APPLICATION OF ZETA POTENTIAL FOR CONTROL OF ALUM
COAGULATION IN THE "PPRIC" EFFLUENT TREATMENT PROCESS
J. Dorica, Associate Research Scientist
A. Wong, Head
Water Pollution Abatement Section
Pulp and Paper Research Institute of Canada
Pointe Claire, Quebec
Canada H9R 3J9
INTRODUCTION
To eliminate the adverse effects of pulp mdl effluents on the environment, pulp mdls in
Canada are now required to decrease the discharges of BOD, suspended sodds and toxic
materials [ 1 ]. Acceptable reductions in BOD and suspended sodds are usuady achieved by
conventional biological treatment in aerated lagoons. This method, however, was found to
be inconsistent for removal of acute toxicity to fish [2].
A physical-chemical method for the detoxification and decolorization of kraft pulp
mid effluents was recently developed at the Pulp and Paper Research Institute of Canada
(PPRIC).* This method uses areation in the presence of catalytic amounts of powdered activated carbon (PAC), fodowed by coagulation with alum and poly electrolyte. The flow diagram of the process is shown in Figure 1.
Figure 1. The PPRIC detoxification and
decolorization process.
In previous pdot-plant studies at a mdl site, we found that complete detoxification of the
combined bleached kraft effluent can be achieved using the PAC dosage of 200 mg/1, air,
14 liter/Uter, alum, 300 mg/1 and poly electrolyte, 1 mg/1. Color removal ranged typically between 70 and 85%. Detaded results of these pdot-plant trials are reported elsewhere [31.
More recently, we also demonstrated that our effluent treatment process can remove about
90% of the chlorinated phenolics present in the effluent, under simdar treatment conditions.
Because alum coagulation is an important step of the process, we undertook further study
in the laboratory for the optimization of this processing stage, using the zeta potential
approach.
In the separation of suspended solids by sedimentation in a clarifier or settling basins, the
removal efficiency depends largely on detention time. But ultimately, only the "discrete"
particles having a definite physical size and shape can be effectively separated from the
solution. The settleable solids in pulp mdl effluents usually consist of cellulose fibers and
fines, and bark particles. In the case of the PPRIC process, the suspended sodds also include
spent carbon particles and alum/color floes.
•Canadian Patent No. 1, 024, 274.
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