Influência da sazonalidade e de plantas na redução da concentração de poluentes em sistema de alagados construídos de escoamento vertical, com alimentação em pulso, empregado para tratar esgoto doméstico bruto

Abstract

The aim of this research was to evaluate the influence of dry and wet seasons and of plant (Tifton 85 grass) on the performance of two vertical-flow constructed wetlands (one planted with tifton 85 and one non-planted). These units are located in the Center for Research and Training in Sanitation (CePTS)/ UFMG-COPASA, near Belo Horizonte city (MG). The constructed wetlands worked in parallel, and each unit received raw domestic sewage for 2.5 days (hydraulic loading rate of 0.38 m3.m-2.d-1), before being rested for 4.5 days. The two wetlands were alternately fed, and influent and effluent samples from the units were collected weekly and were analysed for physical, chemical and biological parameters. The nutrient extraction capacity by Tifton 85 grass was evaluated through dry matter production and chemical bromatological analyses. 6.5% and 1% of total nitrogen and total phosphorus tributary were removed Tifton 85, showing that plant uptake is not the major nutrient removal mechanism in these constructed wetlands. Mean removal efficiencies for the planted and non-planted units were, respectively: BOD 80 e 77%; COD: 72% e 72%; TSS: 83% e 77%; TKN: 55% e 46%; N-NH4 +: 56% e 49%; Total-P: 45% e 50%; helminth eggs: 97% e 96%; E. coli: 90% e 85%. The planted wetland presented significantly better TKN, ammonia and suspended solids removal and also a greater nitrate synthesis. The seasonality influence was noticed only in the performance of the non-planted wetland. A significantly lower BOD removal efficiency and higher effluent COD concentration were seen in the dry and cooler season, with possible reduction of the heterotrophs metabolism. Good removal efficiencies of organic matter, suspended solids, ammonia and helminth eggs were detected in the constructed wetland units, indicating the high applicability of the technology in small communities, under Brazilian environmental conditions.