Ensaios de tratabilidade de águas residuárias da indústria de piso de madeira por processos oxidativos avançados: ozônio e UV-C.

Abstract

The wood-based industry (including the wooden floor production) is characterized by dry process but due to cleaning and washing of machineries and surfaces this industry generates low volumes of highly polluted and recalcitrant wastewater. The purpose of this study was to investigate a technological alternative, easy to operate, with minimum use of chemicals, capable to treat these wastewaters, reducing toxicity and increasing the biodegradability making it feasible the biological treatment of the effluents. In the present study, a number of treatability assays based on advanced oxidation processes (AOPs) were carried out to treat cleaning wastewater from a wooden floor industry in Nybro, Sweden, with an initial COD of approximately 45,000 mg/L and pH of 2.3-2.6. After an initial reduction of 89% of DQO through an in situ sedimentation step, the following processes generating free radicals °OH were tested in lab-scale: Ozonation without pH adjustment (Phase 1); Ozonation with pH adjustment (Phase 2); and Ozonation + UV-C with pH adjustment (Phase 3). The experiments were performed in semibatch reactors using an apparatus with two connected reactors (O3 and UV); between them, the recirculation flow was kept in countercurrent with the gas flow. For the experimental design, the factorial planning of the type Central Composite Rotatable Design (DCCR) was applied with the following independent variables: (i) recirculation flow between reactors (VR) with levels varying from 0.3 to 3.0 L/min; (ii) concentration of O3 in the injected gaseous mixture ([O3]) or dose mode, with levels varying from 40 to 115 g/Nm3; (iii) initial pH (Phases 2 and 3) with levels varying from 3 to 11. The total amount of O3 supplied along the whole treatment was 2 grams of O3 per gram of initial COD (2:1). The efficiency of each treatment was based on the COD reduction, TOC removal and O3 consumption. Ozonation without pH adjustment, promoted a reduction of COD and COT of 65 and 31% respectively. Ozonation with pH adjustment to pHinitial = 7.0 reduced COD and TOC in 85% and 43% respectively. Ozonation, UV and pH adjustment to pHinitial = 9.38 reduced COD and TOC in 93% and 56% respectively. The results of the respirometry tests with the effluent from the AOP treatments without pH adjustment suggested that such treatment generates byproducts, which are even less biodegradable than those found in the wastewater before treatment. However, such products are not generated when ozonation is carried out in higher pH (7.0), even without UV and O3:DQOi doses lower than 1:1. The treatment with O3, can be useful as an intermediate treatment step for the studied wastewater, and be placed before biological treatment.