Optimization of total trihalomethanes' (TTHMs) and their precursors' removal by granulated activated carbon (GAC) and sand dual media by response surface methodology (RSM)

Abstract

A response surface methodology (RSM) applying central composite design with rotatable full factorial (14 non-center and six center points) was used to discern the effect of granular activated carbon (GAC), sand and pH on total trihalomethanes (TTHMs) and humic acid (HA) removal from drinking water. Results showed efficient TTHMs and HA removal by GAC while a sand column showed little effect for TTHMs but was significant for total organic carbon (TOC) removal.With GAC and a sand column of 4 cm, a pH increase from 6 to 8 caused an increase in TTHM removal from 79.8 to 83.6%while a decrease in HA removal from 26.6 to 6.6%was observed. An increase in GAC column depth from 10 to 20 cm caused a slight increase in TTHMremoval from 99.4 to 99.7%, while TOC removalwas increased froman average of 38.85%to 57.4%removal. The developed quadratic model for TTHM removal (p=0.048) and linear model for TOC removal (p=0.039) were significant. GAC column depth (p<0.0117) and column depth2 (p<0.039) were the most significant factors. A 98%TTHMs, 30%TOC and 51%residual chlorine removalwere optimized at 9 cmGAC and 4 cmsand columndepth at pH8 with desirability factor (D) 0.64.