Journal of Water Resource and Protection, 2013, 5, 1-4
http://dx.doi.org/10.4236/jwarp.2013.57A001 Published Online July 2013 (http://www.scirp.org/journal/jwarp)
Sludge Density Prediction in a Wastewater Chemical
Coagulation Process
Margarita Teutli-León1, María Elena Pérez-López2
1Engineering Department, Autonomous University of Puebla (BUAP), Puebla, Mexico
2Interdisciplinary Research Center for the Local Integral Research, National Polytechnical Institute at Durango
(IPN-CIIDIR-DGO), Durango, Mexico
Email: teutli23@hotmail.com, maelena0359@yahoo.com,
Received April 25, 2013; revised May 27, 2013; accepted June 30, 2013
Copyright © 2013 Margarita Teutli-León, María Elena Pérez-López. This is an open access article distributed under the Creative
Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original
work is properly cited.
ABSTRACT
This paper reports an approach to estimate the sludge density in a physicochemical treatment of municipal wastewater,
experiments considered 4 coagulants (aluminum sulfate SAl, iron sulfate SFe, aluminum polychloride PAX, iron poly-
chloride PIX), and 2 flocculant products (cationic CP and anionic AP polymers). Experimental approach is based on
running a set of jar tests at different coagulant concentrations. After the stirring and resting times took place, pH and
conductivity were registered finding that SAl and SFe either with or without polymers are the coagulants producing the
higher pH drop. Conductivity measures also establish two kind of data since higher conductivity (about 2000 μS·cm−1)
was observed for SAl, and PIX, PIX + CP, PIX + AP; otherwise a conductivity about 1300 μS·cm−1 was observed for
SAl + PC, SFe and PAX alone and with CP or AP. Settleable solids (SST) determined with an Imhoff cone were similar
for sulfates and polychlorides, but dry sludge (DS) clearly set up two groups the one with higher sludge content corre-
sponds to sulfates group. The quotient of DS divided by the SST provided an estimation of the apparent sludge density,
in this way it was observed that higher densities were obtained for sludge from sulfates at lower coagulant concentrations;
also sludge from SFe was heavier than the one from SAl. Otherwise, polychlorides produced a lighter sludge in respect to
the one obtained with sulfates, and between them the PIX coagulant provided a heavier sludge than the PAX coagulant.
Keywords: Coagulant; Flocculant; Wastewater Treatment; Sludge Density
1. Introduction
Usually wastewater treatment plants (WWTP) are re-
ferred in three levels: primary, secondary and tertiary
treatment. In Latin America, primary wastewater treat-
ment has been implemented for several communities, but
it has been observed that the organic load is high enough
so additional steps are required in order to process the
wastewater, applied alternatives are either a secondary
treatment (biological) or the named Advanced Primary
Treatment (APT), the last one is a physicochemical
process which allows simultaneous precipitation of sev-
eral contaminants, since simultaneously use both coagu-
lant and flocculant for enhancing floc formation and set-
tling. According to Vesilind [1] an estimation of associ-
ated elimination yields correspond to 60% - 90% in set-
tleable solids (SST), 25% - 40% in biochemical oxygen
demand (BOD), 30% - 60% in chemical oxygen demand
(COD), 70% - 90% in phosphorus (P), and 80% - 90% in
pathogens.
Although an APT process use the same infrastructure
than a primary treatment, the fact that municipal waste-
water exhibit seasonal variations in its chemical compo-
sition leads to the need of running several jar tests in or-
der to find the right reagent dosage, which so far define
the amount of sludge produced and its handling proce-
dures. Usually to increase phosphorus removal, the che-
mical requirements impact increasing 15% the amount of
produced sludge since chemical addition may be in ex-
cess of stoichiometric requirements [2]. Another problem
derived from chemical addition is that sludge dewatering
becomes lowered by a raise in salinity, it has been proven
that both organic polyelectrolytes and alum provide an
improvement on dewaterability [3]. According to Kal-
deris [4] the most important factors in sludge manage-
ment costs are: 1) physical and chemical characteristics;
2) quantity; 3) legal framework; 4) potential valorization
and re-use; and 5) land availability and cost. Therefore, it
is important that WWTP operators have the capacity to
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