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A <br />0.5 <br />0.4 <br />0.1 <br />0.0 <br />09/22/21 <br />09/29/21 10/06/21 10/13/21 10/21 /21 10/28/21 11 /04/21 11 /11 /21 11 /19/21 <br />Date (mm/dd/yy) <br />X Raw Influent ♦ Filter 1 Effluent ❑ Filter 2 Effluent Effluent Target Conc. <br />Figure 5-4. Biological Ammonia Removal <br />Ammonia is removed biologically from the water using a two-step process called nitrification. First, <br />Nitrosomonas microorganisms convert ammonia to nitrite, then Nitrobacter microorganisms convert nitrite <br />into nitrate. The effluent nitrite concentrations increase during the first step of nitrification until the <br />Nitrobacter microorganisms are acclimated, which usually takes 2 to 3 weeks. Due to the expected low <br />concentration of ammonia in the raw water, the MDH did not require monitoring for nitrite or nitrate in Lino <br />Lakes' study. However, since the raw water ammonia was over 0.20 mg/L, randomized testing was <br />completed for nitrite and nitrate by WSB staff to monitor the effluent concentrations. Effluent nitrite and <br />nitrate concentrations were maintained below 0.30 mg/L and around 1 mg/L, respectively, which is <br />significantly below the MLC established by the EPA for each contaminant. Towards the end of the study, <br />the nitrite concentrations were reduced to near zero and almost all the ammonia was converted to nitrate. <br />Filter 1 performed significantly better than Filter 2 during the acclimation phase. However, both filters <br />achieved similar levels of performance towards the end of the study during the treatment efficiency phase. <br />Table 5-4 below summarizes the average ammonia removed by the filters during both phases of the study. <br />Table 5-4. Ammonia Removal Efficiency <br />Phase <br />Avg. Ammonia Removal <br />Filter 1 <br />Filter 2 <br />Acclimation <br />50% <br />37% <br />Treatment Efficiency <br />94% <br />93% <br />5.5 Nutrient Requirements <br />Orthophosphate is a form of phosphorus that is dissolved in the water. Because it is dissolved, it is <br />immediately available to be consumed by microorganisms for growth. Since orthophosphate is consumed <br />by the microorganisms, it is important to maintain an adequate concentration upstream of the filters. The <br />natural raw water orthophosphate concentration from Well 6 averaged 0.13 mg/L. This concentration was <br />sufficient to promote rapid biological growth, so additional nutrients were not required during the pilot study. <br />Water Treatment Pilot Study Report <br />Biological Removal of Ammonia, Iron and Manganese at Well House No. 6 <br />City of Lino Lakes, MN <br />WSB Project No. 0 18601 -000 Page 10 <br />