Filtro anaeróbio aplicado ao tratamento de esgoto sanitário.

Abstract

Anaerobic filters are applied for treatment of wastewater ever since the decade of 1950, but the reactor is still in frank development and needs to be more researched. This Thesis intends to contribute for the technological development of anaerobic filters and to the progress of knowledge of the anaerobic sewage treatment, starting from the hypothesis that anaerobic filters are advantageous for treatment of diluted or concentrated sanitary sewage, using several different media and operated in up-flow or down-flow mode, provided they are submerged. The experimental research focussed on four specific objectives: the analysis of the filters when submitted to both low and high organic loading rates; the comparative evaluation of the performance of several media; the study of the risks of blockage of the voids; and the functional analysis comparing up and down-flow in submerged filters. The experiments were carried out at the experimental station of sewage treatment of the Federal University of Rio Grande do Norte, in Natal, Brazil. Four filters were used with volumes of 3.36 m3 each, that could be fed with raw sewage or with the effluents of a decanter-digestor or of an up-flow anaerobic sludge blanket reactor. The reactors were submitted to several hydraulic and organic loads during different sequential phases, over a period of more than six years. Different media were used in the filters: crushed stone nº4; commercial crushed stone; rolled pebble; clay bricks perforated; rings of corrugated plastic electric conduits; PET plastic bottle tops; and plastic bodies produced specifically as medium for biological reactors. For the comparative analysis of the flow sense, filters were operated in up-flow and down-flow mode while keeping other operational characteristics identical. The scale of the research (flows from 2.5 to 15.0 m3/day) and the use of real sewage, led to important conclusions that can be used immediately in real scale projects. The main conclusions showed that anaerobic filters are effective in the treatment of diluted sanitary sewage, or effluents from other anaerobic reactors, it is possible to obtain high efficiency (retention time of 5 hours and COD removal of more than 85%) operating with high organic load, and they can produce effluents with an average BOD smaller than 30 mg/L and less than 20 mg/L of suspended solids. The perforated ceramic brick, due to its surprisingly high efficiency, turned out to be a good medium alternative. Commercial crushed stone and rolled pebble are both feasible alternatives for the usual crushed stone Nº4. Corrugated plastic electrical conduit rings and bottle tops can be used as good alternative options for manufactured plastic medium for biological reactors. Submerged down-flow anaerobic filters can provide the same efficiency as up-flow filters. Although sludge accumulated and eventually occupied the entire available voids volume, simple discharge of the filter contents proved to be an operation capable of removing the excess sludge. Recommendations are presented as to the frequency of sludge removal from anaerobic filters, which is a fundamental operational procedure.