Influência de mudanças operacionais na qualidade da biomassa de sistema de lodos ativados do tratamento de efluentes de uma indústria de panificação

Abstract

Effluents originating from food industries have a high pollutant load, requiring an effluent treatment system (ETE) to minimize environmental impacts before their release into water bodies. In the secondary stage of the ETE, degradation of organic matter occurs, which can be achieved through the activated sludge process. Activated sludge comprises a microbiota responsible for pollutant degradation through biochemical reactions and the formation of sludge flocs. This microbiota is influenced by operational parameters (e.g., food-to-microorganism ratio, pH, dissolved oxygen (DO), solids, recycle rate, etc.). The quality of the sludge reflects the process efficiency and can be monitored through sedimentability and sludge volume index (SVI), which consider settleable solids as indicators of pollution and siltation. Their results indicate if the system has inefficiencies and/or instabilities. The objective of this study was to investigate how operational parameters influence poor sedimentability in the aerated lagoon of the ETE, implementing operational modifications that promote the development of a good microbiota, with an efficient and low-cost process. For this purpose, 5 sampling points were defined and collected (point 1: raw influent; point 2: effluent from the primary tank; point 3: aerated lagoon; point 4: secondary clarifier; point 5: final effluent). The sampling took place over a period of 60 days, with biweekly frequency, for physicochemical analysis, generating hypotheses for operational improvement opportunities. A sample of biomass from the activated sludge system was used for microorganism analysis. The physicochemical analysis showed that instability impacted the sludge quality, which presented poor sedimentability and SVI results, due to an inappropriate food-to-microorganism ratio (F/M). Proposed operational modifications were suggested, such as the use of intermittent aeration, increased sludge recycle rate, and elimination of the use of commercial biological mix. Since the microbiological analysis of microorganisms reported that the sludge characteristics were light and dispersed, it indicated that the sludge microbiota was not favoring the formation of dense and compact flocs. Before implementing the modifications, a biomass sample (sample L1) from the activated sludge system was collected for metagenomic analysis. After implementing the modifications, another biomass sample (sample L2) was collected for analysis. The results evidenced an improvement in the composition of the activated sludge microbiota, favoring the formation of sludge flocs. The system began to exhibit a microbiota with a higher representation of genera of interest such as Proteobacteria, Actinobacteria, Nitrospiraer, Firmicutes, and others. Additionally, there was a reduction in filamentous microorganisms, which negatively impact the formation of sludge flocs. The SVI result improved from the range of 240 ml/g to 150 ml/g. It can be concluded that operational parameters contribute to the formation of an appropriate sludge microbiota and improved floc formation. This project contributed to reducing operational costs of the effluent treatment system, bringing better cost-effectiveness to the company.