Estudo de casos de wetlands construídos descentralizados na região do Vale do Sinos e Serra gaúcha

Abstract

In the search for treatment systems for domestic sewage that attend to principles of sustainable development, the Constructed Wetlands present itself as technologies of interest. This study evaluates the performance of six different configurations of decentralised constructed wetlands in domestic effluent treatment in the region of Sinos Valley and Rio Grande do Sul's Sierra. There were two community systems of horizontal flow (HFWs), three residential systems of vertical flow (VFWs) and a community system of pre-treatment with floating macrophytes (FMW). This work evaluates the performance of the systems, the efficiency in the removal of organic load and disinfection of sewage relative to legislation, climate, scenery and operation conditions. After 5 months of monitoring, all systems were shown to be effective in the removal of organic load and turbidity, attending to brazilian legislation and presenting mean concentrations at the outlet of the units for BOD of 26,3; 12,5 and 134,0 mg/L in HFWs, VFWs and FMW, respectively. In terms of COD average results in the outlet of the units were 160,5 mg/L; 156,5 mg/L and 234,2 mg/L for the HFWs, VFWs and FMW respectively. The HFWs and VFWs presented removing greater than 70% of organic load, even in saturated systems. The VFWs reached the needs of removing of nutrients load and presented an average of 0,6 mg/L and removal of 72% for total phosphorus, and 7,8 mg/L and 7,7 mg/L for total and ammoniacal nitrogen, respectively, removing over than 90% of nitrogen load. The HFWs operated with overload of application and did not attending the legislation in the removal of nutrients, decreasing on means of 39% of phosphorus load, 52% of total nitrogen and 37% of ammoniacal nitrogen, with averages of 5,8; 52,9 and 50,1 mg/L respectively in the treated effluent. Only the VW1 and VW3 attended to the legislation for the disinfection of E. coli and only the VW3 for total coliform. The mean removal of total coliforms was 73% in HFWs and 87% in VFWs, with means at the outlet of the units of 2,97E+04 e 3,38E+04 NMP/100 mL, respectively, in HFWs and VFWs. In terms of E. coli the average efficiency was 90% in HFWs and 84% in VFWs, with results of 2,86E+04 e 2,58E+03 in the respective outputs of the studied units. The climatic factors indicated influence in dynamic operation of wetlands. All VFWs were effective for the purpose for which it is intended and showed itself appropriate as systems of sewage treatment on site. The HFWs showed the need for a correct dimensioning, technical monitoring and maintenance of collective systems.