Traitement anaérobie à haut débit d'eaux usées contenant des LCFA à basse température

High rate anaerobic treatment of LCFA-containing wastewater at low temperature

• Auteur / Autrice : Suniti Singh
• Direction : Jukka Rintala, Piet N. L. Lens
• Type : Thèse de doctorat
• Discipline(s) : Sciences et Techniques de l'Environnement
• Date : Soutenance le 11/12/2019
• Etablissement(s) : Paris Est en cotutelle avec Tampereen yliopisto
• Ecole(s) doctorale(s) : École doctorale Sciences, Ingénierie et Environnement (Champs-sur-Marne, Seine-et-Marne ; 2015-....)
• Partenaire(s) de recherche : Laboratoire : Laboratoire Géomatériaux et Environnement (Champs-sur-Marne, Seine-et-Marne) - Laboratoire Géomatériaux et Environnement / LGE
• Jury : Président / Présidente : Charles Banks
• Jury : Examinateurs / Examinatrices : Jukka Rintala, Piet N. L. Lens, Alla Nozhevnikova, Marta Carballa, Marika Kokko, Eric Van Hullebusch, Giovanni Esposito
• Jury : Rapporteurs / Rapporteuses : Alla Nozhevnikova, Marta Carballa

Mots clés

Mots clés contrôlés

Basses températures

Acides gras

Méthanisation

Eaux usées

Mots clés libres

Basse température

Acide gras à longue chaîne

Laiterie traitement des eaux usées

Low temperature

Long chain fatty acid

Dairy wastewater treatment

Résumé

La hausse des prix des carburants et les incitations favorisant le marché des énergies renouvelables poussent le marché mondial de l'eau et les technologies des eaux usées vers la digestion anaérobie. Les gains financiers résultant de la réduction de l'empreinte de l'usine et du transport des boues constituent également des moteurs économiques importants. La croissance efficace des méthanogènes est la clé de la fonctionnalité AD, pour laquelle les températures mésophiles (30-35 ° C) ou thermophiles (48-55 ° C) et pH 6,8-7,2 sont optimales. Le goulot d'étranglement dans la polyvalence de la mise en œuvre de la DA est son inefficacité à des températures plus basses. Comme un énorme morceau de biosphère est en permanence à moins de 5 ° C, le développement du DLTA fournirait une meilleure efficacité énergétique pour le traitement des eaux usées dans les régions tempérées

Fats, oil and grease (FOG) is a significant constituent in numerous wastewaters such as those in dairy industry. The hydrolysis of FOG results in the production of long chain fatty acids (LCFA) which destabilize the anaerobic treatment process due to their physico-chemical and microbial toxicity effects. Harnessing the high methanogenic potential of FOG necessitates effective treatment of high LCFA loads, wherein the feasibility of LCFA treatment at low temperatures has been not investigated up to now. The aim of this thesis was to study the feasibility of high-rate anaerobic treatment of LCFA-rich wastewaters at low ambient temperatures using a dairy wastewater matrix.The screening of mesophilic inocula for treatment of mixed LCFA containing synthetic dairy wastewater (SDW) in batch studies showed that granular sludge inoculum achieved faster and higher methane yields (76-82% of theoretical yield) than the two municipal digestates (1-72%) at both 20 and 10°C. The LCFA degradative capacity in the granular sludge inoculum was attributed to the presence of β-oxidizing bacteria from the family Syntrophaceae (Syntrophus and uncultured taxa), the acetotrophic activity from Methanosaeta and putative syntrophic acetate oxidizing bacteria (SAOB). Continuous high-rate treatment of SDW was found to be feasible in expanded granular sludge bed (EGSB) reactors at 20°C (hydraulic retention time (HRT) 24 h, LCFA loading rate (OLR) 670 mgCOD-LCFA/L·d, 33% COD-LCFA) with a COD removal of 84–91% and methane yield of 44–51%. SDW feeding for longer than two months resulted in LCFA accumulation, which led to granular sludge flotation (36-57%) and disintegration. To counter the LCFA induced granular sludge disintegration and flotation, a novel reactor type, dynamic sludge chamber-fixed film (DSC-FF), was designed and achieved sCOD removal of 87-98% at HRTs from 12-72 h (LCFA loading rate 220-1333 mgCOD-LCFA/L·d) at 20°C. Moreover, even at the 12 h HRT, the unsaturated LCFAs (linoleate and oleate) were treated and only part of saturated LCFAs (stearate, palmitate) remained after treatment in the DSC-FF reactors. An increased methanogenic activity was established in the reactor sludges during reactor runs; evidenced by a higher acetotrophic activity in the granular sludge (from DSC), and a higher hydrogenotrophic activity in the biofilm (from FF) indicating development of distinct metabolic capabilities in the different reactor compartments. High throughput 16S rRNA sequencing showed that the relative abundance of the acetoclastic methanogen, Methanosaeta increased in EGSB reactors when fed with increased LCFA concentrations. The relative abundance of Methanosaeta increased also in the active microbiomes of granules (from DSC) and biofilm (from FF) during the 150-d reactor operation, demonstrating acetoclastic methanogenesis as the predominant methanogenesis pathway for SDW and LCFA degradation at 20°C. Microbial communities with a high β-oxidizing along with high methanogenic activity were developed during SDW treatment in DSC-FF reactors at 20°C. In DSC-FF reactors, the biofilm microbiome (from FF) had a prominent presence of the β-oxidizing bacteria Syntrophus and the hydrogenotrophic methanogen Methanospirillum; in comparison to the presence of the acetogenic bacteria - Syntrophobacter, Desulfobulbus, and Geobacter in the granular sludge microbiome, suggesting a role of these taxa at different trophic levels during LCFA degradation. In summary, this work demonstrated successful inoculum selection at low temperatures (10 and 20°C), and high-rate anaerobic LCFA degradation at 20°C using combined approaches of inoculum mixture and novel reactor design (here, DSC-FF). The key bacterial and archaeal taxa involved in the anaerobic conversion of LCFA to methane at 20°C were also deduced