Ceramic water filter - Low-tech Lab

Tutorial de  | Categories : Water, Health Low-Tech Lab Dernière modification le 13/03/2023 Difficulty Hard Duration 3 day(s) Cost20 EUR (€) Description A ceramic water filter is a system for purifying unsanitary water. This tutorial aims to show how a ceramic water filter works and how to build one on a semi-industrial scale. Introduction In 1990, approximately 2.3 billion people do not have access to drinking water in the world (source: UNICEF - UN). Today in 2020, 750,000 people still drink unsanitary water, making it the leading cause of non-age-related death in the world. Qu'est-ce qu'un filtre à eau céramique ? Locally produced ceramics have been used to filter water for hundreds of years. The water is poured into a porous ceramic filter pot and is collected in another container after passing through the ceramic pot. This system also allows for safe storage until the water is used. Ceramic filters are usually made from clay mixed with a combustible material like sawdust or rice husks. Sometimes colloidal silver is added to the clay mixture before firing or it is applied to the fired ceramic pot. Colloidal silver is an antibacterial which helps inctivatae pathogens, while preventing the growth of bacteria in the filter itself. Pathogens and suspended elements are removed from water by physical processes such as mechanical entrapment and adsorption. Quality control regarding the size of the combustible materials used in the clay mixture ensures that the pore size of the filter is small enough to prevent contaminants from passing through the filter. Colloidal silver facilitates the treatment by breaking the membrane of the cells of pathogens, causing their death. Historique This filter was developed in 1981 by Dr Fernando Mazariegos of the Industrial Research Institute of Central America (ICAITI) in Guatemala. The aim was to make water contaminated with bacteria safe for the poorest by developing an inexpensive filter that could be manufactured at community level. The professor decided to freely bequeath this knowledge to Humanity, and began to train potters around the world to produce these filters locally with the NGO Potters for Peace. There are now 61 factories working with this model in 39 countries around the world! This tutorial show how the ceramic filter works and outlines the main stages of manufacturing. It is aimed mainly at entrepreneurs rather than at individuals. Don’t try to create this technology at home (you need an oven, you need to test materials, etc.). If you are interested in setting up a small factory like this, you will need more training. The Potters for Peace organization in partnership with CAWST and the company Ecofiltro (which we visited in Guatemala) offer this kind of training. All this knowledge is freely available in open-source form. Video overview Youtube Materials Materials Sawdust Clay Clean water: for mixing with the clay and the flow tests colloidal silver Container with tap (ceramic, plastic, metal) Plastic bags for the pressing process Fuel for the oven Tools Balance Mixer: to mix clay, sawdust and water Extruder: to extrude the clay mixture into blocks for moulding Hydraulic press equipped with male and female moulds Drying shelves: to dry the pots before firing. Ovens: for the ceramics Basins + Supports: for carrying out the flow tests Step 1 - Step 1 – how it works - role of the different materials Clay : Clay is the base material for the water filter device. A clay pot allows for extremely slow movement of water through the natural pores that exist between the fired clay tablets. The size of these pores has been measured (using an electron microscope) and found to be between 0.6 and 3.0 microns (μm). They are able to eliminate most bacteria, protozoa and helminths (Lantagne, 2001a), as well as dirt or sediment and organic matter. The clay used to make classical pottery may be suitable for the production of water filters. However, hydraulic conductivity and pore size can vary widely depending on the type of clay, potentially to the point of not being suitable for flow rates and / or microbiological removal (Oyanedel-Craver and Smith, 2008, in Lantagne et al, 2010, [1]). A high content of sand or silt in the clay can reduce cross-linking of the clay and weaken the structure of the filter. On the other hand, an overly refined clay (smaller particles) has a greater water holding capacity and is therefore more prone to shrinkage and cracking during firing. As the characteristics of clay are a critical factor in the success or failure of ceramic water filter production, it is recommended that you carefully study the sources and potential types of clay before committing significant resources. Potters for Peace has produced a document providing details of the clay test, listed in the "Reference Note" section [18] Combustible material : "Combustible" organic materials, such as sawdust or ground rice husks, are added to the clay mixture. When exposed to the high temperatures of the kiln, the "combustible material" burns, leaving behind cavities in the fired clay. Water moves more easily through cavities than through pores in clay. Therefore, the presence of the cavities decreases the distance that water must travel through the clay substrate, and therefore increases the overall flow rate of the filter. It is important to carry out tests on your materials. The ratio of clay to combustible material is important for establishing the flow rate and therefore the efficacy of the filters. Colloidal silver : Colloidal silver is a solution made of suspended nanoparticles of silver and silver ions. It has been used as a natural disinfectant in medicine for many years. Although the exact mechanisms of bacterial destruction are not yet fully understood, it appears that colloidal silver breaks down the cell walls of bacteria and then binds to their proteins, thus disrupting their function [2] [3]. Today it is mainly produced by electrolysis. The silver applied to the inside and outside of the filter is absorbed into the pores of the clay. The silver ions are reduced to elemental silver and form colloids inside the walls of the filter. Silver acts as a biocide against bacteria when there is sufficient contact time (= not too large pores). Step 2 - Step 2 – how it works - Efficacy All the laboratory and field efficacy values are the result of independent trials. The details are given in the links in the "Notes and References" section Step 3 - Step 3 - Production - Summary of steps The main steps for producing a ceramic filter are listed in order below : Prepare of raw materials: clay powder, sawdust / ground rice husks, water Mix the raw materials to form a malleable paste: clay powder, sawdust / ground rice husks, water Form cubes of clay for the press Press the clay cubes to turn them into the filter shap Finish the surface and mark / number each filter Dry the filters - to remove the initial excess water finish Baking the filters in an oven - to complete dehydration and vitrification Flow tests for each filter - for validation or downgrading Colloidal silver painting on the surfaces of each validated filter Package filters Step 4 - Step 4 – Production - Preparation of raw materials Clay: Depending on its provenance, clay may need to be crushed, sieved and dried before it can be used. Combustible material: Depending what it is (sawdust, rice husks, etc.), the combustible material will need to be cut, sieved, dried and bagged. Step 5 - Step 5 – Production - Mixing of raw materials Clay powder and combustible material (sawdust, ground rice husks, etc. ) are mixed dry, then water is added evenly and mixed well to form a modulable and homogeneous paste. It is wise to make sure density gradient is consistent throughout the clay mixture to minimise potential defects during the clay firing process (removal of air pockets etc.). The right mix and machinery is therefore crucial. Proportion used by RDIC: 30 kg of clay powder + 8.9 - 10 kg of rice husks + 12.5 L of water Step 6 - Step 6 - Production - Forming clay cubes for the press The wet clay mixture can be manually shaped into cubes before being pressed. But it is strongly advisable to use a machine to compress and extrude the clay mixture as cubes. The extruder is similar to those used for extruding clay bricks, but the outlet opening is larger to obtain the size of clay cube required for pressing. The clay cubes we want should weigh approximately 8kg. Cut a cube of the same length and put it in the press. Step 7 - Step 7 - Production - Pressing the clay cubes to give them the shape of the filter Using a hydraulic press significantly reduces the labour requirements of the process and greatly increases the efficacy and consistency of the product. The filters are squeezed between a male mould and a female mould which are covered with plastic bags to prevent sticking. The hydraulic press includes a fixed plate in the lower mould that pushes the pressed mould outward when the mould opens. This press was originally developed and built by the Potters for Peace teams: The plans are available in open-source form [19] This document describes how small producers can make a hydraulic press [17] Step 8 - Step 8 - Production - Finishing of the surface and marking/numbering each filter Minimum surface finishing is required after molding. It is done to ensure rim strength and surface uniformity. Filters are labelled to indicate pressing date, batch and filter number. Use a plastic scraper to smooth out the edges of the border. Mark each filter with a date, serial number and manufacturer's name using a metal "stamp". A database can then be used for filter tracking Step 9 - Step 9 - Production - Drying the filters