Effects of Operational Strategies in the Performance of a Real Scale Vertical Flow Constructed Wetland for Septic Tank Sludge Treatment : Case Study in Minas Gerais, Brazil.

The septic tank is considered the most common onsite wastewater treatment technology; although not prioritized by many sanitation agencies, septic tank installations will continue to serve the ever growing peri-urban areas in developing countries as well as isolated small communities all over the world. As a consequence, the generation of septic sludge will continue increasing for years to come. On the other hand, the lack of knowledge in septic sludge management has cause serious pollution to terrestrial and aquatic environments. The use of VFCW for septage treatment has shown promising results since its first implementation and is of potential interest for developing countries, especially with tropical climates. Nonetheless, further research work in operational strategies and economic post treatment alternatives should be addressed in order to obtain acceptable effluent qualities according to the final disposal and agricultural reuse regulations In this research, it was evaluated the performance of two different operational strategies in full-scale sludge drying reed bed system, consisting of two VFCW units (W1 and W2) planted with Cynodon dactylon Pers, for the treatment and post treatment of septic tank sludge. For this reason, it was evaluated the removal of COD, BOD5, TKN, NH4+, TS, TVS and E. coli from the liquid fraction; as well as, the pathogenic contamination of the accumulated sludge layer in terms of Total coliforms (NMP/gTS), Escherichia coli (NMP/gTS) and viable Ascaris Lumbricoides eggs (viable egg/g). The two operational strategies (OS) were (i) OS2: after sludge application, the percolate from W1 was retained for 6 days inside this unit, after which it was sent to W2 for post-treatment, without any retention in this unit; (ii) OS3: the percolate from W1 was retained for 6 days inside this unit for initial treatment, after which it was sent to W2 for post-treatment, remaining there for another period of 6 days. The OS2 achieved global removal efficiencies (%), for the percolated fraction, of 89, 98, 78, 82, 56 and 73 for COD, BOD5, NH4+, TKN, TS and TVS respectively, as well as 2.4 log removal units of E. coli. While the OS3 achieved global removal efficiencies (%) for the percolated fraction of 94, 90, 68, 87, 68 and 82 for COD, BOD5, NH4+, TKN, TS and TVS respectively, as well as 4.2 log removal units of E. coli. According to the statistical analysis performed, the OS3 improved significantly the removal efficiencies of COD, TS, TVS and E. coli. It was concluded that OS3 is not worth it for peri-urban or urban regions where the land area is very expensive or not available at all. Nonetheless, for small remote communities this could be a worthwhile option in order to reuse the percolated effluent in restricted irrigation. Regarding the accumulated sludge layer, its pathogenic quality was not good enough during the operational stage, considerable concentrations of E. coli and viable eggs of Ascaris lumbricoides were present; therefore, it would require a treatment for reuse in agriculture or as soil conditionin