4.4. SR 03-20-2017 - Laserfiche WebLink

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transmittance with the change in leachate flow rate were not noticeable as it took some time for the leachate to make it through the treatment plant to the effluent channel. Figure 3.2, shows that the UV transmittance declined each time the leachate feed rate was increased. Once it was determined the leachate feed rate was the primary variable affecting the UV transmittance, the leachate flow was increased again to study the effects of an even higher loading. After 403 hours of run time, the flow rate of leachate was increased to 21 gpm (30,200 gpd). As noted earlier, it took several hours before the transmittance in the effluent began to decline. After approximately 300 hours of run time at 21 gpm, the UV transmittance had decreased to an average of 46%. Over this same period, the rate of decline in the UV transmittance had slowed and the transmittance had become more stable around 46%. Even after extended period of the leachate feed rate of 21 gpm, the UV transmittance was maintained at approximately 46-47%. With the transmittance stabilized near 46-47% after 745 hours of run time, the leachate flow rate was increased to the goal flow rate of 25 gpm (35,000 gpd) for 91 hours. From Figure 3.2, it can be observed that the UV transmittance had slightly decreased during this period to 45%. However, this decrease is insignificant when compared to the increase in volume of leachate that was being fed into the treatment plant. The transmittance was at the bottom of the typical range of 45% to 70% and well below the designed valve of 65% for the existing system. During the next 167 hours (836 to 1003 hours of run time), the feed rate was adjusted to observe the effect of different leachate flows on UV transmittance. During this period, the city was concerned with the effectiveness of the UV disinfection as the transmittance was continually below 50%. The City of Elk River began to add chlorine for supplemental disinfection prior to the sand filters. The purpose of the chlorine was to add additional disinfection and insure the City did not incur a permit violation. During this time, an increase of transmittance was observed. This increase is due to the lower leachate flow and possibly the addition of chlorine to the system. Chlorine is a good oxidizer and will aide in removing some of the color from the water, thus helping to increase the transmittance. Results indicated there was an effect Prepared by: Bolton & Menk, Inc. Results and Discussion Waste Management/Elk River Leachate Pilot Study I T21.109643 Page 11