Processo semicontínuo de tratamento avançado do soro do leite utilizando consórcio microalga e fungo filamentoso em reator aerado

Abstract

It is estimated that up to 10 L of whey can be generated per kilogram of processed cheese and that there is a significant polluting potential in terms of Chemical Oxygen Demand (COD) (44.167-95.000 mg·L-1), Total Nitrogen (TN) (790-2.520 mg·L-1) and Total Phosphorus (TP) (366-549 mg·L-1). In this sense, the objective of this work was to evaluate the treatment of whey (with emphasis on tertiary treatment) in an aerated reactor using the microalgae-filamentous fungus symbiosis (Tetradesmus obliquus LCE-01 and Cunninghamella echinulata) in different organic loads and mode of operation (discontinuous and semi-continuous). The reactors were operated with an aeration rate of 1.5 vvm, pneumatically agitated, at 30-35ºC, evaluated under a light intensity of 100 µmol·m-2 ·s-1. In semi-continuous mode, volumetric replacement rates - TRVs of 40 and 60% were used. The previously characterized whey had values of COD 67,014.48 mg·L-1, TN 1,377.05 mg·L-1 and TP 625.60 mg·L-1. After the secondary (main) biological treatment, carried out with co-culture, reductions in the order of 96.94% for COD, 97.97% for NT and 95.93% for FT were obtained in two sequential stages and 10 days operating totals. After that, advanced treatment analyzes using 3 loads (C1 > C2 > C3) with levels in the range between 1,176.32-6,355.60 mg·L-1 for COD, 21.90-77.32 mg·L-1 TN and 21.95-52.61 mg·L-1 for TP were evaluated. Preliminary studies (with COD:N ratio = 50) showed nitrogen limitation, even with reasonable removal of COD, NT and TF (but within what is required by legislation); which made it possible to continue the study in different DQO:N ratios, seeking to improve the performances obtained. Thus, in the next stage, new experiments were carried out with adjustment of the COD:N ratio to values of 20, 30 and 40 in C2 organic loads (initial contents for COD of 2370.46 ± 26.73, and TN of 37.78 ± 1.88 and TP of 21.95 ± 0.11 mg·L-1 ) and C3 (initial levels for COD of 1176.32 ± 8.91, TN of 21.97 ± 0.03 and TP of 12.32 ± 0.07 mg·L-1 ) and it was shown that there was indeed nitrogen limitation in the previous condition, achieving greater COD and TP removals, with a better COD:N:P ratio between 20-30. In semicontinuous mode at COD:N = 20, maximum removals were obtained for TRVs of 40 and 60% and equal to 84.92% for COD, 99.41% for TP and 84.44% for TN. Only the condition with C2 and TRV of 60% that showed a residual TN (due to supplementation) being outside that required by legislation, but for C2 at TRV of 40% and C3 at TRVs of 40 and 60% the process could operate in satisfactory manner in compliance with legislation. There was production of microbial sludge with potential (1-2 g.L-1) and stabilization of pH during treatment (exempt from adjustment).