Boron Adsorption on Soils and
Biological Sludges and Its Effects on
Endogenous Respiration
SHANKHA K. BANERJI, Assistant Professor
Department of Civil Engineering
University of Delaware
Newark, Delaware
INTRODUCTION
Increased use of boron salts in the household detergents and other industrial
uses has posed questions whether these substances discharged in the wastewater are
deleterious to the environment. In particular, the effect of slug dose of boron salts on
the aerobic biological wastewater treatment has been determined quantitatively by
Banerji, et al. (1). It was shown that boric acid or sodium borate (borax) at a concentration beyond 10 mg/1 produced significant toxicity to the activated sludge
cultures. The effect of boron on the sludge synthesis coefficient was also determined.
It was pointed out that the current levels of boron in the sewage (0.4 - 1.5 mg/1) was
low enough so that there was probably no immediate concern from boron toxicity
to aerobic biological wastewater treatment, unless, however, there was a concentration
or adsorption of boron on the sludge and other solids giving a relatively higher concentration in the micro-environment.
The studies presented here investigate the adsorption of boric acid on clays
(illite and kaolinite) and biological solids. In addition, the effect of boron on the
activated sludge endogeneous respiration has also been presented.
MATERIALS AND METHODS
Adsorption Studies
Two soils, kaolinite and illite clays, were selected for determining the adsorption of boric acid. These materials have been used in many adsorption studies by
other workers (2,3).
Kaolinite clays are two-layered structures consisting of alternate layers of
hydrated Si02 and AI2O3. Illite, on the other hand, is a three-layered clay consisting
of two outer layers of hydrated Si02 and a central layer of hydrated AI2O3. Both of
these clays do not expand or swell with the addition of water or other compounds
because of certain linking arrangement of the ions. Figure 1 shows the grain size
distribution for kaolinite and illite based on hydrometer tests (4). The mean particle
size for kaolinite and illite was 0.009 mm and 0.025 mm, respectively.
In addition, sludge from a stock fill and draw batch activated sludge unit using
glucose and yeast extract as substrate was also used as an adsorbent. The settled
sludge was washed with one per cent saline prior to its use in the adsorption experiment.
In the actual experimentation, known dry weight of adsorbent (soil or sludge)
were added to replicate flasks containing a pH buffer and a known concentration of
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