Improvement of domestic wastewater quality by subsurface flow constructed wetlands

Abstract

A large proportion of households throughout the world and approximately 25% of the households in the US use on-site wastewater disposal systems. Subsurface flow constructed wetlands are gaining popularity as a reduced cost and low-maintenance technology for on-site treatment of septic effluents. Constructed wetlands from residences at eight locations in Texas have been used for the past 2–4 years to determine their effectiveness in improving the quality of septic effluent passing through them. Influent and effluent samples were collected once every month over a period of one year from each location and analyzed to determine the reduction in concentrations of biological oxygen demand (BOD 5), total suspended solids (TSS), volatile suspended solids (VSS), ammonium-N (NH 4 +-N), phosphorus, total and fecal coliform bacteria. Results of these investigations indicate that the organic load, fecal coliform populations and the N and P concentrations of the septic water decreased considerably by passing through the wetlands. Constructed wetlands reduced BOD 5 of septic water by 80–90% which provided for feasible disinfection by chlorination. Reduction in populations of fecal coliforms varied but generally, populations were reduced by 90–99%. Chlorination further reduced populations of fecal coliforms to less than 2 cfu 100 ml −1. Constructed wetlands provided an effective method for secondary treatment of on-site domestic wastewater.