Section Six
PULP AND PAPER MILL WASTES
16    SEASONAL ASPECTS OF ORGANIC HALIDE REMOVAL BY
AN AERATED LAGOON TREATING A PULP AND
PAPER WASTEWATER
Curtis W. Bryant, Assistant Professor
Gary L. Amy, Associate Professor
Bruce C. Alleman, Graduate Student
Environmental Engineering Program
Department of Civil Engineering
University of Arizona
Tucson, Arizona 85721
INTRODUCTION
When chlorine is used as a pulp bleaching agent, the bleaching process liberates and forms various
toxic organic compounds such as resin acids, chlorolignins, and chlorophenolic compounds. The yield
of organically bound chlorine from the bleaching process has been estimated at 4 kilograms per tonne
of pulp, but varies according to pulp type, specific bleaching sequence, and external pulp treatment
steps.1 Because chlorine acts both as an oxidizing agent and a substitution agent, a spectrum of
chlorination byproducts are contained in the waste from pulp bleaching. Simple organo-Cl compounds including various chlorophenols, chlorocatecols, chloroguaiacols, chloro-resin acids, and
chloroform have been identified in Kraft mill wastewaters, as well as a more ill-defined group of
compounds known as chlorolignins, with apparent molecular weights of greater than 1,000. Wastewaters from the chlorination steps are the main source of low-molecular-weight organic chlorine, and
alkali extraction wastes are the main source of organic chlorine with a molecular weight of greater
than 25,000.' The fate of high-molecular-weight constituents such as chlorolignins has not been
established, but would be important since these compounds degrade to lower-molecular-weight potentially toxic chlorophenolic derivatives.^ In addition to persisting in the environment, some of these
compounds exhibit toxicity or mutagenicity.1-9 Recent work by researchers in Sweden,'.'o-ii Norway', and Finland'2 has developed the use of total organic halide (TOX) as an indicator of chlorination byproducts found in pulp and paper wastewater.
Many pulp and paper mills in the United States and Scandinavia employ aerated stabilization basins
(ASBs) for the removal of biochemical oxygen demand, suspended solids, and nitrogenous compounds. A schematic representation of the removal of conventional pollutants and chlorinated organics in an ASB is shown in Figure 1. Recent research by the authors has focused on the fate and
removal of toxic compounds, particularly organo-chlorine compounds, in these lagoon systems.
Results have defined the distribution of organic halide compounds and the volatilization of the
purgeable organic halide (POX) in as ASB.u the sorption of TOX onto biomass with subsequent
deposition within the benthal zone,14'15 and the efficient dehalogenation occurring within the benthal
zone". The primary objective of this paper is to report the seasonal variations of total organic halide
(TOX) and total organic carbon (TOC) distributions throughout an ASB, based upon an extended
data base from that in initial reports.
EXPERIMENTAL METHODS AND PROCEDURES
The ASB studied during this research is shown schematically in Figure 2. The five sampling points
were designated: influent (INFL), reactor 1 (RI), reactor 2 (R2), reactor 3 (R3), and effluent (EFFL).
The energy levels provided by surface aerators in rector zones 1, 2, and 3 were 1.51, 1.59, and 0.89
W/m3, respectively. The hydraulic residence time of the lagoon was 6.5 days, based on an average
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