Monday, February 10, 2014
Jerry Jesky, PE, Public Infrastructure
Many municipalities are aware of the recent Missouri legislation requiring lower wastewater discharge limits for ammonia throughout the State of Missouri. As a result, many municipal leaders have been paying more attention to the various means of nitrification – the conversion of ammonia to nitrate – to meet low ammonia limits in their communities’ wastewater. While extended aeration plants can typically meet ammonia limits by introducing sufficient quantities of air to oxidize ammonia to nitrate, existing wastewater treatment systems that do not use aeration will likely need to be upgraded to provide the nitrification needed to meet effluent discharge limits for ammonia.
As previously mentioned, nitrification is converting ammonia and organic nitrogen to nitrate in an aerobic environment by nitrifying microorganisms. The main ingredients needed to readily accomplish nitrification include ammonia, oxygen (air), media for the nitrifying microorganisms to grow on, favorable temperatures, and sufficient alkalinity (the nitrification process consumes alkalinity in the wastewater).
For non- or minimally aerated treatment processes – such as facultative lagoons – nitrification will require adding aeration equipment and media. Nitrification also requires ensuring adequate water temperatures in the winter and making sure alkalinity concentrations are sufficient for the level of nitrification needed.
Olsson’s engineers have been studying several separate-stage nitrification technologies to address the issue of lower ammonia limits, including discussing solutions with equipment manufacturers and process engineers, reviewing pilot study data and reports, evaluating preliminary nitrification designs, and corresponding with the Department of Natural Resources to ensure regulatory compliance. Potential nitrification technologies include either using concrete-wall or high-density polyethylene (HDPE)-lined earthen basins or using natural or synthetic media. Another area being investigated is the ability to incorporate additional equipment in the future to accommodate further nutrient reduction or disinfection, as needed, to comply with a community’s discharge permit.
Nitrification in Lamar, Missouri
In 2012, one of Olsson’s nitrification designs came online in the City of Lamar, Missouri. For this project, Lamar’s existing single-cell facultative lagoon was supplemented with a Submerged Attached Growth Reactor (SAGR) system that aerated the lagoon effluent in an HDPE-lined gravel bed to nitrify an average daily flow of 770,000 GPD and a peak flow of 2.0 MGD. This SAGR system is the first in the State of Missouri and has proven very effective in reducing effluent ammonia to less than one mg/L, even during the winter.
The SAGR system also clarified the lagoon effluent to the extent that an ultraviolet disinfection system could be reliably added to the treatment train. As a result, the City of Lamar’s wastewater treatment facility is successfully meeting its ammonia and E. coli limits, as well as discharging much lower total suspended solids (TSS) and biochemical oxygen demand (BOD) concentrations as a result of the supplemental nitrification system.
Olsson’s engineers have also successfully used a Moving Bed Biological Reactor (MBBR) to supplement a recirculating sand filter in Cross Timbers, Missouri, to meet low ammonia limits. Separate-stage nitrification techniques, such as the MBBR, offer a specific solution to the issue of lower ammonia limits, which gives a community the option to upgrade its existing treatment process rather than construct a new mechanical plant at a much higher cost. If your community would like to discuss potential options for complying with upcoming ammonia limits, please contact Jerry Jesky at 417.890.8802 or email@example.com.