Chemical and bacterial quality of aeration-type waste water treatment system discharge

On-site waste water treatment systems are a potential source of chemical and bacterial contamination to ground water in areas with highly susceptible aquifers such as the sinkhole plain of southwestern Illinois. Ground water from wells, cave streams, and water that discharges from the numerous springs in this area is typically contaminated with nitrate and enteric bacteria and thus may pose a health hazard to those who come into contact with it. In order to determine if the most popular type of on-site waste water treatment systems in the study area was a potential source, samples of effluents discharged at the land surface from 23 domestic aeration-type on-site waste water treatment systems were collected to characterize their water quality and bacterial contents. Most of the effluents contained relatively large concentrations of sodium (Na⁺), chloride (Cl^-), nutrients (nitrogen [N], phosphate [PO₄^3-], and potassium [K⁺]), and enteric bacteria. Ion concentration ranges (in mg/L) were Na⁺ (46 to 416), Cl^- (21 to 618), N (4.7 to 67), PO_4-P (1.4 to 48), and K⁺ (6.0 to 257). The sources of elevated Na⁺ and Cl^- were human waste and NaCl used in the water softening systems of the houses. Ammonium was usually the dominant inorganic N species, indicating incomplete oxidation of the waste water. Discharge of Na⁺, Cl ^-, and nutrients could also have negative impacts on ground water and surface water quality, subsurface and surface aquatic ecosystems, and vegetation. Our characterization of effluent from these waste water treatment systems revealed their generally poor quality and the likelihood that they can contaminate ground water in areas with highly vulnerable aquifers.