Tratamento de lixiviado de aterro sanitário pela combinação dos processos foto-fenton e biológico

Abstract

The objective of this work was the combination of photo-Fenton and biological processes for the treatment of landfill leachate. First, a conventional biological treatment was performed, consisting of a decantation step, with centrifugation at 5000 rpm for 15 min, followed by aerobic treatment with activated sludge conducted at 2.4±0.1 mg mg-1 (BOD5/MLSS) and 0.57±0.04 vvm (L L-1 min-1) for 40 h. In parallel, a central composite rotatable design (CCRD) was applied to evaluate the effect of the main variables of the photo-Fenton process (hydrogen peroxide concentration, ferrous ion concentration and initial pH). Based on the experimental design, quadratic models of (%) removal of COD and BOD5 were proposed and validated, making it possible to search for the optimal operating conditions of the photo-Fenton process. By the Zahn Wellens test and BOD5/COD ratio it was possible to identify the Fenton reaction time most suitable for the combination with the biological treatment. Then, the photo-Fenton process optimized with treatment time of 120 min was combined with the biological process, performed at 1.57±0.06 vvm and 4.4±0.3 mg mg-1 (BOD5/MLSS) for 150 h. After the treatments, the toxicity of the leachate was evaluated with Artemia salina and Lactuca sativa. The results showed a removal of 87±2% of COD and 84±2% of BOD5 from the leachate after conventional biological treatment, while the photo-Fenton process under optimal conditions (3400 mg H2O2 L-1, 80 mg Fe2+ L-1, pH = 2.40 and 120 min) removed 89±3% COD and 75±1% BOD5. On the other hand, with the combined treatment, 98% of COD and 98% of BOD5 were removed, resulting in a leachate that meets the restrictive standards imposed by state legislation. In addition, the simple and conjugated aromatic compounds were efficiently removed, achieving removal rates of 93 – 96%. In the evaluation of leachate toxicity with Artemia salina, the highest LD50 value was obtained in the combined treatment (LD50 of 0.5364), while conventional photo-Fenton and biological treatments showed statistically equal LD50 values. For Lactuca sativa, the lowest toxicity indices of the leachate were obtained after the combined and photo-Fenton treatments, with LD50 values around 0.945. Thus, in addition to the proven efficiency of removal of the organic load, the combined treatment also reduced the toxicity of the effluent, being environmentally recommended for the treatment of landfill leachate.