Bleach plant

Pollution Control in the Bleachery. The quantity of water necessary for bleaching, and consequently the volume of effluents, has been decreased significantly by various schemes for recycle of Hquors, eg, pulp washing using dilute spent Hquors and countercurrent flow. Effort is underway to close bleach plants and further reduce water consumption. 

Closed-Mill Concept. The closed-mill concept, or water circuit closure, has been studied by the pulp and paper industry for many years. In some parts of the paper manufacturing process, up to 98% of the water is recycled within the process, eg, the wet end of the paper machine. However, in the pulp mill, especiaUy kraft mills, effluents are produced owing to the need to purge from the system various metals that come in with the wood, as weU as organic by-products from the pulping process, additives, and especially chloride ions that originate in the bleach plant. 

D. W. Reeve, Tappi 1989 Bleach Plant Operations Seminar Notes, 1989, pp. 79—82. 

R. G. Hise, "Process Changes to Lower the Eormation of Dioxius During Chemical Pulp Bleaching," Tappi 1991 Bleach Plant Operations Short Course, June 23-28, 1991, pp. 245-258. 

Bleich-anlage, /. bleaching establishment, bleaching plant, bleachery. -anstalt, /. bleachery. -artikel, m. (Calico) bleach style, -bad, n. bleaching liquor or bath. 

Lindstrom and Schubert63 applied GC-MS, GC-MS-MS and direct inlet MS-MS to determine 1,1-dichlorodimethyl sulfone (201, DDS) in aquatic organisms outside a pulp mill bleach plant. Both GC-MS-MS and direct inlet MS-MS of tissue extracts of fish and mussel appeared to be sensitive, selective and fast techniques for the determination of DDS. 

FIGURE 21.5 Typical bleach plant source. (Taken from U.S. EPA, Profile of the Pulp and Paper Industry, 2nd ed., report EPA/310-R-02-002, U.S. EPA, Washington, November 2002.)... 

Chemical pulp is bleached in traditional bleach plants (see Figure 21.5), where the pulp is processed through three to five stages of chemical bleaching and water washing. The desired whiteness, the brightness of the initial stock pulp, and the plant design determine the number of cycles needed. 

Bleach plant washer filtrates Paper machine-water flows Fiber and liquor spills... 

Opportunities for reducing effluent flows and water use are also present in the bleaching plant. Acid filtrates from hypochlorite or chlorine dioxide stages can be used as dilution and wash water for the first bleaching stage. Similarly, second extraction stage filtrates can be used as dilution and... 

Final Effluent (for BAT) or Bleach Plant Effluent (for PSES) AOX (adsorbable organic halides) 1-Day maximum 0.951 kg/Te... 

Increased delignification before the bleach plant by extended or modified cooking and additional oxygen stages... 

Recycling of some, mainly alkaline process water from the bleach plant... 

Closure of the bleach plant when sodium-based cooking processes is being used... 

The two main sources of air pollutants that may be emitted from basic wastewater treatment plant operations are pulping condensates and bleach plant effluent. The pulping condensates may include total reduced sulfur (TRS) compounds as well as volatile organic compounds (VOCs) such as methanol. The primary pollutants of concern for the bleach plant effluent are chloroform and methanol. Any volatile compounds that could be released as air emissions from basic wastewater treatment plant operations are relatively minor and are generally not subject to specific regulation.65-66... 

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