A denitrification process based on a new filtering media for onsite wastewater treatment

During the last decade, groundwater contamination became an important challenge to overcome. The domestic wastewater disposal in soil is pointed out as an important nitrate contamination source in many areas in North America. Also, many states and provinces are revising their regulation to introduce a discharge requirement of total nitrogen (N-T), often set at less than 10 mg/L. Considering these environmental requirements, the need of denitrification systems is growing rapidly. Presently, few systems on the market can reach a total nitrogen reduction of over 65%, which corresponds to an effluent concentration between 15 to 20 mg N-T/L (based on 50 mg NT/L septic tank effluent). Most of these systems include an integrated primary treatment and/or a secondary treatment stage. This paper presents the results obtained in the development of a denitrification unit installed between a conventional septic tank and an Ecoflo(R) Peat-based Biofilter. The design chosen is based on a tank including an anoxic section with short residence time and a nitrifying section using a new synthetic and organic filtering medium designed to support high hydraulic rates. This system demonstrated a nitrification percentage over 95% and a denitrification percentage varying between 65 to 90% which globally corresponds to 65% NT removal. The scale of the bench test might explain the lower percentage in total nitrogen removal than theoretically expected (70%). A full scale system is actually operating to verify this hypothesis. The effluent of the denitrification unit easily meets the secondary treatment standards. With the addition of a peat biofiltration system the effluent reached a tertiary treatment standards (< 5 mg/L of CBOD5, < 5 mg/L of TSS and < 100 CFU/100 mL).