Anaerobic digestion of cellulose fraction of domestic refuse by means of rumen microorganisms (original) (raw)
Related papers
Biological Wastes, 1987
The anaerobic digestion of a cellulose-enriched fraction of domestic refuse by means of rumen microorganisms in an "artificial rumen" digester was studied. Various combinations of solid and liquid retention times and loading rates were applied to establish optimum conditions for the acidogenic phase digestion of the refuse fraction. An optimal substrate conversion of about 72% was obtained at a loading rate of 23.4 g volatile solids (VS)/L d and a solids retention time of 90 h. Variation of dilution rate between 1.04 and 3.14 fermentor volume turnovers per day had no effect on degradation efficiency. At a loading rate of 23.4 g VS/L d a differential removal rate of solids and liquids appeared to be necessary t o obtain an effective degradation of the refuse fraction.
Biotechnology and Bioengineering, 1988
A novel two-stage anaerobic process for the microbial conversion of cellulose into biogas has been developed. In the first phase, a mixed population of rumen bacteria and ciliates was used in the hydrolysis and fermentation of cellulose. The volatile fatty acids (VFA) produced in this acidogenic reactor were subsequently converted into biogas in a UASB-type methanogenic reactor.A stepwise increase of the loading rate from 11.9 to 25.8 g volatile solids/L reactor volume/day (g VS/L/day) did not affect the degradation efficiency in the acidogenic reactor, whereas the methanogenic reactor appeared to be overloaded at the highest loading rate. Cellulose digestion was almost complete at all loading rates applied. The two-stage anaerobic process was also tested with a closed fluid circuit. In this instance total methane production was 0.438 L CH4g VS added, which is equivalent to 98% of the theoretical value. The application of rumen microorganisms in combination with a high-rate methane reactor is proposed as a means of efficient anaerobic degradation of cellulosic residues to methane. Because this newly developed two-phase system is based on processes and microorganisms from the ruminant, it will be referred to as “Rumen Derived Anaerobic Digestion” (RUDAD-) process.
Anaerobic Digestion of Sewage Wastewaters with Sludge and Rumen Fluid
2014
Anaerobic digestion was conducted at mesophilic (37 o C) and thermophilic (55 o C) conditions using sewage wastewaters as the substrate and sludge and/or rumen fluid as the inoculum, with a view to optimize biogas production. The substrate and inoculum were mixed in the ratios 1:1, 1:3, and 3:1 (volume by weight (where sludge was used) or volume by volume (where rumen fluid was used).At mesophilic conditions for both inocula, the 3:1 substrate/inoculum mixture produced the most biogas in a 24 hour period, with the rumen mixture producing the highest yield (20 ml). At thermophilic conditions the 3:1 wastewater/sludge mixture had the highest biogas yield (58 ml), whereas when rumen fluid was used as inoculum, the 1:3 mixture produced the most biogas (66 ml). The thermophilic experiments using rumen as the inoculum were repeated for a 10 day period and the 3:1 mixture achieved the maximum yield (140 ml) faster than the other two (1:1 and 1:3 mixtures) indicating that the 3:1 substrate/...
Anaerobic digestion of lignocellulosic biomass and wastes
Applied Biochemistry and Biotechnology, 1991
Anaerobic digestion represents one of several commercially viable processes to convert woody biomass, agricultural wastes, and municipal solid wastes to methane gas, a useful energy source. This process occurs in the absence of oxygen, and is substantially less energy intensive than aerobic biological processes designed for disposal purposes. The anaerobic conversion process is a result of the synergistic effects of various microorganisms, which serve as a consortium. The ratelimiting step of this conversion process has been identified as the hydrolysis of cellulose, the major polymeric component of most biomass and waste feedstocks. Improvements in process economics therefore rely on improving the kinetic and physicochemical characteristics of cellulose degrading enzymes. The most thoroughly studied cellulase enzymes are produced by aerobic fungi, namely Trichoderma reesei. However, the pH and temperature optima of fungal cellulases make them incompatible for use in anaerobic digestion systems, and the major populations of microorganisms involved in cellulase enzyme production under anaerobic digestion conditions are various bacterial producers. The current state of understanding of the major groups of bacterial cellulase producers is reviewed in this paper. Also addressed in this review are recently developed methods for the assessment of actual ceUulase activity levels, reflective of the digester "hydrolytic potential," using a series of detergent extractive procedures.
Enhancement of solubilization rate of cellulose in anaerobic digestion and its drawbacks
Process Biochemistry, 2011
Hydrolysis is widely acknowledged as the rate-limiting step in anaerobic digestion of solid cellulose to biogas (methane), and pretreatment is generally considered to facilitate the process. However, few studies have investigated how such pretreatment may affect the rest of this complex process. The present study compared the solubilization rate in anaerobic digestion of cotton linter (high crystalline cellulose), with that of regenerated cellulose (amorphous cellulose), using pretreatment with NMMO. Batch digestions were performed, with the initial cellulose concentrations ranging between 5 and 40 g/l, and during 30 days of incubation, biogas and VFAs production as well as pH and COD changes were measured. The lag time before digestion started was longer for the high crystalline cellulose than for the amorphous one. The maximum solubilization rates of treated cellulose were 842 and 517 mg sCOD/g cCOD/day at the initial cellulose concentration of 5 and 30 g/l, respectively, while the solubilization rate of untreated cellulose never exceeded 417 mg sCOD/g cCOD/day. The difference between the two cellulose types was a direct result of the high rate of hydrolysis inhibiting the acetogenesis/methanogenesis microorganisms, a drawback to the rest of the process.
Applied Microbiology and Biotechnology, 1986
An in vitro continuous fermentation device is described which allows the maintenance of a mixed rumen microbial population under conditions similar to those in the rumen. The differences in flow rates of solids and liquids found in the rumen were established in vitro by means of a simple filter construction. A grass-grain mixture was used as a solid growth substrate. During a test period of 65 days the artificial rumen fermenter showed stable operation with respect to ciliate numbers, fibre degradation and volatile fatty acids production. Values obtained were comparable to those found in vivo. Optimal fibre degradation and volatile fatty acids production were maintained when hydraulic retention times (HRT) ranged from 11 to 14h. At these HRT-values ciliate numbers were maintained at about 8.5 x 104 cells per ml. Ciliate numbers declined drastically at HRT-values above 14 h. A fermenter inoculated with a small volume of rumen fluid (1:100, v/v) reached normal protozoal numbers, fibre degradation and volatile fatty acids productions after a start up period of only 8 to 10 days. The possible application of tureen microorganisms for an efficient degradation of lignocellulosic waste material in an artificial rumen digester is discussed.
Utilization of Rumen Content by Indigenous Microorganisms in a Modified Anaerobic Digester
Energy Research Journal, 2020
The current work was designed to assess the effect of modification of model digester on the kinetics that affects efficiency in biogas generation using bovine rumen content as the feedstock. A biogas plant consisting of conventional and modified fixed-dome digesters (each with 2 m 3 capacity) was established; and bovine rumen content was used as feedstock. Standard methods were used to determine the kinetic (physicochemical and microbiological) parameters. Identification of fungal and bacterial species involved in the process was carried out by genomic study of the 18S rRNA and 16S rRNA regions, respectively; amplified using universal forward and backward primers for fungi (NS1/NS4), bacteria ((515F/926R) and archaea (Met86F/Met140R); submitted to GenBank and analysed using Blast Programme at National Centre for Biotechnology Information website. A mass balance approach was used to estimate the theoretical gas yield from the total solid/volatile sold lost. It was found that the temperature in both modified and conventional digesters was uniform throughout the hydraulic retention time, between 32 to 34.5C, indicating a mesophilic range. The pH level was found to be lower in the modified digester compared to the conventional digester, indicating higher accumulation of organic acids. The mean total solid was found to drop from 12.49±0.53 to 3.82±0.21 in the modified digester after digestion, while this was from 13.30±0.4 to 6.69±0.16 in the conventional digester. The mean volatile solid drops from 66.67±1.62 to 36.13±0.27 in the modified digester after digestion, while it was from 69.94±1.54 to 54.23±1.33 in the conventional digester. The theoretical biogas yield was higher in the modified digester (87 mg/l) compared to the conventional one (65 mg/l). The microbial counts were observed to be affected by the kinetic parameters in both the digesters. The organisms identified were: Lactobacillus acidophilus, Bacteroides nordii, Clostridium perfringens, Clostridium acetobutylicum, Proteus vulgaris, Methanosarcina sicilia, Methanosarcina mazei, Methanobrevibacter ruminantium, Fusarium solani, Fusarium graminearum, Aspergillus niger and Penicillium specie. Conclusively, the modified digester, under a manual stirring at 10 round/min, 3 times a day at an interval of six hours, has appreciably generated higher theoretical biogas yield after 8 weeks hydraulic retention time. The agitation of the slurry using the improvised stirrer in the modified digester has significantly facilitated the utilization of the bovine rumen content by the indigenous microorganisms. Modification of digester to enhance mixing of the feedstock should therefore be encouraged in household anaerobic digesters.
Digestate liquor recycle in minimal nutrients-supplemented anaerobic digestion of wheat straw
Biochemical Engineering Journal, 2015
Anaerobic digestion (AD) of minimal nutrient-supplemented wheat straw and digestate liquor recycle was evaluated in semi-continuous processes using a novel BioReactor Simulator developed for easy accurate online normalised-gas measurement. Three scenarios (i) no recycle (NR), (ii) recycle of soluble nutrient (RSN), and (iii) recycle of nutrient and microbes (RNM) were investigated in order to evaluate their respective efficiencies. Although mono-digestion of lignocellulosic biomasses are often performed with very long solid retention times (SRT), the present study demonstrated an efficient process operating with a 30-day SRT and an organic loading rate of 4 g VS/L d. The best methane yield was 303 mLCH 4 /g VS achieved in the RSN process showing a 21% improvement as compared to the NR process. The methanogenic potential of the digestates from the RSN and RNM processes was comparable to fresh inoculum indicating efficient processes. The RNM and RSN processes showed superior process stability evidenced by minimal volatile fatty acid accumulation (<0.5 g/L). As compared to the RNM process, RSN demonstrated the best performance. The improved process performance was probably due to higher nutrient and microbial concentration in the digestate-recycled processes. This study confirms the feasibility of digestate recycle in AD as an appropriate technology for treating nutrient-deficient substrates.
FEMS Microbiology Ecology, 2014
Cellulose hydrolysis often limits the kinetics and efficiency of anaerobic degradation in industrial digesters. In animal digestive systems, specialized microorganisms enable cellulose biodegradation at significantly higher rates. This study aims to assess the potential of ruminal microbial communities to settle and to express their cellulolytic properties in anaerobic digesters. Cellulose-degrading batch incubations were co-inoculated with municipal solid waste digester sludge and ruminal content. 13 C-labeled cellulose degradation was described over time with Gas Chromatography-Combustion-Isotope Ratio Mass Spectrometry. Results were linked to the identification of the microorganisms assimilating 13 C and to the monitoring of their relative dynamics. Cellulose degradation in co-inoculated incubations was efficient but not significantly improved. Transient disturbances in degradation pathways occurred, as revealed by propionate accumulation. Automated Ribosomal Intergenic Spacer Analysis dynamics and pyrosequencing revealed that expected classes of Bacteria and Archaea were active and degraded cellulose. However, despite the favorable co-inoculation conditions, molecular tools also revealed that no ruminal species settled in the bioreactors. Other specific parameters were probably needed for this to happen. This study shows that exploiting the rumen's cellulolytic properties in anaerobic digesters is not straightforward. Co-inoculation can only be successful if ruminal microorganisms manage to thrive in the anaerobic digester and outcompete native microorganisms, which requires specific nutritional and environmental parameters, and a meticulous reproduction of the selection pressure encountered in the rumen.