Household slow sand filters operating in continuous and intermittent flows: Computational fluid dynamics simulation and validation by tracer experiments

• Published in: Chemical engineering science 2022-01, Vol.247, p.117058, Article 117058
• Main Authors: Hojo, Liri Yoko Cruz Prieto, Rezende, Ricardo Vicente de Paula, Lautenschlager, Sandro Rogério, Sabogal-Paz, Lyda Patricia
• Format: Article
• Language: English
• Subjects: Biosand filter; Computational fluid dynamics (CFD); Drinking water; Residence time distribution (RTD); Software ANSYS Fluent
• ISSN: 0009-2509; 1873-4405
• DOI: 10.1016/j.ces.2021.117058

[Display omitted] •CFD was important to verify that the C-HSSFs and I-HSSFs presented a piston type flow without a short circuit and with a dead zone close to the base.•The dead zone volume found was not significant to suggest changes in the HSSF design.•Velocity profiles were similar in continuous and intermittent flow filters and did not influence the hydrodynamic behavior of HSSFs.•Operator filters under the same flow regime but with different diameters showed similar trajectories of velocity flow lines. This paper analysed geometries and flows in household slow sand filters (HSSFs) through computational fluid dynamics (CFD) to evaluate the hydrodynamics of filters. Four HSSFs in full scale were studied with a capacity to produce 48 L.d-1 each with diameters of 190 mm and 250 mm and with a filter medium depth of 0.5 m. The hydrodynamics of the four mathematical models of the HSSFs was validated using the experimental residence time distribution (RTD). The Kruskal Wallis non-parametric test indicates that the results of the experimental RTDs and the simulated RTDs did not show significant differences, therefore the mathematical models represent the physical models, which requires a detailed 3D analysis of the flow in the filters. The results showed that the HSSFs have a flow close to plug flow reactor. Internal recirculation zones were not found, nor short-circuit ones; however, dead zones were verified at the base of the filter with volumes below 3% when compared to the total volume of the filtering and draining layers, not necessary to make changes in geometry. The results of the computational simulation showed that the continuous filters had a smaller velocity variation and the filters with smaller diameter presented a reduction in dead zones when compared to the filters with larger diameters operated in the same flow regime. The study focused on the hydraulic aspects of HSSFs, but it is noteworthy that the choice of the type of operation to be adopted by families that use this type of treatment depends on studies that assess the efficiency of water treatment filters that were not considered in this work.