Jean Philippe Delgenes

Dry anaerobic digestion in batch mode: design and operation of a laboratory-scale, completely mixed reactor.

A laboratory-scale (40 l) reactor was designed to investigate dry anaerobic digestion. The reactor is equipped with an intermittent paddle mixer, enabling complete mixing in the reactor. Three consecutive batch dry digestion tests of municipal solid waste were performed under mesophilic conditions and compared to operation results obtained on a pilot-scale (21 m(3)) with the same feedstock. Biogas and methane production at the end of the tests were similar (around 200 m(3) CH(4)STP/tVS), and the dynamics of methane production and VFA accumulation concurred. However, the maximal levels of VFA transitory accumulation varied between reactors and between runs in a same reactor. Ammonia levels were similar in both reactors. These results show that the new reactor accurately imitates the conditions found in larger ones. Adaptation of micro-organisms to the waste and operating conditions was also pointed out along the consecutive batches.

The effect of aeration on D-xylose fermentation by Pachysolen tannophilus, Pichia stipitis, Kluyveromyces marxianus and Candida shehatae.

SummaryThe fermentation of D-xylose byPachysolen tannophilus Y2460,Pichia stipitis Y7124,Kluyveromyces marxianus Y2415 andCandida shehatae Y12878 was investigated in aerobic, anaerobic and microaerophilic batch cultures. The aeration rate greatly influenced the fermentations; growth, rate of ethanol production and oxidation of ethanol are affected. Of the strains tested,Pichia stipitis appears superior; under anaerobic conditions it converts D-xylose (20 g/l) to ethanol with a yield of 0.40 g/l and it exhibits the highest ethanol specific productivity (3.5 g of ethanol per g dry cell per day) under microaerophilic conditions.

Microvirgula aerodenitrificans gen. nov., sp. nov., a new Gram-negative bacterium exhibiting co-respiration of oxygen and nitrogen oxides up to oxygen-saturated conditions

A denitrifier micro-organism was isolated from an upflow denitrifying filter inoculated with an activated sludge. The cells were Gram-negative, catalase- and oxidase-positive curved rods and very motile. They were aerobic as well as anoxic heterotrophs that had an atypical respiratory type of metabolism in which oxygen and nitrogen oxides were used simultaneously as terminal electron acceptors. The G&C content was 65 mol%. Our isolate was phenotypically similar to Comamonas testosteroni, according to classical systematic classification systems. However, a phylogenetic analysis based on the 165 rRNA sequence showed that the aerobic denitrifier could not be assigned to any currently recognized genus. For these reasons a new genus and species, Microvirgula aerodenitrificans gen. nov., sp. nov., is proposed, for which SGLY2T is the type strain.

Impact of initial biodegradability on sludge anaerobic digestion enhancement by thermal pretreatment

Thermal treatments with temperature ranging from 60 to 210°C were applied to 6 waste-activated sludge samples originating from high or medium load, extended aeration wastewater treatment processes that treated different wastewaters (urban, urban and industrial or slaughterhouse). COD sludge solubilisation was linearly correlated with the treatment temperature on the whole temperature range and independently of the sludge samples. Sludge batch mesophilic biodegradability increased with treatment temperature up to 190°C. In this temperature range, biodegradability enhancement or methane production increase by thermal hydrolysis was shown to be a function of sludge COD solubilisation but also of sludge initial biodegradability. The lower the initial biodegradability means the higher efficiency of thermal treatment.

Cofermentation of glucose and xylose to ethanol by a respiratory-deficient mutant of Saccharomyces cerevisiae co-cultivated with a xylose-fermenting yeast

Abstract As a part of the alcoholic conversion of lignocelluloses, fermentation of a glucose-xylose mixture by a co-culture process was investigated in oxygen-limited conditions. In batch mixed cultures of Saccharomyces cerevisiae CBS 1200 and Candida shehatae ATCC 22984, ethanol was produced only from glucose. During the fermentation by S. cerevisiae consuming glucose, the fermentation and growth activities of the xylose-fermenting yeast were extremely low, although an optimal condition of oxygen transfer rate in the co-culture was used. The use of a respiratory-deficient mutant of S. cerevisiae CBS 1200 allows significant cell growth of C. shehatae in a batch culture under a favourable oxygen condition. The growth of C. shehatae , however, results in the utilization of glucose, due to the catabolic repression of glucose on the xylose consumption. When the two yeast strains were co-cultivated in a continuous culture, the simultaneous conversion of glucose and xylose was obtained: conversion yields of glucose and xylose were respectively 100% and 27% at a dilution rate of 0.02 h −1 . When the mutant of S. cerevisiae was co-cultivated with Pichia stipitis NRRL Y11545, a rapid xylose-fermenting yeast, the co-fermentation of glucose and xylose was enhanced: ethanol was produced with a yield of 0.42 g of ethanol/g of consumed sugars and the respective yields of glucose and xylose conversions were 100% and 69% at the tested dilution rate of 0.02 h −1 . The advantages of the co-cultivation of a respiratory-deficient mutant of hexose-fermenting and a xylose-fermenting yeast are discussed.

Single-phase and two-phase anaerobic digestion of fruit and vegetable waste: comparison of start-up, reactor stability and process performance.

Single-phase and two-phase digestion of fruit and vegetable waste were studied to compare reactor start-up, reactor stability and performance (methane yield, volatile solids reduction and energy yield). The single-phase reactor (SPR) was a conventional reactor operated at a low loading rate (maximum of 3.5 kgVS/m3 d), while the two-phase system consisted of an acidification reactor (TPAR) and a methanogenic reactor (TPMR). The TPAR was inoculated with methanogenic sludge similar to the SPR, but was operated with step-wise increase in the loading rate and with total recirculation of reactor solids to convert it into acidification sludge. Before each feeding, part of the sludge from TPAR was centrifuged, the centrifuge liquid (solubilized products) was fed to the TPMR and centrifuged solids were recycled back to the reactor. Single-phase digestion produced a methane yield of 0.45 m3 CH4/kg VS fed and VS removal of 83%. The TPAR shifted to acidification mode at an OLR of 10.0 kgVS/m3 d and then achieved stable performance at 7.0 kgVS/m3 d and pH 5.5-6.2, with very high substrate solubilization rate and a methane yield of 0.30 m3 CH4/kg COD fed. The two-phase process was capable of high VS reduction, but material and energy balance showed that the single-phase process was superior in terms of volumetric methane production and energy yield by 33%. The lower energy yield of the two-phase system was due to the loss of energy during hydrolysis in the TPAR and the deficit in methane production in the TPMR attributed to COD loss due to biomass synthesis and adsorption of hard COD onto the flocs. These results including the complicated operational procedure of the two-phase process and the economic factors suggested that the single-phase process could be the preferred system for FVW.

Statistical tools for the optimization of a highly reproducible method for the analysis of polycyclic aromatic hydrocarbons in sludge samples

The aim of this study is to develop and optimize an analytical method for the determination of 14 priority PAHs in sludge samples based on Accelerated Solvent Extraction (ASE) coupled to RP-HPLC/fluorescence detection. Statistical tools were used to demonstrate the influence of the parameters during the optimization steps. The final parameters were selected to provide analytical errors statistically as low as possible. First, couples of excitation/emission detection wavelengths were tested, and some were finally selected to provide errors lower than 2%. It was then demonstrated that PAH extraction efficiencies are not statistically influenced by the ASE parameters. It was also found that the ASE extraction from sludge samples provides statistically similar results to those obtained with traditional Soxhlet extraction, but with a lower reproducibility error. After optimization, the accuracy of the method was validated with a certified sludge. In conclusion, an optimized analytical procedure has been proposed to monitor PAHs during lab-scale experiments requiring highly repeatable and accurate results from a low sample volume contaminated by PAHs at trace levels.

Anaerobic co-digestion of solid waste: Effect of increasing organic loading rates and characterization of the solubilised organic matter

The impact of stepwise increase in OLR (up to 7.5kgVS/m(3)d) on methane production, reactor performance and solubilised organic matter production in a high-loading reactor were investigated. A reference reactor operated at low OLR (<2.0kgVS/m(3)d) was used solely to observe the methane potential of the feed substrate. Specific methane yield was 0.33lCH(4)/gVS at the lowest OLR and dropped by about 20% at the maximum OLR, while volumetric methane production increased from 0.35 to 1.38m(3)CH(4)/m(3)d. At higher loadings, solids hydrolysis was affected, with consequent transfer of poorly-degraded organic material into the drain solids. Biodegradability and size-fractionation of the solubilised COD were characterized to evaluate the possibility of a second stage liquid reactor. Only 18% of the organics were truly soluble (<1kD). The rest were in colloidal and very fine particulate form which originated from grass and cow manure and were non-biodegradable.

DEFINITION OF OPTIMAL CONDITIONS FOR THE HYDROLYSIS AND ACIDOGENESIS OF A PHARMACEUTICAL MICROBIAL BIOMASS

The effect of operational parameters such as hydraulic retention time (HRT), influent substrate concentration (So), pH, temperature and recycling on the acidogenic digestion of a pharmaceutical biomass was investigated. The total COD content of the pharmaceutical effluent used was 50 g/litre, only 13·6% occurred in soluble form and consisted mostly of protein (22 g/litre). Substrate degradation was quantified in terms of COD, protein and carbohydrate degradation. Variations in COD solubilization were mainly due to protein solubilization. The best results, in terms of COD solubilization and concentrations of produced VFA, were obtained at pH = 8·5, T = 35°C and OLR = 5·4 gCOD/litre/day. Under these conditions 50·6% of the initial COD content was solubilized and 17·1 g/litre of volatile fatty acids (VFA) were produced. Recycling of biomass resulted in greater COD solubilization but in lower acidogenic activity. Moreover, the effluent of the acidogenic reactor showed poor settling properties.

Anaerobic Digestion of Solid Wastes Needs Research to Face an Increasing Industrial Success

Anaerobic digestion of solid wastes is an emerging solution for both waste management and energy production. The high complexity of the process is mostly attributed to the absence of descriptors for the design and the prediction of such a process. This paper presents an approach for the description of organic matter based on several biochemical parameters, established on 22 different organic wastes. The lignocellulosic content is the most important parameter for the prediction of anaerobic biodegradability and methane production; in addition, the knowledge of the carbohydrate, lipid and protein contents is also crucial and makes possible a prediction of the intrinsic kinetics of the reaction.