Study on Chromium Removal from Tannery Wastewater Using Acorn Extract

In this study, by using two pH controller, NaOH and Ca(OH)2, the effectiveness of the tannin-contained extracts (acorn extract of Quercus branti) in removing chromium from tannery wastewater was examined. Therefore a native species of oak tree in Kohkiloye & Boyerahmad province, namely Quercus branti that its fruits contain more tannin than other existing oak species in Iran was selected. After drying, crushing acorns into a powder and extracting, the average percent of tannin in the extracted acorns was 10.5%.Then, in order to study impact of tannin extract with and without pH controller (Ca (OH)2 & NaOH) on reducing Chromium concentration, two Samples, from chromium standard solution(Cr III=25mg/l, Cr VI=25mg/l, equal to total Cr concentration of 50 mg/l & pH=3.5) as well as tannery wastewater (Concentrated wastewater containing Cr=3200mg/l, pH=3.98 & diluted wastewater containing Cr=160mg/l, pH=4.38) have been collected and tested. Laboratory tests were conducted in bench scale and room temperature (20-25 ºc), the summery of results mentioned below:By adding a concentration of 70 mg/l tannin extract to chromium standard solution, the concentration of chromium reduced to 20% which this removal percentage was increased to 58% by increasing tannin concentration to 100 mg/l together with 70mg/l Ca(OH)2 to the Cr standard solution (pH=4.11).In the other hand adding a concentration of 10 to 100 mg/l tannin extract to the Cr standard solution, in which the residual Cr concentration was decreased to 18.52 by adding Ca(OH)2 and NaOH, pH decreased from 6.99 to 6.76 and Cr removal efficiency was fallen from 63 to 55%.However adding a concentration of 50 to 1000 mg/l tannin extract to alkaline tannery wastewater, which its pH was increased by Ca(OH)2 and NaOH from 4.38 to 9.28 and remaining Cr concentration was decreased from 160 to 7mg/l, pH level decreased to 7.95 and Cr removal efficiency reduced from 95.62 to 80%.Therefore, it was concluded that in alkaline limit (in average from 7 to 10) which pH has a crucial role in removing chromium, it seems there is a relationship between increase in tannin extract concentration and decrease in pH level that will be culminated to release more chromium from precipitation phase into the solution phase.