The DMI-65 is the most sophisticated catalytic water filtration media that has extremely high capabilities of removing both Iron (Fe) and Manganese (Mn) simultaneously through low cost catalytic oxidation and retention of precipitate. The DMI-65 will also remove arsenic from a water supply given the correct conditions.
The DMI-65 is one of the fewer catalytic water filtration media in the world developed to remove iron and manganese that is certified to NSF/ANSI 61 for drinking water applications.
With regards as to how DMI 65 works, this is a catalytic filter media boosting oxidation capacity of low cost oxidant such as NaOCl. The oxidant is injected before water reach the filter.
Iron and manganese in solution are in the form of lower valence oxi-hydroxides (example, ferrous hydroxide). Higher valence oxi-hydroxides (ferric hydroxide, red color) are not soluble in water around neutral pH. When the water with iron and manganese in solution and oxidant reaches the filter bed, the low valence hydroxides oxidize to high valence; insoluble form and precipitated particles are retained in the filter bed. This process would take place normally in a matter of days to weeks. The catalytic filter media makes this happen in minutes accelerating the reaction a few hundred times.
DMI 65 is easy to use and provides flexibility when upgrading old water treatment systems. DMI 65 can be used for modification of existing systems by just replacing ordinary sand or multimedia filter used for mechanical filtration, or for removal of iron and manganese through catalytic oxidation.
DMI 65 Filters have three cycles of operation, the same as other media filters:
1. Filtration mode,
2. Backwash mode, and
3. Rinse mode.
1. Filtration mode
Pressure drop for an initially CLEAN filter depends on the depth of the filter media bed and water velocity. Below is a chart showing the pressure drop for 1 meter bed depth. For other bed depth, the pressure drop can be determined linearly. Thus, to find out the pressure drop for 0.6 m bed depth we multiply the value for pressure drop found in the chart by 0.6.
We relate the pressure drop to velocity of the water through the cross sectional area of the filter because its usefulness and simplicity of relating the data to flow rate. We can calculate the flow rate “Q” in cubic meters per hour by multiplying the velocity ‘v” in meters per hour by the filter area “A” in square meters.
Q = v x A
Water temperature during test for the data in the graph was 24º C.
The depth of filter media needed shall be dependent on the required residual iron and manganese in the filtered water. Filter media depth needed increases with the as the required amount of residual iron and manganese allowed in the filtered water decreases. Maximum bed depth could be just over 1 meter and relates also to the flow capacity of the system and effective height of available filters.
Water velocity through the filter should be selected in accordance with the usage of the filtered water, size of water treatment plant, water quality and other factors.
For large drinking water treatment plants the depth of the bed should be selected towards the maximum and the water velocity around 5 m/hr, and in any case, be not more than 10 m/hr. This maximizes performance in removing iron and manganese, reduces the frequency of backwashing, reduces power consumption because average pressure drop is lower, and could provide redundancy in case one of the filters is out of order and higher flow rate has to be put through the remaining filters.
The upper limit of velocity, up to 30 m/hr should be used for small bed depth and larger allowed amount of residual iron and manganese in the filtered water.
2. Backwash mode
Total pressure drop through the filter before backwashing is recommended to be maximum 100 kPa. The granules of DMI 65 filter media are porous. The larger the pressure drop, the larger compaction forces are applied to the filter media. The interaction between filter media particles during alternated compaction under normal service and expansion of the bed during backwashing leads inevitably to deterioration of granules.
Backwashing the filter when the pressure drop has increased by 50 kPa from the initial clean filter pressure drop is a good reference. Higher or lower values could be set depending on the application and how long the filter media has to last before changing it. Note that during filtration cycle, the filter media would not loose significantly its effectiveness in removing the iron and manganese, but the pressure drop through clean filter bed will increase.
Water velocity for backwashing the filter is limited to 80 m/hr. This is the same as recommended for ordinary sand filtration. Although it is possible to use not filtered water for backwashing in general this is not a good idea unless the water is relatively clean and the system is set up with a rinse operating mode in addition to filtration and backwashing. At low backwashing velocity, longer backwashing time is needed. In general backwashing velocity should be twice the filtration velocity.
Backwashing time should be determined on the backwash discharge line, devise a way to observe when the backwash water discharged is satisfactorily clean. Backwashing time could vary from a few minutes to 15 minutes.
3. Rinse mode
This mode follows backwashing to remove the contaminant solids that would exit the filter before the filter bed is compacted back and operates normally. This mode is not necessary to be implemented in all water treatment systems.
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