Pulp-and-paper mills produce various types of contaminants and a significant amount of wastewater
depending on the type of processes used in the plant. Since the generated wastewaters can be potentially
polluting and very dangerous, they should be treated in wastewater treatment plants before being
released to the environment. This paper reviews different wastewater treatment processes used in the
pulp-and-paper industry and compares them with respect to their contaminant removal efficiencies and
the extent of greenhouse gas (GHG) emission. It also evaluates the impact of operating parameters on the
performance of different treatment processes. Two mathematical models were used to estimate GHG
emission in common biological treatment processes used in the pulp-and-paper industry. Nutrient
removal processes and sludge treatment are discussed and their associated GHG emissions are calculated.
Although both aerobic and anaerobic biological processes are appropriate for wastewater treatment,
their combination known as hybrid processes showed a better contaminant removal capacity at
higher efficiencies under optimized operating conditions with reduced GHG emission and energy costs.