Ozonização e efeito do air stripping no tratamento de água subterrânea contaminada por gasolina aditivada

Abstract

Very little is known about the effect of additives found in fuels regarding the environmental impacts and constraints to the remediation of contaminated waters. With the purpose of investigating a possible technological alternative for the treatment of groundwater contaminated with gasoline with additives, easy to operate, using as little chemicals as possible, the present investigation carried out treatability assays with ozone to treat groundwater spiked with gasoline containing additives with initial COD of 5000 mgO2/L (Phase I) and 1000 mgO2/L (Phases II and III). The experiments were conducted in a semi-batch reactor with recirculation of contaminated groundwater, peristaltic pump and ozone gas injection in countercurrent in the liquid column. The experimental design was based on factorial planning using as independent variables the (i) ozone concentration in the gas ([O3]) varying from 10 to 90 g/Nm³ (Phase I) and from 10 to 80 g/Nm³ (Phase II); (ii) ozone initial DQO ratio (O3/DQO) varying from 0.01 to 0.1 (Phase I) and from 0.1 to 1.0 (Phase II). Initially the efficiency of each treatment was evaluated according to the COD reduction. In Phase I (initial COD 5000 mgO2/L), the best COD reduction achieved was only 8.1% when the lowest ozone concentration [O3] and the highest ratio O3/DQO were applied. In Phase II (initial COD 1000 mgO2/L), the best COD reduction was 42.2% also obtained with the lowest ozone concentration [O3] and the highest ratio O3/DQO applied. In order to assess the percentage of COD, mono-aromatic hydrocarbons BTEX and TPH-GRO (total petroleum hydrocarbon-gasoline range organics) removed by air stripping only (absence of oxidant agent ozone), an assay with air injection (Phase III) was carried out, which resulted in reduction of DQO, BTEX e TPH-GRO respectively in 6.7%, 26.4% and 26.3% in 5 min, 8.4%, 96.0% and 95.9% in 49 min and 8.7%, 99.8% and 99.6% in 200 min. The results of Phase III suggested that air stripping only promote slight reduction of COD but high reduction of BTEX and TPH-GRO after 49 min. The results also indicated that recalcitrance to the treatment reflected by low reductions of COD is related to the presence of additives in the gasoline and not to the target compounds (petroleum hydrocarbons), suggesting the additives remain in the aqueous matrix, even after almost complete removal of BTEX and TPH-GRO.