Efficiency of sewage treatment with septic tanks followed by constructed wetlands with different support materials

Abstract

This study seeks to assess the efficiency of a sewage treatment plant comprised of three compartmentalized septic tanks installed in series followed by three parallel wetlands and seeded with species Typha sp. with subsurface flow, filled with support material of natural gravel, gravel # 2 and washed gravel, respectively. The station treats sewage generated at Unity University for Science and Technology, State University of Goiás – UnUCET/UEG. A total of 20 sewage samples were collected in order to evaluate treatment efficiency from November to December 2010 and March to April 2011. The points of analysis were at the input of the first tank (raw sewage), the output of the third septic tank and the outputs of each of the three wetlands. The total removal efficiencies were: 65.40% for chemical oxygen demand; 79.01% for biochemical oxygen demand; 59.79% for total solids; 87.12% for the total suspended solids; 92.00% for total coliforms; 95.71% for E. coli and 82.54% for turbidity. The system was effective for the treatment of sewage, within the current legislative parameters for pH, turbidity, total solids and biochemical oxygen demand. No significant difference was observed between the three different means of support, suggesting that gravel, natural gravel and washed gravel may potentially be used to fill wetlands.