Identification and isolation of activated sludge bacteria that deflocculate after thermal and phenol-induced stresses and correlation to their auto-aggregation properties

AYARZA, J. M.; ERIJMAN, L.

Tucumán

Congreso; VII Congreso Argentino de Microbiología General SAMIGE DEL BICENTENARIO; 2011

Sociedad Argentina de Microbiología General (SAMIGE)

The efficient solid-liquid separation is a critical step in activated sludge wastewater treatment. The formation and stability of the biological floc depend on the aggregation of multiple species of bacteria within an extracellular matrix. Wastewater treatment plants, especially those treating industrial wastewater, are exposed to various sources of perturbations that affect the stability of the floc, resulting in increased solids loss and an overall reduction of effluent quality. We hypothesized that thermal and chemical stresses induce deflocculation by affecting the aggregation properties of key members of the activated sludge floc community. To test this proposition we identified, isolated and examined the physiological properties of bacteria that displayed a distinctive detachment from the flocs, following thermal and phenol shocks.Four lab-scale bioreactors were operated using synthetic sewage, at a controlled temperature of 25°C in a sequential batch mode, without biomass wasting. After ten days of operation, two reactors were exposed transiently to high temperature (50°C) and the other two reactors were subjected to a shock of phenol. In all cases, shock treatments resulted in an immediate increase in turbidity of the supernatants. At the microscopic level, partial deflocculation was confirmed by a marked decreased in the average size of the flocs. The shifts in the bacterial communities were evaluated by denaturing gradient gel electrophoresis (DGGE) of PCR amplified 16S rRNA genes. Two bands, whose intensity in the supernatant increased significantly after both thermal and phenol shocks, were excised, reamplified and sequenced. Based on the phylogenetic analysis, the two bacteria were clasified as Thauera, a Betaproteobacteria, and Sediminibacterium (phylum Bacteroidetes). Signature portions of the sequenced fragments were targeted with newly designed primers and used in Southern blot DGGE to confirm the response of both bacteria to the deflocculating shocks. Isolation was attempted by direct culturing in a variety of agar media. Screening was performed by PCR, using the novel specific primers. Several strains that were positive for the Thauera-specific primers were isolated, but none of them matched the correct DGGE mobility. PCR-positive colonies of Sediminibacterium were found in standard medium (e.g. R2A) supplemented with autoclaved, particle-free activated sludge extract. Growth of the Sediminibacterium sp. takes several days and requires several vitamins and oligoelements in the growth medium. Auto-aggregation properties depend dramatically on the composition of the medium. We conclude that Sediminibacterium sp. is a floc-forming bacteria that may have an important role in the formation and stability of the activated sludge floc.