El modelo de reducción de signos sociales

Guiot et al. (2000) studied degradation of phenol, ortho- and para-cresol in upflow anaerobic sludge blanket reactors bioaugmented with different amounts of an enriched methanogenic mixed culture that was able to degrade these specific chemicals. Addition of 2 to 5% enrichment culture (expressed as mass/mass with respect to the non-

acclimated granular innoculum biomass) decreased the start-up period of the reactor to 55 days to achieve 80% phenol degradation, whereas the control reactor fed with no

enrichment culture took 100 days to achieve the same level of phenol degradation. During continuous operation of the reactors, the bioaugmented reactors showed at least two-fold more specific activity to degrade the targeted compounds as compared to the non-bioaugmented reactor.

Guiot et al. (2002) studied enrichment of anaerobic sludge for the degradation of pentachlorophenol (PCP) by an on-line control-based selective stress strategy (controlling the feeding rate of PCP by feedback control from methane percentage in the biogas

produced) and bioaugmentation of anaerobic sludge using the PCP-degrading microbe Desulfitobacterium frappieri (PCP-1). Both the selective stress strategy and the PCP-1- augmented culture resulted in a specific degradation rate of 4 mg PCP g-1 VSS day-1, but the selective stress control system culture took 120 days to attain complete degradation capacity while the bioaugmented culture took only 56 days. Furthermore, fluorescent in situ hybridization (FISH) of granule cross sections showed no fluorescence signal for PCP -1 specific probes in the selective stress strategy enrichment culture, whereas a strong fluorescence signal for PCP-1 was present in the culture bioaugmented with PCP-1 after 5 and 9 weeks.

Ahring et al. (1992) bioaugmented anaerobic granules using a pure culture of a 3- chlorobenzene (3-CB) degrading microbe (Desulfomonile tiedjei) to impart 3-CB

dechlorinating ability to UASB reactors. Also a three-member consortium containing D. tiedjei, a benzoate degrading coculture and a hydrogen-utilizing methanogen was used to bioaugment a separate UASB reactor. A third control UASB reactor with no

bioaugmentation was also operated. All the reactors were fed with basal medium,

formate, acetate and 3-CB. Results of the study indicated that 3-CB did not degrade in the control reactor, whereas the reactors bioaugmented with D. tiedjei and the three-member consortium transformed 3-CB at a rate of 54 µmol/day/g granule biomass. Even after reducing the HRT of the bioaugmented reactors to 0.5 days (which is much shorter than the generation time of D. tiedjei), the reactors still dechlorinated 3-CB, indicating immobilization of microbes in the granules which was further confirmed by immunological studies.

Saravanane et al. (2001) bioaugmented fluidized bed reactors with a cephalexin- enriched anaerobic culture to evaluate cephalexin-degrading behavior of the reactor. Results of the study revealed an initial COD removal of 88% for the first 2 to 8 days after which the removal efficiency rapidly declined suggesting cell biomass washout. Further study revealed that periodic inoculation of the enrichment culture every 2 days yielded COD removal efficiency of 88% for the entire duration of the experiment (32 days).

Tartakovsky et al. (1999) inoculated anaerobic sludge granules obtained from a UASB treating food processing wastewater with a stain of pentachlorophenol (PCP) degrader, Desulfitobacterium frappieri PCP-1, and used competitive polymerase chain reaction (cPCR) to observe the adaptability of PCP-1 strains in the granules. Also, the PCP degrading ability of the resulting consortium was tested using a lab-scale UASB reactor. The PCP-1 stain succeeded in competing within the microbial community present in the granule and it increased from 106 to 1010 cells/g volatile suspended solids within 70 days resulting in PCP removal efficiency of 99%.

Tawfiki et al. (2000) studied the effect of mixing two different anaerobic consortiums, one capable of removing phenol and ortho-cresol and the other capable of removing para-cresol, in a fixed film anaerobic reactor. For continuous flow, phenolic compounds removal with the mixed consortia was as good as that achieved by each of the two individual consortia against their respective substrates. Further batch studies revealed that, for the mixture of cultures, phenol removal was complete after 11 days while the phenol degrading consortium alone took 35 days for the same amount of phenol degradation. Also, the mixed consortia totally removed o-cresol after 22 days while no removal of o-cresol was observed even after 35 days in the phenol degrading consortium

alone. On the other hand, the mixed consortium took 17 days more for degradation of p- cresol as compared with the time taken for degradation of p-cresol by the p-cresol degrading consortium alone.

Horber et al. (1998) studied dechlorination of PCE in UASB reactors. A strictly anaerobic, reductively dechlorinating bacterium, Dehalospirillum multivorans, was incorporated into granular sludge used for the test assay. Also a control reactor (R1) containing pre-autoclaved granular sludge was supplied with D. multivorans and a third UASB reactor (R2) was seeded with the same amount of active granular biomass but no bioaugmentation. All the reactors were fed PCE, formate and acetate. Both the test reactor and reactor R1 converted 93% of the PCE to DCE, whereas the non-

bioaugmented reactor (R2) converted only 43% of the PCE to trichloroethane. Interestingly, the test reactor and reactor R1 showed conversion of PCE to DCE at hydraulic retention times (HRTs) much lower than the reciprocal maximum growth rate of D. multivorans, indicating immobilization of the microbe in the living and autoclaved granules which was further confirmed by immunological studies conducted on the granules.

Lenz et al. (2009) studied the effect of bioaugmentation of a UASB reactor with immobilized selenate-accumulating Sulfurospirillum barnesii cells on selenate removal. Initially, S. barnesii cells were immobilized in acrylamide gels and the gel cubes were used for bioaugmentation of a mesophilic anaerobic digester fed with lactate (electron donor) at an organic loading rate (OLR) of 5 gCOD/L-day. The reactor was also fed 2mM sulfate and 10µM selenate and 15mM nitrate (electron acceptor). Selenate was reduced efficiently (more than 97%) in the reactor and the scanning electron micrograph

revealed that the selenate was reduced by the immobilized S. barnesii cells. Furthermore, to validate these findings under a microbial competitive environment, S. barnesii

immobilized cells were added to a granular UASB biomass and the reactor was operated on the same synthetic waste described above. Operation of the reactor showed that the bioaugmented reactor took 24 HRTs to attain 97% selenate removal as compared with 44 HRTs required by the non-bioaugmented reactor. Microbial community analysis of the reactor biomass revealed that the S. barnesii cells were effectively immobilized in the bioaugmented reactor even after 58 days of operation.