A Mathematical Model of Volatile Fatty Acids (VFA) Production in a Plug-Flow Reactor Treating the Organic Fraction of Municipal Solid Waste (MSW)

1993 ◽  
Vol 27 (2) ◽  
pp. 201-208 ◽  
Author(s):  
E. D. Negri ◽  
J. Mata-Alvarez ◽  
C. Sans ◽  
F. Cecchi
Keyword(s):  
Mathematical Model ◽  
Fatty Acids ◽  
Municipal Solid Waste ◽  
Volatile Fatty Acids ◽  
Flow Reactor ◽  
Plug Flow ◽  
Biomass Concentration ◽  
Organic Fraction ◽  
Initial Biomass Concentration ◽  
Suspended Biomass

A mathematical model of a plug-flow reactor with a fluid recycle has been elaborated to simulate the VFA production process treating the organic fraction of the municipal solid waste. An alternative hydrolytic reaction model (homogeneous - heterogeneous) is proposed. The effect of a possible methanization step is also considered. The effect of process parameters (solid retention time (SRT), pH, recycle ratio) on the reactor performance is analyzed for parameters based on fruit and vegetable waste. The sensitivity of the model to proposed parameters (suspended biomass and initial biomass concentration) is also evaluated. It is found that the reactor production is very sensitive to the system pH. At low SRT, the production of volatile fatty acids (VFA) is proportional to this parameter. As the SRT increases methanization can reduce the VFA production. The effect of the recycle is negligible for the system and operating conditions studied. The effect of suspended biomass and initial biomass concentration was found to be also negligible. For the system analyzed, the pH is a critical parameter and a plug-flow arrangement (without recycle) seems to be the more reasonable election.

The Acidogenic Digestion of the Organic Fraction of Municipal Solid Waste for the Production of Liquid Fuels

1993 ◽  
Vol 27 (2) ◽  
pp. 183-192 ◽  
Author(s):  
E. D'Addario ◽  
R. Pappa ◽  
B. Pietrangeli ◽  
M. Valdiserri
Keyword(s):  
Fatty Acids ◽  
Municipal Solid Waste ◽  
Solid Waste ◽  
Volatile Fatty Acids ◽  
Flow Reactor ◽  
Methyl Esters ◽  
Stream Processing ◽  
Continuous Stirred Tank Reactor ◽  
Organic Fraction ◽  
Counter Flow

Several reactors were tested for the anaerobic conversion of the organic fraction of municipal solid waste into volatile fatty acids. The reactors examined included Batch, Semi-Continuous Stirred Tank Reactor and Multistage-Counter Flow Reactor. After reasonable retention times (12 days), Batch systems operating at 15% w/v of dry matter and under pH controlled at 6.5, gave better performances both in terms of total Volatile Fatty Acids (VFA) concentration (23-24 g/l) and conversion yield (215 g VFA/kg volatile solids). However, these conditions of reaction caused a high level of liquefaction of the feedstock which resulted in a difficult down-stream processing. On the contrary, the acidogenesis under uncontrolled pH, allowed the production of leachates directly processable for acids recovery. Based on this reason, the Multistage-Counter Flow Reactor, operating under uncontrolled pH, appeared to be the most promising system. The leachate obtained from such a system was processed to obtain mixtures of C2-C7 methyl esters, potentially usable as octane enhancers. The digested solid was intended to be dried and refined to obtain soil amendment. A process for the treatment of municipal solid waste based on the previous steps and including conventional sorting facilities and units for the incineration of all residual solids, was evaluated to be economically comparable with landfilling. The revenues from the sales of esters and fertilizers were highly sensitive to the yield of the acidogenic step and to the value and the amount of the derived fertilizer. Further research is still in progress to improve the economics of the process. The activities are addressed to study proper procedures for the improvement of the down-stream processing of the mixtures originating from acidogenesis under almost neutral pH.

scholarly journals Anaerobic Digestion of the Organic Fraction of Municipal Solid Waste in Plug-Flow Reactors: Focus on Bacterial Community Metabolic Pathways

Water ◽  
2022 ◽  
Vol 14 (2) ◽  
pp. 195
Author(s):  
Elena Rossi ◽  
Simone Becarelli ◽  
Isabella Pecorini ◽  
Simona Di Gregorio ◽  
Renato Iannelli
Keyword(s):  
Anaerobic Digestion ◽  
Municipal Solid Waste ◽  
Solid Waste ◽  
Volatile Fatty Acids ◽  
Flow Reactor ◽  
Biogas Production ◽  
Plug Flow ◽  
Central Zone ◽  
Bimodal Distribution ◽  
Organic Fraction

The aim of this study is to investigate the performance of a pilot-scale plug-flow reactor (PFR) as a biorefinery system to recover chemicals (i.e., volatile fatty acids (VFAs)), and biogas during the dry thermophilic anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW). The effects of the hydraulic retention time (HRT) on both outputs were studied, reducing the parameter from 22 to 16 days. In addition, VFA variation along the PFR was also evaluated to identify a section for a further valorization of VFA-rich digestate stream. A particular focus was dedicated for characterizing the community responsible for the production of VFAs during hydrolysis and acidogenesis. The VFA concentration reached 4421.8 mg/L in a section located before the end of the PFR when the HRT was set to 16 days. Meanwhile, biogas production achieved 145 NLbiogas/d, increasing 2.7 times when compared to the lowest HRT tested. Defluviitoga sp. was the most abundant bacterial genus, contributing to 72.7% of the overall bacterial population. The genus is responsible for the hydrolysis of complex polysaccharides at the inlet and outlet sections since a bimodal distribution of the genus was found. The central zone of the reactor was distinctly characterized by protein degradation, following the same trend of propionate production.

scholarly journals Volatile fatty acids build-up and its effect on E. coli inactivation during excreta stabilisation in single-stage and two-stage systems

2018 ◽  
Vol 8 (2) ◽  
pp. 257-267 ◽  
Author(s):  
Joy Riungu ◽  
Mariska Ronteltap ◽  
Jules B. van Lier
Keyword(s):  
Fatty Acids ◽  
Decay Rate ◽  
Volatile Fatty Acids ◽  
Flow Reactor ◽  
Plug Flow ◽  
Single Stage ◽  
Pathogen Inactivation ◽  
Two Stage ◽  
E Coli ◽  
Reactor Length

Abstract Digestion and co-digestion of faecal matter collected from urine diverting dehydrating toilet faeces (UDDT-F) and mixed organic market waste (OMW) was studied in single stage pilot scale mesophilic plug-flow anaerobic reactors at UDDT-F:OMW ratios 4:1 and 1:0. Escherichia coli inactivation and volatile fatty acids (VFA) build-up was monitored at sampling points located along the reactor profile. When applying UDDT-F:OMW ratio of 4:1 at 12% total solids (TS), E. coli inactivation achieved was 2.3 log times higher than that achieved in UDDT-F:OMW ratio of 1:0. In subsequent trials, a two-stage reactor was researched, applying a UDDT-F:OMW ratio of 4:1 and 10 or 12% TS slurry concentrations. Highest VFA concentrations of 16.3 ± 1.3 g/L were obtained at a pH of 4.9 in the hydrolysis/acidogenesis reactor, applying a UDDT-F:OMW ratio of 4:1 and 12% TS, corresponding to a non-dissociated (ND)-VFA concentration of 6.9 ± 2.0 g/L. The corresponding decay rate reached a value of 1.6 per day. In the subsequent methanogenic plug-flow reactor, a decay rate of 1.1 per day was attained within the first third part of the reactor length, which declined to 0.6 per day within the last third part of the reactor length. Results show that a two-stage system is an efficient way to enhance pathogen inactivation during anaerobic digestion.

Modelling of a plug-flow pilot reactor producing VFA by anaerobic fermentation of municipal solid wastes

1994 ◽  
Vol 30 (12) ◽  
pp. 125-132 ◽  
Author(s):  
C. Sans ◽  
J. Mata-Alvarez ◽  
F. Cecchi ◽  
P. Pavan
Keyword(s):  
Mathematical Model ◽  
Volatile Fatty Acids ◽  
Flow Reactor ◽  
Anaerobic Fermentation ◽  
Plug Flow ◽  
Solid Wastes ◽  
Plug Flow Reactor ◽  
Volatile Acid ◽  
Municipal Solid Wastes ◽  
Inhibition Effect

The production of volatile fatty acids (VFA) by anaerobic fermentation of municipal solid wastes was studied at pilot-plant level. A plug-flow reactor (80 1 total volume) without solid or liquid recirculation was employed to digest a mixture of two types of organic fraction of the municipal solid waste (OFMSW): OFMSW mechanically selected and OFMSW coming from a market of fruit and vegetables. The acidogenic process was studied at different retention times (between 2 and 6 days) in the mesophilic (37° ± 2°C) range of temperature. The VFA concentration obtained in the first valve of the tubular reactor ranged from 9.1 to 13.4 g 1−1 and in the outlet sludge oscillated between 11.8 and 23.1 g 1−1, increasing when increasing retention time from 2 to 6 days. A mathematical model of a continuous steady state plug-flow reactor proposed in a previous paper was used to represent the VFA production obtained experimentally. The results obtained when fitting the mathematical model with the experimental results were not sufficiently good. Some modifications of the initial model were considered. The best fitting of the results was obtained when the inhibition effect of the fermentation product on microorganisms growth was taken into account. The errors of this fitting, calculated by least squares, can be considered optimal for retention times between 4 and 6 days, while at shorter retention times the inhibition effect of pH and product makes the volatile acid production lower than the values obtained experimentally.

scholarly journals Effect of Biowaste Sludge Maturation on the Diversity of Thermophilic Bacteria and Archaea in an Anaerobic Reactor

2009 ◽  
Vol 75 (8) ◽  
pp. 2566-2572 ◽  
Author(s):  
M. Goberna ◽  
H. Insam ◽  
I. H. Franke-Whittle
Keyword(s):  
Fatty Acids ◽  
Volatile Fatty Acids ◽  
Flow Reactor ◽  
Thermophilic Bacteria ◽  
Plug Flow ◽  
Phylogenetic Groups ◽  
Anaerobic Reactor ◽  
Prokaryotic Diversity ◽  
Major Shift ◽  
Stable Community

ABSTRACT Prokaryotic diversity was investigated near the inlet and outlet of a plug-flow reactor. After analyzing 800 clones, 50 bacterial and 3 archaeal phylogenetic groups were defined. Clostridia (>92%) dominated among bacteria and Methanoculleus (>90%) among archaea. Significant changes in pH and volatile fatty acids did not invoke a major shift in the phylogenetic groups. We suggest that the environmental filter imposed by the saline conditions (20 g liter−1) selected a stable community of halotolerant and halophilic prokaryotes.

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