Riverbank filtration (RBF) is a process during which river water is subjected to subsurface flow prior to abstraction wells, often characterized by improved water quality. The induced infiltration of river water through the riverbed also creates a clogging layer. This decreases riverbed permeability and abstraction rates, particularly if the river water has high turbidity, as in Thailand. As Chiang Mai Province is one of the most favorable sites for future RBF construction in Thailand, two sites, Mae Rim and San Pa Tong, were selected to simulate clogging by using a channel experiment. The mobile experimental apparatus was set up at the bank of the river in order to use fresh river water. Riverbed sediment was used as channel bed and filling material for the columns. The aim was to simulate riverbed clogging using river water with high turbidity and determine the effect of clogging, which can be quantified using vertical hydraulic conductivity (Kv). An increase in channel flow velocity caused partial removal of a clogging layer in only the top 0.03 m of the sediment column. The combination of low channel flow and high turbidity leads to much more clogging than high channel flow and low turbidity. A complete manual removal of the external clogging layer led to an increase in Kv, but the initial Kv values were not recovered. The external clogging had a lower effect on Kv than internal clogging. For planning new RBF sites along high-turbidity rivers, reduction in Kv to estimate RBF well yield cannot be calculated based only on initial Kv but requires field experiments

No abstract

No abstract

No abstract

ResumoA filtração em margem é uma técnica de tratamento de água, que utiliza poços de captação instalados nas margens de rios e lagos. Durante o processo de filtração, o sedimento do manancial está sujeito ao processo de colmatação. O processo de colmatação reduz a capacidade específica dos poços de captação, com reflexo direto nos custos de produção de água. Desta forma, o presente estudo avaliou o efeito desta colmatação na redução da condutividade hidráulica, porosidade total e turbidez, utilizando colunas preenchidas com meios filtrantes de 50 cm de profundidade, constituídos por grãos de areia e esfera de vidro de tamanhos distintos, de granulometria uniforme e mal graduados de acordo com sua distribuição granulométrica. A porosidade total dos meios filtrantes constituídos por areias fina e grossa foi reduzida em 54% e 41%, enquanto que as esferas de vidro finas e grossas reduziram em 44% e 25%, respectivamente. A condutividade hidráulica do meio filtrante formado por areia fina obteve a maior redução entre os meios filtrantes (1,2 log aproximadamente). Este estudo demonstrou que, além de outros importantes parâmetros, a cuidadosa avaliação das características físicas do sedimento do leito do manancial, no que se refere a forma, tamanho e distribuição granulométrica são essenciais para minimizar os impactos causados pelo processo de colmatação quando a técnica da filtração em margem é utilizada. AbstractBank filtration is a water treatment technique, which uses production wells located at bank of rivers or lakes. Because of filtration process, sediment clogging might be developed. Clogging process reduces specific capacity of production wells, which affects directly water production costs. In this way, this study evaluated clogging effect on hydraulic conductivity, total porosity and turbidity removal, by using columns filled with sand and glass beads of different sizes, composed by uniform grains as well as a poorly graded grain size distribution. The column filled with fine sand showed the largest hydraulic conductivity reduction if compared with other media (1,2 log approximately). Total porosity of fine and coarse sand reduced 54% and 41%, while fine and coarse glass beads reduced 44% and 25%, respectively. This study showed that besides other important parameters, a careful river/lake sediment physical characterization considering important factors such as shape, size and size distribution of the grains, are important to minimize impacts caused by sediment clogging process at bank filtration sites.

Este estudo tem como objetivo a avaliação da Lagoa do Peri como local potencial de implantação da técnica da filtração em margem (FM) em escala real. Baseado em estudo hidrogeológico preliminar anterior, um modelo matemático de águas subterrâneas (Processing MODFLOW) foi utilizado para criar cenários para simular diferentes taxas de bombeamento (100 e 200 L s-1) na potencial área de captação. Em paralelo, o nível de água na lagoa e do canal também foi alterado, simulando diferentes condições hidráulicas na área de estudo. Sob condições hidráulicas naturais a Lagoa do Peri age como um corpo hídrico influente. O canal Sangradouro é alimentado não somente pela lagoa, mas também pela exfiltração de água subterrânea. Quando uma taxa de bombeamento de 100 L s-1 é simulada, rebaixamentos de 0,75 m.a.n.m e -1,25 m.a.n.m. são observados sob a melhor e pior condições hidráulica na lagoa, respectivamente. Já quando uma taxa de bombeamento de 200 L.s-1 é simulada, são observados rebaixamentos de -1,50 m.a.n.m sob a melhor condição hidráulica, e -4,0 m.a.n.m. sob a pior condição hidráulica. Em ambos os cenários as taxas de infiltração na lagoa e no canal permaneceram em níveis sustentáveis do ponto de vista do potencial colmatativo por forças hidrodinâmicas.

This study evaluated clogging effects on head loss and water quality in sand prefiltration columns, followed by innovative double-layered slow-filter filtration technology using anthracite coal and sand. The study was divided into two phases. Phase 1 (filtration rate 11 m 3 /m 2 Ád) had a layout of a pre-filter (PF) system followed by a slow filter (SF). In Phase 2 (filtration rates of 5.5 and 11 m 3 /m 2 Ád), two PF systems (PF1 and PF2) followed by SFs (SF1 and SF2) were monitored, be differed only by filtration rate. Phase 1 presents a mean turbidity removal of 45.6% in PF and 23.9% in SF. PF presented a lower head loss in the superficial layers of the filter media, whereas SF presented a more important contribution in the deeper layers of the bed. In Phase 2, the mean results obtained for turbidity removal in PF1 and SF1 were 84.7% and 22.4%, in that order. PF2 and SF2 promoted mean reductions of 84.5% and 22.0%, respectively. Greater clogging is observed in the PF's surface layers, whereas the SFs dissipate greater clogging with depth. Filtration rates and water quality were similar in filter media of different compositions. Practitioner Points• Double-layer filters show better use of the porous media in depth.• Different materials produce different forms of clogging. • Higher filtration rates increase the number of pre-filter and slow filter runs.

No abstract