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5. RESULTS AND DISCUSSION <br />The pilot study was conducted for nine weeks beginning on September 22, 2021 and ending on November <br />26, 2021. The microbial acclimation phase took place over the initial three weeks and the treatment <br />efficiency phase continued until the study was completed. A backwash recovery test was completed during <br />the eighth week and a 1-week shutdown test took place during the last week of the study. Individual <br />treatment results are summarized in the following sections. <br />5.1 Aeration Requirements <br />Atmospheric air was fed upstream of the detention basin to promote biological growth in the filter columns <br />and to oxidize the dissolved iron present in the raw water. The air flow rate was optimized during the <br />microbial acclimation phase with the goal of maintaining a pre -filtration DO concentration of 6 to 8 mg/L and <br />a post -filtration DO concentration above 4 mg/L. The final air flowrate used in this study was 0.50 CFM, <br />which generated an air flow and water flow rate relationship of approximately 0.40 CFM/GPM (concurrent <br />air and water flow). It is possible that a full-scale biological filtration facility in Lino Lakes will require a lower <br />air to water flow rate ratio than used in this study to effectively treat ammonia, iron, and manganese. The <br />DO concentration change through the pilot skid is shown in Figure 5-1. As shown in the figure below, the <br />raw water DO concentration increased from an average of 1.6 mg/L to an average of 6.7 mg/L after aeration <br />and then decreased to an average of 5.9 mg/L after filtration. Both biological filters consumed a similar <br />amount of DO regardless of the media type. <br />M <br />9.0 <br />8.0 <br />7.0 <br />6.0 <br />'P 5.0 <br />0 4.0 <br />U <br />o 3.0 <br />U <br />2.0 <br />im <br />RM <br />O <br />O <br />• <br />i <br />O <br />O <br />O <br />❑ <br />❑ <br />p <br />8 <br />❑ <br />O <br />• <br />O <br />O <br />❑ <br />❑ <br />O <br />O <br />O <br />❑ <br />• <br />o <br />p <br />0 <br />0 <br />❑ <br />X <br />X <br />X <br />X <br />X <br />X <br />X <br />X <br />X <br />X <br />X <br />X <br />09/22/21 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 O Post -Detention O Filter 1 Effluent ❑ Filter 2 Effluent <br />Figure 5-1. DO Concentration Change in the Pilot Skid <br />The DO consumed by the filters increased significantly during the treatment efficiency phase when <br />compared to the acclimation phase due to the larger microorganism population in the filters at that time. <br />Table 5-1 below summarizes the average DO consumed by the filters during both phases of the study. <br />Table 5-1. Changes to DO Consumption <br />Phase <br />Avg. DO Consumption <br />Filter 1 <br />Filter 2 <br />Acclimation <br />7% <br />3% <br />Treatment Efficiency <br />14% <br />13% <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 7 <br />