Jean-Philippe Delgenès

Pretreatment methods to improve sludge anaerobic degradability: a review.

This paper presents a review of the main sludge treatment techniques used as a pretreatment to anaerobic digestion. These processes include biological (largely thermal phased anaerobic), thermal hydrolysis, mechanical (such as ultrasound, high pressure and lysis), chemical with oxidation (mainly ozonation), and alkali treatments. The first three are the most widespread. Emphasis is put on their impact on the resulting sludge properties, on the potential biogas (renewable energy) production and on their application at industrial scale. Thermal biological provides a moderate performance increase over mesophilic digestion, with moderate energetic input. Mechanical treatment methods are comparable, and provide moderate performance improvements with moderate electrical input. Thermal hydrolysis provides substantial performance increases, with a substantial consumption of thermal energy. It is likely that low impact pretreatment methods such as mechanical and thermal phased improve speed of degradation, while high impact methods such as thermal hydrolysis or oxidation improve both speed and extent of degradation. While increased nutrient release can be a substantial cost in enhanced sludge destruction, it also offers opportunities to recover nutrients from a concentrated water stream as mineral fertiliser.

Effects of lignocellulose degradation products on ethanol fermentations of glucose and xylose by Saccharomyces cerevisiae, Zymomonas mobilis, Pichia stipitis, and Candida shehatae

The inhibitory effects of six lignocellulose degradation products on glucose fermentation by Saccharomyces cerevisiae and Zymomonas mobilis on xylose fermentation by Pichia stipitis and Candida shehatae were studied in batch cultures. Toxic compounds were added in varying concentrations and subsequent inhibitions on growth and ethanol production were quantified. Vanillin was shown to be a strong inhibitor of both growth and ethanol production by xylose fermenting yeasts and S. cerevisiae when it was added to the culture media at a concentration of 1 g l−1. Fermentative activities of Z. mobilis were greatly sensitive to the presence of hydroxybenzaldehyde (0.5 g l−1). Analysis of culture media extracts showed that some of the inhibitors, particularly vanillin and furaldehyde, could be assimilated by the tested microbial strains which resulted in the partial recovery in both growth and ethanol production processes on prolonged incubation.

Total solids content drives high solid anaerobic digestion via mass transfer limitation

The role of the total solids (TS) content on anaerobic digestion was investigated in batch reactors. A range of TS contents from 10% to 35% was evaluated, four replicates were performed. The total methane production slightly decreased with TS concentrations increasing from 10% to 25% TS. Two behaviors were observed at 30% TS: two replicates had similar performances to that at 25% TS; for the two other replicates, the methane production was inhibited as observed at 35% TS. This difference suggested that 30% TS content corresponded to a threshold of the solids content, above which methanogenesis was strongly inhibited. The Anaerobic Digestion Model No. 1 (ADM1) was used to describe the experimental data. The effects of hydrolysis step and liquid/gas mass transfer were particularly investigated. The simulations showed that mass transfer limitation could explain the low methane production at high TS, and that hydrolysis rate constants slightly decreased with increasing TS.

Thermo-chemical pretreatment of a microbial biomass: influence of sodium hydroxide addition on solubilization and anaerobic biodegradability

The influence of sodium hydroxide addition during the thermo-chemical pretreatment of a microbial biomass has been evaluated in terms of particulate chemical oxygen demand (COD) solubilization and anaerobic biodegradability. Both COD solubilization and total solid elimination rates increased with the dose of NaOH added: COD solubilization reached 63%, and total solid elimination was 33% when 5 g Na/l were added. Additional sodium hydroxide addition did not increase COD solubilization further. The observed COD solubilization was due mainly to protein hydrolysis that was directly linked to pH variations. Heating emphasized these pH effects. The higher sodium hydroxide addition (26.1 g/l) led to 85% COD solubilization when heated to 140°C for 30 min instead of 53.2% which was at ambient temperature. Biodegradability and biotoxicity tests were run with pretreated samples. Both methane production and acetate degradation in the presence of pretreated samples were affected as 5 g NaOH/l or more were added. Sodium cation was first suspected to account for the limitations observed. Tests run at pH = 12 with other alkali agents (KOH, Mg(OH)2, or Ca(OH)2), led to the same conclusion: COD solubilization was enhanced but the biodegradability performances were limited. Additional tests run with acetate and increasing NaCl concentrations asserted that sodium cation was not at the origin of the limitations that were attributed to OH− additions: refractory compounds were formed as a consequence of pH modifications.

Xylitol production from D-xylose byCandida guillermondii: Fermentation behaviour

SummaryThe ability ofCandida guillermondii to produce xylitol from xylose and to ferment individual non xylose hemicellulosic derived sugars was investigated in microaerobic conditions. Xylose was converted into xylitol with a yield of 0,63 g/g and ethanol was produced in negligible amounts. The strain did not convert glucose, mannose and galactose into their corresponding polyols but only into ethanol and cell mass. By contrast, fermentation of arabinose lead to the formation of arabitol. On D-xylose medium,Candida guillermondii exhibited high yield and rate of xylitol production when the initial sugar concentration exceeded 110 g/l. A final xylitol concentration of 221 g/l was obtained from 300 g/l D-xylose with a yield of 82,6% of theoretical and an average specific rate of 0,19 g/g.h.

Chemical and biological analysis of endocrine‐disrupting hormones and estrogenic activity in an advanced sewage treatment plant

The steroid hormones estrone (E1), 17β-estradiol (E2), estriol (E3), 17α-ethinylestradiol (EE2), and their conjugated forms were surveyed throughout an advanced sewage treatment plant (STP). The estrogen concentrations in water and sludge samples, collected in October 2004 and April 2005, were determined by gas chromatography-mass spectrometry and liquid chromatography-tandem mass spectrometry. Simultaneously, the estrogenic activity was quantified using estrogen-responsive reporter cell lines (MELN) to investigate the behavior of overall estrogenic compounds. The estrogen concentrations in the inlet ranged from 200 to 500 ng/L, with the contribution of conjugated forms being higher than 50%. The major estrogens in influent were E1 and E3. The estrogenic activity was between 25 and 130 ng/L of E2 equivalents (EEQs). Estrogen concentrations and estrogenicity measured in the inlet and in primary treated sewage were similar, showing a weak impact of primary treatment on hormone removal. In contrast, both estrogen concentration and estrogenicity decreased during biological treatment, with high removal efficiencies (>90%). Estrone, E2, and EE2 persisted in the treated water below 10 ng/L, whereas the estrogenicity was lower than 5 ng/L of EEQs. Estrogen mass flux in the effluent and sludge represented less than 2 and 4%, respectively, of the inlet. Consequently, the fraction of estrogens sorbed into the sludge was very small, and biodegradation was the main vehicle for estrogen elimination. This dual approach, comparing chemical and biological analysis, allowed us to confirm that most of the estrogenic activity occurring in this STP, which receives mainly domestic sewage, resulted from sex hormones.

Dynamics of a pig slurry microbial community during anaerobic storage and management.

ABSTRACT The microbial community of a pig slurry on a farm was monitored for 6 months using both molecular and cultural approaches. Sampling was carried out at all the different stages of effluent handling, from the rearing build-up to slurry spreading. Total DNA of each sample was extracted and analyzed by PCR-single-strand conformation polymorphism (SSCP) analysis using primers targeting the 16S rRNA genes from the archaeal and bacterial domains and also the Eubacterium-Clostridium, Bacillus-Streptococcus-Lactobacillus, and Bacteroides-Prevotella groups. A comparison of the SSCP profiles showed that there were rapid changes in the dominant bacterial community during the first 2 weeks of anaerobic storage and that the community was relatively stable thereafter. Several bacterial populations, identified as populations closely related to uncultured Clostridium and Porphyromonas and to Lactobacillus and Streptococcus cultured species commonly isolated from pig feces, remained present and dominant from the rearing build-up to the time of spreading. Enumeration of fecal indicators (enterococci and Escherichia coli) performed in parallel using cultural methods revealed the same trends. On the other hand, the archaeal community adapted slowly during pig slurry storage, and its diversity increased. A shift between two hydrogenotrophic methanogenic Methanobrevibacter populations from the storage pit to the pond was observed. Microorganisms present in pig slurry at the time of spreading could not be detected in soil after spreading by either molecular or cultural techniques, probably because of the detection limit inherent in the two techniques.

Two-phase anaerobic digestion of solid wastes by a multiple liquefaction reactors process

A new solid-waste treatment process was applied to different vegetable substrates: potato peelings, green salad leaves, green peas mixed with carrots, apple pomace. It involved, at a laboratory scale, several liquefaction digesters, each of them treating one type of waste, coupled to a central methane fixed-film reactor. The influence of pH, load and hydraulic retention time on the process performances was studied at 35°C. On average, except for apple pomace, hydrolysis yields were high (up to 80%) during the liquefaction step. Likewise, the mixture of the acidogenic effluents was degraded in a methanation reactor to an extent of 80%. In a final run with average values near 4 g COD l−1 day−1 for loading rate, and 17 days for hydraulic retention time, overall organic matter removal reached 87%.

Characterisation of the microbial 16S rDNA diversity of an aerobic phosphorus-removal ecosystem and monitoring of its transition to nitrate respiration

Abstract. The microbial community of a conventional anaerobic–aerobic sequencing batch reactor was investigated by cloning and sequencing bacterial 16S rDNA. The 92 16S rDNA sequences analysed ranged across 50 different operational taxonomic units (OTU). The majority of these sequences were not closely related to known species. They belonged to 12 different groups, but essentially to the Cytophagales and the Proteobacteria beta, which represented 38% and 17% of the retrieved sequences respectively. No OTU numerically outnumbered the others. However, similarities were observed with previous reports on molecular characterisation of phosphorus-accumulating ecosystems, suggesting an enrichment in microorganisms belonging to the Rhodocyclus group. Thereafter, the ability of this anaerobic–aerobic microbial community to accumulate phosphorus with nitrate as its energy source was investigated. The reactor was shifted from anaerobic–aerobic running conditions to anaerobic–anoxic conditions by injection of nitrate; and its microbial community was monitored by PCR-single strand conformation polymorphism (SSCP). The reactor maintained a good phosphorus accumulation and similar SSCP microbial community patterns for a period of 17 days, suggesting that the same microbial community was able to respire both oxygen and nitrate. However, this situation was unstable, since a breakdown in phosphorus accumulation occurred thereafter.

Aerobic Denitrifiers Isolated from Diverse Natural and Managed Ecosystems

A bstractTwenty-eight bacterial strains were isolated from an ecosystem adapted to fluctuating oxic–anoxic conditions. This ecosystem comprised a mixture of different natural and wastewater treatment environments. Among the 28 strains isolated, 10 exhibited aerobic denitrifying activity, i.e., co-respiration of oxygen and nitrate and simultaneous production of nitrite by 4 of them and of nitrogen gas by the remaining 6. Comparisons between the 16S rDNA sequences of the 10 strains showed that 3 of them were identical to M. aerodenitrificans, whereas RAPD profiles showed that the 3 strains were identical to each other but that they were different from M. aerodenitrificans. This implies that alternating aerobic–anoxic conditions allowed the isolation of a new strain of this aerobic denitrifier. Moreover, other denitrifying bacteria belonging to the genera Paracoccus, Thiobacillus, Enterobacter, Comamonas, and Sphingomonas were isolated in this way. These data imply that a wide variety of bacteria are able to carry out this type of metabolism. M. aerodenitrificans was also detected in methanogenic, denitrifying, nitrifying, phosphate removal, and activated sludge ecosystems by two-step PCR amplification. After 4 months of acclimation to oxic–anoxic phases, the strain was also detected in a canal and in a pond. This suggests that there is no specific natural ecological niche for aerobic denitrifiers but, as soon as selective pressure such as alternating aeration conditions is applied, this metabolism is amplified.