Membrane‐Filtered Olive Mill Wastewater: Quality Assessment of the Dried Phenolic‐Rich Fraction

Abstract

A current trend in olive mill wastewater (OMWW) management is to not only decrease environmental pollution but also to extract and utilize valuable by-products. Therefore, the objectives of this study were to explore different techniques for drying a phenolic-rich membrane filtration fraction of OMWW and compare the techniques in terms of the dried product quality and feasibility of the process. The OMWW from 2 (3-phase and 2-phase) California mills was subjected to a 2-step membrane filtration process using a novel vibratory system. The reverse osmosis retentate (RO-R) is a phenolic-rich coproduct stream, and the reverse osmosis permeate is a near-pure water stream that could be recycled into the milling process. Spray-, freeze-, and infrared-drying were applied to obtain solid material from the RO-R. Drying of the RO-R was made possible only with addition of 10% maltodextrin as a carrier. The total soluble phenolics in dried RO-R were in the range 0.15 to 0.58 mg gallic acid equivalents/g of dry weight for 2-phase RO-R, and 1.38 to 2.17 mg gallic acid equivalents/g of dry weight for the 3-phase RO-R. Spray-dried RO-R from 3-phase OMWW showed remarkable antioxidant activity. Protocatechuic acid, tyrosol, vanillic acid, and p-coumaric acid were quantified in all dried RO-R, whereas 3-hydroxytyrosol was found in 3-phase dried RO-R. This combination of separation and drying technologies helps to add value and shelf-stability to an olive oil by-product and increase environmental sustainability of its production.

Spray drying of a phenolic‐rich membrane filtration fraction of olive mill wastewater: optimisation and dried product quality

“…Total soluble phenolic content and AOX were considerably higher for 3‐phase RO‐R powder than for 3‐phase RO‐R powder, which was expected as the same trend was noticed for RO‐R (Sedej et al ., ). The differences in TSP and solid content between 3‐ and 2‐phase OMWW (and consequently RO‐R) can be explained by the different origins of the two types of OMWW in the oil extraction process, including the type of centrifuge (horizontal or vertical) where wastewater is generated.…”

“…Further operation parameters for the sequential filtration process can be found in Sedej et al . (). Samples from each filtration fraction were collected for analysis.…”

“…For the second filtration step, a reverse osmosis membrane ESPA (composite polyamide, 40 Da) was selected to purify the PES-5/ Tyvek permeate stream and concentrate phenolic compounds. Further operation parameters for the sequential filtration process can be found in Sedej et al (2016). Samples from each filtration fraction were collected for analysis.…”

“…In the present study, the OMWW from two California olive oil producers (one utilising a 3-phase system and the other utilising a 2-phase system) was treated with a novel vibratory sequential membrane filtration system, including UF and RO filters. The retentates and permeates were characterised (Sedej et al, 2016), and the phenolic-rich fraction -RO retentate (RO-R) was generated to obtain a dried material. In our previous work (Sedej et al, 2016), different drying techniques were explored for drying a phenolic-rich RO-R. Based on the physicochemical and antioxidant properties of the dried powders, spray drying was preferable drying technique.…”

“…The retentates and permeates were characterised (Sedej et al, 2016), and the phenolic-rich fraction -RO retentate (RO-R) was generated to obtain a dried material. In our previous work (Sedej et al, 2016), different drying techniques were explored for drying a phenolic-rich RO-R. Based on the physicochemical and antioxidant properties of the dried powders, spray drying was preferable drying technique. Therefore, improving quality of a spray-dried product from OMWW is a step forward in adding value to olive oil by-product.…”