title: Effect of the length of the cycle on biodegradable polymer production and microbial community selection in a sequencing batch reactor.
abstract: The effect of the length of the cycle on the enrichment and selection of mixed cultures in sequencing batch reactors (SBRs) has been studied, with the aim of biodegradable polymers (namely, polyhydroxyalkanoates (PHAs)) production from organic wastes. At a fixed feed concentration (20 gCOD/L) and organic loading rate (20 gCOD/L/day), the SBR was operated at different lengths of the cycle, in the range 1-8 h. Process performance was measured by considering the rates and yields of polymer storage and of the competing phenomenon of growth. The selected biomass was enriched with microorganisms that were able to store PHAs at high rates and yields only when the length of the cycle was 2 or 4 h, even though in these conditions the process was unstable. On the other hand, when the length of the cycle was 1 or 8 h, the dynamic response of the selected microorganisms was dominated by growth. The best process performance was characterized by storage rates in the range 500-600 mgCOD/gCOD/h and storage yields of 0.45-0.55 COD/COD. The corresponding productivity of the process was in the range 0.25-0.30 gPHA/L/h, the highest values obtained until now for mixed cultures. The microbial composition of the selected biomasses was analyzed through denaturing gradient gel electrophoresis (DGGE) and reverse-transcriptase denaturing gradient gel electrophoresis (RT-DGGE). The instability of the runs characterized by high storage rate was associated with a higher microbial heterogeneity compared to the runs with a stable growth response.
authors.affiliation: Department of Chemistry, University of Rome La Sapienza, P.le Aldo Moro 5, 00185 Rome, Italy. davide.dionisi@uniroma1.it
authors.forename: Davide
authors.initials: D
authors.lastname: Dionisi
authors.forename: Mauro
authors.initials: M
authors.lastname: Majone
authors.forename: Giovanni
authors.initials: G
authors.lastname: Vallini
authors.forename: Simona Di
authors.initials: SD
authors.lastname: Gregorio
authors.forename: Mario
authors.initials: M
authors.lastname: Beccari
mesh_terms: D001420:Bacteria, Aerobic / Q000145:classification* / Q000378:metabolism*; D001673:Biodegradation, Environmental; D019149:Bioreactors / Q000382:microbiology*; D018929:Cell Culture Techniques / Q000379:methods*; D003198:Computer Simulation; D007220:Industrial Waste / Q000517:prevention & control; D008954:Models, Biological; D054813:Polyhydroxyalkanoates / Q000378:metabolism*; D012722:Sewage / Q000382:microbiology*; D013045:Species Specificity
chemical_list: D007220:Industrial Waste; D054813:Polyhydroxyalkanoates; D012722:Sewage