Ozone-based advanced oxidation process as pre-treatment of wastewater from the wood-based industry

Abstract

Three ozone-based advanced oxidation treatments (O3; O3 with initial pH adjustment and; O3/UV with initial pH adjustment) were compared for the treatment of a recalcitrant wastewater generated during washing/cleaning of surfaces and equipment used in filling and gluing processes (urea-formaldehyde and phenol-formaldehyde resins) in a wood-floor industry in Sweden. The wastewater (initial COD 3,400-4,000 mg/L) was obtained at the outlet of a sedimentation tank, which receive an inflow with an average COD of 45,000 mg/L. The experiments were performed in a semi-batch microbubble column reactor connected to a UV reactor, where 2.5 L samples of wastewater were submitted to the maximum dose of 2 g of O3 per gram of initial COD. For the full-factorial design, the independent variables were O3 concentration (g O3/Nm3); recirculation flow (L/min); and initial pH (pHi). The evaluation of the treatment performance was based on COD and TOC reductions (in %), and the effluent obtained was used in respirometric assays with activated sludge obtained at a municipal wastewater treatment plant to assess biodegradability/inhibitory effects. The results showed that ozonation at the original low pH promoted a reduction of 65% and 31% of COD and TOC respectively, but made the effluent less biodegradable. The highest COD and TOC reductions were achieved when O3 /UV treatment with pHi = 9.3 were applied (93% e 56% reductions for COD and TOC respectively). The results with the respirometry tests suggest that application of O3 only at higher pH values promoted biodegradability enhancement of the effluent, making it treatable by microbiota obtained with activated sludge from a municipal wastewater treatment plant.