Section 12. PAPER WASTES
WASTEWATER TREATMENT AT A SWEDISH CARDBOARD FACTORY:
POSSIBLE COST SAVINGS
Gerdt Fladda, Research Engineer
Egils Kubulnieks, Research Engineer
Swedish Forest Products Research Laboratory
Stockholm, Sweden
Bengt Boman. Research Engineer
Jonas Norrman. Research Engineer
Swedish Water and Air Pollution Research Institute
Stockholm, Sweden
Lennart Ruus. Research Engineer
1PK, Industrial Process Consulting Engineers
Stockholm, Sweden
Strict environmental pollution laws were enforced in Sweden at times when economic
growth seemed unlimited. In the hard economic climate of today, these laws put a heavy
burden on Swedish industry, and its international competitiveness has decreased. There is
a general agreement about the necessity of environmental protection in Sweden, but industry is investing a lot of effort to decrease its cost.
The aim of the present project was to evaluate possible energy and other cost savings
for external wastewater treatment at a Swedish pulp and paper plant. Methods were developed to save energy and decrease other costs at improved or at least unchanged treatment efficiency.
A survey was made to select a suitable wastewater treatment plant for the investigation.
The cardboard factory chosen has a wastewater treatment plant with a unique sequence of
treatment steps and a great potential for cost savings and automatic control.
To be allowed to enlarge the cardboard factory about seven years ago the owners had
to guarantee an efficient wastewater purification. The recipient (a lake) has a limited capacity, and the discharges of BOD7, suspended solids and phosphorus had to be kept at a low
level.
PRODUCTION PROCESS AND WASTEWATER TREATMENT PLANT
The cardboard factory studied has three cardboard-manufacturing machines and two
integrated lines for production of mechanical pulp. The main product is coated folding
boxboard bleached on one side. The inner layers of the cardboard consist of mechanical
pulp and the outer of chemical pulp produced at another pulp mill.
The wastewater treatment plant is outlined in Figure 1. The treatment sequence consists of the following steps:
1. primary sedimentation (area, 740 m  ; depth, 4.7 m);
2. neutralization and addition of nutrients (urea and H3PO4);
3. trickling filter (volume. 2100 m3;area of the PVC Filter medium, approx. 200,000 m );
4. two activated sludge units in scries (aeration basin volumes approx. 1200 in    each; settler
areas, 600 m   each;depth, 3.5 m);
5. chemical treatment with aluminum sulfate, flocculation and final clarification (area of the
clarifiers, 2 x 1290 m2; depth, 3.0 m); and
6. two parallel microstraincrs.
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