Testing Ceramic Methods for Producing Beads for Biofilm Water Treatment

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By Rosy Heywood, Research Associate at Centre for Print Research.

Main image: Fig 1: Boxes of organic foam impregnated ceramic beads and plain ceramic beads adjacent to a pot of traditional beads

In a previous blog post, by my colleague Sonny Lightfoot, we introduced the research being conducted into creating ceramic beads as a medium to grow biofilm within a water filter. We have now created 3 types of ceramic beads which have been tested for water filtration; organic foam impregnating method, clay and sawdust burn off method and plain ceramic. For each method we used the same terracotta clay, made the beads into 20mm pieces, and fired the beads at the same max kiln temperature of 1100˚.

Organic foam impregnating method

For this set of beads we laser cut compressed cellulose sponge into 20mm circles, expanded them in water and dipped them into clay slip. The beads were then left to dry and fired. During the firing process the sponge burns off leaving the porous structure behind. This method has been used to test beads with high porosity and high surface area creating lots of sites for the biofilm to grow onto.

Figure 2: Dipping laser cut sponges into terracotta clay slip

Sawdust and clay method

For this set of beads we mixed fine sawdust with clay at a 5:3 ratio. We are currently experimenting with the best ratio and method of mixing but to produce these beads we mixed by hand initially then used an electric mixer to fully combine the two components. We then extruded the clay using a hydraulic extruder into lengths and cut using a 3D printed jig into 20mm pieces. The beads were then left to dry and fired. During the firing process the sawdust burns off leaving a porous structure behind. This method has been used to test beads with high porosity.

Figure 3: Freshly extruded and cut sawdust and clay beads before firing

To produce the plain ceramic pieces we used the same method as above but without adding the sawdust. This method will test the effectiveness of the natural porosity of ceramic.

After firing we then tumbled the beads in a ball mill to smooth the edges. The beads were then dried in an oven and tested for effectiveness by MSc student Sadie Hadrill and PhD candidate Josh Steven in the science labs on Frenchay campus. Stayed tuned for another blog post coming soon where Sadie and Josh detail their process and results from the testing.  

Developing the methods and experimental work

Since creating these beads, the team and I in the CFPR labs have been experimenting with ways of combining sawdust with clay in large batches and the ratio of sawdust to clay. We have also been furthering our design research by modelling a coil pot from sawdust clay to test it’s suitability for pot making and experimenting with high surface area to low volume shapes using the organic foam impregnating method. These shapes could be tessellated or interlocked to create a unique structure for a vessel to naturally purify water using the biofilm method. The idea is to create a uniquely beautiful and practical container to filtrate water with the design inspired by natural biomorphic structures that can tesselate into user determined patterns and shapes. This experimental research is at its early stages and will slowly develop over the course of the project alongside our bead and porosity testing.

Figure 8: Organic foam impregnated ceramic tessellating shapes experiment

Initial Ceramic Research

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Written by Sonny Lightfoot, Research Associate and Technician at Centre For Print Research (CFPR)

In the latest issue of Craft Magazine they look at the work of Potters for Peace (PFP)  ‘a non-profit, social justice organization focused on using clay based solutions to address the problems of poverty.’ The amazing work PFP have implemented and published around locally made ceramic water filters has been a big inspiration for us here at UWE working on Heathy Waters. The literature produced by PFP has been a useful resource to start our own research especially around the use of burn-out material to be added to clay to increase precocity. Where PFP have developed a process where the ceramic filters are produced with a mould and a hydraulic press, we are looking at the already existing skills and process of local potter’s to hand building and pit fire water filter, like that of the craft potters in Kisoro Uganda, who currently produce ceramic cooking stoves.

Foam Impregnated Ceramic

Our initial ceramic tests have been focused on producing ceramic beads of different porosity to work as a medium for a biofilm to grow within a water filter. We have looked at two processes for these beads, extrusion, a well-established industrial process, and a organic foam impregnating method in which we laser cut compressed cellulose sponge that is then expanded in water then dipped in a ceramic slurry.

Extruded clay with added burn out material

Our next tests will be looking at producing a hand build ceramic water filter using a basic hand building technique known as coiling, which is more in line with the hand building process of the Ugandan potters. The pots will be made from terracotta clay with sawdust added in different percentages they will then be tested to establish the balance between increasing precocity to reduce time taken for the water to pass through the filter but still maintain a high efficacy of removing bacteria and pathogens.

Mixing clay and saw dust in preparation to coil build ceramic water filter

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