Economic removal of manganese from municipal water supplies

Existing methods of removal

Most methods of removal rely on the oxidation of Mn(II) to Mn(IV) to precipitate out the manganese for subsequent removal through a filter bed of sand.

Precipitation is typically achieved by adjusting the pH to 7 and chlorinating to ensure a residual of chlorine downstream of the filter. The capital cost of these system based on sand beds can be very high and mean treatment at multiple bore holes or surface water resources is just not viable.

Other methods of manganese removal include:

• Sequestration
• Adsorption
• Ion exchange
• Membrane technologies
• Biological removal

Amazon Filters worked closely with Welsh Water to see if using cartridge filtration technology could result in a more viable, flexible option.

The solution

The results of the first round of testing have shown that a system based on polymeric cartridge filters instead of traditional sand beds can lead to below detectable limits of manganese with an estimated overall installation cost 25% that of a traditional sand bed system.

This has been achieved using a polymeric filter composing of meltblown fibres that have proved to be highly effective at promoting the ‘seeding’ of the precipitated manganese. This ‘seeding’ on the fibres establishes areas that accelerate the removal of manganese through a catalytic process. By selecting a filter with the correct combination of fibre diameters, efficiency, and water flux, the optimised system in terms of removal and lifetime can be achieved.

In summary, our polymeric filter solution:

• Accelerates removal through a catalytic process
• Combines the correct combination of fibre diameters, efficiency, and water flux
• Reduces manganese levels below detectable limits of manganese
• Enables maintenance of required flowrates through the filters
• Provides optimal design for retention and lifetime

Test protocol / results

A small side stream filter was set up to process a proportion of the water from a borehole after chlorination and pH adjustment. The initial manganese level was recorded at between 4 and 5ppb before treatment. While this is well inside the DWI regulations it was still in a concentration above that known to cause problems in the distribution network. Flowrates were maintained during the testing between 8 and 10l/min/10” filter.

Measurement of manganese levels were recorded by submitting samples to Welsh Water’s laboratories over an initial test period of 2 weeks. Over this time a marginal decrease in levels was recorded. Water continued to flow through the filter system for a further 2 weeks.

Samples were then taken and analysed and the filtrate levels of manganese had dropped to below detectable limits.

Conclusion

Two different filter constructions were tested to establish the optimal design with respect to retention and lifetime. While these tests were limited to just one bore hole, the results are so encouraging that additional filter systems have been ordered by Welsh Water to replicate the performance at other bore and surface water locations.

To better understand the mechanisms of removal more fully and therefore have the ability to further improve and optimise the system, Welsh Water are looking to conduct a University research project in the near future.

It is hoped this will lead to further improvements in design, installation and operation of the filtration system. Budget proposals for a system to process all the borehole water (8.4Ml/d) have been completed and indicate a saving in the order of 75% over a traditional sand bed installation.

This saving is in conjunction with guaranteeing manganese levels below 1ppb and reducing the amount of manganese entering the distribution by 30kg/year. For further information on this new filter and application please contact Amazon Filters.