Accumulation Of Volatile Fatty Acids Research Articles

Response of Anaerobic Granular Sludge Reactor to Plant Polyphenol Stress: Floc Disintegration and Microbial Inhibition

Plant polyphenols are potential inhibitors for the anaerobic treatment of wastewater from the wood processing, pharmaceutical, and leather industries. Tannic acid (TA) was selected as a model compound to assess the inhibitory effect of plant polyphenols in simulated wastewater in this study. The influences of TA on methanogenic activity, sludge morphology, and the microbial community were investigated under glucose and sodium acetate as carbon substrates, respectively. The results show that a threshold concentration of TA above 1500 mg·L−1 that triggers significant methanogenesis depression and volatile fatty acids (VFAs) accumulation. In addition, granules might be weakened by TA addition, reflected in changes in extracellular polymeric substances (EPS) within the granules and an increase in floc in the effluent. The anaerobic granular sludge (AnGS) fed with sodium acetate was more sensitive than the presence of glucose as the substrate when facing the challenge of TA. The concentration of the mcrA gene in granular sludge decreased markedly in response to TA stress, providing direct evidence that a high concentration of TA caused the inhibition of specific gene expressions. This study provides details about the adverse impacts of TA stress on methane production, the microbial community, and granule integrity, deepening our understanding of the anaerobic treatment of plant polyphenols contained in wastewater.

Role of biochar addition to improve anaerobic membrane bioreactors to resist oil stress in synthetic food wastewater treatment

This study investigated biochar addition to improve the performance and stability of anaerobic membrane bioreactor (AnMBR) to resist different oil contents in food wastewater treatment. Results show that an increase in oil content in synthetic food wastewater from 2 to 4 g/L of oleate-Na aggravated AnMBR performance in terms of methane (CH4) production and membrane fouling as showed by an obvious increase in transmembrane pressure (TMP). The reduced performance was caused by the accumulation of volatile fatty acids (VFAs) to inhibit the growth and activity of Methanobacterium in response to increased oil content. Nevertheless, biochar addition improved AnMBR resistance to against oil increase. The dominance of Methanobacterium and their potential mutualism with genus T78 were enhanced by biochar to sustain CH4 yield. Moreover, biochar reduced the production of extracellular polymeric substance (EPS) to alleviate membrane fouling.

Archaeal community composition as key driver of H2 consumption rates at the start-up of the biomethanation process

The performance of hydrogen consumption by various inocula derived from mesophilic anaerobic digestion plants was evaluated under ex situ biomethanation. A panel of 11 mesophilic inocula was operated at a concentration of 15 gVS.L−1 at a temperature of 35 °C in batch system with two successive injections of H2:CO2 (4:1 mol:mol). Hydrogen consumption and methane production rates were monitored from 44 h to 72 h. Hydrogen consumption kinetics varies significantly based on the inoculum origin, with no accumulation of volatile fatty acids. Microbial community analyses revealed that microbial indicators such as the increase in Methanosarcina sp. abundance and the increase of the Archaea/Bacteria ratio were associated to high initial hydrogen consumption rates. The improvement in the hydrogen consumption rate between the two injections was correlated with the enrichment in hydrogenotrophic methanogens. This work provides new insights into the early response of microbial communities to hydrogen injection and on the microbial structures that may favor their adaptation to the biomethanation process.

Carbon fixation via volatile fatty acids recovery from sewage sludge through electrochemical–pretreatment–based anaerobic digestion

Capturing the carbon in volatile fatty acids (VFA) produced from the anaerobic digestion (AD) of sewage sludge has the potential to not only provide economic benefits but also reduce greenhouse gas production. This study demonstrates a chemical–free method to collect VFA from an AD instead of methane that involves electrochemical pretreatment (EPT) of sludge. Experimental results show that applying 15 V EPT for 45 min enhances acidogenesis and selectively inhibits methanogenesis, leading to a substantial VFA accumulation (2563.1 ± 307.9 mg COD/L) and achieving 2.5 times more carbon fixation than via methane production. Interfacial thermodynamic analysis shows that EPT induces a decrease in both the repulsive electrostatic energy (from 152.9 kT to 12.2 kT) and the energy barrier (from 57.0 kT to 2.6 kT) in the sludge, leading to increased sludge aggregation and entrapment of microorganisms. Molecular docking sheds lights on how the methanogens interacts with the organic matter released from EPT (e.g., alanine–tRNA ligase), showing that these interactions potentially interfere with the proteins that are associated with the activities of the methanogens and the electron transfer pathways, thereby impeding methanogenesis. Integrating EPT into AD therefore facilitates the recovery of valuable VFA and the capture of carbon from freshwater sludge, providing notable economic and environmental benefits in sewage sludge treatment.

How to develop a bio-based phosphorus mining strategy for eutrophic marine sediments: Unlocking native microbial processes for anaerobic phosphorus release

This study examined the anaerobic release of phosphorus (P) from two different Baltic Sea sediments (B and F), focusing on the impact of initial concentration of externally introduced waste-derived volatile fatty acids (VFA) as the carbon source, temperature, pH, and mixing conditions. The first batch bioreactor set was operated to demonstrate the effect of VFA on anaerobic P release at different concentrations (1000–10000 mg/L as COD) at 20 °C. A notable P release of up to 15.85 mg/L PO4–P was observed for Sediment B at an initial carbon concentration of 10000 mg COD/L. However, VFA consumption in the bioreactors was minimal or no subsequent. The second batch bioreactor set was carried out to investigate the effect of temperature (20 °C-35 °C), pH (5.5, 7.0 and 8.5) and mixing conditions on P release by introducing lower initial carbon concentration (1000 mg COD/L) considering the potential risk for VFA accumulation in the bioreactors. Maximum P releases of 4.4 mg/L and 3.5 mg/L were for Sediment B and Sediment F, respectively. Two-way ANOVA tests revealed that the operation time and pH and their interactions were statistically significant (p < 0.05) for both sediments while the effect of mixing was not statistically significant. Most of the sulfate was reduced during batch bioreactor operation and Desulfomicobiaceae became dominant among other sulfate-reducing bacteria (SRB) possibly shows the importance of SRB in terms of anaerobic P release. This study gives an insight into future implementations of phosphorus mining from eutrophic environment under anaerobic conditions.

Effects of microbial electrolysis cell on anaerobic digestion of food waste: Acidification and recovery

The effects of a microbial electrolysis cell (MEC) applying 1.2 V on the acidification and recovery in the anaerobic digestion (AD) of food waste were studied by semi-continuous experiments. The experimental results showed that the MEC reduced the accumulation of volatile fatty acids (VFAs), enhanced acidification, accelerated the conversion of VFAs during recovery, and accelerated recovery by decreasing the relative abundance of Aminobacterium and norank_f__W27 and increasing that of Methanobacterium. The MEC reduced the production of propionic and butyric acids by decreasing the abundance of functional enzymes (such as fumarate reductase, propionate CoA-transferase, phosphate butyryltransferase, and butyrate kinase) and bacteria (such as Aminobacterium and norank_f__W27). The MEC increased the rates of four AD steps with a maximal rate of 11.47–32.32 %. The MEC promoted electron transfer by enriching the electroactive bacterium Trichococcus (10.91–28.80 %) and Methanosaeta (8.17–24.43 %). The MEC increased the abundance of the most critical functional enzymes in the bacterial community during the entire test and those in the archaeal community during recovery.

Biohydrogen, Volatile Fatty Acids, and Biomethane from Mezcal Vinasses—A Dark Fermentation Process Evaluation

Mezcal is a drink made in Mexico, the production of which generates vinasses with a high content of organic matter (OM) that is not utilized. However, these residues have the potential to be drawn upon in dark fermentation (DF) processes to obtain biogas rich in biohydrogen, biomethane, and volatile fatty acids (VFAs) with the potential to become biofuels. In the present work, the effect of reaction time (RT) and organic load (OL) was assessed based on the efficiency of removing OM, the production of VFAs, and the generation and composition of biogas in a process of DF fed with mezcal vinasses. The results show that increasing the RT and decreasing the OL increases COD removal but decreases biohydrogen production. The maximum production of H2 (64 ± 21 NmL H2/Lreactor) was obtained with the lowest RT (1 d) and the highest OL (13.5 gCODm3d−1), while the highest accumulation of VFAs (2007 ± 327 mg VFA/L) was obtained with an RT of 3 d. It was determined that RT and OL are key parameters in DF processes for biohydrogen and VFA production.

Novel Insights into Alkyl Polyglucoside Biosurfactant Promoting Anaerobic Dark Fermentation for Hydrogen Production in Sludge.

Anaerobic fermentation of excess sludge (ES) for hydrogen production is a crucial strategy for resource utilization and environmentally friendly treatment. However, the low hydrolysis efficiency of ES and the depletion of produced hydrogen have become the limiting factors for low hydrogen yield. This study innovatively applied the bio-based surfactant alkyl polyglucoside (APG) to enhance the efficiency of dark fermentation for hydrogen production from ES. When the APG content was 100mg/g (calculated based on total suspended solids), the maximum hydrogen production reached 17.8 mL/g VSS, approximately 3.7 times that in the control group. Mechanistic analysis revealed that APG promoted the release of organic matter from ES. APG also facilitated the release of soluble protein and soluble polysaccharide, increasing the organic matter reduction rate to 34.8%, significantly higher than other groups. APG enhanced the accumulation of volatile fatty acids and promoted the proportion of small molecular carboxylic acids. Enzyme activity analysis revealed that APG promoted the activity of hydrolytic enzymes but inhibited the activity of hydrogen-consuming enzymes. The research results provide a green and environmentally friendly strategy for the efficient resource utilization of ES.

Thermophilic self-fermentation of chicken manure for enhanced soluble metabolite products and bio‑hydrogen production

Treating chicken manure (CM) through anaerobic digestion encounters a hurdle due to its high nitrogen content, leading to volatile fatty acid accumulation and methanogenesis disruption. To overcome this, redirecting the process to yield soluble metabolite products (SMPs) and hydrogen is proposed. Mesophilic (30 °C) and thermophilic (55 °C) acidogenesis were employed, utilizing self-fermentation and sludge augmentation at various total solids (TS) concentrations ranging from 2.5 % to 20 %. SMP production showed direct proportionality to TS concentration. Optimal conditions were observed in thermophilic self-fermentation at 15 % TS, yielding 0.20 ± 0.01 g SMPs/g volatile solid. Moreover, the mass balance analysis revealed 46.68 g of SMPs, equivalent to 53.82 g of soluble chemical oxygen demand (SCOD) solubilized in the total SCOD of 63.56 g in the effluent. Although thermophilic bioaugmentation enhanced hydrogen production, its impact on SMPs was insignificant. This study underscores the potential of CM self-fermentation, highlighting its organic matter and microorganism-rich characteristics.

Enhanced hydrolysis and acidification of corn straw via liquid fraction of digestate: Environmental adaptability and microbial mechanisms

Anaerobic digestion (AD) of abandoned straws is an eco-friendly approach to realize its recycling. However, the low hydrolysis rate of lignocellulose poses a hindrance to achieving efficient AD. In this study, the enhanced hydrolysis and acidification of corn straw (CS) utilizing the liquid fraction of digestate (LFD) was investigated across varying solid-to-liquid inoculum ratio (SIR), pH levels, and temperature conditions. The succession patterns of the microbial community, driven by different parameters, were simultaneously identified. The findings revealed that the optimal yield of volatile fatty acids (VFAs) was observed under conditions with an SIR of 4, pH of 10, and a temperature of 45℃, predominantly dominated by acetic acid. And both pH and temperature were not conducive to VFAs accumulation in extreme environments. Comparatively, changes in pH had a greater impact on the acid production of the LFD-enhanced system and was also the primary environmental factor leading to differentiation in microbial community structure. Although Firmicutes was an absolutely dominant bacterium at the phylum level, the abundances of Caproiciproducens and Clostridum_sensu_stricto_1 at the genus level, mainly transforming complex organic substances into simpler metabolic byproducts, were greatly sensitive to the variations in SIR, pH, and temperature. This study could have practical implications for guiding improvements in large-scale AD systems with lignocellulosic straws.

Biochar-enhanced anaerobic mixed culture for biodegradation of 1,2-dichloroethane: Microbial community, mechanisms, and techno-economics

While anaerobic digestion (AD) has been employed for the degradation of chlorinated aliphatic hydrocarbons, the associated digester performance might suffer from volatile fatty acids accumulation, insufficient substrate-microbes interaction, and lower biogas yields. To overcome these limitations, this study is the first to augment the hydrocarbon-degrading microbial capacities by adding agricultural waste-based biochar to the digestion medium. 1,2-dichloroethane (1,2-DCA) was selected as the target pollutant because it is discharged in large quantities from oil refining, petrochemical, and chemical industries, causing serious environmental and human health concerns. A multi-chamber anaerobic reactor (MAR) was operated at a 1,2-DCA loading rate of 1.13 g/L/d, glucose dosage (as an electron donor) range of 200–700 mg/L, and hydraulic retention time of 11.2 h, giving dechlorination = 32.2 ± 6.9% and biogas yield = 210 ± 30 mL/g CODremoved. These values increased after biochar supplementation (100 mg/g volatile solids, VS, as an inoculum carrier) up to 60.2 ± 11.5% and 290 ± 40 mL/g CODremoved, respectively, owing to the enhancement of dehydrogenase enzyme activities. Burkholderiales (15.3%), Clostridiales (2.3%), Bacteroidales (3.5%), Xanthomonadales (3.3%), and Rhodobacterales (6.1%) involved in 1,2-DCA degradation were dominant in the reactor supplemented with biochar. It's suggested that biochar played a major role in facilitating the direct interspecies electron transfer (DIET) between syntrophic bacteria and methanogens, where chloride, ethylene glycol, and acetate derived from 1,2-DCA dechlorination could be further used to promote methanogenesis and methane production. The synergetic effect of adsorption and dechlorination towards 1,2-DCA removal was validated at various biochar dosages (50–120 mg/g) and 1,2-DCA concentrations (50–1000 mg/L). The techno-economic results showed that the cost of treating 1,2-DCA-laden discharge (100 m3/d) by the MAR module could be 0.83 USD/m3 with a payback period of 6.24 years (NPV = 2840 USD and IRR = 10%), retrieving profits from pollution reduction (9542 USD/yr), biogas selling (10418 USD/yr), and carbon credit (10294 USD/yr).

An integrated evaluation strategy for anaerobic digestion monitoring based on acid-base balance and thermodynamics of volatile fatty acid degradation

Process monitoring is a top priority for anaerobic digestion (AD), yet it poses a significant challenge due to its inherent inaccuracies and case-specific nature in diagnosing reactor status. Herein, a long-term instability simulation experiment using lignocellulosic biomass was conducted with varying organic loading rate (OLR) and hydraulic retention time (HRT) levels. The increase in OLR (0.75 to 20 kg VS m−3·d−1) and decrease in HRT (20 to 4 d) led to substantial total volatile fatty acids (TVFA) accumulation (>14 g/L) with a concomitant decrease in methane yield and organics removal. Full processing capacity with considerable conversion efficiency at four steps (hydrolysis: 60.43 ± 2.82 %, acidogenesis: 56.13 ± 3.27 %, acetogenesis: 56.03 ± 3.31 %, methanogenesis: 55.93 ± 3.32 %) and optimal methane yield (3.13 ± 0.17 L/(L·d)) was achieved at an OLR of 18 Kg VS·m−3·d−1 and HRT of 4 days. An integrated evaluation strategy for AD process stability is proposed based on the acid-base balance and thermodynamics of VFA degradation. Propionate, iso-valerate, TVFA/bicarbonate alkalinity (BA), and BA/total alkalinity (TA) were identified as potential auxiliary indicators for diagnosing AD imbalances, while ΔG for propionate and valerate degradation served as the early warning signs. To enhance the efficacy and universality of early warnings, relative variations for acid-base indicators based on steady-state (∼15 %) and the absolute threshold value for ΔGPropionate (-40 KJ/mol) and ΔGValerate (-55 KJ/mol) were adopted. This approach integrates considerations for microbial adaption, thereby enhancing an assessment of whether a given signal reflects irreversible acidification or is merely a temporary fluctuation induced by reversible acidification. The proposed strategy enables a reliable and accurate early warning, holding great promise for practical applications.

The Advantage of Citrus Residues as Feedstock for Biogas Production: A Two-Stage Anaerobic Digestion System

Anaerobic digestion (AD) is an important step in waste recovery. In Colombia, the production of citrus food significantly contributes to environmental impact via waste generation. In 2021, the waste produced, specifically citrus rind, amounted to 725,035 tons/year. During degradation, wastes generate leachate and greenhouse gases (GHGs), which negatively impact water sources (leachate), soil, and human and animal health. This article describes the design of a two-phase biodigestion system for the degradation of organic matter and biogas production. The system uses citrus waste to produce biogas with neutral emissions. The biodigestion process begins with the stabilization of the methanogenesis reactor (UASB), which takes approximately 19 days. During this period, the biogas produced contains approximately 60% methane by volume. Subsequently, the packed bed reactor operates for 7 days, where hydrolytic and acetogenic bacteria decompose the citrus waste, leading to the production and accumulation of volatile fatty acids. The final step involves combining the two phases for 5 days, resulting in a daily biogas production ranging from 700 to 1100 mL. Of this biogas, 54.90% is methane (CH4) with a yield of 0.51 LCH4gSV−1. This study assesses the methane production capacity of citrus waste, with the process benefiting from the pH value of the leachate, enhancing its degradability. Consequently, this approach leads to a notable 27.30% reduction in solids within the digestion system. The two-phase anaerobic biodigestion system described in this article demonstrates a promising method to mitigate the environmental impact of citrus waste while concurrently producing a renewable source of energy.

Optimum Magnetite–Zeolite Nanoparticles Loading on the Cathode of Microbial Electrochemical–Anaerobic Digestion System for Enhancing Methane Generation

Microbial electrochemical systems (MESs) can enhance methane production in anaerobic digestion, but their performance is hindered by inadequate electron transfer between the cathode and microbes. Magnetite–zeolite (MZ)‐based catalysts accelerate electron exchange; however, the optimal loading of MZ is crucial for maximizing MES performance. In this study, different loadings of the MZ catalyst ranging from 0 to 2 mg cm−2 on the cathode were evaluated to obtain an optimum loading for maximizing methane recovery from MES. Electrochemical analyses demonstrated enhanced electrochemical reduction kinetics of the cathode with increased MZ loading from 0 to 2 mg cm−2. Among the tested loadings, the MES with 1 mg cm−2 MZ on the cathode exhibited the highest methane production rate at 548 mL L−1 d−1, surpassing other MES operations with 2 and 0.5 mg cm−2 (499 and 434 mL L−1 d−1, respectively). Additionally, the MES with 1 mg cm−2 MZ demonstrated the highest soluble chemical oxygen demand removal efficiency of 87% and total coulomb recovery of 1444.06C ± 42.60C, with the lowest amount of volatile fatty acids accumulation. Consequently, MZ is recommended as a superior catalyst for enhancing MES performance and suggested to utilize 1 mg cm−2 MZ loading on the cathode to maximize methane production.

Anaerobic co-digestion of food waste and bio flocculated sewage sludge towards bio-methane production

The existing sewage treatment plants are energy consumers rather than producers and integration of anaerobic reactor can be a viable approach for enhancing their commercial viability. Therefore, anaerobic co-digestion of food waste and bio-flocculated sewage sludge was studied in a continuous stirred tank reactors (R1 and R2) having a working volume of 6.5 Litre at organic loading rates of 2.5 and 2.4g VS L-1D-1. At mesophilic temperature, the stabilisation of inoculum was performed in batch mode for 60 days followed by continuous mode feeding for 120 days. The feeding ratio was decided based on availability of food waste and bio-flocculated sewage sludge from a typical domestic household for analysing the effect of volatile fatty acids accumulation on reactor performance. The R1 was fed with equal proportion of bio-flocculated sewage sludge and food waste while R2 was fed in 98:2 (v/v), respectively. To analyse the mixing and temperature distribution within the digester, the velocity and temperature profiles were obtained using Ansys Fluent. In R1, more biogas yield was observed than R2 due to 80% average VS reduction as compared to 55% in case of R2. The highest volatile fatty acids accumulation of 10951mgL-1 was observed in R1 whereas R2 showed 2800mgL-1, respectively. The more fluctuations in pH were observed in R1 as compared to R2 due to more food waste concentration and maximum bio-methane yield was found to be 133 and 233mL CH4 g-1 VSadded for R1 and R2, respectively.

Acclimation of Microbial Consortia to Ammonia and Salt in Methane Fermentation

As methane fermentation is inhibited by ammonia derived from organic waste, anaerobic microbial communities tolerant to enriched wastewater with high concentrations of ammonia and salt must be obtained for methane fermentation. Therefore, acclimation cultures were prepared in bottles for 60–80 weeks with artificial wastewater medium added every 2 weeks, using three types of sludge from wastewater treatment plants in food factories. These cultures were maintained without substantially decreasing methanogenesis and gradually increasing NH4-N and salt concentrations to 5 and 34 g/L, respectively, via the accumulation of ammonia and salt through anaerobic digestion and direct addition. The culture did not show the severe inhibition of methanogenesis or the accumulation of volatile fatty acids (VFAs) such as acetic and propionic acids. The analysis of bacterial consortia in the acclimated sludge based on the 16S rRNA sequence showed that hydrogenotrophic methanogenic bacteria of the genus Methanoculleus were dominant among archaea, whereas bacteria from the orders Clostridiales and Bacteroidales were dominant among eubacteria. Further, VFA-assimilating bacteria, including synthetic acetate-oxidizing bacteria coupled with hydrogenotrophic Methanoculleus to convert methane from acetate, were present to prevent the excessive accumulation of VFAs in the acclimation culture. The proposed acclimation process can enhance the anaerobic digestion of wastewater for methane production.

Enhancing anaerobic digestion performance of oxytetracycline-laden wastewater through micro-nano bubble ozonation pretreatment

This study investigated the potential of micro-nano bubble (MNB) ozonation pretreatment to eliminate oxytetracycline (OTC) from wastewater and improve subsequent anaerobic digestion (AD) performance. The findings revealed that MNB ozonation achieved efficient OTC oxidation (>99 % in 60 min), and significantly enhanced methane production by 51 % compared to conventional ozonation (under 30 min of pretreatment). Additionally, MNB ozonation resulted in a decrease in the soluble chemical oxygen demand and reduced volatile fatty acid accumulation compared to conventional ozonation. Furthermore, the study sheds light on the profound impact of OTC and its oxidation by-products on the sludge microbiome. Exposure to OTC and its oxidation by-products resulted in alterations in extracellular polymeric substances composition and led to significant shifts in microbial community structure. This study highlights the promise of MNB ozonation as an effective approach for pharmaceutical pollutant removal and the optimization of AD performance in wastewater treatment, with implications for improved environmental sustainability.

Restoring the Stability of Long-Term Operated Thermophilic Anaerobic Digestion of Maize Straw by Supplying Trace Elements

Maize straw has been widely used for the production of energy through anaerobic digestion, but biogas production can be hindered by a lack of trace elemental nutrients. To address this issue, a lab-scale anaerobic plug flow reactor was continuously operated at 55 °C for 300 days, with a hydraulic retention time of 42 days and an organic loading rate of 2.1 g total solids/(L·day). Results from this study showed that between days 101 and 194, the methane yield slightly decreased from 0.26 ± 0.04 to 0.24 ± 0.03 L/g volatile solids (VS), but significant volatile fatty acid accumulation was observed by reaching up to 2759 ± 261 mg/L. After trace elements were added to the reactor, the methane yield increased to 0.30 ± 0.03 L/g VS, with 53% methane content. Around 62% of the total chemical oxygen demand and volatile solids were broken down into methane. Volatile fatty acid levels dropped and stabilized at around 210 ± 50 mg/L, indicating restored process stability. The addition of trace elements increased the abundance of Firmicutes and decreased Synergistetes in bacteria while simultaneously increasing the abundance of Methanosarcina in archaea. In conclusion, trace element supplementation was experimentally found to be necessary for stable thermophilic anaerobic digestion of maize straw.

Using landfill leachate to indicate the chemical and biochemical activities in elevated temperature landfills

Landfill leachate properties contain important information and can be a unique indicator for the chemical and biochemical activities in landfills. In the recent decade, more landfills are experiencing elevated temperature, causing an imbalance in the decomposition of solid waste and affecting the properties of the landfill leachate. This study analyzes the properties of leachate from two landfills that were experiencing elevated temperature (ETLFs), samples were collected from both elevated temperature impacted and non-impacted areas in each landfill. The accumulation of volatile fatty acids (VFA) in leachates from elevated temperature impacted areas of both landfill sites revealed that methanogenesis was inhibited by the elevated temperature, which was further confirmed by the more acidic pH, higher H/C elemental ratio, and lower degree of aromaticity of the elevated temperature impacted leachates. Also, carbohydrates depletion indicated possible enhancement of hydrolysis and acidogenesis by elevated temperature, which was supported by compositional comparison of isolated acidic species by negative-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICRMS) at 21 T derived from both elevated temperature impacted and non-impacted areas in the same landfill site. Furthermore, leachate organics fractionation showed that leachates not impacted by elevated temperature contain less hydrophilic fraction and more humic fraction than elevated temperature-impacted leachates for both ETLFs.

Anaerobic co-digestion of cabbage waste and cattle manure: Effect of mixing ratio and hydraulic retention time

The aim of this study is to optimize the process parameters for the anaerobic co-digestion of cabbage waste and cattle manure, with the objective of maximizing methane production. Batch experiments were conducted using five different mixing ratios (1:0, 3:1, 1:1, 1:3, and 0:1), and continuous experiments were run at six different hydraulic retention times (HRTs) of 25, 20, 15, 10, 8, and 5 days. The results indicate that the co-digestion displayed a synergistic effect, as evidenced by a cooperative index greater than 1. Additionally, an appropriate cabbage waste to cattle manure ratio of 3:1 yielded a maximum methane production of 440 mL/g-VS. During the continuous study, the highest methane production rate of 1.55 L/(L·d) was achieved at 10-day HRT. Efficient methane yields in the range of 322–336 mL/g-VS were obtained at HRTs of 25, 20, and 15 days. Methane yield decreased when HRTs were shortened to 10 or 8 days due to the accumulation of volatile fatty acids and the loss of methanogens. At an HRT of 4 days, methane production nearly ceased. These results provide insights for the optimization of anaerobic co-digestion of cabbage waste and cattle manure, leading to higher methane production.