Comportamento do sistema anaeróbio-aeróbio com o reator anaeróbio de fluxo ascendente e manta de lodo e o sistema de lodo ativado no tratamento de esgoto doméstico na região tropical.

Abstract

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.