Increase In Volatile Fatty Acid Production Research Articles

Distinct effects of chemical- and bio- flocculants on the sludge acidogenic fermentation for volatile fatty acids production by affecting the acidogenic steps, microbial community structure and metabolic functions

Flocculants play crucial roles in sludge treatment, while the specific impact of chemical and bio-flocculants on sludge anaerobic fermentation was unknown. This study unveiled the contrasting effects of chitosan (CTS) and poly‑aluminum chloride (PAC) on volatile fatty acids (VFAs) generation during sludge fermentation. CTS supplementation resulted in 17.2 % increase in VFAs production, while PAC exposure led to 7.6 % reduction compared to the control. Further investigation revealed that CTS facilitated sludge solubilization and hydrolysis, thus providing sufficient organic substrates for VFAs generation. Additionally, environmental-friendly CTS exposure positively influenced the abundance and activity of functional anaerobes, as well as the expression of genes associated with VFAs biosynthesis. In contrast, PAC exposure resulted in the formation of larger sludge flocs, which hindered WAS solubilization and hydrolysis. Meanwhile, its potential microbial toxicity also impeded the microbial metabolic activity (i.e., genetic expressions), resulting in unsatisfactory VFAs production.

Fractional factorial experimental design for optimizing volatile fatty acids from anaerobic fermentation of municipal sludge: Microbial community and activity investigation

Volatile fatty acids (VFAs) production from municipal sludge is a promising venture for resource recovery while ensuring wastewater treatment plants' ecological and economic sustainability. This study used a fractional factorial design (FFD) and response surface methodology (RSM) to optimize VFAs production from municipal sludge in semi-continuous flow acid fermenters (AFs) based on four critical parameters (i.e., sludge retention time (SRT), sludge composition, pH, and temperature) interactively and individually. To ascribe the mechanisms to VFAs production dynamics, non-methanogenic microbial activity assays and microbial community composition linked to the VFAs yields were explored. FFD and RSM successfully optimized VFAs production in the AFs, and a second-order polynomial model with an R-squared of 0.83 was derived. Optimal model conditions for VFAs production were 3-days SRT, 45 °C, pH 8.1, and 0.92 sludge composition (VS/TS ratio). Under these conditions, the model predicted a 3.47-fold increase in VFAs production, close to the experimental value of 3.48. AFs at pH of 8.1 and varying temperatures harbored the highest proportion of fermentative bacteria, mainly Clostridia, and lowest community diversity, indicating strong selective pressure for VFAs-producing populations. Furthermore, the microbial activities assays provided quantitative functional information linked to the microbial communities in each AF configuration consistent with VFAs production.

Octylphenol facilitates fermentative volatile fatty acids recovery from waste activated sludge

The presence of endocrine disruptor compounds (EDCs) in wastewater treatment plants has attracted widespread attention, but their potential impact on anaerobic fermentation of waste activated sludge (WAS) remains unclear. Therefore, this study aims to reveal the effect of typical EDC octylphenol (OP) on the recovery of volatile fatty acids (VFAs) in anaerobic fermentation. The results show that OP has a positive effect on the recovery of VFAs from WAS. The presence of 200 mg/kg dry sludge of OP increased the cumulative amount of VFAs from 3245 in the control (without OP) to 6828 mg COD/L. The increase in VFA production was mainly attributed to the accumulation of acetic acid, which rose from 1511 to 4425 mg COD/L, almost tripled. Further research found that OP promoted solubilization and hydrolysis by improving the biodegradability of WAS, and severely inhibited the methanogenesis process by inhibiting the activity of coenzyme F420, thereby significantly increasing the accumulation of acetic acid. These findings are of great significance to clarify the role of OP in anaerobic fermentation, and provide theoretical basis and guidance for the selection of target products in anaerobic fermentation of WAS containing OP.

Effect of polyvinyl alcohol hydrogel as a biocarrier on volatile fatty acids production of a two-stage thermophilic anaerobic membrane bioreactor

This work studied the effect of polyvinyl alcohol hydrogel (PVA-gel) beads, as an effective biocarrier for volatile fatty acid (VFA) production in hydrolytic reactor of a two-stage thermophilic anaerobic membrane bioreactor (TAnMBR). The two-stage TAnMBR, treating synthetic high strength particulate wastewater with influent chemical oxygen demand (COD) [16.4±0.8g/L], was operated at 55°C. Under steady state conditions, the reactor was operated at an organic loading rate of 8.2±0.4kg COD/m3d. Operational performance of the system was monitored by assessing VFA composition and quantity, methane production and COD removal efficiency. Increment of VFA production was observed with PVA-gel addition. Hydrolytic effluent contained large amount of acetic acid and n-butyric acid. However, increase in VFA production adversely affected the methanogenic reactor performance due to lack of methanogenic archaea.

Influence of the organic loading rate on the performance and the granular sludge characteristics of an EGSB reactor used for treating traditional Chinese medicine wastewater

The effects of the organic loading rate (OLR) on the performance and the granular sludge characteristics of an expanded granular sludge bed (EGSB) reactor used for treating real traditional Chinese medicine (TCM) wastewater were investigated. Over 90% of the COD removal by the EGSB reactor was observed at the OLRs of 4 to 13 kg COD/(m(3) day). However, increasing the OLR to 20 kg COD/(m(3) day) by reducing the hydraulic retention time (HRT 6 h) reduced the COD removal efficiency to 78%. The volatile fatty acid (VFA) concentration was 512.22 mg/L, resulting in an accumulation of VFAs, and propionic acid was the main acidification product, accounting for 66.51% of the total VFAs. When the OLR increased from 10 to 20 kg COD/(m(3) day), the average size of the granule sludge decreased from 469 to 258 μm. There was an obvious reduction in the concentration of Ca(2+) and Mg(2+) in the granular sludge. The visible humic acid-like peak was identified in the three-dimensional excitation-emission matrix (EEM) fluorescence spectra of the soluble microbial products (SMPs). The fatty acid bond, amide II bond, amide III bond, and C-H bond bending were also observed in the Fourier transform infrared (FTIR) spectra of the SMPs. Methanobacterium formicicum, Methanococcus, and Bacteria populations exhibited significant shifts, and these changes were accompanied by an increase in VFA production. The results indicated that a short HRT and high OLR in the EGSB reactor caused the accumulation of polysaccharides, protein, and VFAs, thereby inhibiting the activity of methanogenic bacteria and causing granular sludge corruption.

Effect of bromochloromethane on methane emission, rumen fermentation pattern, milk yield, and fatty acid profile in lactating dairy goats

Several technologies have been tested to reduce enteric methanogenesis, but very few have been successfully used in practical conditions for livestock. Furthermore, the consequences of reduced rumen methane production on animal performance and milk quality are poorly understood. The aim of this work was to investigate the effect of feeding bromochloromethane (BCM), a halogenated aliphatic hydrocarbon with potential antimethanogenic activity, to dairy goats on rumen methane production, fermentation pattern, the abundance of major microbial groups, and on animal performance and milk composition. Eighteen goats were allocated to 2 experimental groups of 9 animals each: treated (BCM+) or not (BCM−) with 0.30g of BCM/100kg of body weight per day. The BCM was administered per os in 2 equal doses per day from parturition to 2 wk postweaning (10 wk). After weaning, methane emissions were recorded over 2 consecutive days (d 57 and 58 on treatment) in polycarbonate chambers. On d 59, individual rumen fluid samples were collected for volatile fatty acid (VFA) analysis and quantification of bacterial, protozoal, and archaeal numbers by real-time PCR. On d 69 and 70, daily milk production was recorded and samples were collected for determination of fat, protein, lactose, casein, and total solids concentration by infrared spectrophotometry, and fatty acid composition by gas chromatography. Treatment with BCM reduced methane production by 33% (21.6 vs. 14.4L/kg of DMI) compared with nontreated animals, although it did not affect the abundance of rumen bacteria, protozoa, and total methanogenic archaea. The observed improvement in the efficiency of digestive processes was accompanied by a 36% increase in milk yield, probably due to the more propionic type of rumen fermentation and an increase in VFA production. The increase in milk yield was not accompanied by any changes in the concentrations or yields of fat, protein, or lactose. Despite the substantial decrease in methane production, only minor changes in milk fatty acid profile were observed, suggesting that ruminal biohydrogenation pathways were not affected. Compounds that influence terminal biochemical pathways for methane production deserve further development for future application in the dairy goat sector.

Effect of micro-aeration and leachate replacement on COD solubilization and VFA production during mono-digestion of grass-silage in one-stage leach-bed reactors

The effect of micro-aeration and leachate replacement with fresh water on chemical oxygen demand (COD) solubilization and volatile fatty acid (VFA) production during the mono-digestion of grass-silage in one-stage leach-bed reactors (LBRs) was investigated in four LBRs, L0 (control), L1, L2 and L3 in batch mode at 35 + or - 1 degrees Celsius for 57 days. Results showed that leachate replacement without pH adjustment (L3) resulted in 2.7 and 1.3 times more SCOD in the leachate compared to control (L0) or leachate replacement with initial pH adjustment (L1), respectively. Micro-aeration at flow rate of 1 L min(-1) (2.5 L of air) in L2 resulted in 4-fold increase in VFA production (from 2.2 to 9 g L(-1)) without any significant increase in cumulative SCOD in the leachate. Increasing the air flow rate to 4 L min(-1) (24 L of air) in L2 resulted in a decrease in SCOD extraction. Leachate replacement without pH adjustment (L3) resulted in higher (mean) specific SCOD production (0.51 g SCOD g(-1) VS(added)) than control (L0, 0.34 g SCOD g(-1) VS(added)), leachate replacement with initial pH adjustment (L1, 0.33 g SCOD g(-1) VS(added)) or micro-aeration (L2, 0.32 g SCOD g(-1) VS(added)). These results suggest that the challenge of hydrolysis during anaerobic digestion of particulate substrates like grass-silage can be improved by micro-aeration and leachate replacement methods with or without pH adjustment.

Effect of enzymatic pretreatment on solubilization and volatile fatty acid production in fermentation of food waste

Food waste can be a valuable carbon source in biological nutrient removal (BNR) systems because of the high C/N and C/P ratio. However, pretreatment is necessary to promote hydrolysis of food waste because of the high concentration of volatile solids associated with organic matter. The influence of the enzymatic pretreatment on acid fermentation of food waste was investigated in this study. Solubilization of particulate matter in food waste was carried out using commercial enzymes. The acidification efficiency and the volatile fatty acid (VFA) production potential of enzymatically pretreated food waste were examined. The highest volatile suspended solid (VSS) reduction was obtained with an enzyme mixture ratio of 1:2:1 for carbohydrase: protease: lipase. An optimum enzyme dosage for solubilization of food waste was 0.1% (V/V) with the enzyme mixture ratio of 1:2:1. In the acid fermentation of enzymatically pretreated food waste, the maximum VFA production and the highest VFA fraction in soluble COD (SCOD) were also achieved at 0.1% (V/N) of total enzyme dosage. Increase in VFA production at this level of enzyme dosage was over 300% compared with the control fermenter. The major form of VFA produced by fermentation was n-butyrate followed by acetate.

Effect of pretreatment on acid fermentation of organic solid waste

The effect of various pretreatment methods on acidogenesis of food waste from a cafeteria was investigated. Thermal, enzymatic, and combined thermal-enzymatic batch pretreatment were conducted. Solubilization of food waste in thermal or enzymatic pretreatment increased with either increasing thermal duration or enzyme dosage, respectively. An optimal condition in thermal or enzymatic pretreatment was 60 min of thermal processing or 0.1% (v/v) of enzyme dosage level, respectively, based on volatile suspended solids (VSS) reduction. In the combined pretreatment, increased thermal duration also increased VSS reduction and the solubilization efficiency was higher than that in only enzymatic or thermal pretreatment. The maximum volatile fatty acids (VFAs) production and the highest VFAs fraction in soluble COD in the acid fermentation were achieved with the food waste after 60 min of thermal processing followed by 0.1% (v/v) enzymatic treatment. Increase in VFAs production of the fermenter was over 380% compared to the control fermenter without any pretreatment.

Effect of the addition of Peptostreptococcus productus ATCC 35244 on reductive acetogenesis in the ruminal ecosystem after inhibition of methanogenesis by cell-free supernatant of Lactobacillus plantarum 80

The addition of the cell-free supernatant of Lactobacillus plantarum 80 (LP80) to ruminal samples during short-term batch experiments (24 h) led to significant increases in volatile fatty acid (VFA) production (5–30%) and to significant decreases in CH 4 production (5–15%), accompanied by H 2 accumulation. The supplemental addition of the reductive acetogen Peptostreptococcus productus ATCC35244 gave rise to an additional increase in VFA production, while CH 4 production was decreased further ( p<0.01) and H 2 accumulation was abolished. The addition of P. productus without the addition of supernatant had no effect on the fermentation patterns. The utilization of H 2, the lowering of the H 2 recovery (2Hr) value and the high acetate production observed in the experiment indicated that both the addition of either the supernatant or the addition of the supernatant and P. productus stimulated reductive acetogenesis. The persistence of the obtained effects was further evaluated in vitro by incubation of rumen contents under pH control (6.4–6.6) during 72 h. Compared to short-term batch experiments, the stimulation of VFA production was lower (8–15%), while inhibition of CH 4 production was higher (18–30%). These effects became manifest during the first 24 h of incubation and persisted during the 72 h incubation period. Infusion of both supernatant of LP80 and P. productus in the rumen of two rumen fistulated rams revealed that during the first days of administration, the addition of supernatant and P. productus decreased methanogenesis much more strongly than was observed in vitro (80%), whereas no clear effect on fermentation rate or patterns was observed. However, the effect was only transient, since at the sixth day of the administration period methanogenesis was again at the same level as during the control period. These results indicate that the supernatant of LP80 contains compounds which inhibit methanogenesis in the rumen, but that either resistance to the compound, or stimulation of rumen microbial breakdown of these compounds had occurred. Also, the ability to stimulate reductive acetogenesis by additional introduction of P. productus was only important during short-term incubations, while the effect diminished during long-term in vitro incubations or disappeared in vivo.

Volatile fatty acids production by mesophilic fermentation of mechanically-sorted urban organic wastes in a plug-flow reactor

Volatile fatty acids (VFA) production by anaerobic fermentation of municipal solid wastes was studied at pilot-plant level. A plug-flow reactor (80 l total volume), with and without concentrated sludge recirculation, was employed to digest an organic fraction of the municipal solid waste (OFMSW)-based substrate. This was composed of OFMSW mechanically-selected in a full-scale plant with OFMSW collected from fruit and vegetable markets and mixed in a way to obtain a feed mixture with a proportion of total volatile solids (TVS)/total solids (TS) of 60%. The fermentation process was studied at different retention times (RT) (from 8 h to 8 days) and at very high organic loading rates (OLR) (from 22·4 to 85·2 kg VS/m 3 d) at mesophilic temperature (37 ± 2°C). Results showed an increase in VFA production at higher retention times (from 11·8 g/l at 2 days to 23·1 g/l at 6 days RT) when no recirculation was used. VFA production was also high when part of the digested sludge was recirculated (19·5 g/l at 2 days of hydraulic RT and 8 days of solid RT). Acetic and butyric were the acids produced in the largest quantities.

Anaerobic acidogenesis of primary sludge: The role of solids retention time

This research investigates the effect of solids retention time (SRT) on the acid-phase anaerobic digestion of primary sludge. A series of experiments were conducted using two continuous-flow 3-L units with the following configuration: a completely mixed reactor (CMR) with clarifier and solids recycle and an upflow anaerobic sludge blanket (UASB) reactor. Results show that C(2) to C(5) volatile fatty acids (VFA) were the predominant compounds formed. At a constant hydraulic retention time (HRT) of 12 h, variation in SRT from 10 to 20 days resulted in a slight increase in VFA production in both systems, but at a shorter SRT (5 days) a drastic drop in acid production was observed. In addition, the percent distribution of VFA was to some extent affected by the change in SRT. On the other hand, organic matter degradation [measured by the chemical oxygen demand (COD) specific solubilization rate or the percent volatile suspended solids (VSS) reduction] appeared to be independent of SRT, at least in the range investigated. The percent soluble COD in the form of VFA, however, increased steadily with increasing SRT, approaching the 90% level at 20 days. The remaining soluble COD in the effluent from these systems may be mainly attributed to metabolic intermediates and unused soluble substrate.