Removal of Arsenate in drinking water sources by combined coagulation process

Abstract

The objective of this study is to examine arsenate (As(V)) removal from drinking water sources with combined coagulation processes using Single-Walled Carbon Nanotubes (SWCNTs) and Multiwalled Carbon Nanotubes (MWCNTs). Ulutan Lake Water (ULW) in Zonguldak-Turkey, was used as drinking water source. Conventional coagulation experiments was conducted on using aluminum sulfate (Alum) and ferric chloride (FeCl3). Water samples were synthesized by spiking 300 µg/L As(V) into ULW samples and also all arsenic removal tests were performed with As(V). The maximum removal percentages of As(V) (97%) was observed with combined SWCNTs and FeCl3 in ULW. Similar to that of SWCNTs, the removal of As(V) (92%) during the coagulation processes occurred at MWCNT with the addition of FeCl3. Compared to SWCNTs, the removal percentage of As(V) was slightly lower when using only MWCNTs (76%). This result demonstrated that SWCNTs were generally more powerful than MWCNTs for removing the As(V). The presence of humic acid (HA) increased As(V) removal with related the solution pH. On the other hand, the changing of As(V) residual concentrations in ULW was observed as a function of pH and the removal of As(V) increases in the acidic pH levels whereas decreases alkaline pH levels. While As(V) removal efficiency was remained constant at acidic pH values, it decreased about 10% at pH 6, 7 and 8 as a result of the competitive adsorption between As(V) and HA. It was observed that the As(V) removal efficiency increased both low and high pH with monovalent electrolyte (NaCl) whereas di-valent ions (Ca+2 and Mg+2) improved As(V) removal only at pH 9 and 10 during the coagulation processes in ULW samples. The results of this study display that combined coagulation process is more effective than conventional coagulation alone for the As(V) removal.