Preparation and characterization of adsorbent media from olive stones

Agricultural activities such as olive mills generate highly polluted wastewater together with solid residues (usually referred to as olive pits) which need to be properly managed and disposed of. The objective of this study was to prepare adsorbent materials from olive pits to be used in place of activated carbons for the total phenol (TP) and Chemical Oxygen Demand (COD) removal from olive mill wastewater (OMW). The adsorbents were prepared by two different thermal-chemical activation methods: (1) thermal treatment combined with impregnation of 2N HNO3 (char-HNO3), and (2) thermal treatment combined with impregnation with 75% KOH solution (char-KOH). The raw material was initially characterized by measuring the contents of: Total and Volatile Solids (TS and VS, respectively), ash, water, total heavy metal, Total Organic Carbon (TOC) and Total Kjeldahl Nitrogen (TKN). Sorption properties of the new adsorbents were evaluated through batch experiments and compared with those achieved by commercial activated carbons (Activated Carbon, AC) under the same operative conditions. The following average removal efficiencies at equilibrium were obtained with the activated olive pits: for filtered COD, 80% by AC, 40% by char-HNO3 and 20% by char-KOH; for total polyphenols, over 90% by AC, about 60% by both char-HNO3 and char-KOH. These results confirm that the activated olive stones display appreciable adsorption capacity, particularly in the case of HNO3 activation