Table Olive Manufacturing Wastewater Treatment Using the Peroxymonosulfate/Fe(III) System

Abstract

Wastewater generated in table olive manufacturing processes (WWTOMP) is a seasonal waste difficult to manage due to the high salinity content. The treatment of WWTOMP has been accomplished by including a precoagulation stage with aluminum sulfate, oxidation using the peroxymonosulfate/Fe(III) system, and a final aerobic biological stage. The optimum conditions of precoagulation led to a chemical oxygen demand removal rate of roughly 30–35% without the need for pH adjustment. The peroxymonosulfate(PMS)/Fe(III) system was thereafter applied to the effluent after coagulation. The addition of PMS lowered the initial pH to acidic conditions (pH = 1.5–2.0). Under these operating conditions, the initial PMS concentration and the initial Fe(III) dose showed optimum values. An excess of the oxidant and/or the catalyst partially inhibited the process efficiency, and pH exerted a significant influence. COD removal was substantially increased as the pH of the solution was moved toward circumneutral values in the interval 5–4. Moreover, at pH values of 5 and 7, PMS was capable of reducing COD without the need for Fe(III) presence. The direct oxidation of organics by PMS or the generation of chloride-based oxidants (Cl2 or HClO) is suggested to occur in parallel to the radical attack from PMS decomposition. An attempt to biologically reduce the final COD to discharge limits failed, mainly due to the high salinity content; however, the 1:2 dilution led to the reduction in COD from 6 to 2 g L−1. Acclimated sludges or saline content reduction should be first considered.