Effects of co-digestion of food waste, corn straw and chicken manure in two-stage anaerobic digestion on trace element bioavailability and microbial community composition

Comprehensive insights into the effects of acidogenic off-gas utilization on successive biogas production, microbial community structure and metabolite distribution during two-stage anaerobic digestion

Although two-stage anaerobic digestion (TSAD) technology has been investigated, the mechanisms regarding the impact of acidogenic off-gas (AOG) on successive methane production have not been well addressed. In this study, a novel TSAD system was designed. Food waste, as the main substrate, was co-digested with chicken manure and corn straw. The acidogenic gas beyond atmospheric pressure was introduced into the bottom of the methanogenesis reactor through a stainless steel diffuser. Results showed the addition of AOG increased the methane yield from 435.2 to 597.1 mL/g VSin in successive methanogenesis stage, improved by 37.2 %, and increased the energy yield from 9.0 to 11.3 kJ/g VSsubstrate. However, the theoretical contribution of hydrogenotrophic methanogenesis using H2 contained in AOG was only 15.2 % of the increased methane yield. After the addition of AOG, the decreased levels of ammonia nitrogen and butyrate indicate that the stability of the AD system was improved. The electron transfer system and co-enzyme F420 activity were enhanced; however, the decrease in acetate kinase activity indicates aceticlastic methanogenesis may have been weakened. The microbial diversity and species richness were improved by the added AOG. Methanosarcina was more competitive than Methanothermobacter, enhancing the syntrophic effect. The relative abundance of protein degradation bacteria norank_f_Anaerolineaceae and lipid degradation bacteria Syntrophomonas was increased. Metabolite analysis confirmed that the addition of AOG promoted amino acid metabolism, the biosynthesis of other secondary metabolism and lipid metabolism. The improved degradation of recalcitrant organic components (lipids and proteins) in food waste was responsible for the increased methane yield. This study provides an in-depth understanding of the impact of AOG utilization on successive methane production and has practical implications for the treatment of food waste.

Biohythane production from two-stage anaerobic digestion of food waste: A review

The biotransformation of food waste (FW) to bioenergy has attracted considerable research attention as a means to address the energy crisis and waste disposal problems. To this end, a promising technique is two-stage anaerobic digestion (TSAD), in which the FW is transformed to biohythane, a gaseous mixture of biomethane and biohydrogen. This review summarises the main characteristics of FW and describes the basic principle of TSAD. Moreover, the factors influencing the TSAD performance are identified, and an overview of the research status; economic aspects; and strategies such as pre-treatment, co-digestion, and regulation of microbial consortia to increase the biohythane yield from TSAD is provided. Additionally, the challenges and future considerations associated with the treatment of FW by TSAD are highlighted. This paper can provide valuable reference for the improvement and widespread implementation of TSAD-based FW treatment.

Hydrogen and methane production through two stage anaerobic digestion of straw residues

Anaerobic digestion of agricultural waste can contribute to the European renewable energy needs. The 71% of the 20,000 anaerobic digestion plants in operation already uses these agro-waste as feedstock; part of these plants can be converted into two stage processes to produce hydrogen and methane in the same plant. Biomethane enriched in hydrogen can replace natural gas in grids while contributing to the sector decarbonisation. Straw is the most abundant agricultural residue (156 Mt/y) and its conventional final fate is uncontrolled soil disposal, landfilling, incineration or, in the best cases, composting. The present research work focuses on the fermentation of spent mushroom bed, an agricultural lignocellulosic byproduct, composed mainly from wheat straw. The substrate has been characterized and semi-continuous tests were performed evaluating the effect of the hydraulic retention time on hydrogen and volatile fatty acids production. It was found that all the tests confirmed the feasibility of the process even on this lignocellulosic substrate, and also, it was identified HRT 4.0 d as the best option to optimize the productivity of volatile fatty acids (17.09 gCODVFAs/(KgVS*d)), and HRT 6.0 d for hydrogen (7.98 LH2/(KgVS*d)). The fermentation effluent was used in biomethanation potential tests to evaluate how this process affects a subsequent digestion phase, reporting an increase in the energetical feedstock exploitation up to 30%.

Effect of reactor operation modes on mitigating antibiotic resistance genes (ARGs) and methane production from hydrothermally-pretreated pig manure

Numerous efforts have been made to enhance the performance of anaerobic digestion (AD) for accelerating renewable energy generation, however, it remains unclear whether the intensified measures could enhance the proliferation and transmissions of antibiotic resistance genes (ARGs) in the system. This study assessed the impact of an innovative pig manure AD process, which includes hydrothermal pretreatment (HTP) and a two-stage configuration with separated acidogenic and methanogenic phases, on biomethane (CH4) production and ARGs dynamics. Results showed that HTP significantly increase CH4 production from 0.65 to 0.75 L/L/d in conventional single-stage AD to 0.82 and 0.91 L/L/d in two-stage AD. This improvement correlated with a rise in the relative abundance of Methanosarcina, a key methanogenesis microorganism. In the two-stage AD, the methanogenic stage offered an ideal environment for methanogens growth, resulting in substantially faster and higher CH4 production by about 10% compared to single-stage AD. Overall, the combined use of HTP and the two-stage AD configuration enhanced CH4 production by 40% compared to traditional single-stage AD. The abundance and diversity of ARGs were significantly reduced in the acidogenic reactors after HTP. However, the ARGs levels increased by about two times in the following methanogenesis stage and reached similar or higher levels than in single stage AD. The erm(F), erm(G), ant(6)-Ia, tet(W), mef(A) and erm(B) were the six main ARGs with significant differences in relative abundances in various treatments. The two-stage AD mode could better remove sul2, but it also had a rebound which elevated the risk of ARGs to the environment and human health. Network analysis identified pH and TVFAs as critical factors driving microbial communities and ARG proliferation in the new AD process. With the results, this study offers valuable insights into the trade-offs between AD performance enhancement and ARG-related risks, pinpointing essential areas for future research and practical improvements.

Anaerobic co-digestion of corn straw, sewage sludge and fresh leachate: Focusing on synergistic/antagonistic effects and microbial mechanisms

Effects of sewage sludge (SS) and fresh leachate (FL) addition on corn straw (CS) digestion and underlying mechanisms were investigated. Co-digestion of CS, SS and FL significantly increased cumulative methane production by 7.2-61.1%. Further analysis revealed that co-digestion acted mainly on slowly degradable substrates and exerted dual effects on methane production potential, which was closely related to the volatile solids (VS) content. Antagonistic effects of co-digestion resulted from the dominance of norank_c_Bathyarchaeia, a mixotrophic methanogen that may generate methane inefficiently and consume existing methane. The synergistic enhancement of methane production (0.7-12.7%) was achieved in co-digestion with 33.5-45.5% of total VS added as SS and FL. Co-digestion with more balanced nutrients and higher buffering capacity enriched Actinobacteriota, Firmicutes, and Synergistota, thereby facilitating the substrate degradation. Furthermore, the predominant acetoclastic methanogens, increased hydrogenotrophic methanogens, and decreased methylotrophic methanogens in the digester combined to prompt the synergy.

Effects of food wastes based on different components on digestibility and energy recovery in hydrogen and methane co-production

This study was conducted for four organic fractions (carbohydrates, proteins, cellulose, lipids) at an inoculum concentration of 30 % and a total solid (TS) of 8 % to investigate the effect of the main components of food waste on the performance of the two-stage anaerobic digestion. The results showed that the gas phase products were closely related to the composition of the substrate, with the carbohydrate and lipid groups showing the best hydrogen (154.91 ± 2.39mL/gVS) and methane (381.83 ± 12.691mL/gVS) production performance, respectively. However, the increased protein content predisposes the system to inhibition of gas production, which is mutually supported by changes in the activity of dehydrogenase and coenzyme F420. Butyric acid (53.19 %) dominated the liquid phase products in both stages, indicating that all four organic fractions were butyric acid-based fermentation and that the final soluble chemical oxygen demand degradation reached 72.97 %-82.86 %. The carbohydrate and cellulose groups achieved the best energy recovery performance, with conversion rates exceeding 65 %. The above results can provide a useful reference for the resource utilization of food waste.

Optimization of semi-continuous dry anaerobic digestion process and biogas yield of dry yellow corn straw: Based on "gradient anaerobic digestion reactor"

In China, the problem of low biogas yield of traditional biogas projects has become increasingly prominent. This study investigated the effects of different hydraulic retention times (HRTs) on the biogas production efficiency and microbial community under pilot conditions. The results show that the "Gradient anaerobic digestion reactor" can stably carry out semi-continuous dry anaerobic digestion and improve biogas yield. The highest volatile solids (VS) biogas yield (413.73 L/kg VS and 221.61 L CH4/kg VS) and VS degradation rate (48.41%) were observed at an HRT of 25 days. When the HRT was 15 days, the volumetric biogas yield was the highest (2.73 L/L/d, 1.43 L CH4/L/d), but the VS biogas yield and degradation rate were significantly decreased. Microbial analysis showed that HRT significantly affected microbial community. It provides basic data support for the development of a new anaerobic digestion process and the practical application of the straw biogas project in China.

Enhancing bio-hydrogen and bio-methane production of concentrated latex wastewater (CLW) by Co-digesting with palm oil mill effluent (POME): Batch and continuous performance test and ADM-1 modeling

This study aimed at investigating the biohydrogen and biomethane potential of co-digestion from palm oil mill effluent (POME) and concentrated latex wastewater (CLW) in a two-stage anaerobic digestion (AD) process under thermophilic (55 ± 3 °C) and at an ambient temperature (30 ± 3 °C) conditions, respectively. The batch experiments of POME:CLW mixing ratios of 100:0, 70:30, 50:50, 30:70, and 0:100 was investigated with the initial loadings at 10 g-VS/L. The highest hydrogen yield of 115.57 mLH2/g-VS was obtained from the POME: CLW mixing ratio of 100:0 with 29.0 of C/N ratio. While, the highest subsequent methane production yield of 558.01 mLCH4/g-VS was achieved from hydrogen effluent from POME:CLW mixing ratio of 70:30 0 with 21.8 of C/N ratio. This mixing ratio revealed the highest synergisms of about 9.21% and received maximum total energy of 19.70 kJ/g-VS. Additionally, continuous hydrogen and methane production were subsequently performed in a series of continuous stirred tank reactor (CSTR) and up-flow anaerobic sludge blanket reactor (UASB) to treat the co-substate. The results indicated that the highest hydrogen yield of POME:CLW mixing ratio at 70:30 of 95.45 mL-H2/g-VS was generated at 7-day HRT, while methane production was obtained from HRT 15 days with a yield of 204.52 mL-CH4/g-VS. Thus, the study indicated that biogas production yield of CLW could be enhanced by co-digesting with POME. In addition, the two-stage AD model under anaerobic digestion model no. 1 (ADM-1) framework was established, 9.10% and 2.43% of error fitting of hydrogen and methane gas between model simulation data and experimental data were found. Hence, this research work presents a novel approach for optimization and feasibility for co-digestion of POME with CLW to generate mixed gaseous biofuel potentially.

Post-hydrolysis versus side-stream ammonia stripping in semi-continuous two-stage anaerobic digestion of high nitrogen feedstock

With the increased popularity of two-stage anaerobic digesters, post-hydrolysis ammonia stripping (PHAS) has resurfaced as a new possible treatment configuration. This study discusses for the first time the semi-continuous operation of PHAS and compares it with the most used stripping configuration nowadays, side-stream ammonia stripping (SSAS), under similar conditions using air or renewable natural gas (RNG) as stripping mediums. Ammonia stripping operating conditions were set to pH 9.5, 55 °C, and flowrate of 100 L gas/L/hour. RNG removed 50-58% of ammonia while air removed 70-78%. Interestingly, the PHAS system showed more flexibility and resilience than the SSAS system when testing parameters were changed. Volumetric and specific biogas production from PHAS and SSAS scenarios averaged up to 1.91 and 1.26 L/L/day and 831 and 701 L biogas/ kg VS/day under organic loading rates of 2.61 and 1.8 g VS/L/day, respectively.

Comparison of the basic processes of aerobic, anaerobic, and aerobic-anaerobic coupling composting of Chinese medicinal herbal residues

Chinese medicinal herbal residues (CMHRs) are waste generated after extracting Chinese medicinal materials, and they can be used as a renewable bioresource. This study aimed to evaluate the potential of aerobic composting (AC), anaerobic digestion (AD), and aerobic-anaerobic coupling composting (AACC) for the treatment of CMHRs. CMHRs were mixed with sheep manure and biochar, and composted separately under AC, AD, and AACC conditions for 42 days. Physicochemical indices, enzyme activities, and bacterial communities were monitored during composting. Results showed that AACC- and AC-treated CMHRs were well-rotted, with the latter exhibiting the lowest C/N ratio and maximal germination index (GI) values. Higher phosphatase and peroxidase activities were detected during the AACC and AC treatments. Better humification was observed under AACC based on the higher catalase activities and lower E4/E6. AC treatment was effective in reducing compost toxicity. This study provides new insights into biomass resource utilisation.

Strategies for enhancing the efficacy of anaerobic digestion of food industry wastewater: An insight into bioreactor types, challenges, and future scope

Food waste have become a growing concern worldwide with raising population and economic growth. Wastewater discharged from food industries contains many valuable and toxic components that have a negative impact on the ecological system. Large amounts of wastewater are discharged from the food industry, which necessitates the creation of effective technologies. Wastewater from the food industry can be seen as a rich source of energy and a primary source for generating valuable products. Waste disposal and resource recovery are sustainably valued by anaerobic digestion of wastewater from the food sector. The characteristics, composition, and nature of wastewater produced from various food sectors are elaborated upon in this review. An overview of the anaerobic digestion process for wastewater treatment in the food industry is included. Enhancement strategies for the anaerobic digestion process have been discussed in detail. In addition, various types of reactors utilized for performing anaerobic digestion is illustrated. Though anaerobic digestion process possesses advantages, the challenges and future scope are examined for improving the outcome.

Study on the chemical compositions and microbial communities of cigar tobacco leaves fermented with exogenous additive

Fermentation process plays an important role in the biochemical properties and quality of cigar tobacco leaves (CTLs). In industry, exogenous additive (EA) was usually adopted for improving the quality of CTLs during fermentation. However, the mechanism of enhanced quality of CTLs fermented with EA was confused. Herein, the chemical compositions and microbial communities of CTLs during fermentation with EA were analyzed. The increased contents of total nitrogen and total sugar, as well as the improved consumption rate of reducing sugar in CTLs were found with the addition of EA. Besides, fermentation with EA reduced the content of total nonvolatile organic acid, especially unsaturated fatty acid. The contents of total and several representative aroma components were improved. Additionally, the increased abundance of Staphylococcus and decreased abundance of Aspergillus were detected. Combined with the changes of chemical compositions and microbial communities, it was confirmed that the carbohydrates and alcohols originated from EA promote the enrichment of Staphylococcus and accelerate biochemical reactions, such as Maillard reaction and esterification reaction, thus improving the contents and quality of aroma components in CTLs. This study demonstrated the mechanism of enhanced quality of CTLs fermented by EA, which provides more ideas for developing novel and efficient EAs.

Biohydrogen and Methane Production from Sugarcane Leaves Pretreated by Deep Eutectic Solvents and Enzymatic Hydrolysis by Cellulolytic Consortia

This study determined the optimal conditions for the deep eutectic solvent (DES) pretreatment of sugarcane leaves and the best fermentation mode for hydrogen and methane production from DES-pretreated sugarcane leaves. Choline chloride (ChCl):monoethanolamine (MEA) is the most effective solvent for removing lignin from sugarcane leaves. The optimum conditions were a ChCl: MEA molar ratio of 1:6, 120 °C, 3 h, and substrate-to-DES solution ratio of 1:12. Under these conditions, 86.37 ± 0.36% lignin removal and 73.98 ± 0.42% hemicellulose removal were achieved, whereas 84.13 ± 0.77% cellulose was recovered. At a substrate loading of 4 g volatile solids (VS), the simultaneous saccharification and fermentation (SSF) and separate hydrolysis and fermentation (SHF) processes yielded maximum hydrogen productions of 3187 ± 202 and 2135 ± 315 mL H2/L, respectively. In the second stage, methane was produced using the hydrogenic effluent. SSF produced 5923 ± 251 mL CH4/L, whereas SHF produced 3583 ± 128 mL CH4/L. In a one-stage methane production process, a maximum methane production of 4067 ± 320 mL CH4/L with a substrate loading of 4 g VS was achieved from the SSF process. SSF proved to be more efficient than SHF for producing hydrogen from DES-pretreated sugarcane leaves in a two-stage hydrogen and methane production process as well as a one-stage methane production process.

Startup of Demo-Scale Anaerobic Digestion Plant Treating Food Waste Leachate: Process Instability and Recovery

A demo-scale (600 m3 working volume) anaerobic digester treating food waste leachate was monitored during its startup period. The operation strategy was adjusted twice (i.e., three distinct phases) during the operation to recover the process from instability. During the first phase, the organic loading rate (OLR) > 2.7 kg chemical oxygen demand (COD)/m3∙day corresponded to volatile fatty acid (VFA) accumulation along with a decreasing pH, resulting in the drop in biogas yield to 0.43 ± 0.9 m3/kg CODin. During phase 2, fast recovery of this process was aimed at using a sequencing batch operation. One batch cycle (5 to 2 days) consisted of the combined drawing and feeding step (5 h), the reacting step (91 to 17 h), and the settling step (24 h). The duration of the reacting step was determined for each cycle such that (1) the biogas production ceased before the cycle end and (2) the residual VFA concentration was < 1 g/L. In total, 11 cycles were operated with a gradual increase in biogas yield to 0.55 m3/kg CODin with the absence of any sign of system disturbance. After phase 2, the digester was fed at the designed OLR of 4.1 ± 0.3 kg COD/m3∙day. The biogas yield was elevated to 0.58 ± 0.2 m3/kg CODin during phase 3 with the residual VFA concentration maintained at 2.2 ± 0.6 g/L. Methanogen populations, as determined by real-time PCR, did not change significantly throughout the period. These results imply that the adaptation of this process to the OLR of ca. 4 kg COD/m3∙day was not due to the increase in methanogen population but due to the elevation of its activity. Overall, this study suggests that the sequencing batch operation with adjustable cycle duration can be one successful recovery strategy for biogas plants under system instability.