comparison of ca(oh)2 and naoh on hexavalent chromium removal in drinking water treatment

in parts of desert regions in our country, groundwater is the only source of fresh water and due to geological formation, the concentration of hexavalent chromium in groundwater will reach beyond the allowed limits. furthermore, previous studies showed that hexavalent chromium is a cancerous substance for humans and toxic for other organisms. in this study the removal of hexavalent chromium from drinking water using reclamation method which turns hexavalent chromium into cr(iii) using fe(ii) as a function of ph and amount of fe(ii) injection were investigated. the removal of hexavalent chromium (cr(vi)) from drinking water using fe(ii) increased at ph 7.8-8.15, then any increase or decrease in ph leaded to decrease in the efficiency of hexavalent chromium removal. the ph adjustments were done by adding ca(oh)2 solution and o.ln naoh. results showed that cr(vi) reduction will be higher if we use ca(oh)2 solution for ph adjustment instead of o.1n naoh. not only ca(oh)2 solution improves the cr(vi) removal efficiency but also it increases the final turbidity of water and it should be noticed in drinking purposes. on the other hand, ca(oh)2 solution can be used because of its safety and lower cost.