Development of biological and process technologies for the reduction and degradation of pulp mill wastes that pose a threat to human health

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Abstract
The pulp and paper industry produces large quantities of organic and chlorinated organic wastes. Those compounds that are toxic and/or mutagenic, difficult to degrade, and have a propensity to bioaccumulate pose a serious human health hazard. Of prime concern are chlorophenols, chlorinated aliphatic hydrocarbons, and resin acids. Under anaerobic conditions, highly chlorinated aromatic and aliphatic compounds can be reductvely dechlorinated to lightly chlorinated compounds, or completely mineralized. In the aerobic environment, highly chlorinated compounds, such as pentachlorophenol, are slowly degraded, whereas tetrachloroethylene is inert. In contrast, mono‐and dichlorinated compounds are rapidly degraded by aerobic microorganisms. Sequential anaerobic‐aerobic biological treatment of pulp mill wastes holds the greatest promise for complete mineralization of hazardous chlorinated wastes. This biological treatment process also will degrade other components of pulp mill waste such as chlorinated dioxins and furans, chloroacetones, and the potent mutagen 3‐chloro‐4‐(dichloromethyl)‐5‐hydroxy‐2(5H)‐furanone. Methanogenic activity is sensitive to sulfur compounds, resin acids, and oxidants. Physical removal of these compounds or pretreatment prior to effluent entry into the anaerobic reactor will be required to ensure maximum anaerobic digestion. Resin acids can be degraded aerobically but not anaerobically. Resin acids should be removed from the effluent stream and collected as a tall‐oil byproduct or degraded separately. The development of new pulping procedures, such as oxygen delignification, and the replacement or partial replacement of chlorine by chlorine dioxide or hydrogen peroxide for pulp bleaching can greatly reduce the emission of toxic chlorinated compounds. Decreased risks to human health and improved environmental quality will be achieved through the adoption of alternative pulping and bleaching methods coupled with effective anaerobic‐aerobic treatment technologies.