Organic Loading Rate Research Articles

Synergistic Promotion of Direct Interspecies Electron Transfer by Biochar and Fe₃O₄ Nanoparticles to Enhance Methanogenesis in Anaerobic Digestion of Vegetable Waste

When vegetable waste (VW) is used as a sole substrate for anaerobic digestion (AD), the rapid accumulation of volatile fatty acids (VFAs) can impede interspecies electron transfer (IET), resulting in a relatively low biogas production rate. In this study, Chinese cabbage and cabbage were selected as the VW substrates, and four continuous stirred tank reactors (CSTRs) were employed. Different concentrations of biochar-loaded nano-Fe3O4(Fe3O4@BC) (100 mg/L, 200 mg/L, 300 mg/L) were added, and the organic loading rate (OLR) was gradually increased during the AD process. The changes in biogas production rate, VFAs, and microbial community structure in the fermentation tanks were analyzed to identify the optimal dosage of Fe3O4@BC and the maximum OLR. The results indicated that at the maximum OLR of 3.715 g (VS)/L·d, the addition of 200 mg/L of Fe3O4@BC most effectively promoted an increase in the biogas production rate and reduced the accumulation of VFAs compared to the other treatments. Under these conditions, the biogas production rate reached 0.658 L/g (VS). Furthermore, the addition of Fe3O4@BC enhanced both the diversity and abundance of bacteria and archaea. At the genus level, the abundance of Christensenellaceae_R-7_group, Sphaerochaeta, and the archaeal genus Thermovirga was notably increased.

Response of Metabolic Gene Panel to Organic Loading Stress in Propionate-Degrading Methanogenic Anaerobic Digesters

Propionate, a critical intermediate in anaerobic digestion, and its syntrophic removal, is sensitive to stress. To our knowledge, this study investigates for the first time the response of a metabolic gene panel to organic loading rate (OLR) stress in propionate-degrading methanogenic consortia in lab-scale upflow anaerobic sludge blanket (UASB) reactors. The experimental phases included stabilisation (1.4–2.8 g COD/L/day), electroactive enrichment, OLR shock (6 g COD/L/day), and early recovery. Quantitative PCR was used to assess the abundance of key functional genes (16SrRNA, mcrA, pilA, and hgtR). During stabilisation, ~200 mLCH₄/h was produced, the mcrA/16SrRNA ratio was 0.78–2.64, and pilA and hgtR abundances were 1.29–2.27 × 105 and 2.12–4.37 × 104 copies/gVS. Following the OLR shock, methane production ceased entirely, accompanied by a sharp decline in the mcrA/16S ratio (0.08–0.24) and significant reductions in pilA (1.43-log) and hgtR (1.34-log) abundance. Partial recovery of pilA and hgtR abundance (1.19 × 105 and 8.57 × 104) was observed in the control reactor after the early recovery phase. The results highlight the utility of mcrA, 16SrRNA, pilA, and associated ratios, as reliable indicators of OLR stress in lab-scale UASB reactors. This study advances the understanding of molecular stress responses in propionate-degrading methanogenic consortia, focusing on direct interspecies electron transfer in process stability and recovery.

Trace concentrations of graphene oxide and magnetic graphene oxide rescue anaerobic municipal sludge digesters under stress

This study evaluated long-term performance of graphene oxide (GO) and magnetic GO (MGO) nanosheets in semi-continuous-flow anaerobic digestion (AD) of municipal sludge over 230 days. At organic loading rates (OLRs) of 2.6 and 3.4 g chemical oxygen demand (COD)fed/L/day, 20 and 200 mg/L of GO and MGO did not affect AD performance. However, at an OLR of 5.2 g CODfed/L/day, where control digesters failed, 20 and 200 mg/L of GO and MGO sustained biogas yields at 190 mL/g CODfed/day, similar to yields at lower OLRs (2.6 and 3.4 g CODfed/L/day). This performance persisted after thedaily nanosheet replenishment stopped. Improvements were due to enhanced conductivity and microbial syntropy. The results showed a strong correlation with previous biochemical methane potential (BMP) assays, positioning BMPs as a predictive tool for continuous-flow AD performance. Overall, this study demonstrated potential of GO/MGO nanosheets to improve the stability and efficiency of AD systems under stress.

Feasibility of successive hydrogen and methane production: Effects of temperature and organic loads on energy potential and microbial dynamics

This study aims to assess the co-digestion of Cassava Wastewater (CW) and glycerol in a two-stage process using fluidized bed reactors (AFBR), verifying the effect of organic loading rate (OLR) and temperature (mesophilic [SMR] and thermophilic [STR]) in sequential reactors on CH4 production. The OLR ranged from 1.2 to 15 g COD.L−1.d−1 and the hydraulic retention time (HRT) was set at 20 h. The mesophilic sequential reactor (MSR) (average temperature of 30 °C) showed greater tolerance to high OLR and its best MPR was 101.12 mL of CH4.d−1.L−1 h−1, obtained at a OLR of 15 g COD.L−1.d−1). The maximum yield was 341.10 mL of CH4.g−1CODcons, found at the OLR of 1.2 g COD.L−1.d−1. The sequential thermophilic reactor (STR) showed the maximum yield and MPR of 333.03 mL of CH4.g−1CODcons (1.2 g COD.L−1.d−1) and 58.84 mL of CH4.d− 1.L−1 h−1 (12 g COD.L−1.d−1), respectively. Through the massive sequencing analysis of the 16S rRNA gene, it was possible to observe a greater diversity of microorganisms in the TSR than in the MSR. A predominance of acetoclastic microorganisms was observed, with the genera Methanobacterium, Methanosarcina and Methanobrevibacter being the most abundant in both reactors. The two-stage system composed of mesophilic acidogenic reactor + MSR was more suitable for the co-digestion of CW and glycerol than the acidogenic reactor + TSR. These results support the notion of standard operating conditions at the industrial plant, where the cassava processing process is carried out at room temperature (25–30 °C).

Investigating the Influence of Organic Loading Rate, Temperature and Stirring Speed on Biogas Production Using Agricultural Waste in South Africa

Biogas production offers an alternate method for managing agricultural waste and contributes to sustainable renewable energy generation. Anaerobic digestion (AD) enables the transformation of organic waste, including agricultural substrates, into biogas, mostly consisting of methane, carbon dioxide, and trace gases such as ammonia and hydrogen sulphide. The objective of this study was to employ a 30 L semi-continuous stirred tank reactor to evaluate the effects of organic loading rate, temperature, and speed of stirring on biogas production. The reactor was inoculated with 8.6 L and filled with 11.4 L of a mixed substrate including cattle manure, potato waste, potato starch waste, fruit waste, and expired dry dog food. The reactor was evaluated with organic loading rates (OLRs) of 11.2, 12.2, and 13.2 g VS/L d, and stirring speeds of 25.5, 35.5, and 45.5 rpm. The results indicated that the maximum yield was 12.2 g VS/L d at 45.5 rpm, and in thermophilic conditions, the biogas yield surpassed that of mesophilic conditions, measuring 105,860 NmL/g VS compared to 69,800 NmL/g VS. This study emphasises the significance of optimising operational parameters to improve biogas output, thereby contributing to sustainable energy resources and advancing the Sustainable Development Goals (SDGs).

Anaerobic membrane bioreactor (AnMBR) with external ultrafiltration membrane for the treatment of sugar beet vinasse.

Vinasse, a by-product of ethanol production, is generated at significant rates. While rich in nutrients such as calcium, magnesium, and potassium, its high solids, organic matter, acidity, and sulfate content pose challenges when disposed directly on soil, necessitating treatment. Anaerobic digestion is a viable solution, reducing organic pollution while recovering energy in the form of biogas, aligning with the biorefinery concept. Traditionally, sludge bed reactors and anaerobic contact reactors are utilized for vinasse processing, with sludge granulation being vital for treatment success. However, challenges such as sludge wash-out due to recalcitrant compounds, high solids concentration in the influent, low pH, salinity, and temperature hinder granule formation. Anaerobic membrane bioreactors (AnMBR) offer an alternative, simplifying treatment by integrating intensified pre- and post-treatment units. Due to complete sludge retention, AnMBRs achieve high COD removal efficiencies, yielding a suspended solids-free and largely disinfected effluent. Therefore, AnMBRs show promise for vinasse treatment, eliminating the need for sludge granulation and producing nutrient-rich effluent with minimal residual organics and suspended solids. In this study, an AnMBR equipped with an inside-out external crossflow ultrafiltration membrane was proposed for the treatment of vinasse. The AnMBR reached a COD removal efficiency of 95% ± 2.6% and produced 0.3 CH4 L.g COD removed -1 working at organic loading rates of 8g COD. L-1 d-1 and membrane fluxes of 10 LMH. At organic loading rates of 10g COD. L-1 d-1 and fluxes of 12 and 14 LMH, the COD removal efficiency decreased to 77% ± 11% and 73% ± 7.9%, respectively. The AnMBR technology represents an innovation for wastewater treatment, however, more research using the cross-flow configuration and different types of effluents is needed. Literature studies that address the treatment of sugar beet or sugarcane vinasse using AnMBR are still scarce. This study explored the potentials of AnMBR technology for vinasse treatment and contributes to the dissemination of this technology, opening new possibilities for vinasse processing.

Food Waste as Feedstock for Anaerobic Mono-Digestion Process

There is a growing recognition that food waste (FW) comprises a significant amount of unused energy. Indeed, FW shows great potential to produce methane (CH4)-rich biogas via an anaerobic digestion (AD) process. Nevertheless, to ensure high AD process performance, deepening the knowledge of FW characteristics is required. Furthermore, the biogas yield is strongly influenced by several operational parameters. Taking into account the above, in the current study, based on the data in the literature, the physicochemical parameters of FW generated throughout the world are presented and discussed. In addition, the performance profile of the single-stage anaerobic mono-digestion process with the use of FW as a feedstock was investigated. The performed analysis clearly demonstrated that FW is characterized by significant variations in several parameters, such as pH, the total solid (TS) and volatile solid (VS) contents, the volatile solids to total solids ratio (VS/TS), soluble chemical oxygen demand (sCOD), the concentrations of VFAs and ammonium nitrogen (NH4+-N), and the carbon-to-nitrogen ratio (C/N). Moreover, it was shown that the selected operational parameters, such as temperature, pH, the ratio of food waste to inoculum (I) (FW/I), and the organic loading rate (OLR), may have the most significant impact on the performance of the single-stage anaerobic mono-digestion process. In addition, it was found that most of the experimental investigations presented in the literature were conducted on a laboratory scale. Hence, in future research, more effort should be made to determine the biogas yield with the use of full-scale systems. To summarize, it should be clearly highlighted that the analysis presented in this study may have important implications for the management and application of FW as feedstock for an anaerobic mono-digestion process on an industrial scale.

Improving in-situ biomethanation of sewage sludge under mesophilic conditions: Performance and microbial community analysis

This research investigated the application of in-situ biological hydrogen methanation within a continuous stirred tank reactor (CSTR) system under mesophilic conditions, with sewage sludge used as the substrate. Two CSTRs with an effective capacity of 5 L were installed and loaded with inoculum sludge with a volatile solid (VS) concentration of 1.2–1.5 %. They were fed mixed waste sludge with an organic loading rate (OLR) of 1.5 g VS/L and an average sludge retention time (SRT) of 19 days under mesophilic conditions at 37 °C. One of the reactors operated as a control, while the other was injected with H2 through a microceramic membrane diffuser with a H2:CO2 ratio of 4:1. The results of this study revealed that the addition of H2 and the recirculation of residual hydrogen in biogas led to a substantial increase in the production of methane from 157 L/kg VS to 275 L/kg VS. Increasing the methane content in biogas from 52 % to 78 % yielded an impressive 42.8 % higher methane production rate. Metataxonomic analysis of the microbial community via high-throughput sequencing techniques revealed that the dominant acetoclastic and hydrogenotrophic methanogens were Methanosaeta and Methanoregula, respectively, with greater abundances of both groups in the experimental bioreactor. The dynamics of their activity in both bioreactors were analyzed via qPCR, and the functional genes encoding methyl-coenzyme M reductase (mcrA gene) and hydrogenase Ni-Fe presented comparable changes between RI and RII. By optimizing key operational parameters and closely examining the dynamics of the microbial community, this approach can contribute significantly to sustainable bioenergy solutions while minimizing environmental impact.

Optimizing food waste anaerobic digestion in Kuwait: Experimental insights and empirical modelling using artificial neural networks.

This study investigates, for the first time, the anaerobic digestion of food waste in Kuwait to optimize methane production through a combination of artificial neural network (ANN) modelling and continuous reactor experiments. The ANN model, utilizing eight hidden neurons and a 70-20-10 split for training, validation and testing sets, yielded mean squared error values of 0.0056, 0.0048 and 0.0059 and coefficient of determination (R²) values of 0.9942, 0.9986 and 0.9892, respectively. Methane percentages in biogas were predicted using six parameters: biomass type, pH, organic loading rate (OLR), hydraulic retention time (HRT), temperature and reactor volume. To validate the ANN results, continuous reactor experiments were conducted under an OLR of 3 kg VS m⁻³ d⁻¹ and HRT of 20 days at varying temperatures (35°C, 40°C, 45°C, 50°C and 55°C). The experiments demonstrated optimal methane production in the mesophilic range, with ANN predictions closely aligning with experimental data up to 45°C. However, deviations were observed at higher temperatures, particularly under thermophilic conditions beyond 50°C. This study provides novel insights into waste-to-energy initiatives in Kuwait and highlights the potential of integrating computational models with empirical data to enhance biogas production processes.

Treatment of sugarcane vinasse in AnMBR and UASB: process performance and microbial community comparison.

Vinasse is a by-product of sugarcane processing which is often used in fertigation; however, the direct use of vinasse harms the environment and reduces soil productivity due to its physicochemical properties. Anaerobic digestion (AD) offers an alternative to mitigate part of the negative effects. Anaerobic high-rate reactors, which mainly rely on sludge granulation, are mostly used in AD of vinasse wastewater. However, the composition of vinasse such as high concentration of solids and organic matter, high salinity, low pH, and high concentrations of sulfate, affect granule formation, leading to sludge washout. Anaerobic membrane bioreactors (AnMBR) present an alternative for vinasse treatment, eliminating the need for sludge granulation and producing a nutrient-rich effluent with minimal residual organics and no suspended solids. Research on sugarcane vinasse treatment using AnMBRs is limited. Most studies have employed submerged internal membrane modules, highlighting the need for further research with different reactor configurations to enhance process performance. In this study, an AnMBR equipped with an external inside-out crossflow ultrafiltration membrane was compared to an upflow anaerobic sludge blanket (UASB) reactor for the treatment of sugarcane vinasse. At a volumetric organic loading rate of up to 6g COD. L-1.d-1, the UASB reactor reached 75% ± 7% of COD removal efficiency whereas the AnMBR generated a solids-free effluent and reached 88% ± 2% of COD removal efficiency. Microorganisms such as Clostridia, Bacteroidia, Mesotaga, Syner-01, Dehalococcoidia, Bacteroidia-DMER64, and Methanolinea were found as the most abundant. The results highlight the AnMBR potential as an effective alternative for treating sugarcane vinasse while overcoming the challenges posed by unsatisfactory sludge granulation.

Wastewater biotreatment and bioaugmentation for remediation of contaminated sites at an oil recycling plant

ABSTRACT This work focused on the biotreatment of wastewater and contaminated soil in a used oil recycling plant located in Bizerte. A continuous stirred tank reactor (CSTR) and a trickling filter (TF) were used to treat stripped and collected wastewater, respectively. The CSTR was started up and stabilized for 90 days. Over the following 170 days, the operational organic loading rates of the TF and the CSTR were around 1,200 and 3,000 mg chemical oxygen demand (COD) L−1 day−1, respectively. The treatment efficiency was 94% for total petroleum hydrocarbons, 89.5% for COD, 83.34% for biological oxygen demand (BOD5), and 91.25% for phenol. Treated industrial wastewater from the TF was used for bioaugmentation (BA) of contaminated soil. The assessment of the soil took 24 weeks to complete. The effectiveness of the soil BA strategy was confirmed by monitoring phenolic compounds, aliphatic and polycyclic aromatic hydrocarbons, heavy metals, and germination index. The biodegradation rate of contaminants was improved and the time required for their removal was reduced. The soil bacterial communities were dominated by species of the genera Mycobacterium, Proteiniphilum, Nocardioides, Luteimicrobium, and Azospirillum, which were identified as hydrocarbon and phenol-degrading bacteria.

Enrichment of Methanothrix species via riboflavin-loaded granular activated carbon in anaerobic digestion of high-concentration brewery wastewater amidst continuous inoculation of Methanosarcina barkeri

Effective treatment of high-concentration brewery wastewater through anaerobic digestion (AD) has always been a challenging issue. Enhancing direct interspecies electron transfer (DIET) was demonstrated to increase methane production during AD under high organic loading rate (OLR). Herein, the feasibility of enhancing DIET with the addition of riboflavin-loaded granular activated carbon (RF-GAC) as well as co-addition with Methanosarcina barkeri (Rf-GAC+M.barkeri) was investigated (M.barkeri is well-known to be capable of DIET with electroactive bacteria). During the whole process, the Rf-GAC and the Rf-GAC+M.barkeri group both achieved average COD removal rates above 97 %, which was 14 % higher than that of the control. The average methane production in the Rf-GAC group and the Rf-GAC+M.barkeri group respectively reached 0.334 ± 0.02 L(stp)/g COD and 0.345 ± 0.02 L(stp)/g COD, 1.35 and 1.39 times higher than the 0.247 ± 0.03 L(stp)/g COD reached by the control. The control reactor deteriorated at an OLR of 12 kg COD/(m3·d), whereas the Rf-GAC and the Rf-GAC+M.barkeri group maintained stable as the OLR reached as high as 17.5 kg COD/(m3·d) and the volatile fatty acids concentration was consistently below 10 mM. The RF-GAC performed better than Rf-GAC+M.barkeri in enriching Methanothrix, whose relative abundance was 60.6 % in the former group. Metabolic pathway analysis revealed the addition of RF-GAC upregulated genes related to DIET in Methanothrix species, including hdrA and fpoD. Furthermore, Methanothrix remained the dominant archaea even continuously inoculating pure strains of M.barkeri during the entire operational period. Pure culture experiments proved that GAC inhibited M.barkeri growth. The results of this study can be optimized for practical application of AD treating high-concentration brewery wastewater.

The kinetics of a two-stage completely stirred tank reactor for treating tofu wastewater by anaerobic digestion

ABSTRACT Tofu wastewater is an inevitable by-product of the bean curd production process. In this study, we used a two-stage continuous stirred tank reactor (CSTR) to treat tofu wastewater. The kinetic analysis of two CSTR reactors was conducted utilizing the material accounting model, microbial accounting model, and first-order kinetic model. The results demonstrated that the methane production coefficient of reactor 1 was 0.00573 LCH4·mg−1 greater than that of reactor 2, which is 0.00533 L CH4·mg−1. The first-order kinetic constants of reactor 1 were poorer than those of reactor 2, and their values are 0.15700 d−1 and 0.11574 d−1, respectively. The microbial yield coefficients of reactors 1 and 2 were 0.009648 and 0.060704, respectively. Under different organic loading rates, the average microbial concentrations were 25.24000 and 2.706667 mg·L−1 for reactors 1 and 2, respectively. The operational performance of the two-stage CSTR anaerobic digestion system was evaluated in order to design a novel and unique method as well as provide a new perspective for enhancing the performance of anaerobic digestion.

Thermophilic and mesophilic anaerobic digestion of soybean molasses: A performance vs. stability trade-off

One of the factors that has a direct impact on anaerobic digestion is the applied organic loading rate (OLRA). Increasing OLRA can boost methane production but can also cause process failure. As a result, establishing the appropriate OLRA for the procedure is critical. This study evaluated the effect of increasing the OLRA using soybean molasses in a thermophilic anaerobic reactor (R-Thermo), as well as the effect of feeding strategy and co-processing with okara. Furthermore, the performance versus stability trade-off between R-Thermo and mesophilic anaerobic digestion (R-Meso) was investigated. The increase of OLRA from 10 to 15 and 20 kg-COD/m³/d led to a decrease in COD removal efficiency (90, 86, and 75%), methane yield (12.0, 11.6, and 9.9 mol-CH4/kg-COD) and an increase in total volatile acids concentration (251, 456, and 1393 mg-HAc/L, respectively). At 15 kg-COD/m³/d, R-Meso performed similarly to R-Thermo, and at 20 kg-COD/m3/d, R-Meso outperformed (81% COD removal efficiency, 9.3 mol-CH4/kg-CODrem and 154.5 mol-CH4/m3/d). Temperature greatly influenced the distribution of metabolic pathways, as shown by thermodynamic and kinetic analyses, thus impacting bacterial diversity. At 55 °C, amongst the bacterial genera, Tepidiphilus stood out (>28.2%), followed by Acetomicrobium, Coprothermobacter and Candidatus_Caldatribacterium. The OLRA clearly impacted the archaeal community; Methanothermobacter (77.4%) was favored over Methanosarcina (14.8%). Under thermophilic temperature, it seems that syntrophic acetate oxidation (SAO) bacteria might have competed for substrate with acetoclastic methanogens, while in R-Meso microorganisms responsible for the initial steps of organic matter breakdown, such as members of the Firmicutes and Proteobacteria phyla (at least 67%), were dominant. In summary, R-Meso, characterized by a more uniform distribution of metabolic pathways, as well as a diverse and well-adapted microbial consortium, have exhibited enhanced stability and outperformed R-Thermo at high-loads.

Performance of a pilot-scale microbial electrolysis cell coupled with biofilm-based reactor for household wastewater treatment: simultaneous pollutant removal and hydrogen production.

The septic tank is the most commonly used decentralized wastewater treatment systems for household wastewater treatment in on-site applications. The removal rate of various pollutants is lower in different septic tank configurations. The integration of a microbial electrolysis cells (MEC) into septic tank or biofilm-based reactors can be a green and sustainable technology for household wastewater treatment and energy production. In this study, a 50-L septic tank was converted into a 50-L MEC coupled with biofilm-based reactor for simultaneous household wastewater treatment and hydrogen production. The biofilm-based reactor was integrated by an anaerobic packed-bed biofilm reactor (APBBR) and an aerobic moving bed biofilm reactor (aeMBBR). The MEC/APBBR/aeMBBR was evaluated at different organic loading rates (OLRs) by applying voltage of 0.7 and 1.0V. Result showed that the increase of OLRs from 0.2 to 0.44kg COD/m3 d did not affect organic matter removals. Nutrient and solids removal decreased with increasing OLR up to 0.44kg COD/m3 d. Global removal of chemical oxygen demand (COD), biochemical oxygen demand (BOD), total nitrogen (TN), ammoniacal nitrogen (NH4+), total phosphorus (TP) and total suspended solids (TSS) removal ranged from 81 to 84%, 84 to 85%, 53 to 68%, 88 to 98%, 11 to 30% and 76 to 88% respectively, was obtained in this study. The current density generated in the MEC from 0 to 0.41 A/m2 contributed to an increase in hydrogen production and pollutants removal. The maximum volumetric hydrogen production rate obtained in the MEC was 0.007 L/L.d (0.072 L/d). The integration of the MEC into biofilm-based reactors applying a voltage of 1.0V generated different bioelectrochemical nitrogen and phosphorus transformations within the MEC, allowing a simultaneous denitrification-nitrification process with phosphorus removal.

Methanogenesis—General Principles and Application in Wastewater Remediation

The first discovery of methanogens led to the formation of a new domain of life known as Archaea. The Archaea domain exhibits properties vastly different from previously known Bacteria and Eucarya domains. However, for a certain multi-step process, a syntrophic relationship between organisms from all domains is needed. This process is called methanogenesis and is defined as the biological production of methane. Different methanogenic pathways prevail depending on substrate availability and the employed order of methanogenic Archaea. Most methanogens reduce carbon dioxide to methane with hydrogen through a hydrogenotrophic pathway. For hydrogen activation, a group of enzymes called hydrogenases is required. Regardless of the methanogenic pathway, electrons are carried between microorganisms by hydrogen. Naturally occurring processes, such as methanogenesis, can be engineered for industrial use. With the growth and emergence of new industries, the amount of produced industrial waste is an ever-growing environmental problem. For successful wastewater remediation, a syntrophic correlation between various microorganisms is needed. The composition of microorganisms depends on wastewater type, organic loading rates, anaerobic reactor design, pH, and temperature. The last step of anaerobic wastewater treatment is production of biomethane by methanogenesis, which is thought to be a cost-effective means of energy production for this renewable biogas.

Innovative system to maximize methane production from fruit and vegetable waste.

Anaerobic digestion of fruit and vegetable waste (FVW) offers an environmentally friendly alternative for waste disposal, converting it into methane for energy recovery. Typically, FVW digestion is conducted in a continuously stirred tank reactor (CSTR) due to its ease of use and stability with solid concentrations between 5 and 10%. However, CSTRs are limited to organic loading rates (OLRs) of about 3kg COD/m3.day, resulting in large reactor volumes, low methane productivity, and costly wet digestate handling. This work introduces a novel method for methane production from FVW using a high-rate reactor system. The proposed approach involves grinding, centrifuging, and/or pressing the FVW to separate it into liquid and solid phases. The liquid phase is then digested in an up-flow anaerobic sludge blanket (UASB) reactor, while the solid phase undergoes digestion in a dry methanization reactor. A model incorporating all biological reactors was implemented in the Anaerobic Digestion Model 1 (ADM1) to provide a theoretical basis for the experimental development of this system. The current simulation scenarios offer initial references for operating the experimental system, which will, in turn, generate data for further model refinement. For instance, constrained liquid-gas mass transfer was considered for dry fermentation, with additional potential biochemical kinetic limitations to be incorporated following on experimental evidence. The success of this system could enable energy recovery in 72 Central Wholesale Markets across Brazil, offering a critical tool for planning, operating, and optimizing such systems.

Metabolic cross-feeding interactions modulate the dynamic community structure in microbial fuel cell under variable organic loading wastewaters.

The efficiency of microbial fuel cells (MFCs) in industrial wastewater treatment is profoundly influenced by the microbial community, which can be disrupted by variable industrial operations. Although microbial guilds linked to MFC performance under specific conditions have been identified, comprehensive knowledge of the convergent community structure and pathways of adaptation is lacking. Here, we developed a microbe-microbe interaction genome-scale metabolic model (mmGEM) based on metabolic cross-feeding to study the adaptation of microbial communities in MFCs treating sulfide-containing wastewater from a canned-pineapple factory. The metabolic model encompassed three major microbial guilds: sulfate-reducing bacteria (SRB), methanogens (MET), and sulfide-oxidizing bacteria (SOB). Our findings revealed a shift from an SOB-dominant to MET-dominant community as organic loading rates (OLRs) increased, along with a decline in MFC performance. The mmGEM accurately predicted microbial relative abundance at low OLRs (L-OLRs) and adaptation to high OLRs (H-OLRs). The simulations revealed constraints on SOB growth under H-OLRs due to reduced sulfate-sulfide (S) cycling and acetate cross-feeding with SRB. More cross-fed metabolites from SRB were diverted to MET, facilitating their competitive dominance. Assessing cross-feeding dynamics under varying OLRs enabled the execution of practical scenario-based simulations to explore the potential impact of elevated acidity levels on SOB growth and MFC performance. This work highlights the role of metabolic cross-feeding in shaping microbial community structure in response to high OLRs. The insights gained will inform the development of effective strategies for implementing MFC technology in real-world industrial environments.

Predicting photosynthetic bacteria-derived protein synthesis from wastewater using machine learning and causal inference

Causal inference-assisted machine learning was used to predict photosynthetic bacterial (PSB) protein production capacity and identify key factors. The extreme gradient boosting algorithm effectively predicted protein content, while the gradient boosting decision tree algorithm excelled in predicting protein production, protein productivity, and protein energy yields. Driving factors were identified, with suitable ranges: protein content (pH 6.0–7.5, hydraulic retention time (HRT) < 3.8 d), protein production (biomass > 1.7 g, organic loading rate (OLR) > 9.2 gL–1d–1, temperature 26.7–35.0 °C), protein productivity (HRT < 3.5 d, biomass > 1.6 g, OLR > 10.0 gL–1d–1), and protein energy yields (light energy 0.1–4.4 kWh, biomass 1.7–65.0 g, chemical oxygen demand (COD) 0.1–2.5 gL–1). Illuminance, dissolved oxygen, COD, and COD/total nitrogen ratio were causal factors influencing protein production. Two-dimensional partial dependence plot revealed the interaction between two driving factors. This study enhances information on PSB protein production and offers insights for wastewater treatment and sustainable resource development.

Different aspects of biochar addition on semi-dry anaerobic digestion of organic fraction of municipal solid waste in continuous mode

This study investigated the use of biochar, derived from a wood gasifier, in semi-dry anaerobic digestion of organic fraction of municipal solid waste (OFMSW). The experiment was conducted in three phases, without biochar and changing the hydraulic retention time (HRT) from 50 to 15 days until first acidification condition (on pH = 6.5), with biochar at an optimal concentration of 30 g/L in HRT= 20–10 day. Also, countermeasures for the acidified reactor with biochar during the dormancy period were investigated. The results demonstrated that adding biochar led to a rapid recovery of the acidified reactor, improved stability parameters, and removed foaming as a disturbance. Biochar addition (30 g/L) enhanced the organic loading rate (OLR) up to 11 kgVS/m3.day with an HRT of 20 days leading to specific methane production of 383 L/kgVS and a volumetric production increase of biomethane by 85 %. However, at higher OLRs with HRT of 10 days, acidification condition resurfaced leading to homogeneous foaming. Excess adding of biochar did not have significant treatment effects but necessitated a no-feeding period (about 45 days) and gentle stirring with long intervals for stable conditions. Overall, the use of biochar along with the OFMSW biogas plant was demonstrated to enhance production efficiency.