Avaliação do tratamento do lodo de caminhões limpa-fossa e do percolado em sistemas alagados construídos de escoamento vertical

Abstract

The study consisted in evaluating the treatment of septic tanks sludge in vertical-flow constructed wetland (VFCW), using a full-scale unit and two columns on a pilot scale. The full-scale units were built according to the French system of VFCW and operate since 2009 for the treatment of sewage. In September 2013, one of the beds, with an area of 29.1 m², height of 0.7 m of the support medium and planted with Tifton-85 (Cynodon dactylon Pers), started to receive the application of sludge once a week. The remaining of the week was used as rest period for stabilization and dewatering of the accumulated sludge. The percolated liquid was recirculated in two other beds. The pilot columns were made of PVC, diameter 145 mm, with the same plant and support medium of the full-scale unit, and allowed the investigation of the effect of double recirculation of the percolated liquid. The main physical, chemical and biological parameters (DO, pH, temperature, BOD, COD, TS, TVS, TFS, TKN, N-NH4+, Total Coliforms, E. coli) were monitored in raw sludge, percolated liquid and recirculated liquid. Measurements were also made in the accumulated sludge in the bed, for solids and moisture content; in the flow, to generate hydrographs and pollutographs; and plants, for verification of the productivity and monitoring of its general aspects and growth. The study included also the statistical analysis of the results and discussion of the applicability of the system. The application of raw sludge had a hydraulic loading rate (HLR) of 13.1 m³/m².year and solid (SLR) of 81 kgTS/m².year. Raw sludge had, for all parameters, concentrations lower than those reported in the literature for septic tank sludge and it was concluded that the system improved the quality of the percolated liquid in terms of organic matter (46% median removal efficiency of TS, 70% of BOD and 72% of COD) and nitrogen (59% median removal efficiency of TKN and 52% of N-NH4+). For the removal of coliform, treatment in the VFCW did not lead to a significant difference. The recirculation and double recirculation strategies adopted in systems did not result in better conditions of the percolated liquid. The systems in full and pilot scales presented a similar behavior. Regarding the accumulated sludge, dewatering occurred in a satisfactory way, reaching a percentage of 55% dry solids. Tifton-85 was resistant to the system operating conditions and even with the large variation in HLR and SLR, the VFCW maintained its performance. The evaluation of the applicability of SAC confirmed the system to be of low cost and interesting for smaller locations.