Microbial and functional characterization of granulated sludge from full-scale UASB thermophilic reactor applied to sugarcane vinasse treatment

Enhancing anaerobic digestion of food waste with chemically vapor-deposited biochar: Effective enrichment of Methanosarcina and hydrogenotrophic methanogens

The effects and mechanisms of chemically vapor-deposited (CVD) biochar on anaerobic digestion (AD) remain unexplored. This study proposes a novel approach to simultaneously address plastic waste management and bioenergy production by applying CVD biochar in the anaerobic digestion of food waste. Results indicate that CVD biochar, particularly PE900, significantly reduces the lag phase (from 15 to 9 days) and increases methane yield by 46 % compared to the control. The effectiveness of polyethylene-derived biochar is further confirmed through three consecutive fermentation batches, where it consistently improves methane production. CVD biochar also alters extracellular polymeric substance (EPS) composition and enriches key microbial communities, including hydrogenotrophic methanogens and Methanosarcina. The nanofiber structure and higher sp2-hybridized carbon content of PE900 biochar are likely the main factors influencing EPS, microbial composition, and methane production performance. This study demonstrates the potential of CVD biochar for enhancing anaerobic digestion and valorizing plastic waste in waste-to-energy conversion.

Harnessing the Energy Potential and Value-Added Products from the Treatment of Sugarcane Vinasse: Maximizing Methane Production Through Co-Digestion with Sugarcane Molasses and Enhanced Organic Loading

This study assessed the impact of organic loading rate (OLR) on methane (CH4) production in the anaerobic co-digestion (AcoD) of sugarcane vinasse and molasses (SVM) (1:1 ratio) within a thermophilic fluidized bed reactor (AFBR). The OLR ranged from 5 to 27.5 kg COD.m-3.d-1, with a fixed hydraulic retention time (HRT) of 24 h. Organic matter removal varied from 56 to 84%, peaking at an OLR of 5 kg COD.m-3.d-1. Maximum CH4 yield (MY) (272.6 mL CH4.g-1CODrem) occurred at an OLR of 7.5 kg COD.m-3.d-1, while the highest CH4 production rate (MPR) (4.0 L CH4.L-1.d-1) and energy potential (E.P.) (250.5 kJ.d-1) were observed at an OLR of 20 kg COD.m-3.d-1. The AFBR exhibited stability across all OLR. At 22.5 kg COD.m-3.d-1, a decrease in MY indicated methanogenesis imbalance and inhibitory organic compound accumulation. OLR influenced microbial populations, with Firmicutes and Thermotogota constituting 43.9% at 7.5 kg COD.m-3.d-1, and Firmicutes dominating (52.7%) at 27.5 kg COD.m-3.d-1. Methanosarcina (38.9%) and hydrogenotrophic Methanothermobacter (37.6%) were the prevalent archaea at 7.5 kg COD.m-3.d-1 and 27.5 kg COD.m-3.d-1, respectively. Therefore, this study demonstrates that the organic loading rate significantly influences the efficiency of methane production and the stability of microbial communities during the anaerobic co-digestion of sugarcane vinasse and molasses, indicating that optimized conditions can maximize energy yield and maintain methanogenic balance.

Insights of energy potential in thermophilic sugarcane vinasse and molasses treatment: does two-stage codigestion enhance operational performance?

The study evaluated the performance of thermophilic co-digestion in both single-stage methanogenic reactors (TMR) and two-stage systems, consisting of a thermophilic acidogenic reactor and a thermophilic sequential methanogenic reactor (TSMR). A 1:1 mixture of sugarcane vinasse and molasses was codigested in anaerobic fluidized bed reactors, with varying organic matter concentrations based on chemical oxygen demand (COD) ranging from 5 to 22.5 g COD L-1. Both systems achieved high organic matter removal efficiency (51 to 86.5%) and similar methane (CH4) yields (> 148 mL CH4 g-1CODremoved). However, at the highest substrate concentration (22.5 g COD L-1), the TSMR outperformed the TMR in terms of energy generation potential (205.6 kJ d-1 vs. 125 kJ d-1). Phase separation in the two-stage system increased bioenergy generation by up to 43.5% at lower substrate concentrations (7.5 g COD L-1), with hydrogen (H2) generation playing a critical role in this enhancement. Additionally, the two-stage system produced value-added products, including ethanol (2.3 g L-1), volatile organic acids (3.2 g lactate L-1), and H2 (0.6-2.7 L H2 L-1 d-1). Microbial analysis revealed that Thermoanaerobacterium, Caldanaerobius, and Clostridium were dominant at 5 g COD L-1, while Lactobacillus prevailed at concentrations of ≥ 15 g COD L-1. The primary methane producers in the single-stage system were Methanosarcina, Methanoculleus, and Methanobacterium, whereas Methanothermobacter, Bathyarchaeia, and Methanosarcina dominated in the two-stage system.

Phase separation as a strategy to prevent sulfide-related drawbacks in methanogenesis: performance and energetic aspects

The establishment of sulfate (SO42-) reduction during methanogenesis may considerably hinder the efficient energetic exploitation of methane, once removing sulfide from biogas is obligate and can be costly. In addition, sulfide generation can negatively impact the performance of methanogens by triggering substrate competition and sulfide inhibition. This study investigated the impacts of removing SO42- during fermentation on the performance of a second-stage methanogenic continuous reactor (R2), comparing the results with those obtained in a single-stage system (R1) fed with SO42--rich wastewater (SO42- of up to 400 mg L-1, COD/SO42- of 3.12-12.50). The organic load (OL) was progressively increased to 5.0 g COD d-1 in both reactors, showing completely discrepant performances. Sulfate-reducing bacteria outperformed methanogens in the consumption for organic matter during the start-up phase (OL = 2.5 g COD d-1) in R1, directing up to 73% of the electron flow to SO42- reduction. An efficient methanogenic activity was established in R1 only after decreasing the OL to 0.625 g COD d-1, after which methanogenesis prevailed by consuming ca. 90% of the removed COD. Nevertheless, high sulfide proportions (up to 3.1%) were measured in biogas. Conversely, methanogenesis was promptly established in R2, resulting in a methane-rich (> 80%) and sulfide-free biogas regardless of the operating condition. From an economic perspective, processing the biogas evolved from R2 would be cheaper, although the techno-economic impacts of managing the sulfur pollution in the fermentative reactor still need to be understood.

Biomethane recovery through co-digestion of cheese whey and glycerol in a two-stage anaerobic fluidized bed reactor: Effect of temperature and organic loading rate on methanogenesis

Anaerobic digestion for CH₄ recovery in wastewater treatment has been carried out with different strategies to increase process efficiency, among which co-digestion and the two-stage process can be highlighted. In this context, this study aimed at evaluating the co-digestion of cheese whey and glycerol in a two-stage process using fluidized bed reactors, verifying the effect of increasing the organic loading rate (OLR) (2-20 g-COD.L^-1.d^-1) and temperature (thermophilic and mesophilic) in the second stage methanogenic reactor. The mesophilic methanogenic reactor (R-Meso) (mean temperature of 22 °C) was more tolerant to high OLR and its best performance was at 20 g-COD.L^-1.d^-1, resulting in methane yield (MY) and methane production (MPR) of 273 mL-CH₄.g-COD^-1 and 5.8 L-CH₄.L^-1.d^-1 (with 67% of CH₄), respectively. Through 16S rRNA gene massive sequencing analysis, a greater diversity of microorganisms was identified in R-Meso than in R-Thermo (second stage methanogenic reactor, 55 °C). Firmicutes was the phyla with higher relative abundance in R-Thermo, while in R-Meso the most abundant ones were Proteobacteria and Bacteroidetes. Regarding the Archaea domain, a predominance of hydrogenotrophic microorganisms could be observed, being the genera Methanothermobacter and Methanobacterium the most abundant in R-Thermo and R-Meso, respectively. The two-stage system composed with a thermophilic acidogenic reactor + R-Meso was more adequate for the co-digestion of cheese whey and glycerol than the single-stage process, promoting increases of up to 47% in the energetic yield (10.3 kJ.kg-COD^-1) and 14% in organic matter removal (90.5%).

Two problems in one shot: Vinasse and glycerol co-digestion in a thermophilic high-rate reactor to improve process stability even at high sulfate concentrations

Anaerobic co-digestion (AcoD) of sugarcane vinasse and glycerol can be profitable because of the destination of two biofuel wastes produced in large quantities in Brazil (ethanol and biodiesel, respectively) and the complementary properties of these substrates. Thus, the objective of this study was to assess the effect of increasing the organic loading rate (OLR) from 2 to 20 kg COD m^-3 d^-1 on the AcoD of vinasse and glycerol (50 %:50 % on a COD basis) in a thermophilic (55 °C) anaerobic fluidized bed reactor (AFBR). The highest methane production rate was observed at 20 kg COD m^-3 d^-1 (8.83 L CH₄ d^-1 L^-1), while the methane yield remained stable at around 265 NmL CH₄ g^-1 COD_rem in all conditions, even when influent vinasse reached 1811 mg SO₄^2- L^-1 (10 kg COD m^-3 d^-1). Sulfate was not detected in the effluent. Bacterial genera related to sulfate removal, such as Desulfovibrio and Desulfomicrobium, were observed by means of shotgun metagenomic sequencing at 10 kg COD m^-3 d^-1, as well as the acetoclastic archaea Methanosaeta and prevalence of genes encoding enzymes related to acetoclastic methanogenesis. It was concluded that process efficiency and methane production occurred even in higher sulfate concentrations due to glycerol addition.