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The pulp and paper (P&P) industry worldwide has achieved substantial progress in treating both process water and wastewater, thus limiting the discharge of pollutants to receiving waters. This review covers a variety of wastewater treatment methods, which provide P&P companies with costeffective ways to limit the release of biological or chemical oxygen demand, toxicity, solids, color, and other indicators of pollutant load. Conventional wastewater treatment systems, often comprising primary clarification followed by activated sludge processes, have been widely implemented in the P&P industry. Higher levels of pollutant removal can be achieved by supplementary treatments, which can include anaerobic biological stages, advanced oxidation processes, bioreactors, and membrane filtration technologies. Improvements in the performance of wastewater treatment operations often can be achieved by effective measurement technologies and by strategic addition of agents including coagulants, flocculants, filter aids, and optimized fungal or bacterial cultures. In addition, P&P mills can implement upstream process changes, including dissolved-air-flotation (DAF) systems, filtration save-alls, and kidney-like operations to purify process waters, thus reducing the load of pollutants and the volume of effluent being discharged to end-of-pipe wastewater treatment plants. Keywords: Wastewater treatment; Pulp and paper manufacturing; Advanced oxidation; Membrane technologies; Clarification; Activated sludgeContact information: a: North Carolina State University, Dept. of Forest Biomaterials, Campus Box 8005, Raleigh, NC 29695-8005; b: WestRock Company, Water and Waste Treatment, 600 S 8th St, Fernandina Beach, FL 32034; c: Department of Agricultural and Forestry Engineering, University of Valladolid, Campus Duques de Soria, E-42004 Soria, Spain; d: Complutense University of Madrid, Department of Chemical Engineering, Ingn. Quim, Facultad de Ciencias Químicas, Ciudad Universitaria s/n,S-N, E-28040 Madrid, Spain; e: Concordia University, Dept. Bldg. Civil & Environm. Engn., 1455 Maisonneuve Blvd, West Montreal, PQ H3G 1M8, Canada; f: University of Jyväskylä, Dept. Chem., Box 35, FI-40014 Jyväskylä, Finland; g: Department of Biology, Center for Environmental and Marine Studies, CESAM, University of Aveiro, 3810-193 Aveiro, Portugal; h: Department of Environment and Planning, Center for Environmental and Marine Studies, CESAM, Aveiro & Department of Materials and Ceramics, Institute of Materials, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal; i: FPInnovations, 570 St. Jean Blvd., Pointe Claire, PQ H9R 3J9, Canada; * Corresponding author: hubbe@ncsu.edu Contents of the Article INTRODUCTIONThe pulp and paper (P&P) industry occupies a challenging position with respect to the natural environment. On the positive side, the industry is based on the usage of renewable, photosynthetic resources. On the other hand, the industry discharges huge quantities of aqueous effluents. Large volumes (up to 70 m 3 ) of wastewater ...

a b s t r a c tThe role of iron on the degradation of different organic compounds, differing in their structure (aliphatic versus aromatic) and iron complex formation capacity, by conventional and photo-Fenton processes was investigated. Results show that these chemical characteristics can affect the degree of treatment in terms of COD and TOC removals. While aromatics exhibited a fast and great reduction in the COD by the conventional Fenton process, aliphatic compounds, apart from acetic acid, required the presence of UV light to enhance treatment results. EDTA and oxalic acid responded very positively to UV irradiation in both COD removal and mineralization, reaching the highest values showed by aromatics; and results depended on the intensity of the UV light applied. Phenol and 4-nitrophenol responded favourably to UV irradiation in terms of mineralization and slightly in COD removal. Reductions in the COD were almost total (95.99%), while only an 80% of reduction in the TOC was achieved, for the best photo-Fenton treatment of oxalic acid, phenol and nitrophenol. 60% COD and 40% TOC removals were achieved correspondingly in the case of EDTA. Acetic acid showed almost no mineralization and low COD removal (≈20%) when treated by a conventional Fenton process; and did not enhanced results when assisting the treatment with UV light. Photo-regeneration of ferrous ion and photo-decarboxylation of iron carboxylates are assessed in the framework of these results.

Paper industry is adopting zero liquid effluent technologies to reduce fresh water use and meet environmental regulations, which implies water circuits closure and the progressive accumulation of pollutants that must be removed before water re-use and final wastewater discharge. The traditional water treatment technologies that are used in paper mills (such as dissolve air flotation or biological treatment) are not able to remove recalcitrant contaminants. Therefore, advanced water treatment technologies, such as advanced oxidation processes (AOPs), are being included in industrial wastewater treatment chains aiming to either improve water biodegradability or its final quality. A deep review of the current state of the art regarding the use of AOPs for the treatment of the organic load of effluents from the paper industry is herein addressed considering mature and emerging treatments for a sustainable water use in this sector. Wastewater composition, which is highly dependent of the raw materials being used in the mills, the selected AOP itself, and its combination with other technologies, will determine the viability of the treatment. In general, all AOPs have been reported to achieve good organics removal efficiencies (COD removal >40%; and about an extra 20% if AOPs are combined with biological stages). Particularly, ozonation has been the most extensively reported and successfully implemented AOP at an industrial scale for effluent treatment or reuse within pulp and paper mills; although Fenton processes (photo-Fenton particularly) have actually addressed better oxidative results (COD removal ≈65-75%) at lab scale, but still need further development at large scale.