Enhancement of biomethane recovery from batch anaerobic digestion by exogenously adding an N-acyl homoserine lactone cocktail.

Biomethane recovered through anaerobic digestion (AD) is a renewable, sustainable, and cost-effective alternative energy source that has the potential to help address rising energy demands. Efficient bioconversion during AD depends on the symbiotic relationship between hydrolytic bacteria and methanogenic archaea. Interactions between microorganisms occur in every biological system via a phenomenon known as quorum sensing (QS), in which signaling molecules are simultaneously transmitted and detected as a mode of cell-to-cell communication. However, there's still a lack of understanding on how QS works in the AD system, where diverse bacteria and archaea interact in a complex manner. In this study, different concentrations (0.5 and 5 µM) of signaling molecules in the form of an N-acyl homoserine lactone cocktail (C6-, C8-, C10-, and 3-oxo-C6-HSL) were prepared and introduced into anaerobic batch reactors to clearly assess how QS affects AD systems. It was observed that the methane yield increased with the addition of AHLs: a 5 µM AHL cocktail improved the methane yield (341.9 mL/g-COD) compared to the control without AHLs addition (285.9 mL/g-COD). Meanwhile, evidence of improved microbial growth and cell aggregation was noticed in AHLs-supplemented systems. Our findings also show that exogenously adding AHLs alters the microbial community structure by increasing the overall bacterial and archaeal population counts while favoring the growth of the methanogenic archaea group, which is essential in biomethane synthesis.

The effects of ammonia acclimation on biogas recovery and the microbial population in continuous anaerobic digestion of swine manure.

This study investigated the ammonia toxicity and the acclimation of anaerobic microbiome in continuous anaerobic digestion of swine manure using unacclimated inoculum. When the total ammonia nitrogen concentration (TAN) reached 2.5 g N/L, the methane yield decreased from 254.1 ± 9.6 to 154.6 ± 9.9 mL/g COD. The free ammonia nitrogen concentration of the inhibited condition was 190 mg N/L. The methane yield was eventually recovered as 269.6 ± 3.6 mL/g COD with a further operation. Anaerobic toxicity assay (ATA) showed that mixed liquor from the recovered phase possessed enhanced tolerance to ammonia, not only within the exposed level in continuous operation (<2.5 g NH3/L) but also over the range (>2.5 g NH3/L). Microbial analysis revealed that continuous operation under ammonia stress resulted in the change of both bacterial and archaeal populations. The ammonia adaptation was concurrent with the archaeal population shift from Methanosaeta to Methanosarcina and Methanobacterium. The dominancy of Clostridia in bacterial population was found in the recovered phase. It is highly recommended to use an inoculum acclimated to a target ammonia level which can be pre-checked by ATA and to secure a start-up period for ammonia adaptation in the field application of anaerobic digestion for swine manure.

Sludge disintegration and anaerobic digestion enhancement by alkaline-thermal pretreatment: Economic evaluation and microbial population analysis.

Alkaline-thermal pretreatment was examined for waste activated sludge (WAS) disintegration and subsequent anaerobic digestion (AD). Pretreatment at 60 °C was estimated to provide better economic benefits than higher temperature conditions. The maximum methane yield of 215.6 mL/g COD was achieved when WAS was pretreated at 60 °C and pH 10 for 24 h, which was 46.6% higher than untreated WAS. The pretreatment condition also provided the maximum net savings. The degree of sludge disintegration, considering both loosely bound-extracellular polymeric substance and soluble COD, would be a better indicator to predict anaerobic digestibility than the solubilization rate that considers soluble COD alone. Microbial analysis implied that pretreatment facilitated the growth of hydrolytic bacteria, phyla Bacteroidetes and Firmicutes. In addition, sludge pretreatment enhanced the growth of both acetoclastic and hydrogenotrophic methanogens, genera Methanosaeta and Methanobacterium. The mild AT-PT would be useful to enhance the digestion performance and economic benefit of WAS digestion.

Biofilm formation as a method of improved treatment during anaerobic digestion of organic matter for biogas recovery.

The efficiency of anaerobic digestion could be increased by promoting microbial retention through biofilm development. The inclusion of certain types of biofilm carriers has differentiated existing AD biofilm reactors through their respective mode of biofilm growth. Bacteria and archaea engaged in methanogenesis during anaerobic processes potentially build biofilms by adhering or attaching to biofilm carriers. Meta-analyzed results depicted varying degrees of biogas enhancement within AD biofilm reactors. Furthermore, different carrier materials highly induced the dynamicity of the dominant microbial population in each system. It is suggested that the promotion of surface contact and improvement of interspecies electron transport have greatly impacted the treatment results. Modern spectroscopy techniques have been and will continue to give essential information regarding biofilm's composition and structural organization which can be useful in elucidating the added function of this special layer of microbial cells.

Effect of low-thermal pretreatment on the methanogenic performance and microbiome population of continuous high-solid anaerobic digester treating dewatered sludge.

Undigested and dewatered sludge at 10% total solids was pretreated at 60 °C for 3 h and fed to a lab-scale horizontal anaerobic bioreactor for 130 days with solids retention time (SRTs) from 25 to 16 d. The low-thermal pretreatment enabled higher net energy production, improved sludge treatment efficiency, and enhanced digestion stability. The highest average biomethane yield and production rate were 138.5 mL/g VS and 0.43 L/L.d, respectively, and the economic benefit was expected to be the maximum at SRT 16 d. Pretreatment did not increase the specific methanogenic activity per unit methanogen, but resulted in higher abundance of methanogenic archaea and hydrolytic bacteria. Methanogenic population shifted from hydrogenotrophic to acetoclastic, consistent with predicted gene expression at SRT equal or below 20 d. Anaerobic digestion along with low-thermal could be a feasible management strategy for undigested dewatered sludge from small WWTPs.

Enhanced anaerobic digestion of waste-activated sludge via bioaugmentation strategy-Phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt2) analysis through hydrolytic enzymes and possible linkage to system performance.

In this study, anaerobic digestion of waste-activated sludge was bioaugmented with hydrolytic bacteria, Bacteroidetes uniformis (Bacteroidetes, B) and Clostridium sp. (Firmicutes, F) at various dosages. Bioaugmentation resulted in enhanced methane conversion of waste-activated sludge. The highest methane yield of 298.1 mL CH4/g-COD, 85.2% COD conversion efficiency was obtained when Bacteroidetes uniformis and Clostridium sp. were augmented at 100 and 900 CFU/mL, respectively. The microbial community analysis demonstrated that bioaugmentation increased the proportion of Bacteroidetes, Firmicutes, and Proteobacteria. Furthermore, at the highest methane yield, the principal methanogenic pathway was altered from acetoclastic to a mixture of hydrogenotrophic and acetoclastic; the major species shifted from Methanosaeta concilii to Methanobacterium subterraneum. Predicted gene analysis revealed that increased expression of hydrolases resulted in enhanced methane conversion through bioaugmentation.

Assessment of Chlorella sp. as a potential feedstock for biological methane production.

Microalgal biomass sequestrates CO2 and is regarded as a promising renewable feedstock for anaerobic digestion because of its adequate carbohydrate content and lignin-free structure. This study optimizes the dilute-acid pretreatment of Chlorella sp. and subsequent biomethane production using response surface methodology and central composite design with temperature, pretreatment time and solid-to-liquid ratio as variables. A temperature of 64.1 °C, pretreatment time of 1.2 h, and a solid to liquid ratio of 0.29 were the optimal pretreatment conditions and resulted in a methane yield of 302.22 mL CH4/g COD and methane production rate of 110.04 mL CH4/g VSS-d. The severity factor of 1.5-1.6 was adequate to render the Chlorella sp. bioavailable for high methane recovery. The results obtained from the experiments conformed to those predicted by the model. This study effectively utilizes algal biomass for biomethane production and enables the possibility of scaled-up studies using a closed-loop approach.

Comparative evaluation of biochemical methane potential of various types of Ugandan agricultural biomass following soaking aqueous ammonia pretreatment.

The feasibility of pretreatment involving soaking in aqueous ammonia (SAA) for the anaerobic digestion (AD) of eight different types of agricultural biomass of Ugandan origin was investigated. Moderate pretreatment temperatures of 60 and 90 °C were employed, and the NH3 concentration, solid-to-liquid ratio, and pretreatment time were fixed at 15.0% (w/w), 1:6, and 6 h, respectively. The delignification efficiencies of the SAA pretreatment ranged from 51.1 to 76.6%, and the maximum value was observed for maize bran pretreated at 90 °C. Biochemical methane potential experiments proved that the breaking of the complex bonds of lignin made fermentable sugars easily accessible to microorganisms. In all cases, the SAA pretreatment enhanced the methane potential of the eight types of Ugandan biomass compared with its untreated counterparts. The pretreated maize bran exhibited the highest methane yield of 291.5 mL CH4/g COD, which is 83.1% of the theoretical conversion. SAA followed by AD is useful for employing Ugandan agricultural biomass as a renewable energy source.

Effect of shear velocity and feed concentration on the treatment of food waste in an anaerobic dynamic membrane Bioreactor: Performance Monitoring and microbial community analysis.

The formation of the dynamic membrane (DM) in an anaerobic dynamic membrane bioreactor (AnDMBR) treating food waste was, previously, found to be beneficial to the stable performance of an anaerobic digestion system. This study examines the effect of shear velocity and feed concentration on the performance and microbial community of an AnDMBR treating food waste. The shear velocity was varied from 0.04 to 1.74 m/h, using three different feed concentrations (50, 80, and 100 g-COD/L). The highest average methane production rate of 2.6 L-CH4/L/d was achieved at a feed concentration and shear velocity of 100-g COD/L and 0.34 m/h, respectively. Increasing shear velocity, within certain limits, is beneficial to AnDMBR systems, promoting better mixing, substrate-biomass interactions, and DM layer formation. Methanosarcina flavescens proliferated (69%) at high shear velocities when acetic acid was the major volatile fatty acid. The abundance ratio between Bacteroidetes and Firmicutes showed a linear relationship to methanogenic performance.

Food waste treatment in an anaerobic dynamic membrane bioreactor (AnDMBR): Performance monitoring and microbial community analysis.

The applicability of a dynamic membrane (DM) was examined in the anaerobic treatment of high-strength food waste. A DM was established on woven polyester with a pore size of 50 µm, which achieved a solids retention time to hydraulic retention time ratio of 2.1:12.1. The highest average rate of methane production (1.1 L CH4/L/d) was achieved with an organic loading rate (OLR) of 5.0 g chemical oxygen demand (COD)/L/d. Propionate was the most abundant volatile fatty acid (VFA) for OLRs above 3.1 g/L/d, but concentrations were maintained below 0.9 g/L. Up to 82% of the VFAs in the mixed liquor was reduced in the effluent, implying high methanogenic activity of the DM. Microbial assays confirmed a higher archaeal and bacterial content in the DM than in the mixed liquor at shear velocities above 1.0 cm/s. Methanolinea tarda, which is known to be propionate tolerant, was the predominant archaea in the DM.

Two-stage processing of Miscanthus giganteus using anhydrous ammonia and hot water for effective xylan recovery and improved enzymatic saccharification.

A two-stage method using gaseous ammonia and hot water was proposed to recover xylan and lignin from Miscanthus. In this method, Miscanthus was treated with gaseous ammonia at elevated temperatures (60-150 °C) for various reaction times (1-48 h) in the first stage, termed as LMAA (low-moisture anhydrous ammonia) treatment. In the following stage, the LMAA-treated solid was subjected to hot-water treatment in a flow-through column reactor under various reaction conditions (170-220 °C, 30-90 min). After two-stage processing, the remaining solid contained mostly glucan (∼80% cellulose), which became highly digestible by enzymes. The optimal treatment conditions for sugar recovery using two-stage process were 120 °C and 12 h for the 1st stage and 190 °C, 90 min, and 5 mL/min for the 2nd stage, which resulted in 84.2% xylan recovery in liquid phase and 95.3% glucan digestibility of the treated solid, using 15 FPU/g-glucan enzyme loading after the two-stage treatment.

Effects of Low Moisture Anhydrous Ammonia (LMAA) Pretreatment at Controlled Ammoniation Temperatures on Enzymatic Hydrolysis of Corn Stover.

Corn stover was treated using low-moisture anhydrous ammonia (LMAA) at controlled ammoniation temperature. Moisturized corn stover (50 % moisture) was contacted with anhydrous ammonia (0.1 g NH3/g-biomass) in a batch reactor at various temperatures (ambient to 150 °C). After ammoniation at elevated and controlled temperature, ammoniated corn stover was pretreated at various temperatures (60-150 °C) for 72-144 h. Change in composition was marginal at low pretreatment temperature but was relatively severe with pretreatment at high temperature (130-150 °C). The latter resulted in low enzymatic digestibility. It was also observed that extreme levels (either high or low) of residual ammonia affected enzymatic digestibility, while residual ammonia improved by 1.0-1.5 %. The LMAA method enhanced enzymatic digestibility compared to untreated corn stover (29.8 %). The highest glucan and xylan digestibility (84.1 and 73.6 %, respectively) was obtained under the optimal LMAA conditions (i.e., ammoniation at 70 °C for 20 min, followed by pretreatment at 90 °C for 48 h).