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7. CONCLUSIONS AND RECOMMENDATION The final conclusions and recommendations from this pilot study to assess the feasibility of biological filtration as a water treatment method in Lino Lakes are summarized as follows: 7.1 Performance Takeaways Aeration Requirements: An air flow rate to water flow rate ratio of 0.40 CFM/GPM was sufficient to promote rapid biological growth and to maintain an effluent DO concentration above 4 mg/L. Iron Removal: The iron concentration in the raw water was reduced from an average of 0.05 mg/L to an average 0.02 mg/L, which is 93-percent below the EPA Secondary Standard for iron. Both biological filters produced similar effluent iron concentrations throughout the pilot study. Manganese Removal: The manganese concentration in the raw water was reduced from an average of 0.410 mg/L to an average of 0.040 mg/L in Filter 1 and 0.023 mg/L in Filter 2. All effluent manganese concentrations during the treatment efficiency phase were below EPA's Secondary Standard and MDH's guidance values for manganese. Ammonia Removal: The ammonia concentration in the raw water was reduced from an average of 0.35 mg/L to an average 0.02 mg/L in Filter 1 and 0.03 mg/L in Filter 2. All effluent concentrations during the treatment efficiency phase were below the target concentration of 0.10 mg/L. Nutrient Requirements: The raw water orthophosphate concentration was sufficient to promote rapid biological growth, and additional nutrients were not required during the pilot study. Filter Headloss and Backwash Frequency: Terminal headloss was never reached during the study and the biological pilot filters were backwashed every 7 to 15 days. The rate of headloss buildup was slightly higher in Filter 2 when compared to Filter 1. Filter Performance Testing: Filter performance testing determined that the effluent treatment goals were met within 30 minutes following a filter backwash and within 1 hour following a 1-week plant shutdown. Filter 1 recovered slightly faster than Filter 2. 7.2 Financial Takeaways Implementing biological filtration in Lino Lakes has the potential of generating approximately $950,000 in chemical savings over the next 20 years when compared to conventional filtration. In addition to generating operational savings, utilizing fewer chemicals produces less processed and more sustainable water. 7.3 Recommendation As recommended in the City's Water Treatment Plant Feasibility Study, it is recommended to design and construct a gravity filtration water treatment plant with biological filtration in Lino Lakes given its piloted treatment performance and projected operational cost savings. Both media types piloted exhibited similar removal performance, headloss buildup rates, and responded similarly to filter performance testing. However, gravity filters with silica sand and anthracite are recommended for Lino Lakes since the silica sand filter had a lower rate of headloss than the greensand filter and should require less frequent filter backwashing. In addition, silica sand is less expensive than greensand filter media. Water Treatment Pilot Study Report Biological Removal of Ammonia, Iron and Manganese at Well House No. 6 City of Lino Lakes, MN WSB Project No. 0 18601 -000 Page 16