Succession from acetoclastic to hydrogenotrophic microbial community during sewage sludge anaerobic digestion for bioenergy production.

To assess microbial dynamics during anaerobic digestion (AD) of sewage sludge (SWS) from a municipal Wastewater Treatment Plant (WWTP), a Biochemical Methane Potential (BMP) assay at 37 °C under mono-digestion conditions was conducted. Utilizing the Illumina MiSeq platform, 16S ribosomal RNA (rRNA) gene sequencing unveiled a core bacterial community in the solid material, showcasing notable variations in profiles. The research investigates changes in microbial communities and metabolic pathways to understand their impact on the efficiency of the digestion process. Prior to AD, the relative abundance in SWS was as follows: Proteobacteria > Bacteroidota > Actinobacteriota. Post-AD, the relative abundance shifted to Firmicutes > Synergistota > Proteobacteria, with Sporanaerobacter and Clostridium emerging as dominant genera. Notably, the methanogenic community underwent a metabolic pathway shift from acetoclastic to hydrogenotrophic in the lab-scale reactors. At the genus level, Methanosaeta, Methanolinea, and Methanofastidiosum predominated initially, while post-AD, Methanobacterium, Methanosaeta, and Methanospirillum took precedence. This metabolic transition may be linked to the increased abundance of Firmicutes, particularly Clostridia, which harbor acetate-oxidizing bacteria facilitating the conversion of acetate to hydrogen.

Anaerobic digestates in agricultural soils: A systematic review of their effects on antibiotic resistance genes.

Tackling the dissemination of antibiotic resistance is one of the main global challenges. Manures from animal production are a recognized source of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) requiring appropriate treatment methods. One of the main approaches for manure treatment is anaerobic digestion (AD). Meta-analyses have demonstrated that AD can significantly reduce the load of ARGs. However, antibiotics, ARGs and MGEs still remain in the final product (digestate). A sustainable agricultural use of digestates under the One Health framework requires wide assessments of their effects in the soil resistome. The objective of this review was to present the state of the art of digestate effects on ARGs of agricultural soils, focusing exclusively on digestates from animal manures. A systematic review was conducted. The examination of the resulting literature indicated that although temporal decays are observed for a variety of ARGs in single-application and repeated-applications experiments, for certain ARGs the pre-treatment or control levels are not restored. However, the low number of studies and the heterogeneous experimental conditions preclude a clear understanding of the fate of ARGs in soil and their risk for agroecosystems. The inclusion of multiple MGEs and the assessment of the long-term influence of digestates on soil properties and microbial communities could be keystones for a better understanding of the risks associated with digestate-induced changes in the soil resistome.

Combined use of digestate and inorganic fertilizer alleviates the burden of class 1 integrons in perennial ryegrass rhizosphere without compromising aerial biomass production.

Antimicrobial resistance (AMR) is one of the main global health challenges. Anaerobic digestion (AD) can significantly reduce the burden of antibiotic resistance genes (ARGs) in animal manures. However, the reduction is often incomplete. The agronomic use of digestates requires assessments of their effects on soil ARGs. The objective of this study was to assess the effect of digestate on the abundance of ARGs and mobile genetic elements (MGEs) in the rhizosphere of ryegrass (Lolium perenne L.) and to determine whether half-dose replacement of digestate with urea (combined fertilizer) can be implemented as a safer approach while maintaining a similar biomass production. A greenhouse assay was conducted during 190 days under a completely randomized design with two experimental factors: fertilizer type (unfertilized control and fertilized treatments with equal N dose: digestate, urea and combined fertilizer) and sampling date (16 and 148 days after the last application). The results indicated that the digestate significantly increased the abundance of clinical class 1 integrons (intI1 gene) relative to the unfertilized control at both sampling dates (P < 0.05), while the combined fertilizer only increased them at the first sampling. Sixteen days after completing the fertilization scheme only the combined fertilizer and urea significantly increased the biomass production relative to the control (P < 0.05). Additionally, by the end of the assay, the combined fertilizer showed significantly lower levels of the macrolide-resistance gene ermB than digestate and a cumulative biomass similar to urea or digestate. Overall, the combined fertilizer can alleviate the burden of integrons and ermB while simultaneously improving biomass production.

Compounding one problem with another? A look at biodegradable microplastics.

Environmental concerns about microplastics (MPs) have motivated research of their sources, occurrence, and fate in aquatic and soil ecosystems. To mitigate the environmental impact of MPs, biodegradable plastics are designed to naturally decompose, thus reducing the amount of environmental plastic contamination. However, the environmental fate of biodegradable plastics and the products of their incomplete biodegradation, especially micro-biodegradable plastics (MBPs), remains largely unexplored. This comprehensive review aims to assess the risks of unintended consequences associated with the introduction of biodegradable plastics into the environment, namely, whether the incomplete mineralization of biodegradable plastics could enhance the risk of MBPs formation and thus, exacerbate the problem of their environmental dispersion, representing a potentially additional environmental hazard due to their presumed ecotoxicity. Initial evidence points towards the potential for incomplete mineralization of biodegradable plastics under both controlled and uncontrolled conditions. Rapid degradation of PLA in thermophilic industrial composting contrasts with the degradation below 50 % of other biodegradables, suggesting MBPs released into the environment through compost. Moreover, degradation rates of <60 % in anaerobic digestion for polymers other than PLA and PHAs suggest a heightened risk of MBPs in digestate, risking their spread into soil and water. This could increase MBPs and adsorbed pollutants' mobilization. The exact behavior and impacts of additive leachates from faster-degrading plastics remain largely unknown. Thus, assessing the environmental fate and impacts of MBPs-laden by-products like compost or digestate is crucial. Moreover, the ecotoxicological consequences of shifting from conventional plastics to biodegradable ones are highly uncertain, as there is insufficient evidence to claim that MBPs have a milder effect on ecosystem health. Indeed, literature shows that the impact may be worse depending on the exposed species, polymer type, and the ecosystem complexity.

Design of experiments to evaluate pH and temperature parameters with different inoculums in domestic biodigester.

The comprehensive management of organic urban solid waste is a concern due to its direct and indirect impact on the environment. Anaerobic Digestion (AD) has been recognized as an alternative and environmentally friendly technology for waste disposal, converting them into organic fertilizers and renewable energy. This research presents an experiment involving four reactors fed with household organic waste, three inoculated with canine, goat, and rabbit manure, and one without inoculum. The experiment was observed for 30 consecutive days to analyze the pH and temperature parameters involved in the AD process in domestic reactors. Statistical methodology, including one-way analysis of variance for assessing the effect of the type of inoculum, Tukey's simultaneous confidence intervals for mean differences, and 90 % confidence intervals for µ in temperature and manure, was utilized. Additionally, main effects analysis of the factors of average temperature and pH were conducted. The results of the one-factor experiment show that the type of inoculum does not significantly influence the variation in pH, while temperature remains relatively stable throughout the AD process. However, the analysis of main effects indicates that goat manure tends to stabilize the temperature with minimal variation, whereas variation is more heterogeneous in the other experiments.

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.

Microaeration promotes volatile siloxanes conversion to methane and simpler monomeric products.

The ubiquitous use of volatile siloxanes in a myriad of product formulations has led to a widespread distribution of these persistent contaminants in both natural ecosystems and wastewater treatment plants. Microbial degradation under microaerobic conditions is a promising approach to mitigate D4 and D5 siloxanes while recovering energy in wastewater treatment plants. This study examined D4/D5 siloxanes biodegradation under both anaerobic and microaerobic conditions ( [Formula: see text]  = 0, 1, 3 %) using wastewater sludge. Results show that the use of microaeration in an otherwise strictly anaerobic environment significantly enhances siloxane conversion to methane. 16S rRNA gene sequencing identified potential degraders, including Clostridium lituseburense, Clostridium bifermentans and Synergistales species. Furthermore, chemical analysis suggested a stepwise siloxane conversion preceding methanogenesis under microaerobic conditions. This study demonstrates the feasibility of microaerobic siloxane biodegradation, laying groundwork for scalable removal technologies in wastewater treatment plants, ultimately highlighting the importance of using bio-based approaches in tackling persistent pollutants.

Toilet effluent separation and brown water treatment: Survey and initial feasibility testing in Mexico.

Separation of domestic effluents at the source and the utilization of low-flush toilets offer alternative approaches for developing efficient wastewater treatment systems while promoting energy generation through anaerobic digestion. This study focused on assessing toilet usage in Mexico and exploring the potential of anaerobic co-digestion of brown water (feces) and toilet paper as influential factors in wastewater treatment systems. A survey was conducted on a representative sample of Mexicans to gather information on toilet usage frequency, toilet paper use and disposal practices, as well as the type and quantity of commercial disinfectants and pharmaceutical compounds they use or consume. The survey revealed that per capita toilet paper consumption is 2.9 kg annually, that 58 % of respondents do not dispose used paper in the toilet, and that about 47 % use two to three cleaning and disinfection products. Notably, 97 % of the sampled Mexican population expressed a willingness to transition to more eco-friendly toilet options. Subsequently, in a second step, the anaerobic co-digestion of brown water with toilet paper was evaluated, demonstrating a relatively high production of volatile fatty acids but low methane production. This suggests an efficient hydrolysis/acidogenesis process coupled with restrained methanogenesis, probably due to pH decrease caused by acidogenesis. This study underscores that toilet paper and brown water are potential suitable substrates for anaerobic co-digestion. Furthermore, it sheds light on the behaviors of Mexican society regarding bathroom use and cleaning, contributing to the establishment of foundations for wastewater treatment systems with effluent separation at the source.

Wet anaerobic digestion of organic fraction of municipal solid waste: experience with long-term pilot plant operation and industrial scale-up.

This paper presents the analysis of a pilot anaerobic digestion plant that operates with organic fraction of municipal solid waste (OFMSW) from a wholesale market and can treat up to 500 kg d-1. The process was monitored for a period of 524 days during which the residue was characterized and the biogas production and methane content were recorded. The organic load rate (OLR) of volatile solids (VS) was 0.89 kg m-3 d-1 and the Hydraulic Retention Time (HRT) was 25 d during the process. The yield was 82 Nm3 tons OFMSW-1 biogas, equivalent to 586 Nm3 tons CH4 VS-1. The results obtained in the pilot plant were used to carry out a technical-economic evaluation of a plant that treats 50 tons of OFMSW from wholesale markets. A production of 3769 Nm3 d-1 of biogas and 2080 Nm3 d-1 of methane is estimated, generating 35.1 MWh d-1 when converted to electricity.

Analysis of biogas production from sewage sludge combining BMP experimental assays and the ADM1 model.

The Anaerobic Digestion Model No. 1 (ADM1) was employed to simulate methane (CH4) production in an anaerobic reactor (AR), and the associated bench-scale biochemical methane potential (BMP) assay, having sewage sludge (SWS) from a municipal wastewater treatment plant (WWTP) as feedstock. The SWS presented the following physical-chemical characteristics: pH (7.4-7.6), alkalinity (2,382 ± 100 mg CaCO3 L-1), tCOD (21,903 ± 1,000 mg L-1), TOC (895 ± 100 mg L-1), TS, TVS, and VSS (2.0%, 1.1%, and 0.8%, respectively). The BMP assay was conducted in six replicates under anaerobic mesophilic conditions (37 ± 0.1°C) for 11 days with a CH4 yield registered of 137.6 ± 6.39 NmL CH4 or 124 ± 6.72 CH4 g-1 VS-1. When the results obtained with the BMP bench-scale reactors were compared to the output generated with computational data by the ADM1 model having as input data the same initial sewage tCOD, similar cumulative CH4 production curves were obtained, indicating the accuracy of the ADM1 model. This approach allowed the characterization of the sludge and estimation of its biogas production potential. The combination of BMP assays, experimental data, and ADM1 model simulations provided a framework for studying anaerobic digestion (AD) processes.

Improving the Continuous Multiple Tube Reactor: an Innovative Bioreactor Configuration with Great Potential for Dark Fermentation Processes.

The continuous multiple tube reactor (CMTR) has been developed as a promising technology to maximize biohydrogen production (BHP) by dark fermentation (DF) by preventing excess biomass accumulation, leading to suboptimum values of specific organic loading rates (SOLR). However, previous experiences failed to achieve stable and continuous BHP in this reactor, as the low biomass retention capacity in the tube region limited controlling the SOLR. This study goes beyond the evaluation of the CMTR for DF by inserting grooves in the inner wall of the tubes to ensure better cell attachment. The CMTR was monitored in 4 assays at 25ºC using sucrose-based synthetic effluent. The hydraulic retention time (HRT) was fixed at 2 h, while the COD varied between 2-8 g L-1 to obtain organic loading rates in the 24 - 96 g COD L-1 d-1. Long-term (90 d) BHP was successfully attained in all conditions due to the improved biomass retention capacity. Optimal values for the SOLR (4.9 g COD g-1 VSS d-1) were observed when applying up to 48 g COD L-1 d-1, in which BHP was maximized. These patterns indicate a favorable balance between biomass retention and washout was naturally achieved. The CMTR looks promising for continuous BHP and is exempt from additional biomass discharge strategies.

Effect of inoculum composition on the microbial community involved in the anaerobic digestion of sugarcane bagasse.

In anaerobic digestion (AD), the choice of inoculum type seems to be relevant for methane production for complex substrates, such as lignocellulosic material. Previous work demonstrated that the addition of fresh manure and ruminal fluid to anaerobic sludge improved methane productivity and kinetics of AD of crude sugarcane bagasse (CSB). Considering that the improvement of methane production could be a result of a more adapted microbial community, the present study performed the Next Generation Sequencing analysis to identify changes in the microbiome of anaerobic sludge inoculum, resulting from fresh manure and ruminal fluid addition. In comparison with AD performed only with anaerobic sludge inoculum (50:50, U), accumulated methane production was 15% higher with anaerobic sludge plus ruminal fluid inoculum (50:50, UR) and even higher (68%) with anaerobic sludge with fresh bovine manure inoculum (50:50, UFM), reaching the value of 143 NmLCH4.gVS-1. Clostridium species were highly abundant in all inocula, playing an important role during the hydrolysis and fermentation of CSB, and detoxifying potential inhibitors. Microbial composition also revealed the occurrence of Pseudomonas and Anaerobaculum at UFM inoculum that seem to have contributed to the higher methane production rate, mainly due to their hydrolytic and fermentative ability on lignocellulosic substrates. On the other hand, the presence of Alcaligenes might have had a negative effect on methane production due to their ability to perform methane oxidation.

Livestock waste management for energy recovery in Brazil: a life cycle assessment approach.

Livestock farming has exerted intense environmental pressure on our planet. The high emissions to the environment and the high demands of resources for the production process have encouraged the search for decarbonization and circularity in the livestock sector. In this context, the objective of this study was to evaluate and compare the environmental performance of two different uses for biogas generated in the anaerobic digestion of animal waste, either for electricity generation or biomethane. For this purpose, a life cycle assessment approach was applied to evaluate the potential of anaerobic digestion as a management technology for three different livestock wastes, related to beef cattle, dairy, and sheep in the Brazilian animal production context. The results suggest that the treatment scenarios focusing on biomethane generation were able to mitigate the highest percentage of damages (77 to 108%) in the global warming category when compared to the scenarios without the use of anaerobic digestion (3.00·102 to 3.71·103 kgCO2 eq) or in the perspective of electricity generation (mitigation of 74 to 96%). In terms of freshwater eutrophication, the generation of electricity (- 2.17·10-2 to 2.31·10-3 kg P eq) is more favorable than the purification of biogas to biomethane (- 1.73·10-2 to 2.44·10-3 kg P eq), due to the loss of methane in the upgrading process. In terms of terrestrial ecotoxicity, all scenarios are very similar, with negative values (- 1.19·101 to - 7.17·102 kg 1,4-DCB) due to the benefit of nutrient recovery, especially nitrogen, associated with the use of digestate as fertilizer, which was one of the critical points in all scenarios. Based on these results, it is evident that proper management of all stages of the treatment life cycle is the key to decarbonization and circularity in livestock waste management. The biogas use does not present different effects on the environmental performance of the scenarios studied, demonstrating that the purpose should be chosen according to the needs of each plant or management system.

Influence of water electrolysis on hydrolysis and methanogenesis stages of anaerobic digestion at room temperature: Kinetic and metabolic analysis.

Batch cultures were performed to study hydrolysis and methanogenesis in the presence of an electric field at room temperature (i.e., 23 °C). Kinetic and metabolic analyses using RuO2/Ti electrodes were carried out in short reaction times to avoid biofilm formation, allowing the evaluation of the effect of O2 and H2 produced on anaerobic digestion during the imposition of three electric fields: 1.21, 1.45, and 1.64 V/cm. Results highlighted that at 1.21 V/cm, the electrolysis produced 0.0753 mg O2/L·min, where facultative microorganisms consumed 21 % oxygen, enhancing the hydrolysis phase by 52 %. Additionally, methane production was noticeably improved with an activity of 0.89 ± 0.02 g COD-CH4/g VSS·d, meaning 39 % higher than the control. The imposition of an electric field showed promising results since the methanogenic activity at room temperature was very close to the activities observed in conventional reactors at 35 °C.

Organic stabilization and methane production under different organic loading rates in UASB treating swine wastewater.

This study proposes the was to evaluate the stability and methane production with organic load differents in an upflow anaerobic sludge blanket reactor (UASB) treating swine wastewater by methods of multivariate analysis. Four organic loads were used with average hydraulic holding times of one day. The methods of data analysis of linear regression, Pearson correlation, principal component analysis and hierarchical clustering analysis were used for understanding stability and methane production in the reactor. The highest concentrations of bicarbonate alkalinity of 683 mg L-1 CaCO3 and total volatile acids of 1418 mg L-1 HAc with maximum organic loading applied were obtained. The optimal stability conditions occurred at an intermediate and partial alkalinity ratio between 0.24 and 0.25 observed in initial phases with a chemical oxygen demand (COD) removal of 47-57%. Maximum methane production was 9.0 L CH4 d-1 observed with linear regression positive and occurred at the highest applied organic load, corresponding to the highest COD removal efficiency and increased microbial biomass. Positive and negative correlation between functional stability in anaerobic digestion showed regular activity between acids, alkalinity and organic matter removal. This fact was also proven by the analysis of principal components that showed three components responsible for explaining 83.2% of the data variability, and the alkalinity, organic matter influent and organic acids had the greatest effects on the stability of the UASB reactor. Hierarchical clusters detected the formation of five groupings with a similarity of 50.1%, indicating that temperature and pH were variables with unitary influences on data dimensionality.

Role of the hydrolytic-acidogenic phase on the removal of bisphenol A and sildenafil during anaerobic treatment.

This paper presents the main results of the removal of two pharmaceutical and personal care products (PPCPs), bisphenol A (BPA) and sildenafil (SDF), by applying anaerobic biological batch tests. The biomass used was previously acclimatized and the experiment lasted 28 days. The effect of factors such as compound (BPA and SDF), concentration and type of inoculum was assessed, considering the factorial experimental design. The results indicated that evaluated factors did not significantly affect the PPCPs elimination in the evaluated range with a confidence level of 95%. On the other hand, the removal percentages obtained with BPA were mainly related to mechanisms, such as sorption and abiotic reactions. Regarding SDF, biodegradation was the predominant mechanism of removal under the experimental conditions of this study; however, the degradation of SDF was partial, with percentages lower than 43% in the tests with hydrolytic/acidogenic inoculum (H/A) and lower than 41% in the tests with methanogenic inoculum (MET). Finally, these findings indicated that hydrolysis/acidogenesis phase is a main contributor to SDF biodegradation in anaerobic digestion. The study provides a starting point for future research that seeks to improve treatment systems to optimize the removal of pollutants from different water sources.

Integrated production of hydrogen and methane in a dairy biorefinery using anaerobic digestion: Scale-up, economic and risk analyses.

Anaerobic digestion has emerged as the most appealing waste management strategy in biorefineries. Particularly, recent studies have highlighted the energy advantages of waste co-digestion in industrial biorefineries and the use of two-stage systems. However, there are some concerns about moving the system from laboratory testing to industrial scale. One of them is the high level of investment that is required. Therefore, this study carried out a techno-economic analysis (scale-up and energy production, economic and risk analysis, and factorial design) to assess the feasibility of single- and two-stage systems in the treatment of cheese whey and glycerin for the production of hydrogen and methane. Scenarios (S1 to S9) considered thermophilic and mesophilic single and two-stage systems with different applied organic loading rates (OLRA). The analyses of scale-up and energy production revealed that S3 (a thermophilic single-stage system operated at high OLRA 17.3 kg-COD.m-3.d-1) and S9 (a thermophilic-mesophilic two-stage system operated at high OLRA 134.8 kg-COD.m-3.d-1 and 20.5 kg-COD.m-3.d-1, respectively) were more compact and required lower initial investment compared to other scenarios. The risk analysis performed by a Monte Carlo simulation showed low investment risks (10 and 11%) for S3 and S9, respectively, being the electricity sales price, the key determining factor to define whether the project in the baseline scenario will result in profit or loss. Lastly, the factorial design revealed that while the net present value (NPV) is positively impacted by rising inflation and electricity sales price, it is negatively impacted by rising capitalization rate. Such assessments assist in making decisions regarding which system can be fully implemented, the best market circumstances for the investment, and how market changes may favorably or unfavorably affect the NPV and the internal rate of return (IRR).

Implementation of anaerobic digestion for valorizing the organic fraction of municipal solid waste in developing countries: Technical insights from a systematic review.

Anaerobic digestion (AD) as a waste management strategy for the organic fraction of municipal waste (OFMSW) has received attention in developed countries for several decades, leading to the development of large-scale plants. In contrast, AD of OFMSW has only recently drawn attention in developing countries. This systematic review was carried out to investigate the implementation of AD to treat the OFMSW in developing countries, focusing on assessing pilot and full-scale AD plants reported in the last ten years. Studies that met the selection criteria were analyzed and data regarding operating parameters, feedstock characteristics, and biogas, digestate, and energy production were extracted. As outlined in this systematic review, AD plants located in developing countries are mostly one-stage mesophilic systems that treat OFMSW via mono-digestion, almost exclusively with the aim of producing electrical energy. Based on the analysis done throughout this systematic review, it was noted that there is a large difference in the maturity level of AD systems between developing and developed countries, mainly due to the economic capacity of developed countries to invest in sustainable waste management systems. However, the number of AD plants reported in scientific papers is significantly lower than the number of installed AD systems. Research articles regarding large-scale implementation of AD to treat OFMSW in developed countries were analyzed and compared with developing countries. This comparison identified practices used in plants in developed countries that could be utilized in the large-scale implementation and success of AD in developing countries. These practices include exploiting potential products with high market-values, forming partnerships with local industries to use industrial wastes as co-substrates, and exploring different biological and physical pretreatment technologies. Additionally, the analysis of capital and operational costs of AD plants showed that costs tend to be higher for developing countries due to their need to import of materials and equipment from developed countries. Technical, economical, and political challenges for the implementation of AD at a large-scale in developing countries are highlighted.

Granular activated carbon enhances the anaerobic digestion of solid and liquid fractions of swine effluent at different mesophilic temperatures.

OBJECTIVES: This study evaluated the effect of particle size and dosage of granular activated carbon (GAC) on methane production from the anaerobic digestion of raw effluent (RE) of swine wastewater, and the solid (SF) and liquid (LF) fractions. The effect of temperature using the selected size and dosage of GAC was also evaluated. METHODS: 60 mL of swine wastewater were inoculated with anaerobic granular sludge and GAC at different dosages and particle size. The cultures were incubated at different temperatures at 130 rpm. The kinetic parameters from experimental data were obtained using the Gompertz model. RESULTS: The cultures with the LF and GAC (75-150 µm, 15 g/L) increased 1.87-fold the methane production compared to the control without GAC. The GAC at 75-150 µm showed lower lag phases and higher Rmax than the cultures with GAC at 590-600 µm. The cumulative methane production at 45 °C with the RE + GAC was 7.4-fold higher than the control. Moreover, methane production at 45 °C significantly increased with the cultures LF + GAC (6.0-fold) and SF + GAC (2.0-fold). The highest production of volatile fatty acids and ammonium was obtained at 45 °C regardless of the substrate and the addition of GAC contributed to a higher extent than the cultures lacking GAC. In most cases, the kinetic parameters at 30 °C and 37 °C were also higher with GAC. CONCLUSIONS: GAC contributed to improving the fermentative and methanogenesis stages during the anaerobic digestion of fractions, evidenced by an improvement in the kinetic parameters.

Advances, trends and challenges in the use of biochar as an improvement strategy in the anaerobic digestion of organic waste: a systematic analysis.

A recently strategy applied to anaerobic digestion (AD) is the use of biochar (BC) obtained from the pyrolysis of different organic waste. The PRISMA protocol-based review of the most recent literature data from 2011-2022 was used in this study. The review focuses on research papers from Scopus® and Web of Knowledge®. The review protocol used permits to identify 169 articles. The review indicated a need for further research in the following challenges on the application of BC in AD: i) to increase the use of BC in developing countries, which produce large and diverse amounts of waste that are the source of production of this additive; ii) to determine the effect of BC on the AD of organic waste under psychrophilic conditions; iii) to apply tools of machine learning or robust models that allow the process optimization; iv) to perform studies that include life cycle and technical-economic analysis that allow identifying the potential of applying BC in AD in large-scale systems; v) to study the effects of BC on the agronomic characteristics of the digestate once it is applied to the soil and vi) finally, it is necessary to deepen in the effect of BC on the dynamics of nitrogen and microbial consortia that affect AD, considering the type of BC used. In the future, it is necessary to search for new solutions in terms of the transport phenomena that occurs in AD with the use of BC using robust and precise mathematical models at full-scale conditions.