Sanitation Water Nitrogen Reduction with Two-Stage Biofiltration

Reduction of nitrogen in domestic sanitation water is a concern in many environmentally sensitive areas. This paper reports on an eight month field demonstration of integrated two-stage biofiltration systems to reduce nitrogen in primary wastewater effluent. Three systems were operated in parallel, each employing a single-pass unsaturated trickle biofilter followed by a horizontal saturated denitrification biofilter. Unsaturated media were clinoptilolite, expanded clay, and granular rubber, while elemental sulfur was the electron donor in denitrification biofilters. Unsaturated biofilters were operated at a 2.9 gallon/ft2-day and 48 dose /day. Two of the systems achieved average nitrogen reductions exceeding 96%, with average effluent total and inorganic nitrogen less than 3 mg/L and 1 mg/L, respectively. Two-stage biofiltration is an appropriate technology for distributed infrastructure systems that can operate relatively passively. Issues to be further elucidated include sustained longer term performance, media longevity, required maintenance, and acceptability of sulfate levels in the effluent.