FULL SCALE ANAEROBIC TREATMENT OF A
PULP AND PAPER INDUSTRY WASTEWATER
Bjorn Frosted, Technical Director
William Bonkoski, Vice President and Manager
Jan E. Sointio, Manager of Process Engineering
A. C. Biotechnics, Inc.
Woodbury, New York 11797
INTRODUCTION
Much interest is presently being focused on anaerobic treatment of pulp and paper mill effluents
[1-3]. The major reasons for this are:
• More strict environmental protection regulations are coming, limiting possibilities for discharge of untreated wastewater.
• Competing technologies are expensive and energy consuming.
• Pulp and paper mills generate large quantities of water on a year-round basis, and therefore considerable
amounts of energy can be recovered in anaerobic treatment.
• The wastewaters are often warm and limited in nutrients, factors that favor anaerobic treatment compared lo aerobic.
Anaerobic treatment of pulp and paper industry effluents is, however, not fully straight-forward.
The wastewaters usually exert inhibitory effects on microorganisms, either from remaining wood
constituents, from chemicals added, or from products formed in the treatment. Sometimes, therefore,
it may be necessary to consider pretreatment [4-5].
Of special interest in connection with anaerobic treatment of pulp and paper industry wastewater
is sulfur. Most pulp and paper industry effluents contain considerable amounts of oxidized sulfur.
In anaerobic treatment, it will be reduced to hydrogen sulfide to a great extent. Hydrogen sulfide
interferes negatively in many ways during anaerobic treatment. First, it may severely inhibit biological
activity especially during the start-up phase. Second, there are concerns regarding odors and health
risks. In addition to this, corrosion problems are enhanced, and problems in burning the biogas must
be addressed. Fundamental aspects of sulfur problems in connection with anaerobic treatment have
been investigated by Kroiss and Plahl-Wabnegg [6] and Eis et al [7].
Properly addressed, problems associated with biomethanation of pulp and paper industry wastewaters seem manageable. A substantial amount of experimental work is necessary due to the relatively
unique situation at each mill, but application of anaerobic treatment is likely to spread rapidly.
AC Biotechnics, formerly AB Sorigona, started investigations on anaerobic treatment of pulp and
paper industry wastewaters in 1980. Several lab scale and five pilot scale experiments have been
performed. So far, the work has resulted in the construction of three full scale plants. Progress from
the program has been reported elsewhere [8-11].
Hylte Bruks AB Sweden, operates a newsprint mill with a capacity of 500,000 metric tons per
year. All pulp is produced on site and there are lines for thermomechanical pulp (TMP), groundwood
- magnetite - and deinked pulp. The location of the mill is on the Nissan river in the south-western
part of the country. The river is rather small with a flow of only 7 m'/s during summer low-flow
conditions. Due to the low water flow, and the in-land location of the mill, environmental protection
regulations are strong. Authority requirements are further strengthened by the fact that a salmon
population has been re-established in the river, down-stream of the mill.
At Hylte Bruk, a decision was taken to convert part of the groundwood pulp production to TMP
production. With this change, an increased discharge of COD and BOD, was anticipated. Despite
the fact that the capacity of the existing aerobic plant was more than adequate, the installation of
extra capacity was judged as necessary. Two major alternatives were considered:
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