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Although naturally occurring in the environment, manganese at elevated levels in drinking water can pose serious health risks when untreated at the water treatment facility. A link exists between manganese in drinking water and negative neurological issues in children and infants.
A public utility in West Virginia had between 0.45 mg/L and 0.62 mg/L of manganese in their raw water along with a number of water discoloration complaints from the local community. Aulick was asked to address the issue of manganese and develop a solution that would effectively treat the problem.
The 168 days of data included in this case study were provided by the water treatment plant operators and cover a period of over 6 months. The average manganese concentration in the raw water was 0.54 mg/L with a standard deviation of 0.04 mg/L. The highest concentration of manganese was recorded in March of the study at 0.62 mg/L, and the lowest was recorded in December of the study at 0.45 mg/L. The first graph (black) shown below in the gallery illustrates the frequency of various manganese levels as measured by the number of days per concentration.
Aulick proposed feeding Clarus, Patented Water Treatment Technology, before the filter and prior to applying an oxidizer in order to sequester the unoxidized manganese with the Clarus. Our results were better than expected.
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The data reveals that on average 92% of the manganese was sequestered with a standard deviation of 7%. The graph in the gallery below shows the number of days that correspond to each level of the recorded percentage of total manganese removal. For instance, there were 29 days when 96% of the total manganese was sequestered (see graph 2 in the gallery below).
Instead of looking at the percentage of manganese removed from the raw water at the treatment facility in West Virginia, it’s more important to consider how much manganese was removed from the water in terms of mg/L. The average amount of manganese removed from the raw water in mg/L over the 168 day period was 0.49 mg/L with a standard deviation of 0.05 (see graph 3 in the gallery below).
The variation in the amount of sequestered manganese can be explained by a mismatch in the calculated feed rate and changes in raw water chemistry. For instance, if the Clarus feed rate were set to sequester 0.5 mg/L of manganese in the raw water, but the actual level of manganese was 0.55 mg/L, then the additional 0.05 mg/L of manganese would not be sequestered. Since it would be difficult to perfectly match a feed rate to the constantly changing raw water chemistry, it would be best to use a rolling average to sequester the majority of the unoxidized manganese.
As shown in this study, sequestering unoxidized manganese prior to oxidation can be an effective method of reducing water-color related customer complaints.