Sand filter maintenance

When the movement price becomes unacceptably reasonable, the filter may be cleansed by removing gathered soil from the top few centimetres of sand. Various methods are feasible, but all disrupt the biological level, which leads to less effective filtration for quite a while. Some methods nevertheless tend to be less troublesome than the others.

Damp harrowing

Advised cleaning technique is known as 'wet harrowing'. This is done by completing the filter with a container of liquid, after blocking the spout (for instance utilizing a cork). Following elimination of the diffuser dish, liquid is gradually swirled around manually inside filter. Do not touch the sand while performing this. The motion of liquid loosens gathered soil, which has suspension system. This muddy water-can after that be very carefully decanted, using a cup. The procedure is duplicated until many dirt is eliminated. Take away the cork and circulation rate need increased dramatically.

The benefit of damp harrowing is the fact that it does not disturb the biologically energetic slime layer which has cultivated within the sand and all over individual sand grains. Which means cleaning activity regarding the filter is just slightly impacted in comparison to including getting rid of sand, washing it and returing it in to the filter. Finally: damp harrowing is effective. This system works well, needs less work and disturbs the biological level less (Lukacs, 2002 [ref_01]), enabling water becoming intoxicated after a shorter time than where various other strategies are utilized.

Do households discover how to carry out maintenance?

Adequate instruction during set up and sufficient followup could very well be a poor link in just about any biosand filter project, as householders will forget or dismiss advice offered concerning maintenance, adding to sub-standard overall performance of filters.

An evaluation of a filter project in Kenya unearthed that some filter owners clean their particular filter out of routine, in the place of considering blockage or inconveniently decreased movement price. This bad practise, because these types of filters unnecessarily produce water of sub-standard quality, since their particular bio-layer is disturbed more often than essential. If this is the actual situation, much better training of proper maintenance could therefore be an effective and easy method to increase the quality of liquid made by lots of filters. Occasionally reducing circulation prices are a seasonal problem. For-instance, during rainy season water can become more turbid. It appears that during this time, blockages may appear in filters every couple of weeks.

An assessment of a demand-led BSF project by Tearfund in Afghanistan indicated that 51per cent regarding the participants were utilizing and might properly explain the damp “swirl and dump” method of cleaning the BSF, 17percent suggested that they're utilizing the “sand removal” method, and 13percent either could not explain the cleansing technique or described it wrongly. Difficulty of incorrect level of liquid above the top surface associated with the sand layer was noted in 47per cent of BSF surveyed. It absolutely was noted that dilemmas identified with set up, procedure and maintenance will probably affect the filtered liquid high quality, and may even be contributing element the 22.2per cent of filtered liquid samples that have been measured to have higher than 10 cfu/100ml (Burt, 2012; [ref_02]).

Making use of ‘convenience’ to measure filter upkeep period

It is essential to keep in mind that a ‘dirty’ filter in fact can create liquid of better quality. Because of a low flow rate much better purification happens, while there is a heightened contact time with a mature biological level. Cleansing should for that reason only happen if the outflow of water is inconveniently slow. While a bio-sand filter if at all possible produces 1 litre each and every minute, filling a 20-litre jerry can in 2 hours can certainly still be really convenient to an African family, even though this equals a flow price of only 0.16 litres each minute.

In some projects it's discovered that a lot of households will either forget or dismiss cleaning advice. In such cases, bio-sand filters cannot be considered a 100% failsafe method of water purification despite their particular prospective, but rather as a ‘better-than-nothing’ interim way of water treatment. This highlights the need for intensive teaching techniques. Chances are that better information, teaching of cleansing methods, or enhanced or higher frequent followup will cause much better results.

Recommendations: (leap straight back)

Ref 01: Lukacs, H.A. (2002). From Design to Implementation: Innovative sluggish Sand Filtration for usage in Developing Countries. MSc Thesis. Massachusetts Institute of Technology, USA.

Ref 02: Burt, M. (2012) analysis of a demand led biosand filter programme within the complex disaster context of Afghanistan. Tearfund, Teddington, UNITED KINGDOM.