Anaerobic Fermentation Process Research Articles

Effect of exogenous CaO addition on H2S production from waste activated sludge and its influence mechanism.

Hydrogen sulfide (H2S) production from waste activated sludge (WAS) is the main reason for odor emission during anaerobic fermentation system. CaO has been reported to effectively improve the resources recovery of WAS, but its potential effect on H2S production in anaerobic fermentation process remains unrecognized. In present study, it was found that the addition of 60mg/g VSS CaO greatly inhibited H2S production and the maximum yield of H2S was 60.1±1.8% lower than the control. Mechanism investigation demonstrated that CaO destroyed sludge structure and increased the release of intracellular organic matter with hydrogen bonding networks destroying, but had a mild effect on the transformation of sulfur containing organic matters and inorganic sulfate reduction. Additionally, the enhancement in H+ and S2- consumption by alkaline condition and metal ions release was another reason for the inhibition of H2S production in CaO addition reactors. Furthermore, microbial analysis showed that CaO addition importantly reduced the hydrolysis microorganism, particularly denitrification hydrolytic bacterias (e.g.,unclassified_f_Chitinophagaceaeand Dechloromonas), sulfate reducing bacterias (SRBs) (e.g., unclassified_c_Deltaproteobacteria and Desulfosarcina) and genes (e.g.,PepD, cysN/D, CysH/C and Sir) involved in organic sulfur hydrolysis and sulfate reduction. Results from this study provides theoretical insights into the practical applications of CaO.

Characteristics of photothermal transfer and biochemical reaction in up-flow direct absorption hydrogen reactor with embedded ribs

The anaerobic fermentation process of microbial community is a promising method to treat wastewater with high ammonia nitrogen, but it needs to provide suitable temperature. An innovative direct absorption anaerobic reactor was established to reduce the temperature fluctuation of biogas slurry by adding ribs to ensure the high efficiency and stability of anaerobic fermentation process. The effects of flow rate and number of ribs on gas production in the process of photothermal conversion and anaerobic fermentation were analyzed by numerical simulation. The results show that the addition of ribs can effectively reduce temperature fluctuation and increase gas production. Compared with 2269.7 mL/L gas production and temperature fluctuation of up to 8 K without ribs, the gas production increased by 863.1 mL/L and decreased to 0.1624 K when the number of ribs was 9, respectively. Simultaneously, a curve was fitted according to gas production to predict the best working conditions.

Analysis of biogas production and prospects for the development of biogas technologies in Ukraine

The relevance of this study is determined by the fact that over the years the trend of finding new types of raw materials and technologies for their processing into biogas is growing rapidly. Not only people in European countries but all over the world tend towards the advantages of its production. For Ukraine, the development of infrastructure and a detailed study of this industry will later become a necessary stimulus for the reconstruction of the economy in the post-war period. The aim of the work is to analyze the biomass potential of fallen leaves for biogas production, taking into account the possibilities of technological development of this field in Ukraine. Several methods and approaches were used to achieve the goal. In particular, the physicochemical basis of the process of anaerobic fermentation of organic matter to obtain biogas was studied. A mathematical model of the process of obtaining biogas in a reactor from fallen leaves was also developed. And at the very end, the calculation of the economic efficiency of using a biogas plant for utilization of fallen leaves in a bioreactor was carried out. Summarizing the main results, it is possible to highlight the development of the patent-protected design of the bioreactor, the engineering methodology and the mathematical model for calculating the methane tank for the production of biogas from fallen leaves. First of all, the potential of biomass of plant origin for biogas production was analyzed and this led to the conclusion that the use of fallen leaves is a promising direction, but the significant advantages of using the raw material base are ignored. One of the main environmental problems of Ukraine remains the utilization of fallen leaves and other organic matter of plant origin. At the same time, the conducted research produces not only a number of solutions to this issue, but also turns the problem into an economically profitable solution and eliminates all ecologically unjustified processing methods

Co-production of biohydrogen and biomethane utilizing halophytic biomass Atriplexcrassifolia by two-stage anaerobic fermentation process.

The excessive use of fossil has resulted in the drastic exhaustion of natural energy sources, leading to environmental challenges and energy crises. Owing to rising energy demand there is a dire need to shift towards renewable energies from lignocellulosic biomass. The present study assessed the co-production of biohydrogen (H2) and biomethane (CH4) by utilizing a less explored halophyte Atriplexcrassifolia. Various reaction parameters were evaluated for their effect on biohydrogen and biomethane production in batch experiments. One parameter at a time experimental strategy was chosen for production optimization. Hydrogen and methane yields along with their production rates were assessed at different incubation times, temperatures, pH, substrate concentrations, and inoculum sizes in acidogenesis and methanogenesis stages, respectively. In the first stage, maximum cumulative hydrogen production of 66 ± 0.02mL, with hydrogen yield of 13.2 ± 0.03mL/g, and hydrogen production rate (HPR) of 1.37 ± 0.05mL/h was attained when the reaction mixture (5g Atriplexcrassifolia and 10mL pretreated sewage sludge) was processed at 37°C and pH 5.5 after 48h of incubation. While in the second stage, maximum cumulative methane production, i.e., 343 ± 0.12mL, methane yield (MY) of 8.5 ± 0.07mL/mL, and methane production rate (MPR) of 0.8 ± 0.05mL/h was achieved after 18days of incubation of reaction mixture (40mL of hydrogenic slurry with 80mL inoculum) at 45°C and pH 8. Furthermore, a 51% and 24% rise in biohydrogen and biomethane production respectively were recorded when the gases were produced at these optimized reaction conditions. The results ensure halophyte Atriplexcrassifolia as an imperative renewable energy resource and proposed that effective optimization of the process further increased the coproduction of biohydrogen and biomethane.

Enhancement of waste activated sludge hydrolysis and decomposition by combined free nitrous acid and sodium citrate pretreatment

Hydrolysis of waste activated sludge (WAS) is the limiting step in the anaerobic fermentation process. In view of this, this study evaluated the feasibility of a combination of free nitrous acid (FNA) and sodium citrate (SC) pretreatment to promote WAS hydrolysis and anaerobic fermentation. The results showed that the combined treatment of FNA and SC could promote the decomposition of WAS. Under the conditions of 2.504 mg/L FNA and 0.25 g/g total suspended solids of SC pretreatment for 5 h, the soluble chemical oxygen demand release rate (DDSCOD) was 1.86 and 1.42 times that of FNA and SC pretreatment alone. Meanwhile, the contribution rate of intracellular organic compounds reached 84.18 %. The maximum short-chain fatty acids yield was obtained at the 8th day of fermentation, which was 580.34 mg COD/g volatile suspended solids. The protein utilization rate of combined pretreatment was increased to 74.10 %, which was much higher than that of single treatment. Moreover, FNA-SC also changed the activities of key enzymes, increasing the activities of protease and α-glucosidase but inhibiting the activities of coenzyme F420. Microbial analysis showed that the combined pretreatment significantly changed the composition of microbial community and effectively enriched acid-producing bacteria (such as Petrimonas and Macellibacteroides).

Bacterial antioxidant mechanism in calcium peroxide aided sludge anaerobic fermentation

Although calcium peroxide (CaO2) can enhance the short-chain fatty acids (SCFAs) production in sludge anaerobic fermentation, the microbiological mechanisms underlying this process remain unclear. In this study, it is aimed to elucidate the bacterial protective mechanisms in response to the oxidative stress induced by CaO2. Results show that extracellular polymeric substance (EPS) and anti-oxidant enzymes play vital roles in protecting bacterial cells from CaO2. The addition of CaO2 resulted in increased relative abundances of genes exoP and SRP54, which are associated with EPS secretion and transportation. Superoxide dismutase (SOD) played a crucial in alleviating oxidative stress. The dosage of CaO2 significantly influences the succession of the bacterial community in the anaerobic fermentation system. With 0.3 g CaO2/g VSS, the net income was approximately 4 USD/ton of sludge treated. The CaO2-assisted anaerobic fermentation process has the potential to recover more resources from sludge and thus, benefit the environment.

A comparative study of Cu and Zn passivation by humic acid, fly ash, biochar, and zeolite during pig manure anaerobic fermentation process

A comparative study of Cu and Zn passivation by humic acid, fly ash, biochar, and zeolite during pig manure anaerobic fermentation process

Magnetite enhancing sludge anaerobic fermentation to improve wastewater biological nitrogen removal: Pilot-scale verification

Alkaline anaerobic fermentation for acids production has been considered as an effective method to recover resources from waste activated sludge, and magnetite could improve the quality of fermentation liquid. Here, we have constructed a pilot-scale sludge alkaline anaerobic fermentation process enhanced by magnetite to produce short chain fatty acids (SCFAs), and used them as external carbon sources to improve the biological nitrogen removal of municipal sewage. Results showed that the addition of magnetite could significantly increase the production of SCFAs. The average concentration of SCFAs in fermentation liquid reached 3718.6 ± 101.5 mg COD/L, and the average concentration of acetic acid reached 2368.8 ± 132.1 mg COD/L. The fermentation liquid was used in the mainstream A2O process, and its TN removal efficiency increased from 48.0% ± 5.4% to 62.2% ± 6.6%. The main reason was that the fermentation liquid is conducive to the succession of sludge microbial community the denitrification process, increasing the abundance of denitrification functional bacteria and realizing the enhancement of denitrification process. Besides, magnetite can promote the activity of related enzymes to enhance the biological nitrogen removal. Finally, the economic analysis showed that magnetite-enhanced sludge anaerobic fermentation was economically and technically feasible to promote the biological nitrogen removal of municipal sewage.

Extraction of Carboxylic Acids from Anaerobic Fermentation Processes by the Anion Exchange Resin Amberlite IRA-400(Cl)

This work describes a methodology for the valorization of non-food biomass for the production of biosourced molecules via the production of biohydrogen and metabolites of fermentations such as volatile fatty acids. The commercial anion exchange resin Amberlite IRA-400(Cl) was chosen for the extraction of carboxylic acids. Different operating conditions were set up namely the amount of resin to be used, activation methods, pH and their effects on the extraction capacity of the solvent.

Synergistic Ball Milling–Enzymatic Pretreatment of Brewer’s Spent Grains to Improve Volatile Fatty Acid Production through Thermophilic Anaerobic Fermentation

Brewer’s spent grain (BSG) as the major byproduct in the brewing industry is a promising feedstock to produce value-added products such as volatile fatty acids (VFAs). Synergistic ball mill–enzymatic hydrolysis (BM-EH) process is an environmentally friendly pretreatment method for lignocellulosic materials before bioprocessing. This study investigated the potential of raw and BM-EH pretreated BSG feedstocks to produce VFAs through a direct thermophilic anaerobic fermentation process without introducing a methanogen inhibitor. The highest VFA concentration of over 30 g/L was achieved under the high-solid loading fermentation (HS) of raw BSG. The synergistic BM-EH pretreatment helps to increase the cellulose conversion to 70%. Under conventional low TS fermentation conditions, compared to the controlled sample, prolonged pretreatment of the BSG substrate resulted in increased VFA yields from 0.25 to 0.33 g/gVS, and butyric acid became dominant instead of acetic acid.

Effect and mechanism of benzalkonium bromide on short chain fatty acid production from anaerobic sludge fermentation process

Quaternary ammonium compounds (QACs) was frequently detected in wastewater treatment plants and leads to potential toxicity to the related biological processes. In this study, the effect of benzalkonium bromide (BK) on anaerobic sludge fermentation process for short chain fatty acid (SCFAs) production was investigated. Batch experiments indicated that BK exposure significantly enhanced the SCFAs production from anaerobic fermentation sludge and the maximum concentration of total SCFAs increased from 474.40 ± 12.35 mg/L to 916.42 ± 20.35 mg/L with BK increasing from 0 to 8.69 mg/g VSS. Mechanism exploration exhibited that the presence of BK enhanced much more bioavailable organic matters release, little affected on hydrolysis, acidification, but seriously inhibited methanogenesis. Microbial community investigation revealed that BK exposure importantly enhanced the relative abundances of hydrolytic-acidifying bacteria and also improved the metabolic pathways and functional genes for sludge lysis. This work further supplement the information for environmental toxicity of emerging pollutants.

Analysis on methane production from various coal slime fermentations based on metagenomics

Metagenomic sequencing technology was applied to evaluate differences in the anaerobic fermentation process of coal slimes by analyzing microbial diversity, functional activity structure, and cooperative relationship during the anaerobic fermentation of coal slimes with different coal ranks. The obtained results showed that the production of biomethane from coal slime was decreased by increasing metamorphism degree. Internal reason was higher abundance of microbial community in low rank coal slimes compared to that in high rank coal which had higher activity in the gene expression of key steps such as hydrolysis and acidification, methanation and the production of hydrogen and acetic acid. Acetic acid decarboxylation and CO2 reduction are two key pathways of methanation process. At the same time, K11261 (formylmethanofuran dehydrogenase subunit) and K01499 (methenyltetrahydromethanopterin cyclohydrolase) genes were further enriched in low rank slime systems, which enhanced the proportion of CO2 reduction in methanation pathway and was beneficial to biomethane production. Research revealed the roles of different coal slime ranks in biomethane production process and is considered as an important reference significance for further exploration of coal slime resource utilization.

Bioprocessing of Waste for Renewable Chemicals and Fuels to Promote Bioeconomy

The world’s rising energy needs, and the depletion of fossil resources demand a shift from fossil-based feedstocks to organic waste to develop a competitive, resource-efficient, and low-carbon sustainable economy in the long run. It is well known that the production of fuels and chemicals via chemical routes is advantageous because it is a well-established technology with low production costs. However, the use of toxic/environmentally harmful and expensive catalysts generates toxic intermediates, making the process unsustainable. Alternatively, utilization of renewable resources for bioprocessing with a multi-product approach that aligns novel integration improves resource utilization and contributes to the “green economy”. The present review discusses organic waste bioprocessing through the anaerobic fermentation (AF) process to produce biohydrogen (H2), biomethane (CH4), volatile fatty acids (VFAs) and medium chain fatty acids (MCFA). Furthermore, the roles of photosynthetic bacteria and microalgae for biofuel production are discussed. In addition, a roadmap to create a fermentative biorefinery approach in the framework of an AF-integrated bioprocessing format is deliberated, along with limitations and future scope. This novel bioprocessing approach significantly contributes to promoting the circular bioeconomy by launching complete carbon turnover practices in accordance with sustainable development goals.

Multi-functional core-shell pomegranate peel amended alginate beads for phenol decontamination and bio-hydrogen production: Synthesis, characterization, and kinetics investigation

Phenolic compounds discharged from different industries comprise a great threatening to environmental system and human health. They are toxic even at a low concentration (<1.0 μg/L). Adsorption is attractive scenario for successful removal of phenolic compounds from wastewater. Herein, a facile strategy was employed to fabricate amended alginate beads based on pomegranate peel. The constructed beads were intensively scrutinized, and introduced for the remediation of phenol from wastewater under various operational parameters of pHi (e.g., 2.1–10.7), adsorbent dose (e.g., 0.5 – 5.0 g L−1), initial phenol concentrations (e.g., 10.0 – 500.0 mg L−1), and residence time (e.g., 5.0 – 270.0 min). Consequently, the efficacy of bio-hydrogen production via dark fermentative process of co-substrate metabolism of phenol and glucose in presence of beads was systematically inspected. Our findings revealed that the maximum adsorption capacity of beads was 119.048 mg g−1 at pH 7.2. Comfortingly, the fitting isotherms experiments expounded that the adsorption of phenol by beads conformed to the Langmuir model. The kinetics modelling findings matched with pseudo-second-order model. Otherwise, the as-prepared beads have remarkably improved anaerobic co-substrate fermentation process of glucose (synergism) and phenol removal efficiency (91.1–97.0%), with bio-hydrogen yield of 0.35 up to 2.65 mol-H2 mol−1 glucose. Overall, the present study illustrates an ample perspective of natural resources feasibility as a futuristic rational platform for wastewater decontamination and bio-hydrogen production.

Revealing an unrecognized role of free ammonia in sulfur transformation during sludge anaerobic treatment

Free ammonia (FA), the unionized form of ammonium, is presented in anaerobic fermentation of waste activated sludge (WAS) at high levels. However, its potential role in sulfur transformation, especially H2S production, during WAS anaerobic fermentation process was unrecognized previously. This work aims to unveil how FA affects anaerobic sulfur transformation in WAS anaerobic fermentation. It was found that FA significantly inhibited H2S production. With an increase of FA from 0.04 to 159 mg/L, H2S production reduced by 69.9%. FA firstly attacked tyrosine-like proteins and aromatic-like proteins in sludge EPSs, with CO groups being responded first, which decreased the percentage of α-helix/(β-sheet + random coil) and destroyed hydrogen bonding networks. Cell membrane potential and physiological status analysis showed that FA destroyed membrane integrity and increased the ratio of apoptotic and necrotic cells. These destroyed sludge EPSs structure and caused cell lysis, thus strongly inhibited the activities of hydrolytic microorganisms and sulfate reducing bacteria. Microbial analysis showed that FA reduced the abundance of functional microbes (e.g., Desulfobulbus and Desulfovibrio) and genes (e.g., MPST, CysP, and CysN) involved in organic sulfur hydrolysis and inorganic sulfate reduction. These findings unveil an actually existed but previously overlooked contributor to H2S inhibition in WAS anaerobic fermentation.

Mathematical Modeling for Evaluating the Sustainability of Biogas Generation through Anaerobic Digestion of Livestock Waste

The paper investigates the mathematical modeling of anaerobic fermentation for the utilization of animal wastes. It analyzes various approaches to the mathematical modeling of anaerobic digestion processes. However, most of the models previously proposed do not take into account a number of key parameters such as the levels of micro and macronutrientls (such as K, Na, Ca, Mg, Mo, etc.), values of volatile fatty acids, C/N ratio, pH levels, extent of grinding, moisture, and others. This paper proposes a new mathematical model of anaerobic fermentation under industrial scale conditions. The model was developed on the basis of regression analysis and correlation. It found empirical relationships between biogas yield and 26 different parameters. These parameters are measured by appropriate biosensors in industrial production. Some of them have more significant influence on the fermentation process than others. Overall, the developed mathematical model has the potential to provide useful insights into biogas production and can be used to optimize anaerobic fermentation processes.

Sustainable utilization of residual grass: effect of anaerobic storage days on chemical composition, fermentation performance, microbial community, and functional profiles of Pennisetum giganteum.

The seasonal surplus and putrefactive property of moist forages inevitably increase the pressure on environmental protection and residual grass disposal. In the current work, the anaerobic fermentation approach was adopted to assist the sustainable recycling of leftover Pennisetum giganteum (LP), and its chemical composition, fermentation performance, bacterial community and functional profiles during anaerobic fermentation were studied. Fresh LP was spontaneously fermented for up to 60 d. At the end of anaerobic fermentation, fermented LP (FLP) displayed homolactic fermentation with low pH value, ethanol, and ammonia nitrogen concentrations but high lactic acid concentration. Weissella was dominant in 3-day FLP, yet Lactobacillus was the overwhelming genus (92.6%) in 60-day FLP. The anaerobic fermentation process promoted (P < 0.05) the metabolism of carbohydrate and nucleotide while suppressing (P < 0.05) that of lipid, cofactors, vitamins, energy, and amino acid. The results showed that the residual grass with LP as an example could be successfully fermented even if no additives were added, without signs of clostridial and fungal contamination.

Development of an oil-sealed anaerobic fermentation process for high production of γ-aminobutyric acid with Lactobacillus brevis isolated by directional colorimetric screening

γ-aminobutyric acid (GABA) is an important inhibitory neurotransmitter in the brain with many physiological functions. Therefore, this work establishes an efficient biosynthesis process to achieve the high production of food-grade GABA. Firstly, we adopted a directional colorimetric screening method and then obtained the strain Lactobacillus brevis (Lb. brevis) CGMCC 24975 with 22.61 g/L GABA in shake flasks, much higher than Lb. brevis ATCC 367 (3.07 g/L) due to its more efficient and stable expression of its glutamate decarboxylase (GAD) system. After exploring the effects of optimal fermentation conditions and oxygen on GABA production, we found that anaerobic fermentation could increase GABA production by up-regulating gad operon expression and activating GADase. Finally, we developed an oil-sealed anaerobic fermentation process with 157.90 g/L GABA in a 5 L bioreactor, which was 6.98-fold of that in shake flasks. This work includes a complete process from screening GABA-producing strains to developing efficient fermentation processes, laying the foundation for producing food-safe GABA.

Optimization of the anaerobic fermentation process for phosphate release using food waste

Phosphorus (P) problem worries the whole world due to the increasing demand for finite and non-renewable natural phosphate resources and the inadequacy of sustainable phosphate production technologies. In this study, bio-acidification processes using waste sludge and food waste for simultaneous sustainable phosphate release and biogas production were investigated. Response surface methodology (RSM) was used for bio-acidification optimization. High performance was achieved with the addition of 10% FW and a temperature of 45 °C, which provided 5.30 pH and 371 mg/L P release for 10 days. A total of 196 mL of cumulative biogas was produced. Using food waste potentially reduces operating costs, eliminating the need for external chemical additions for pH control. Also, this approach offers benefits such as waste management, recovery of valuable resources, cost reduction, and environmental friendly.

Divalent cation chelation enhancing carbon migration and recovery from anaerobic fermentation of waste activated sludge

Recently, the short-chain fatty acids (SCFAs) production with carbon recovery from waste activated sludge has received increasing attention. Despite that numerous approaches have been investigated, the divalent cation chelation towards enhancing anaerobic fermentation and the carbon migration fates has been rarely reported. This work attempted to chelate structural divalent cations from sludge flocs by sodium pyrophosphate (SP) at the dosages of 0–0.6 g/g SS, facilitating sludge disintegration and hydrolysis with particulate organic matters solubilization. At the optimal SP dosage of 0.4 g/g SS, the chemical oxygen demand (COD) and carbon source content in sludge solid were reduced by 45.24 % and 35.50 % within 1-day treatment, leading to considerable sludge hydrolysis and carbon release performances with soluble COD/total COD of 23.21 % and carbon release rate of 26.94 % in 2-day anaerobic fermentation, respectively. Numerous SCFAs of 237.43 mg COD/g VSS were produced by 4-day anaerobic fermentation, with the overall carbon recovery rate of 21.19 %, which were dominantly composed by acetate and propionate. Meanwhile, the SP-inhibited biogas generation also contributed to SCFAs accumulation. The divalent cation chelation obviously improved rate constant and equilibrium performances of anaerobic fermentation process, which were 1.81–5.21 and 1.36–2.82 times higher than those without SP, respectively. The carbon migration pattern was proposed by interphase carbon source balance and the mechanism was also illustrated. The crucial novelty was to propose an innovative and economic sludge hydrolysis pattern by divalent cation chelation towards improving carbon recovery.