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

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