Semi-continuous anaerobic digestion for biogas production: influence of ammonium acetate supplement and structure of the microbial community

Enhancement of Biodegradability of Chicken Manure via the Addition of Zeolite in a Two-Stage Dry Anaerobic Digestion Configuration

Leach bed reactors (LBRs) are dry anaerobic systems that can handle feedstocks with high solid content, like chicken manure, with minimal water addition. In this study, the chicken manure was mixed with zeolite, a novel addition, and packed in the LBR to improve biogas production. The resulting leachate was then processed in a continuous stirred tank reactor (CSTR), where most of the methane was produced. The supernatant of the CSTR was returned to the LBR. The batch mode operation of the LBR led to a varying methane production rate (MPR) with a peak in the beginning of each batch cycle when the leachate was rich in organic matter. Comparing the MPR in both systems, the peaks in the zeolite system were higher and more acute than in the control system, which was under stress, as indicated by the acetate accumulation at 2328 mg L-1. Moreover, the presence of zeolite in the LBR played a crucial role, increasing the overall methane yield from 0.142 (control experiment) to 0.171 NL CH4 per g of volatile solids of chicken manure entering the system at a solid retention time of 14 d. Zeolite also improved the stability of the system. The ammonia concentration increased gradually due to the little water entering the system and reached 3220 mg L-1 (control system) and 2730 mg L-1 (zeolite system) at the end of the experiment. It seems that zeolite favored the accumulation of the ammonia at a lower rate (14.0 mg L-1 d-1) compared to the control experiment (17.3 mg L-1 d-1). The microbial analysis of the CSTR fed on the leachate from the LBR amended with zeolite showed a higher relative abundance of Methanosaeta (83.6%) compared to the control experiment (69.1%). Both CSTRs established significantly different bacterial profiles from the inoculum after 120 days of operation (p < 0.05). Regarding the archaeal communities, there were no significant statistical differences between the CSTRs and the inoculum (p > 0.05).

Temperature drives microbial communities in anaerobic digestion during biogas production from food waste

Resource depletion and climate changes due to human activities and excessive burning of fossil fuels are the driving forces to explore alternatives clean energy resources. The objective of this study was to investigate the potential of potato peel waste (PPW) at various temperatures T15 (15 °C), T25 (25 °C), and T35 (35 °C) in anaerobic digestion (AD) for biogas generation. The highest biogas and CH4 production (117 mL VS-g and 74 mL VS-g) was observed by applying 35 °C (T35) as compared with T25 (65 mL VS-g and 22 mL VS-g) on day 6. Changes in microbial diversity associated with different temperatures were also explored. The Shannon index of bacterial community was not significantly affected, while there was a positive correlation of archaeal community with the applied temperatures. The bacterial phyla Firmicutes were strongly affected by T35 (39%), whereas Lactobacillus was the dominant genera at T15 (27%). Methanobacterium and Methanosarcina, as archaeal genera, dominated in T35 temperature reactors. In brief, at T35, Proteiniphilum and Methanosarcina were positively correlated with volatile fatty acids (VFAs) concentration. Spearman correlation revealed dynamic interspecies interactions among bacterial and archaeal genera; facilitating the AD system. This study revealed that temperature variations can enhance the microbial community of the AD system, leading to increased biogas production. It is recommended for optimizing the AD of food wastes.

Maximizing the energy recovery from rice straw through two-step conversion using eggshell-catalytic pyrolysis followed by enhanced anaerobic digestion using calcium-rich biochar

Anaerobic digestion of lignocelluloses for biogas production is greatly restricted by the poor biomass degradability. Herein, a novel approach is suggested to enhance the energy recovery from rice straw through a two-step conversion using eggshell-based catalytic pyrolysis followed by biochar-based anaerobic co-digestion. Pyrolysis with eggshell significantly enhanced the crude bio-oil yield by 4.6 %. Anaerobic digestion of rice straw using 4 g L^-1 of rice straw biochar (RB) showed the highest recorded biogas yield of 503.7 L kg^-1 VS, with 268.6 L kg^-1 VS biomethane yield. However, 4 g L^-1 of calcium-enriched eggshell rice straw biochar (ERB) enhanced the biomethane yield to 281.8 L kg^-1 VS, which represented 95.6 % higher than the control. It was attributed to enhancement of biomethanation, which resulted in 74.5 % maximum recorded biomethane content at the 7th day of anaerobic digestion. Microbial analysis confirmed that Methanosarciniales was the most dominant Archael group in the control (14.84 %), which increased sharply to 73.91 % and 91.66 % after addition of 4 g L^-1 RB and ERB, respectively. The suggested route enhanced the energy recovery in the form of bio-oil and biomethane by 41.6 %.

Conductive materials as fantastic toolkits to stimulate direct interspecies electron transfer in anaerobic digestion: new insights into methanogenesis contribution, characterization technology, and downstream treatment

Direct interspecies electron transfer (DIET) stimulated by conductive materials (CMs) enables intercellular metabolic coupling that can address the unfavorable thermodynamical dilemma inherent in anaerobic digestion (AD). Although the DIET mechanism and stimulation have been extensively summarized, the methanogenesis contribution, characterization techniques, and downstream processes of CMs-led DIET in AD are surprisingly under-reviewed. Therefore, this review aimed to address these gaps. First, the contribution of CMs-led DIET to methanogenesis was re-evaluated by comparing the effect of various factors, including volatile fatty acids, free ammonia, and functional enzymes. It was revealed that AD systems are usually intricate and cannot allow the methanogenesis stimulation to be singularly attributed to the establishment of DIET. Additionally, considerable attention has been attached to the characterization of DIET occurrence, involving species identification, gene expression, electrical properties, cellular features, and syntrophic metabolism, suggesting the significance of accurate characterization methods for identifying the syntrophic metabolism interactions. Moreover, the type of CMs has a significant impact on AD downstream processes involving biogas purity, sludge dewaterability, and biosolids management. Finally, the central bottleneck consists in building a mathematical model of DIET to explain the mechanism of DIET in a deeper level from kinetics and thermodynamics.

The role of biochar on alleviating ammonia toxicity in anaerobic digestion of nitrogen-rich wastes: A review

This paper reviewed the mechanisms of biochar in relieving ammonia inhibition. Biochar affects nitrogen-rich waste's anaerobic digestion (AD) performance through four ways: promotion of direct interspecies electron transfer (DIET) and microbial growth, adsorption, pH buffering, and provision of nutrients. Biochar enhances the DIET pathway by acting as an electron carrier. The role of DIET in relieving ammonia nitrogen may be exaggerated because many related studies don't provide definite evidence. Therefore, some bioinformatics technology should be used to assist in investigating DIET. Biochar absorbs ammonia nitrogen by chemical adsorption (electrostatic attraction, ion exchange, and complexation) and physical adsorption. The absorption efficiency, mainly affected by the properties of biochar, pH and temperature of AD, can reach 50 mg g^-1 on average. The biochar addition can buffer pH by reducing the concentrations of VFAs, alleviating ammonia inhibition. In addition, biochar can release trace elements and increase the bioavailability of trace elements.

Influence of initial pH on the production of volatile fatty acids and hydrogen during dark fermentation of kitchen waste

The purpose of this work was to determine the effect of initial pH on the production of volatile fatty acids (VFA) and hydrogen (H₂) in the dark fermentation processes of kitchen waste. The study was conducted in batch bioreactors of working volume 1 L for different initial pH in the range from 5.5 to 9.0. The dark fermentation processes were carried out for 4 days at 37°C. Initial organic load of the kitchen waste in all bioreactors amounted to 25.5 gVS/L. Buffering of pH during the fermentation process was carried out with the use of ammonia contained mainly in digested sludge. The optimal conditions for the production of VFA and H₂ were achieved at the initial pH of 8. Production of VFA and H₂ in these conditions was, respectively, 13.9 g/L and 72.4 mL/gVS. The main produced components of VFA were acetic and butyric acids. The production of ethanol and lactic acid was at very low levels due to the high ratio of the volatile fatty acids to total organic content of 0.86. With the optimal initial pH of 8 the yield of CO₂ production was 0.30 gC/gC. High initial pH value (above 8) extended the lag phase duration in the course of H₂ production. The dominant groups of micro-organisms at the most favourable initial pH of 8 for the production of VFA and H₂ were Bacteroidetes, Firmicutes, Spirochaetes and Waste Water of Evry 1 (WWE1) at the phylum level.

Microbial mechanism of enhancing methane production from anaerobic digestion of food waste via phase separation and pH control

Phase separation and pH control are commonly used to improve methane production during anaerobic digestion (AD) of food waste, but their influencing mechanisms have not been fully discovered through microbial analysis. In this study, single-phase AD (SPAD), two-phase AD without pH control (TPAD-pHUC), and TPAD with fermentation pH controlled at 6.0 and 4.5 were conducted. The results showed that phase separation decreased the ratio of total bacteria to total archaea in the methanogenic phase. At the organic loading rate (OLR) of 1.9 g/(L·d), methanogenesis was dominated by acetoclastic Methanosaeta in both SPAD and TPAD-pHUC, while elevated Methanoculleus and active hydrogen production initiated a shift from the acetoclastic to hydrogenotrophic pathway in SPAD as OLR increased, eventually resulting in excessive acidification at OLR 3.2 g/(L·d). TPAD-pHUC was dominated by Methanosaeta with scarce hydrogen production genes, and thus maintained a delicate balance between fewer acidogens and methanogens at OLR 3.2-3.7 g/(L·d). TPAD with pH control exhibited higher methane yield (460-482 ml/g) at OLR 1.9 g/(L·d) due to the enhancement of protein degradation and the conversion from methylated compounds to methane by Methanosarcina. High Na⁺ concentration facilitated the proliferation of hydrogen production bacteria, but inhibited acetoclastic methanogenesis at OLR 2.4 g/(L·d). In comparison with SPAD and pH control, TPAD without pH control, integrating 4 d acidogenesis and 22 d methanogenesis, exhibited the best and steady performance at OLR 3.7 g/(L·d) with methane production exceeding 370 ml/g.

Simultaneous carbon dioxide reduction and enhancement of methane production in biogas via anaerobic digestion of cornstalk in continuous stirred-tank reactors: The influences of biochar, environmental parameters, and microorganisms

The composition of biogas produced by anaerobic digestion (AD) is typically not ideal due to high CO₂ content. In the study, cottonwood biochar was used as an enhanced mediator for the continuously stirred tank reactor AD of cornstalk. The effects of substrate loading and biochar dosage on biogas composition, volatile fatty acids (VFAs), NH₃-N, and microbial community characteristics were systematically explored. The results showed that the highest volumetric biogas production rate with biochar was 1.40 L/L/d, at the same time, the CO₂ content in the biogas decreased by 5.90%, while the CH₄ content increased by 7.40%, compared with the values in AD without biochar. Moreover, VFAs were degraded effectively, in particular, the propionic acid concentration decreased by 55.7%. Besides, microbial abundance had positive correlations with environmental parameters. This study could provide valuable information for both the elucidation of strengthening mechanisms of biochar and further large-scale engineering application.

Production of volatile fatty acids and H2 for different ratio of inoculum to kitchen waste

The aim of this study was to evaluate the effect of different inoculum ratio on the dark fermentation of kitchen waste in terms of volatile fatty acids (VFAs) and H₂ production. The experiments were performed in batch bioreactors of effective volume 1 L without pH regulation. The ratio between the DS and KW was being increased from 0.11 to 0.51 on a volatile solids (VS) basis, while the initial content of KW was equal to 34.1 g VS/L. Increase of the DS/KW ratio from 0.11 to 0.28 resulted in the rise of VFAs and H₂ production. Further increase in the amount of added DS did not cause a significant change in the production of VFAs and H₂. In the bioreactor with the DS/KW ratio of 0.28, the production of VFAs and H₂ was equal to 16.0 g/L and 68.1 mL/g VS, respectively. Acetic and butyric acids were produced in the largest amount and their content, for DS/KW ratio of 0.28, were equal 37% and 43%, respectively. At the ratio of DS/KW above 0.4, the caproic acid content attained the level of 25%. Based on the DS and KW microbiological analysis, it was observed that dominant bacteria were Bacteroidetes, Firmicutes, Proteobacteria, Spirochaetes and WWE1 at the phylum level.

Biochar triggering multipath methanogenesis and subdued propionic acid accumulation during semi-continuous anaerobic digestion

The semi-continuous anaerobic digestion (AD) performances of dry chicken manure (DCM) were investigated at the temperature of 35 ± 1 °C with and without biochar. The average specific methane productions of 0.18 L/g VS_added and 0.17 L/g VS_added were achieved without biochar at the organic loading rate (OLR) of 3.125 and 6.25 g VS/L/d, respectively. An increase of 12% in methane production was obtained in the presence of biochar at the two operational OLRs. Accumulation of propionic acid was observed associating with AD of DCM, which was substantially alleviated by biochar supplement. The buffer capacity of biochar was supposed to develop through strengthening the buffer system established by NH₄⁺ and volatile fatty acids. Methanosarcina that can utilize multiple nutrients for methanogenesis was the dominant archaea in the presence of biochar, while the strictly aceticlastic Methanosaeta was dominant in control digester. These results suggest that biochar enhanced methanogenesis through intensifying its available pathway.

Different response of bacteria, archaea and fungi to process parameters in nine full-scale anaerobic digesters

Biogas production is a biotechnological process realized by complex bacterial, archaeal and likely fungal communities. Their composition was assessed in nine full-scale biogas plants with distinctly differing feedstock input and process parameters. This study investigated the actually active microbial community members by using a comprehensive sequencing approach based on ribosomal 16S and 28S rRNA fragments. The prevailing taxonomical units of each respective community were subsequently linked to process parameters. Ribosomal rRNA of bacteria, archaea and fungi, respectively, showed different compositions with respect to process parameters and supplied feedstocks: (i) bacterial communities were affected by the key factors temperature and ammonium concentration; (ii) composition of archaea was mainly related to process temperature; and (iii) relative abundance of fungi was linked to feedstocks supplied to the digesters. Anaerobic digesters with a high methane yield showed remarkably similar bacterial communities regarding identified taxonomic families. Although archaeal communities differed strongly on genus level from each other, the respective digesters still showed high methane yields. Functional redundancy of the archaeal communities may explain this effect. 28S rRNA sequences of fungi in all nine full-scale anaerobic digesters were primarily classified as facultative anaerobic Ascomycota and Basidiomycota. Since the presence of ribosomal 28S rRNA indicates that fungi may be active in the biogas digesters, further research should be carried out to examine to which extent they are important players in anaerobic digestion processes.

Biochemical engineering in China

Chinese biochemical engineering is committed to supporting the chemical and food industries, to advance science and technology frontiers, and to meet major demands of Chinese society and national economic development. This paper reviews the development of biochemical engineering, strategic deployment of these technologies by the government, industrial demand, research progress, and breakthroughs in key technologies in China. Furthermore, the outlook for future developments in biochemical engineering in China is also discussed.

Refined soybean oil wastewater treatment and its utilization for lipid production by the oleaginous yeast Trichosporon fermentans

BACKGROUND

The release of refined soybean oil wastewater (RSOW) with a high chemical oxygen demand (COD) and oil content burdens the environment. The conversion of RSOW into lipids by oleaginous yeasts may be a good way to turn this waste into usable products.

RESULTS

The oleaginous yeast Trichosporon fermentans was used for treating the RSOW without sterilization, dilution, or nutrient supplementation. It was found that the COD and oil content of the RSOW were removed effectively; microbial oil was abundantly produced in 48 h; and the phospholipids in the RSOW tended to contribute to a higher biomass and microbial lipid content. With Plackett-Burman design and response surface design experiments, the optimal wastewater treatment conditions were determined: temperature 28.3 °C, amount of inoculum 5.9% (v/v), and initial pH 6.1. The optimized conditions were used in a 5-L bioreactor to treat the RSOW. The maximum COD degradation of 94.7% was obtained within 40 h, and the removal of the oil content was 89.9%. The biomass was 7.9 g/L, the lipid concentration was 3.4 g/L, and the lipid content was 43% (w/w). The microbial oil obtained, with a main component of unsaturated fatty acids, was similar to vegetable oils and was suggested as a potential raw material for biodiesel production.

CONCLUSION

Trichosporon fermentans can be effectively used for RSOW treatment, and lipid production and can complete pretreatment and biochemical treatment simultaneously, allowing the utilization of RSOW, which both solves an environmental problem and positively impacts the use of resources. These results provide valuable information for developing and designing more efficient waste-into-lipid bioprocesses.

Substrate-Induced Response in Biogas Process Performance and Microbial Community Relates Back to Inoculum Source

This study investigated whether biogas reactor performance, including microbial community development, in response to a change in substrate composition is influenced by initial inoculum source. For the study, reactors previously operated with the same grass–manure mixture for more than 120 days and started with two different inocula were used. These reactors initially showed great differences depending on inoculum source, but eventually showed similar performance and overall microbial community structure. At the start of the present experiment, the substrate was complemented with milled feed wheat, added all at once or divided into two portions. The starting hypothesis was that process performance depends on initial inoculum source and microbial diversity, and thus that reactor performance is influenced by the feeding regime. In response to the substrate change, all reactors showed increases and decreases in volumetric and specific methane production, respectively. However, specific methane yield and development of the microbial community showed differences related to the initial inoculum source, confirming the hypothesis. However, the different feeding regimes had only minor effects on process performance and overall community structure, but still induced differences in the cellulose-degrading community and in cellulose degradation.

Exploration of the relationship between biogas production and microbial community under high salinity conditions

High salinity frequently causes inhibition and even failure in anaerobic digestion. To explore the impact of increasing NaCl concentrations on biogas production, and reveal the microbial community variations in response to high salinity stress, the Illumina high-throughput sequencing technology was employed. The results showed that a NaCl concentration of 20 g/L (H group) exhibited a similar level of VFAs and specific CO2 production rate with that in the blank group, thus indicating that the bacterial activity in acidogenesis might not be inhibited. However, the methanogenic activity in the H group was significantly affected compared with that in the blank group, causing a 42.2% decrease in CH4 production, a 37.12% reduction in the specific CH4 generation rate and a lower pH value. Illumina sequencing revealed that microbial communities between the blank and H groups were significantly different. Bacteroides, Clostridium and BA021 uncultured were the dominant species in the blank group while some halotolerant genera, such as Thermovirga, Soehngenia and Actinomyces, dominated and complemented the hydrolytic and acidogenetic abilities in the H group. Additionally, the most abundant archaeal species included Methanosaeta, Methanolinea, Methanospirillum and Methanoculleus in both groups, but hydrogenotrophic methanogens showed a lower resistance to high salinity than aceticlastic methanogens.

Evaluation of A Novel Split-Feeding Anaerobic/Oxic Baffled Reactor (A/OBR) For Foodwaste Anaerobic Digestate: Performance, Modeling and Bacterial Community

To enhance the treatment efficiency from an anaerobic digester, a novel six-compartment anaerobic/oxic baffled reactor (A/OBR) was employed. Two kinds of split-feeding A/OBRs R2 and R3, with influent fed in the 1^st, 3^rd and 5^th compartment of the reactor simultaneously at the respective ratios of 6:3:1 and 6:2:2, were compared with the regular-feeding reactor R1 when all influent was fed in the 1^st compartment (control). Three aspects, the COD removal, the hydraulic characteristics and the bacterial community, were systematically investigated, compared and evaluated. The results indicated that R2 and R3 had similar tolerance to loading shock, but the R2 had the highest COD removal of 91.6% with a final effluent of 345 mg/L. The mixing patterns in both split-feeding reactors were intermediate between plug-flow and completely-mixed, with dead spaces between 8.17% and 8.35% compared with a 31.9% dead space in R1. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis revealed that the split-feeding strategy provided a higher bacterial diversity and more stable bacterial community than that in the regular-feeding strategy. Further analysis indicated that Firmicutes, Bacteroidetes, and Proteobacteria were the dominant bacteria, among which Firmicutes and Bacteroidetes might be responsible for organic matter degradation and Proteobacteria for nitrification and denitrification.

Production of carotenoids and lipids by Rhodococcus opacus PD630 in batch and fed-batch culture

Production of carotenoids by Rhodococcus opacus PD630 is reported. A modified mineral salt medium formulated with glycerol as an inexpensive carbon source was used for the fermentation. Ammonium acetate was the nitrogen source. A dry cell mass concentration of nearly 5.4 g/L could be produced in shake flasks with a carotenoid concentration of 0.54 mg/L. In batch culture in a 5 L bioreactor, without pH control, the maximum dry biomass concentration was ~30 % lower than in shake flasks and the carotenoids concentration was 0.09 mg/L. Both the biomass concentration and the carotenoids concentration could be raised using a fed-batch operation with a feed mixture of ammonium acetate and acetic acid. With this strategy, the final biomass concentration was 8.2 g/L and the carotenoids concentration was 0.20 mg/L in a 10-day fermentation. A control of pH proved to be unnecessary for maximizing the production of carotenoids in this fermentation.

Anaerobic digestion of biowaste under extreme ammonia concentration: Identification of key microbial phylotypes

Ammonia inhibition represents a major operational issue for anaerobic digestion (AD). In order to get more insights into AD microbiota resistance, anaerobic batch reactors performances were investigated under a wide range of Total Ammonia Nitrogen (TAN) concentrations up to 50.0g/L at 35°C. The half maximal inhibitory concentration (IC50) value was determined to be 19.0g/L. Microbial community dynamics revealed that above a TAN concentration of 10.0g/L, remarkable modifications within archaeal and bacterial communities occurred. 16S rRNA gene sequencing analysis showed a gradual methanogenic shift between two OTUs from genus Methanosarcina when TAN concentration increased up to 25.0g/L. Proportion of potential syntrophic microorganisms such as Methanoculleus and Treponema progressively raised with increasing TAN up to 10.0 and 25.0g/L respectively, while Syntrophomonas and Ruminococcus groups declined. In 25.0g/L assays, Caldicoprobacter were dominant. This study highlights the emergence of AD key phylotypes at extreme ammonia concentrations.

Identification and genome reconstruction of abundant distinct taxa in microbiomes from one thermophilic and three mesophilic production-scale biogas plants

BACKGROUND

Biofuel production from conversion of biomass is indispensable in the portfolio of renewable energies. Complex microbial communities are involved in the anaerobic digestion process of plant material, agricultural residual products and food wastes. Analysis of the genetic potential and microbiology of communities degrading biomass to biofuels is considered to be the key to develop process optimisation strategies. Hence, due to the still incomplete taxonomic and functional characterisation of corresponding communities, new and unknown species are of special interest.

RESULTS

Three mesophilic and one thermophilic production-scale biogas plants (BGPs) were taxonomically profiled using high-throughput 16S rRNA gene amplicon sequencing. All BGPs shared a core microbiome with the thermophilic BGP featuring the lowest diversity. However, the phyla Cloacimonetes and Spirochaetes were unique to BGPs 2 and 3, Fusobacteria were only found in BGP3 and members of the phylum Thermotogae were present only in the thermophilic BGP4. Taxonomic analyses revealed that these distinctive taxa mostly represent so far unknown species. The only exception is the dominant Thermotogae OTU featuring 16S rRNA gene sequence identity to Defluviitoga tunisiensis L3, a sequenced and characterised strain. To further investigate the genetic potential of the biogas communities, corresponding metagenomes were sequenced in a deepness of 347.5 Gbp in total. A combined assembly comprised 80.3 % of all reads and resulted in the prediction of 1.59 million genes on assembled contigs. Genome binning yielded genome bins comprising the prevalent distinctive phyla Cloacimonetes, Spirochaetes, Fusobacteria and Thermotogae. Comparative genome analyses between the most dominant Thermotogae bin and the very closely related Defluviitoga tunisiensis L3 genome originating from the same BGP revealed high genetic similarity. This finding confirmed applicability and reliability of the binning approach. The four highly covered genome bins of the other three distinct phyla showed low or very low genetic similarities to their closest phylogenetic relatives, and therefore indicated their novelty.

CONCLUSIONS

In this study, the 16S rRNA gene sequencing approach and a combined metagenome assembly and binning approach were used for the first time on different production-scale biogas plants and revealed insights into the genetic potential and functional role of so far unknown species.