COURA, M. A.; http://lattes.cnpq.br/8234481367230599; COURA, Mônica de Amorim.
Resumo:
This work describes the findings of an experimental investigation on a pilot-scale
anaerobic/aerobic system treating domestic wastewater in a tropical region during a
continuous period of three years (April 1997-May 2000). The experimental system
comprised an Upflow Anaerobic Sludge Blanket Reactor, UASB, treating raw sewage and
excess activated sludge, altogether, followed by an activated sludge reactor treating the
effluent of the UASB reactor. This reactor was able to work in a steady state with
hydraulic retention times within the range 6-8 h, reaching a treatment performance
comparable to that of UASB reactors treating only raw sewage. Excess sludge volatile
fraction was reduced from the range 31-38% down to 13.9%, /'. e., increased excess sludge
stability, as the sludge age in UASB reactor increased from 14 to 28 days. Thus, it is
possible to conclude that sludge ages of 14 days are insufficient for the operation of the
UASB reactor in the anaerobic/aerobic system, being recommended to adopt sludge ages
around 28 days. Nitrification kinetics in the activated sludge system was greatly influenced
by the previous treatment in the UASB reactor, being the maximum specific growth rate
(u.m) for Nitrosomonas 0.28 d"1, at 25 °C, which is much lesser (2-4 times) than a typical
value for the conventional activated sludge reactor. Minimum sludge age in the activated
sludge system for providing the occurrence of nitrification in the anaerobic/aerobic system
was 14.8 days. A comparative analysis between a treatment system having the
configuration of the anaerobic/aerobic system and another having the configuration of a
conventional activated sludge one demonstrated that the first is comparable to the latter
with relation to both the effluent quality and sludge production; however its COD digested
influent fraction is much greater and its COD influent oxidised fraction is much lesser
leading to more reduced operational costs. In a conventional system the utilization of the
energy from the digester would supply only 18,6% of the energetic demand for aeration
while in anaerobic/aerobic system the potential energy generation is nearly 50% superior
the energy demand.