Adventus Americas Inc.

Nitrate: AQUAMEND™ Denitrification Units (Septic Water)


Courtesy of Adventus Americas Inc.

The AQUAMEND® process has proven to be successful for the treatment of a wide range of constituents of interest. Much work was performed by Adventus in the area of treatment of high-strength industrial wastewater, with concentrations as high as 3,000 mg/L NO3-N (nitrate as nitrogen). In recent years development focused on use of the technology for the treatment of nitrate from on-site treatment of domestic or septic waste water. In cases where aerobic treatment of this type of water is performed, once the biological oxygen demand (BOD) is primarily consumed, reduced forms of nitrogen such as ammonia or ammonium can be converted by nitrifying bacteria to first nitrite, and then nitrate. Discharging nitrate to the environment is coming under increased scrutiny for mainly two reasons. Nitrate in the blood stream of especially infants can cause Methemoglobinemia, a condition where oxygen is not used properly by the body. Thus, drinking water should not contain high levels of nitrate. An ecological impact of nitrate in surface water bodies is the promotion of eutrophication, a process where an excess of nutrients such as nitrogen and phosphorus will result in algal blooms and the reduction of dissolved oxygen in the water.

The AQUAMEND Denitrification Unit, or ADU, has been designed and implemented using a patent pending process that provides significant advantages over other types of denitrification technologies. There are few technologies designed to deal specifically with nitrate for on-site wastewater treatment. One approach for reduction of nitrogen that is at a fundamental disadvantage in terms of reaching very low nitrogen levels is to cycle between aerobic and anoxic conditions. The BOD that is present in the water is used as the carbon source that is required for the denitrification zone, but the water will always contain some amount of either nitrate or ammonia, which can be later converted to nitrate in the environment. Another approach that has been used is to provide an over-abundance of a carbon source following a purely aerobic treatment system. Although this system is capable of reaching very low nitrogen levels, there is little control on the amount of carbon released, and thus an excess of BOD is likely to result. It is for these reasons that the ADU was designed to meet very low nitrogen and BOD levels.

ADUs are installed following aerobic treatment units, where virtually all the nitrogen is converted to nitrate. This influent is then passed through a highly efficient fixed-film denitrification region where the nitrate is removed. ADU Liquid Carbon (ADU LC) is added to the water in controlled excess. This ensures there is more than enough carbon to achieve essentially complete removal of nitrate. Once the nitrate is removed, the water is transferred to an aerobic fixed-film region where the excess of Liquid Carbon is removed, thereby preventing an overall increase in the BOD. Because the process is fixed-film, the suspended solids are retained in the reactors until such time that they are removed in a controlled fashion through an air sparging event. Approximately once every 3 to 6 months, a portion of the biomass in the reactors is dislodged and returned back to the septic tank of the treatment system. This results in very low total suspended solids (TSS) in the final effluent. Finally, due to the highly efficient design, the contact time required is very low. The denitrification process requires a design contact time of 2 hours based on the average flow, or 1 hour based on the peak flow, whichever is greater. The aerobic process requires half this time.

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