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Wageningen Universiteit (2003)

Integrated application of the UASB reactor and ponds for domestic sewage treatment in tropical regions

Cavalcanti, P.F.F.

Titre : Integrated application of the UASB reactor and ponds for domestic sewage treatment in tropical regions

Auteur : Cavalcanti, P.F.F.

Université de soutenance : Wageningen Universiteit

Grade : PhD thesis 2003

Waste stabilization ponds are widely applied for domestic sewage treatment in Brazil. The main objective of conventional waste stabilisation ponds (WSP’s) is, nomen est omen , to remove the organic material from wastewater. To achieve this objective, a quite long liquid retention time ( R h ) is required : even under the favourable conditions of the tropics (high temperature, sunshine) a minimum liquid retention time of 20 to 30 days is necessary. It is well established that the optimal ponds configuration for domestic sewage treatment consists of a serial system composed of an anaerobic pond, followed by a partially aerobic (facultative) and one or more predominantly aerobic (maturation) ponds.
By substituting the anaerobic pond by an efficient high rate anaerobic reactor like the Up Flow Anaerobic Sludge Bed (UASB) reactor, the pond receiving the effluent of this reactor - an polishing pond - will receive a relatively very low organic load and therefore the design criteria for this pond are very similar to those for maturation ponds, that is the polishing pond is designed for pathogen and/or nutrient removal.
In semi-arid regions, like the North-East of Brazil, the use of treated sewage for irrigation water is an ecologically sound solution if precautions are taken to avoid contamination of the workers and of the consumers of the produced crops. According to the very sticky World Health Organization (WHO) standards for unrestricted irrigation, the helminth concentration must be less than 1 per litre and the faecal coliform ( FC ) concentration less than 10 3colony forming unit (CFU) per 100 ml. On the other hand, other important fact in design of pond systems is the evaporation from the pond needs to be minimal, and consequently the pond area must be as small as possible. When UASB effluent (with low organic material and suspended solids concentrations) is post-treated in polishing ponds, these systems can be designed specifically for FC removal. For that reason, their surface area can be kept smaller than that of conventional ponds, designed for organic material removal. For reducing the liquid retention time (and surface area) of a polishing pond it is necessary to minimize the degree of mixing as much as possible, so that the hydraulic regime approaches a plug flow regime.
This thesis deals with aspects of design, performance and operation of sewage treatment systems consisting of an UASB reactor followed by a polishing pond. The thesis is directed to an experimental pilot plant investigation for assessing design and operation parameters with respect to the performance of the UASB reactor followed by post-treatment in different configurations of polishing ponds. With such a treatment system it was possible to produce an effluent that can be well used for unrestricted irrigation. The advantage of the system is that it allows a substantial reduction in the required surface area compared to the area required in conventional waste stabilization pond systems.

Mots clés : sewage sludge / waste treatment / brazil / anaerobic treatment


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