Comparação do desempenho de um sistema de reator UASB unitário com dois sistemas de reatores em série tratando esgoto doméstico.

Abstract

If more than one reactor of the UASB (Upflow Anaerobic Sludge Blanket) type is to be constructed, the question rises if the reactors must be placed in parallel or in series. When there are two reactors of the same size, there are two alternatives for the dispositions in series; (1) the reactores may have the same depth as that of the reactors in parallel and hence will have double the upflow velocity or (2) the reactors in series have only half the depth of the parallel reactor so that the same upflow velocity as in those is maintained. The present master thesis reports on na experimental investigation that had the aim to verify the advantages of UASB reactors operated in series compared to those unitary reactor with respect to operational stability, organic removal efficiency and sludge production for this three systems of UASB reactors were operated at pilot scale: System 1 was a single (equivalent to one of two parallel units) with a height of 4 m; System 2 was composed of two equal UASB reactors with equal volume and also 4 m height each and System 3 was composed of two equal UASB reactors with a height of 2 m each. The systems were fed with raw sewage of the City of Campina Grande. Three series of experiments were earned out characterised by three hydraulic retention times: Total HRTs of 6, 3,5 and 2 hours were applied inthe three systems. The evaluated parameters during the investigation were related to the operational stability (pH, total and bicarbonate alkalinity and volatie fatty acid concentration) to the performance of the systems in terms or organic material removal efficiency (influent and effluent COD) and to the development of the sludge bed. The results show that for the range of investigated HRT values series operations does not offer advantages compared to operation in unitary reactor as far as operatinal stability, organic material removal efficiency or sludge bed development and sludge production is concerned. Since there arc no advantages in the operation in series in general it will be preferable to operate the reactors in parallel for pratical reasons: ( I ) this configuration leads to higher operational flexibility, allowing close down of of the units and dividing the influent over those that remain in operation and (2) in the parallel configuration peak values of organic and hydraulic loads that may occur, are absorbed more easily.