BATISTA, M. M.; http://lattes.cnpq.br/9968256068572098; BATISTA, Mariana Medeiros.
Résumé:
The present work aimed to evaluate the operation and performance in sequential batch polishing
ponds treating UASB reactor effluent and the application of post-treatment by coagulation,
flocculation and sedimentation. The experimental apparatus consisted of a UASB reactor, fed
with municipal sewage, an intermediate tank (temporary storage) and 05 polishing ponds (PP).
In Phase 01 of the research, the following were investigated: a) variations in environmental
conditions (pH, temperature and dissolved oxygen) as a function of seasonality (hot and cold
period) and depth (surface and bottom) in the PP, as well as the dynamics of the algal
community throughout the treatment as a function of seasonality, by identification and counting
of microalgae; b) the influence of the agitation condition (continuous, intermittent and without
agitation) on the ponds performance; c) the dissolved oxygen balance in the liquid, including
the determination of the processes rates (photosynthesis, respiration and air-liquid transfer); d)
the effect of inoculation with microalgae (12.5%, 25% and 50% inoculum volume) on the
nutrients removal in the PP. In Phase 02, the post-treatment of the effluent from the UASB-PP
system was carried out by coagulation, flocculation and sedimentation (CFS) processes, on a
bench scale. The factorial design technique was used to identify, define and optimize the main
interfering variables in the processes for the experimental conditions. As a result, it was possible
to observe that the PP presented daily cycles of stratification and vertical mixing of temperature
and chemical components (pH and DO), whether in hot or cold periods. The dominant
microalgae species throughout the treatment was Chlorella vulgaris. The agitation mode did
not statistically affect the performance of the PP. Regarding the DO balance, it was observed
that photosynthesis is the main source of oxygen in the pond and of the total produced in the
treatment cycle, 42.7% was consumed, 42.6% remained in the effluent and 14.7% was lost to
the atmosphere. Inoculation favored faster nutrient removal; among the percentages tested, the
12.5% inoculum showed the highest treatment capacity to remove ammonia (117 ± 26.8 L m-3
d
-1) and orthophosphate (100 ± 30.6 m-3 d-1), being, therefore, the optimal value to be applied
when starting the PP. It was also verified that the coagulant concentration (PAC) and pH were
the main interfering variables in the CFS process, considering the removal of color, turbidity
and total phosphorus. The optimal operational ranges obtained for the variables were: dosage ≥
13.5 mg Al L-1 and pH between 6 and 8. Finally, the UASB-PP system presents itself as an
efficient treatment alternative, in terms of organic material and nutrients, compared to
conventional stabilization ponds, contributing to minimize the environmental problems related
to the release of sewage into water bodies. Furthermore, the effluent produced can constitute a
source of water for the agricultural and/or urban sectors in the municipalities. In the latter case,
the use of post-treatment is necessary.
