Arsenic leaching from ceramic water filters: Effects of firing temperature and influent conditions

Abstract

Ceramic water filters (CWFs), fabricated using local sourced clay, have been widely acknowledged as sustainable and effective point-of-use (POU) drinking water treatment approach. However, arsenic leaching from CWFs poses a potential risk of arsenic exposure, thereby limiting their safe application. In this study, CWFs were made from red clay to investigate the critical roles of firing temperatures (900–––1050 °C), solution chemistry conditions (i.e., pH, Na+, Ca2+), as well as operational conditions on arsenic leaching. Overall, arsenic leaching from CWFs followed a flushing-out pattern, with up to 61 % of total leachable arsenic released during initial first 100-pore-volume filtration. Specially, higher firing temperature led to lower initial arsenic leaching but higher cumulative leaching from resulting CWFs over long-term filtration. Feed solutions at circumneutral pH, with low Na+ or high Ca2+ resulted in less cumulative arsenic leaching, while POU operational conditions (intermittent operation and fluctuating flow rate) had negligible effects. Mechanism investigation found that firing process enhanced arsenic mobility, i.e., the exchangeable arsenic fraction was only 5.34 % in unfired clay but 26.7 % − 37.3 % in CWFs. The enhanced arsenic mobility was mainly caused by the thermal transformation of source clay, especially the thermal alteration in the hematite lattice. Our findings provide not only new insights into the process controlling arsenic leaching from CWFs but also shed light on ways to mitigate leaching, thereby improving the safety of CWFs application.