Microbial ecology of novel bioprocesses for biogas recovery and short-cut nutrients removal from wastewater

L’ecologia microbica è focalizzata su come le popolazioni microbiche si associno per formare comunità e come queste comunità interagiscano tra loro e con l’ambiente. Le performances dei processi biologici dipende strettamente dall’attività e dalle interazioni tra le comunità microbiche. Perciò avere informazioni sulle identità dei microrganismi responsabili di specifiche attività è importante ai fini di ottimizzare questi processi. Le caratteristiche di biofilm problematici (come fouling e clogging) sono stati studiati ponendo l’attenzione sulla rimozione e il destino dei metalli in tracce durante l’attività di un impianto a membrane in scala pilota per il trattamento di acque reflue reali di una zona industriale. I risultati mostrano che il biofilm era più efficace della biomassa sospesa nell’assorbimento di Az>Zn>Ni>Cd>Sb>Fe>Se a causa dell’effetto sinergico dei composti polimerici extracellulari e la presenza di batteri resistenti ai metalli. Infatti è stata osservata la speciazione selettiva verso il phylum Bacteriodetes, altamente resistente ai metalli, nel fango di clogging di membrana, nonostante la bassa concentrazione di metalli disciolti nel bioreattore. In confronto alla biomassa sospesa, il biofilm incrementa il bioassorbimento di sostanze molto tossiche come As, Cd e Ni. L’effetto combinato del pH e della comunità microbica selezionata, e il minor effetto del potenziale redox, ci permette di concludere che sono maggiormente importanti i meccanismi di bio-assorbimento/rilascio piuttosto che la bio-precipitazione/dissoluzione. È stato effettuato un processo di digestione anaerobica in 2 fasi per la produzione contestuale di idrogeno e metano attraverso il trattamento della frazione organica di rifiuti solidi urbani in scala pilota. I risultati mostrano che anche senza un inoculo è possibile la produzione stabile di bio-hytane. Analisi sulla popolazione microbica mostrano che le specie dominanti il fermentatore sono appartenenti alla famiglia Lactobaccillus, mentre la popolazione del digestore anaerobico era composta prevalentemente da Defluviitoga tunisiensis. La popolazione Archaea cambiò da Methanothermobacter a Methanobacteriales e Methanosarcinales, l’ultimo trovato anche nel fermentatore, dove veniva prodotta una considerevole quantità di metano. Il liquame suino può essere un eccellente substrato per la digestione anaerobica, ma ha una bassa resa in biogas e produce alte concentrazioni di ammoniaca. Rifiuti contenenti grassi possono essere co-substrati ideali per la produzione di metano. Studi hanno evidenziato una serie di problematiche dovute all’utilizzo di questo substrato. Nel nostro caso abbiamo raggiunto il carico organico di 3 g COD/Ld di lipidi. La comunità Archaea non cambiò tra biomassa adattata e non adattata ai lipidi, mentre la comunità batterica della biomassa capace di degradare i lipidi era dominata dal phylum Firmicutes , dove membri del genere Pseudomonas erano probabilmente responsabili della degradazione degli acidi grassi a catena lunga.

The science of microbial ecology is focused on how microbial populations assemble to form communities and how these communities interact with each other and their environment. The performance of biological processes in operation in the wastewater treatment plants strongly depends on the activities and interaction of the microbial community. Thus, information on the identity of microorganisms responsible for specific activities are important for optimizing these processes. The characteristics of problematic biofilms (i.e., fouling and clogging layers) were studied with regards to the removal and fate of trace metals during the long-term operation of a pilot-scale membrane bioreactor for the treatment of real wastewaters from a large industrial area. Results showed that clogging layer was more effective than suspended activated sludge in the biosorption of As > Zn > Ni > Cd > Sb > Fe > Se due to the synergic effects of extracellular polymeric compounds and metal-resistant bacteria. In fact the selective microbial speciation of the phylum of Bacteroidetes, which is highly resistant to heavy metals, was observed in the clogging sludge in spite of the very low concentration of dissolved metals in the bioreactor. Compared to the suspended activated sludge, the clogging layer enhanced the biosorption of very toxic substances such as As, Cd and Ni. Then, the potential desorption of metals during the membrane acid cleanings was estimated as relevant as 10–15% of the metals associated to the clogging sludge. The combined effects of pH and the selected microbial community, and the minor effect of the redox potential, let us conclude on the major importance of bio-sorption/desorption mechanisms with respect to bio-precipitation/dissolution. A thermophilic two-phase anaerobic digestion process for the concurrent production of H2 and CH4 through the treatment of source sorted organic fraction of municipal solid waste was carried out over a long-term pilot scale experience. The results showed that stable production of bio-hythane without inoculum treatment could be obtained. The pH of the dark fermentation reactor was maintained in the optimal range for hydrogen producing bacteria activity through sludge recirculation from a methanogenic reactor. An average specific bio-hythane production of 0.65 m3/kg of volatile solids fed was achieved when the recirculation flow was controlled through an evaporation unit in order to avoid inhibition problems for both microbial communities. Microbial analysis indicated that dominant bacterial species in the dark fermentation reactor are related to the Lactobacillus family, while the population of the methanogenic reactor was mainly composed of Defluviitoga tunisiensis. Archaeal community of the methanogenic reactor shifted, moving from Methanothermobacter-like to Methanobacteriales and Methanosarcinales, the last one found also in the dark fermentation reactor, with considerable methane production. Pig manure (PM) can be an excellent base substrate for anaerobic digestion due to its inherent buffering capacity and high content of a wide range of nutrients required for the development of anaerobic microorganisms. However, PM has a low biogas yield and high ammonium concentrations. Consequently, PM is preferably co-digested with high carbon content wastes, to improve the C/N ratio and increase the biogas production, essential for the plant’s economy. Lipid wastes are ideal substrates for methane production, since theoretically their degradation produces more biogas with higher methane content, when compared with proteins or carbohydrates. Studies investigating the anaerobic digestion of high-strength lipid wastes have reported a wide assortment of operational challenges. The aims of this project were to understand the degradation pathways of real wastes containing high percentages of lipids, to determine the optimal conditions to treat lipid wastes in anaerobic co-digestion with pig manure and to characterize the microbial community responsible for specific Long Chain Fatty Acid degradation pathways using PCR-DGGE and FISH analyses. In this work we demonstrated that anaerobic biomass can be adapted to high lipid concentration using a continuous feeding strategy in co-digestion with pig manure as a source of humidity and alkalinity and the adaptation is not related to the type of LCFA composing the lipid substrate. In our case the maximum reached OLR was 4 g COD/Ld, where the lipid OLR was 3 g COD/Ld. The Archaeal community did not change between adapted and non-adapted biomasses, while the Bacterial community of the lipid degrading bacterial community was dominated by the phyla Firmicutes, where members of the Pseudomonas genus are probably responsible of the LCFA degradation. Biological nutrients removal via-nitrite has gained interest recently due to several advantages over the conventional processes. In this processes the role of certain short chain fatty acids as carbon source is crucial for the nutrients removal. but a gap of knowledge about their influence on the speciation of heterotrophic denitrifying microbial populations. including denitrifying phosphorus accumulating organisms. The purpose of this study is to investigate the microbiological composition of a via-nitrite process when different carbon sources for nutrients removal are used. A demonstration sequencing batch reactor treating supernatant from anaerobic co-digestion of sewage sludge and OFMSW was stably operated via-nitrite pathway. In long term operation different external carbon sources were tested. In particular. microbial community of the sludge during acetic acid and fermentation liquid of the organic fraction of municipal solid waste (OFMSW) dosage was analyzed through PCR-DGGE technique using primer set for the universal eubacterial V3 region within 16S rRNA gene. Results showed that the microbial community was mainly composed of Bacteroidetes. including Sphingobacteriaceae. and Proteobacteria. In particular a strong speciation to a few species of denitrifying bacteria commonly present in reactors with high F/M was observed. This result is in accordance with the operating conditions and observed denitrifying activity of the biomass (NUR 0.65÷1.14 kgNO2-N kgVSS-1day-1). Using the OFMSW fermentation liquid as external carbon source. the highest biological phosphorous removal was observed. with a Maximum Phosphorus Uptake Rate of 0.37±0.09 kgPO4-P kgVSS-1day-1. In this specific case. a high NLR (1.14 gN-NH3/d) and F/M. coupled with OFMSW fermentation liquid were the driving forces to the speciation of a biomass composed of members of the CFB group related to the genus Cytophaga and γ-Proteobacteria (genus Thermomonas). which are related to the enhanced phosphorus biological removal via-nitrite.