Development and optimization of a combined small scale low cost point of use water treatment system

Siwila, Stephen (2019-12)

Thesis (PhD)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT:Access to safe drinking water is still limited in many rural and suburban areas of developing countries. Point-of-use (PoU) water treatment is the most feasible solution to fight waterborne diseases which pose a serious threat in such areas. Only user friendly, affordable and grid-independent but effective approaches are deemed feasible for poorer communities. Although efforts to develop cost-effective PoU technologies are underway globally, challenges still exist. This study was aimed at developing a combined small-scale low-cost gravity-driven PoU system able to provide bacteriologically safe and aesthetically acceptable drinking water. A range of PoU system configurations were developed and tested. Knowledge gained culminated in the development of a final novel PoU system incorporating silver-coated ceramic granular media (SCCGM) for filtration and inbuilt disinfection, geotextile for pre-filtration (to significantly reduce particulate loads in the water before it passes through the SCCGM thereby increasing pathogen contact with the silver), granular activated carbon (GAC) as an adsorption media (for improving aesthetic aspects and removal of selected heavy metals), and a built-in storage compartment for treated water. No chemical addition is needed. It is a replicable, scalable, and user and environmentally friendly cost-effective technology primarily for particle and bacterial removal and aesthetic improvement. Geotextile and GAC filtration steps enhanced the system’s ability to treat a broader variety of raw water and extended filter runs. Laboratory tests on the system showed high potential for significant E.coli and fecal coliforms removal (>99.99%) at an optimum flow of 2 L/h. In addition, the system exhibited substantial improvements of aesthetic aspects (color, odor and taste) with average turbidity removals of 99.2%. Mathematical modelling was done using E.coli as an indicator organism to aid in optimization of the final novel PoU system and to support future research in terms of configuration, process combination, flow rate, material combination, etc. The system was modelled as a series of three compartments using suitable disinfection kinetic models for silver inactivation and specialized colloidal filtration theory models for fibrous and granular filtration. The modelling demonstrated that suitable removal mechanisms can be applied integrally to model a combined PoU system to predict overall effluent bacterial quality. Such modelling can be used to optimize similarly combined systems by allowing engineers to systematically vary design parameters until desired system effectiveness is attained. The system was developed after investigation and evaluation of local treatment materials and approaches over a period of 18 months, which resulted in three simple, yet innovative water treatment systems namely the: (i) modified intermittently operated slow sand filtration system incorporating geotextile and GAC (ISSFGeoGAC), (ii) eight-layer four-pot bidim sequential filtration (BidimSEQFIL) system, and (iii) wood filtration system combined with GAC (WFSGAC). The ISSFGeoGAC and WFSGAC were designed for removal of bacteria, particles, color, taste, odor and selected heavy metals while BidimSEQFIL was designed for particle and bacterial removal. These were then comparatively evaluated alongside two commercially available PoU systems using a comparison framework developed in this study for evaluating low-cost PoU technologies. The findings will be helpful to engineers, NGOs, etc. for possible application of the novel systems, modelling and optimization of combined PoU systems, and comparative evaluation of low-cost PoU systems.

AFRIKAANSE OPSOMMING: Toegang tot veilige drinkwater is steeds beperk in baie landelike en stedelike gebiede van ontwikkelende lande. Gebruikspunt (GP) watersuiwering is die mees haalbare oplossing om wateroordraagbare siektes te beveg wat 'n ernstige bedreiging is in sulke areas. Slegs gebruikersvriendelike, bekostigbare en formele sisteem onafhanklike, maar effektiewe benaderings word as haalbaar beskou vir armer gemeenskappe. Hoewel pogings om kostedoeltreffende GP-tegnologieë wêreldwyd te ontwikkel tans bestaan, is daar steeds uitdagings. Hierdie studie was daarop gemik om 'n gekombineerde lae-koste swaartekrag-aangedrewe GP-stelsel op klein skaal te ontwikkel wat in staat is om bakteriologies veilige en esteties aanvaarbare drinkwater te voorsien. ‘n Reeks GP-stelsel konfigurasies was ontwikkel en getoets. Kennis hierdeer verkry was verder gebruik in die verdere ontwikkeling van ‘n nuwe GP-stelsel bestaande uit silwerbedekte keramiek granulêre media (SBKGM) vir filtrasie en ingeboude ontsmetting, geotekstiel vir prefiltrasie (om partikels in die water aansienlik te verminder voordat dit deur die SBKGM beweeg, waardeur die kontak met die silwer verhoog word), granulêre geaktiveerde koolstof (GAK) as 'n adsorpsiemedium (vir die verbetering van estetiese aspekte en verwydering van geselekteerde swaar metale), en 'n ingeboude stoorkompartement vir behandelde water. Geen chemikaliese toevoeging is nodig nie. Die ontwikkelde stelsel is 'n herhaalbare, skaalbare, gebruikersvriendelike en omgewingsvriendelike koste-effektiewe tegnologie. Dit kan hoofsaaklik vir verwydering van partikels en bakterieë sowel as estetiese verbetering van drinkwater toegepas word. Geotekstiel en GAK-filtrasiestappe het die stelsel se vermoë verbeter om 'n groter verskeidenheid rou water en uitgebreide filterlopies te behandel. Laboratoriumtoetse op die stelsel het 'n potensiaal uitgewys vir beduidende verwydering van E.coli en fekale koliforme (> 99,99%) met 'n optimale vloei van 2 L/h. Boonop het die stelsel aansienlike verbeterings aan estetiese aspekte (kleur, reuk en smaak) getoon, met 'n gemiddelde verwydering van troebelheid van 99,2%. Wiskundige modellering is gedoen met gebruik van E.coli as 'n indikatororganisme om die finale nuwe GP-stelsel te optimaliseer en om toekomstige navorsing ten opsigte van konfigurasie, proseskombinasie, vloeitempo, materiaalkombinasie, ens. te ondersteun. Die stelsel is gemodelleer as 'n reeks van drie kompartemente met gebruik van geskikte ontsmettings kinetiese modelle vir inaktivering met silwer sowel as gespesialiseerde kolloïdale filtrasie teorie modelle vir vesel- en granulêre-filtrasie. Die modellering het aangetoon dat geskikte verwyderings meganismes integraal toegepas kan word om 'n gekombineerde GP-stelsel te modelleer om die uitvloeiwater bakteriele inhoud te voorspel. Hierdie tipe modellering kan gebruik word om soortgelyke gekombineerde GP-stelsels te optimaliseer deur ingenieurs in staat te stel om die ontwerpparameters stelselmatig te wissel totdat die gewenste stelseldoeltreffendheid bereik word. Die finale GP-stelsel is ontwikkel na die ondersoek en evaluering van plaaslike behandelingsmateriaal en benaderings oor 'n periode van 18 maande. Dit het gelei tot drie nuwe eenvoudige, dog innoverende waterbehandelingstelsels, naamlik: (i) ‘n gewysigde, tussenpose bedryfde, stadige sandfiltrasiestelsel met geotekstiel en GAK (TSSFGeoGAK), (ii) ‘n ag-laag, vier pot “bidim” opeenvolgende filtrasie stelsel (BidimOFIL), en (iii) ‘n houtfiltrasiestelsel gekombineer met GAK (HFSGAK). Die TSSFGeoGAK en HFSGAK was ontwerp vir die verwydering van bakterieë, partikels, kleur, smaak, geur en geselekteerde swaar metale; terwyl BidimOFIL ontwerp is vir die verwydering van partikels en bakterieë. Hierdie sisteme was vergelykend geëvalueer saam met twee kommersieel beskikbare GP-stelsels met behulp van 'n vergelykingsraamwerk wat in hierdie studie ontwikkel is vir hierdie doel. Die bevindinge is nuttig vir ingenieurs, NROs, ens. vir die moontlike toepassing van die nuwe GP-stelsels, modellering en optimalisering van gekombineerde GP-stelsels, en vergelykende evaluering van lae-koste GP-stelsels.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/107052
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