English English.   Español  Español.

The application of Appropriate Technology

Articles for Keyword "sand filters"

An Introduction to Slow Sand Filtration

Posted on Oct 26, 2011

The use of sand and gravel as filter media for water supplies can me split into three basic filter types: slow sand filters, rapid filters and roughing filters. Apart from desalination and reverse osmosis, slow sand filters are perhaps the most effective single treatment for purifying drinking water supplies. They are use on a large scale as part of the water supply for large cities, as part of systems for small villages and on a much smaller scale they can be adapted for use in individual households. Rapid sand filters are normally require a subsequent chlorination process and are thus of less use for small village supplies unless the raw (untreated) water supply is of a reliably high quality. Roughing filters are used to reduce the turbidity of water supplied and often used as a pre-treatment before slow sand filtration. This short document gives an introduction to these filtration methods. You can read the whole document as a PDF file (7...

Read More

Biosand Filters

Posted on Oct 29, 2011

The biosand filter is a modified form of the traditional slow sand filter in such a way that the filters can be built on a smaller scale and can be operated intermittently. These modifications make the biosand filter suitable for household or small group use. The biosand filter can be produced locally anywhere in the world using materials that are readily available. It was considered impractical to operate a slow sand filter intermittently, due to the need for a continuous supply of food and oxygen. However, Dr. Manz of the University of Calgary re-designed the traditional sand filter, making it suitable for intermittent use at a household level. This adaptation, brilliant in simplicity, consists of raising the under drain pipe back up to between 1 and 8 cm above the sand level, ensuring a foolproof method for maintaining the water level just above the sand. Manz proved that, even when water is not continually added to the filter, oxygen can still permeate into the water to reach the organisms living in the sand by diffusion accross this shallow layer of standing water. Intermittently-operated slow sand filters can be small units that easily supply enough clean water for a family. Therefore, they are particularly suited for use in low-income countries, where the majority of people rely on untreated, contaminated surface water. Find out in detail how intermittently-operated slow sand filters work. A couple of great manuals from Biosandfilter.org on making moulds and casting biosand filters for domestic use: Mould Construction Guidelines (960 Kb) Filter Casting Instructions (1.2 Mb) Another document about casting the filters from concrete, this one is from CAWST (Centre for Affordable Water and Sanitation Technology): An Introduction To Slow Sand Filtration (7.1...

Read More

Horizontal Flow Roughing Filter

Posted on Oct 26, 2011

Manual detailing how to estimate and design horizontal flow roughing filters. Among pre-treatment methods used before slow sandfilters (SSF), horizontal-flow roughing filters( HRF) have been found to be the most effective and appropriate for application in developing countries. This is because they are simple, require no mechanical parts, have low capital cost, can be operated for a long time due to their high solids retention capacity, and with a wide variety of raw surface water characteristic. Most research on HRFs has concentrated on turbidity (solids) removal whereas the way to estimate and design the run duration time before filter cleaning is necessary has received little attention. In this research, a large gravel (size l0-20 mm) filter media were placed as a single package, uncovered and outlet at the top. You can read the whole of this paper as  a PDF document (640...

Read More

Life Water Slow Sand Filter

Posted on Oct 29, 2011

Plans, construction guide and operation instructions for Life Water’s slow sand filter, suitable for a town of 1 or 2 thousand people. Lifewater is a water charity based in the USA. This document is available as 3 PDF files: Design (1 Mb) Construction (720 Kb) Operation & Maintenance (436...

Read More

Slow Sand Filtration

Posted on Oct 29, 2011

By L. HUISMAN and W.E. WOOD. A WHO document from 1974 outlining the action, construction, operation and maintenance of slow sand filters. This is the standard text on the subject. (PDF Files) Contents & Preface (13 KB) Chapter 1 – Introduction (41 KB) Chapter 2 – Filtration of water supplies (1.2 MB) Chapter 3 – Theory of biological filtration (1 MB) Chapter 4 – Filter design and construction (7.9 MB) Chapter 5 – Operation and maintenance (9.8 MB) Chapter 6 – Slow sand filtration and artificial recharge (1.8 MB) Annex (234...

Read More

Surface Water Treatment By Roughing Filters

Posted on Oct 26, 2011

Excellent manual on roughing filters by SANDEC, detailing water treatment alternatives applicable to rural water supplies and processes for solid matter separation. For further SANDEC publications, go here:http://www.eawag.ch. You can read the whole document as a PDF file (12.4...

Read More