The effect of surface albedo and grain size distribution on eveporation losses in sand dams

Sand dams are very useful in arid and semi arid lands (ASALs) as facilities for water storage and conservation. Soils in ASALs are mainly sandy and major water loss is by evaporation and infiltration. This study investigated the effect of sand media characteristics, specifically surface albedo, grain  size and stratification on water table recession using experimental model. Tanks of 220 litres capacity and 0.9 m depth were set as evaporation  media at the JKUAT weather station in Kenya. Experimental media investigated were; fine ballast, fine sand, coarse sand, in situ sand and stratified combination. Surface albedo were varied by painting top sand media with colours such as white, grey and natural brown sand colour asa control. Albedo were indexed using luminance factor. The study  concluded that evaporation losses are inversely proportional to the albedo of the evaporating surface measured in terms of luminance factor. The relation between water table recession in porous medium and pan evaporation is an exponential decay curve. The study showed that stratification of media have significant influence on water loss particularly, if the overlying material is courser than the underlying layers

An Assessment of Soil Materials in Kenya as Sorbent Media for Defluoridation of Water

Three clay soil materials obtained from different parts of Kenya were studied for their feasibility as adsorption media for fluoride removal from water through batch tests. The soil materials were characterized by particle size distribution based on sieve analysis and oxides fraction percentage determined by X-ray fluorescence analytical technique. The soils clay content ranged from 68% to 75% and dominant oxides were SiO2(39-53%), Al2O3(35-39%) and Fe2O3(8-22%). Soils thermally treated at temperatures ranging from 500 to 850o C as well as pristine soil samples were compared for their fluoride adsorption efficiency. Fluoride removal efficiency of the soil materials increased with the clay content and the total percentage of the dominant oxides. The soils as collected in the field were of low permeability and; achieved very low fluoride removal of between 27-48%, whilst materials calcined at 650oC had the highest removal efficiency of between 52-80%, using raw water of 5mg/l fluoride concentration. Optimum conditions were achieved at pH 6, media dosage of 8g/200ml and contact time of 1hr. The soil sample MN obtained from Meru North achieved the highest removal of 80%. The Langmuir isotherm analysis indicated both the soil materials from Meru North and Nyeri to be feasible as an adsorption media for fluoride removal and further tests and actual performance evaluation will be undertaken on the Meru North soil.Key words: fluoride, adsorption, calcined clay material, isother