Resumo

Activated Sludge is the most common technology for the treatment of wastewater. Despite being highly effective, it is possible that recalcitrant compounds, like Polyaromatic Hydrocarbons (PAH), accumulate on exceeding sludge, becoming an additional environmental problem. This work is being developed in a Petrochemical WWTP, where surplus sludge is being disposed in soils of “Sludge Farms” for longer than 30 years, and aim of addressing the following questions. I) Is this soil able to degrade PAHs? II) The degradation can be improved with changes in soil management, including biostimulation or bioaugmentation? Microbial activity was monitored in microcosms during 60 days, submitting Sludge Farms Soil to 5 different managements after contamination with benzo(a)pyrene (15 mg/kg), phenanthrene and naphtalene (30 mg/kg each). The soil pH was adjusted to 7.0, and the humidity to the field capacity. The treatments where: a) Natural Attenuation, which consisted on aeration of the soil every 3 days; b) Bioaugmentation once; c) Bioaugmentation every 20 days; d) Biostimulation; e) Biostimulation + Bioaugmentation; f) Control 1 (Sludge Farm soil without addition of contaminants) and; Control 2 (soil from adjacent areas under no direct influence of the Petrochemical Plant. Microbial activity (soil respiration) was measured via quantification of CO₂ released in the process. Results confirm the need for a specific management plan for each situation. As it concerns the Sludge Farm soil, one can consider it undergoes continuous bioaugmentation, as the sludge surplus disposed there, is composed mainly of microorganisms already adapted to petrochemical waste. Based on accumulated production of C-CO₂/kg of soil, the highest metabolic activity was found in Natural Attenuation (2,869 mg CO₂/kg). This management is feasible, requiring only liming and soil aeration. Bioaugmentation either once or every 20 days, presented similar results with production of respectively 2,661 and 2,624 mg CO₂/Kg. The Biostimulation treatment produced 2,413 mg CO₂/Kg, and Biostimulation + Bioaugmentation produced 2,353 mg CO₂/Kg. All soil management presented metabolic rates significant higher than those from control soils (p<0.05). Reduction of hydrocarbons measured by chromatography and identification of microorganisms by high throughput 16S sequencing are being done and will enrich even more the understanding of the process, serving as a solid basis for application of the soil management.