Leach Bed Reactor Research Articles

Chicken manure and wheat straw co-digestion in batch leach bed reactors: optimization of the start-up conditions

Chicken manure and wheat straw co-digestion in batch leach bed reactors: optimization of the start-up conditions

Evaluation of a leach bed reactor for the anaerobic digestion of drylot collected cattle manure

Conventional anaerobic digestion (AD) technologies are not appropriate for processing drylot collected manure without excessive water addition. An alternative AD approach, the leach bed reactor (LBR), may facilitate the digestion of drylot manures with minimal water use but leach bed reactors (LBRs) are known to experience hydraulic failures with manure wastes. The addition of a top sand layer to LBRs is investigated to facilitate the processing of drylot cattle manure containing up to 90% total solids (TS) without hydraulic failure. Here, LBRs were operated to overcome clogging issues and assess the extent of hydrolysis of organic matter in the manure. The system was operated as a batch process with a digestion time of 42 days. The LBRs showed a mean total chemical oxygen demand (COD) reduction of 51.6% and a total volatile solids reduction of 44.7% in manure. Biochemical methane potential tests on leachate indicated a mean methane yield of 0.13 L CH4/g COD leached. The appropriate operational time for the system was found to be 14 days.

Optimization of water replacement during leachate recirculation for two-phase food waste anaerobic digestion system with off-gas diversion

An integrated two-phase AD with acidogenic off-gas diversion from a leach bed reactor to an upflow anaerobic sludge blanket was developed for improving methane production. However, this system had its own technical limitation such as mass transfer efficiency for solid-state treatment. In order to optimize the mass transfer in this two phase AD system, leachate recirculation with various water replacement rates regulating the total solids contents (TS) at 12.5%, 15%, and 17.5% was aim to investigate its effect on methane generation. The solubilization of food waste was increased with decreasing TS content, while the enzymatic hydrolysis showed the opposite trend. A TS contents of 15% presented the best acidogenic performance with the highest hydrogen yield of 30.3 L H2/kg VSadded, which subsequently resulted in the highest methane production. The present study provides an easy approach to enhance food waste degradation in acidogenic phase and energy conversion in methanogenic phase simultaneously.

Optimal conditions for high solid co-digestion of organic fraction of municipal solid wastes in a leach-bed reactor

Anaerobic co-digestion of organic fraction of municipal solid waste with solid content greater than 20% and chicken manure was investigated using leach-bed reactors in the framework of Middle East and North African countries. The objectives of the experiments were to determine the optimal ratio of organic fraction, chicken manure and solid inoculum, to compare temperature conditions and usage of liquid inoculum or water in percolation process. The highest specific methane yield (SMY) (236 LN ∙ kg−1 VS) was received in the reactors with 20/80 organic fraction/solid inoculum ratio under thermophilic conditions with liquid inoculum percolation. Under the same conditions but mesophilic temperature, SMY dropped by 12%. Replacing liquid inoculum by water led to 172 LN ∙ kg−1 VS. Addition of chicken manure to the substrate mixture positively influences a start-up phase and keeps pH in optimal range 6.5–8, despite the high ammonia concentration.

Dry mesophilic anaerobic co-digestion of vegetable wastes with animal manures using leach bed reactor

Anaerobic digestion is an environmentally sustainable technology for converting a variety of organic solid feedstocks to energy in the form of methane. To improve methane yield, the digestion of more than one waste is commonly applied. This study aimed to investigate the dry anaerobic co-digestion (TS of 20%) of vegetable wastes (VW) and animal manures (cow manure (CM) and poultry manure (PM)) through conducting biochemical methane potential (BMP) assays at different substrate to inoculum (S/I) ratio. Fractionation and fluorescence analyses showed that organic matter of VW was less accessible and less complex compared to that of CM and PM. The highest methane yields of mono-digestion experiments were registered with S/I 0.5. Best results of methane yield were observed by the co-digestion of VW and CM (284 mL/g VS), which was about 2.3-fold higher than that of VW mono-fermentation. This finding was confirmed at a laboratory-scale leach bed reactor. Result showed an increase of biogas yield from 220 to 445 mL/g VS, during mono and co-digestion, respectively. The co-digestion of VW and CM mixture led to the enhancement of both methane yield and digestate quality in comparison to mono-digestion.

Two-Stage Leach-Bed Reactor System is Advantageous Over Single-Stage Continuously Stirred Tank Reactor in Mesophilic Anaerobic Digestion of Fibrous Sorghum

Two-Stage Leach-Bed Reactor System is Advantageous Over Single-Stage Continuously Stirred Tank Reactor in Mesophilic Anaerobic Digestion of Fibrous Sorghum

Quantifying porosity changes in solid biomass waste using a disruptive approach of water retention curves (WRC) for dry anaerobic digestion

Knowledge of the porosity distribution of biomass is crucial to understand the liquid flow through porous solid biomass treated in dry anaerobic digestion (D-AD). In this study, a novel adaptation of Water Retention Curve (WRC) analysis was validated to characterize the pore distribution of representative lignocellulosic biomasses; Cattle Manure (CM), roadside grass and corn stover. WRC analysis is composed of a drainage analysis (DA) and thermogravimetry analysis (TGA). Macro, meso and micropores values ranged from 33 to 63%, 25 to 44% and 7 to 16% for listed raw biomasses. Additionally, changes in porosity distribution of CM treated in sacrificed Leach-Bed Reactor (LBR) were quantifying; macropore volume decreased from 30.4 to 1.7% with the fiber degradation reducing considerably the permeability and increasing the solid bed compaction. The findings of this study suggest that the daily recirculated liquid volume could be progressively adapted considering the physical evolution of the solid bed.

Valorization of food waste and economical treatment: Effect of inoculation methods

We evaluated cost-effective food waste (FW) treatment and synthesis of volatile fatty acids (VFA) using a leach bed reactor (LBR) operated at neutral pH and room temperature to maximize the profit from recovered products. Three inoculation strategies that include (1) inoculum pretreatment, (2) pretreatment plus leachate recycle, and (3) sole leachate recycle were examined and LBR performance was compared in these inoculation conditions. The inoculation method influenced the hydrolysis of FW in the LBR. Hydrolysis yield was as high as 771 ± 4 g cum.sCOD/kg VSadded with the second inoculation method only in a short reaction time of 6 d. Butyric and acetic acids consistently dominated VFA, and the LBR achieved the highest VFA yield of 649 ± 13 g COD/kg VSadded in the second inoculation. Bacterial community dynamics targeting 16S rRNA gene suggested that Roseburia would be the key player to fermentation of slowly biodegradable FW (e.g., fibers), while multiple types of bacteria affiliated with Enterobacteriaceae, Lactococcus, and Bacteroides mainly fermented FW to butyric and acetic acids at initial phase. The operating cost for FW treatment was calculated $88.1-$126.8 per ton of VSadded in the LBR. This study suggests that LBRs can economically stabilize FW only in 6 d without regular inoculation of exogenous microorganisms, along with high VFA recovery.

Acidogenic and methanogenic properties of corn straw silage: Regulation and microbial analysis of two-phase anaerobic digestion

Corn straw silage (CSS) is one of the organic solid residues available for biogas production. The aim of this study was to investigate the possibility and optimal controlling strategy for anaerobic digestion (AD) of CSS. Four leaching bed reactors (LBR) were operated at different pH. Maximum volatile fatty acids (VFAs) concentration of 19.34 g/L was reached at pH 8.0 with acetic and propionic acids as dominant VFAs. The subsequent microbial analysis indicated that abundant bacteria were Firmicutes, Bacteroidetes and Proteobacteria. UASB as methanogenic reactor was integrated with the LBR. The organic loading rate (OLR) could reach 8 g COD/L·d with effective conversion of VFAs. Acetotrophic Methanosaeta and hydrogenotrophic Methanobacterium played major roles in methanogenic process. In the whole process, the results showed that methane yield of 143.4 mL CH4/g volatile solid (VS) was obtained. pH and OLR controls in two-phase AD were feasible for methane production from CSS.

Anaerobic Digestion of Napier Grass (Pennisetum purpureum) in Two-Phase Dry Digestion System Versus Wet Digestion System

Napier grass (Pennisetum purpureum) is a high yield tropical grass with great potential for anaerobic digestion. Two-phase anaerobic dry digestion (TADD), considered an alternative for anaerobic wet digestion system (AWD) with only front-end leach bed reactor (LBR), is added to existing liquid digester, was tested under different leachate circulations, and was compared with AWD. Leachate circulation frequency in LBR was found to highly influence hydrolysis rate and hence improved overall digestibility of the grass fiber. Additional methane yield of 32.5% was achieved when leachate circulation increased from 1 to 4 times per day and diminished to merely 13.7% more at continuous circulation. A shift in methane generation from leachate digester to LBR as digestion time progressed and important biochemical characteristics were discussed. In AWD, operation at an organic loading of 4 kgVS/m3 d gave the highest methane yield at 145.2 m3/tondry, which is 2.3 times higher than TADD due to an advantage in mass transfer in a total wet environment. This work had advanced our understandings on phase separation in anaerobic digestion system and the key methanation performance among dry and wet digestions of the prototypical lignocellulosic biomass.

Efecto de las condiciones de incubación en el pretratamiento aeróbico de los residuos sólidos orgánicos y la producción de ácidos grasos volátiles

In the present work, the effect of an aerobic pretreatment on the hydrolysis and acidogenesis of the organic solid wastes (OSW) was evaluated. The aerobic pretreatment was carried out under three incubation conditions: the first condition was at 30°C for 24 hours (isothermal), the second condition was at 30°C for 12 hours followed by 12 hours at 35°C, and the third condition was at 35°C for 12 hours followed by 12 hours at 40°C. During the aerobic pretreatment, the enzymatic activity was analyzed and the product obtained from the pretreatment was subsequently fermented in anaerobic hydrolytic leach bed (AHLB) reactors to obtain volatile fatty acids (VFA). The best hydrolysis results were achieved with the aerobic pretreatment at 30°C for 24 hours, obtaining activities of xylanases and pectinases of 115 and 73 U g-1 dry matter (DM) respectively after 18 hours and 100 U g-1 DM of proteases at the beginning of the process; values that are 2.7, 2 and 4 times higher than previously report. Also, a hydrolysis constant (k) of 0.081 d-1 was obtained, with the productivity of VFA of 0.82gLr-1d-1, with predominance in acetate, the main precursor of methanogenesis in the final stage of anaerobic digestion.

Leachate recirculation effects on solid‐state anaerobic digestion of Pennisetum hybrid and microbial community analysis

AbstractBACKGROUNDA leach‐bed reactor (LBR) with leachate recirculation is a suitable technology for lignocellulosic biomass anaerobic digestion. In this study, the effect of percolate reflux strategies (continuous recirculation and intermittent recirculation) on methane production from Pennisetum hybrid, a type of energy crop, was investigated using a two‐layered LBR.RESULTSCompared to a solid‐state anaerobic digestion batch test, LBRs with percolate recirculation provide a stable process with a short lag phase by avoiding inhibition of volatile fatty acid accumulation and inoculation effect. The results also indicated that continuous reflux led to a lower accumulative methane yield (56.20 L kg−1 VS) compared to intermittent reflux (78.50 L kg−1 VS), resulting from washing effect and poorer distribution on the lower layer. According to microbial analysis, Bacteroidetes, Firmicutes, Proteobacteria and Synergistetes were the most predominant bacterial phyla in each LBR test sample and aceticlastic methanogen (at least >55%) plays a predominant role for methane production in all samples.CONCLUSIONSThe results indicate that leachate recirculation could provide stable conditions for methane yield; however, two‐layer reactor designs which cannot guarantee the desired distribution in the lower layer result in a low methane yield. Suitable design of LBRs to maintain a well‐distributed reflux leachate should be further investigated. © 2019 Society of Chemical Industry

Green biomass to biogas – A study on anaerobic monodigestion of para grass

Recently, biogas production through anaerobic digestion technology has advanced massively. At the moment, caused by high energy demand and environmental concerns as the world’s population increases, the drive for anaerobic digestion processes is achievement drive within research and the industry for sustainable energy generation. The study evaluated biogas production from anaerobic mono-digestion of para grass in laboratory scale studies. In addition, improvement of the biogas yield from the grass via chemical pretreatment and leaching bed reactors was studied. Methane content of biogas was 54.36 % by mono- substrate. The results revealed that para grass can be treated anaerobically and are a good source of biogas.

Optimizing the Acidification of Cabbage Waste in Leaching Bed Reactor and Analysis of Microbial Community

Optimizing the Acidification of Cabbage Waste in Leaching Bed Reactor and Analysis of Microbial Community

Bio-hydrogen and methane production from two-phase anaerobic digestion of food waste under the scheme of acidogenic off-gas reuse.

Anaerobic hydrolysis of food wastes sourced from bakery (T1), Chinese restaurant (T2), western-style restaurant (T3), and wet market (T4) were performed in leach bed reactors under the scheme of acidogenic off-gas reuse in methanogenic reactor. Results showed that food waste in T3 achieved the highest hydrogen production of 61.0 L/kg·VSadded. Highest activity of hydrogenase in both leachate and digestate samples confirmed the superior performance of H2 production in T3. Mixed acid fermentation with domination of acetate and butyrate was observed in all four treatments, whereas variations in quantification and speciation of the acidogenic products were closely related to the composition of substrates. High volatile solids (VS) removal (76.7%) was observed in T3 while VS reduction rates of the other treatments ranged from 37 to 55%. High COD production of 0.65 gCOD /g·VSadded together with the reuse of elevated acidogenic off-gas ensured the highest specific CH4 production of 0.42 L/g·VSadded in T3.

The production of volatile fatty acids from Napier grass via an anaerobic leach bed process: The influence of leachate dilution, inoculum, recirculation, and buffering agent addition

The production of volatile fatty acid (VFA)-rich leachate as feedstock for methane production is an essential and rate-limiting step in two-stage grass biogasification. Batch experiments were conducted to investigate the influence of leachate dilution, inoculum, recirculation, and buffering agent addition on the acidification of Napier grass in anaerobic leach bed reactors (AnLBRs). Four AnLBRs with 14.17 L effective volume were operated at ambient temperature for 28 days in each experiment. The results clearly demonstrate the significance of the control parameters, particularly leachate dilution and inoculum, in the regulation of grass solubilization. Different dilutions of leachate produced different grass degradation rates. These different dilutions generated 95.62–112.63 g of soluble chemical oxygen demand (SCOD) or 0.52–0.62 g SCOD/g VSadded for those diluted at 1.0–7.0-day intervals compared to 51.50 g SCOD or 0.28 g SCOD/g VSadded for those without dilution. Adding inoculums of 10–30% increased the SCOD to 67.01–115.65 g SCOD or 0.40–0.59 g SCOD/g VSadded. While leachate recirculation and the addition of a buffering agent had less influence on solubilization, which increased by only 6.80–16.41% of SCOD produced. These produced leachates contained orderly acetic, propionic, and butyric acids. The proposed conditions (20% of added inoculum and leachate dilution at a 3.0-day interval), yielded practical degrees of solubilization and acidification of 46.61% and 62.21%, respectively, or 0.56 g SCOD/g VSadded and 0.26 g VFA/g VSadded. These results demonstrate that beneficial control conditions can promote the rapid and practical production of VFAs from grass biomass via an AnLBR.

Changes in microbial community and methanogenesis during high-solid anaerobic digestion of ensiled corn stover

Abstract The stability of corn stover high-solid anaerobic digestion is affected by the low efficiency of solid-liquid mass transfer while the total volatile fatty acids accumulation often occurs during the process leading to acidification of the system and influencing the functional anaerobic microbial community of the system. Therefore, the problems of slow start and unstable process often occurred. In this study, the effects of different leachate spraying working conditions on total volatile fatty acids and microbial community structure were studied. Three batch tests of three 45 L leach bed reactors (LBRs) were conducted with continuously domesticated leachate and operated at different process (total solids of 15–30%, spray time of 2–6 min and spray interval of 3–8 h) to determine the relative influence of biotic and abiotic factors on microbial community structure and methanogenesis. Consequently, that within a certain range of parameter setting, biotic effects please an important role than abiotic effects, revealing microbiological mediation of methanogenesis. Higher methane yield of 188.2 mL/g VS was obtained under the conditions of 30%TS, spray time of 4 min in the first two weeks and 2 min in the third week, and spray interval of 6 h. The sludge reacting for two months was used as inoculum. After two months’ cultivation, the seeding sludge became stability and increased activity, and the microbial colony richness and diversity tend to be stable regardless of the operational parameters. This study enriches the understandings of biotic and abiotic factors of microbial community structure and methanogenesis in high-solid anaerobic digestion.

The role of reflux time in a leach bed reactor coupled with a methanogenic reactor for anaerobic digestion of pig manure: Reactor performance and microbial community

Abstract A leach bed reactor coupled with a continuous stirred tank reactor (LBR-CSTR) is a set of clean production systems that can reduce pig manure (PM) pollution at the source. In this work, the VFA yield in LBR was increased, and then the methane yield was increased by investigating the role of the reflux time in the LBR-CSTR for anaerobic digestion of PM. With 2 reflux times per day, a significant impact on Proteobacteria was observed (the species had increased in abundance by the 6th day), and the methanogenic archaeal diversity increased by 27.08%, the highest methane yield of 167.6 mL/g volatile solids (VS) of PM and the highest solids reduction of 97.35% were obtained. The process improves both the reduction of piggery waste and the production of methane, making it a green and sustainable development process.

An improved hydrodynamic model for percolation and drainage dynamics for household and agricultural waste beds

This study focuses on the hydrodynamic modelling of percolation and drainage cycles in the context of solid-state anaerobic digestion and fermentation (VFA platform) of household solid wastes (HSW) in leach bed reactors. Attention was given to the characterization of the water distribution and hydrodynamic properties of the beds. The experimental procedure enabled the measurement of water content in waste beds at different states of compaction during injection and drainage, and this for two types of HSW and for two other type of wastes. A numerical model, set up with experimental data from water content measurements, highlighted that a capillary-free dual-porosity model was not able to correctly reproduce all the hydrodynamic features and particularly the drainage dynamics. The model was improved by adding a reservoir water fraction to macroporosity which allowed to correctly simulate dynamics. This model, validated with data obtained from agricultural wastes, enabled to explain more precisely the water behaviour during percolation processes and these results should be useful for driving either solid-state anaerobic digestion or fermentation reactors. Indeed, this implies that the recirculation regime will impact the renewal of the immobile water fraction in macroporosity, inducing different concentration levels of fermentation products in the leachate.

Influence of reflux ratio on the anaerobic digestion of pig manure in leach beds coupled with continuous stirred tank reactors

The effect of reflux ratio on the anaerobic mono-digestion of pig manure (PM) in leach beds coupled with continuous stirred tank reactors (CSTRs) has been studied in this work, and contents of volatile fatty acids (VFAs) and biogas yields were determined for three groups of leach bed reactor (LBR) – CSTR systems. The obtained results indicated that the reflux of biogas slurry increased both the pH of the acid-producing phase and acetic acid yield and repeatedly degraded the refractory organic matter in the biogas slurry. The larger reflux ratio increased the inoculation volume and substantially enhanced the mass transfer process. The maximum values of the biogas and methane yields equal to 259.49 and 167.44 mL/g volatile solids, respectively, were achieved at a reflux ratio of 100%. Moreover, the weight of the PM leachate residue was reduced by 94.14%, and the total nutrient content (N + P2O5 + K2O) was relatively high (1.48%), which was suitable for vegetable seedling substrates. In conclusion, during the treatment of PM in LBR–CSTRs, the solid phase remains on the leach bed, and the leachate is supplied to a biogas tank, which effectively increases its stability of operation.