Respirometria aplicada ao sistema de lodo ativado: influência de interrupções da oxigenação sobre a viabilidade e atividade do lodo ativado.

Abstract

The working principle of aerobic treatment systems consists of maintaining a bacterial population in the system and supply sufficient oxygen for the bacterial mass to metabolise the organic matter that is present in the influent. In most aerobic systems oxygen is transferred from the atmosphere by mechanical aerators which normally are driven by electrical motors. The availability of oxygen is necessary in order to maintain the bacterial mass alive and with a high metabolic capacity however in practice there may be interruptions of the aeration due to power failures or to planned interruptions during hours of high tariff of electrical power. On the other hand it may be possible that there is no organic load during certain periods (for example during weekends in the case of industrial effluents, so that in principle it would be convenient to reduce oxygen consumption. For these reasons there is an interest to evaluate the influence of interruptions of the aeration on the survival of activated sludge and on its activity just after such an interruption. In this thesis a study was carried out to evaluate the feasibility of the sludge from a Bardenpho system after periods without aeration. For this the oxygen uptake rate (OUR) of a sludge batch was determined during the phase of endogenous respiration before and after applying different periods without aeration. Also the influence of the duration of the aeration interruption on the activity of the heterotrophic bacteria (those that metabolise the organic matter) and the autotrophic bacteria (the nitrifiers of ammonium). For this purpose, OUR was determined after adding excess sodium acetate (for the heterotrophs) and ammonium chloride (for the autotrophs). The experimental results indicate that interruption periods of up to one week have little effect on the survival and the activity of activated sludge. For periods of two to three weeks there was a gradual decrease of the active sludge mass as well as of the sludge activity of the surviving organisms. It was also established that both the heterotrophic and the autotrophic bacteria preserve their metabolic capacity for a period of up to one month. It is concluded that the bacterial mass that develops in the activated sludge system is capable of withstanding long periods without aeration.