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5.8 Filter Performance Testing <br />The MDH biological filtration pilot protocol requires two performance tests to be completed when the filters <br />are fully acclimated with microorganisms. The first performance test is a backwash recovery test which is <br />used to evaluate the filtration efficiency of the biological filters immediately after a backwash. The second <br />performance test is a shutdown recovery test which his used to evaluate the filtration efficiency of the <br />biological filters after the filters are out of service for one week. <br />5.8.1 Backwash Recovery Test <br />It is almost inevitable that some microorganisms will be washed away when backwashing a <br />biological filter. Therefore, it is important to utilize a backwash strategy that effectively cleans the <br />filters while minimizing the loss of microorganisms. In order to assess the biological filter recovery, <br />water quality samples were obtained in 15-minute intervals following a backwash for 30 to 45 <br />minutes. Prior to sampling the post backwash effluent water, the media was allowed to settle for 5 <br />minutes in each filter. The post backwash results were compared to the pre backwash results to <br />determine how long it required the filter to recover its pre backwash performance. The backwash <br />recovery test results are summarized in Table 5-5. The backwash recovery test was completed <br />during the eighth week of the pilot study. <br />Table 5-5. Backwash Recovery Test Results <br />Filter <br />No. <br />Contaminant <br />Pre -Backwash <br />Conc. m /L <br />( 9 ) <br />Post Backwash Conc. (mg/L) <br />Target Effluent <br />Conc. m /L <br />( 9 ) <br />15-min <br />30-min <br />45-min <br />Iron <br />0.00 <br />0.02 <br />0.02 <br />N/A <br />0.30 <br />1 <br />Manganese <br />0.029 <br />0.032 <br />0.032 <br />0.023 <br />0.050 <br />Ammonia <br />0.03 <br />0.01 <br />0.03 <br />N/A <br />0.10 <br />Iron <br />0.01 <br />0.03 <br />0.01 <br />N/A <br />0.30 <br />2 <br />Manganese <br />0.021 <br />0.030 <br />0.036 <br />0.033 <br />0.050 <br />Ammonia <br />0.03 <br />0.12 <br />0.03 <br />N/A <br />0.10 <br />All post backwash concentrations for Filter 1 were below the target effluent concentrations set for <br />this pilot study within 15 minutes of conducting a backwash. The pre backwash iron concentration <br />was not recovered within 45 minutes of the backwash. This is not a concern as the effluent iron <br />concentration was maintained below the target effluent goal following the backwash. <br />All post backwash concentrations for Filter 2 were below the target effluent concentrations set for <br />this pilot study within 30 minutes of conducting a backwash. The pre backwash manganese <br />concentration was not recovered within 45 minutes of the backwash. This is not a concern as the <br />effluent manganese concentration was maintained below the target effluent goal following the <br />backwash. <br />5.8.2 Shutdown Recovery Test <br />Microorganisms need "food" (oxygen, nutrients, and contaminants) in order to survive. Therefore, <br />a portion of the microorganisms may not survive if water flow is stopped and "food" is not available. <br />In order to test the survivability of the microorganisms, both filters were shut down for a period of <br />one week. Similar to the backwash recovery test, the performance of each filter was measured <br />before and after the shutdown to determine the recovery time of each filter for up to 24 hours. The <br />shutdown recovery test results are summarized in Table 5-6. The shutdown recovery test was <br />completed during the last week of 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 <br />Page 13 <br />