Improvement of domestic wastewater quality by subsurface flow constructed wetlands

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 (BOD5), total suspended solids (TSS), volatile suspended solids (VSS), ammonium-N (NH4+-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 BOD5 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.