This study investigates the application of chelate-modified homogeneous Fenton oxidation as a tertiary treatment for wine distillery wastewater (WDW) at near-neutral pH, proposing an alternative to costly pH correction steps (Zhang et al., 2019) currently employed.
Four biodegradable chelating agents (CAs) were used, including sodiumpyrophosphate (PPP), oxalic acid (OA), tartaric acid (TA), and ethylenediamine-N,N'-disuccinic acid (EDDS), at different CA-to-catalyst molar ratios ([CA]:[Fe²⁺]) and pHs (6.0 – 8.0). A characterization of the final effluent according to APHA (1998) was carried out to assess Class A reuse standards in the European Legislation (Regulation 2020/741).
The results obtained for PPP were deemed more satisfactory. For an equimolar to Fe²⁺ ratio, hydrogen peroxide and catalyst concentrations of 8.7 g/L and 0.87 g/L were used, respectively, at pH 8.0, and a total organic carbon (TOC) removal of 31.2% was obtained after a 2-hour experiment at 35 ºC. This represented a 12% increase compared to a blank run without the chelant. A 5-hour run with real, biologically treated WDW validated this result, with a similar TOC reduction of 37.4%.
In the face of reutilization purposes in the European Union, i) the treatment was able to get the effluent’s biological oxygen demand (BOD5) below 10 mg O2/L, thus inside quality standards; ii) the process was not able to reduce the effluent’s final turbidity below the legislation’s threshold (5 NTU); and iii) total phosphorus was considerably increased by the addition of PPP.
PPP was deemed the most promising chelating agent due to its affinity with iron ions at the desired pH range and its inorganic characteristic, which is not a major target for hydroxyl radicals and does not add to the wastewater’s organic load.
The development of an optimized catalyst settling step to reduce leftover haziness in colloidal chelated species could enable water reutilization perspectives. An additional step to remove excess phosphorus might also be necessary for some applications.
