Mechanical pulp mills produce groundwood pulp by grinding logs, which can
be done in combination with chemical and/or thermal treatment. The manufacture
of mechanical pulps is often integrated with a paper or board mill. The latter can
contribute to the sulfur load of the wastewater because of the use of fillers and
whiteners in the paper production. Thermomechanical pulping (TMP) wastewaters
typically have a pH of 4.5 to 5.0 and contain 0.2 to 0.7 g/l SO
4
2–and 2 to 5 g/l COD
(Habets and de Vegt, 1991; Rintala et al., 1991). CTMP have a higher pH (7 to 9)
and COD (7.5 to 10.4 g/l) and contain sulfide (0.05 to 0.20 g/l) in addition to sulfate
(1.2 to 1.5 g/l) (Habets and de Vegt, 1991)