Study of an enhanced dry anaerobic digestion of swine manure: Performance and microbial community property

Bulking agent in dry anaerobic digestion as a key factor for the enhancement of biogas production

Dry anaerobic digestion (dry-AD) is an attractive process for solid wastes such as agri-food waste. However, some limitations mainly associated to lack of effective mixing, can hinder the methane production capacity of the systems. Bulking agent (BA) has been proposed as a solution to the compaction issues in systems without mechanical agitation, such as leaching bed reactors. However, effects of BA are still not clear, and, thus, the factors to consider for its dose has not been optimized yet. This work studies the effect of BA in dry-AD. Two substrates with different characteristics were proposed as models, bean peel as a lignocellulosic substrate and a mixture of food waste as a readily biodegradable substrate. Inert plastic rings were used as BA at different BA:S ratios. Assessed BA:S ratio did not affect the performance of methane production for the lignocellulosic waste, but it did significantly affect to the easily biodegradable substrate, showing up to a 28% of methane production increase. This result could be due to the presence of lignocellulosic compounds in the bean peel, behaving like a natural BA. In assays with an increased bed height, the compaction of the system was more severe, resulting in the rapid acidification of the processes. At these conditions, the positive effect of BA addition was more marked, allowing methane production and no acidification of the system. Thus, the addition of BA is a suitable strategy for improving methane production or stability in dry-AD systems without requiring the stirring of the systems.

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

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

Effect of Ecuadorian natural zeolite on the performance of anaerobic digestion of swine waste in semicontinuous regime

This study explores the potential of zeolite as an amendment to mitigate ammonium inhibition in the anaerobic digestion of swine waste. Two 50 L reactors, one with and one without zeolite amendment were operated at an OLR of 3.0 g VS L-1d-1 for 130 days, and fed with swine waste from a full-scale pig farm. Under these conditions, zeolite doses of 4 g L-1 allowed total ammonia nitrogen (TAN) concentrations to be kept below 1000 mgNH3-N L-1. The zeolite-amended reactor not only showed an average increase of 8% in methane production under stable conditions but also exhibited 34% reduction in H2S concentrations in the biogas, compared to the reactor without zeolite. The community of archaea originating from the inoculum was conserved in the reactor with zeolite amendment, particularly the acetoclastic methanogens of the genus Methanosaeta. On the other hand, in the reactor without zeolite addition, the microbial community went from being dominated by the acetoclastic methanogen Methanosaeta to having a high relative abundance of hydrogenotrophic methanogens. The zeolite addition also favoured the reactor stability, prevented foaming, and produced an enriched natural zeolite with N, P and K. However, additional studies on the potential of enriched zeolite as a fertilizer are required, which could make the use of zeolite in Anaerobic Digestion of swine waste not only energetically favourable but also economically feasible.

Mass Transfer Enhancement in High-Solids Anaerobic Digestion of Organic Fraction of Municipal Solid Wastes: A Review

The increasing global population and urbanization have led to a pressing need for effective solutions to manage the organic fraction of municipal solid waste (OFMSW). High-solids anaerobic digestion (HS-AD) has garnered attention as a sustainable technology that offers reduced water demand and energy consumption, and an increased biogas production rate. However, challenges such as rheology complexities and slow mass transfer hinder its widespread application. To address these limitations, this review emphasizes the importance of process optimization and the mass transfer enhancement of HS-AD, and summarizes various strategies for enhancing mass transfer in the field of HS-AD for the OFMSW, including substrate pretreatments, mixing strategies, and the addition of biochar. Additionally, the incorporation of innovative reactor designs, substrate pretreatment, the use of advanced modeling and simulation techniques, and the novel conductive materials need to be investigated in future studies to promote a better coupling between mass transfer and methane production. This review provides support and guidance to promote HS-AD technology as a more viable solution for sustainable waste management and resource recovery.

Effect of optimized intermittent mixing during high-solids anaerobic co-digestion of food waste and sewage sludge: Simulation, performance, and mechanisms

Inadequate mixing has been proven to be a major cause of anaerobic digester failure. This study revealed the mechanism of mixing intervals on high-solids anaerobic co-digestion (HS-AcoD) of food waste (FW) and sewage sludge (SS). Optimized intermittent mixing time (15 min/h) was determined through computational fluid dynamics (CFD) simulation. Experimental results indicated that the simulated intermittent mixing could shorten digestion time and increase cumulative methane output (366.8 mL/gVS) compared with continuous mixing and unmixing. Mixing could considerably accelerate substrate solubilization and hydrolysis. Maximum rates of acidogenesis (53.35 %) and methanogenesis (49.41 %) were observed with an optimized intermittent mixing (15 min/h). Vigorous mixing induced apoptosis and disrupted syntrophic metabolism, whereas intermittent mixing promoted the syntrophic metabolism between Syntrophomonas and Methanobacterium, and led to an enrichment of genes involved in acidogenic and methanogenic pathways. These findings have important implications for the development of an optimized intermittent mixing strategy for maximizing HS-AcoD efficiency of FW and SS.

Dry anaerobic digestion of ammoniated straw: Performance and microbial characteristics

This paper explores the influence of the mixing ratio of ammoniated straw to biogas residue on the stability and methane yield of dry anaerobic digestion and analyzes the structure of the microbial community with digestion time. Five reactors containing ammoniated straw and swine manure biogas residue at ratios of 5:1, 4:2, 3:3, 2:4 and 1:5 (total solids) were constructed, and neither total ammonia nitrogen nor free ammonia nitrogen was inhibited. Three reactors produced gas successfully. The reactor with a ratio of 3:3 (R3-3) yielded the best methane production, with a cumulative methane production of 115.13 mL/(g·VS_added). Analysis of the R3-3 microbial community showed that bacteria were dominant species. Archaea, mainly Methanosarcina, played an important role in anaerobic digestion and methane production. Methanobacterium, with high acid tolerance, was positively related to total volatile fatty acids (TVFA), playing a key role in preventing the acidification of the anaerobic digestion system.

Impact of temperature, inoculum flow pattern, inoculum type, and their ratio on dry anaerobic digestion for biogas production

This study is aimed to apply dry anaerobic digestion (DAD) for methane (CH₄) enriched biogas production from unsorted organic municipal solid waste (MSW). Cumulative biogas production was monitored for 35 days of operation in batch digesters at fixed feedstock to inoculum (F/I) ratio 2. Anaerobic sludge (AS) and cow manure (CM) were used as inoculum in single and mixed modes. Several process parameters such as inoculum flow pattern (single layer, multilayer, and spiral), digestion temperature (25 to 40 °C), inoculation modes (single and mixed mode), and inoculation proportion (AS:CM = 1:1, 1:2, 1:3, and 2:1) were investigated to determine the optimum DAD conditions to maximize the CH₄ laden biogas yield. The study of inoculum flow pattern showed that digester with multilayer inoculum configuration generated the maximum 555 mL cumulative biogas with the production rate of 195 mL/day (at 25 °C). Biogas production rate and cumulative biogas production were found to increase with a rise in temperature and the maximum values of 380 mL/day and 1515 mL respectively were observed at 37 °C. The mixed mode of inoculation containing AS and CM augmented the biogas yield at previously optimized conditions. Final results showed that digester with multilayer inoculum flow pattern at 37 °C produced 1850 mL cumulative biogas with 1256.58 mL CH₄/kg volatile solid (VS) when the mixed inoculum was used at the AS:CM—1:2 ratio. Biogas production with this significant amount of CH₄ justifies the use of the DAD process for energy (biogas) generation from widely available biomass feedstock (MSW), offering various advantages to the environment.

Roles of micro-aeration on enhancing volatile fatty acids and lactic acid production from agricultural wastes

Micro-aeration was proven to be an environmentally friendly strategy for efficiently enhancing volatile fatty acids (VFAs) and lactic acid (LA) production. The roles of micro-aeration on mono-digestion of swine manure (SM) for VFAs production and co-digestion of SM with corn silage (CS) for LA production were investigated, respectively. In this study, micro-aeration increased the maximum VFAs concentration by 20.3% to 35.71 g COD/L, and shortened the time to reach the maximum from 18 days to 10 days. Micro-aeration limited the conversion of LA into VFAs, leading to LA accumulation effectively to be 26.08 g COD/L. Microbial community analysis suggested that Clostridium and Terrisporobacter were always the dominant bacteria with or without micro-aeration for VFAs production, but the relative abundance increased notably during the same period. However, Bifidobacterium, which could use the higher productivity metabolism pathway, i.e., Bifidum pathway to produce LA, increased from lower than 1% to 22.9% by micro-aeration.

Quantitative hydrodynamic characterization of high solid anaerobic digestion: Correlation of "mixing-fluidity-energy" and scale-up effect

High solid anaerobic digestion (HSAD)'s complex rheological behavior exhibits short-circuiting and dead zone. Mixing optimization is potential to enhance HSAD hydrodynamics. Besides, scale-up effect is quite essential for HSAD's applications, but remains rarely studied yet. Effect of impeller with different width on the correlation of "mixing-fluidity-energy" at different rotating speeds was first investigated at pilot-scale in present work. Then, scale-up effect based on rotating speed and a generalized Reynolds number was revealed from the aspects of fluidity and energy consumption. Results show that impeller width of 100 mm (10 rpm), 200 mm and 300 mm (5 and 10 rpm) are preferred for hydrodynamics and energy economics. Furthermore, Re similarity has better referential significance for the scale-up. In this study, new insight is gained into the correlation of "mixing-fluidity-energy" within a pilot-scale digester. Scale-up effect based Re similarity could potentially offer guidance for HSAD's application in the practical engineering.

Recovery of Household Waste by Generation of Biogas as Energy and Compost as Bio-Fertilizer—A Review

Nowadays, organic waste and especially household waste represents a significant global issue due to population growth. The anaerobic digestion (AD) process is an essential operation contributing powerfully to the valorization of organic waste including food waste in terms of renewable energy generation (biogas) and the rich-nutrient residue that can be utilized as bio-fertilizer. Thus, this process (AD) allows for good recovery of household waste by generating biogas and compost. However, the AD operation has been affected by several key factors. In this paper, we aim to involve different critical parameters influencing the AD process, including temperature, pH, organic loading rate (OLR), carbon to nitrogen ratio (C/N), and total solid content (TS(%)). Further, the paper highlights the inhibition caused by the excessive accumulation of volatile fatty acids (VFAs) and ammoniac, which exhibits the positive effects of co-digestion, pretreatment methods, and mixing techniques for maintaining process stability and enhancing biogas production. We analyze some current mathematical models explored in the literature, such as distinct generic, non-structural, combined, and kinetic first-order models. Finally, the study discusses challenges, provides some possible solutions, and a future perspective that promises to be a highly useful resource for researchers working in the field of household waste recovery for the generation of biogas.

Engineering and microbial characteristics of innovative lab and pilot continuous dry anaerobic co-digestion system fed with cow dung and corn straw

Dry anaerobic digestion (dry-AD) allows high-solid digestion; however, dry-AD application is limited because it is prone to blockage and intermediate inhibition. Here, we reported innovative continuous dry co-digestion systems at both lab and pilot scales. The effects of digestate recirculation ratio, dry mass ratio of cow dung to corn straw (CD:CS), and TS content on the digestion performance were investigated. The effects of the three factors were ranked as follows: TS content > CD:CS > digestate recirculation ratio. The daily biogas production rate reached 0.386 NL/d/g VS with the optimal parameter combination, which was determined to be TS content of 30%, a substrate ratio of 1:3, and a digestate recirculation ratio of 40%. In addition, increasing the CD:CS and TS content increased digestate viscosity, which inhibited biogas production; however, increased abundance of Proteiniphilum and acetoclastic methanogens facilitated biogas production. This study provides empirical support for further application of dry-AD.

Thermal treatment's enhancement on high solid anaerobic digestion: effects of temperature and reaction time

The methane production rate of high solid anaerobic digestion (HSAD) was poor although it was a promising technology with the advantages of small reactor, low energy consumption, and less digestate. In our research before, thermal treatment was proved to enhance HSAD's methane production rate via both batch experiments and continuous experiments of swine manure. However, the effect or investigation of thermal treatment's temperature-time combinations was not yet reported. In this study, swine manure was firstly thermally treated in 500-mL glass bottles with 400-mL work volume at 45-65 °C for 1-4 days. HSAD experiment of 10% solid content was then set up. The VS ratio of substrate to inoculum was 1:1. Thermal treatment at 45 °C (3 days), 55 °C (1 day), and 65 °C (3 days) could obtain the highest methane production rate, which was around 40% higher. Kinetics analysis suggested that the degradation of swine manure was quite different at different temperatures. Furthermore, energy assessment indicated that "thermal treatment + HSAD" had significant advantages in improving HSAD economic feasibility, because the improved methane production rate could compensate for the extra energy utilized for thermal treatment. Heat treatment at 45 °C (4 days) was preferred when the heating equipment was limited. Heat treatment at 55 °C (1 day) was preferred when the floor space and reactor volume were restricted. Heat treatment at 65°C (3 days) was preferred when the requirement of the digestate's sanitary condition is strict.

Comparison of anaerobic co-digestion of pig manure and sludge at different mixing ratios at thermophilic and mesophilic temperatures

The objective of this study is to assess the effects of the mixing ratio on the methane production and digestate dewaterability of co-digestion of pig manure (P) and sludge (S). Batch experiments were carried out at five different P/S mixing ratios at mesophilic and thermophilic temperatures. Compared to sludge anaerobic digestion, co-digestion of pig manure with sludge increased methane yield 83.0%-136.5% at mesophilic temperature and 31.3%-68.0% at thermophilic temperature. The normalized capillary suction time (NCST) and total solids (TS) of sediment (centrifugal dewatering) increased when pig manure proportion of substrate increased. The NCST at thermophilic temperatures (4.87-17.58 s g^-1-TSS) was higher than that at mesophilic temperatures (1.89-10.95 s g^-1-TSS). However, the TS of sediment was close at thermophilic and mesophilic temperatures. The results indicated that anaerobic co-digestion of pig manure and sludge at a proper mixing ratio (P/S = 2:1) provides a good choice for energy recovery and land utilization.

Novel insights of impacts of solid content on high solid anaerobic digestion of cow manure: Kinetics and microbial community dynamics

High solid anaerobic digestion has become the mainstream technology for sustainable on-farm treatment of solid wastes but has not been optimized with respect to increasing solid content in cow manure (CM). In the present study, CM was batch digested at total solid (TS) of 5%, 10%, 15% and 20% and microbial communities were investigated. The process remained stable up to 15% TS. The biomethane production rate at TS of 10% and 15% was reported to be 352.2 mL g^-1 VS and 318.6 mL g^-1 VS, reaching up to 83% and 75% of TS 5% biomethane, respectively. Kinetics results disclosed that the biodegradable organics could be utilized at increasing solid content with decreasing hydrolysis rate. The abundances of hydrogenotrophic and methylotrophic methanogens increased significantly with increasing solid content. This study is of great importance for understanding and application of high solid anaerobic digestion of cow manure.

Perspectives on microbial community in anaerobic digestion with emphasis on environmental parameters: A systematic review

This paper review is aiming to comprehensively identify and appraise the current available knowledge on microbial composition and microbial dynamics in anaerobic digestion with focus on the interconnections between operational parameters and microbial community. We systematically searched Scopus, Web of Science, pubmed and Embase (up to August 2019) with relative keywords to identify English-language studies published in peer-reviewed journals. The data and information on anaerobic reactor configurations, operational parameters such as pretreatment methods, temperature, trace elements, ammonia, organic loading rate, and feedstock composition and their association with the microbial community and microbial dynamics were extracted from eligible articles. Of 306 potential articles, 112 studies met the present review objectives and inclusion criteria. The results indicated that both aceticlastic and hydrogenotrophic methanogenesis are dominant in anaerobic digesters and their relative composition is depending on environmental conditions. However, hydrogenotrophic methanogens are more often observed in extreme conditions due to their higher robustness compared to aceticlastic methangoens. Firmicutes and Bacteroidetes phyla are most common fermentative bacteria of the acidogenic phase. These bacteria secrete lytic enzymes to degrade organic matters and are able to survive in extreme conditions and environments due to their spores. In addition, among archaea Methanosaeta, Methanobacterium, and Methanosarcinaceae are found at high relative abundance in anaerobic digesters operated with different operational parameters. Overall, understanding the shifts in microbial composition and diversity as results of operational parameters variation in anaerobic digestion process would improve the stability and process performance.

LC-MS/MS-based non-isotopically paired labeling (NIPL) strategy for the qualification and quantification of monosaccharides

Investigation into monosaccharides is critical for studies of oligosaccharides structure and function in biological processes. However, monosaccharides quantification is still challenge due to their isomeric structure and high hydrophilic properties. Besides, it was difficult to obtain isotopic internal standards (IS) of each monosaccharide in complex matrixes. Herein, we developed a novel strategy for the qualification and quantification of monosaccharides in urine using two structure analogs 1-(4-methylphenyl)-3-methyl-5-pyrazolone (MPMP) and1-phenyl-3-methyl-5-pyrazolone (PMP) as non-isotopically paired labeling (NIPL) reagents by liquid chromatograph-tandem mass spectrometry (LC-MS/MS). The derivatized monosaccharides by NIPL method not only had sufficient retention time differences on reversed-phase column, but also exhibited predominant product ion pairs (m/z 189 & m/z 175) in the multiple reaction monitoring (MRM) mode. In this method, PMP labeled standards were adopted as one-to-one internal standards (ISs). 12 urinary monosaccharides were successfully determined and the linear ranges expanded five orders of magnitude with limit of quantification (LOQ) varied from 0.09 ng mL^-1 to 0.36 ng mL^-1 as well as the accuracy higher than 98.15% and the relative standard derivation (RSD) lower than 7.92%. With assistance of multivariate analysis, the targeted monosaccharide biomarkers were firstly obtained for the diagnosis of bladder cancer. By the inexpensive NIPL reagents-MPMP/PMP, the developed strategy possessed the specific advantages of low cost, simple operation, high sensitivity and high accuracy for the qualification and quantitation of monosaccharides. As expected, this method will provide an alternative application potential for targeted metabolomics analysis.

Investigation of hydrodynamics in high solid anaerobic digestion by particle image velocimetry and computational fluid dynamics: Role of mixing on flow field and dead zone reduction

High solid anaerobic digestion (HSAD) was a potential organic waste treatment. Compared with low solid anaerobic digestion, it had the advantages of small footprint, less digestate, and low heating energy. However, HSAD's methane production is poor, mainly due to the complex hydrodynamics. In this study, computational fluid dynamics were utilized for HSAD's hydrodynamics investigation at 14.3% solid content and compared to the particle image velocimetry measurement. Then, effects of mixing on hydrodynamics were investigated. The results indicated that the diameter of impeller was critical for the radial mixing, and the distance between the impellers dictated the axial mixing. Besides, rotating speed affected flow velocities significantly, but displayed less effect on expanding the mixing range. Furthermore, HSAD's treating capacity could be increased at large extent by optimizing mixing. The visualization of the hydrodynamics in this study could potentially offer conceptual basis for HSAD's design in practical engineering.

Relieving ammonia inhibition by zero-valent iron (ZVI) dosing to enhance methanogenesis in the high solid anaerobic digestion of swine manure

Relieving from ammonia inhibition and enhancing the utilization of thermodynamically unfavorable propionate are crucial for methane harvest in the high solid anaerobic digestion (HSAD) of ammonia-rich swine manure. In this study, the potential of dosing zero-valent iron (ZVI, 150 um) for enhancing the methanogenesis to resist total ammonia (TAN) over 5.0 g-N·L^-1 was investigated via batch experiments under mesophilic condition. The cumulative methane production was enhanced by 22.2% at ≥160 mM ZVI dosage and the HSAD duration was further shortened by 50.6% at ≥320 mM ZVI dosage. The enhanced methanogenesis was mainly resulted from the full utilization of propionate and the accelerated collapse of posterior-biodegradable organics which might be driven by ZVI. Results of microbial community and qPCR (mcrA) showed that ZVI might trigger the blooming of Methanosarcina (from 27.9% to 78.3%) and Syntrophomonas (0.5% to 3.7%) and attribute to their possible direct interspecies electron transfer (DIET) to enhance propionate utilization. Besides, the main methanogenesis might remain in the effective aceticlastic pathway even under free ammonia (FAN) almost 1.0 g-N·L^-1 because syntrophic acetate oxidizing bacteria (SAOB) decreased to almost none at 320 mM ZVI dosage. Dosing ZVI could relieve HSAD from TAN inhibition and more dosage was required to resist FAN inhibition.

Using air instead of biogas for mixing and its effect on anaerobic digestion of animal wastewater with high suspended solids

This study proposed a new mixing method for anaerobic digestion treating animal wastewater using air as gas source of agitation (named "air mixing") and demonstrated its feasibility by comparing with other mixing modes. The results indicated that the methane production for air mixing was increased by 6.4%, 11.9% and 19.6% compared with biogas mixing, mechanical mixing and no mixing. Air mixing improved the mass transfer and the homogeneous mixing time was shortened from 10 min of mechanical mixing to 1.5 min at the same power input. A transient microaerobic environment was created by air mixing, which increased the hydrolysis efficiency by 1.7-11.4% compared with biogas mixing and facilitated VFAs generation and consumption, as well as promoted the syntrophic relationship between facultative bacteria and hydrogenotrophic methanogens. The relative contribution of the improvement of mass transfer and the reaction of microaerobic environment to methane production was 62.9% and 37.1%, respectively.

Optimizing dry anaerobic digestion at pilot scale for start-up strategy and long-term operation: Organic loading rate, temperature and co-digestion

Dry anaerobic digestion (AD) with high total solid content might upgrade conventional wet AD by enhancing digestion and reducing liquid digestate generation, which was not so popular due to lack of adequate knowledge and perceived operational complexity. In this study long term (447 days) pilot scale investigation was performed for various feedstocks including pig manure, corn straw and sludge. It was found dry method was more suitable for reactor start-up than wet method with relieved inhibition. Volatile fatty acid (VFA)/alkalinity (0.1 ~ 0.4) was effective as dry AD system stability indicator. Organic loading rate of 4.8 kg/(m³·d) and temperature of 48 °C was optimized. Co-digestion achieved better volatile solid removal and system stability. Both hydrogenotrophic and acetoclastic methanogens stably existed in rector while hydrogenotrophic obtained higher abundance. This research contributed to understanding of reactor start-up, system stability indicator and optimized operational conditions (organic loading rate and temperature) during dry AD process.

Experimental research of efficiency of semi-continuous and periodic biogas production processes by using chicken manure bioloadings

Semi-continuous and periodic biogas production processes were investigated. Dry chicken manure containing 40.0 ± 0.5% volatile solids (VS) was used for the production of bioloading. Semi-continuous operation bioreactor and periodic bioreactor were used to implement research. Bioloading was additionally supplemented with newly prepared parts by removing 10% of decomposed mass and by adding the same amount of preheated mass every 7 days (semi-continuous process). The process was periodic when the mass was completely decomposed (after 45 days of the experiment) and fully removed (bioreactor was loaded with a new portion of raw material to 100% of the working volume again). Total duration of both experiments was 90 days. The results show that biogas production by semi-continuous process is more effective than periodic process due to higher total biogas yield (up to 39.7%) and higher methane yield (up to 33.5%). The maximum concentration of CH₄ was determined during the periodic biogas production process, but the difference was only up to 2.1% (68.9% and 66.8%, respectively). Since the produced biogas had quite high average CO₂ and H₂ S concentrations (<40.0% and 2.1 g/m³ , respectively), it is recommended to use filter-adsorbers or biofilters. According to the results, semi-continuous type bioreactor is more effective than periodic. PRACTITIONER POINTS: Maximum CH₄ concentration in biogas, produced during periodic process, is 2.1% higher than during the semi-continuous process. Average CH₄ concentration in biogas, produced during periodic and semi-continuous process, reaches 52.7% and 53.0%, respectively. Biogas and methane yield (during periodic process) is 39.7% and 33.5% lower than during the semi-continuous process. CH₄ concentration decreases (after supplement) about 6.0%-7.0% (during the semi-continuous process), but increases to the next cyclic bioloading supplement. Semi-continuous biogas production process is more efficient than periodic.

Dry anaerobic digestion of organic waste: A review of operational parameters and their impact on process performance

Dry digestion is a suitable technology for treating organic wastes with varying composition such as the organic fraction of municipal solids waste. Yet, there is a need for further research to overcome some of the disadvantages associated with the high total solids content of the process. Optimisation of inoculum to substrate ratio, feedstock composition and size, liquid recirculation, bed compaction and use of bulking agents are some of the parameters that need further investigation in batch dry anaerobic digestion, to limit localised inhibition effects and avoid process instability. In addition, further attention on the relation between feedstock composition, organic loading rate and mixing regimes is required for continuous dry anaerobic digestion systems. This paper highlights all the areas where knowledge is scarce and value can be added to increase dry anaerobic digestion performance and expansion.

Improved biogas production of dry anaerobic digestion of swine manure

In this work, wrapped granular activated carbon (GAC) and acclimated sludge were employed to enhance the efficiency of the dry anaerobic digestion of swine manure in semi-continuous tests. The addition of wrapped GAC increased the volumetric biogas production rate by 10.6%, and the removal efficiencies of TS and VS were enhanced by 5.3% and 6.6%, respectively. The concentration of total volatile fatty acids (TVFA) was 30.3% lower in the GAC reactor, but the total ammonia nitrogen (TAN) content was 15.3% higher. Inoculating with acclimated sludge helped the system survive unfavorable conditions, where the TAN and TVFA contents were around 5,200 mg/L and 8,800 mg/L, respectively, but it failed to improve the biogas production efficiency_. The mechanisms that allowed GAC to increase the production of biogas were related to the improved hydrolysis process, enhanced microbial adhesion, the provision of electronic bridges, and enrichment of functional microorganism.