Paper360 - March/April 2015 - (Page 52)

techlink | EFFLUENT TREATMENT Ultimate effluent Treatment Allows for ever-larger Pulp Mill Capacities Combining ozone treatment of secondary effluent with aerobic biologically-aerated flooded filtration, is a clean, economic treatment alternative that lowers operating costs. ALEXIS MÉTAIS, JEAN-CHRISTOPHE HOSTACHY and IVAN ZHU The pulp and paper industry has been sharply improving its effluent quality since the 1990s with the spread of secondary (or biological) effluent treatment for removal of organic matter and the ban on chlorine bleaching. The Finnish Forest Industries Federation, for example, reports that since 1992, COD and AOX emissions have decreased by 69 percent and 88 percent respectively per produced ton.1 However, effluent discharge remains a major social concern for our industry as local events recently demonstrated. Startup of the Oji Paper Jiangsu mill in China was postponed from 2012 to 2014 because of opposition by local residents to wastewater discharge, 2 and in 2013 local residents along the Uruguay River demonstrated against UPM Fray Bentos' plans to increase production.3 Those actions could seem to be the work of activists if it weren't for the fact that governments today are strengthening their effluent regulations. In 2011, China enforced COD discharge limits of 100 mg/l for pulp mills and 90 mg/l for integrated mills, which makes implementation of tertiary effluent treatment for recalcitrant COD (or hard COD) removal almost compulsory. In Brazil, the latest pulp mill projects of Klabin and CMPC were also required to include tertiary effluent treatment. However, contrary to what one may think, the need to remove hard COD is not due to the latest environmental fad but to the excellent progress made by the pulp and paper industry. COD discharge guidelines were being discussed in the 90s when the largest fiberline (Alberta-Pacific) had less than a half million tons adt/y of capacity. Since 1992, specific COD discharge has been reduced threefold, but is offset by a threefold increase in fiberline capacity. For instance, Eldorado started the first 1,500,000 adt/y fiberline in 2012, but COD discharge at one single point is potentially the same as 20 years ago. To improve further, a third effluent treatment is required. COAGULATION-FLOCCULATION TREATMENT The most widely used tertiary treatment solution is the traditional coagulationflocculation process, which is based on the use of coagulants such as aluminum or iron salts that produce flocks (aggregates) from colloid materials. The flocks then settle and are removed in the form of sludge. The coagulation-flocculation process has low investment and maintenance costs since it consists primarily of concrete tanks and mixers. Moreover, it can be quickly implemented in only a few months, since only civil work is required. This explains why the coagulationflocculation process is the most widely used globally. However, the process results in large amounts of sludge which need to be dealt with. Pulp and paper sludge is disposed of in three basic ways: landfilling, incinerating and land-spreading (composting or fertilization). But sludge management is already a burden for pulp and paper mills, requiring investment in dewatering facilities and operating Figure 1. Ozonation+biofiltration treatment. 52 Paper360º MARCH/APRIL 2015

Table of Contents for the Digital Edition of Paper360 - March/April 2015

Guest Editorial
Over the Wire
TAPPI's Centennial: A Celebration 100 Years in the Making
Precision Alignment of Winders
Single-stream Waste Processing
iRoll at Irving
Fully Automated Continuous Digester
Twin Roll Press Upgrade
TAPPI Journal Summaries
Effluent Treatment
Microfibrils to Transform Paper Furnish
Consolidation Watch
Knowledge Builder
New Energy Windfall
Power from Waste
Safety Survey
Association News
Online Exclusives
Advertisers Index

Paper360 - March/April 2015