Tratamento de efluente kraft por sistemas de lodos ativados com adição de carvão ativado e grafeno

Abstract

The present study aimed to evaluate the treatment of kraft effluents by activated sludge systems with the addition of support medium of powdered activated carbon (PAC) and graphene (GO), separately. Operated two treatment systems, activated sludge with PAC (AS-PAC) and sludge activated with GO (AS-GO) in 4 stages each, the first only activated sludge (stage I) and the rest with support medium 2, 4 and 6 g L-1 (stages II, III and IV, respectively). Organic load rate (OLR) of 1.2 kgCODm-3 d-1 was applied at both levels and inoculum of 2500 mgVSS L -1. It was possible to observe how the chemical oxygen demand (COD), biochemical oxygen demand (BOD5) and total organic carbon (TOC) removals were greater in the stages with a medium support presence for both systems. In AS-PAC, the removals were similar during stages II, III and IV of AS-GO, the average removal of COD, BOD5 and TOC were 55, 94 and 58%, respectively. In AS-GO, the best results were shown in stage IV, with the COD, BOD5 and TOC average of 70, 96 and 74%, respectively. As for color, the stage II AS-PAC showed better efficiency with a removal of 28%. While in the treatment with GO, the best removal was found in stage IV with 47% removal efficiency. There was an increase in total phenolic compounds (TPC) in both systems, with an increase of 45% in stage IV, the highest observed value. Although the specific compounds derived from lignin were removed in all stages, stage IV had the best results in the treatment systems, with AS-PAC removing 36% of ligninics and aromatic compounds and 29% of lignosulfonic compounds, while in AS-GO, removals were 57% and 60%, respectively. From the analysis of the Fluorescence Emission and Excitation Matrix (FEEM), it was observed a reduction in intensity between the influent and effluent samples during all stages of application, indicating removal efficiency of fluorogenic compounds. A characterization of the support medium demonstrated that the surface area of the PAC is 5 times bigger than the GO, however, the diameter and volume pores of GO were larger than the CAP and both had an irregular surface, favoring the adherence of microorganisms. The highest concentration of microorganisms was in stage IV, for both treatments, and the highest value was for AS-GO with 4457 mg VSS L -1. From the analysis of Scanning Electron Microscopy (SEM), it was observed the development of the biofilm adhered to PAC and GO, with greater aggregation in AS-GO. In general, the use of AS-PAC with an addition of PAC improved the efficiency of the treatment, however, the increase in the concentration of this material did not contribute to the improvement of the system. In AS-GO, a stage IV with 6 g L-1 of GO showed the best results, even when compared with the stages of AS-PAC, being, therefore, the best treatment configuration for kraft effluent, under the conditions applied in that study.