Search Results (175)

Microbial coal gasification technology is a new, efficient, and clean method for coal resource mining; however, its commercial application remains limited by gasification efficiency and cost. To examine the impact of biomass on microbial coal gasification processes, improve gas production efficiency, and identify economically viable nutrient supplements with broad availability, this study employed culture medium (CM), sawdust (SD), and blue-green algae (BA) as nutritional additives. An anaerobic fermentation experiment with three-stage nutrient supplementation was conducted using a fed-batch reactor. The comparison of gas and liquid compositions within reactors throughout the reaction process demonstrated that key nutrient supplementation could reactivate methane production in reactors in which gas generation had ceased. Gas composition analysis revealed that under identical conditions, BA supplementation achieved the highest methane yield (24.49 ± 1.31 mL/g), followed by SD (1.56 ± 0.1 mL), representing 24.13-fold and 1.53-fold increases, respectively, compared with the yield in CM control group. Analysis of 16S rRNA sequencing indicated that nutrient supplementation induced microbial community differentiation, with dominant bacterial genera (Herbinix, Proteiniborus) shifting according to the organic composition of the liquid environment. A positive feedback relationship between microbial life activities and functional performance further confirmed the dominance of these superior strains. This study advances the understanding of substrate degradation characteristics in microbial coal degradation systems and provides theoretical support for the clean and efficient coal exploitation. Full article

This study investigates the efficient biogenic production of hydrogen via the thermophilic bacterium Thermotoga neapolitana, focusing on optimising process configurations to maximise yield and productivity. To determine optimal conditions, a 1 L anaerobic bioreactor with online gas analytics was designed and tested for batch, fed-batch and continuous fermentation. A maximum hydrogen production rate of 96.1 ± 1.7 Nml·L⁻¹·h⁻¹ was observed in the continuous reactor. The optimal dilution rate was 0.07 h⁻¹. Each dilution rate was kept for ≥56 h fermentation time and resulted in yields of 2.7–3.0 mol_H2·mol_glucose⁻¹. A consistently high cell viability (97%) was also observed across various dilution rates. A detailed carbon balance indicates acetate as the main by-product, closely linked to the hydrogen production pathway. Compared to fed batch and batch, the hydrogen production rate could be increased and remain constant over a longer time. In this way the continuous reactor design showed an additional method to produce hydrogen to the established ones. Fermentative hydrogen production is particularly promising when using carbohydrate containing biomass and biowaste, as it can be considered carbon dioxide neutral. Full article

Anaerobic digestion (AD) is an environmentally friendly, promising solution for the recycling of agro-industrial wastes. However, overloading an anaerobic digester with substrate may cause the inhibition of the AD process. The present study investigated the effects of the substrate/inoculum (S/I) ratio on the AD of potato chip processing (PCP) waste from the potato chip processing industry (PCPI). The PCP waste included expired potato chips (EPCs), recovered potato starch (RPS), and potato peel (PP). Mesophilic AD was carried out in batch-wise static reactors at 35 ± 1 °C using four different S/I ratios (0.5, 1.0, 1.5, and 2.0 g VS/g VS) for each type of waste. Different optimum S/I ratios were obtained for the different wastes; however, the pH ranges were comparable (7.0 to 7.5) for all batches. The optimum S/I ratios for EPCs, RPS, and PP were 1.0, 1.5, and 2.0, respectively. The cumulative biogas yields for EPCs, RPS, and PP were 367.5 ± 6.3, 310.0 ± 5.5, and 202.5 ± 4.9 mL/g VS added, respectively. The methane content of the biogas yields ranged between 60% and 70%. There was a variable remarkable shift in the microbial population at the optimum S/I ratio of each type of waste. The abundance of Firmicutes increased in the case of EPCs and RPS but decreased in the case of PP. Conversely, Proteobacteria increased when using PP as a substrate and decreased in the case of EPCs. Herein, the results of the AD of PCP wastes confirm its potential for the onsite production of renewable bioenergy and reductions in energy bills in the PCPI. In addition, this study provides guidance for optimizing the AD of PCP wastes for large-scale applications. Full article

Anaerobic digestion (AD) is a mature industrial fermentation technology for converting organic matter into renewable bioenergy, and chicken manure (CM) is a promising feedstock due to its high organic content. However, the industrial-scale AD of CM is often hindered by ammonium inhibition, particularly under high organic loading rates (OLRs). Biochar has emerged as a sustainable additive that can enhance microbial activity, buffer pH, and improve system stability. In this study, the effects of biochar on the methane production and fermentation performance of CM in terms of AD were evaluated under both batch and continuous conditions, where batch experiments were conducted at different biochar-to-CM ratios. Ammonium nitrogen and methane production were monitored to determine the optimal biochar addition ratio. Continuous stirred-tank reactors (CSTRs) were then operated with the optimal biochar addition ratio under stepwise-increasing OLR conditions to assess methane production, fermentation parameters, and methanogen community composition. The results showed that an optimal biochar addition of 9% reduced total ammonium nitrogen (TAN) by 31.75% and increased cumulative methane production by 25.93% compared with the control. In continuous operation, biochar addition mitigated ammonium inhibition, stabilized pH, enhanced system stability and organic loading capacity, and improved methane production by 21.15%, 27.78%, and 83.33% at OLRs of 2.37, 4.74, and 7.11 g volatile solids (VS)/(L·d), respectively, compared to the control. Biochar also inhibited the growth of methylotrophic methanogen of RumEn_M2. These findings provide scientific and technical support for applying biochar as a process enhancer during the AD of CM. Full article

Heterotrophic nitrification and aerobic denitrification (HN–AD) is an emerging biological process capable of achieving efficient nitrogen removal in a single reactor. This study investigates the HN–AD performance of a sequencing batch reactor (SBR) operated with a simple anaerobic–aerobic cycle for treating high C/N wastewater. Over a 220-day operation, the system achieved average removal efficiencies of 98.6% for COD, 93.3% for NH₄⁺-N, and 87.1% for total nitrogen. Effluent concentrations of NO₂⁻-N and NO₃⁻-N remained negligible at the end of each aerobic phase. Concentration profiles of NH₄⁺-N, NO₂⁻-N, and NO₃⁻-N throughout the operation cycles confirmed the occurrence of simultaneous nitrification and aerobic denitrification. The consistently high COD removal and robust nitrogen reduction highlight the stability of the HN–AD microbial consortia enriched from activated sludge. Phosphorus removal (average removal efficiency 66.3%) may be enhanced by increasing the activity of phosphate-accumulating organisms (PAOs) through process optimization. This study demonstrated effective HN–AD using activated sludge in SBRs. Future work will focus on evaluating the system with real wastewater and continuous-flow setups to further refine operational parameters for sustained HN–AD performance. Full article

This study evaluated the viability of using the solid residues (bagasse) of the mezcal industry produced with Agave durangensis as a substrate for biogas production, using two chemical pretreatments, acid (HCl) and alkaline (KOH + Ca(OH)₂), to enhance its biodegradability and improve the anaerobic digestion (AD) process. The chemical composition of bagasse was analyzed before and after the chemical pretreatments and then AD experiments were conducted in anaerobic sequential batch reactors (A-SBR) to analyze the effect of pretreatments on biogas production performance. The results showed that acid pretreatment increased cellulose content to 0.606 g, which represented an increase of 34%, and significantly reduced hemicellulose. In contrast, alkaline pretreatment did not show significant changes in cellulose composition, although it caused a swelling of the Agave durangensis mezcal bagasse (Ad-MB) fibers. In terms of biogas production, Ad-MB pretreated with acid (Ad-MB-acid) increased cumulative production by 76% compared to the Agave durangensis mezcal bagasse that was not pretreated (Ad-MB-not pretreated) and by 135% compared to Agave durangensis mezcal bagasse pretreated with an alkaline solution (Ad-MB-alkaline). These results confirmed that Agave durangensis solid waste from the mezcal industry that receives acidic chemical pretreatment has the potential to generate biogas as a sustainable biofuel that can be used to reduce the ecological footprint of this industry. Full article

This study evaluated the efficacy of acclimated cow manure as a seed microbiome to enhance food waste hydrolysis. Anaerobic hydrolysis was performed on simulated food waste in a hydrolytic–acidogenic leach bed reactor (LBR) operated in batch mode under mesophilic conditions (35 °C) for 16 days. The acclimation process involved three sequential runs: Run-1 utilized 20% (w/w) cow manure as seed, Run-2 employed the digestate from Run-1 (day 5), and Run-3 used the digestate from Run-1 (day 10). Run-3 achieved 70.4% removal of volatile solids (VSs), surpassing Run-1 (47.1%) and Run-2 (57.1%). Compared with the first run, the production of chemical oxygen demand (COD) and total soluble products (TSPs) increased by 48.7% and 75.9%, respectively, in Run-3. The hydrolysis rate of proteins was 48.4% in Run-1, while an increase of 16.9% was achieved in Run-3 with the acclimatized consortium. A molecular analysis of the microbial community existing in the reactors of Run-2 and Run-3 indicated that the improvement in process performance was closely related to the selection and enrichment of specific hydrolytic–acidogenic bacteria in the reactor. A functional analysis showed that the gene copy numbers for pyruvate synthesis and fatty acid synthesis and metabolism pathways were higher in all bacterial species in Run-3 compared to in those of the other two runs, indicating improved capacity through acclimation in Run-3. The experimental results demonstrate that the hydrolysis of food waste can be enhanced through the acclimation of seed microbes from cow manure. Full article

Adequate treatment of the organic fraction of municipal solid waste (OFMSW) in co-digestion with sewage sludge (SS) through dark fermentation (DF) technologies has been widely studied and recognized. However, there is little experience with a high-solids approach, where practical and scalable conditions are established to lay the groundwork for further development of feasible industrial-scale projects. In this study, the biochemical hydrogen potential of OFMSW using a 7 L batch reactor at mesophilic conditions was evaluated. Parameters such as pH, redox potential, temperature, alkalinity, total solids, and substrate/inoculum ratio were adjusted and monitored. Biogas composition was analyzed by gas chromatography. The microbial characterization of SS and post-reaction percolate liquids was determined through metagenomics analyses. Results show a biohydrogen yield of 38.4 NmLH₂/gVS OFMSW, which forms ~60% of the produced biogas. Aeration was proven to be an efficient inoculum pretreatment method, mainly to decrease the levels of methanogenic archaea and metabolic competition, and at the same time maintain the required total solid (TS) contents for high-solids conditions. The microbial community analysis reveals that biohydrogen production was carried out by specific anaerobic and aerobic bacteria, predominantly dominated by the phylum Firmicutes, including the genus Bacillus (44.63% of the total microbial community), Clostridium, Romboutsia, and the phylum Proteobacteria, with the genus Proteus. Full article

This laboratory study investigated the anaerobic co-digestion process of the halophyte S. ramosissima (Sram) together with swine manure (SM) in different mixing ratios in batch and continuous reactor experiments. In the batch experiments, a methane yield of 214 mL_CH4·gVS⁻¹ was obtained for Sram in mono-digestion. In co-digestion with SM, the methane yields were slightly higher than calculated from the yields of each substrate in mono-digestion. Also, the kinetic rate constant in the co-digestion with swine manure increased from 0.219 d⁻¹ for mono-digested S. ramosissima to 0.318 d⁻¹ in the co-digestion of 50:50 Sram:SM (based on VS). Two continuous 5 L lab-scale CSTR reactors were operated: one as a control (100% SM) and the other as a co-digestion reactor with an increasing VS share of Sram (15, 25, and 35%) in the feed. Both reactors were operated at an organic loading rate (OLR) of 2.5 gVS.L⁻¹·d⁻¹ and a hydraulic retention time (HRT) of 20 days. In the continuous process, the highest methane yield of 276 mL_CH4·gVS⁻¹ was achieved at a co-digestion VS ratio of Sram:SM 25:75, corresponding to a methane yield from the added S. ramosissima of 277 mL_CH4·gVS⁻¹. This showed successful operation of the continuous co-digestion process of S. ramosissima and swine manure, with higher methane yields of S. ramosissima than in the mono-digestion batch tests. Full article

Industrial activated sludge plants in many sectors, including the dairy industry, face sludge separation problems caused by sludge bulking. Aerobic granular sludge (AGS) could be a solution by forming well-settling granules. The key to successful granulation is the microbial selection of slow-growing glycogen-accumulating organisms (GAOs) by introducing an anaerobic feeding/reaction step. The objective of the current study was to investigate the impact of two slow feeding strategies to achieve granulation in existing sequencing batch reactors treating real dairy wastewater, by microbial selection only. The first strategy consisted of slow 90 min mixed feeding. The second strategy combined 45 min static and 45 min mixed feeding to build up a substrate gradient. The feeding strategies did not affect the effluent quality, but significantly impacted the sludge morphology, settling properties, and microbial community composition. Mixed feeding led to filamentous overgrowth by Thiothrix species, up to 45% abundance, and deteriorating settling, with sludge volume index (SVI) values up to 125 mL/g. In contrast, static feeding yielded densified sludge with SVI values below 45 mL/g and up to 35% GAO abundance. In conclusion, the results show successful granulation when using a simple static slow feeding mode, which could benefit the industrial application of AGS technology. Full article

Dewatering anaerobic digested sludge leaves a liquid fraction known as reject water, a liquid organic fertilizer containing high amounts of ammonium nitrogen (NH₄-N). However, its concentration should be enhanced to produce commercial fertilizer. Thus, reject water nitrification for stabilization as well as for nitrate capture in biochar to be used as a slow-release fertilizer is proposed. This study attempted to accomplish enhanced nitrification by tuning the operating parameters in two lab-scale sequential-batch reactors (SBRs), which were fed reject water (containing 520 ± 55 mg NH₄-N/L). Sufficient alkalinity as per stoichiometric value was needed to maintain the pH and free nitrous acid (FNA) within the optimum range. A nitrogen loading rate (NLR) of 0.14 ± 0.01 kg/m³·d and 3.34 days hydraulic retention time (HRT) helped to achieved complete 100% nitrification in reactor 1 (R₁) on day 61 and in reactor 2 (R₂) on day 82. After a well-developed bacterial biomass, increasing the NH₄-N concentration up to 750 ± 85 mg/L and NLR to 0.23 ± 0.03 kg/m³·d did not affect the nitrification process. Moreover, a feeding sequence once a day provided adequate contact time between nitrifying sludge and reject water, resulting in complete nitrification. It can be concluded that enhanced stable nitrification of reject water can be achieved with quick adjustment of loading, alkalinity, and HRT in SBRs. Full article

The thermophilic anaerobic bioconversion of various wastes is still challenging, mainly due to process instability and economic profitability. This group includes orange wastes (OWs) and brewery spent grain (BSG), the main by-products generated by the beverage industry. In this study, a strategy allowing for improving methane production by the multicomponent co-digestion of sewage sludge (SS), OW, and BSG was proposed. To overcome the difficulties in the thermophilic co-digestion of those wastes, the application of natural zeolite (Z), i.e., clinoptilolite, was proposed. The experiment was performed in the batch mode at a temperature of 55 °C. Four experimental series were conducted with differing feedstock compositions, one of which was a control supplied only by SS. As compared with the control, in the series supplied by OW and OW with BSG, methane production decreased by 20% and 13%, respectively. In turn, significant improvements were achieved in the presence of Z. The most beneficial results were observed in the reactor supplied by SS, OW, and Z, characterized by a methane yield of 420.2 mLCH₄/gVS, which is an increase of almost 14% as compared with the control. In this case, significantly improved stability parameters, as well as decreased presence of inhibitors, i.e., limonene and phenols, were achieved. It was also characterized by enhanced energy balance by 69%, as compared with the control. Full article

In this study, we explore the use of C. kluyveri in synthetic biofilms for the production of 1-butyrate and 1-hexanoate, investigating the impact of inoculation temperature during biofilm formation and the presence of yeast extract. Therefore, a novel synthetic biofilm reactor has been designed and constructed. Prior to investigating synthetic biofilms in this reactor, we carried out preliminary batch experiments in anaerobic flasks containing an inoculated agar hydrogel fixed at the bottom and overlaid medium. For the operation of the novel synthetic biofilm reactor, specific volumes of inoculated agar hydrogel were dispensed into a cylindrical mold with a diameter of 102 mm, forming the synthetic biofilm with a height of 4 mm, which was then transferred into the biofilm reaction chamber onto the support grid. The biofilm support grid separates the gas phase (CO₂, N₂) above the synthetic biofilm from the aqueous phase (medium) below. Our results show that C. kluyveri remains metabolically active at biofilm preparation temperatures of up to 45 °C, with extended lag phases observed at 70 °C. The synthetic biofilm demonstrated efficient chain elongation in batch processes, converting ethanol and acetate into 1-butyrate and 1-hexanoate, with final concentrations of 2.7 g L⁻¹ and 10.1 g L⁻¹, respectively, with yeast extract in the circulating liquid medium of the synthetic biofilm reactor setup. The maximum estimated space-time yields for 1-butyrate and 1-hexanoate, referenced to the biofilm volume, were 1.331 g L⁻¹ h⁻¹ and 4.947 g L⁻¹ h⁻¹, respectively. Experiments without yeast extract lead to final concentrations of 2.0 g L⁻¹ 1-butyrate, and 7.3 g L⁻¹ 1-hexanoate and maximum estimated space-time yields, referenced to the biofilm volume, were 0.332 g L⁻¹ h⁻¹ and 1.123 g L⁻¹ h⁻¹, respectively. The use of synthetic biofilms, even without yeast extract, eliminates the need for significant cell growth during chain elongation. However, product concentrations were lower without yeast extract. Full article

The research aimed to study the effects of straw-derived biochar and two types of chemically modified biochar on biomethane production from glucose as a model substrate and sugar beet pulp as a real substrate. The biochar chemical modification with H₃PO₄ acid and KOH base resulted in a change in biochar surface area properties and its functional group’s abundance and a decrease in biochar mass yield production. The anaerobic digestion process was performed in batch reactors kept at 37 °C for 20 days. The substrate-to-inoculum ratio by volatile solids was 0.5, while the mass of added biochar corresponded to 16 g·L⁻¹. The results showed that neither the addition of biochar nor the chemically modified biochar had any positive effects on biomethane production or its kinetics in the case of both substrates. The highest methane production was found in reactors without biochar added, respectively, 385 and 324 mL·g_VS⁻¹ for glucose and sugar beet pulp. It is hypothesized that the anaerobic digestion process was performed under optimal conditions, and therefore, biochar could not enhance methane production. Additionally, biochar may have adsorbed some volatile fatty acids, making them less available to anaerobic microorganisms. Full article

Anaerobic digestion is a critical method for producing bioenergy from organic waste; however, its efficiency is highly influenced by several factors. This study aimed to enhance the AD process using the removed solid phase generated by the canning plant Amor Benamor (CAB) during the production of harissa. This research sought to identify the optimum pH conditions and inoculum/substrate ratio (I/S) for achieving the maximum biogas production while ensuring a high methane yield, using response surface methodology (RSM) and numerical optimization. The batch anaerobic digestion of pepper waste as a substrate and sewage sludge as an inoculum was conducted. The 11 experimental runs generated by Design Expert Software were conducted in reactors with a capacity of 150 mL and a working volume of 90 mL, under thermophilic conditions. The effects of pH in the range of 7 to 8 and an I/S ratio in the range of 0.167 to 0.5, and their interaction in terms of biogas and methane yield (mL/g VS), were evaluated using a central composite design (CCD). The findings highlighted that a pH of around 7.5 and an I/S ratio of 0.48 could give the highest predicted yield of 884.35 mL/g VS for biogas and 422.828 mL/g VS for methane. These predicted values were confirmed with an experimental validation run which exhibited a deviation of less than 5%. These results offer new opportunities for enhanced biogas production from accumulated waste, contributing to the growth of sustainable energy alternatives. Full article