Influence of different household Food Wastes Fractions on Volatile Fatty Acids production by anaerobic fermentation

Effects of exogenous thermophilic bacteria and ripening agent on greenhouse gas emissions, enzyme activity and microbial community during straw composting

This research examined the impact of exogenous thermophilic bacteria and ripening agents on greenhouse gas (GHG) emission, enzyme activity, and microbial community during composting. The use of ripening agents alone resulted in a 30.9 % reduction in CO2 emissions, while the use of ripening agents and thermophilic bacteria resulted in a 50.8 % reduction in N2O emissions. Pearson's analysis showed that organic matter and nitrate nitrogen were the key parameters affecting GHG emissions. There was an inverse correlation between CO2 and CH4 releases and methane monooxygenase α subunit and N2O reductase activity (P<0.05). Additionally, N2O emissions were positively related to β-1, 4-N-acetylglucosaminidase, and ammonia monooxygenase activity (P<0.05). Deinococcota, Chloroflexi, and Bacteroidota are closely related to CO2 and N2O emissions. Overall, adding thermophilic bacteria represents an effective strategy to mitigate GHG emissions during composting.

Advanced anaerobic digestion of household food waste pretreated by in situ-produced mixed enzymes via solid-state fermentation: Feasibility and application perspectives

Enzymatic pretreatment is an effective method which can improve the anaerobic digestion (AD) efficiency of household food waste (HFW). As an alternative to expensive commercial enzymes, mixed enzymes (MEs) produced in situ from HFW by solid-state fermentation (SSF) can greatly promote the hydrolysis rate of HFW and achieve advanced anaerobic digestion (AAD) economically sustainable. In this paper, strategies for improving the efficiency of the enzyme-production process and the abundance of MEs are briefly discussed, including SSF, fungal co-cultivation, and stepwise fermentation. The feasibility of using HFW as an applicable substrate for producing MEs (amylase, protease, and lignocellulose-degrading enzymes) and its potential advantages in HFW anaerobic digestion are comprehensively illustrated. Based on the findings, an integrated AAD process of HFW pretreated with MEs produced in situ was proposed to maximise bioenergy recovery. The mass balance results showed that the total volatile solids removal rate could reach 98.56%. Moreover, the net energy output could reach 2168.62 MJ/t HFW, which is 9.79% higher than that without in situ-produced MEs and pretreatment. Finally, perspectives for further study are presented.

Microbiome dynamics and products profiles of biowaste fermentation under different organic loads and additives

Biowaste fermentation is a promising technology for low-carbon print bioenergy and biochemical production. Although it is believed that the microbiome determines both the fermentation efficiency and the product profiles of biowastes, the explicit mechanisms of how microbial activity controls fermentation processes remained to be unexplored. The current study investigated the microbiome dynamics and fermentation product profiles of biowaste fermentation under different organic loads (5, 20, and 40 g-VS/L) and with additives that potentially modulate the fermentation process via methanogenesis inhibition (2-bromoethanesulfonate) or electron transfer promotion (i.e., reduced iron, magnetite iron, and activated carbon). The overall fermentation products yields were 440, 373 and 208 CH4-eq/g-VS for low-, medium- and high-load fermentation. For low- and medium-load fermentation, volatile fatty acids (VFAs) were first accumulated and were gradually converted to methane. For high-load fermentation, VFAs were the main fermentation products during the entire fermentation period, accounting for 62% of all products. 16S rRNA-based analyses showed that both 2-bromoethanesulfonate addition and increase of organic loads inhibited the activity of methanogens and promoted the activity of distinct VFA-producing bacterial microbiomes. Moreover, the addition of activated carbon promoted the activity of H2-producing Bacteroides, homoacetogenic Eubacteriaceae and methanogenic Methanosarcinaceae, whose activity dynamics during the fermentation led to changes in acetate and methane production. The current results unveiled mechanisms of microbiome activity dynamics shaping the biowaste fermentation product profiles and provided the fundamental basis for the development of microbiome-guided engineering approaches to modulate biowaste fermentation toward high-value product recovery.

Temperature-driven carboxylic acid production from waste activated sludge and food waste: Co-fermentation performance and microbial dynamics

This work aims to improve the continuous co-fermentation of waste activated sludge (WAS) and food waste (FW) by investigating the long-term impact of temperature on fermentation performance and the underpinning microbial community. Acidogenic co-fermentation of WAS and FW (70:30 % VS-basis) to produce volatile fatty acids (VFA) was studied in continuous fermenters at different temperatures (25, 35, 45, 55 °C) at an organic loading rate of 11 gVS/(L·d) and a hydraulic retention time of 3.5 days. Two batches of WAS (A and B) were collected from the same wastewater treatment plant at different periods to understand the impact of the WAS microbioota on the fermenters' microbial communities. Solubilisation yield was higher at 45 °C (575 ± 68 mgCOD/gVS) followed by 55 °C (508 ± 45 mgCOD/gVS). Fermentation yield was higher at 55 °C (425 ± 28 mgCOD/gVS) followed by 35 °C (327 ± 17 mgCOD/gVS). Temperature also had a noticeable impact on the VFA profile. At 55 °C, acetic (40 %) and butyric (40 %) acid dominated, while acetic (37 %), butyric acid (31 %), and propionic acid (17 %) dominated at 35 °C. At 45 °C, an accumulation of caproic acid was detected which did not occur at other temperatures. Each temperature had a distinct microbial community, where the WAS microbiota played an important role. The biomass mass-balance showed the highest growth of microorganisms (51 %) at 35 °C and WAS_B, where a consumption of acetic acid was observed. Therefore, at 35 °C, there is a higher risk of acetic acid consumption probably due to the proliferation of methanogens imported from WAS.

Revealing discrepancies and drivers in the impact of lomefloxacin on groundwater denitrification throughout microbial community growth and succession

The coexistence of antibiotics and nitrates has raised great concern about antibiotic's impact on denitrification. However, conflicting results in these studies are very puzzling, possibly due to differences in microbial succession stages. This study investigated the effects of the high-priority urgent antibiotic, lomefloxacin (LOM), on groundwater denitrification throughout microbial growth and succession. The results demonstrated that LOM's impact on denitrification varied significantly across three successional stages, with the most pronounced effects exhibited in the initial stage (53.8% promotion at 100 ng/L-LOM, 84.6% inhibition at 100 μg/L-LOM), followed by the decline stage (13.3-18.2% inhibition), while no effect in the stable stage. Hence, a distinct pattern encompassing susceptibility, insusceptibility, and sub-susceptibility in LOM's impact on denitrification was discovered. Microbial metabolism and environment variation drove the pattern, with bacterial numbers and antibiotic resistance as primary influencers (22.5% and 15.3%, p < 0.01), followed by carbon metabolism and microbial community (5.0% and 3.68%, p < 0.01). The structural equation model confirmed results reliability. Bacterial numbers and resistance influenced susceptibility by regulating compensation and bacteriostasis, while carbon metabolism and microbial community impacted energy, electron transfer, and gene composition. These findings provide valuable insights into the complex interplay between antibiotics and denitrification patterns in groundwater.

Effect of electron acceptors on product selectivity and carbon flux in carbon chain elongation with Megasphaera hexanoica

Megasphaera hexanoica is a bacterial strain following the reverse β-oxidation pathway to synthesize caproate (CA) using lactate (LA) as an electron donor (ED) and acetate (AA) or butyrate (BA) as electron acceptors (EA). Differences in the type and concentration of EA lead to distinctions in product distribution and energy bifurcation of carbon fluxes in ED pathways, thereby affecting CA production. In this study, the effect of various ratios of AA, BA, and AA+BA as EA on carbon flux and CA specific titer during the carbon chain elongation in M. hexanoica was explored. The results indicated that the maximum levels of CA were 18.81 mM and 31.48 mM when the molar ratios of LA/AA and LA/BA were 10:1 and 3:1, respectively. Meanwhile, when AA and BA were used as combined EA (LA, AA, and BA molar amounts of 100, 23, and 77 mM), a maximum CA production of 39.45 mM was obtained. Further analysis revealed that the combined EA exhibited a CA production carbon flux of 49 % (4.3 % and 19.5 % higher compared to AA or BA, respectively) and a CA production specific titer of 45.24 mol (80.89 % and 58.51 % higher compared to AA or BA, respectively), indicating that the effective carbon utilization rate and CA production efficiency were greatly improved. Finally, a scaled-up experiment was conducted in a 1.2 L (working volume) automated bioreactor, implying high biomass (optical density at 600 nm or OD600 = 1.809) and a slight decrease in CA production (28.45 mM). A decrease in H2 production (4.11 g/m3) and an increase in CO2 production (0.632 g/m3) demonstrated the appropriate metabolic adaptation of M. hexanoica to environmental changes such as stirring shear.

Impacts of seasonal variation on volatile fatty acids production of food waste anaerobic fermentation

This study aims to investigate the influence of seasonal variations on Volatile fatty acids (VFAs) production from food waste (FW) and to quantify their impact. Results of batch experiments with external pH control indicated that the properties of FW exhibited significant seasonal variations and were markedly different from kitchen waste (KW). The spring group demonstrated the highest VFA concentration and VFA/SCOD, at 31.24 g COD/L and 92.20 % respectively, which were 1.22 and 1.27 times higher than those observed in the summer season. The combined proportion of acetic acid and butyric acid accounted for 81.10 % of the total VFAs in spring, suggesting the highest applicability to the carbon source. The VFA content of all seasonal groups in descending order was butyric acid, propionic acid and acetic acid. Carbohydrates, along with spicy and citrusy substances, promoted the conversion of total VFA and butyric acid, while proteins and lipids favored the production of acetic acid and propionic acid.

Effects of food wastes based on different components on digestibility and energy recovery in hydrogen and methane co-production

This study was conducted for four organic fractions (carbohydrates, proteins, cellulose, lipids) at an inoculum concentration of 30 % and a total solid (TS) of 8 % to investigate the effect of the main components of food waste on the performance of the two-stage anaerobic digestion. The results showed that the gas phase products were closely related to the composition of the substrate, with the carbohydrate and lipid groups showing the best hydrogen (154.91 ± 2.39mL/gVS) and methane (381.83 ± 12.691mL/gVS) production performance, respectively. However, the increased protein content predisposes the system to inhibition of gas production, which is mutually supported by changes in the activity of dehydrogenase and coenzyme F420. Butyric acid (53.19 %) dominated the liquid phase products in both stages, indicating that all four organic fractions were butyric acid-based fermentation and that the final soluble chemical oxygen demand degradation reached 72.97 %-82.86 %. The carbohydrate and cellulose groups achieved the best energy recovery performance, with conversion rates exceeding 65 %. The above results can provide a useful reference for the resource utilization of food waste.

Hydrogen production promotion and energy saving in anaerobic co-fermentation of heat-treated sludge and food waste

The objective of this paper is to gain insights into the synergistic advantage of anaerobic co-fermentation of heat-treated sludge (HS) with food waste (FW) and heat-treated food waste (HFW) for hydrogen production. The results showed that, compared with raw sludge (RS) mixed with FW (RS-FW), the co-substrate of HS mixed with either FW (HS-FW) or HFW (HS-HFW) effectively promoted hydrogen production, with HS-HFW promoted more than HS-FW. The maximum specific hydrogen production (MSHP) and the maximum hydrogen concentration (MHC) of HS-HFW were 40.53 mL H2/g dry weight and 57.22%, respectively, and 1.21- and 1.45-fold as high as those from HS-FW. The corresponding fermentation was ethanol type for HS-HFW and butyric acid type for HS-FW. The net energy production from RS-FW and HS-FW was both negative, but it was positive (2.57 MJ) from 40% HFW addition to HS-HFW. Anaerobic fermentation was more viable for HS-HFW.

Carbon/nitrogen flows and associated microbial communities in full-scale foodwaste treatment plants

Microorganisms play key roles in the conversion of organic matter in foodwaste. However, both the microbially-mediated element (carbon/C and nitrogen/N) flows and associated microbial communities in foodwaste treatment plants (FWTPs) remain unclear. This study collected samples of different foodwaste treatment units from five full-scale FWTPs to analyze the C/N flows and microbial communities in foodwaste treatment processes. Results showed that 39.8-45.0% of organic carbon in foodwaste was converted into biogas. Hydrolytic acidogenic bacteria (e.g., Lactobacillus and Limosilactobacillus) and eukaryota (e.g., Cafeteriaceae, Saccharomycetales, and Agaricomycetes) were more abundant in feedstock and pretreatment units. Redundancy analyses showed that acidogens were major players in the transformation of foodwaste organic matter. Populations of W27 and Tepidanaerobacter were major contributors to the difference in conversion of C/N in these FWTPs. This study could support foodwaste treatment efficiencies improvement by providing insights into C/N flows and associated microbiota in FWTPs.

Enhancing propionic acid production in the acidogenic fermentation of food waste facilitated by a fungal mash under neutral pH

Fungal mash derived from Aspergillus spp. is a green enzymatic additive for food waste (FW) valorization. In this study, the production of volatile fatty acids (VFAs) and the proportion of propionic acid (PA) in VFAs were increased by utilizing a complex enzyme (CE) obtained from Aspergillus oryzae. Results showed that CE addition significantly promoted SCOD concentration in the hydrolysis at a wide pH range from 4 to 9. In contrast, the production of VFAs was influenced by pH, and the highest yields of VFAs and PA were found at pH 7. At the CE dosage of 0.2 g/g VSS, the concentration of VFAs in the FW fermentation liquid reached 38.1 g COD/L with the PA proportion up to 42.7%, which increased by 107.9% and 63.7%, respectively, relative to that in the zero-dosage group. With CE continuing to be added, the C/N ratio declined, and the primary metabolic pathway was converted from acetic acid-type to PA-type. Further investigation of the dominant microbial communities and their metabolic capacities showed that the acrylate-mediated pathway was the potential metabolic reaction in PA-type fermentation. These results indicated that CE pretreatment was a feasible strategy to enhance the PA-rich fermentation of FW under neutral pH conditions.

Thauera sp. Sel9, a new bacterial strain for polyhydroxyalkanoates production from volatile fatty acids

Thauera is one of the main genera involved in polyhydroxyalkanoate (PHA) production in microbial mixed cultures (MMCs) from volatile fatty acids (VFAs). However, no Thauera strains involved in PHA accumulation have been obtained in pure culture so far. This study is the first report of the isolation and characterization of a Thauera sp. strain, namely Sel9, obtained from a sequencing batch reactor (S-SBR) set up for the selection of PHA storing biomass. The 16S rRNA gene evidenced a high sequence similarity with T. butanivorans species. Genome sequencing identified all genes involved in PHA synthesis, regulation and degradation. The strain Sel9 was able to grow with an optimum of chemical oxygen demand-to-nitrogen (COD:N) ratio ranging from 4.7 to 18.9. Acetate, propionate, butyrate and valerate were used as sole carbon and energy sources: a lag phase of 72 h was observed in presence of propionate. Final production of PHAs, achieved with a COD:N ratio of 75.5, was 60.12 ± 2.60 %, 49.31 ± 0.7 %, 37.31 ± 0.43 % and 18.06 ± 3.81 % (w/w) by using butyrate, acetate, valerate and propionate as substrates, respectively. Also, the 3-hydroxybutyrate/3-hydroxyvalerate ratio reflected the type of carbon sources used: 12.30 ± 0.82 for butyrate, 3.56 ± 0.02 for acetate, 0.93 ± 0.03 for valerate and 0.76 ± 0.02 for propionate. The results allow a better elucidation of the role of Thauera in MMCs and strongly suggest a possible exploitation of Thauera sp. Sel9 for a cost-effective and environmentally friendly synthesis of PHAs using VFAs as substrate.

Impact of food waste composition on acidogenic co-fermentation with waste activated sludge

The impact of food waste (FW) composition on co-fermentation performance was studied to elucidate if adjusting FW composition can be used to drive the fermentation yield and profile, which is relevant for biorefinery applications. First, the impact of individual FW components (i.e., fruit, vegetables, pasta, rice, meat, fish, and cellulose) was assessed. Subsequently, the effect of mixing a protein-rich component and a carbohydrate-rich component was studied (i.e., fish/fruit and fish/cellulose, and meat/rice and meat/vegetable). All experiments were carried out in mesophilic batch assays using waste activated sludge (WAS) as main substrate, the same mixture ratio (70 % WAS +30 % FW on VS basis), and no pH control. Results showed that each FW component had a distinct effect on VFA yield and profile, with protein-rich components reaching the highest VFA yields; 502 and 442 mgCOD/gVS for WAS/Fish and WAS/Meat, respectively. A positive interaction on VFA yield was observed when mixing a protein-rich and a carbohydrate-rich component. This interaction was not proportional to the co-substrates proportion in the mixtures. On the other hand, the VFA profile was clearly driven by the components in the mixture, including both WAS and FW composition. Overall, these results indicate that predicting the VFA yield of WAS/FW co-fermentation is not just related to FW composition, but FW composition could be used to adjust the VFA profile to a certain extent.

Producing volatile fatty acids and polyhydroxyalkanoates from foods by-products and waste: A review

Dairy products, extra virgin olive oil, red and white wines are excellent food products, appreciated all around the world. Their productions generate large amounts of by-products which urge for recycling and valorization. Moreover, another abundant waste stream produced in urban context is the Organic Fraction of Municipal Solid Wastes (OFMSW), whose global annual capita production is estimated at 85 kg. The recent environmental policies encourage their exploitation in a biorefinery loop to produce Volatile Fatty Acids (VFAs) and polyhydroxyalkanoates (PHAs). Typically, VFAs yields are high from cheese whey and OFMSW (0.55-0.90 g_{COD_VFAs}/g_COD), lower for Olive Mill and Winery Wastewaters. The VFAs conversion into PHAs can achieve values in the range 0.4-0.5 g_PHA/g_VSS for cheese whey and OFMSW, 0.6-0.7 g_PHA/g_VSS for winery wastewater, and 0.2-0.3 g_PHA/g_VSS for olive mill wastewaters. These conversion yields allowed to estimate a huge potential annual PHAs production of about 260 M tons.

Direct lactic acid production from household food waste by lactic acid bacteria

China is vigorously promoting garbage classification, but the treatment of classified waste, especially household food waste (HFW) has yet to be studied. Lactic acid (LA), a high value-added platform molecule has broad market prospects. Although there have been many studies on the production of LA from food waste, open fermentation often produces lots of by-products, while the traditional fermentation under a pure bacteria system often requires the saccharification process, which increases the production cost. We sought to analyze the comprehensive properties of classified HFW in Shanghai, then to produce LA by inoculating lactic acid bacteria (LAB) directly. The effects of strains, temperature, sterilized or not, initial pH, inoculum size, and substrate concentration on LA production were investigated. HFW was rich in nutrients and growth factors which provided the possibility for direct LA production from HFW by inoculating LAB. The results showed that Lactobacillus rhamnosus ATCC 7469, Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus all could be used as the inoculum, however, no significant synergistic effect of the three strains on LA production was found. LA concentration of 30.25 g/L at 37 °C, pH 6.8 could be obtained by inoculating Lactobacillus rhamnosus ATCC 7469 from sterilized HFW. High inoculum size and substrate concentration resulted in high LA concentration, but not high LA yield. The result of ANOVA indicated that there was a significantly positive relationship between substrate concentration and LA concentration (r = 0.942, p < 0.01), while no statistically significant difference between these groups at different inoculum size was evident (p = 0.318). In addition, an average LA concentration of 26.8 g/L, LA yield of 0.20 g/g TCOD was obtained by repeated batch fermentation for 32 d.

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.

Evaluation of the synergistic effects of biochar and biogas residue on CO2 and CH4 emission, functional genes, and enzyme activity during straw composting

This study examined the effects of biochar, biogas residue, and their combined amendments on CO₂ and CH₄ emission, enzyme activity, and related functional genes during rice straw composting. Results showed that the biogas residue increased CO₂ and CH₄ emissions by 13.07 % and 74.65 %, while biochar had more obvious inhibition. Biogas residue addition enhanced functional gene abundance more than biochar. Biogas residue raised the methanogens mcrA gene by 2.5 times. Biochar improved the Acetyl-CoA synthase and β-glucosidase activities related to carbon fixation and decreased coenzyme activities related to methanogens. Biochar and biogas residue combined amendments enhanced the acsB gene abundance for CO₂ assimilation process and decreased methyl-coenzyme M reductase α subunit activity. Pearson correlation analysis indicated that organic matter was the significant variable affecting CO₂ and CH₄ emissions (P < 0.01). These results indicated biochar played significant roles in carbon loss and greenhouse emissions caused by biogas residue incorporation during composting.

Antihypertensive Activity of Milk Fermented by Lactiplantibacillus plantarum SR37-3 and SR61-2 in L-NAME-Induced Hypertensive Rats

Probiotic fermented milk can lower the incidence rate of hypertension and is beneficial to the regulation of the intestinal microecology. However, the underlying molecular mechanism remains elusive. Here, we evaluated the role of the gut microbiota and its metabolites in the antihypertensive effect of milk fermented by the Lactiplantibacillus plantarum strains SR37-3 (PFM-SR37-3) and SR61-2 (PFM-SR61-2) in Ng-nitro-L-arginine methyl ester induced hypertensive rats. The results showed that PFM-SR37-3 and PFM-SR61-2 intervention significantly lowered the blood pressure (BP) of NG-nitro-L-arginine methyl ester induced hypertensive rats and attenuated renal injury. In particular, long-term administration of PFM inhibited a progressive elevation in SBP (170.22 ± 8.40 and 133.28 ± 6.09 by model group and PFM-SR37-3 treated model group, respectively, at the end of the 4 weeks; p < 0.01 PFM-SR37-3 treated model group versus model group) and DBP (133.83 ± 5.91 and 103.00 ± 6.41 by model group and PFM-SR37-3 treated model group, respectively, at the end of the 4 weeks; p < 0.01 PFM-SR37-3 treated model group versus model group). PFM-SR37-3 and PFM-SR61-2 reshaped the gut microbiome and metabolome, and especially regulated the metabolic levels of L-phenylalanine, L-methionine and L-valine in the intestine and blood circulation. The analysis of the target organ’s aortic transcriptome indicated that the protective effects of PFM-SR37-3 and PFM-SR61-2 were accompanied by the modulation of the BP circadian rhythm pathway, which was conducive to cardiovascular function. Vascular transcriptomic analysis showed that circadian rhythm and AMPK might be potential targets of hypertension. In addition, the ACE inhibition rates of Lactiplantibacillus plantarum SR37-3 and Lactiplantibacillus plantarum SR61-2 in vitro were 70.5% and 68.9%, respectively. Our research provides new insights into novel and safe options for hypertension treatment.

Next-generation -omics approaches to drive carboxylate production by acidogenic fermentation of food waste: a review

Acidogenic fermentation of food waste using mixed microbial cultures can produce carboxylates [or volatile fatty acids (VFA)] as high-valued bioproducts via a complex interplay of microorganisms during different stages of this process. However, the present fermentation systems are incapable of reaching the industrially relevant VFA production yields of ≥50 g/L primarly due to the complex process operation, competitive metabolic pathways, and limited understanding of microbial interplays. Recent reports have demonstrated the significant roles played by microbial communities from different phyla, which work together to control the process kinetics of various stages underlying acidogenic fermentation. In order to fully delineate the abundance, structure, and functionality of these microbial communities, next-generation high-throughput meta-omics technologies are required. In this article, we review the potential of metagenomics and metatranscriptomics approaches to enable microbial community engineering. Specifically, a deeper analysis of taxonomic relationships, shifts in microbial communities, and differences in the genetic expression of key pathway enzymes under varying operational and environmental parameters of acidogenic fermentation could lead to the identification of species-level functionalities for both cultivable and non-cultivable microbial fractions. Furthermore, it could also be used for successful gene sequence-guided microbial isolation and consortium development for bioaugmentation to allow VFA production with high concentrations and purity. Such highly controlled and engineered microbial systems could pave the way for tailored and high-yielding VFA synthesis, thereby creating a petrochemically competitive waste-to-value chain and promoting the circular bioeconomy.Research HighlightsMixed microbial mediated acidogenic fermentation of food waste.Metagenomics and metatranscriptomics based microbial community analysis.Omics derived function-associated microbial isolation and consortium engineering.High-valued sustainable carboxylate bio-products, i.e. volatile fatty acids.

High salinity slowed organic acid production from acidogenic fermentation of kitchen wastewater by shaping functional bacterial community

The high salinity of kitchen wastewater might have adverse effects on the production of short-chain fatty acids (SCFAs) in anaerobic fermentation. The effects and mechanisms of salinity on SCFA production in the anaerobic fermentation of kitchen wastewater were studied by varying the salt concentration, as follows: 0 g/L (S0), 2 g/L (S2), 6 g/L (S6), 10 g/L (S10), 15 g/L (S15), and 20 g/L (S20). Experimental results showed that hypersaline conditions (>10 g NaCl/L) accelerated the release of soluble proteins at the initial stage of anaerobic fermentation. They also significantly prohibited the hydrolysis and degradation of soluble proteins and carbohydrates. Compared with low salinity tests, the SCFA concentrations under hypersaline conditions (>10 g NaCl/L) only reached approximately 43% of the highest concentration on day 10, although the SCFA concentrations in all tests were very close on day 10 (14 g COD/L). High salinity delayed the production of n-butyric acid but did not change the composition of the total SCFAs. High salinity enriched Enterococcus and Bifidobacterium, the relative abundance levels of which reached 27.57% and 49.71%, respectively, before the depletion of substrate. High salinity showed a negative correlation with the relative abundance of the genera Clostridium_sensu_stricto_1, Prevotella and unclassified_f_Oscillospiraceae which are responsible for SCFA production. This study provided a theoretical basis for the fficient utilization of kitchen wastewater.

Changes in volatile fatty acid production and microbiome during fermentation of food waste from hospitality sector

Due to the increasing demand for low carbon-footprint bioproducts in the markets, innovative processes technologies and products are needed. The objective of this study was to assess the quality and potential of food waste (FW) from the hospitality sector to produce volatile fatty acids (VFAs). A batch type acid fermentation system was used to study VFA production in different process conditions (a decreased pH and increased organic loading rate). The evolution of VFAs and long-chain fatty acids was followed. Amplicon sequencing of the 16S rRNA gene was used to investigate the bacterial and archaeal community, and elucidate microbial communities in different FW and process conditions. The results show that high VFA concentrations (of up to 18 g/L) were achieved in overloaded conditions, which were also affected by the activity and composition of the inoculum. FW played an important role in modulating microbial composition, especially the bacterial communities belonging to the lactic acid bacteria group.

Potential of anaerobic co-fermentation in wastewater treatments plants: A review

Fermentation (not anaerobic digestion) is an emerging biotechnology to transform waste into easily assimilable organic compounds such as volatile fatty acids, lactic acid and alcohols. Co-fermentation, the simultaneous fermentation of two or more waste, is an opportunity for wastewater treatment plants (WWTPs) to increase the yields of sludge mono-fermentation. Most publications have studied waste activated sludge co-fermentation with food waste or agri-industrial waste. Mixing ratio, pH and temperature are the most studied variables. The highest fermentation yields have been generally achieved in mixtures dominated by the most biodegradable substrate at circumneutral pH and mesophilic conditions. Nonetheless, most experiments have been performed in batch assays which results are driven by the capabilities of the starting microbial community and do not allow evaluating the microbial acclimation that occurs under continuous conditions. Temperature, pH, hydraulic retention time and organic load are variables that can be controlled to optimise the performance of continuous co-fermenters (i.e., favour waste hydrolysis and fermentation and limit the proliferation of methanogens). This review also discusses the integration of co-fermentation with other biotechnologies in WWTPs. Overall, this review presents a comprehensive and critical review of the achievements on co-fermentation research and lays the foundation for future research.

Molecular diversity of liquid digestate from anaerobic digestion plants for biogenic waste

The treatment and valorization of liquid digestate (ADLD) after anaerobic digestion of biogenic waste are challenging. This study used ultra-high resolution mass spectrometry to determine the molecular characteristics of ADLD collected from different full-scale plants for food waste treatment. The results indicated that there were regular differences in the dissolved organic matter (DOM) indicators among the samples from dry and wet anaerobic processes. ADLD DOM had higher H/C and O/C, and contained more easily degradable proteins. In addition, sCOD and pH were the drivers of the molecular distribution of ADLD common compounds. The same common compounds were present in the ADLD from different anaerobic digestion plants. They had a significant correlation with physicochemical characteristics. The compounds relating to plant hormones and nutrients as well as xenobiotics were both identified, suggesting that comprehensive considerations should be taken into account for the land application of ADLD.