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Pollution - emissions to water
Studies on emissions from recycling plants are much more limited than those for virgin pulp and paper mills and the data available is not conclusive. However, the indications from two fairly comprehensive and independent studies is that effluents from recycling plants have less environmental impact than virgin pulp effluents [14;15].
Pollutants from paper making can be divided into three categories: emissions to water, emissions to air and solid wastes.
Emissions to water
Production of both virgin and recycled paper gives rise to pollutants which are discharged to water, called effluents. When assessing these pollutants produced in paper making, four key parameters, among others, are monitored: total suspended solids (TSS); biological oxygen demand (BOD); chemical oxygen demand (COD); and chlorinated organic compounds (AOX) (see glossary).
In order to produce white recycled paper the printing ink has first to be removed, a process known as de-inking. One study showed that the effluent from de-inked paper had slightly higher levels of suspended solids (TSS) and Biological Oxygen Demand (BOD) than effluent produced from virgin pulp [16]. However, chemical oxygen demand (COD) and the level of chlorinated organic compounds was lower in the effluent from recycled pulp.
Effluents can be treated by clarification and activated sludge and/or anaerobic processes to control BOD and COD and “in a few cases waste paper processing paper mills already have realized a totally effluent-free process”[17].
In the past, heavy metals (from printing inks) in recycling mill effluents have been a cause for concern. Metals such as copper, chromium, lead, zinc, nickel and cadmium have been commonly used in printing inks and are discharged not only to wastewater but also to waste sludges and some remain in the final paper product. Dioxins and furans also occur in re-pulped effluents, although little is known about their precise source[18].
However, the toxicity of heavy metals and organic compounds, such as dioxins, in effluents and sludges is a matter of debate within the industry. One study suggests that much of the published data on pollution from heavy metals and organic chemicals from recycling mills are already outdated [19].The levels of these materials in recovered paper, and therefore in recycling mill wastes, have dropped dramatically in recent years as a result of similarly dramatic reductions in the levels of these materials in inks and pigments.
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