Utilization Of Volatile Fatty Acids Research Articles

Treatment of sewage sludge with γ‐ray irradiation for volatile fatty acids and lipid production

AbstractThe production of value‐added products from sewage sludge is considered to be one of the solutions for the sustainable management of sludge in wastewater treatment plants (WWTPs). The presence of carbon, nitrogen, and phosphorus sources has made the sewage sludge of WWTPs a valuable and low‐cost substrate for the production of fermentative products. In the current study, a process was developed for microbial lipid production from two types of sewage sludge from a WWTP in northern Isfahan: anaerobic digester inlet sludge (DIS) and anaerobic digester outlet sludge (DOS). This process was based on the release of volatile fatty acids (VFAs) from the sludge by combinations of γ‐ray irradiation, anaerobic digestion, and acidogenic fermentation followed by utilization of VFAs in a microbial process by the oleaginous yeast Cryptococcus aureus UIMC65. After γ‐ray irradiation, the acidogenic fermentation of the treated sludge released 72% of the organic matter content of the sludge with acidification efficiency of 12% leading to 0.516 g L−1 VFAs. The oleaginous fermentation of the released VFAs for 7 days was accompanied by production of 1.58 g L−1 dry cell biomass with 40% lipid content. The results of this study indicate that the sewage sludge from urban WWTP has the potential to be used for the production of microbial lipids.

Enhanced biological phosphorus removal from wastewater and dynamics of microbial population in dual PAOs symbiosis system

Low level of volatile fatty acids (VFAs) is a key factor limiting the performance of enhanced biological phosphorus removal (EBPR) by traditional polyphosphate accumulating organisms (PAOs). A newly discovered PAOs capable of fermenting macromolecular organic matter into short-chain VFAs could solve the problem. However, the roles of traditional and fermented PAOs in wastewater treatment processes and the collaboration between functional microorganisms remain unknown. In this study, a sequencing batch reactor (SBR) was operated with alternating anaerobic oxic (An/O) mode to investigate the effect of mixed carbon source ratios, namely, acetate (NaAc):casein hydrolysate (Cas aa) = 4:0, 3:1, 1:1, 1:3 and 0:4, on EBPR performance and microbial community structure. The results showed that the phosphorus removal efficiency remained stable as NaAc was the sole carbon source. When NaAc:Cas aa varied from 3:1 to 1:3, the recovery of system performance took less time compared to the last Run, implying an adaptation of PAOs to Cas aa. Moreover, the anaerobic phosphorus release time was found to increase with the increasing amount of VFAs from Cas aa degradation, indicating the enrichment of fermented bacteria and the utilization of VFAs by traditional PAOs. Increasing the dose of Cas aa also generated more NH4+-N, owing to the reaction of the groups in the amino acids with water, causing a drastic decrease of ammonium removal efficiency from 88.9 % to 15.2 %. The ideal process performance implied that EBPR by dual PAOs synergistic symbiosis occurred in the system with NaAc:Cas aa = 1:1. Meanwhile, the results of 16S ribosomal RNA (16S rRNA) genes-Illumina MiSeq high-throughput sequencing showed that the abundance of traditional PAOs decreased from 22.4 % (4:0) to 11.6 % (1:1) and to 4.9 % (0:4), but fermented PAOs increased from 9.9 % to 19.5 %, then decreased to 17.3 %. Dual PAOs synergistic symbiosis could be of great potential for EBPR in treating low VFAs wastewater.

Simultaneous biomethane production and nutrient remineralization from aquaculture solids

The rapid expansion of the aquaculture industry has brought about a heightened focus on the waste produced by high intensity fish farming. In closed-containment, recirculating aquaculture systems (RAS), fish solids are mechanically separated and/or coagulated before being disposed as waste. Subsequent revalorization is typically limited to the direct dispersal of aquaculture solids onto agricultural fields. Here, we developed a novel, continuous flow, low-cost solids waste treatment system for freshwater and saline RAS. Rotating drum filter backwash was collected as the primary feedstock for anaerobic digestion. A laboratory scale set up was used to monitor the conversion of the solids into a methane-rich (60–80% purity) biogas stream. Iron supplementation (ferric iron at 100 mg/L and 1000 mg/L) improved salt tolerance of the methanogenic community, leading to higher methane yields in a supplemented (FeCl3 at 1000 mg/L) saline treatment than the saline control. The application of iron additionally improves pH stability and volatile fatty acid utilization. The methane yield ranged from 0.1 to 0.4 NL CH4/ g VS across the three freshwater treatments and the iron-supplemented saline treatment, however, it was significantly lower for the saltwater control: ranging between 0.08 and 0.25 NL CH4/ g VS. These values correspond to a percentage yield of 57–86% of the total biomethane potential. Overall, implementing anaerobic digestion for RAS waste valorization may generate significant amounts of biomethane to be used in electricity and heating for large-scale aquaculture facilities, while even for smaller facilities it may off-set costs and mitigate environmental impacts of the waste streams.

Oil-rich filamentous algae cultivation in anaerobic digestate effluent: Inhibition effect of undissociated fatty acids

Microalgae cultivation using organic carbon waste has been proved as a promising way to enhance filamentous algal biomass bio-protection. However, the carbon source in anaerobic digestate (AD; the effluent of biogas plants) contains various organic carbon source and other components, with a complex metabolic process in algae. The utilization of organic carbon including volatile fatty acids (VFAs) and glycerin by Tribonema minus were investigated. The results showed that the utilization of VFAs as the carbon source by T. minus with the addition of 0.3% CO2 decreased pH value below 6.0 and accumulated the undissociated VFAs (UVFAs) (UVFAs contents: 99.29 ± 8.34 mg L−1, 176.52 ± 4.05 mg L−1, 115.02 ± 5.86 mg L−1, and 127.52 ± 7.24 mg L−1 for acetic acid, propanoic acid, butyric acid, and valeric acid, respectively after 1st day cultivation), which inhibited T. minus growth. However, this inhibition effect was not observed when using glycerin as a carbon source (Biomass: 2.95 g L−1). To study the inhibition mechanism of UVFAs on the algae, the growth and metabolism of algae using acetic acid and butyric acid as carbon source was studied under different pH (4.5, 5.5, 6.5). The study found that the UVFAs content at pH 4.5–5.5 was higher than that at pH 6.5 with the same carbon concentrations. UVFAs inhibited the biomass accumulation of T. minus and decreased photosynthetic and enzymatic activities. This study concluded that T. minus can be cultivated with a mixotrophic mode using AD that contains VFAs with controlled pH value around neutral.

Targeted addition of CeO2 nanoparticles to promote methane production in anaerobic digestion systems of wheat straw

As a large agricultural country, China produces a large amount of wheat straw each year that needs to be treated harmlessly. Anaerobic digestion (AD) has a great potential to produce clean energy biogas while treating wheat straw. AD as a typical fermentation process, the regeneration of NAD+ is achieved by fermentation using NADH to reduce metabolic intermediates and therefore there is a lack of reduction capacity in the metabolic process. The low reducing power of the digestion system and the low methane yield of wheat straw in the AD process have limited the further development of this technology. Cerium dioxide nanoparticles (CDNs) are known for their excellent reducing powers. At the same time the large amount of cerium contained in the earth provides the conditions for its large-scale use. In this study, we evaluated the effects of CDNs on the AD of wheat straw. The CDNs were successfully prepared via hydrothermal synthesis. The particle size of CDNs was about 5 nm, the measured specific surface area was 168.02 m2/g, and the zeta potential was 10.70 mV. Experiments involving volatile fatty acids (VFAs), cyclic voltammetry curves, electrochemical impedance spectroscopy, oxidation-reduction potential, and NADH/NAD+ showed that CDNs effectively enhanced the reducing power and utilization of VFAs. Additionally, the cumulative methane production of the C10 group was 20.15% higher than CK group, reaching 367.78 mL CH4/g·VS. The cumulative methane production was well fitted using the modified Gompertz equation (R2 = 0.99677). Analysis of microbial community structure showed that CDNs increased bacterial abundance in hydrolytic acidification. The reduction ability of CDNs is very important for the improvement of the methane production efficiency of AD, which is of great interest for the study of nanoparticles that promote AD.

Enhancing two-phase anaerobic digestion of mixture of primary and secondary sludge by adding granular activated carbon (GAC): Evaluating acidogenic and methanogenic efficiency

Although the granular activated carbon (GAC) has been proved to enhance conventional single-phase anaerobic digestion (AD), how it impacts on acidogenic and methanogenic fermentation is still unknown. In this study, GAC was introduced to elevate the efficiency of two-phase AD, with mixture of primary and secondary sludge as substrate. Five dosages: 0, 0.1, 0.3, 0.5 and 0.7 g GAC/g TSS (Total Suspended Solids) were investigated to determine influences of GAC. The variations of biogas (hydrogen and methane), volatile fatty acids (VFAs), organics degradation and transformation in extracellular polymeric substances (EPS) and dissolved organic matters (DOM) were analyzed. Modified Gompertz model and first-order reaction equation was applied to analyze the kinetics of biogas yield and VFAs utilization, respectively. Sludge reduction, electrical conductance and pH were also quantified to evaluate the system performance. The results showed that GAC could improve two-phase AD performance by enhancing methane production and organics conversion.

Valorization of pretreated waste activated sludge to organic acids and biopolymer.

Polyhydroxybutyrate (PHB) is a natural polyester that may be made by utilizing volatile fatty acids (VFAs) as a substrate. VFA generated by continuous anaerobic fermentation of waste activated sludge (WAS) was fed into bioreactors for PHB synthesis in this work. Series of optimization tests were conducted to increase the biodegradability and hydrolysis of waste activated sludge. It was found out that 0.05g/g TS of SDBS (sodium dodecylbenzene sulfonate), 70°C (heat treatment) and 2hr (time) as pretreatment condition would give the highest solubilization. Impact of pH adjustment on the acidogenesis of pretreated WAS was evaluated in batch experiments at varying initial pH (4-10). The result indicated that when operational pH was between 7.5 and 8, the VFA yield was increased by 5.3-18.1%. Continuous acidogenic operation validated the SDBS pretreatment and pH adjustment warranted stable VFA conversion from WAS at a yield of 47% in COD basis. Firmicutes, Actinobacteria and Proteobacteria were affiliated as dominant bacterial phyla in the continuous acidogenesis. The effluent of the continuous acidogenesis was converted to biopolymer with the average yields of 0.23g PHB-COD/g VFAadded-COD in the feast mode and 0.34g PHB-COD/g VFAadded-COD in the famine mode. In feast and famine cycle, the average VFA utilization was 55% and 60% respectively. The sequential SDBS pretreatment, acidogenesis and PHB production would produce 162g of PHB from 1kg of WAS as COD basis.

Enhanced waste hot-pot oil (WHPO) anaerobic digestion for biomethane production: Mechanism and dynamics of fatty acids conversion

Resource depletion and climate changes due to human activities and excessive burning of fossil fuels are the driving forces to explore alternatives clean energy resources. Anaerobic digestion of bio-waste provides a unique opportunity to fulfil this objective through biogas production. The present study aimed to evaluate waste hot-pot oil (WHPO) at different feeding ratios as a novel lipidic waste for anaerobic mono-digestion. The highest recorded maximum biomethane potential (Mmax) was 274.1 L kg−1 VS at 1.2% WHPO, which showed significant differences with those of 0.8% and 1.6% (227.09 and 237.62 L kg−1 VS, respectively). The changes in volatile fatty acids (VFAs), medium chain fatty acids (MCFAs), and long-chain fatty acids (LCFAs) as intermediates of WHPO decomposition were investigated before and after anaerobic digestion. Results showed efficient production and utilization of VFAs at all studied WHPO ratios, whereas the maximum utilization of VFAs (90–95%) was recorded in the reactors with up to 1.2 %WHPO. Although lipid conversion efficiency decreased by increasing the WHPO ratio, 81.2% lipid conversion efficiency was recorded at the highest applied WHPO treatment, which confirms the potential of WHPO as a promising feedstock for anaerobic digestion. The present results will have major implications towards efficient energy recovery and biochemical management of lipidic-waste through efficient anaerobic digestion.

Effectiveness of layered inoculation in solid-state anaerobic co-digestion of pig manure and corn straw: Focus on macro-, micro-, and genetic-levels

Layered inoculation can achieve rapid start-up and promote methanation performance of anaerobic digesters. Daily specific methane yield (SMY) rapidly increased to 2.93 mL/g VS/d during 0–13 days, and cumulative SMY reached 212 mL/g VS in the solid-state anaerobic co-digestion (SS-AcoD) of pig manure and corn straw. Data were collected at macro-, micro-, and genetic-levels of each substrate layer. The results showed that layered inoculation could improve volatile fatty acids utilization and prevent adverse effects of high total ammonium nitrogen concentrations. Layered inoculation accelerated hydrolysis, acidification, and methanogenesis of substrates, as evidenced by the efficient inoculation of Bacteroidetes, Anaerolineales, Methanosphaerula, and Methanothrix, which were primarily from inocula. The various stages of SS-AcoD were synergistically initiated during the first 13 days, and acetoclastic pathway was boosted. These results further explain why layered inoculation is an efficient method for improving methanation performance of SS-AcoD and achieving efficient utilization of organic solid waste.

Insights into the role of biochar on the acidogenic process and microbial pathways in a granular sulfate-reducing up-flow sludge bed reactor

In this study, the effect of biochar on sulfate reduction and anaerobic acidogenic process was explored in a granular sulfate-reducing up-flow sludge bed reactor in both long-term operation and batch tests. Both bioreactors had a high sulfate reduction efficiency of over 95% during the long-term operation, while the reactor with biochar addition showed higher sulfate reduction efficiency and stronger robustness against volatile fatty acids accumulation with a higher organic loading and sulfate loading rate. Batch tests showed that adding biochar significantly lessened the lag phase of the sulfate-reducing process, accelerated the adaption of acidogens, and facilitated both production and utilization of volatile fatty acids. The microbial pathways proved that biochar could regulate the acidification fermentation pathway and facilitate the enrichment of assimilative desulfurization bacteria. Overall, this study revealed that the acidogenic sulfate-reducing metabolic pathway could be enhanced by biochar, offering a potential application for effective sulfate-laden wastewater treatment.

Evaluating the impact of Iron Oxide nanoparticles (IO-NPs) and IO-NPs doped granular activated carbon on the anaerobic digestion of food waste at mesophilic and thermophilic temperature

The impact of Iron oxide nanoparticles (IO-NPs) and IO-NPs doped granular activated carbon (GAC) at three concentration levels of 0.16 g/L, 0.32 g/L and 0.48 g/L for IO-NPs and 2 g/L, 4 g/L and 6 g/L for IO-NPs doped GAC on the anaerobic digestion (AD) of food waste (FW) at mesophilic (35 ± 2 oC) and thermophilic (55 ± 2 oC) temperature has been investigated. Results revealed that the % utilization of volatile fatty acids (VFAs) ranged between 83% and 92% in mesophilic reactors (MRs) while it was between 79% and 84% in thermophilic (TRs) indicating elevated temperatures may lead to VFAs accumulation in the long term operation. Results disclosed that the CH4 (%) and yield was 60% and 0.25 L CH4/g VSreduced in MR-Control and 62% and 0.29 L CH4/g VSreduced in TR-Control respectively. Similarly, in the reactors with 0.32 g/L of IO-NPs the maximum CH4 of 72% and 77% with an yield of 0.43 and 0.54 L CH4/g VSreduced was achieved at mesophilic and thermophilic temperature. Likewise using 4 g/L of IO NPs doped GAC, the maximum CH4 of 74% and 78%, with an yield of 0.41 and 0.53 L CH4/g VSreduced was achieved. This could be attributed to the syntrophic balance between the bacterial groups (Firmicutes, Bacteroidetes, Chloroflexi, Thermotogae) and archaeal groups (Methanosarcina, Methanothrix and Methanosaeta) that enhanced the electron transfer between cell to cell resulting in improved performance.

Effect of mixed primary and secondary sludge for two-stage anaerobic digestion (AD)

As an energy-efficient and eco-friendly sludge treatment process, two-stage anaerobic digestion (AD) is widely employed to recovery biomass energy from waste sludge. However, the effect of primary and secondary sludge for two-stage AD was not clear. In this study, two-stage AD of mixed sludge in different volume ratio was investigated. The maximum cumulative H2 yield (100.5 ml) and CH4 yield (2643.6 ml) were obtained in volume ratio of 1:3 (primary sludge: secondary sludge). In two-phase AD, mixed sludge could induce positive effect on both organics releasing in extracellular polymeric substances (EPS) and the utilization of volatile fatty acids (VFAs). By investigating the compositional characteristics of dissolved organic matters (DOM) through excitation-emission matrix (EEM) coupling with fluorescence regional integration (FRI), it revealed more degradable substances utilization in mixture of sludge. Results from this work suggest that two-phase AD with mixed sludge is efficient for renewable energy recovery.

Volatile Fatty Acid Production from Organic Waste with the Emphasis on Membrane-Based Recovery

In recent years, interest in the biorefinery concept has emerged in the utilization of volatile fatty acids (VFAs) produced by acidogenic fermentation as precursors for various biotechnological processes. This has attracted substantial attention to VFA production from low-cost substrates such as organic waste and membrane based VFA recovery techniques to achieve cost-effective and environmentally friendly processes. However, there are few reviews which emphasize the acidogenic fermentation of organic waste into VFAs, and VFA recovery. Therefore, this article comprehensively summarizes VFA production, the factors affecting VFA production, and VFA recovery strategies using membrane-based techniques. Additionally, the outlook for future research on VFA production is discussed.

Dynamic Changes of Microbiome with the Utilization of Volatile Fatty Acids as Electron Donors for Denitrification

Volatile fatty acids can be used as carbon sources for denitrification and are easily supplied as by-products from the anaerobic digestion of waste materials. Nitrification and denitrification processes were carried out in a single reactor feeding volatile fatty acids as electron donors and the changes in microbial communities in the reactor were investigated. The microbial communities in the alternating aerobic and anoxic systems were different, and their structure flexibly changed within one reactor. Bacteroidetes and Firmicutes were highly distributed during denitrification, whereas Proteobacteria was a major phylum during nitrification. In addition, in the denitrification system, the microbial community was substrate dependent. It showed the sequential nitrogen removal in one reactor and the microbial community also followed the change of environmental condition, cyclic nitrification, and denitrification.

Enhanced production of volatile fatty acids by adding a kind of sulfate reducing bacteria under alkaline pH

Anaerobic digestion could make sludge stable and harmless, and the volatile fatty acids (VFAs) produced from it. The objective of this study was to reduced sludge production and realize the resource utilization of VFAs through enhance anaerobic sludge fermentation by adding sulfate reducing bacteria (SRB) under alkaline pH. Under the neutral and alkaline pH, SRB was added into the sludge fermentation liquid with sole stock solution and sterilization treatment respectively, while the liquid without any additives was used as control. The results indicated that obvious increase of the production of VFAs was observed after adding SRB under alkaline pH. And, more protein and polysaccharide were obtained which were the main substrates for the production of VFAs. The concentration of ammonia nitrogen (NH4+-N) and phosphate (PO43−-P) were also increased with the addition of SRB. So, a high yield production of VFAs could be achieved through the addition of SRB + alkaline pH.

Tackling antibiotic inhibition in anaerobic digestion: The roles of Fe3+ and Fe3O4 on process performance and volatile fatty acids utilization pattern

The anaerobic treatment of antibiotic-contaminated organic wastes is often challenged by the reduction of the overall anaerobic digestion (AD) process performance. This study aimed to investigate the roles of ferric ion (Fe3+) and magnetite (Fe3O4) on process performance and volatile fatty acids (VFA) utilization pattern in an oxytetracycline (OTC)-pressured AD. Three sets of batch experiment were conducted where OTC, FeCl3 and Fe3O4 concentrations were varied from 0.07 to 0.19 g/gCOD, 0.04 to 0.15 g/gCOD and 0.07 to 0.14 g/gCOD, respectively. The results showed that the conversion of propionic and butyric acids into intermediate products was delayed by OTC. Moreover, OTC reduced methane yields (MY) between 25 and 27%. However, when FeCl3 and Fe3O4 were added, MY was increased by 7% and 33% at FeCl3 of 0.07 g/gCOD and Fe3O4 of 0.07 g/gCOD, respectively, along with the improvement of propionic and butyric acids conversion.

In vitro Evaluation of Corn Germ Meal as Ruminant Feed

The present study was taken up to assess the chemical composition and in vitro nutritional worth of corn germ meal (CGM) in comparison to conventional oilseed cakes used in livestock feeding. The CP content of protein sources varied from 18.59% in CGM to 49.41% in soybean meal (SBM). CGM had the highest ether extract (EE) content, neutral detergent fibre (NDF), acid detergent fibre (ADF) and total carbohydrates. However, total ash, acid detergent insoluble crude protein (ADICP) and neutral detergent insoluble crude protein (NDICP) was lowest in CGM. In vitro net gas production in CGM (267.91 ml/g DM/24 h) was higher (P<0.05) than other conventional oil cakes. The digestibility of organic matter varied from 85.12% in DMC (deoiled mustard cake) to 96.19% in SBM. The ME availability was highest (P<0.05) in CGM (9.63 MJ/kg DM). Ammonical nitrogen in CGM was lower (P<0.05) than SBM and GNC (groundnut cake).The total volatile fatty acids (TVFA) production (mM/dl) was highest (P<0.05) in GNC (12.56) and lowest (P<0.05) in CGM (9.31). Methane production was lowest (P<0.05) in CGM than other conventional oil cakes. Hydrogen recovery (%) was higher (P<0.05) in CGM (65.76) and SBM (65.78) than other protein sources tested. Fermentation efficiency (%) was higher (P<0.05) in SBM (77.02) and GNC (76.75) while volatile fatty acids utilization index (VFA UI) was higher (P<0.05) in CGM (2.92) and DMC (2.84) than other protein sources tested. The results revealed that CGM can be used as a potential protein source for ruminants.

Impact of the volume and the profile of volatile fatty acids in the rumen fermentation on cow productivity and milk composition

The aim of the research was to establish relations between the selected rumen fermentation products and the milk composition in dairy cows. The experiment was conducted on 10 Polish Holstein-Friesian cows of black and white variety. The animals were kept in the free stall housing system and fed with the total mixed ration (TMR). The herd’s milk production was assessed using the A4 method and the milk analyses were obtained from the milk recordings. The rumen digesta were sampled two hours after the morning delivery of TMR using a stomach pump. The sampled digesta were diluted with buffer, homogenized and the obtained suspension was analysed using gas chromatograph with the FID detector to determine the total concentration of volatile fatty acids (VFA) and the percentage of individual VFAs. Milk composition was obtained from the RW-1 reports, and the Pearson correlation coefficient was calculated for the obtained parameters. It was determined that propionate and the relation of propionate to butyrate in the rumen digesta increased the protein content and its fractions in milk. The volatile fatty acids utilization coefficient in the rumen digesta a positive correlation to protein contents and a negative correlation to the level of caseins in milk were shown. Processes taking place in the cow rumen significantly influence the composition and quality of milk. The knowledge of volatile fatty acids content and the of individual VFAs allows for the management of the rumen fermentation in order to obtain better technological parameters of milk.

Generation and Utilization of Volatile Fatty Acids and Alcohols in Hydrothermally Altered Sediments in the Guaymas Basin, Gulf of California

AbstractVolatile fatty acids (VFAs) and alcohols are key intermediates of anaerobic carbon metabolism, yet their biogeochemical cycling remains poorly constrained in hydrothermal systems. We investigated the abundance, stable carbon isotopic composition, and metabolic cycling of VFAs and alcohols to elucidate their generation and utilization pathways in hydrothermally influenced sediments (4 °C to 90 °C) from the Guaymas Basin. Acetate (up to 229 μM) and methanol (up to 37 μM) were abundant in porewaters. The δ13C values of acetate varied between −35.6‰ and −18.1‰. Carbon isotopic signatures, thermodynamic predictions, and experimental incubations suggested biological sources such as fermentation and acetogenesis for acetate. Acetate and methanol were predominantly consumed by nonmethanogenic processes (e.g., sulfate reduction), as reflected in high oxidation rates versus low methanogenesis rates, and further evidenced through inhibition experiments with molybdate. These results reveal an important role for VFAs and alcohols as energy sources for diverse chemoheterotrophs in organic‐rich hydrothermally influenced sediments.

Generation and Utilization of Volatile Fatty Acids and Alcohols in Hydrothermally Altered Sediments in the Guaymas Basin, Gulf of California

Generation and Utilization of Volatile Fatty Acids and Alcohols in Hydrothermally Altered Sediments in the Guaymas Basin, Gulf of California