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Designing and Piloting a household filter for the peri-urban population of Douala (Cameroon)

dc.contributor.advisorNoubacteb, Chicgoua Dr.
dc.contributor.authorTepong Tsinde, Raoul
dc.titleDesigning and Piloting a household filter for the peri-urban population of Douala (Cameroon)de
dc.contributor.refereeNoubacteb, Chicgoua Dr.
dc.description.abstractengIn rural and peri-urban regions of the developing world, many tube wells used as drinking water sources are microbially and chemically polluted. Consequently, hundreds of millions of people lack access to “safe” drinking water worldwide. People drinking tube well water may suffer from preventable water-borne diseases including diarrhea, skin lesions, and cancer. To address this problem, the United Nations have launched the Sustainable Development Goals (UN SDGs) which are regarded as a global urgent call for action by all countries, in a global partnership. The UN SDGs for safe drinking water (Goal 6) aims to achieve universal water supply by 2030. This goal can only be achieved if affordable and efficient water treatment technologies are made available for households and small communities for simultaneous removal of chemicals and pathogens. Ideally, such systems should be constructed using locally available materials and labor. Filtration on metallic iron (Fe0) based beds has been identified as such an appropriate technology and steel wool (SW) a universally available material. Moreover, Fe0-based filters have been designed and disseminated in some parts of the world but have not yet reached global applicability. A critical review on the abundant literature on using Fe0-based filters for safe drinking water provision revealed that existing devices were not designed on the knowledge basis of the science of aqueous iron corrosion (corrosion science). Iron corrosion induces generation of solid iron corrosion products (FeCPs) which are well-documented contaminant scavengers. FeCPs consisting of Fe-oxide hydroxides are formed in the vicinity of the Fe0 surface and act as a diffusion barrier for dissolved species. Iron corrosion is additionally a volumetric expansive process because the volume of each oxide or hydroxide is at least twice larger than that of iron metal (Fe0). These two main characteristics imply that (i) the efficiency of each Fe0-based filter depends on the kinetics of production of FeCPs (reactivity loss), and (ii) Fe0- based filters will experience porosity loss with increasing service life (permeability loss). In other words, reactivity loss and permeability loss are inherent characteristics of Fe0-based filters which should be addressed in the design stage. Moreover, designed systems should be tested for months or years, given the incertitude on the kinetics of iron corrosion. The objective of the present work was to design a science-based household filter and to test it for one year in the coastal city of Douala (Cameroon). The work started with a systematic review of available designs and a presentation of two main potentially durable designs. The one with a Fe0/sand filter sandwiched between two biological sand filters (BSFs) was tested with polluted well water from Logpom (Douala, Cameroon) using 300 g of a commercial SW (grade 000; d = 50 􏰀m) as Fe0 source. Previous works using Fe0 SW in water filters revealedthat grade 00 (d = 25 􏰀m) was depleted after some 6 months. The used well water was slightly turbid, polluted with pathogens (total coliforms = 1950 UFC mL−1), and contaminated with nitrate ([NO3−] = 24.0 mg L−1). The following parameters were monitored twice per month for one year in the influent and effluent water of the filter unit: (i) nitrate concentration, (ii) coliform level, (iii) pH value, and (iv) turbidity. The iron concentration and the hydraulic conductivity (permeability) were also determined. Prior to pilot testing, the impact of chloride ions (Cl-) on the efficiency of Fe0 filters was characterized in laboratory column experiments, using the methylene blue discoloration method. Results of laboratory column experiments revealed that the chloride concentrations expected in well waters in Douala would not negatively impact the efficiency of Fe0 filters. The tested design could produce safe drinking water for at least one year. Coliforms (> 99% decrease), nitrate (> 99%) and turbidity (> 96%) were nearly quantitatively removed over the whole testing period and well below the recommended limits of the World Health Organization (WHO). The effluent pH increased continuously from 6.6 to 8.4. The effluent iron concentration was constantly lower than 0.2 mg L−1. These values are within the WHO drinking water quality standards. The initial flow velocity of 20 L h-1 decreased to ~8.33 L h–1 after one year, corresponding to a permeability loss of nearly 41.5 %. At the end, the filter was still producing 200 L of drinking water These results confirmed the suitability of commercial Fe0 SW as efficient material to construct durable water filters for households. It appears that the success of the design relied on the low ratio of Fe0 SW (10 vol %) dispersed in the matrix of sand (90 vol %). The tested design can be immediately be applied practically, provide that appropriate construction materials are found. Future research should include (i) testing lower Fe0 SW ratios (same grade), (ii) testing other grades of Fe0 SW in parallel experiments (1 year or more); (iii) testing the same systems for the removal of arsenic and uranium which are the most widespread natural pollutants. Fe0 SW based water filters can be considered as one of the best tools for the achievement of Goal 6 of the United Nations sustainable development goals (SDGs), despite the threat of
dc.contributor.coRefereeRuppert, Hans Prof. Dr.
dc.contributor.thirdRefereeLicha, Tobias Prof. Dr.
dc.subject.engFe0-based filterde
dc.subject.enghousehold filterde
dc.subject.engpermeability lossde
dc.subject.engsteel woolde
dc.subject.engzero-valent ironde
dc.affiliation.instituteFakultät für Geowissenschaften und Geographiede
dc.subject.gokfullGeologische Wissenschaften (PPN62504584X)de

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