Multistage recovery process of biophenolic antioxidants with focus on hydroxytyrosol from olive mill wastewater concentrates

Abstract

A number of phenolic compounds (PCs) and their environmental contamination problems as consequences of olive oil production process in the countries surrounding the Mediterranean Sea propel the need for extraction of high-added value phenolic antioxidants from olive mill wastewater (OMWW) to reduce the toxicity of the effluent. Since existing treatment methods for OMWW are not efficient for recovery approaches of phenolic antioxidants due to the consumption of high amount of solvent, new methods of isolation that require low solvent will still be on-demand in foreseeable future. In this regard, this research utilizes concentrated decanter and lagoon OMWW treated with mechanical vapor recompression evaporator to recover natural antioxidants mainly hydroxytyrosol (HTyr). A multistage recovery process including pretreatment by acidification, extraction with organic solvent and/or solid phase extraction (SPE) using nonionic polymeric adsorbent was applied to both types of concentrates. While solvent/solid ratio, extraction time and stage were the parameters used to optimize solid-liquid extraction (SLE) process, for aqueous two-phase extraction (ATPE) ethanol concentration, temperature and extraction time were optimized by 23 full factorial experimental design. The results clearly revealed the requirement of ultrasonic assistance for the extraction of PCs from decanter concentrate. The acidification of OMWW concentrates enhanced the overall recovery of HTyr and the highest recoveries were 6.6 g/kg and 4.6 g/kg achieved by ATPE from lagoon and decanter concentrates, respectively. The results also showed that HTyr selectivity of the SPE process using XAD16N is pretty high with approximately 81 % HTyr recovery from the extracts of both concentrates.