Constructed wetland for septic tank sludge management: drained water quality under different operating strategies on a bench-scale experiment

Abstract

The septic tank is commonly used for treating domestic effluents, especially decentralized treatment. However, it requires periodic maintenance, including the removal, treatment, and disposal of sludge, which can be difficult and costly. An alternative approach, aligned with the principles of the circular economy, is the use of wetlands sludge management units (WSMU). In this study, a bench-scale experiment was conducted using six WSMU (0.0177 m2 each) planted with Canna x generalis. Different total solids (TS) loads (15, 28, and 42 kg TS m-2 year-1) and saturation levels (0.10 m and 0.20 m) were tested, and a super-loading strategy was adopted at the beginning of the operation. Monitoring and analyses were carried out over the first 150 days of operation. The results demonstrated that already at the beginning of the operation, high removal efficiencies were obtained, especially in units with a 0.20 m saturation level, reaching 80% for TS, 93% for chemical oxygen demand, 98% for total Kjeldahl nitrogen, and 97% for orthophosphate. This work showed that WSMU are capable of a high level of treatment even with high solids loads at the beginning of operation. Furthermore, these results indicate that even larger loads can be tested to optimize treatment performance and reduce area demand. Thus, the WSMU configuration, as well as the operational strategies adopted in this paper, can be used in future, long-term, and full-scale research to better understand the active treatment mechanisms.