Desempenho de sistema modificado de lagoa aerada com meio de suporte em leito móvel no tratamento de efluente de celulose kraft

Abstract

The pulp industry uses more than 40 m3 of water per ton of pulp produced, generating high effluent flows. In general, this presents high values of chemical oxygen demand (COD), biochemical oxygen demand (BOD5), colour and ecotoxicity. The effluent treatment systems most used in the pulp industry are biological treatments, such as aerated lagoon systems that are efficient in the removal of biodegradable organic matter, but have limitations for the removal of recalcitrant organic matter and colour. In addition, there is concern about the ecotoxicity of these effluents. Because of it they use Daphnia magna estimating ecotoxicity removal during treatment processes effluent. The objective of this work was to evaluate the treatment of Kraft effluent by aerated lagoon systems modified with the addition of sponge support media (APG) through, firstly, the arrangement of the support media in the aerated lagoons in the organic load 0.2 kgCOD m-3 d-1 and sequentially with organic load rate charge variation of 0.2 to 1.2 kgCOD m-3 d-1. Influent and effluent samples were characterized and evaluated by the parameters: BOD5, COD, Colour, lignin derivatives, total phenolic compounds and acute ecotoxicity in D. magna in the different stages. The solids were evaluated in the mixed liquor of the aerated lagoons by analysis of solids adhered to the support media and suspended in the reactor. Under optimal treatment conditions, where the biodegradability of the sample was favorable to the biological treatment (BOD5/COD> 0.3), the COD and BOD5 removal was 32% and 88%, respectively, in the free and confined support media, maintaining the volumetric organic load at 0.2 kgCOD m-3 d-1. When the sample had a higher recalcitrance, its performance was of 8% and 64%, on average, in the removal of COD and BOD5, respectively. Regarding Colour, there was an increase during the treatment, reaching values higher than 20% in this increasing. Removal of total phenolic compounds was not verified during the treatment by aerated ponds with spongy support medium. Statistical test showed no significant difference in the treatment dispositions. Considering the treatment in which there was a variation of the organic load rate in aerated lagoon with APG confined in plastic cage, the best performance was in the load 1.2 kgCOD m-3 d-1, with organic matter removal of 50% and 75% for COD and BOD5, respectively. Removal of Colour was near to 20%, removal of total phenolic compounds was of 18% and removal of lignin derivatives was greater than 10%. Regarding the solids these were concentrated in the mixed liquor during the treatments by aerated lagoons modified with spongy support means. On acute ecotoxicity, this was reduced to toxicity factor equal to 1 in all treatment conditions used. Comparing the aerated lagoon modified systems without the addition of APG, it was suggested to apply spongy carrier media specially in higher organic load rate than these typically used to treated lagoon even effluent with low biodegradability.