New Route for Valorization of Oil Mill Wastes: Isolation of Humic-Like Substances to be Employed in Solar-Driven Processes for Pollutants Removal

Abstract

The valorization of olive oil mill solid wastes (OMW) has been addressed by considering it as a possible source of humic-like substances (HLSs), to be used as auxiliary substances for photo-Fenton, employing caffeine as a target pollutant to test the efficiency of this approach. The OMW-HLS isolation encompassed the OMW basic hydrolysis, followed by ultrafiltration and drying. OMW-HLS structural features have been investigated by means of laser light scattering, fluorescence, size exclusion chromatography, and thermogravimetric analysis; moreover, the capability of OMW-HLS to generate reactive species under irradiation has been investigated using spin-trap electronic paramagnetic resonance. The caffeine degradation by means of photo-Fenton process driven at pH = 5 was significantly increased by the addition of 10 mg/L of OMW-HLS. Under the mechanistic point of view, it could be hypothesized that singlet oxygen is not playing a relevant role, whereas other oxidants (mainly OH • radicals) can be considered as the key species in promoting caffeine degradation.

Study of Catalysts’ Influence on Photocatalysis/Photodegradation of Olive Oil Mill Wastewater. Determination of the Optimum Working Conditions

“…This pond only accumulated olives washing wastewater, which normal COD value is below 1000 mg O 2 /L [22]. According to the literature [17,22,23,27,28], COD values of olive oil washing wastewater from the two-phase process normally vary from 4000 to 16,000 mg O 2 /L. In this sense, only COD of Seville 1 (6187 mg O 2 /L) was found in the range.…”

“…Recent studies claim the benefits of combined Fenton process with ultraviolet/solar light irradiation (H 2 O 2 /catalyst/UV or Visible) due to the reaction time being shorter and the removal rate being higher, which makes it possible to work with smaller equipment and reduce operating costs [14,[27][28][29]. In addition, in these conditions, the Fenton reaction increases its oxidizing capacity due to the decomposition of the photoactive Fe(OH) 2 + species by UV/visible light, promoting an additional generation of OH • radicals (Equation (3)) in the solution [30,31].…”

Photo-Fenton Degradation of Pentachlorophenol: Competition between Additives and Photolysis

“…Taking this into account, it is important to show the performance of HLS as an auxiliary for larger-scale, direct solar light photo-remediation of a wider number of pollutants, focusing on pollutants that undergo scarce photolysis, and when they are at relatively high concentrations. This would allow the assessment of the actual viability of HLS-assisted photo-Fenton application to real polluted waters remediation processes, and to promote the production and use of eco-friendly waste-derived chemicals to be used in place of fossil-derived products, in order to drive photo-Fenton at mild conditions [7,8,9,12].…”

“…The amount of aromatic groups was slightly below 10% of the total amount of carbon. The molecular weight, determined by size exclusion chromatography, was around 4500 Da, while its hydrodynamic radius was 135 nm [9].…”

“…SBO have been produced at relatively large scales by alkaline hydrolysis of urban bio-wastes, and sampled from various process streams of the AceaPinerolese waste treatment plant, located in Piemonte, Italy. More recently, other humic-like substances (HLS) have been isolated from oil mill solid wastes [9]. These substances have been demonstrated to be photo-active and able to catalyze degradation of pollutants, namely phenols, although the process is slow [10].…”