Phosphorus removal by blast furnace slag and cement
clinker – flow cell studies for estimation of sorptive
capacity for use with constructed treatment wetlands
Anamika Sikdar Paul and Bruce Anderson
ABSTRACT
Blast furnace slag and cement clinker were explored in long-term flow cell experiments for
estimation of their phosphorus (P) removal efficiencies. A local gravel, typically used in constructed
treatment wetlands, was used as a control medium. The experiments examined the removal of
phosphorus from a solution initially containing 4 mg P/L. The slag and clinker were nearly 100%
efficient due to very high sorptive capacities. The control gravel medium removed 50% of the influent
phosphorus. Results from this study indicate that the use of blast furnace slag in constructed
wetlands or filter beds is a promising solution for P removal via sorption mechanisms.
Anamika Sikdar Paul (corresponding author)
AMEC Earth and Environmental,
160, Traders Blvd (E),
Suite 110, Mississauga, ON,
L4Z 3K7 Canada
E-mail: anamika.sikdar@gmail.com
Bruce Anderson
Department of Civil Engineering,
Queen’s University,
Kingston ON,
Canada,
K7L 3N6 Canada
Key words | adsorption, clinker, constructed wetland, phosphorus, slag, sorption capacity
INTRODUCTION
The adverse effects of eutrophication due to the presence of
phosphorus in surface waters are well established (Orive
et al. ). The Ontario Water Resources Act 1990 Guideline
F-5 sets the total phosphorus limit of 1 mg/L for municipal and
private sewage treatment systems discharging into a water-
body. Sunny Creek Estates (SCE) is a mobile home village
using a combination lagoon–CW system to treat its sewage
and discharges directly into the Bay of Quinte. The Bay of
Quinte on the north eastern shore of Lake Ontario is a recog-
nized Area of Concern. The Bay of Quinte Remedial Action
Plan (BQRAP) set an objective of 0.3 mg/L of total phos-
phorus and a further stringent guideline of 0.1 mg/L is
presently being considered. Currently, the SCE treatment
system does not achieve compliance with respect to effluent
concentrations of phosphorus, and better treatment is needed.
Conventional technologies for removal of phosphorus
from point source wastewater discharges are physical pro-
cesses (settling, filtration), chemical precipitation (with
aluminum, iron and calcium salts) and biological processes
that rely on biomass growth (bacteria, algae, plants) or
intracellular bacterial polyphosphates accumulation
(Bashan & De-Bashan ). Long-term studies and
increased operational experience indicate that phosphorus
removal is variable or inconsistent (Richardson & Craft
; Reed & Brown ; Wood ) in subsurface con-
structed wetlands (CW) that can be attributed to the
complexity of phosphorus removal mechanisms, and the
lack of consideration of these complexities in design.
The major factors that make P removal by the wetlands
particularly difficult are the type, quantity and diversity of
the influents that need to be treated. The principal phos-
phorus removal mechanism, adsorption/precipitation,
being a finite process, requires the P saturated substrate to
be replaced after a certain operational period (Faulkner &
Richardson ; Mann & Bavor ; Drizo et al. ;
Shilton et al. ). Given these, the sorption and deso-
rption of phosphorus in constructed wetlands is impacted
not only by the physical and/or chemical characteristics of
the substrate media, but also by phosphorus loading, hydrau-
lic conditions, temperature, time and dissolved oxygen.
When designing a CW for P removal, the selection of the
material to be used as the wetland substrate (rooting medium)
plays a crucial role (Mann & Bavor ; Drizo et al. ,
; Johansson & Gustafsson ). A potential medium
300 © IWA Publishing 2011 Water Quality Research Journal of Canada | 46.4 | 2011
doi: 10.2166/wqrjc.2011.112
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