of the chemical oxygen demand (COD) removal and the highest acidification degree (20.9 ± 3.1%) were obtained when OLRs were less than 4.0 ± 0.1 kgCOD/m³ d. However, further increasing OLRs to 6.1 ± 0.1 kgCOD/m³ d subsequently led to the significant reductions of COD removal and acidification degree. In addition, it could be preliminarily inferred that 2H-pyran-2-one tetrahydro-4-(2-methyl-1-propen-3-yl), 5-formyl-6-methyl-4,5-dihydropyran and ethyl sorbate were the main refractory and toxic organics for microorganisms in the wastewater. The soluble microbial product (SMP) and extracellular polymeric substance (EPS) contents (protein, polysaccharide, nucleic acid) had obvious changes under different OLRs. With parallel factor (PARAFAC) model, four fluorescent components were identified. The F_max of protein-like substances in SMP significantly decreased with increasing OLRs to 6.1 ± 0.1 kgCOD/m³ d, which might attribute to fluorescence quenching. Illumina MiSeq sequencing revealed that Pseudomonas, Longilinea, T78, Clostridium, WCHB1-05, Acinetobacter, SHD-231 and Oscillospira were dominant genera at different OLRs.

Mesophilic, thermophilic and hyperthermophilic acidogenic fermentation of food waste in batch: Effect of inoculum source

Distinctions in hydrolysis and acidogenesis were examined for a series of anaerobic batch reactors inoculated with three different anaerobic mixed cultures (mesophilic, thermophilic and hyperthermophilic anaerobic sludge) and operated at the temperature of inoculum's origin and additionally at 70 °C. Hyperthermophilic temperatures led to increased hydrolysis rates during the start-up stage but a rapid drop in pH limited the overall hydrolysis efficiency, indicating the importance of pH control to sustain the high reaction rates at higher temperatures. No significant difference (P > 0.05) was observed among hydrolysis efficiencies obtained for different reactors which ranged between 27 ± 3% and 40 ± 14%. The highest fermentation yield of 0.44 g COD of fermentation products/g VSS-COD_added was obtained under thermophilic conditions, followed by mesophilic (0.33 g COD ferm. prod./g VSS-COD_added) and hyperthermophilic conditions (0.05-0.08 g COD ferm. prod./g VSS-COD_added). Fermentative performance was better at mesophilic and thermophilic conditions as indicated by improved production of volatile fatty acids (VFA). VFAs accounted for 60-71% of the solubilised matter at thermophilic and mesophilic conditions. Acetic acid formed the primary VFA (70%) at mesophilic temperatures, while butyric acid was the major VFA at thermophilic (60%) conditions. Hyperthermophilic conditions led to increased production of lactic acid, which comprised up to 32% of the solubilised matter. Overall, the results indicate that different operating temperatures may not significantly affect the substrate degradation efficiency but clearly influence the biotransformation pathways.

A cellulolytic fungal biofilm enhances the consolidated bioconversion of cellulose to short chain fatty acids by the rumen microbiome

The ability of the multispecies biofilm membrane reactors (MBM reactors) to provide distinguished niches for aerobic and anaerobic microbes at the same time was used for the investigation of the consolidated bioprocessing of cellulose to short chain fatty acids (SCFAs). A consortium based consolidated bioprocess (CBP) was designed. The rumen microbiome was used as the converting microbial consortium, co-cultivated with selected individual aerobic fungi which formed a biofilm on the tubular membrane flushed with oxygen. The beneficial effect of the fungal biofilm on the process yields and productivities was attributed to the enhanced cellulolytic activities compared with those achieved by the rumen microbiome alone. At 30 °C, the MBM system with Trichoderma reesei biofilm reached a concentration 39% higher (7.3 g/L SCFAs), than the rumen microbiome alone (5.1 g/L) using 15 g/L crystalline cellulose as the substrate. Fermentation temperature was crucial especially for the composition of the short chain fatty acids produced. The temperature increase resulted in shorter fatty acids produced. While a mixture of acetic, propionic, butyric, and caproic acids was produced at 30 °C with Trichoderma reesei biofilm, butyric and caproic acids were not detected during the fermentations at 37.5 °C carried out with Coprinopsis cinerea as the biofilm forming fungus. Apart from the presence of the fungal biofilm, no parameter studied had a significant impact on the total yield of organic acids produced, which reached 0.47 g of total SCFAs per g of cellulose (at 30 °C and at pH 6, with rumen inoculum to total volume ratio equal to 0.372).

Simultaneous enhancement of nonylphenol biodegradation and short-chain fatty acids production in waste activated sludge under acidogenic conditions

Nonylphenol (NP) biodegradation in waste activated sludge (WAS) under anaerobic conditions is usually slow, and no information on NP biodegradation under acidogenic conditions is currently available. In this study, the simultaneous enhancement of NP biodegradation and short-chain fatty acids (SCFAs) accumulation in a WAS fermentation system under acidogenic conditions was accomplished by controlling pH 10 and adding sodium lauryl sulfate (SLS). The biodegradation efficiency of NP was found to be 55.5% within 8 d under acidogenic conditions, much higher than that in the control (24.6%). Meanwhile, the concentration of SCFAs under the same conditions for NP biodegradation was increased from 2234 mg COD/L (control) to 4691 mg COD/L (at pH 10 with SLS). Mechanism study revealed that the abundances of both NP-degrading microorganisms and acidogenic bacteria increased under acidogenic conditions. Altering the enzymatic activity and the quantity of functional genes in the acidogenic fermentation system were beneficial to NP biodegradation and SCFAs accumulation. Furthermore, organic substrates available for uptake by NP-degrading and acidogenic bacteria, i.e. NP, protein and carbohydrate, were released from WAS under acidogenic conditions. More importantly, intermediate substrates involved in acidogenic fermentation were advantageous to the cometabolic biodegradation of NP.

Characteristics of acidogenic fermentation for volatile fatty acid production from food waste at high concentrations of NaCl

This study explored the effects of NaCl on volatile fatty acid (VFA) production from food waste by acidogenic fermentation. The production and composition of VFAs, and the microbial community in acidogenic fermentation were investigated at four different NaCl concentrations: 10, 30, 50, and 70 g/L, and at 0 g/L (control). The highest VFA production was 0.542 g/g dry weight of food waste at 10 g/L NaCl, and about 23% lower but still high at 70 g/L NaCl. Interestingly, as NaCl concentration increased, the residence time of lactic acid in the reactor increased, and the maximum production also increased. The type of acidogenic fermentation also changed from butyric acid to propionic acid as the NaCl concentration increased. Microbial community analysis showed that a large number of propionibacteria were present at the end of fermentation, indicating their high tolerance to NaCl.

Shifting product spectrum by pH adjustment during long-term continuous anaerobic fermentation of food waste

Anaerobic fermentation is widely used to recover different products from food waste, and in this study, the evolution of fermentation products and microbial community along with pH variation was investigated thoroughly using four long-term reactors. Lactic fermentation dominated the system at pH 3.2-4.5 with lactic acid concentration of 5.7-13.5 g/L, and Lactobacillus was the superior sort. Bifidobacteria increased significantly at pH 4.5, resulting in the increase of acetic acid. Butyric acid fermentation was observed at pH 4.7-5.0. Bifidobacterium, Lactobacillus, and Olsenella were still dominant, but the lactic acid produced by them was converted to volatile fatty acids (VFAs) rapidly by Megasphaera, Caproiciproducens, Solobacteria, etc. Mixed acid fermentation occurred at pH 6.0 with the highest concentration 14.2 g/L of VFAs, and the dominant Prevotella and Megasphaera converted substrates to VFAs directly. On the whole, pH 4.5 and 4.7 led to the highest hydrolysis rate of 50% and acidification rate of 45%.

Volatile fatty acids production from food wastes for biorefinery platforms: A review

Volatile fatty acids (VFAs) are a class of largely used compounds in the chemical industry, serving as starting molecules for bioenergy production and for the synthesis of a variety of products, such as biopolymers, reduced chemicals and derivatives. Because of the huge amounts of food waste generated from household and processing industry, 47 and 17 million tons per year respectively only in the EU-28 Countries, food wastes can be the right candidate for volatile fatty acids production. This review investigates all the major topics involved in the optimization of VFAs production from food wastes. Regarding the best operative conditions for the anaerobic fermenter controlled pH in the neutral range (6.0-7.0), short HRT (lower than 10 days), thermophilic temperatures and an organic loading rate of about 10 kgVS/m³d, allowed for an increase in the VFAs concentration between 10 and 25%. It was also found that additions of mineral acids, from 0.5 to 3.0%, and thermal pretreatment in the range 140-170 °C increase the organic matter solubilisation. Applications of VFAs considered in this study were biofuels and bioplastics production as well as nutrients removal in biological wastewater treatment processes.

Bio-based volatile fatty acid production and recovery from waste streams: Current status and future challenges

Bio-based volatile fatty acid (VFA) production from waste-stream is getting attention due to increasing market demand and wide range usage area as well as its cost-effective and environmentally friendly approach. The aim of this paper is to give a comprehensive review of bio-based VFA production and recovery methods and to give an opinion on future research outlook. Effects of operation conditions including pH, temperature, retention time, type of substrate and mixed microbial cultures on VFA production and composition were reviewed. The recovery methods in terms of gas stripping with absorption, adsorption, solvent extraction, electrodialysis, reverse osmosis, nanofiltration, and membrane contractor of VFA were evaluated. Furthermore, strategies to enhance bio-based VFA production and recovery from waste streams, specifically, in-line VFA recovery and bioaugmentation, which are currently not used in common practice, are seen as some of the approaches to enhance bio-based VFA production.

The use of out-of-date frozen food as a substrate for biogas in anaerobic methane fermentation

The declining quantity of fossil fuels and the increasing demand for energy are two of the many problems that are affecting current times. This is why there is an increasing interest in and introduction of operations related to renewable sources of energy. One of many such possibilities is to conduct the biomass methane fermentation process and to obtain clean energy in the form of biogas. The aim of this research was to analyse the biogas-generating potential (Biochemical Methane Potential) of out-of-date frozen products in the laboratory anaerobic fermentation process and the near-infrared method with appropriate Biochemical Methane Potential calibration. The results obtained showed that selected frozen products are an excellent material for use as substrates resulting in the production of high quality biogas. It gives the opportunity to continue research, mainly in terms of applications, e.g. for biogas plants, using other available products on the market and the selection of their mixtures.

Performance of pilot scale anaerobic biofilm digester (ABD) for the treatment of leachate from a municipal waste transfer station

The anaerobic treatment of leachate from a municipal waste transfer station in Malaysia was tested using a pilot scale anaerobic biofilm digester system that was operated under HRT sequence of 30-day, 25-day, 20-day and 10-day for 163 days under mesophilic conditions. Despite the leachate's complex characteristics, the system showed great performance given its maximum COD, BOD₅ and total phosphorus removal efficiencies of 98 ± 1%, 99 ± 1% and 92 ± 9% respectively. The system was stable throughout its operation and showed optimal average values for the monitored parameters such as pH (7.53 ± 0.14), total VFA (79 ± 66 mg HOAc/L), alkalinity (10,919 ± 1556 mg CaCO₃/L) and a non-toxic value for accumulated ammonia (960 ± 106 mg NH₃-N/L). Measurement of the average daily biogas production yielded a value of 25 ± 1 m³/day throughout the system's operation with a composition of 57 ± 12% methane and 26 ± 6% carbon dioxide.

Acidogenic fermentation of the organic fraction of municipal solid waste and cheese whey for bio-plastic precursors recovery - Effects of process conditions during batch tests

The problem of fossil fuels dependency is being addressed through sustainable bio-fuels and bio-products production worldwide. At the base of this bio-based economy there is the efficient use of biomass as non-virgin feedstock. Through acidogenic fermentation, organic waste can be valorised in order to obtain several precursors to be used for bio-plastic production. Some investigations have been done but there is still a lack of knowledge that must be filled before moving to effective full scale plants. Acidogenic fermentation batch tests were performed using food waste (FW) and cheese whey (CW) as substrates. Effects of nine different combinations of substrate to inoculum (S/I) ratio (2, 4, and 6) and initial pH (5, 7, and 9) were investigated for metabolites (acetate, butyrate, propionate, valerate, lactate, and ethanol) productions. Results showed that the most abundant metabolites deriving from FW fermentation were butyrate and acetate, mainly influenced by the S/I ratio (acetate and butyrate maximum productions of 21.4 and 34.5g/L, respectively, at S/I=6). Instead, when dealing with CW, lactate was the dominant metabolite significantly correlated with pH (lactate maximum production of 15.7g/L at pH = 9).

Selective VFA production potential from organic waste streams: Assessing temperature and pH influence

This study explored the volatile fatty acid (VFA) production potential of seven waste streams from urban and agroindustrial sources. For that purpose, batch assays were performed under acidic (pH 5.5) and alkaline (pH 10) conditions at both mesophilic (35°C) and thermophilic (55°C) temperature. Overall, the VFA yield was influenced by temperature, and it was positively affected by pH, ranging between 220 and 677mgCODg^-1COD_fed for liquid waste streams and between 127 and 611mgCODg^-1COD_fed for solid waste streams and urban sludge. The highest VFA concentration and highest VFA/sCOD ratio was obtained during the organic fraction of municipal solid waste (OFMSW) fermentation, with 8,320mgCODL^-1 and 94% at alkaline pH and mesophilic temperature. The results of this study suggest that selective VFA production, i.e. via propionic, butyric and acetic acid production, might be feasible for scaling-up purposes with specific waste streams by adjusting the process parameters.

Improved methane production from sugarcane vinasse with filter cake in thermophilic UASB reactors, with predominance of Methanothermobacter and Methanosarcina archaea and Thermotogae bacteria

Biogas production from sugarcane vinasse has enormous economic, energy, and environmental management potential. However, methane production stability and biodigested vinasse quality remain key issues, requiring better nutrient and alkalinity availability, operational strategies, and knowledge of reactor microbiota. This study demonstrates increased methane production from vinasse through the use of sugarcane filter cake and improved effluent recirculation, with elevated organic loading rates (OLR) and good reactor stability. We used UASB reactors in a two-stage configuration, with OLRs up to 45gCODL^-1d^-1, and obtained methane production as high as 3LL^-1d^-1. Quantitative PCR indicated balanced amounts of bacteria and archaea in the sludge (10⁹-10¹⁰copiesg^-1VS), and of the predominant archaea orders, Methanobacteriales and Methanosarcinales (10⁶-10⁸copiesg^-1VS). 16S rDNA sequencing also indicated the thermophilic Thermotogae as the most abundant class of bacteria in the sludge.

Acidogenic fermentation characteristics of different types of protein-rich substrates in food waste to produce volatile fatty acids

In this study, tofu and egg white, representing typical protein-rich substrates in food waste based on vegetable and animal protein, respectively, were investigated for producing volatile fatty acids (VFAs) by acidogenic fermentation. VFA production, composition, conversion pathways and microbial communities in acidogenesis from tofu and egg white with and without hydrothermal (HT) pretreatment were compared. The results showed HT pretreatment could improve the VFA production of tofu but not for egg white. The optimum VFA yields were 0.46g/gVS (tofu with HT) and 0.26g/gVS (egg white without HT), respectively. Tofu could directly produce VFAs through the Stickland reaction, while egg white was converted to lactate and VFAs simultaneously. About 30-40% of total protein remained in all groups after fermentation. Up to 50% of the unconverted soluble protein in the HT groups was protease. More lactate-producing bacteria, mainly Leuconostoc and Lactobacillus, were present during egg white fermentation.