Remoção de coliformes fecais e matéria orgânica numa série de dez lagoas de estabilização, em escala-piloto, tratando esgotos domésticos em região de clima tropical.

Abstract

This work describes the performance of a pilot-scale experimental pond system (System XVII), treating domestic sewage from Campina Grande, Paraíba, northeast Brazil (7°13'11"S, 35°52'31"W, 550m above ms.l), in terms of both organic matter (BOD5 and COD) and faecal coliform removals, during the second period of monitoring (Experiment 2). System XVII was made up a long series of 1.5m deep-ponds comprising an anaerobic pond (A 12) fed with sewage, followed by a secondary facultative pond (F25) and eight maturation ponds (M25 to M32), each one fed by gravity with the effluent of the previous pond. The total hydraulic retention time was 28.5d (1.5d in the anaerobic pond and 3d in the others). The experimental system was investigated from November-1993 to September- 1994. Monitoring was based on the analyses of grab samples of pond effluents collected weekly at 8.00 a.m. and raw sewage daily composite samples. Samples were analysed for the parameters BODs, COD, faecal coliform, suspended solids, dissolved oxygen, pH and temperature. With the exception of raw sewage and the anaerobic pond effluent, samples were also analysed for chlorophyll a. The long series (System XVII - Experiment 2) presented high efficiency in tide removal of BOD5 (95%), COD (82.1%) and faecal coliform (99.9997%). The final effluent presented a BOD5 of less than 20mg/l and the number of faecal coliform complied with the WHO guideline for unrestricted irrigation (less than 1000 cfu/lOOml). However, the increase in the hydraulic retention time from 19d, in the first exrjeriment, to 28.5d, in the second, did not correspond to an increase in the performance of the pond system. Thus, both experiments presented results quite similar. The long series of ponds was concluded to be a land-saving alternative compared to other configurations of series previously studied at EXTRABES, even under the operational conditions of the second experiment.