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day. Backwashing impacts the production capacity of a filter as it cannot treat water when being <br />backwashed. Consequently, it is the goal of any utility to reduce backwashes as much as possible. <br />The headloss buildup in Filter 1 is shown in Figure 5-5 and the headloss buildup in Filter 2 is shown in <br />Figure 5-6. The pilot filters were not backwash for a period of 3 to 4 weeks at the beginning of the study to <br />minimize media disturbance during the acclimation phase and to analyze if terminal headloss could be <br />reached. However, since the raw water iron concentration was very low, the biological filters never reached <br />terminal headloss. Consequently, the filters were backwashed every 7 to 15 days after the first month of <br />the study following the procedure described in Section 4. The rate of headloss buildup was slightly higher <br />in Filter 2 since greensand media is smaller than silica sand media and can obstruct more water flow. Also, <br />headloss data collected for Filter 2 in November 2021 is inaccurate. It is suspected that media blocked the <br />pressure gauge pipe assembly during this month and then dislodged from the pressure gauge. <br />140 <br />120 <br />-�;- 100 <br />80 <br />° 60 <br />m <br />= 40 <br />20 <br />0 T <br />09/09/21 <br />140 <br />120 <br />100 <br />U) <br />a� <br />E: 80 <br />U) <br />U) <br />° 60 <br />0 <br />° <br />aD <br />= 40 <br />20 <br />� �i � �i �i i� i I� � e it ��1♦ <br />♦ I I O <br />I I I 1 <br />I I OI I <br />I I 1 I <br />I I I I <br />I I I I <br />09/18/21 09/28/21 10/07/21 10/17/21 10/26/21 11 /05/21 11 /14/21 11 /24/21 <br />Date (mm/dd/yy) <br />Terminal Headloss ♦ Filter 1 Headloss — — Backwash Event <br />Figure 5-5. Filter 1 Headloss <br />0; I I I I. I I <br />09/09/21 09/18/21 09/28/21 10/07/21 10/17/21 10/26/21 11 /05/21 11 /14/21 11 /24/21 <br />Date (mm/dd/yy) <br />Terminal Headloss ❑ Filter 2 Headloss — — Backwash Event <br />Figure 5-6. Filter 2 Headloss <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 12 <br />