BOD & COD in Effluent of Pulp and Paper Mills

Types of Environmental Pollutants generated in the Pulp and Paper Industry

Air Emissions

Air pollutants are mainly generated through fuel consumption by boilers used to generate steam and/or electricity, and from various production processes. Power boilers used to generate steam are common to all mills. Some air pollutants of current regulatory significance are TSP (total suspended particulates), SO₂, and TRS (from production processes) and TSP, SO₂, NOx, and CO (from power boilers).

Bleached Kraft pulping processes that produce air emissions include the digester/evaporator, brown stock waster, recovery furnace, smelt dissolving tank, and lime kiln. The latter three are where the majority of particulates are emitted. The hydrogen sulfide emissions resulting from Kraft pulping give it a characteristic odor. The direct-contact evaporator is the major source of hydrogen sulfide emissions.

Sulfur dioxide is generally the major pollutant in Sulfite pulping. The major source in the process is the digester and the blow pit system. Particulate emissions result mainly from the recovery furnace exhaust and the characteristic Kraft odor is not present because there are no reduced sulfur compound emissions.

Solid Wastes

Solid wastes are generated by production processes, wastewater treatment facilities, and air pollution control systems. Pulp and paper mill solid wastes are classified as conventional and toxic wastes. The waste generated by water pollution is generally organic while air production processes waste is characterized by metals.

Water Effluents

Probably the most important type of pollutant in pulp and papermaking is contaminated water, since it is used in wood preparation, pulping, bleaching, and papermaking (all the major operations except dry debarking). The categories of pollutants include conventional, toxic and nonconventional. The pollutant parameters of current regulatory significance to the EPA are: BOD, TSS (total suspended solids), and pH (conventional pollutants), and tricholorophenol, pentachlorophenol, and zinc (toxic pollutants). TSS includes wet additives that are applied, and is mainly produced in wood preparation, pulp washing and papermaking. The magnitude of the water use problem is demonstrated by the sheer volume used. "For every ton of manufactured pulp, the wastewater discharge volume ranges from 30 to 180m^3... The estimated total annual world capacity of pulp production in 1992 will amount to 261 million tons..."(Anaerobic Treatment in Pulp and Paper Mill Waste Management: A Review).

Regulations

The federal laws regarding air pollutants include the 1970 Clean Air Act Amendments, the 1980 Precipitation Act, and the 1990 Proposed Clean Air Act. Those regarding solid wastes include the 1984 Hazardous and Solid Waste Amendments. The 1972 FWPCA Amendments (with zero discharge as a goal), and the 1977 Clean Water Act regulate water pollutants. Many countries are now developing legislation which limits effluent discharge on chlorine, dioxins, furans, BOD, NOx, and provides acute toxicity limits. Also some countries are making secondary treatment required. In the present state of environmental concern (for dwindling resources), future legislation can be expected to increase regulation. Already legislators have seen the logic in assaulting the major polluters first, and in the United States the pulp and paper industry is the third largest polluter.

Comparing the different types of pulping and their impacts on the environment

*Mutagenic compounds are chlorinated compounds created from the bleaching process which have detrimental effects on the environment.

**Oxygen delignification in the sulfite process create mutagenic precursors because of the oxidation of the residual lignin. Treatment with alkali destroys most of the mutagenic compounds.

A look at the Different Kinds of Pulping and Environmental Pulping in the Year 2020

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