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Russian Journal of Applied Chemistry, Vol. 74, No. 2, 2001, pp. 344!346. Translated from Zhurnal Prikladnoi Khimii, Vol. 74, No. 2, 2001,
Original Russian Text Copyright + 2001 by Feofanov, Litmanova.
Mechanism of Coagulation Purification of Wastewater
with Aluminum Oxochloride
Yu. A. Feofanov and N. L. Litmanova
St. Petersburg University of Architecture and Construction, St. Petersburg, Russia
Received August 1, 2000
Abstract-Results of a coagulation purification of solutions modeling weakly contaminated wastewater
from dairy shops are presented. The influents of detergents (HNO
and NaOH) and aluminum oxochloride on
the process of contaminant removal from a milk solution in the pH range 2312 is considered. Distinctions
are noted in the behavior of model milk solutions with contaminant concentration. The results of studies
performed at varied doses of aluminum oxochloride by the optical and electrophoretic methods are used to
explain the mechanism of coagulation purification of model wastewater.
The great bulk of waste produced by plants is con-
stituted by wastewater formed in washing of the dairy
equipment. The washing process consists in several
successive operations, each using one of the follow-
ing reagents: acids, alkalis, or sterilizing agents, with
the entire process completed by rinsing in pure water.
As a result, the wastewater delivered to the purifica-
tion facilities has qualitative and quantitative composi-
tion abruptly varying with time.
The results obtained in a study of the coagulation
purification of solutions modeling strongly contam-
inated wastewater of dairy shops with the use of alu-
minum oxochloride (AOC) were reported in .
The aim of the present study was to analyze the be-
havior of wastewater with low content of impurities
upon addition of various reagents: detergents and
AOC. To reveal the influence exerted by each kind
of contaminant on the process of coagulation, waste-
water was replaced by model solutions.
The solution under study, obtained by diluting milk
with distilled water, contained (mg l
): fat 350 and
protein 280, and were characterized by chemical oxy-
gen demand of 900 mg O
, which corresponds to
the composition of dairy plant wastewater with mod-
erate contamination. The pH was varied by adding in-
dustrial detergents: 1% solution of nitric acid and
0.1 N solution of sodium hydroxide. As coagulant
was used freshly prepared 1% solution of AOC with
basicity factor [OH
) ratio] of 5/6.
After mixing a milk solution with a coagulant by
the procedure described in  and allowing the sam-
ples to stand for 1 h, the efficiency of purification
was evaluated by the residual content of organic sub-
stances, determined from the loss in calcination of
the dry residue .
The kinetics of impurity sedimentation was studied
by measuring the optical density of solutions treated
with a coagulant for 1 h on a KFK-2MP photocol-
orimeter in 1-cm-long cuvettes at light wavelength
l = 440 nm.
The electrokinetic potential of milk particles with-
out AOC and with varied concentration of this com-
pound was determined by microelectrophoresis  in
a modified Abramson cell and PZO microscope (Po-
land). The x-potential was calculated using the Smo-
luchowski formula from the arithmetic-mean value of
the electrophoretic velocity of 15320 particles.
The efficiency of removal of organic impurities,
, is presented in Figs. 1 and 2 in relation to the pH
value. The presence of only detergents without AOC
in weakly contaminated solutions (Fig. 1, curve 1) de-
stabilizes the system (acid coagulation) at pH 4.753
5.10, with the maximum degree of purification (40%)
observed at pH 5.0, which can be attributed to the elec-
trical properties of the emulsion stabilizer-casein,
whose isoelectric point lies in the above pH interval
. This is confirmed by the results of electrophoretic
measurements (Fig. 1, curve 3) indicating that
the particle charge is the smallest in this pH range.
In a more concentrated solution , the system co-
agulated at pH 435, with 50% removal of impurities