AFM activated filter media for drinking water treatment, an Eco-India project
AFM is an activated filter media designed to replace sand in any type of sand filter for the filtration of drinking water, tertiary treatment of municipal waste water and process water. AFM is manufactured by Dryden Aqua in the most adv
anced filter media manufacturing factory in Scotland for up-cycling coloured container glass. The factory has the capacity to up-cycle 50,000 tonnes of container glass and produce 30,000 tonnes of high performance water filtration media every year.
AFM is a certified product for drinking water, under United Kingdom Regulation 31 by the Drinking Water Inspectorate and by WQA Water Quality Association in the USA under NSF50 and NSF61. However, certification is not verification that a product is fit for purpose. Also for the Eco-India product we needed to benchmark the performance of AFM against sand under controlled conditions in order to fully quantify the material benefits that can be achieved. The laboratory scale tests quantify the performance of AFM under controlled conditions and then the trails in West Bengal compare the performance of AFM in actual working conditions. The tests were also required in order to optimise the operational parameters required to optimise system performance for rural community drinking water systems as well as water supply systems for cities.
The laboratory scale tests confirmed that AFM performed substantially better than a high quality silica sand (sourcedfrom Leighton Buzzard deposit England) used for drinking water in Europe. Sand is used for most drinking water systems in Europe, surprisingly and for historical reason no sand in Europe requires any form of certification or verification. Sand quality varies greatly from country to country, between deposits and even different locations form the same deposit. It is loophole in the regulations which should not be permitted because it can impact on the quality of potable water and the performance of the water treatment system which has implications for public health in India, Europe and around the world. AFM is an ISO manufactured product to a precise specification that does not vary.
The sand used in The Eco-India project was sourced from India, slow bed sand filters typically use quite large particle size of sand. The performance of the filters depends upon the sand becoming a biological filter. Once the filters have matured, slow bed sand filters usually give a very good quality water. However, water flow must always be maintained, even at night. If water flow stops, the retained organic matter acts as a food source for the resident bacteria, the oxygen is consumed and the filter goes anoxic. Any arsenic in the filter may be reduced to the soluble As5+ form and exit from the filter when the water supply is turned on in the morning. Bacteria and dissolved organic matter will also exit the filter. In order to prevent such an events, the slow bed sand filter has to continuously filter and discharge water. This is not such an issue for AFM because it contains less organic mater and AFM filter media does not support the growth of bacteria.
The laboratory scale tests fully quantified the mechanical filtration performance of both AFM and sand, the data shows that AFM grade 1, is 10 times better at removing sub <4 micron particles than sand, and that grade 0 AFM was 100 times more effective. At 20 microns the performance of sand and AFM are similar. The results from the field trials showed that AFM delivered a turbidity value 50% lower than sand, the difference relates to the better performance of AFM below 20 microns, and more specifically to a greater difference in performance below 4 microns. Given that 50% of all disease may be caused by Cryptosporidium protozoans measuring 5 microns, the performance of the filters for the removal of small suspended particles is very important.
Ground water should not contain any parasites; however, tube wells are often located close to latrines that are are subject to water getting into the ground adjacent to the tube well. The suspended solids from the tube wells will also contain arsenic. Mechanical filtration is therefore equally important for surface water as it is for ground water. The problem of tube well contamination and high arsenic concentrations is well recognised in India, for this reason tube wells are now going down to deeper aquifers, up to 300m below the surface. For rural communities in India this makes it very difficult as well as energy intensive to abstract the water. The villages therefore either use surface water, or shallow tube wells. The only practical solution for water security in India is therefore to provide high quality water from shallow tube wells and / or surface water.