Long-term reliability assessment of ceramic water filters: strength and electro-kinetic parameter studies

Ceramic water filters (CWF) are an effective, affordable, and widely accepted household water treatment technology in developing countries. The efficacy of these filters decreases with time depending upon multiple factors. The changes in the strength of CWF with continuous usage is one such important aspect. Literature indicates that 65% of CWF rejections were due to filter unit breakage, either of the ceramic filter element, the spigot, or the container. In this context, this study presents the long-term study (19 weeks) of CWF named as G-filters. The filters were made using locally available salty clay and sawdust in an equal volume ratio. A total of 29 filters of capacity 9 L each were used for the study. All the filters were completely filled twice a day. Normal tap water with mean pH, total dissolved solids (TDS) and conductivity values of 7.7, 215 ppm, and 350 μS/cm, respectively were used during the study. Ambient temperature, relative humidity and temperature of the influent tap water used during the experiment were recorded. Each time, a set of two filters were used for strength study when approximately 427; 807; 1,035; 1,263 and 1,472 L of water passed through them. The T-specimens were taken from circular base of G-filters with notch at centre and in a direction parallel to the circumference of the base. Fracture toughness tests were performed on a single-edge notched bend (SENB) specimens with equal thickness and width of approximately 12.6 mm and span of 75 mm. The findings indicate a significant decrease of 47.8% in mean fracture load when compared with control G-filter. This may be attributed to the gradual erosion of ceramic particles during usage. The fracture toughness KIc was determined as per the ASTM E-399 standards. The KIc results lies within the range of 0.1–2.0 MPa·m1/2. A relationship between fracture toughness and the volume of water passed has been established. This investigation also evaluated the performance of G-filters in terms of pH, TDS, and conductivity. These were collected during a time span of 19 weeks when 9; 503; 541; 684; 855; 1,035; 1,225; 1,510 and 1,600 L were passed through the filters. The results indicate a slight increase in pH during the initial days showing a large variation in the filter’s performance. A considerable reduction in TDS and conductivity has been observed in all G-filter’s performance during long-term use. During the first run, filters showed large variations in their performance parameters wh