Avaliação da bioaumentação com B. thuringiensis imobilizada em cascas de arroz no tratamento de efluentes da indústria de celulose em lagoa aerada facultativa

Abstract

The pulp and paper industry is undergoing significant growth in Brazil, which currently ranks as the second-largest producer worldwide. However, this production consumes large volumes of water, ranging from 25 to 225 m3 per ton of pulp, depending on the process and the size of the industry. As a result, effluents are generated that, if not properly treated, may cause negative environmental impacts on receiving water bodies. Although biological systems such as facultative aerated lagoons (FAL) are widely used for wastewater treatment, they show low efficiency in removing recalcitrant compounds derived from the pulp production process. The goal of this study was to evaluate the bioaugmentation process using Bacillus thuringiensis immobilized on rice husks in the treatment of pulp and paper industry effluents in FAL systems. The benchscale FAL was operated at an organic loading rate (ORL) of 0.2 kg COD·m-3·d-1, with a hydraulic retention time (HRT) of 3.3 d. Influent and effluent samples were characterized and evaluated according to the following parameters: chemical oxygen demand (COD), biochemical oxygen demand (BOD5), total phenolic compounds (TPC), lignin compounds (LC), lignosulfonic compounds (LSC), aromatic compounds (AC), and color. Organic matter removal efficiencies were 47% and 55% for COD and BOD₅, respectively. Additionally, TPC and AC were reduced by 16% and 1%, respectively, while no removal of LC, LSC, or color was observed. In parallel, a pilotscale FAL was installed at the industrial site, near the wastewater treatment plant. The applied ORL was 0.1 kg COD·m-3·d-1 with an HRT of 2.5 d. Similarly to the bench-scale FAL, influent and effluent were evaluated. COD removal efficiency reached 45%, and the maximum BOD5 removal achieved was 72%. Regarding TPC, LC, LSC, and AC, removals of 19%, 16%, 9%, and 13%, respectively, were observed, while color was reduced by 22%. In both lagoons, organic loading shocks followed by bioaugmentation were applied to evaluate their effects on treatment performance and system recovery. To determine the optimal bioproduct concentration, batch tests were conducted at concentrations of 0.2 g·L-1 (A), 0.5 g· L-1 (B), and 1.0 g· L-1 (C), with analyses performed on days 2, 5, and 7 of treatment. The highest efficiencies were obtained on day 5 at concentration A, with COD removal of 56%. TPC, LC, LSC, and AC were reduced by 67%, 51%, 35%, and 52%, respectively, and color reduction reached 35%. Bioaugmentation with B. Thuringiensis immobilized on rice husks contributed to the maintenance of the microbial community after organic shock loads, especially in the bench-scale FAL. Bioaugmentation proved to be effective, achieving COD and BOD5 removals above 50%. The elimination of specific compounds was higher in the batch bioaugmentation system (25-50%), followed by the pilot-scale system (5-25%), and was negligible in the bench-scale system. In this context, bioaugmentation may represent an effective strategy to enhance biological resilience and promote organic matter removal in pulp and paper wastewater.