Efeito da estabilização de lodo aeróbio excedente no reator UASB sobre o desempenho do sistema de tratamento

Abstract

Among the existing configurations of biological treatment for domestic and industrial effluents, the association of UASB (Upflow Anaerobic Sludge Blanket) reactors with activated sludge systems has been widely used, mainly in hot climate regions. It provides the reduction of the influent organic load to the activated sludge system, resulting in savings in its implementation and operation. Besides the anaerobic sewage treatment, the UASB reactor can also be used to stabilize the excess sludge produced in the aerobic reactor. However, some studies show that wastewater treatment plants with this configuration have had a low efficiency in removing organic material and high suspended solids concentration in the effluent. Therefore, the aim of the research is to evaluate the effect of the excess aerobic sludge stabilization in the UASB reactor on the treatment system performance and to present suitable alternatives for improve wastewater treatment plants with this conception. Thus, experimental research was conducted at pilot-scale wastewater treatment plants, consisting of a UASB reactor followed by a conventional activated sludge system, with excess aerobic sludge stabilization in the UASB. The difference between the experimental systems was an intermediate settler between the anaerobic reactor and the aeration tank of the activated sludge system. To evaluate the influence of aerobic sludge return on the treatment system, physical-chemical analysis were carried out to monitor organic matter (COD) and solids. Moreover, the physical characteristics of the anaerobic sludge were analysed, through settleability. During the experiment, the UASB reactors maintained satisfactory efficiency, in terms of COD removal, average of 66% and low suspensed solids expulsions in the effluent, average of 26 mg/L. The aeration tank without the previous intermediate settler retained a greater biomass amount, average of 1.141 mg/L, due to the greater influent organic material. However, this pilot system showed greater solids expulsion in the final effluent, average of 51 mg/L, since non-biodegradable part of the excess aerobic sludge accumulated in the treatment system until it was discharged into the final effluent, deteriorating the quality. In the system with intermediate settler, non-biodegradable solids were retained in the settler subsequent to the UASB reactor.