AUTOTROPHIC SULFUR OXIDIZING DENITRIFICATION FOR TOTAL NITROGEN REMOVAL IN ON SITE WASTEWATER TREATMENT SYSTEMS

The overall objective of this research was to develop a reliable and easy to operate method for removing total nitrogen from the effluent of on-site wastewater treatment systems. The process relies on sulfur oxidizing denitrifying bacteria in upflow packed bioreactors. Sulfur oxidizing autotrophic denitrification consumes alkalinity; therefore, it is necessary to add a source of alkalinity to control the pH. This study investigated the use of limestone, marble chips and crushed oyster shell as sources of alkalinity.Two bench-scale upflow column reactors and two field-scale bioreactors were constructed and packed with sulfur pellets and an alkalinity source. The field scale bioreactors (~ 200 L each) were installed at the Massachusetts Alternative Septic System Test Center in Sandwich, Ma. When oyster shell was used as alkalinity source, the field bioreactors showed a high degree of nitrogen removal (average of 80%), with the effluent NO3- - N concentration consistently below 8 mg/L; while the bench scale bioreactors had an average nitrogen removal of 82 % and a maximum nitrogen removal of 99.9 %.