Sand is used in rapid gravity sand filters for the treatment of sewage effluent. However the sand is prone to blockage due to biofouling of the media. Steps can be taken to reduce the effects of biofouling such as aggressive back-flushing, air scouring and the use of chemicals.  These cleaning techniques add to the cost of the process and are not always effective, consequently the sand usually requires cleaning at frequent intervals. In some cases the sand starts to foul after only 6 weeks, in other cases the media may last around 6 months.  If the sand is not changed or completely cleaned on bacterial cell biomass,  then the product water quality is going to deteriorate.

The use of AFM appears to eliminate the biofouling issues of filter media used in RGF ( Rapid Gravity Filters) and allows the filters to operate as they were designed. Trials have been conducted in sewage effluent using the same filter media for over 5 years.  There would therefore seem to be no requirement to change AFM media when installed in a good quality sand filter.

The net result is excellent water quality, no filter maintenance or replacement of the media and reduced operating costs.

After long term exposure of AFM to sewage effluent it has been confirmed that the media does not support the growth of bacteria and that the filter beds will remain free from fouling. The filters still need to be well designed and effectively back-flushed in order for performance to be maintained. However assuming a good quality filter is used,  it is unlikely that the AFM media will need to be changed.

Two identical RGF filters operating in parallel,  the difference in performance between sand and AFM is quite clear

Sand  |  AFM | influent water

AFM in a sewage works rapid gravity filter