Located in Nova Scotia, Canada, the Cape Brenton Regional Municipality recently conducted a pilot test of GreensandPlus, a new water filter media introduced by the Inversand Co. This filter media is an enhanced version of the firm's manganese greensand, an industry standard for this type of treatment for more than 50 years.
The manganese greensand filtration process efficiently and economically removes iron, manganese, arsenic, radium and hydrogen sulfide in municipal, industrial, and point-of-use treatment applications. According to the manufacturer. GreensandPlus has the same effective size, uniformity coefficient, density, weight, capacity, backwash and pressure drop curve as the original media, therefore, it can be used as an exact substitute for manganese greensand.
The Cape Breton Regional Municipality operates Hungerford & Terry manganese greensand filters, however a sodium aluminate feed is used to help reduce the breakdown of the media due to low silica levels in the raw water. Without the added sodium aluminate, the breakdown of manganese greensand would gradually shorten the run length between backwashes. By incorporating the new filter media, sodium aluminate feed is not be required to prevent breakdown.
In early 2005, a test plant was created at Cape Brenton Regional Municipality by Hungerford & Terry to conduct filter media test operation using the same feed as the full-scale units.
The test plant operated at flow rates between 4.4 to 6.2 Imperial gpm/square foot, and run lengths between backwashes of 120 to 200 hours were experienced. Influent manganese was 0.3 to 0.33 mg/L while iron varied between 0.045 and 0.09 mg/L. With seven runs complete, an average loading of 1,200 grains/square foot of filter area was obtained.
Manganese greensand has a capacity between 500 to 700 grains/square feet of filter area, demonstrating that the new filer media offered significantly greater capacity when operated on this water supply.
Results attained
The normal pressure drop end point for the full-scale plant and the test plant was 10 psi. In an attempt to extend the run, the plant was operated to a 334 hour run with a pressure drop of 17.9 psi at the end of the run. The test plant was still producing good quality water with less than 0.005 mg/L manganese and 0.001 mg/L iron in the effluent. After backwashing, there was no sign of damage to the media, and the pressure drop at the start of the next run was consistent with that of a clean bed.
During testing, the water treated by the test plant consistently averaged less than 0.01 mg/L manganese and less than 0.01 mg/L iron. The effluent-free chlorine averaged between 1.5 and 1.8 mg/L as determined by the chlorine feed to the full-scale plant and required for the distribution system.
The results of the test plant indicated that GreensandPlus filter media could treat the water at the Cape Brenton Regional Municipality filter plant in Nova Scotia, Canada without breakdown due to the low silica level water. It can also be operated to higher pressure drops and longer filter runs without any detrimental effects.
The test also demonstrated that while being operated for longer periods of time to higher pressure drops, it could still produce extremely high water quality.
This is just one in a continuing series of on-site tests being conducted around the world the water filter media that continues to produce high water quality results.
It is an exact replacement for manganese greensand, can be used in CR and IR applications, and requires no changes in backwash rate or time or chemical feeds.
