In April 2017 we were approached to investigate the possibility of providing potable water to a large processing site from a borehole supply.
It transpired that we knew the site as the borehole in question had been drilled by one of our authorised distributors some 23 years ago. We had quoted for Iron and Manganese equipment in 1999, however this did not go ahead and the BH was moth balled.
After some positive dialogue it was agreed to conduct a site visit in May 2017. The visit comprised of an investigation of the current system but also to run a pilot trial to ascertain an appropriate new treatment regime.
It transpired that circa 2015 an iron and manganese removal system had been installed. However, due to poor performance the system had never supplied water to the site.
This system used two treatment streams and was based on the ‘Triplex’ design. This design uses separate vessels for aeration and filtering.
Water coming from the borehole passes through a venturi device (Bernoulli pump). This device draws air into the water and the oxygen starts to react with the dissolved iron and to a lesser extent the Manganese.
The water then passes into the first vessel. This is generally known as a ‘contact’ vessel, however it’s more accurately described as a ‘detention’ vessel. The contact has already occurred at the venturi, or momentarily after, leaving the reaction between the iron and oxygen to continue within the vessel, in detention!
The water then passes to a second vessel which contains an iron removal media, this appeared to be a solid Manganese dioxide type (possibly Filox or Pyrolox, which are in essentially the same thing).
Then the water passes through the third vessel which appeared to be a smaller version of the second vessel which also contained the same type of filter medium.
Based on the limited on site information it appeared that the system had been run to waste for around 7-8 months while the suppliers/installers tried different modifications to improve iron and especially manganese removal.
It was apparent that some of the modifications tried were through desperation rather than based on sound practice. This was most evident in the fitting of a 2” Venturi in the raw water supply ahead of the two venturis already associated with the detention vessels.
The additional 2” item could not draw anymore air into the water stream as the back pressure created by the two smaller venturis prevented this.
Other attempts involved dosing oxidants into the water to try and improve the Manganese reduction.
The filters themselves were basic generic units. The iron/manganese filters were top mount units. This is where the control valve is attached to the top of the filter vessel (the big blue tank)) and the detention vessels used top and bottom connections.
As with any aerating iron removal filter once air and therefore oxygen is introduced into the iron rich water the iron will start to precipitate (the water typically turns orange). The iron will start to build up within the pipe work and can seriously reduce filter performance.