COD is a parameter that represents the amount of oxygen needed for complete decomposition
of organic matter. In terms of pulp and paper production, COD originates from dissolved raw
materials, process aids and all substances formed during pulp cooking that are not removed with
the black liquor. These types of substances are often very persistent and cannot be removed
efficiently, causing negative effects on environment. (sdguide.org, 2008)
The BOD/COD ratio is a parameter of great importance for quantification of biodegradability of a
contaminated effluent. A high ratio (>0.5) indicates good biodegradability as reported by Ghaly
et al. (2009) as cited in Jamil et al. (2011). A ratio less than 0.3 is considered low, and
corresponds to low biodegradability of the organic material present in the wastewater.