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4. OPERATIONAL OVERVIEW <br />Influent flow to the pilot skid was maintained at 1.2 gallons per minute (GPM). From there, water was <br />pumped into each filter at a flow rate of 0.6 GPM per filter to achieve a filter loading rate of 3.0 GPM per <br />square foot (SF) of filter media per recommended Ten States Standards. The above water flow rates <br />achieved a 30-minute detention time in the detention basin and an empty bed contact time (EBCT) of 6.2 <br />minutes in each filter column. The filters were backwashed with raw water when a terminal headloss of 120 <br />inches was achieved. <br />Following set up and staff training, this pilot study was conducted in two operational phases, the microbial <br />acclimation phase and the treatment efficiency phase. The microbial acclimation phase consisted of <br />adjusting the aeration flow rate to promote rapid biological growth. Nutrients were not required in this pilot <br />study as it was determined that the natural orthophosphate concentration in the raw water was sufficient to <br />promote biological filtration. The second phase of the study (treatment efficiency phase) started when the <br />filters were fully acclimated and removing the majority of the manganese. Towards the end of this phase, <br />biological filter performance was measured following a backwash and a 1-week shutdown period. <br />Regardless of the operational phase, day to day monitoring procedures and water quality sampling <br />remained the same throughout the study. Daily operations included monitoring the flow rates (air and water) <br />and water pressure. Water quality sampling consisted of testing the water at various treatment stages <br />throughout the pilot skid. The majority of the water quality sampling and testing was completed on site by <br />City staff with some samples being shipped to a certified laboratory for testing and QA/QC purposes. City <br />staff were also responsible for daily monitoring of the pilot skid. <br />Filter backwashing was accomplished using a combination of air and raw water. The duration of the entire <br />backwash was approximately 12 to 15 minutes (for each filter). After draining the filter columns for about a <br />minute, air was introduced through the underdrain system for 5 minutes. The air scouring loading rate was <br />maintained at 2 cubic feet per minute per square foot of filter media (CFM/SF) for the first 3 minutes and <br />then increased to 3 CFM/SF for the following 2 minutes. After the initial 5 minutes of air scouring, a <br />simultaneous air and water backwash took place for 2 minutes. During that time, the air scouring loading <br />rate was reduced to 1 CFM/SF and the water loading rate was maintained at 8 GPM/SF. Following the <br />simultaneous backwash, the filter columns were backwashed with water for a period of 4 minutes. During <br />the water -only backwash, the water loading rate was varied from 8 GPM/SF to 15 GPM/SF. The backwash <br />water flow was stopped when the filter media achieved 50-percent stratification for approximately 1 minute. <br />Following the backwash, the media was allowed to settle for a short period (3 to 5 minutes) to ensure that <br />no media was lost when normal filter operation resumed. This backwashing strategy was effective removing <br />particle clusters without losing a significant quantity of microorganisms. WSB staff conducted all <br />backwashes. <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 6 <br />