18 research outputs found
Designing Iron-Amended Biosand Filters for Decentralized Safe Drinking Water Provision
No full textThere are ongoing efforts to render conventional biosand filters (BSF) more efficient for safe drinking water provision. One promising option is to amend BSF with a reactive layer containing metallic iron (Fe0). The present communication presents some conceptual options for efficient Fe0-amended BSF in its fourth generation. It is shown that a second fine-sand layer should be placed downwards from the Fe0-reactive layer to capture dissolved Fe. This second fine-sand layer could advantageously contain adsorbing materials (e.g. activated carbons, wooden charcoals). An approach for sizing the Fe0-reactive layer is suggested based on 3 kg Fe0 per filter. Working with the same Fe0 load will ease comparison of results with different materials and the scaling up of household BSF to large scale community slow sand filters (SSF)
Chemical and Bacteriological Analysis of Drinking Water from Alternative Sources in the Dschang Municipality, Cameroon
No full textCuirassement ferrugineux actuel de bas de versants en zone forestière humide du Sud-Cameroun.
No full textWhile iron crusts are widespread in West and Central Africa savannahs, they generally disappear in the tropical rain forest region. Tropical environments are generally characterised by degradation and dismantling of these ferricretes, which seem to have formed under a climate characterised by alternating humid and dry seasons. Under the present humid rainforest conditions typical for tropical zones, iron crusts are in desequilibrium ; they are degrading and dismantling. The dismantling evolves from the top down and from the bottom up the profile or inside the crust. It affects the landscape morphology. The new land surface shows two levels : the first level is higher in altitude, old, represented by large hills with tabular summits and covered by savannah. The second is lower, recent, covered by forest and represented by half-orange shaped hills. This level, characteristic of tropical and equatorial climate, shows actual iron accumulation found on the lower part of hill slopes. Iron crusting is not known as tropical humid zone process. The main goal of this study is to characterise recent ferruginous accumulations which occur on lower part of hill slopes in Southern Cameroon and to identify the iron crust building processes in the humid rainforest zone. This work deals with (micro) morphological, mineralogical and geochemical aspects, based on more than about 70 up to 15 m deep soil profiles on an area of a 250 hectares, situated on a half-orange shaped hill between local rivers at an average altitude of 700 m. The relationship between different soil facies, slope angles and groundwater level fluctuations has been established. Three types of topographic profiles characterise the study area : in the Northern part, the slopes are short, high in altitude (from 705 to 660 m a.s.l.), and very steep, ranging up to 50% near the entailed zone ; in the southern and eastern part, they are long, low in altitude (from 705 to 635 m a.s.l.) and gentle, less than 5% near the swamping zone. The third down slope type shows an intermediate morphology ; it is observed at the head of W, SW, SE thalwegs and presents the moderate slope. The whole landscape appears to derive from the same undulated surface, that was entailed and eroded leaving behind tabular buttes and half-orange shaped hills.
The Meyomessala study area in particular contains the old thick ferricrete near the top of the plateau part and the present day forming carapace on the lower part of slope. The soil shows fifteen horizons that have been grouped on three types : (I) weathering horizons (isalterite, alloterite and grey clay), (II) ferricrete and ferricrete dismantling horizons (pebbly horizon, ferricrete, spotted nodular horizon, soft nodular horizon, soft clayey horizon) and (III) downslope iron accumulations (yellow grey clay, variegated clay, mottled clay, variegated massive carapace, variegated vesicular carapace, spotted massive carapace). The petrography data and water table fluctuation show that the ferruginous accumulations of the downslope are linked with the hydromorphological process.
On the steep slope, the mottled clay horizon represents the only iron accumulation pattern. These pattern is confined to the extreme part of the slope. It is developed as ferruginous core nodules, becoming more consistent into a clayey soft matrix, without continuous crusting process, despite that the iron is concentrated even more inside the nodules. The mottled clay are overlain by red soft clay of the crust dismantling patterns, on place as relics or transferred by crawling processes.
The moderate slope represents the valley head. Here, from the bottom to the top of the profile, the soil patterns consist of yellow grey clay with a homogenous matrix constituted of the mineral kaolinite. The variegated clay follows on top of the first pattern and consists of large mottled sectors, either purplish red, less hardened with goethite, or yellow and soft with goethite and kaolinite minerals, or whitish grey and flabby with kaolinite. On the variegated clay follows the variegated massive carapace and is distinguished from the latter by its harden mottles with goethite, hematite and kaolinite minerals, and by the increase of the consistency of the yellow and yellow brown mottles. The accumulation of these materials is related to a perched groundwater aquifer that generates permanent humidity due to rising capillary water. At the top of the variegated patterns, a spotted massive carapace shows very reduced yellow and whitish mottles, and abundant red mottles. The latter tend to form a continuous ferruginous frame constituted by hematite and goethite. These massive accumulations are richer in iron (~25% Fe2O3). Here, the induration seems to be related to the seasonal humidity conditions.
With the subsidence of the land surface, the slope becomes gentle. Pedological features on the bottom of the profile are essentially whitish grey to greenish grey clay patterns, richer in quartz, kaolinite and cracks. The cracks are filled, either by purplish red and less relatively soft material with goethite, or by yellow soft materials with kaolinite and goethite. The variegated vesicular carapace follows on top of the variegated clay and is distinguished from the latter by harder domains, and by the increase of the consistency and the appearance of vesicles. These domains are filled out by a dark red ferruginous network and the variegated clay-filling vesicles. The mottled clay pattern takes over from the variegated clay zone and the vesicular carapace towards the upper part of the slope. The mean iron content is less here (~15% Fe2O3). However, the lateral extension of the iron accumulations has a length of about 400 m and the vesicular carapace represents the hardest downslope patterns. The ferruginous network, developed through the fissures, is due to high groundwater fluctuations between dry and rainy seasons observed in the field. Also here, the iron accumulation is linked to the water table fluctuation zone. These conditions are favourable to mobilise the iron during the humid period and to precipitate it during the dry one and explain why the iron is highly accumulated at the top of the ferruginous patterns.
Iso-element mass balance calculation allows to estimate the chemical transfer of the younger downslope soils. It appears that the ferricrete (group II) and the ferruginous downslope accumulations (group III) show an allochthonous enrichment. This enrichment is significant for the downslope patterns and indicates that iron is transferred from the hill summit to the downslope sequences. The high iron contribution observed on the moderate slope than on the gentle slope indicates that after transfer, the iron is also redistributed during the transformation of the massive carapace to the vesicular carapace when the slope becomes gentle.
The high weathering state of the old ferricrete on the top of the hill is always accompanied by subsidence of land surface and the ground water rising. By subsidence the slope becomes first steep and then gentle. The present study shows that the iron mobilised by ferricrete weathering is an important allochthonous contribution to the downslope of the hill. The carapace crust-building process starts at the spring head where the slope is still steep and remains confined to the slope extremity. These sequence might represent the first stage of the landscape transformation during the Eocene period. When the slope is moderate, the ferruginous accumulation moves upstream and becomes hard in the upper part of the profile, and the massive carapace appears. When by subsidence the slope becomes gentle, the ferruginous accumulations extend more on the slope, while the vesicular carapace replaces the massive carapace. In the present climatic conditions, the carapace crust-building process is able to invade completely the planar landscape.
The ferruginous accumulation here are at their starting stage towards the vesicular crust-building process. There are generalised at the southern Cameroon rain forest zone. Beauvais 1991 has identified the vesicular crust on the low plateau in the Central African Republic. The observed vesicular carapace might be the precursor of these vesicular crust which characterises the actual rain tropical environment
Water supply, sanitation and health risks in Douala 5 municipality, Cameroon
No full textIn the poor zones of sub-Saharan Africa, the conventional drinking water network is very weak. The populations use alternative groundwater sources which are wells and springs. However, because of urbanization, the groundwater sources are degrading gradually making pure, safe, healthy and odourless drinking water a matter of deep concern. There are many pollutants in groundwater due to seepage of organic and inorganic pollutants, heavy metals as well as microbiological contamination. This study was carried out in October 2012 and aimed to analyze the practices and behaviors of populations related to water supply that may constitute potential risks of microbiological contamination and emergence of waterborne diseases
Water supply, sanitation and health risks in Douala 5th municipality, Cameroon
No full textBackground: In the poor zones of sub-Saharan Africa, the conventional drinking water network is very weak. The populations use alternative groundwater sources which are wells and springs. However, because of urbanization, the groundwater sources are degrading gradually making pure, safe, healthy and odourless drinking water a matter of deep concern. There are many pollutants in groundwater due to seepage of organic and inorganic pollutants, heavy metals as well as microbiological contamination. This study was carried out in October 2012 and aimed to analyze the practices and behaviors of populations related to water supply that may constitute potential risks of microbiological contamination and emergence of waterborne diseases.
University of Rome “Tor Vergata”, Rome, Italy

Method: This study was carried out on a sample of 285 households, distributed in twelve principal quarters of the Douala V municipality in Cameroon. After data collection through the questionnaires, the selection of vulnerable quarters was done by the tabulation of some specific results on the questionnaire.
The microbiological analysis was carried out using an innovative rapid test called “Micro Biological Survey (MBS)” that has been developed and patented by MBS srl, a recent spin-off that collaborates with the Biology Department of the University of Roma Tre.
Result: We found out that 42.30% of households used water from forages, 33.80% from Cameroon National Water Company (CDE) distribution network, 9.50% from spring, and 9.40% used other source of water such as buying industrial mineral water. However, it should be noted that, as dangerous as it may be, wells water is used as permanent source of drinking water by 5% of households. In general, 63.2% of households affirmed not to have benefited the fitting of public water point. Moreover, among the quarters were the households affirmed to have benefited from the development of a public water point, 52.5% of these water point were no longer functional. From the obtained data we have assessed that 83% of wells analyzed are faecally contaminated and all the forages analyzed (100%) are not contaminated. The most affected people by water-related diseases are children under 5 years (43%).
Conclusion: We highly recommend the City Council of Douala V to restrict the use of the contaminated wells and provide alternative water sources such as forages for public use and to ensure that microbiological quality of the new and already existing water sources is controlled regularly by the Technical Service
SANITARY QUALITY OF IRRIGATED VEGETABLES IN THE SWAMPY LOWLANDS OF DSCHANG CITY, CAMEROON
No full textModeling the permeability loss of metallic Iron water filtration Systems
No full textInternational audienceOver the past 30 years the literature has burgeoned with in situ approaches for groundwater remediation. Of the methods currently available, the use of metallic iron (Fe0) in permeable reactive barrier (PRB) systems is one of the most commonly applied. Despite such interest, an increasing amount of experimental and field observations have reported inconsistent Fe0 barrier operation compared to contemporary theory. In the current work, a critical review of the physical chemistry of aqueous Fe0 corrosion in porous media is presented. Subsequent implications for the design of Fe0 filtration systems are modeled. The results suggest that: (i) for the pH range of natural waters (>4.5), the high volumetric expansion of Fe0 during oxidation and precipitation dictates that Fe0 should be mixed with a non-expansive material; (ii) naturally occurring solute precipitates have a negligible impact on permeability loss compared to Fe0 expansive corrosion; and (iii) the proliferation of H2 metabolizing bacteria may contribute to alleviate permeability loss. As a consequence, it is suggested that more emphasis must be placed on future work with regard to considering the Fe0 PRB system as a physical (size-exclusion) water filter device
Land use and soil texture effects on organic carbon change in dryland soils, Senegal
No full textSoil organic carbon (SOC) losses due to poor soil management in dryland are now well documented. However, the in- fluence of soil properties on organic carbon change is not well known. The groundnut plant (Arachis hypogaea L.), and the dominant crop system in the Senegal’s Soudanian zone, have been compared with semi-natural savanna. Leaves, stems and roots biomass were measured, and soil characteristics were analysed. The total leaves and stems biomass was 1.7 and 2.7 Mg ha−1 dry matter in groundnut fields and savanna respectively. Total SOC stocks were low (8 to 20 Mg C·ha−1 within upper 0.2 m depth, 20 to 64 Mg C·ha−1 within upper 1 m depth) and were significantly lower (P < 0.05) in sandy soils than in sandy clayey soils, and lower (approximately 27% - 37%) in groundnut fields than in savanna soils. δ13C values show that SOC quality is transformed from the savanna plants (C4/C3 mixed-pools) to C3-pools in groundnut cultivated zone, with the organic matter signature more preserved in the clayey soils. This study confirms that converting woodland to groundnut fields provokes texture transformation and SOC loss. The results call for the extreme necessity to regenerate the wooded zone or encourage practices that favour SOC restitution.ECO
Assessment of soil compaction using soil shrinkage modelling : experimental data and perspectives
No full textInternational audienceSoil compaction assessment is an important and difficult issue. In particular, it is difficult to quantify separately the compaction of macro-pores and micro-pores in the soil, and to account for spatial variability in soil properties at field scale. According to recent publications, the measurement and modelling of soil shrinkage curves (ShC) could help to overcome these difficulties. This is discussed in this paper on the basis of a field study. Control and compacted undisturbed samples originating from the surface layer of a cropped field are compared. The methods for measurement and modelling of the ShC are presented. Calculations of the micro-porosity, identified to be the soil plasma-porosity, and of the macro-porosity in the soil samples, at any water content, are described, and the accuracy of the results is discussed. A good agreement between field observation and ShC modelling is observed. The method allows for quantifying the compaction, with distinction between plasma-porosity and macro-porosity compaction. The forming of occluded macro-pores is also detected and quantified. The presented method offers numerous advantages in soil compaction assessment. It is precise, simple and easy to operate. It can be realized on clods of unspecified shape and containing a coarse fraction, and can be calculated for the fine earth fraction without the coarse fraction. The pore systems are quantified at any water content, and the determination covers the full range of pore sizes with quantitative distinction between the plasma-porosity and the macro-porosity compaction. According to previous results, it is possible to remove a certain amount of spatial variability in soil clay content by scaling the shrinkage parameters with clay content. The measurement and modelling of soil ShC is, therefore, a promising tool for soil compaction assessment
