Avaliação do tratamento de lodo anaeróbio e emissões de gases de efeito estufa em wetlands de escoamento vertical

Abstract

In sewage treatment plants, sludge management has been a frequent concern, requiring efficient and cost-effective solutions for treating this solid byproduct. Given that the presence of plants can accelerate sludge drying, stabilization, and sanitization, vertical flow constructed wetland (VF CW) systems have been evaluated as an alternative to traditional drying beds. Thus, this study aimed to assess the treatment of sanitary sewage sludge and greenhouse gas emissions in VF CWs using pilot-scale units at the Center for Research and Training in Sanitation (CePTS - UFMG/COPASA), located in Belo Horizonte, Minas Gerais, Brazil. Twelve units were assembled, each with a surface area of 1 m², a height of 80 cm, and a 60 cm vertical support layer. Three units were loaded at a rate of 75 kg of total solids (TS) per m² per year; another three at 100 kg TS/m²/year; three at 150 kg TS/m²/year; and the final three at 200 kg TS/m²/year. Among these, four units were planted with Tifton-85 grass (Cynodon spp.), four with purple elephant grass (Pennisetum purpureum Schum), and the remaining four were left unplanted (control units). Over an operational and monitoring period of one year and nine months, physical, chemical, and biological analyses were conducted on the accumulated sludge and percolated effluent. Additionally, greenhouse gas emissions (CO₂ and CH₄) were analyzed, considering seasonal variations, using the closed static chamber methodology. The increase in loading rates did not significantly alter total carbon and nitrogen levels in the planted units. Anaerobic sludge treatment in VF CWs achieved good stabilization and dewatering, even at the highest loading rate (200 kg TS/m²/year). Higher loading rates led to increased methane emissions, with greater emissions observed during the rainy season, along with higher moisture content in the accumulated sludge. Emissions peaked shortly after loading and decreased over time (until the next loading cycle). The presence of vegetation reduced methane emissions, particularly during resting periods. The treated sludge met the criteria established by Brazilian environmental legislation for agricultural use.