Organic Matter Accumulation and Hydrology as Drivers of Greenhouse Gas Dynamics in Newly Developed Artificial Channels.

Artificial channels, common features of inland waters, have been suggested as significant contributors to methane (CH4) and carbon dioxide (CO2) dynamics and emissions; however, the magnitude and drivers of their CH4 and CO2 emissions (diffusive and ebullitive) remain unclear. They are characterized by reduced flow compared to the donor river, which results in suspended organic matter (OM) accumulation. We propose that in such systems hydrological controls will be reduced and OM accumulation will control emissions by promoting methane production and outgassing. Here, we monitored summertime CH4 and CO2 concentrations and emissions on six newly constructed river-fed artificial channels, from bare riparian mineral soil to lotic channels, under two distinct flow regimes. Chamber-based fluxes were complemented with hydrology, total fluxes (diffusion + ebullition), and suspended OM accumulation assessments. During the first 6 weeks after the flooding, inflowing riverine water dominated the emissions over in-channel contributions. Afterwards, a substantial accumulation of riverine suspended OM (≥50% of the channel's volume) boosted in-channel methane production and led to widespread ebullition 10× higher than diffusive fluxes, regardless of the flow regime. Our finding suggests ebullition as a dominant pathway in these anthropogenic systems, and thus, their impact on regional methane emissions might have been largely underestimated.

Estimated greenhouse gas emissions in the Mbalmayo thermal power plant between 2016-2020 using the genetic-Gaussian algorithm coupling.

The greenhouse gas (GHG) emissions inventories in our context result from the production of electricity from fuel oil at the Mbalmayo thermal power plant between 2016 and 2020. Our study area is located in the Central Cameroon region. The empirical method of the second level of industrialisation was applied to estimate GHG emissions and the application of the genetic algorithm-Gaussian (GA-Gaussian) coupling method was used to optimise the estimation of GHG emissions. Our work is of an experimental nature and aims to estimate the quantities of GHG produced by the Mbalmayo thermal power plant during its operation. The search for the best objective function using genetic algorithms is designed to bring us closer to the best concentration, and the Gaussian model is used to estimate the concentration level. The results obtained show that the average monthly emissions in kilograms (kg) of GHGs from the Mbalmayo thermal power plant are: 526 kg for carbon dioxide (CO2), 971.41 kg for methane (CH4) and 309.41 kg for nitrous oxide (N2O), for an average monthly production of 6058.12 kWh of energy. Evaluation of the stack height shows that increasing the stack height helps to reduce local GHG concentrations. According to the Cameroonian standards published in 2021, the limit concentrations of GHGs remain below 30 mg/m3 for CO2 and 200 µg/m3 for N2O, while for CH4 we reach the limit value of 60 µg/m3. These results will enable the authorities to take appropriate measures to reduce GHG concentrations.

Including Methane Emissions from Agricultural Ponds in National Greenhouse Gas Inventories.

Agricultural ponds are a significant source of greenhouse gases, contributing to the ongoing challenge of anthropogenic climate change. Nations are encouraged to account for these emissions in their national greenhouse gas inventory reports. We present a remote sensing approach using open-access satellite imagery to estimate total methane emissions from agricultural ponds that account for (1) monthly fluctuations in the surface area of individual ponds, (2) rates of historical accumulation of agricultural ponds, and (3) the temperature dependence of methane emissions. As a case study, we used this method to inform the 2024 National Greenhouse Gas Inventory reports submitted by the Australian government, in compliance with the Paris Agreement. Total annual methane emissions increased by 58% from 1990 (26 kilotons CH4 year-1) to 2022 (41 kilotons CH4 year-1). This increase is linked to the water surface of agricultural ponds growing by 51% between 1990 (115 kilo hectares; 1,150 km2) and 2022 (173 kilo hectares; 1,730 km2). In Australia, 16,000 new agricultural ponds are built annually, expanding methane-emitting water surfaces by 1,230 ha yearly (12.3 km2 year-1). On average, the methane flux of agricultural ponds in Australia is 0.238 t CH4 ha-1 year-1. These results offer policymakers insights into developing targeted mitigation strategies to curb these specific forms of anthropogenic emissions. For instance, financial incentives, such as carbon or biodiversity credits, can mobilize widespread investments toward reducing greenhouse gas emissions and enhancing the ecological and environmental values of agricultural ponds. Our data and modeling tools are available on a free cloud-based platform for other countries to adopt this approach.

Optimizing bioelectromethanosynthesis of CO2 and membrane fouling mitigation in MECs via in-situ biogas recirculation.

The CO2 bioelectromethanosynthesis via two-chamber microbial electrolysis cell (MEC) holds tremendous potential to solve the energy crisis and mitigate the greenhouse gas emissions. However, the membrane fouling is still a big challenge for CO2 bioelectromethanosynthesis owing to the poor proton diffusion across membrane and high inter-resistance. In this study, a new MEC bioreactor with biogas recirculation unit was designed in the cathode chamber to enhance secondary-dissolution of CO2 while mitigating the contaminant adhesion on membrane surface. Biogas recirculation improved CO2 re-dissolution, reduced concentration polarization, and facilitated the proton transmembrane diffusion. This resulted in a remarkable increase in the cathodic methane production rate from 0.4 mL/L·d to 8.5 mL/L·d. A robust syntrophic relationship between anodic organic-degrading bacteria (Firmicutes 5.29%, Bacteroidetes 25.90%, and Proteobacteria 6.08%) and cathodic methane-producing archaea (Methanobacterium 65.58%) enabled simultaneous organic degradation, high CO2 bioelectromethanosynthesis, and renewable energy storage.

Green synthesis of Fe3O4@ceramsite from sludge improving anaerobic digestion performance of waste activated sludge.

Anaerobic digestion (AD) is a promising technique for waste management, which can achieve sludge stabilization and energy recovery. This study successfully prepared Fe3O4@ceramsite from WAS and applied it as an additive in sludge digestion, aiming to improve the conversion of organics to biomethane efficiency. Results showed that after adding the Fe3O4@ceramsite, the methane production was enhanced by 34.7% compared with the control group (88.0 ± 0.1 mL/g VS). Further mechanisms investigation revealed that Fe3O4@ceramsite enhanced digesta stability by strong buffering capacity, improved sludge conductivity, and promoted Fe (III) reduction. Moreover, Fe3O4@ceramsite has a larger surface area and better porous structure, which also facilitated AD performance. Microbial community analysis showed that some functional anaerobes related to AD such as Spirochaeta and Smithella were enriched with Fe3O4@ceramsite treatment. Potential syntrophic metabolisms between syntrophic bacteria (Syntrophomonas, associated with DIET) and methanogens were also detected in the Fe3O4@ceramsite treatment AD system.

Sulfur cycling likely obscures dynamic biologically-driven iron redox cycling in contemporary methane seep environments.

Deep-sea methane seeps are amongst the most biologically productive environments on Earth and are often characterised by stable, low oxygen concentrations and microbial communities that couple the anaerobic oxidation of methane to sulfate reduction or iron reduction in the underlying sediment. At these sites, ferrous iron (Fe2+) can be produced by organoclastic iron reduction, methanotrophic-coupled iron reduction, or through the abiotic reduction by sulfide produced by the abundant sulfate-reducing bacteria at these sites. The prevalence of Fe2+in the anoxic sediments, as well as the availability of oxygen in the overlying water, suggests that seeps could also harbour communities of iron-oxidising microbes. However, it is unclear to what extent Fe2+ remains bioavailable and in solution given that the abiotic reaction between sulfide and ferrous iron is often assumed to scavenge all ferrous iron as insoluble iron sulfides and pyrite. Accordingly, we searched the sea floor at methane seeps along the Cascadia Margin for microaerobic, neutrophilic iron-oxidising bacteria, operating under the reasoning that if iron-oxidising bacteria could be isolated from these environments, it could indicate that porewater Fe2+ can persist is long enough for biology to outcompete pyritisation. We found that the presence of sulfate in our enrichment media muted any obvious microbially-driven iron oxidation with most iron being precipitated as iron sulfides. Transfer of enrichment cultures to sulfate-depleted media led to dynamic iron redox cycling relative to abiotic controls and sulfate-containing cultures, and demonstrated the capacity for biogenic iron (oxyhydr)oxides from a methane seep-derived community. 16S rRNA analyses revealed that removing sulfate drastically reduced the diversity of enrichment cultures and caused a general shift from a Gammaproteobacteria-domainated ecosystem to one dominated by Rhodobacteraceae (Alphaproteobacteria). Our data suggest that, in most cases, sulfur cycling may restrict the biological "ferrous wheel" in contemporary environments through a combination of the sulfur-adapted sediment-dwelling ecosystems and the abiotic reactions they influence.

Enhancing physicochemical, rheological properties, and in vitro rumen fermentation of starch with Melastoma candidum D. Don fruit extract.

The utilization of polyphenol-modified starch in ruminants has not undergone extensive exploration. This study aimed to investigate the impact of the complex formed between starch and Melastoma candidum D. Don fruit extract on physicochemical properties, phenol release kinetics in various buffers simulating the gastrointestinal tract, methane production, and post-rumen digestibility. The interaction between starch and M. candidum D. Don fruit extract significantly (p < 0.001) increased resistant starch and particle size diameter. The maximum phenolic release from complex between starch and M. candidum D. Don fruit extract, due to gastrointestinal tract-simulated buffers, ranged from 22.96 to 34.60 mg/100 mg tannic acid equivalent. However, rumen and abomasum-simulated buffers released more phenolic content, whereas the intestine-simulated buffer showed higher antioxidant activity (ferric ion-reducing antioxidant power). Furthermore, complex between starch and M. candidum D. Don fruit extract significantly decreased dry matter rumen digestibility (p < 0.001) and maximum methane gas production (p < 0.001).

Metal-(Acyclic Diaminocarbene) Complexes Demonstrate Nanomolar Antiproliferative Activity against Triple-Negative Breast Cancer.

Invited for the cover of this issue are Tatiyana Serebryanskaya, Mikhail Kinzhalov and co-workers at St. Petersburg State University, the Research Institute for Physical Chemical Problems, Belarusian State University, Togliatti State University and Blokhin National Medical Research Center of Oncology. The image depicts the shield of Pallas Athena with the structure of a palladium carbene complex that protects against triple-negative breast cancer. Read the full text of the article at 10.1002/chem.202400101.

Contrasting impacts of fertilization on topsoil and subsoil greenhouse gas fluxes in a thinned Chinese fir plantation.

Globally, forest soils are considered as important sources and sinks of greenhouse gases (GHGs). However, most studies on forest soil GHG fluxes are confined to the topsoils (above 20 cm soil depths), with only very limited information being available regarding these fluxes in the subsoils (below 20 cm soil depths), especially in managed forests. This limits deeper understanding of the relative contributions of different soil depths to GHG fluxes and global warming potential (GWP). Here, we used a concentration gradient-based method to comprehensively investigate the effects of thinning intensity (15% vs. 35%) and nutrient addition (no fertilizer vs. NPK fertilizers) on soil GHG fluxes from the 0-40 cm soil layers at 10 cm depth intervals in a Chinese fir (Cunninghamia lanceolata) plantation. Results showed that forest soils were the sources of CO2 and N2O, but the sinks of CH4. Soil GHG fluxes decreased with increasing soil depth, with the 0-20 cm soil layers identified as the dominant producers of CO2 and N2O and consumers of CH4. Thinning intensity did not significantly affect soil GHG fluxes. However, fertilization significantly increased CO2 and N2O emissions and CH4 uptake at 0-20 cm soil layers, but decreased them at 20-40 cm soil layers. This is because fertilization alleviated microbial N limitation and decreased water filled pore space (WFPS) in topsoils, while it increased WFPS in subsoils, ultimately suggesting that soil WFPS and N availability (especially NH4+-N) were the predominant regulators of GHG fluxes along soil profiles. Generally, there were positive interactive effects of thinning and fertilization on soil GHG fluxes. Moreover, the 35% thinning intensity without fertilization had the lowest GWP among all treatments. Overall, our results suggest that fertilization may not only cause depth-dependent effects on GHG fluxes within soil profiles, but also impede efforts to mitigate climate change by promoting GHG emissions in managed forest plantations.

Metagenomics reveals the variations in functional metabolism associated with greenhouse gas emissions during legume-vegetable rotation process.

Legume-based rotation is commonly recognized for its mitigation efficiency of greenhouse gas (GHG) emissions. However, variations in GHG emission-associated metabolic functions during the legume-vegetable rotation process remain largely uncharacterized. Accordingly, a soybean-radish rotation field experiment was designed to clarify the responses of microbial communities and their GHG emission-associated functional metabolism through metagenomics. The results showed that the contents of soil organic carbon and total phosphorus significantly decreased during the soybean-radish process (P < 0.05), while soil total potassium content and bacterial richness and diversity significantly increased (P < 0.05). Moreover, the predominant bacterial phyla varied, with a decrease in the relative abundance of Proteobacteria and an increase in the relative abundance of Acidobacteria, Gemmatimonadetes, and Chloroflexi. Metagenomics clarified that bacterial carbohydrate metabolism substantially increased during the rotation process, whereas formaldehyde assimilation, methanogenesis, nitrification, and dissimilatory nitrate reduction decreased (P < 0.05). Specifically, the expression of phosphate acetyltransferase (functional methanogenesis gene, pta) and nitrate reductase gamma subunit (functional dissimilatory nitrate reduction gene, narI) was inhibited, indicating of low methane production and nitrogen metabolism. Additionally, the partial least squares path model revealed that the Shannon diversity index was negatively correlated with methane and nitrogen metabolism (P < 0.01), further demonstrating that the response of the soil bacterial microbiome responses are closely linked with GHG-associated metabolism during the soybean-radish rotation process. Collectively, our findings shed light on the responses of soil microbial communities to functional metabolism associated with GHG emissions and provide important insights to mitigate GHG emissions during the rotational cropping of legumes and vegetables.

Impact of using glucose as a sole carbon source to analyze the effect of biochar on the kinetics of biomethane production.

The adaptation of biochar in anaerobic digestion (AD) positively influences the conversion of substrate to biomethane and promotes system stability. This study investigated the influence of biochar (BC) doses (0 to 8 g/L) on the Biochemical Methane Potential (BMP) of glucose during a 60-day AD in a mesophilic batch-type reactor. The first 6.5 weeks of the experimentation were dedicated to the microorganism's adaptation to the biochar and degradation of organics from the used inoculum (3 phases of the glucose feeding). The last 2 weeks (4th phase of glucose feeding) represented the assumption, that glucose is the sole carbon source in the system. A machine learning model based on the autoregressive integrated moving average (ARIMA) method was used to model the cumulative BMP. The results showed that the BMP increased with the amount of BC added. The highest BMP was obtained at a dose of 8 g/L, with a maximum cumulative BMP of 390.33 mL CH4/g-VS added. Likewise, the system showed stability in the pH (7.17 to 8.17). In contrast, non-amended reactors produced only 135.06 mL CH4/g-VS and became acidic at the end of the operation. Reducing the influence of carbon from inoculum, sharpened the positive effect of BC on the kinetics of biomethane production from glucose.

Greenhouse gas emissions from on-site sanitation systems: A systematic review and meta-analysis of emission rates, formation pathways and influencing factors.

Onsite sanitation systems (OSS) are significant sources of greenhouse gases (GHG) including carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). While a handful of studies have been conducted on GHG emissions from OSS, systematic evaluation of literature on this subject is limited. Our systematic review and meta-analysis provides state-of-the- art information on GHG emissions from OSS and identifies novel areas for investigation. The paper analyzes GHG emission rates from different OSS, the influence of various design, operational, and environmental factors on emission rates and proffers mitigation measures. Following the Preferred Reporting Items for Systematic reviews and Meta-analysis (PRISMA) guidelines, we identified 16 articles which quantified GHG emissions from OSS. Septic tanks emit substantial amounts of CO2 and CH4 ranging from 1.74 to 398.30 g CO2/cap/day and 0.06-110.13 g CH4/cap/day, respectively, but have low N2O emissions (0.01-0.06 g N2O/cap/day). CH4 emissions from pit latrines range from 0.77 to 20.30 g CH4/cap/day N2O emissions range from 0.76 to 1.20 gN2O/cap/day. We observed statistically significant correlations (p < 0.05) between temperature, biochemical oxygen demand, chemical oxygen demand, dissolved oxygen, storage period, and GHG emissions from OSS. However, no significant correlation (p > 0.05) was observed between soil volumetric water content and CO2 emissions. CH4 emissions (expressed as CO2 equivalents) from OSS estimated following Intergovernmental Panel for Climate Change (IPCC) guidelines were found to be seven times lower (90.99 g CO2e/cap/day) than in-situ field emission measurements (704.7 g CO2e/cap/day), implying that relying solely on IPCC guidelines may lead to underestimation of GHG emission from OSS. Our findings underscore the importance of considering local contexts and environmental factors when estimating GHG emissions from OSS. Plausible mitigation measures for GHG emissions from OSS include converting waste to biogas in anaerobic systems (e.g. biogas), applying biochar, and implementing mitigation policies that equally address inequalities in sanitation service access. Future research on GHG from OSS should focus on in-situ measurements of GHGs from pit latrines and other common OSS in developing countries, understanding the fate and transport of dissolved organics like CH4 in OSS effluents and impacts of microbial communities in OSS on GHG emissions. Addressing these gaps will enable more holistic and effective management of GHG emissions from OSS.

Characterization and evaluation of the anaerobic treatability of a dairy wastewater.

In this study, the characteristics, anaerobic treatability, and energy potential of wastewater samples taken from a dairy products industry were investigated. It was determined that the wastewater has a high organic load (COD = 2800 mg O2/L) and a large proportion of this load is biodegradable. The biochemical methane potential (BMP) value of wastewater was measured as 1118.71 ± 122 ml CH4/L. Volatile solids (VS) removal of 67.25 ± 4.98% was achieved during batch tests and the obtained methane yield was calculated as 411.59 ± 22.8 ml CH4/g VS. Peak methane formation rate and lag time of microorganisms were determined as 163.42 ± 3.83 ml CH4/g VS d and 0.584 ± 0.023 d, respectively. Rate constant for the first-order kinetic model was 0.384 ± 0.072 d-1. The volatile fatty acid (VFA) yield was measured as 155.19 mg COD/g VSS. It was concluded that the wastewater can be treated anaerobically without any inhibition and it has great energy potential. PRACTITIONER POINTS: Dairy wastewater has a large organic load and that most of the organics can be easily biodegradable. Although there are many components considered to be toxic for anaerobic treatment in wastewater, they were found to be very under the inhibition thresholds and did not pose any risk of toxicity. At a satisfactory level, organic matter removal and methane formation were observed in batch anaerobic tests. A rapid microbial adaptation was achieved and the system reached equilibrium in a short time without any acid accumulation. The electrical and caloric energy potentials of the obtained methane gas were calculated as 2.12 and 4.25 kWh/m3, respectively.

Driving an ecological transformation: unleashing multi-objective optimization for hydrogenated compressed natural gas in a decarbonization perspective.

Integrating hydrogen with CNG is crucial for carbon neutrality and environmental goals, as it enhances flame temperature, reduces emissions, and combats global warming. This study employs the CHEMKIN tool to examine combustion characteristics, including adiabatic flame temperature, mole fraction, normalization, and production rate, in H2-CNG mixtures under various atmospheric and operating conditions. Blending 50% hydrogen with CNG results in significant changes, including a temperature increase from 2322 to 2344 K when the hydrogen content is at 50%. The introduction of hydrogen causes a notable 30-35% reduction in CH4 mole fraction and a simultaneous 26.6% increase in C-normalized CH4 production. Free radicals play a role in affecting CO2 production, with the normalization of CO species increasing from 0.068 to 0.087. Through NSGA-II multi-objective optimization methods, the study identifies a 50% H2-50% CNG blend as the optimal choice for thermal and environmental performance. The study explores the energy and environmental impacts of incorporating hydrogen into CNG-air combustion, with a specific focus on the effects of 50% H2 blending with CNG. Hydrogen blending benefits from elevated adiabatic flame temperature and increased free radical formation, ultimately leading to emission reduction. These findings firmly establish H2-CNG mixtures as promising environmentally friendly alternatives with superior combustion characteristics. Their potential paves the way for significant progress towards achieving carbon neutrality and combating climate change through cleaner, more efficient fuel options.

Assessment of the in situ biomethanation potential of a deep aquifer used for natural gas storage.

The dihydrogen (H2) sector is undergoing development and will require massive storage solutions. To minimize costs, the conversion of underground geological storage sites, such as deep aquifers, used for natural gas storage into future underground hydrogen storage sites is the favored scenario. However, these sites contain microorganisms capable of consuming H2, mainly sulfate reducers and methanogens. Methanogenesis is, therefore expected but its intensity must be evaluated. Here, in a deep aquifer used for underground geological storage, 17 sites were sampled, with low sulfate concentrations ranging from 21.9 to 197.8 µM and a slow renewal of formation water. H2-selected communities mainly were composed of the families Methanobacteriaceae and Methanothermobacteriaceae and the genera Desulfovibrio, Thermodesulfovibrio, and Desulforamulus. Experiments were done under different conditions, and sulfate reduction, as well as methanogenesis, were demonstrated in the presence of a H2 or H2/CO2 (80/20) gas phase, with or without calcite/site rock. These metabolisms led to an increase in pH up to 10.2 under certain conditions (without CO2). The results suggest competition for CO2 between lithoautotrophs and carbonate mineral precipitation, which could limit microbial H2 consumption.

A comparative assessment of biomethane potential of fresh fecal matter and fecal sludge and its correlation with malodor.

Comprehensive and proper management of fecal sludge (FS) is an ongoing concern in many nations. Decentralized fecal sludge treatment plants (FSTPs) are effective in this regard; however, many have experienced strong public opposition based partly on suspicion of malodor. Fecal sludge and freshly generated fecal matter (FM) samples from various FSTPs were collected, characterized, and investigated for biomethane potential. The homogenized samples were anaerobically digested for 28 days. Digestion successfully reduced total suspended solids, biochemical oxygen demand, and threshold odor number values of 97,350-97,420 mg/l, 43,230-43,260 mg/l, and 130-150 for FM, to 49,500-49,650 mg/l, 23,760-23,850 mg/l, and 3338, respectively, for FS samples. The comprehensive gas yield from Bhongir, Boduppal, and Shadnagar FS samples was 40, 55, and 31 ml, respectively. In contrast, cumulative gas generation from the FM was 26,361 ml. Digestion of FS samples also reduced concentrations of volatile solids and coliforms by 66-72% and 99%, respectively. Characterization of gas samples revealed methane and carbon dioxide concentrations as 56% and 22% for FM, and 0.4% and 61% for FS samples, respectively. Hydrogen sulfide and ammonia gas were absent in FS samples, dispelling common societal misconceptions of FSTPs being associated with malodor.

Carbene Footprinting Directs Design of Genetically Encoded Proximity-Reactive Protein Binders.

Genetically encoding proximal-reactive unnatural amino acids (PrUaas), such as fluorosulfate-l-tyrosine (FSY), into natural proteins of interest (POI) confer the POI with the ability to covalently bind to its interacting proteins (IPs). The PrUaa-incorporated POIs hold promise for blocking undesirable POI-IP interactions. Selecting appropriate PrUaa anchor sites is crucial, but it remains challenging with the current methodology, which heavily relies on crystallography to identify the proximal residues between the POIs and the IPs for the PrUaa anchorage. To address the challenge, here, we propose a footprinting-directed genetically encoded covalent binder (footprinting-GECB) approach. This approach employs carbene footprinting, a structural mass spectrometry (MS) technique that quantifies the extent of labeling of the POI following the addition of its IP, and thus identifies the responsive residues. By genetically encoding PrUaa into these responsive sites, POI variants with covalent bonding ability to its IP can be produced without the need for crystallography. Using the POI-IP model, KRAS/RAF1, we showed that engineering FSY at the footprint-assigned KRAS residue resulted in a KRAS variant that can bind irreversibly to RAF1. Additionally, we inserted FSY at the responsive residue in RAF1 upon footprinting the oncogenic KRASG12D/RAF1, which lacks crystal structure, and generated a covalent binder to KRASG12D. Together, we demonstrated that by adopting carbene footprinting to direct PrUaa anchorage, we can greatly expand the opportunities for designing covalent protein binders for PPIs without relying on crystallography. This holds promise for creating effective PPI inhibitors and supports both fundamental research and biotherapeutics development.

Towards a circular bioeconomy to produce methane by co-digestion of coffee and brewery waste using a mixture of anaerobic granular sludge and cattle manure as inoculum.

Coffee processing wastes, such as solid (pulp and husk) and wastewater, co-digested with industrial brewery wastewater, serve as excellent substrates for generating methane in the anaerobic digestion process. This study compared methane production using different compositions of cattle manure (CM) and granular sludge from an Upflow Anaerobic Sludge Blanket (UASB) reactor used in poultry wastewater treatment (GS). Four anaerobic batch reactors (500 mL) were assembled, A (50% CM and 50% GS), B (60% CM and 40% GS), C (70% CM and 30% of GS) and D (60% CM and 40% GS). Equal concentrations of substrates were added to all reactors: pulp and husk pretreated by hydrothermolysis (1 g L-1), coffee (10 g COD L-1) and brewery (1.5 g COD L-1) wastewaters. Assays A, B and C were supplemented with 2 g L-1 of yeast extract, except for assay D. The reactors were operated at 37 °C and pH 7.0. In assay B, the highest CH4 production of 759.15 ± 19.20 mL CH4 g-1 TS was observed, possibly favored by the synergistic interactions between cellulolytic bacteria Christensenellaceae_R-7_group and Methanosaeta archaea, as inferred by genes encoding enzymes related to acetoclastic methanogenesis (acetyl-CoA synthetase). Consequently, the electricity production potential of assay B (45614.08 kWh-1 year-1) could meet the energy demand of a farm producing coffee and beer, contributing to a positive energy balance concerning methane generation.

The flow pattern effects of hydrodynamic cavitation on waste activated sludge digestibility.

The disintegration of raw sludge is of importance for enhancing biogas production and facilitates the degradation of substrates for microorganisms so that the efficiency of digestion can be increased. In this study, the effect of hydrodynamic cavitation (HC) as a pretreatment approach for waste activated sludge (WAS) was investigated at two upstream pressures (0.83 and 1.72 MPa) by using a milli-scale apparatus which makes sludge pass through an orifice with a restriction at the cross section of the flow. The HC probe made of polyether ether ketone (PEEK) material was tested using potassium iodide solution and it was made sure that cavitation occurred at the selected pressures. The analysis on chemical effects of HC bubbles collapse suggested that not only cavitation occurred at low upstream pressure, i.e., 0.83 MPa, but it also had high intensity at this pressure. The pretreatment results of HC implementation on WAS were also in agreement with the chemical characterization of HC collapse. Release of soluble organics and ammonium was observed in the treated samples, which proved the efficiency of the HC pretreatment. The methane production was improved during the digestion of the treated samples compared to the control one. The digestion of treated WAS sample at lower upstream pressure (0.83 MPa) resulted in higher methane production (128.4 mL CH4/g VS) compared to the treated sample at higher upstream pressure (119.1 mL CH4/g VS) and control sample (98.3 mL CH4/g VS). Thus, these results showed that the HC pretreatment for WAS led to a significant increase in methane production (up to 30.6%), which reveals the potential of HC in full-scale applications.

From grass to gas and beyond: Anaerobic digestion as a key enabling technology for a residual grass biorefinery.

Roadside grass clippings hold potential as a sustainable source of bioenergy as they do not compete with crops for land use, and are only partially utilized for low-value applications. In this study, we proposed using roadside grass as a sole feedstock for anaerobic digestion (AD) in three different settings, and assessed the potential of producing biomaterials and fertilizers from grass-based digestate. Wet continuous digestion at pilot scale and dry batch digestion at pilot and large scales resulted in biogas yields up to 700 Nm3.t-1 DOM with a methane content of 49-55 %. Despite promising results, wet AD had operational problems such as clogging and poor mixing; once upscaled, the dry digestion initially also presented an operational problem with acidification, which was overcome by the second trial. Digested grass fibers from the pilot dry AD were processed into biomaterials and performed similarly or better than the undigested fibers, while around 20 % performance reduction was observed when compared to reference wood fibers. A mass balance indicated reduced fiber recovery when higher biogas production was obtained. The liquid fraction from the pilot dry AD was characterized for its nutrient content and used as a biofertilizer in another study. In contrast, the leachate collected from the large-scale dry AD had a low nitrogen content and high chloride content that could hinder its further use. Finally, a regional market analysis was conducted showing that the biocomposites produced with the available grass fibers could substitute at least half of the current European market based on our results.