High Concentrations Of Volatile Fatty Acids Research Articles

66 In vitro comparison of six raw materials on gastric ecosystem activity and acidity

The great biochemical variability of the raw materials used in horse feeds can induce changes in gastric fermentation, and therefore affect gastric health through the resulting acidity of the bacterial end products. This in vitro trial compared the effect of 6 raw materials (BA: barley; WB: wheat bran; OA: oats; SM: sunflower meal; SB: sugar beet pulp; AL: alfalfa – Table 1) commonly used in horse feeds on gastric bacterial fermentation and buffering capacity. In 3 horses fed a mixture of the 6 raw materials 3h before sampling, gastric chyme was collected via a nasogastric tube and mixed. Bottles containing 1mL of the mixed gastric chymes, 50mL dilution medium and 1.0g of substrate (50% pilled barley + 50% one pilled raw material) were incubated in a shaking water bath at 39°C for 10h. Gas production, volatile fatty acids (VFAs), pH and buffering capacity of the solution (HCl 0.1M volume added to lower pH to 4 in the 50mL solution) were measured every 2h in duplicate. Effect of the substrate, time and their interaction were analyzed using a mixed procedure (SAS). From 4h to 10h incubation, gas production was greater with WB than BA, SM and AL ( P < 0.001), reflecting higher bacterial fermentations, probably associated with WB highest soluble sugars content. Higher VFAs concentration were observed with AL than OA and WB at 2h, than BA and SB at 8h, than all other substrates at 10h ( P > 0.001). This intense VFAs production with AL suggested environmental conditions more adapted for starch and soluble sugars fermentation, maybe combined with protein fermentation. Little differences were observed between raw materials regarding pH evolution. However, all along the 10h, buffering capacity of the solutions containing AL remained significantly higher than all others ( P = 0.002, Table 1). The inclusion of alfalfa in horse feeds could be of interest to delay the decrease in gastric pH associated with HCl secretions and fermentation end products appearance, and to limit the exposure time of gastric mucosa to pH ≤ 4.

Two-Step Pretreatment of Hydrothermal with Ammonia for Cow Bedding: Pretreatment Characteristics, Anaerobic Digestion Performance and Kinetic Analysis

Cow bedding is one of the dominant livestock wastes among agricultural waste in China. The bedding is a good raw material for anaerobic digestion (AD) and produces biogas of sustainable energy. To improve the AD performance of bedding, a two-step pretreatment of hydrothermal with ammonia (TPHA) was used at 100, 150, and 200 °C holding for 5–30 min. The results revealed that the highest volatile fatty acids concentration was 4720.1 mg/L at a TPHA of 200 °C for 5 min. The highest removal rates of cellulose and hemicellulose were 35.4% and 97.4% at a hydrothermal pretreatment (HP) of 100 °C for 30 min and 200 °C for 10 min, respectively. The highest methane yield of cow bedding was 169.1 mL/g VS using the TPHA at 150 °C for 10 min, which was 54.5% higher than that of the untreated group. Kinetic analysis showed that the modified Gompertz model was more suitable for TPHA for cow bedding. Therefore, TPHA could improve pretreatment characteristics and enhance the methane yield of cow bedding.

Process Improvement of a Two-Stage Upflow Anaerobic Sludge Blanket System by Micronutrient Supplement in Relation to Sulfur Transport

The main purpose of this research was to elucidate the influence of the addition of iron alone (0–100 ppm) or with 2 ppm each of cobalt, copper, and nickel on the performance of a two-stage UASB system treating ethanol wastewater. The system consisted of two reactors connected in series. The system was maintained at a fixed chemical oxygen demand loading rate (16 kg/m3d) and 37 °C with a recycle ratio of 1:1. Both Co and Ni were found to be deficient in the ethanol wastewater, while Fe and Cu became inadequate in two-stage UASB. The addition of Fe provided dual benefits of a reduction in both sulfide toxicity and hydrogen sulfide content in produced gas, resulting in marginally improved hydrogen and methane productivities. When the Fe dosage was increased beyond the optimum value of 50 ppm, the process performance drastically declined, as a result of high total volatile fatty acid concentrations that inhibited acidogens and methanogens predominantly present in the 1st and 2nd reactors, respectively. The chemical precipitation of iron sulfide was responsible for the reduction of produced H2S in both aqueous and gaseous phases. The addition of 2 ppm each of Co, Cu, and Ni together with 50 ppm Fe resulted in an enhanced process performance, as indicated by the improved CH4 yield (mL/g COD applied) to about 42.3% compared to that without micronutrient supplement. Supplementation to fulfill the sufficiency of all micronutrients was vital for the maximization of anaerobic digestion (AD) performance, as generally indicated in methanogenic activity.

Lower temperature hydrothermal pretreatment improves the anaerobic digestion performance of spent cow bedding

Abstract The anaerobic digestion (AD) performance of spent cow bedding was investigated with different hydrothermal pretreatment (HP) conditions. Spent cow bedding was pretreated with low temperatures (50, 70, and 90°C) and different pretreatment times (2-72 h) with ammonia and without ammonia. The results showed that spent cow bedding was a good raw material for AD. After pretreatment, the concentration of volatile fatty acids (VFAs) in the group of hydrothermal pretreatments with ammonia (HPA) was higher than that in the HP group at the same pretreatment temperature and time. The optimal pretreatment condition was achieved with an HPA of 50℃ holding for 72h. At the optimal condition, the highest concentration of VFAs was 1.58-10.85 times higher than that of the other pretreated groups. The highest hemicellulose and lignin removal rates were 58.07% and 10.32%, respectively. The highest methane yield was 163.0 ml·(g VS)-1, which was 48.9% higher than that of the untreated group. The VFAs, pH, and reducing sugars showed positive relationships with the methane yield. Therefore, HP at low temperature can enhance the AD performance of spent cow bedding.

Two step process for volatile fatty acid production from brewery spent grain: Hydrolysis and direct acidogenic fermentation using anaerobic granular sludge

Brewery spent grain (BSG) is an industrial waste stream with large potential for biorefining purposes. This work evaluated the production of volatile fatty acids (VFAs) by a two-step process using BSG as renewable feedstock by combining a single direct hydrolysis step (without removing the acid or potential inhibiting compounds) with an acidogenic fermentation step of the carbohydrate rich leachate. For the first step, a thermal diluted acid hydrolysis was carried (20 min at 121 °C), using eighteen different combinations in terms of total solid (TS) of BSG (4, 7 and 10 % w/w) and H2SO4 (0.0, 0.5, 1.0, 1.5, 2.0 and 3.0 % v/v). The 7.0 % TS of BSG and 1.5 % of H2SO4 combination was the most efficient in terms of total carbohydrate recovery (0.44 g of total carbohydrates per gram of TS). For the second step, an acidogenic batch fermentation of the hydrolysate was performed using anaerobic granular sludge at five different pH conditions (uncontrolled pH from an initial pH 7.0, and constant pH controlled at 4.5, 5.0, 6.0 and 8.0). The highest VFAs concentration was obtained at pH 6.0 and reached 16.89 (± 1.33) g COD/L, composed of mainly (99.5–99.8 %) acetate and butyrate.

Microalgae-based anaerobic fermentation as a promising technology for producing biogas and microbial oils

Abstract This study assessed the potential of using microalgae anaerobic fermentation as a novel choice for producing microbial oils and biogas. Microalgae biomass (Chlorella vulgaris) was used for volatile fatty acids (VFAs) production at three organic loading rates (OLR = 6, 9, 12 g COD/Ld). Regardless of the OLR, anaerobic systems displayed similar organic matter conversion yields into VFAs (VFAs-COD/CODin = 38%) and VFAs distribution profiling. Obtained digestates were further used with a two-fold purpose, producing microbial oils from the VFA rich liquid fraction, and generating methane from the remaining solid spent. The yeast Yarrowia lipolytica was able to grow on VFAs concentration up to 17.6 g/L while the highest VFAs concentration (24.2 g/L, digestate obtained at 12 g COD/Ld) resulted inhibitory. Despite of that, Y. lipolytica exhibited remarkably high lipid content (15–23%) when grown in digestates. The three spent solid fractions (corresponding to the 3 OLRs) reached the same methane potential.

Long-term high-grain diet alters ruminal pH, fermentation, and epithelial transcriptomes, leading to restored mitochondrial oxidative phosphorylation in Japanese Black cattle

To increase intramuscular fat accumulation, Japanese Black beef cattle are commonly fed a high-grain diet from 10 to 30 months of age. Castrated and fistulated cattle (n = 9) were fed a high-concentrate diets during the early, middle, and late stages consecutively (10–14, 15–22, 23–30 months of age, respectively). Ruminal pH was measured continuously, and rumen epithelium and fluid samples were collected on each stage. The 24-h mean ruminal pH during the late stage was significantly lower than that during the early stage. Total volatile fatty acid (VFA) and lactic acid levels during the late stage were significantly lower and higher, respectively, than those during the early and middle stages. In silico analysis of differentially expressed genes showed that “Oxidative Phosphorylation” was the pathway inhibited most between the middle and early stages in tandem with an inhibited upstream regulator (PPARGC1A, also called PGC-1α) but the most activated pathway between the late and middle stages. These results suggest that mitochondrial dysfunction and thereby impaired cell viability due to acidic irritation under the higher VFA concentration restored stable mitochondrial oxidative phosphorylation and cell viability by higher lactic acid levels used as cellular oxidative fuel under a different underlying mechanism in subacute ruminal acidosis.

Effect of preweaning diet on performance, blood metabolites and rumen fermentation around weaning in calves of two beef breeds

Context Good transition from suckling to high-concentrate diets is essential to avoid nutritional disorders during the fattening period of beef calves. Aims Assessing the optimal feeding strategies during the preweaning period of beef calves for an adequate adaptation to high-concentrate diets. Methods A total of 30 female beef calves (15 Parda de Montaña and 15 Pirenaica), managed under restricted suckling, were assigned to three preweaning diets (milk only [MO], milk plus hay [MH], milk plus concentrate [MC]), fed from the third month until weaning at 5 months. During the subsequent transition period (1 month), all animals received a fattening concentrate plus wheat straw ad libitum. Key results Milk intake did not differ among diets; solids intake was similar for MH and MC calves. Preweaning supplementation improved performance at the end of the suckling period (MC &amp;gt; MH &amp;gt; MO). During transition, concentrate intake was lower for MO calves; MH calves showed the lowest feed efficiency. At the end of transition, MC calves showed the highest liveweight and average daily gain (MC &amp;gt; MH = MO). Rumen pH at weaning did not differ from that at the end of transition in MC calves, whereas MH and MO animals showed lower values at the latter. Supplemented calves showed higher volatile fatty acids concentration than MO calves at weaning; MC calves showed the lowest values at the end of the transition period. Ammonia and lactic acid concentration at weaning was the highest for MO and MC calves respectively, with no differences between diets at the end of transition. Glucose and non-esterified fatty acids concentrations were only affected by age; urea and β-hydroxybutyrate were affected by the interaction between diet and age. Economic profitability at weaning was higher for supplemented calves (MH = MC &amp;gt; MO), and ranked MC &amp;gt; MO &amp;gt; MH at the end of the transition. Gains during the suckling period, and hence the economic margin, were higher for Parda de Montaña than for Pirenaica calves; during transition the economic margin was similar. Conclusions Preweaning supplementation with concentrates is the most interesting option in terms of performance and profitability. Implications Preweaning solid supplementation increases calf performance and provides better rumen development, essential for a smooth transition to fattening diets.

Digestibility Value and Fermentation Level of Local Feed-Based ration for Sheep

Feed Digestibility is an important indicator which can be used as a guideline to determine the amount of nutrient and feed that can be absorbed by digestive tract. The objective of the research was to determine the value dry matter digestibility (DMD), organic matter digestibility (OMD), NH3 fermentation level and volatile fatty acid (VFA) fermentation level. The research was conducted on January 2018 in Animal Feed and Nutrition Laboratory of Animal Husbandry and Agriculture Faculty, Diponegoro University Semarang. The research method used was in vitro analysis with complete randomized design with five treatments and four replicates. The data were analyzed with analysis of variance at 95% significant level, followed by Duncan Multiple Range Test. The results showed that the highest score of DMD was T5=56.51±0.33%, T4=56.41±2.11; T3=55.86±0.83; highest score of OMD was T5=62.48±0.39%, T4=61.87±1.60; T3=60.86±1.10, the highest NH3 concentration was T3=6.07±1.55 mM, and the highest VFA concentration was T5=55.25±3.40 mM. Sheep’s local feed-based ration was significantly (P&lt;0.05) influenced in vitro DMD, OMD, NH3 fermentation level and VFA fermentation level

Hydrothermal treatment of Chlorella sp.: Influence on biochemical methane potential, microbial function and biochemical metabolism

This study focused on the effect of hydrothermal treatment (HTT) on biochemical methane potential (BMP) of Chlorella sp. The BMP was in the range of 119.16–485.90 mLCH4/gVS, and increased by 80.31%–210.16% after HTT, while reduced 23.94% at hydrothermal treatment severity (HTS) 5.21. The cell wall was more greatly disrupted with increasing HTS, accompanied with the increase of volatile fatty acids (VFAs) and fermentation inhibitors (5-HMF and more complex chemical compositions) recoveries. The reducing sugar yields were 0.94–3.65% and obtained its maximum at a retention time of 30 min. Illumina MiSeq sequencing clarified that, the phylum Chloroflexi with functions of hydrolysis and acidogenesis, decreased with increasing HTS. The family Methanosaetaceae belonging to acetoclastic methanogens, had an unexpected decrease at HTS 5.21. As the response, VFAs concentration was less than 1 g/L after biochemical metabolism, while high concentrations of VFAs and inhibitors at HTS 5.21 led to the poor performance.

Engineering Trichosporon oleaginosus for enhanced production of lipid from volatile fatty acids as carbon source

Trichosporon oleaginosus is one of the most promising hosts for microbial lipid production owing to its high-productivity; In an effort to develop an economical production process, we engineered T. oleaginosus towards high-lipid production from volatile fatty acids (VFA) derived from anaerobic fermentation of food waste. First, we established a method for labeling intracellular lipid with lipophilic BODIPY fluorescent dye. Next, a random library was constructed by treatment with a chemical mutagen, and high-lipid producers were screened using fluorescence-activated cell sorting. Subsequently, one clone, N14, was successfully isolated, which exhibited 3-fold higher lipid production (19.4%) in VFA (6 g/L) media than the wild-type strain, and also showed increased lipid production in higher concentrations of VFA (18 or 24 g/L). Based on fatty acid methyl ester (FAME) analysis, N14 contained higher stearic acid (C18:0) and oleic acid (C18:1) content compared with those of the wild-type strain.

A New Adjustment Strategy to Relieve Inhibition during Anaerobic Codigestion of Food Waste and Cow Manure

A new adjustment strategy (controlling temperature, pH, inoculum dose, and liquid supernatant replacement in different digestion stages) was used to relieve volatile fatty acid (VFA) inhibition during anaerobic codigestion of FW and CM. Three digestion stages and groups were designed: initial stage (on days 1–5 the temperature was 45 °C), the second stage (on days 6–10 the temperature was 35 °C and inoculum was supplied), and the third stage (on days 11–50 the temperature was 35 °C and liquid supernatant was replaced). Groups A, B, and C had initial inoculums of 0, 100, and 200 mL and were supplied inoculums of 200, 100, and 0 mL, respectively. Results showed that in the initial stage, Group A had the highest VFA concentration (876.54 mg/L) and the lowest pH (3.6). In the second and third stages, pH (~5.5 and ~7.5) and VFA concentrations showed no significant differences in all groups. The highest VFA concentration (3248 mg/L), volatile solid (VS) removal rate (49.72%), and total methane production (TMP) (10,959 mL), the shortest λ (19.92 d), and the T90% (39.25 d) were obtained in Group B (pH 8.5). Group C had the highest chemical oxygen demand (COD) removal rate (96.91%). Group A obtained the maximal TBP of 25,626 mL (pH 8.0).

The effect of acidogenic and methanogenic conditions on the availability and stability of carbon, nitrogen and phosphorus in a digestate

Acidification and drying of digestate are important post-treatment for, respectively, improving nutrient availability and hygiene. These approaches are expected to reduce digestate soil application mass and increase its value. This study compared eleven organic feedstocks under acidogenic and methanogenic conditions as a sustainable approach to improving phosphorus availablity, organic carbon and stabilising ammoniacal nitrogen of the resulting digestate under thermal drying. The result showed increases in phosphate concentration under acidogenic conditions and reduction in ammonium nitrogen after drying at 100 °C. The highest phosphate values of 3.2 ± 0.38 g/kg were achieved using whey permeate substrate while the effect of drying on ammonium nitrogen concentration was lowest for acidogenic bird seed fermentation with an ammonium loss of 59.7%. Both results were facilitated by high total volatile fatty acid concentration produced from available organic carbon which reached a maximum value of 5.71 ± 0.53 g/L, respectively. Increases in phosphate and ammonium nitrogen stability under acidogenic conditions was a consequence of lower pH, a condition synonymous with acidogenic only fermentation. The accumulated volatile fatty acid contributed to higher carbon to nitrogen ratio under acidogenic fermentation. Higher labile carbon to nitrogen ratio can trigger immobilization of ammonium nitrogen in the soil and this presents a case for subsequent experimentation into acidogenic digestate application in soil.

The use of sugar beet pulp stillage for co-digestion with sewage sludge and poultry manure.

The anaerobic mesophilic co-digestion of sugar beet pulp stillage with poultry manure and municipal sewage sludge was investigated in this study. The sugar beet pulp stillage (SBPS) mono-digestion failed owing to an accumulation of volatile fatty acids, leading to a pH value lower than 5.5. A 20% addition of poultry manure to stillage allowed for stable digestion performance despite high volatile fatty acid (total volatile fatty acids) concentrations of 5500-8500 g m-3 with propionic acid being the predominant one and constituting 72%-76% total volatile fatty acids. For this mixture, the maximum methane production of 418 dm3 kgVSfed-1 was achieved when the reactor was operated at a solids retention time of 20 days and an organic loading rate of 4.25 kgVS m-3 d-1. The co-digestion of stillage with 60% municipal sewage sludge gave the average methane yield of around 357 dm3 kgVSfed-1 for all operational conditions applied, however, the methane percentage of biogas (up to 70%) was far greater than the corresponding values obtained for sugar beet pulp stillage-poultry manure co-digestion. Neither ammonia nor volatile fatty acids destabilised the biogas production, and the volatile fatty acid profile showed the dominance of acetic acid (72%-82% total volatile fatty acids) followed by propionic and butyric acids.

Acidogenic properties of carbohydrate-rich wasted potato and microbial community analysis: Effect of pH

Vegetable waste is one of the major organic solid residues available for sustainable biogas production. The aim of this study was to investigate the possibility and optimal controlling strategy for acidogenic fermentation of wasted potato (WP). Three leaching bed reactors (LBRs) were operated at various pH values (6.0, 7.0 and 8.0) with an organic loading rate (OLR) of 6.7g volatile solid/(L·d) and hydraulic retention time of 6d. Butyric acid-type fermentation with butyric acid as predominant volatile fatty acid (VFA) was observed with a concentration and proportion (of total VFAs) of butyric acid, which were 7.8g/L, 49.7 % and 9.6g/L and 52.2 % at pH 6.0 and 7.0, respectively. Conversely, at pH 8.0, mixed acid-type fermentation was observed with acetic and butyric acid as the major VFAs. Control experiment without pH manipulation didn't perform well in VFAs production at first 6 days and then VFAs concentration increased as pH value was adjusted to 8. It was indicated that the inhibition was caused by high undissociated VFAs concentration due to low pH and the VFAs production could be improved through pH control strategy to regulate the undissociated VFAs concentration. According to the bacterial analysis, the microbial community was diverse and Firmicutes were the most important bacteria at different pH conditions. Therefore, the results suggested that a process of pH control might be feasible for stable and efficient acidogenic fermentation.

Nutrient composition and in vitro fermentability of corn grain and stover harvested at different periods in Goesan, a mountainous area.

With South Korea’s limited capability of feed production because of its relatively small cultivable area, the country is pushed to depend on foreign feed imports despite the immensely fluctuating price of corn. Hence, intensive efforts to increase the total cultivable area in Korea like extending of farming to mountainous area is being practiced. Corn was planted in Goesan County, a mountainous area in the country. Grain and stover were harvested separately in three harvest periods: early-harvest (Aug 8), mid-harvest (Aug 18), and late-harvest (Aug 28). The nutrient composition such as dry matter (DM), crude protein (CP), crude fat (EE), organic matter (OM), neutral detergent fiber (NDF), acid detergent fiber (ADF), and non-fibrous carbohydrates (NFC) was determined after harvest. Effective degradability (ED) of the major nutrients (DM, NDF, ADF, and CP) were measured through in vitro fermentation of rumen fluid from Hanwoo (Korean cattle). pH, ammonia-N concentration, volatile fatty acid (VFA) concentration, and gas production were periodically measured at 0, 3, 6, 12, 24, 48, and 72 h. Corn grain showed higher nutrient content and ED than stover. It also had higher gas production but its pH, ammonia-N, and total VFA concentration were lower than corn stover. The best nutrient composition of corn grain was observed in early-harvest (high CP, EE, NDF, OM, NFC, and low ADF). Early-harvest of corn grain also had high effective degradability of dry matter (EDDM), effective degradability of neutral detergent fiber (EDNDF), effective degradability of acid detergent fiber (EDADF), and total VFA concentration. On the other hand, the best nutrient composition of stover was observed in mid-harvest (high DM, CP, NDF, and low ADF). EDDM, EDNDF, and EDADF were pronounced in early-harvest and mid-harvest of stover but the latter showed high total VFA concentration. Hence, early and mid-harvested corn stover and grain in a mountainous area preserved their nutrients, which led to the effective degradation of major nutrients and high VFA production.

Enhancing Anaerobic Digestion of Waste Activated Sludge by Solid–Liquid Separation via Isoelectric Point Pretreatment

Anaerobic bioconversion of waste activated sludge (WAS) into methane is often limited by the slow hydrolysis rate and/or poor methane potential. In this study, a novel pretreatment strategy based on the isoelectric point of sludge particulate is proposed to enhance methane production from WAS. Pretreatment of WAS for 4 h at room temperature substantially changed the physicochemical properties of sludge particulate, resulting in the disintegration of WAS. The experimental results showed that the apparent activation energy of sludge organic solubilization was decreased by 49.5% and the surface site density of sludge particulate was increased by 71.2%, indicating that by this pretreatment WAS solubilization was enhanced and the surface binding sites for enzymes were decreased. In addition, compared to the conventional pretreatment methods, the main metal contents of WAS were decreased by 41.4% after this pretreatment, suggesting the possibility of simultaneously enhancing methane conversion and removing heavy metals from WAS. The biochemical methane potential assays demonstrated that after pretreatment the hydrolysis and acidification of sludge were significantly improved, with the highest volatile fatty acid concentration (3364 ± 28 mg/L) being more than twice that of the untreated samples. Model-based analysis indicated that pretreatment improved methane potential by approximately 19% (from 197.5 ± 8.3 to 242.8 ± 6.2 mL CH4/g volatile solids (VS)), thereby changing methane production kinetics. Further analysis indicated that after pretreatment the methanogenic bacteria growth, rather than the hydrolysis reaction of sludge, became the rate-limiting step in the anaerobic digestion (AD) process. These findings, however, may provide a new direction for enhancing the AD efficiency of WAS.

Optimization of hydraulic retention time and organic loading rate for volatile fatty acid production from low strength wastewater in an anaerobic membrane bioreactor

This study aims to investigate the production of volatile fatty acids (VFAs) from low strength wastewater at various hydraulic retention time (HRT) and organic loading rate (OLR) in a continuous anaerobic membrane bioreactor (AnMBR) using glucose as carbon source. This experiment was performed without any selective inhibition of methanogens and the reactor pH was maintained at 7.0 ± 0.1. 48, 24, 18, 12, 8 and 6 h-HRTs were applied and the highest VFA concentration was recorded at 8 h with an overall VFA yield of 48.20 ± 1.21 mg VFA/100 mg CODfeed. Three different ORLs were applied (350, 550 and 715 mg CODfeed) at the optimum 8 h-HRT. The acetic and propanoic acid concentration maximums were (1.1845 ± 0.0165 and 0.5160 ± 0.0141 mili-mole/l respectively) at 550 mg CODfeed. The isobutyric acid concentration was highest (0.3580 ± 0.0407 mili-mole/l) at 715 mg CODfeed indicating butyric-type fermentation at higher organic loading rate.

Comparative study of polyhydroxyalkanoates production from acidified and anaerobically treated brewery wastewater using enriched mixed microbial culture

The production of polyhydroxyalkanoates (PHA) from wastewaters using microbial mixed cultures (MMC) has been attracting increased interest because of PHA's biodegradability characteristics. Production of PHA by an MMC enriched with PHA-accumulating bacteria was compared using anaerobically treated and acidified brewery wastewaters under various feeding strategies, namely pulse and batch feed addition. To obtain an enriched MMC, a sequencing batch reactor was inoculated with activated sludge fed with acetate and subjected to aerobic dynamic feeding. The enriched MMC was able to accumulate PHA up to 72.6% of cell dry weight (CDW) with pulse addition of acetate controlled by the dissolved oxygen (DO) concentration in the reactor. In a batch accumulation experiment with acetate, the PHA content achieved (28.5% CDW) was less than that of the pulse feeding strategy with the same amount of acetate (~2000 mg C/L). Using anaerobically treated and acidified brewery wastewater fed in pulses, the maximum PHA accumulated by the enriched MMC was similar for both wastewaters (45% CDW), in spite of the higher volatile fatty acid concentration in acidified brewery wastewater. The pulse feed addition controlled by the DO concentration was difficult to implement for wastewater as compared to acetate because the difference in DO concentration between substrate availability and depletion was low. For the batch addition of acidified wastewater, a slightly lower PHA content (39% CDW) was obtained. These results show that both brewery wastewaters can be utilized for PHA production with a similar maximum PHA storage capacity.

Inhibition of volatile fatty acids on methane production kinetics during dry co-digestion of food waste and pig manure

Compared with wet digestion, dry digestion of organic wastes reduces reactor volume and requires less energy for heating, but it is easily inhibited by high volatile fatty acid (VFA) or ammonia concentration. The inhibition on methane production kinetics during dry co-digestion of food waste and pig manure is rarely reported. The aim of this study was to explore the inhibition mechanisms and the microbial interactions in food waste and pig manure dry co-digestion systems at different inoculum rates (25% and 50% based on volatile solids) and food waste/pig manure ratios (0:100, 25:75, 50:50, 75:25 and 100:0 based on volatile solids). The results showed that the preferable operation conditions were obtained at the inoculum rate of 50% and food waste/pig manure ratio of 50:50, with a specific methane yield of 263 mL/g VSadded. High VFA concentration was the main inhibition factor on methane production, and the threshold VFA inhibition concentrations ranged 16.5–18.0 g/L. Syntrophic oxidation with hydrogenotrophic methanogenesis might be the main methane production pathway in dry co-digestion systems due to the dominance of hydrogenotrophic methanogens in the archaeal community. In conclusion, dry co-digestion of food waste and pig manure is feasible for methane production without pH adjustment and can be operated stably by choosing proper operation conditions.