Volatile Fatty Acid Production Research Articles

Simultaneous production of biogas and volatile fatty acids through anaerobic digestion using cereal straw as substrate

Cereal straw is one of the most abundant wastes worldwide, with 30.000 million tons produced per year. Bioconversion of this residual material into carboxylates by anaerobic digestion could potentially replace conventional production based on fossil feedstocks (oil). In this work, fundamental issues of this bioconversion have been explored, including: different kinds of straw (wheat, barley and rye), biomass size reduction, mass balances and modeling of the different steps of the digestion. Under optimum conditions, 44% of the raw material was effectively converted into VFAs (mainly acetate) when barley was used as substrate. Wheat and rye straw presented lower conversion rates due to the higher lignin content compared to barley straw. According to the modeling proposed, methanogenesis and hydrolysis presented very similar reaction rates, which resulted in a simultaneous production of VFAs and biogas. In view of these results, a process integration is proposed where biogas covers the thermal needs of the biotransformation of barley biomass into VFAs.

Effect of physically effective neutral detergent fiber on nutrient intake and digestibility, ruminal and blood parameters, and ingestive behavior of confined beef cattle.

We aimed to evaluate the effect of levels of physically effective neutral detergent fiber from forage (NDFfor) on confined cattle's metabolism and ingestive behavior. Four crossbred steers (514.0 ± 4.54 kg BW) rumen-cannulated were used. The animals were randomly distributed in a 4×4 Latin square design, and the treatments were diets with 9.5%, 5.5%, 2.5%, and 0.0% NDF from whole plant corn silage. The trial was divided into 4 periods of 21 days. The dry matter, organic matter (OM), crude protein, neutral detergent fiber (NDF), physically effective NDF 8mm (peNDF8mm) and NDF1.18mm intakes, and the digestibility of OM and NDF showed a quadratic behavior. The rumen pH values showed a decreasing linear, and the time at pH below 5.8 increased linearly in the diets with lower NDFfor. The production of volatile fatty acids and the proportions of propionate and butyrate showed an increasing quadratic behavior. On the other hand, the proportion of acetate fitted a decreasing quadratic equation. With the lower participation of forage in the diets, the time spent on rumination activity decreased in a quadratic way, and the time spent in idleness increased in a quadratic way. The corn silage can be reduced to 135 g/kg DM in the diet to obtain a minimum of 5.5% of NDF from roughage.

Single-Chamber Electrofermentation of Rumen Fluid Increases Microbial Biomass and Volatile Fatty Acid Production without Major Changes in Diversity

Rumen fermentation (RF) is a complex system of oxidation–reduction reactions governed by the rumen microbiota, and its end-products are the volatile fatty acids (VFAs) which constitute the main energy source for the host animal. We speculated that the process could be manipulated through electrofermentation (EF) by utilizing solid-state electrodes as electron sources. This study aimed to evaluate the effects of single-chamber EF applied (0.4 vs. 0.9 V) for 6, 12, or 24 h to rumen fluid on the resulting microbial biomass, dry matter digestibility (DMD), VFA production, NADH/NAD ratio, and composition of the rumen fluid’s bacterial communities. The application of a 0.9 V electric potential for 24 h produced the most significant changes in RF compared to the control treatment (0V), increasing microbial biomass (12%), DMD (58%), and VFA concentrations (~84%), and reducing NAD/NADH ratio (~50%) without a significant impact on bacterial diversity. These results suggest that the application of a 0.9 V electric potential allows the microbiota to better hydrolyze and digest the feed’s components and could offer an electron sink for the production of VFAs. Hence, EF can provide innovative solutions to a range of challenges that limit the RF process. Nonetheless, more studies are needed to understand how the solid electrodes and external electric energy function.

Anaerobic fermentation of aerobic granular sludge: Insight into the effect of granule size and sludge structure on hydrolysis and acidification

Aerobic granular sludge (AGS) has different physicochemical properties and microbial communities compared to conventional activated sludge (CAS), which may result in different behaviors during anaerobic fermentation and require further investigation. This study investigated the effect of granule size and sludge structure on the hydrolysis and acidification of AGS. Experimental results show that AGS exhibited significantly higher soluble chemical oxygen demand (SCOD) dissolution and total volatile fatty acids (TVFA) production (330.6–430.3 mg/gVSS and 231.0–312.5 mgCOD/gVSS) compared to conventional activated sludge (CAS) (167.0 mg/gVSS and 133.3 mgCOD/gVSS). This is because AGS (90.6–96.9 mg/gVSS) had higher extracellular polymeric substances (EPS) content than CAS (81.2 mg/gVSS). EPS can not only serve as substrates but also release the trapped hydrolases. Moreover, the relative abundances of hydrolytic/acidogenic bacteria and genes were higher in AGS (0.46%–3.60% and 3.01 × 10−3%-4.04 × 10−3%) than in CAS (0.30% and 1.23 × 10−3%). The optimal granule size for AGS fermentation was found to be 500–1600 μm. The crushing of granule structure promoted the dissolution of small amounts of EPS and the release of some trapped hydrolases, thereby potentially enhancing the enzyme-substrate contacts and bacteria-substrate interactions. Therefore, the highest SCOD dissolution (510.6 mg/gVSS) and TVFA production (352.1 mgCOD/gVSS) from crushed 500–1600 μm AGS were observed. Overall, the findings of this study provide valuable insights into the recovery of organic carbon from AGS via anaerobic fermentation.

Nitrate reduction pathways and microbial community to different COD/NO3−-N ratios in mesophilic and thermophilic denitrification systems

Hydrolytic acidification integrated with denitrification (DEN) presents a promising treatment strategy for high-temperature industrial wastewater, such as oil, leather and ethanol wastewater. This study aimed to investigate the synergistic influence of temperature and the COD/NO3−-N ratio on the nitrogen reduction pathway using a series of semi-continuous flow reactors. The results revealed that the optimal total nitrogen (TN) removal performance was achieved under thermophilic (T = 60 °C) and COD/NO3−-N ratio of 37, with the highest TN reduction amount of 594.3 ± 41.8 mg/L. However, under other conditions, the TN removal efficiency reduced due to NH4+-N accumulation. Higher temperature facilitated the nitrogen reduction rate and butyrate yield rate, while inhibiting the dissimilatory reduction to ammonium (DNRA) process to 20.7 %. Furthermore, the higher temperature increased the bacterial diversity and the relative abundances of Clostridium, Acidaminococcus and Ruminococcus, thus, enhancing organic matter hydrolysis and nitrogen removal efficiency. In contrast, Carnobacterium, with percentage account of 34.4 %, was only detected under thermophilic conditions with a low COD/NO3−-N ratio. The COD/NO3−-N ratio only generated a slight effect on the production of volatile fatty acids (VFAs) and nitrogen reduction pathways, but had significant influence on the microbial community. These findings provide novel insight into the implementation of hydrolysis acidification coupled with anaerobic denitrification process in thermophilic wastewater treatment.

Kinetic study on the effects of elevated temperature and micro aeration in volatile fatty acids production by anaerobic fermentation of alkaline-pretreated oil palm empty fruit bunch

This research studied the conversion of alkaline-pretreated oil palm empty fruit bunch (OPEFB) into volatile fatty acids (VFA) through anaerobic fermentation (AF). In AF, the methanogens that consume VFAs must be suppressed to increase the accumulated VFA as an intermediate product of AF. In-depth research has not been conducted on the effects of temperature and micro aeration to maximize the VFA accumulation. To investigate the temperature effect, the experiment was run at mesophilic (RM) and thermophilic conditions (RT). The impact of the micro aeration dose was studied in the thermophilic reactor set to the ORP −50 mV (RTM −50) and ORP −150 mV (RTM −150). The experimental data were fitted to the Anaerobic Digestion Model 1 (ADM 1) using AQUASIM®. The khyd.ch value of the RT reactor is higher than that of the RM, suggesting that high temperatures encourage hydrolysis and enhance hydrolase activity. Based on the simulation results, RT reactors without micro-aeration had a substantially higher specific growth rate of methanogens compared to RM. Therefore, micro aeration should be applied in RT to suppress the potentially faster growth of methanogen bacteria at elevated temperature. The result of this study indicated that both temperature and micro-aeration were important process variable to be further optimized to make VFAs production from OPEFB attractive.

Choline chloride pretreatment on volatile fatty acids promotion from sludge anaerobic fermentation: In-situ deep eutectic solvents-like formation for EPS disintegration and associated microbial functional profiles upregulation

Slow solubilization/hydrolysis efficiency has been widely recognized as a limiting factor for volatile fatty acids (VFAs) production from waste activated sludge (WAS) via anaerobic fermentation. This study developed an innovative choline chloride (ChCl)-based approach for WAS treatment. Accordingly, the VFAs yield was increased by 2.5–623.3%, which was attributed to the concurrent acceleration of WAS solubilization, hydrolysis, and acidification. Fourier transform infrared spectrometer (FTIR) and molecular docking analysis showed that ChCl can attack and disrupt extracellular polymeric substances (EPS) by forming hydrogen bonds with organics occurred in WAS (i.e. proteins). More importantly, the generated VFAs in turn interacted with ChCl for in-situ deep eutectic solvents (DES)-like formation to significantly improve the organics dissolution of WAS for more bioavailable substrates associated with VFAs biosynthesis, and such effects were intensified with the VFAs level. Besides, ChCl exhibited “screening-effects” to enrich the hydrolytic and acidogenic anaerobes in WAS fermentation systems, while reduced VFAs-consumers. Meanwhile, the microbial metabolic profiles shift to favor the protein metabolism, and the genetic traits associated with extracellular and intracellular substrates metabolism, membrane transport, and fatty acid biosynthesis were all upregulated. Noteworthily, the functional hydrolytic and acidogenic species maintained their microbial activity for efficient VFAs production via quorum sensing (QS) and two-component systems (TCS) to counteract ChCl stress. The ranking efficiency product (REP) indices revealed that ChCl pretreatment showed a higher sustainable footprint (84.0%) over other traditional pretreatment approaches for WAS fermentation in view of both economic and environmental benefits. This work provides an innovative niche for efficient VFAs production from WAS with the sustainable application.

Evaluation of Rumen Fermentation and Microbial Adaptation to Three Red Seaweeds Using the Rumen Simulation Technique.

Several red seaweeds have been shown to inhibit enteric CH4 production; however, the adaptation of fermentation parameters to their presence is not well understood. The objective of this study was to examine the effect of three red seaweeds (Asparargopsis taxiformis, Mazzaella japonica, and Palmaria mollis) on in vitro fermentation, CH4 production, and adaptation using the rumen simulation technique (RUSITEC). The experiment was conducted as a completely randomized design with four treatments, duplicated in two identical RUSITEC apparatus equipped with eight fermenter vessels each. The four treatments included the control and the three red seaweeds added to the control diet at 2% diet DM. The experimental period was divided into four phases including a baseline phase (d 0-7; no seaweed included), an adaptation phase (d 8-11; seaweed included in treatment vessels), an intermediate phase (d 12-16), and a stable phase (d 17-21). The degradability of organic matter (p = 0.04) and neutral detergent fibre (p = 0.05) was decreased by A. taxiformis during the adaptation phase, but returned to control levels in the stable phase. A. taxiformis supplementation resulted in a decrease (p < 0.001) in the molar proportions of acetate, propionate, and total volatile fatty acid (VFA) production, with an increase in the molar proportions of butyrate, caproate, and valerate; the other seaweeds had no effect (p > 0.05) on the molar proportions or production of individual VFA. A. taxiformis was the only seaweed to suppress CH4 production (p < 0.001), with the suppressive effect increasing (p < 0.001) across phases. Similarly, A. taxiformis increased (p < 0.001) the production of hydrogen (H2, %, mL/d) across the adaptation, intermediate, and stable phases, with the intermediate and stable phases having greater H2 production than the adaptation phase. In conclusion, M. japonica and P. mollis did not impact rumen fermentation or inhibit CH4 production within the RUSITEC. In contrast, we conclude that A. taxiformis is an effective CH4 inhibitor and its introduction to the ruminal environment requires a period of adaptation; however, the large magnitude of CH4 suppression by A. taxiformis inhibits VFA synthesis, which may restrict the production performance in vivo.

Effects of seasonal and interspecies differences in macroalgae procured from temperate seas on the Northern hemisphere on in vitro methane mitigating properties and rumen degradability

Enteric methane (CH4) from cattle constitutes a large proportion of the emission of anthropogenic greenhouse gasses. The objectives of this study were to investigate interspecies and seasonal variations in macroalgae, procured from the Northern Hemisphere, on CH4 production and rumen feed degradability in vitro. Corn silage or grass/clover silage (0.5 g), were incubated separately in buffered rumen fluid with addition of one of 22 different macroalgae (0.1 g), including both red, green, and brown species, hereof four brown species harvested at different seasons, resulting in an inclusion rate of 17 %. Rumen degradability of the pure macroalgae was determined by incubating macroalgae (0.5 g) without any basal feed. Accumulated gas production during 48 h of incubation was determined using the AnkomRF system equipped with airtight gasbags. Basal feeds without macroalgae addition served as controls, while the red macroalgae Asparagopsis taxiformis was included as a methane-inhibiting control. Each sample type was tested in triplicate in two separate runs. Amount of undegraded dry matter (DM) and organic matter (OM) after incubation was determined by filtration. Gas composition and concentration of volatile fatty acids (VFA) were determined by gas chromatography. Both A. taxiformis and Fucus serratus significantly reduced CH4 production, expressed per g DM, OM, degraded DM, and OM, when added to corn silage. Similar CH4 mitigating effect was observed when A. taxiformis was added to grass/clover silage, while F. serratus only significantly reduced the CH4 production expressed per g DM. None of the species included in the investigation of seasonal variations decreased CH4 production compared to the basal feeds. Palmaria palmata had the highest rumen degradability and associated VFA production, while F. vesiculosus and F. serratus had the numerically lowest rumen degradability and VFA production, respectively. In conclusion, F. serratus was the only Northern procurable macroalga showing CH4 mitigating potential, which depended on the nature of the basal feed.

Effect and mechanism analysis of dual enzyme pretreatment on enhancement of volatile fatty acids production in kitchen waste anaerobic acidification

The high content of cellulose and hemicellulose in kitchen waste (KW) results in a slow hydrolysis rate and subsequently hinders the yields of volatile fatty acids (VFAs) in anaerobic acidification. In this study, cellulase and hemicellulase were used for the pretreatments of KW to tackle the problem of difficult hydrolysis in anaerobic acidification. The results indicated that the joint use of double enzymes significantly improved the hydrolysis of cellulose and hemicellulose during pretreatment, thus enhancing the VFAs production in anaerobic acidification. The highest production of TVFAs was 50.73 ± 2.10 g COD/L and it was improved by 62.77% compared with the unpretreated group. In addition, the 16S rRNA amplicon sequencing analysis showed that the relative abundance of Firmicutes related with the VFAs production increased from 17.77% to 50.55%. The potential metabolism function analysis (PICRUSt2) indicated that the enrichment of glyceraldehyde-3-phosphate dehydrogenase (EC:1.2.1.9) and acetyl-CoA C-acetyltransferase (EC:2.3.1.9) contributed to the production of VFAs in AD. The results suggested that collaborative enzyme pretreatment could be one of the effective methods for the hydrolysis of cellulose and hemicellulose in KW and provided constructive mechanistic insights into recovering valuable products from KW.

Metabolic influence of core ciliates within the rumen microbiome

Protozoa comprise a major fraction of the microbial biomass in the rumen microbiome, of which the entodiniomorphs (order: Entodiniomorphida) and holotrichs (order: Vestibuliferida) are consistently observed to be dominant across a diverse genetic and geographical range of ruminant hosts. Despite the apparent core role that protozoal species exert, their major biological and metabolic contributions to rumen function remain largely undescribed in vivo. Here, we have leveraged (meta)genome-centric metaproteomes from rumen fluid samples originating from both cattle and goats fed diets with varying inclusion levels of lipids and starch, to detail the specific metabolic niches that protozoa occupy in the context of their microbial co-habitants. Initial proteome estimations via total protein counts and label-free quantification highlight that entodiniomorph species Entodinium and Epidinium as well as the holotrichs Dasytricha and Isotricha comprise an extensive fraction of the total rumen metaproteome. Proteomic detection of protozoal metabolism such as hydrogenases (Dasytricha, Isotricha, Epidinium, Enoploplastron), carbohydrate-active enzymes (Epidinium, Diplodinium, Enoploplastron, Polyplastron), microbial predation (Entodinium) and volatile fatty acid production (Entodinium and Epidinium) was observed at increased levels in high methane-emitting animals. Despite certain protozoal species having well-established reputations for digesting starch, they were unexpectedly less detectable in low methane emitting-animals fed high starch diets, which were instead dominated by propionate/succinate-producing bacterial populations suspected of being resistant to predation irrespective of host. Finally, we reaffirmed our abovementioned observations in geographically independent datasets, thus illuminating the substantial metabolic influence that under-explored eukaryotic populations have in the rumen, with greater implications for both digestion and methane metabolism.

Effects of dietary N-carbamylglutamate on rumen fermentation parameters, and bacterial community diversity of Holstein dairy cows in Tibet.

The Tibetan Plateau is characterized by low temperature and hypoxia. N-carbamylglutamic acid (NCG) can increase blood oxygen saturation, and have the potential to be used to prevent the high-altitude hypoxia stress state of cows. However, its beneficial effect on the rumen microbiota of Holstein dairy cows remains unclear. Hence, the experiments 12 multiparous (parity ranged from 2 to 7) Holstein dairy cows (413.0 ± 42 kg) were randomly assigned to 2 treatments with 6 replicates in each treatment: basal diet (CON, control group) and basal diet plus 20 g/d/cow of NCG (NCG, experiment group), respectively. To study the effects of dietary NCG supplementation on rumen microbiota of Holstein dairy cows in Tibet. The experiment lasted for 45 days, with 15 days of pre-feeding and 30 days of formal trail period. The results showed that ruminal NH3-N concentration in NCG group was lower (p < 0.05) than that in the CON group, while molar proportion of acetic acid and total volatile fatty acid (VFA) concentration were increased (p < 0.05) with the addition of NCG. Microbial diversity increased (p < 0.05) in NCG group, with Bacteroidetes, Firmicutes, and Patescibacteria as the most abundant phyla. The KEGG pathway analysis showed that the potential function of ruminal bacteria was mainly enriched in metabolism (carbohydrates, amino acids, lipids, energy, and nucleotides) and genetic information processing (replication, repair, and translation). In conclusion, NCG can improve rumen nitrogen utilization, total VFA and acetic acid production, and increase rumen microbial diversity, all of which could make the introduced Holstein dairy cows to better adapt to the harsh environment in Tibet and improve their production performance.

Fe-loaded alginate hydrogel beads activating peroxymonosulfate for enhancing anaerobic fermentation of waste activated sludge: Performance and potential mechanism

The recovery of volatile fatty acids (VFAs) through anaerobic fermentation (AF) is usually restricted by the poor biodegradability of waste activated sludge (WAS). This study proposed a novel strategy, i.e. peroxymonosulfate (PMS) activated by Fe-loaded sodium alginate hydrogel beads (Fe-SA), to enhance AF performance. Experimental results demonstrated that the as-synthesized Fe-SA and PMS co-pretreatment synergistically enhanced WAS solubilization and VFAs production. The maximal VFAs yield of 2013 mg COD/L was achieved at the Fe-SA dosage of 4.0 mM/g TSS, which was 93.7% higher than that with sole PMS addition and 8.82 times higher than that of the control. Mechanistic studies elucidated that the generation of reactive radicals such as SO4•− and •OH from PMS was greatly induced by Fe-SA, which contributed to WAS disintegration and degradation of refractory compounds. Additionally, analysis of the key enzyme activities indicated that the Fe-SA could strengthen biological hydrolysis and acidogenesis of sludge during AF. Microbial analysis illustrated that Fe-SA evidently improved the abundances of fermentative microorganisms as well as functional gene expression via creating a favorable environment for microbial growth. This study demonstrated the applicable potential of Fe-SA hydrogel beads activating PMS for VFAs production and provides an important reference for developing advanced oxidation processes-based application in AF.

191 Effect of Inclusion of Hempseed Meal on Rumen Papillae Morphology And Rumen Fermentation of Boer X Spanish Intact Male Goats

Abstract The objective of this study was to evaluate the effect of inclusion of increasing levels of hempseed meal (HSM) on the morphology of the rumen papillae and volatile fatty acids production in the rumen of intact male goats. Boer x Spanish intact male goats (n = 36), 0 to1 months of age and bodyweight of 44.1 ± 3.8 kg, were randomly assigned to one of the four experimental diets (n = 9 goats/diet): 0% (control), 0%, 20%, and 30% HSM included on an as-fed basis and fed ad-libitum for 60 days. Experimental diets were formulated as total mixed ration (TMR), and the nutrient content of each diet was formulated to be iso-nitrogenous (18% crude protein) and to meet or exceed the nutrient requirement of breeding male goats. At the end of the trial, experimental goats were humanely processed as per USDA standards. Rumen fluid and necropsy samples of rumen tissue from the ventral sac of the rumen were collected, and rumen tissue was processed for histological examination. Morphometric variables of rumen papillae; height and width of rumen papillae, and density (number of papillae/cm2) were recorded, and total absorptive surface area was calculated. The thickness of the stratum corneum (SC) and the thickness of stratum granulosum (SG) was measured from the histological slides of rumen tissue. The rumen fluid was analyzed for the volatile fatty acids (acetate, propionate, and butyrate) concentration. Data were analyzed using one-way ANOVA and orthogonal contrast test for equally spaced treatments using R version 4.2.1. There was no significant difference (P &amp;gt; 0.05) in height of papillae, the width of papillae, papillae density, total absorptive surface area, SC thickness, and SG thickness among the goats feeding different experimental diets. The concentration of propionic acid decreased linearly (P &amp;gt; 0.01) with increasing inclusion of HSM (12.90, 9.51, 8.12 and 7.34 mmol/L for 0 %,0 %, 20 % and 30 % HSM, respectively), whereas the concentration of acetic acid and butyric acid were similar among the experimental groups (P &amp;gt; 0.05). These observed results indicate that the inclusion of HSM at least up to 30 % in the diet does not affect the rumen papillae morphology, and acetate and butyrate concentration in the rumen in intact male goats.

Role of pretreatment type and microbial mechanisms on enhancing volatile fatty acids production during anaerobic fermentation of refinery waste activated sludge

This study compared the effects of alkaline, thermal, thermal-peroxymonosulfate (PMS), and alkyl polyglucose (APG) pretreatments on volatile fatty acids (VFAs) production from refinery waste activated sludge (RWAS), including VFAs yield, composition, organics components, microbial communities, and the potential improvement of mechanisms. All pretreatments effectively enhanced the bioconversion of RWAS and consequently promoted the hydrolysis process, which inhibited the methanogenesis process. However, the release of lignin/carboxyl-rich alicyclic molecules (CRAM)-like compounds and tannin substances in Thermal-PMS and APG groups significantly influenced the acidogenesis and acetogenesis processes. Among all pretreatments, alkaline pretreatment showed the highest VFAs yield of 95.06 mg/g volatile solids (VS) and VS removal of 17%. This result could be associated with the enrichment of functional hydrolytic-acidification bacteria, such as Planococcus and Soehngenia, and increased metabolism of amino acids, carbohydrates, and nucleotides. By considering an economical and efficient perspective, this study recommended the alkaline pretreatment for the anaerobic fermentation of RWAS.

Application of nanoparticles to increase biological hydrogen production: the difference in metabolic pathways in batch and continuous reactors

ABSTRACT An alternative to improve the production of biorefinery products, such as biohydrogen (H2) and volatile fatty acids (VFA), is the combination of nanotechnology and biological processes. In order to compare the use of both processes in two different reactor configurations, batch reactors and continuous anaerobic fluidized bed reactors (AFBR) were studied under the same conditions (37°C, pH 6.8, Clostridium butyricum as an inoculum and glucose as a substrate) to evaluate the influence of zero valence iron and nickel nanoparticles (NPs) on H2 and VFA production. There was a shift in the production of acetic and butyric acids to produce mainly valeric acid when NPs were added in batch reactors. Meanwhile, in AFBR the change was from lactic acid to butyric and acetic acids with the addition of NPs. It showed that the effect of NPs on the fermentation process was different when the configuration of batch and continuous reactors was compared. The H2 yield in both reactor configurations increased with the addition of NPs. In batch reactors from 6.6 to 8.0 mmol H2 g−1 of COD and in AFBR from 4.9 to 6.2 mmol of H2 g−1 of COD. Therefore, given the simplicity and low cost of the synthesis of metallic NPs, it is a promising additive to optimize the fermentation process in different reactor configurations.

Conceptual system for sustainable and next-generation wastewater resource recovery facilities

Shifting the concept of municipal wastewater treatment to recover resources is one of the key factors contributing to a sustainable society. A novel concept based on research is proposed to recover four main bio-based products from municipal wastewater while reaching the necessary regulatory standards. The main resource recovery units of the proposed system include upflow anaerobic sludge blanket reactor for the recovery of biogas (as product 1) from mainstream municipal wastewater after primary sedimentation. Sewage sludge is co-fermented with external organic waste such as food waste for volatile fatty acids (VFAs) production as precursors for other bio-based production. A portion of the VFA mixture (product 2) is used as carbon sources in the denitrification step of the nitrification/denitrification process as an alternative for nitrogen removal. The other alternative for nitrogen removal is the partial nitrification/anammx process. The VFA mixture is separated with nanofiltration/reverse osmosis membrane technology into low-carbon VFAs and high-carbon VFAs. Polyhydroxyalkanoate (as product 3) is produced from the low-carbon VFAs. Using membrane contactor-based processes and ion-exchange techniques, high-carbon VFAs are recovered as one-type VFA (pure VFA) and in ester forms (product 4). The nutrient-rich fermented and dewatered biosolid is applied as a fertilizer. The proposed units are seen as individual resource recovery systems as well as a concept of an integrated system. A qualitative environmental assessment of the proposed resource recovery units confirms the positive environmental impacts of the proposed system.

Steel slag assists potassium ferrate to improve SCFAs production from anaerobic sludge fermentation

Potassium ferrate (PF) pretreatment in anaerobic sludge and its potential influence mechanisms have received widely attention. This study investigated the coupling effect of PF loading on steel slag (SS) on excess sludge anaerobic fermentation. Results showed that SS loading increase the treatment performance of PF on short chain volatile fatty acids (SCFAs) production from anaerobic fermented sludge. It was showed that the modified PF loaded SS (MPF-SS) promoted the dissolution and release of organic substrates from intracellular to extracellular. Further exploration showed the promotion of PF and MPF-SS exposure to acid production microorganisms was much more than that to acid consumption microorganisms. MPF-SS addition can also effectively reinforce the carbohydrate transport, amino acid metabolism and the key enhanced genes associated with fatty acid biosynthesis pathways. This study fills the knowledge gap about modified PF on sludge treatment and also expands a new perspective for its application for sludge resource recovery.

The Fibre Requirements of Horses and the Consequences and Causes of Failure to Meet Them.

Failure to meet the minimum forage requirement of 1.5% of the horse's bodyweight and the opportunity for foraging for a minimum of 8 h a day (not going without this opportunity longer than four to five consecutive hours) can have both physiological and behavioural consequences. To provide an energy source for horses, rations often include starch rather than fibre. This can result in health issues related to the gastrointestinal tract (GIT) in the horse. In the stomach, the main concern is equine gastric ulcer syndrome (EGUS) and, more specifically, equine squamous gastric disease (ESGD). Ulcerations are caused either by increasing acidity in the stomach (from starch ingestion and reduced saliva production) or splashing of acidic juices caused by a lack of a forage barrier prior to exercise or prolonged periods without fibrous feed intake, which allows the stomach to collapse and spread acidic gastric fluids into the upper squamous regions of the stomach. In the hindgut, starch that has escaped digestion in the small intestine causes microbial instability and increased production of volatile fatty acids (VFA) and lactic acid. This puts horses at great risk for acidosis and subsequent laminitis. Shifts in the hindgut microbiota will also affect a horse's behaviour via the gut-brain axis, as well as potentially compromise immune function. Reduced fluid intake caused by reduced saliva production can result in colic. Choosing a fibrous alternative for starch in a high-energy diet greatly reduces the risk of EGUS and acidosis and improves digestion, GIT pH, body condition, behaviour, immune functions, and performance. Providing hay can reduce crib-biting, wood-chewing, coprophagia, the consumption of bedding, aggression, and stress, and subsequently increase social bonding and affiliation with conspecifics. Adequate fibre intake is related to reduced clinical signs of EGUS, reduced reactivity, and better adaptation to weaning. Lignophagia (wood chewing) has also been observed in horses that are foraging, and this is thought to reflect low fibre content in the available forage (for example, early vegetative, lush pasture).

Assessment of two-stage anaerobic digestion of blackwater and kitchen waste for reducing environmental impact of residential buildings

In recent years, much attention has been directed towards municipal waste management since these residues has become a global challenge with increasing public health, environmental, social, and economic costs. Therefore, there is an urgent need to adopt widely accepted sustainable alternatives and circular economy approaches. In that sense, the decentralized waste management approach has become a feasible and sustainable strategy to valorise and minimize wastes at source. Among the available technologies, anaerobic digestion is widely used as it allows to recover energy in form of biogas from organic waste. This study proposes a decentralized system based on a two-stage anaerobic digestion for the joint valorisation of organic wastes -blackwater and kitchen wastes-in residential buildings. In the first stage (dark fermentation), different ratios of blackwater:kitchen waste were assessed and a maximum volatile fatty acids production of 5000–7000 mg L−1 was reached when 5 kg of black water and 0.30 kg of kitchen waste were added to the system. Then, during second stage, the volatile fatty acids rich stream was valorised in an upflow anaerobic sludge blanket reactor resulting in a biogas production of 5.45 ± 1.34 L d−1, containing 75.6 ± 7.3% of methane and 22.8 ± 5.7% of carbon dioxide while reporting a low content of impurities - 0.02% of hydrogen sulphide and 0.002% of hydrogen -.