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Nano-Based Wastewater Treatment Technology
Published in M. H. Fulekar, Bhawana Pathak, Environmental Nanotechnology, 2017
Slow sand filters are the oldest type of municipal water filtration. Today, they remain a promising filtration method for small systems with low turbidity or algae containing source waters. Slow sand filtration does not require pre-treatment or extensive operator control, which can be important for a small system operator with several responsibilities. Slow sand filtration is a simple and reliable process. They are relatively inexpensive to build, but do require highly skilled operators. The process percolates untreated water slowly through a bed of porous sand, with the influent water introduced over the surface of the filter, and then drained from the bottom. Slow sand filtration is also effective at treating groundwater with high iron and sulphur gases. With iron and dissolved gases are removed, other processes such as softening and demineralization can be incorporated into an overall in-house treatment process. Slow sand filters are not backwashed like rapid rate filters, but are instead scraped or harrowed periodically when head loss reaches 3–4 feet across the filter bed. Typically, slow sand filters must be scraped or harrowed every 1–12 months depending on water quality. Some facilities with very high water quality can experience even longer filter runs. During scraping, the top 1/8–1/2 inch of sand is removed from the filter bed. Eventually, after years of operation, the sand layer must be replaced to restore the depth of the filter bed.
Filtration
Published in Subhash Verma, Varinder S. Kanwar, Siby John, Environmental Engineering, 2022
Subhash Verma, Varinder S. Kanwar, Siby John
The filtration rate, defined as the flow rate per unit surface area, of slow sand filters is extremely low. The removal mechanisms employed in slow sand filters are straining, adsorption and biological action. The main advantage of this method is low maintenance and simplicity of operation. Due to low hydraulic loading, most of the removal takes place in the top portion of the bed. When the bed becomes clogged with turbidity, the top layer is scraped off and replaced with new media. Due to high labour and area requirements, combined with its unsuitability for treating turbid waters (> 10 NTU), slow sand filtration is not very common in larger plants.
Urban water supply and water treatment
Published in Sandy Cairncross, Richard Feachem, Environmental Health Engineering in the Tropics, 2018
Sandy Cairncross, Richard Feachem
However, because of their construction cost, their complexity and their need for regular backwashing, rapid sand filters are inappropriate for many applications in low income countries. They are certainly not as widely suitable as the oldest and simplest method – slow sand filtration. Slow sand filters are simpler to build and operate, and also improve microbiological water quality substantially, a result the other types of filter cannot reliably achieve. In particular, they can remove chlorine-resistant pathogens such as cryptosporidium.
Household slow sand filters with and without water level control: continuous and intermittent flow efficiencies
Published in Environmental Technology, 2020
Paulo Marcos Faria Maciel, Lyda Patricia Sabogal-Paz
In populations not served by distribution networks, interventions aimed at combating the microbiological risk of point-of-use drinking water are important provisional measures [5] in conjunction with public health surveillance activities to provide support to target consumers [6]. Among the point-of-use water treatment technologies, Household Slow Sand Filters (HSSFs) have important characteristics, such as low investment, simple maintenance and daily production of safe water, as long as the biological layer of the filter is mature.