Volatile Fatty Acids Consumption Research Articles

Non-targeted facilitation of primary sludge anaerobic fermentation by micro-aeration and the simultaneous nutrients transformations

Anaerobic fermentation is a widely used technology for resource recovery from municipal sludge (e.g., primary sludge). Micro-aeration is an emerging strategy which can be incorporated into this technology. However, the effect of micro-aeration on the anaerobic fermentation performance and the nutrients transformations are not well known. This study investigated the impact of micro-aeration on the production of volatile fatty acids (VFAs) from primary sludge as well as the simultaneous nitrogen (N) and phosphorus (P) transformations in the system. The obtained results indicated that application of micro-aeration improved the microbial activities and facilitated all the hydrolysis, acetogenesis and methanogenesis processes. Hydrogenotrophic methanogen was enriched by micro-aeration while the acetoclastic methanogenesis was still the dominant CH4 production pathway at gene level. The concentration of VFAs was lower with micro-aeration than in the control system, which could be attributed to the enhanced consumption of VFAs. The simultaneous transformations of N and P were observed with different patterns. Micro-aeration led to removal of up to 131.6 mg/L of N, with occurrence of nitrification and denitrification found to be responsible for the N removal. In contrast, the total P content remained unchanged in the reactor. However, micro-aeration was found to inhibit both extracellular organic-P mineralization and intracellular poly-P degradation, resulting in lower soluble PO43−-P and more P distributed in the organic-P fraction in solid phase. This study provides novel insights into the microscopic mechanisms of the micro-aeration on anaerobic fermentation and the simultaneous regulation of N and P release.

Improving anaerobic digestion performance after severe acidification: Unveiling the impacts of Fe3O4-bentonite composites in co-digestion of waste activated sludge and food waste

Acidification recovery in anaerobic digestion of food waste is challenging. This study explored its in-situ recovery using a co-substrate of food waste and waste activated sludge. Fe3O4 and bentonite were used as conductor and carrier, respectively, to enhance AD performance under severe acidification. The application of Fe3O4-bentonite resulted in a 152% increase in cumulative methane in the Fe3O4-bentonite 10 digester, demonstrating its effectiveness in restoring the acidified AD system. In acidified systems, bentonite enhanced the diversity and richness of microbial communities due to its buffering capacity. The excessive non-conductive polysaccharides excreted by bacteria in extracellular polymeric substances reduced the possibility of electron transfer by Fe3O4. However, in the synergistic application of Fe3O4 and bentonite, this resistance was alleviated, increasing the possibility of direct interspecies electron transfer, and accelerating the consumption of volatile fatty acids. This approach of integrating carrier and conductive materials is significant for in-situ restoration of acidified systems.

How to develop a bio-based phosphorus mining strategy for eutrophic marine sediments: Unlocking native microbial processes for anaerobic phosphorus release

This study examined the anaerobic release of phosphorus (P) from two different Baltic Sea sediments (B and F), focusing on the impact of initial concentration of externally introduced waste-derived volatile fatty acids (VFA) as the carbon source, temperature, pH, and mixing conditions. The first batch bioreactor set was operated to demonstrate the effect of VFA on anaerobic P release at different concentrations (1000–10000 mg/L as COD) at 20 °C. A notable P release of up to 15.85 mg/L PO4–P was observed for Sediment B at an initial carbon concentration of 10000 mg COD/L. However, VFA consumption in the bioreactors was minimal or no subsequent. The second batch bioreactor set was carried out to investigate the effect of temperature (20 °C-35 °C), pH (5.5, 7.0 and 8.5) and mixing conditions on P release by introducing lower initial carbon concentration (1000 mg COD/L) considering the potential risk for VFA accumulation in the bioreactors. Maximum P releases of 4.4 mg/L and 3.5 mg/L were for Sediment B and Sediment F, respectively. Two-way ANOVA tests revealed that the operation time and pH and their interactions were statistically significant (p < 0.05) for both sediments while the effect of mixing was not statistically significant. Most of the sulfate was reduced during batch bioreactor operation and Desulfomicobiaceae became dominant among other sulfate-reducing bacteria (SRB) possibly shows the importance of SRB in terms of anaerobic P release. This study gives an insight into future implementations of phosphorus mining from eutrophic environment under anaerobic conditions.

Enhanced methane production via anaerobic digestion assisted with Fe3O4 nanoparticles supported on microporous granular activated carbon

Granular activated carbon (GAC) was used as supporting material for different loading of magnetite (Fe3O4) nanoparticles using the wet impregnation method, for its use as biocatalysts during the anaerobic digestion (AD). The highest responses in terms of methane productivity were achieved with the two modified materials using 1.5% and 3% of Fe3O4. With (1.5%)Fe3O4/GAC, the conversion efficiency to methane was 97.1%, with a methane yield of 388.1 mL CH4/g COD, which was higher than the control without GAC, achieving only 72.1% of conversion and a yield of 286.6 mL CH4/g COD, representing an increment of ∼ 26% for these two parameters with the modified material. Also, the (1.5%)Fe3O4/GAC promotes the highest consumption of volatile fatty acids (VFAs) and ethanol compared to other cultures. The improvement in the AD by the modified materials could be attributable to its surface chemistry composed of a greater extent of Fe2+ and Fe3+, the external surface area, and the electron-accepting capacity. In addition, the close association between microorganisms and the (1.5%)Fe3O4/GAC biocatalyst within the anaerobic medium could be evidence that the direct interspecies electron transfer (DIET) process is occurring.

Autogenerative high-pressure anaerobic digestion modelling of volatile fatty acids: Effect of pressure variation and substrate composition on volumetric mass transfer coefficients, kinetic parameters, and process performance

Pressurised anaerobic digestion is a valuable process that allows the production of biogas with a high methane content, reducing the energy costs for the biogas upgrading and injection into the distribution grid. This technology has attracted scientific research attention in the last decade, and kinetic models have been formulated. In this work, a modified Anaerobic Model Digestion n.1 of an autogenerative high‑pressure anaerobic digestion of volatile fatty acids in batch configuration is proposed by evaluating the effect of increasing the autogenerative pressure in the reactor on the prediction of the dynamic performances and kinetic parameters. Experimental results from the literature were used for developing, calibrating, and validating the model. Results highlighted the dependence of the mass transfer coefficient of the main component of biogas on the increasing autogenerative pressure: the higher the pressure, the higher the volumetric mass transfer coefficient. At atmospheric pressure, the volumetric mass transfer coefficient is almost equal (about 0.065–0.067 1/s). By increasing the pressure, H2 showed the highest value (0.098 1/s at 20 bar), while for CH4 and CO2, comparable values were assessed (0.085 1/s at 20 bar). Results also highlighted the effect of the pressure variation on acetate, butyrate, and propionate Monod maximum specific uptake rate, half saturation value, the first order decay rate, and the Upper and Lower pH levels for acetate degraders. Moreover, hydrogen produced during the process was considered an additional substrate, for which the kinetic parameters were assessed. Finally, simulation findings are consistent with the literature data in terms of volatile fatty acid consumption.

Magnetite Alters the Metabolic Interaction between Methanogens and Sulfate-Reducing Bacteria.

It is known that the presence of sulfate decreases the methane yield in the anaerobic digestion systems. Sulfate-reducing bacteria can convert sulfate to hydrogen sulfide competing with methanogens for substrates such as H2 and acetate. The present work aims to elucidate the microbial interactions in biogas production and assess the effectiveness of electron-conductive materials in restoring methane production after exposure to high sulfate concentrations. The addition of magnetite led to a higher methane content in the biogas and a sharp decrease in the level of hydrogen sulfide, indicating its beneficial effects. Furthermore, the rate of volatile fatty acid consumption increased, especially for butyrate, propionate, and acetate. Genome-centric metagenomics was performed to explore the main microbial interactions. The interaction between methanogens and sulfate-reducing bacteria was found to be both competitive and cooperative, depending on the methanogenic class. Microbial species assigned to the Methanosarcina genus increased in relative abundance after magnetite addition together with the butyrate oxidizing syntrophic partners, in particular belonging to the Syntrophomonas genus. Additionally, Ruminococcus sp. DTU98 and other species assigned to the Chloroflexi phylum were positively correlated to the presence of sulfate-reducing bacteria, suggesting DIET-based interactions. In conclusion, this study provides new insights into the application of magnetite to enhance the anaerobic digestion performance by removing hydrogen sulfide, fostering DIET-based syntrophic microbial interactions, and unraveling the intricate interplay of competitive and cooperative interactions between methanogens and sulfate-reducing bacteria, influenced by the specific methanogenic group.

Recovery of an acidified food waste anaerobic digestion reactor via NH4+-N and trace metals addition: Performance, microbial community response, and mechanisms

An increased organic loading rate can lead to an imbalance in the production and consumption of volatile fatty acids (VFAs) during anaerobic digestion of food waste, ultimately resulting in reactor acidification. In this study, VFA consumption was enhanced by adding NH4+-N and trace metals (TMs) (Fe, Co, Mo, and Ni). The addition of NH4+-N (330 mg/L) decreased the VFAs concentration in the reactor from 1477.54 to 223.83 mg/L, and remained below 400 mg/L during subsequent operation. The addition of NH4+-N enhanced the acid-base buffering capacity of the reactor, thereby detaching methanogens from the acidified environment and restoring their activity. The addition of TMs gradually decreased the VFAs concentration in the reactor from 3926.23 to 230–330 mg/L. TMs directly enhanced the methanogenic activity and enriched functional methanogens (Methanosarcina) with high acetic acid utilisation efficiency, thereby alleviating reactor acidification.

Impacts of biochar derived from oil sludge on anaerobic digestion of sewage sludge: Performance and associated mechanisms

The addition of biochar is a promising strategy to improve methane production via strengthening direct interspecies electron transfer (DIET) in anaerobic digestion (AD) field. In this study, a novel oil sludge biochar (OSBC) prepared at 500/600/700 °C was used to investigate its dosage effects on performances of sewage sludge AD. The characterization results indicated that OSBC prepared at 600 °C had highest electron accepting and donating capacity, meanwhile, it also contained moderate functional groups such as CO, which were in favor of methane production. Therefore, the highest accumulative methane yield (143.96 mL (g VS)−1) accompanying with the fast consumption of volatile fatty acids (VFAs) was achieved at dosage of 1.2 g. Additionally, the conductivity and enzyme activity (electron transport system activity and coenzyme F420) of AD with OSBC addition were also enhanced. Microbial community structures manifested that the potential syntrophic microbes including archaea Methanothrix, Methanospirillum, and bacteria Comamonas, Petrimonas and Syntrophomonas were enriched by OSBC due to its large surface area and microelement such as iron, and contributed to the improved methane production. The results suggested that OSBC exhibited excellent practical application potential in enhancing anaerobic sewage sludge treatment and biogas productivity.

Optimization of polyhydroxyalkanoate production in Halomonas sp. YLGW01 using mixed volatile fatty acids: a study on mixture analysis and fed-batch strategy

Polyhydroxyalkanoate (PHA) is one of the most promising materials for replacing petroleum-based plastics, and it can be produced from various renewable biomass sources. In this study, PHA production was conducted using Halomonas sp. YLGW01 utilizing mixed volatile fatty acids (VFAs) as carbon sources. The ratio and concentration of carbon and nitrogen sources were optimized through mixture analysis and organic nitrogen source screening, respectively. It was found that the highest cell dry weight (CDW) of 3.15 g/L and PHA production of 1.63 g/L were achieved when the ratio of acetate to lactate in the mixed VFAs was 0.45:0.55. Furthermore, supplementation of organic nitrogen sources such as soytone resulted in a ninefold increase in CDW (reaching 2.32 g/L) and a 22-fold increase in PHA production (reaching 1.60 g/L) compared to using inorganic nitrogen sources. Subsequently, DO-stat, VFAs consumption rate stat, and pH–stat fed-batch methods were applied to investigate and evaluate PHA productivity. The results showed that when pH–stat-based VFAs feeding was employed, a CDW of 7 g/L and PHA production of 5.1 g/L were achieved within 68 h, with a PHA content of 73%. Overall, the pH–stat fed-batch strategy proved to be effective in enhancing PHA production by Halomonas sp. YLGW01 utilizing VFAs.

Dosage effect of micron zero-valent iron during thermophilic anaerobic digestion of waste activated sludge: Performance and functional community

This work examined the performance and microbial traits in a thermophilic anaerobic digestion (TAD) of waste activated sludge that was impacted by micron zero valent iron (mZVI). Results showed that methane production was promoted by 0.8, 11.9, and 12.0 times, respectively, when mZVI was at dosages of 25, 100, and 250 mg/g total solid (TS). Also, the consumption of volatile fatty acids was increased by mZVI at higher dosages (100 and 250 mg/g TS). Furthermore, 16S rRNA sequencing demonstrated that microbial community stabilized after day 18 regardless of the dosage of mZVI, and that different dosages of mZVI induced different shifts in the functional community of the archaea rather than the bacteria involved in TAD. As a result, mZVI at 100 mg/g TS could increase the relative abundance of archaeal genera Methanothermobacter the most, increasing by 22.8% at the end of TAD compared to CK. Besides, redundancy analysis revealed that the physicochemical properties explained 79.65% and 89.10% of the variations of bacterial and archaeal abundance, respectively. Also, the findings of the correlation analysis revealed that total dissolved iron, ferrous iron, pH, and ammonium nitrogen, may be the key divers of altering functional communities, particularly archaea. Moreover, mZVI at 100 and 250 mg/g TS boosted the metabolic pathways of environmental information processing (ABC transporters) in bacteria and carbon metabolism and methane metabolism for archaea, as well as relative abundances of enzymes and their activities involved in various methanogenic pathways. This study provides new perspectives on the application of mZVI in solid wastes treatments.

Multifaceted roles of methylisothiazolinone intervention in sludge disintegration and acidogenic and methanogenic pathways for efficient carboxylate production during anaerobic fermentation

Anaerobic fermentation is a promising approach for sludge treatment, although it is frequently hindered by the tight structure of extracellular polymeric substances (EPS) and limited metabolic activities. This work firstly discovered that methylisothiazolinone (MIT, a commonly used antimicrobial agent in water treatment) effectively disintegrated the sludge structure and stimulated metabolic pathways, leading to efficient volatile fatty acids (VFAs) production. The presence of MIT (ranging from 10 to 40 mg/g TSS) contributed to the acidogenic process but strongly restrained the methanogenesis, and the distinct interfering effect is highly associated with the MIT dose. The VFAs accumulation reached a maximum of 1776.7 mg COD/L (5.2 times of control) but faced a complete inhibition of methanogenic activity at 40 mg/g TSS. Spectroscopic and molecular docking analysis revealed that MIT interacted with and disrupted the EPS (mainly proteins) structure by forming hydrogen bonds with N-H groups. This disruption facilitated the release of biodegradable organics, which served as fermentation substrates. Furthermore, the MIT-mediated improvement selectively enriched the hydrolytic-acidifying bacteria (i.e., Clostridium and Caloramator) and stimulated the associated metabolic functions, particularly in the uptake, hydrolysis, and metabolism of amino acids considering the high expressions of encoding genes (e.g., oppA, pepP, gdhA). However, methanogens' reproductive and metabolic abilities were suppressed due to their inefficient response and adaptation to MIT. This suppression was evident through downregulated genetic expressions involved in DNA replication and aminoacyl-tRNA synthesis. Consequently, a decline in methanogens abundance (e.g., Methanothrix, and Methanosarcina) and methanogenic activity occurred, impeding the consumption of VFAs. This work provided an innovative niche to promote resource recovery in the sludge anaerobic system and deciphered the underlying mechanisms at both biochemical interactive steps and microbial genetic traits.

Emerging Strategies for Enhancing Propionate Conversion in Anaerobic Digestion: A Review.

Anaerobic digestion (AD) is a triple-benefit biotechnology for organic waste treatment, renewable production, and carbon emission reduction. In the process of anaerobic digestion, pH, temperature, organic load, ammonia nitrogen, VFAs, and other factors affect fermentation efficiency and stability. The balance between the generation and consumption of volatile fatty acids (VFAs) in the anaerobic digestion process is the key to stable AD operation. However, the accumulation of VFAs frequently occurs, especially propionate, because its oxidation has the highest Gibbs free energy when compared to other VFAs. In order to solve this problem, some strategies, including buffering addition, suspension of feeding, decreased organic loading rate, and so on, have been proposed. Emerging methods, such as bioaugmentation, supplementary trace elements, the addition of electronic receptors, conductive materials, and the degasification of dissolved hydrogen, have been recently researched, presenting promising results. But the efficacy of these methods still requires further studies and tests regarding full-scale application. The main objective of this paper is to provide a comprehensive review of the mechanisms of propionate generation, the metabolic pathways and the influencing factors during the AD process, and the recent literature regarding the experimental research related to the efficacy of various strategies for enhancing propionate biodegradation. In addition, the issues that must be addressed in the future and the focus of future research are identified, and the potential directions for future development are predicted.

Comparation of mesophilic and thermophilic anaerobic co-digestion of food waste and waste activated sludge driven by biochar derived from kitchen waste

Anaerobic co-digestion of food waste and wasted sludge is a promising practice to integrate waste management and improve energy balance. In this study, the effects of kitchen waste biochar on the mesophilic and the thermophilic co-digestion were compared. Biochar showed a better performance in thermophilic treatments, and the highest methane production was obtained at 15 g L−1 biochar, while the time for complete digestion was shortened from 20 days in the controls without biochar to 13 days in the 15 g L−1 biochar-assisted treatments. Compared to the mesophilic treatments, thermophilic treatments demonstrated fast pH drop and volatile fatty acids accumulation. Based on the Gompertz model, 15 g L−1 biochar increased the maximum specific methane production rate by 2-fold and reduced the lag time by 31.6%, which was attributed to fast volatile fatty acids consumption and recovery from pH drop. pH, temperature and volatile fatty acids were significant factors shaping the distinct microbial dynamics. Methanosaeta dominated in archaeal community in mesophilic treatments, while Methanosarcina and Methanothermobacter were favored in thermophilic treatments. The higher acetogenesis rate integrated with enriched acetoclastic methanogenesis led to its better performance in biochar-assisted thermophilic co-digestion.

Mesophilic anaerobic digestion of waste activated sludge in an intermittent mixing reactor: Effect of hydraulic retention time and organic loading rate

An anaerobic digester was operated at mesophilic temperature and with intermittent mixing conditions to treat waste activated sludge. The organic loading rate (OLR) was increased by decreasing the hydraulic retention time (HRT), and the effect on process performance, digestate characteristics and inactivation of pathogens was investigated. The removal efficiency of total volatile solids (TVS) was also measured by biogas formation. The HRT varied from 50 to 7 days, corresponding to OLR from 0.38 to 2.31 kgTVS.m−3.d−1. The acidity/alkalinity ratio remained within stable limits (lower than 0.6) at 50-, 25- and 17-day HRT; due to an imbalance between the production and consumption of volatile fatty acids, the ratio increased to 0.7 ± 0.2 at HRT of 9 days and 7 days. The highest TVS removal efficiencies were 16, 12 and 9%, which were obtained at 50-, 25- and 17 day-HRT, respectively. Intermittent mixing provided solids sedimentation greater than 30% for almost all HRT tested. The highest methane yields (0.10–0.05 m3.kgTVSfed−1.d−1) were obtained when the reactor was operated at a higher HRT (50-17 days). At lower HRT, methanogenic reactions were likely limited. Zinc and copper were the main heavy metals found in the digestate, while the most probable number (MPN) of coliform bacteria remained below 106 MPN.g TVS−1. Neither Salmonella nor viable Ascaris eggs were found in the digestate. In general, increasing the OLR by decreasing the HRT to 17 days under intermittent mixing conditions provided an attractive alternative to treat sewage sludge despite some limitations due to biogas and methane yields.

Effect of Fe Addition on Anaerobic Digestion Process in Treating Vinasse: Experimental and Kinetic Studies

Vinasse is a continuously resulting waste by a bioethanol industry with a high chemical oxygen demand (COD) concentration and a large volume. Anaerobic digestion (AD) is the best method to treat vinasse because it converts COD to biogas, so the biogas can support the Indonesia's primary energy need. The goal of this study was to study the effect of Fe concentration on the AD process in treating the vinasse. The Fe concentration was varied to 0.06, 0.29, 0.64, 0.99 g/L. The results showed that increasing the Fe concentration from 0.06 to 0.29 g/L intensified the biogas yield by 360% (from 10.8 to 49.6 mL/g COD). However, further increasing the Fe concentration to 0.99 g/L decreased the biogas yield by 37.8% (from 10.8 to 6.7 mL/g COD). The Fe significantly affected the methane formation stage, but not the acid formation stage. A mechanistic model was built and successfully applied to predict the AD process. Based on the simulation results, Fe concentration of 0.29 g/L resulted in the highest values of YVFA/X2 (yield of volatile fatty acids (VFAs) consumption per biomass of X2 ), μm,2 (specific growth rate for X2 ), fCH4 (composition of methane in biogas) and the lowest values of Ks,VFA (affinity coefficient in VFAs consumption), kd2 (death rate constant for X2 ), kVFA (consumption rate of VFAs for maintenance). The addition of Fe until 0.29 g/L was recommended to increase the quantity and quality (methane content reached 53.4%) of biogas production.

Volatile fatty acids changed the microbial community during feammox in coastal saline-alkaline paddy soil.

In order to indicate the effect of volatile fatty acids (VFAs) on the characteristics of feammox and dissimilatory iron reducing bacteria (DIRB) in paddy soils, different VFAs were selected with paddy soils for anaerobic cultivation. Five treatments were set up, respectively, only adding N and both adding N and C (formate + NH4+ (Fo-N), acetate + NH4+ (Ac-N), propionate + NH4+ (Pr-N), and butyrate + NH4+ (Bu-N)) treatments. The concentration of Fe(II), Fe(III), NH4+, and VFAs was assessed within 45 d, and the bacterial community was determined after cultivation. The oxidation rates of NH4+ were the highest in N treatment, while it was the lowest in Fo-N treatment. Under the four C treatments, the consumption of NH4+ and Fe(III) was the fastest in Pr-N treatment, which was consumed by 31.2% and 76.3%, respectively. Different VFAs selected for distinct DIRB. Compared with N treatment, Ac-N and Bu-N treatment increased the relative abundance of DIRB, such as Geobacter and Clostridia, which increased the consumption of VFAs during incubation. Overall, VFAs, especially formate, could promote Fe(III) reduction and compete with the feammox process for the electron acceptors to decrease the feammox reaction, and prohibited soil NH4+ loss. Therefore, VFAs, which was released from organic fertilizer, could reduce NH4+ loss in feammox process of saline-alkaline paddy soils.

Anaerobic Digestion of Chicken Manure Assisted by Carbon Nanotubes: Promotion of Volatile Fatty Acids Consumption and Methane Production

In this study, the effect of different concentrations of carbon nanotubes (Taunit-M; 0.5–6.5 g L−1) on the efficiency of anaerobic digestion of chicken manure is investigated. The highest positive effect on the specific production of methane is obtained when 5.0 g L−1 of carbon nanotubes are added to the anaerobic reactors. In addition, carbon nanotubes at these concentrations stimulate the biodegradation of volatile fatty acids, mainly acetate, butyrate, and finally propionate. The maximum production rate of methane increases by 15–16% in the presence of carbon nanotubes (5.0–6.5 g L−1). Also, addition of carbon nanotubes at certain concentrations increases total methane production. Finally, the addition of carbon nanotubes to the anaerobic reactors is found to the favor consumption of volatile fatty acids and improve the methane production kinetics and productivity during the anaerobic digestion of chicken manure.

Optimization of volatile fatty acid production by sugarcane vinasse dark fermentation using a response surface methodology. Links between performance and microbial community composition

The recovery of volatile fatty acids (VFA) from waste and wastewaters has recently been pointed out as a promising strategy for adding value to residues, which characterizes the carboxylate platform. The exploitation of sugarcane vinasse within the carboxylate platform is still an incipient approach and has to be further investigated to determine the conditions which optimize the process. This study aimed to optimize the production of VFA (as the sum of concentrations of acetic, butyric and propionic acids) through the dark fermentation (DF) of sugarcane vinasse. A central composite design (CCD, factorial 22) and response surface methodology (RSM) regarding two independent variables, namely, temperature (33–47 °C) and initial pH (7.1–9.9), was performed. Experiments were conducted in batch reactors using diluted vinasse (COD = 10 gL−1) without nutrient supplementation. The results showed that the production of VFA reached a peak of 2,980 mgL−1 (as the sum of VFA produced), yield of 332 mg-CODVFAg−1CODtinicial and productivity of 619 mg-CODL−1d−1) at 39.6 °C and initial pH of 8.8. The microbial community analysis performed by 16S rRNA gene amplicon sequencing showed that organisms from the families Clostridiaceae, Enterobacteriaceae and Lachnospiraceae, and Veillonellales-Selenomonadales order prevailed during higher VFA production, whilst the presence of Desulfotomaculales and Lactobacillaceae families could be associated with VFA consumption and lactic acid production, respectively. These results provide a basis for vinasse management within the carboxylate platform context, potentially diversifying the product portfolio of sugarcane biorefineries.

From laboratory to farm-scale psychrophilic anaerobic co-digestion of cheese whey and cattle manure

This paper aims to prove the feasibility of cheese whey (CW) and cattle manure (CM) anaerobic co-digestion, from biomethane potential (BMP) laboratory assays to monitoring a farm-scale digester under psychrophilic conditions, and the impact on surrounding communities. The results show that while CW mono-digestion at 15 °C suffers inhibition, the CW:CM blend (70:30 volatile solids -VS- basis) is favorable at a similar temperature generating 0.24 m3 CH4/kg VS (35 °C yield: 0.60 m3 CH4/kg VS). A farm-scale digester (8 m3) installed in a rural school operated at 17.7 °C reached 0.42 m3CH4/kg VS, 0.31 m3 CH4/m3digester d with an organic loading rate of 0.61 kg VS/m3digester d (CW:DM 54:46). Even with CW's high volatile fatty acids (VFA) load, the digester did not show metabolic activities inhibition: VFA consumption was around 96.45 ± 2.25 %. In the rural school, biogas generation replaced the wood utilization and reduced propane consumption by 33 %. Despite these results, there are issues around psychrophilic BMP test to be reviewed, and user's misperceptions of biogas technology to overcome.

Biohythane production from swine manure and pineapple waste in a single-stage two-chamber digester using gel-entrapped anaerobic microorganisms

A mixture of swine manure and pineapple waste was used to check the feasibility of producing biohythane in a newly-developed single-stage anaerobic fermentation system that having immobilized H2 and CH4-producing microbes in a two-chamber digester. Tested hydraulic retention times (HRT) were from 96 h to 6 h. HRT 6 h resulted in peak gas production performance with hydrogen production rate 1240 and methane production rate 812 mL/L-d. Besides, the synergistic function of generation and consumption of volatile fatty acids in this hybrid biosystem had a significant impact on biohythane composition with acetate and butyrate being the dominant liquid metabolites. Chemical oxygen demand and ammonium removal efficiencies were 52.4 and 78.8%, respectively during steady-state conditions. Based on the experimental findings, prospects for field applications of single-stage biohythane fermentation were suggested.