(206h) Evaluation of the Efficacy and Mechanism of Cactus (Opuntia ficus-indica) As a Natural Coagulant for Pre-Treatment of Oil Sand Process Affected Water

Abstract

Third-largest demonstrated crude oil reserve in the world, next to Saudi Arabia
and Venezuela occurs in the oil sands of western province of Canada. Oil sands
production in Canada is expected to upsurge
from 4.1 million barrels per day in 2015 to 5 million barrels per day in 2024.
About three to five barrels of fresh water per barrel of crude produced is used
by mining operations and 0.5 barrels for in situ operations. Due to high
concentrations of organic acids leached from the bitumen during extraction, the oil sand process affected water
(OSPW) is brackish, alkaline in
nature and contains dissolved organic and inorganic pollutants. The existence of these substances in
processed water makes it highly toxic to aquatic life [1]. To address this critical issue, Environment
and Climate Change Canada (ECCC) introduced zero discharge policy. As per the
mandate of this policy, oil sand industries are required to store all
OSPW and to recycle it after treatment. The treatment of OSPW has become a
serious issue for Canada’s oil sand industry, because the fine particles in
tailing pond wastewater take decades to
consolidate and dry out, which can delay reclamation. In currently available technologies, such
as composite tailings (CT), whereby gypsum is added to mature fine tailings,
further increases the salinity and hardness of process water [2]. In
conventional pre-treatment techniques, chemical coagulants are used, namely, aluminum sulphate (Al₂(SO₄)₃),
ferric chloride (FeCl₃) etc. Though the effectiveness of these
chemicals as coagulants is well-recognized, still there are disadvantages
associated with their usage, such as reduced efficiency in low-temperature
water, relatively high procurement costs, detrimental effects on human health
and production of large sludge volumes. Moreover, they significantly affect pH
of the treated water. There is also strong evidence linking aluminium-based
coagulants to the development of Alzheimer's disease and detrimental impact on
the environment and health [3].

Maintaining
good recyclable water quality and ensuring more efficient and limited use of
fresh water are the most important challenges that must be met in the oil sands
production sector. Therefore, it is critical to develop an effective and
appropriate strategy to treat OSPW to sustain production. The combinations of
the concerns with chemical coagulants and limited available technologies have led
the researchers to focus on development of plant based natural coagulants. Due
to their inherently renewable
characteristics, abundance, low
toxicity, and biodegradability, these
naturally occurring and environmentally benign agents are rapidly gaining
interest in water treatment. The mucilage extracted from Opuntia ficus-indica (OFI), a species of cactus, was
evaluated for turbidity removal from synthetic turbid water and oil sand
process affected water (OSPW), and an effort was made towards elucidating the
underlying coagulation mechanism. For the first time, a natural coagulant derived
from OFI was used to treat OSPW. Fourier transform infrared spectroscopy (FTIR) analysis was performed to
understand chemical properties of the extracted mucilage. The functional groups
observed in FTIR analysis signify the presence of l-arabinose,
D-galactose, l-rhamnose,
and D-xylose, as well as galacturonic
acid. Preliminary jar test of synthetic turbid water achieved maximum turbidity
removal of 98% under alkaline condition with coagulant dosing of 60 mg/l. The highest
turbidity removal from OSPW was obtained up to 76% for 1200 mg/l coagulant dosage at neutral and
alkaline pH (as shown in Figure 1 below). The effect of
different ions commonly present in OSPW, on the process performance was also
studied. The comparison of zeta potential measurements and microscopic images
of thread like large flocs reveals the possibility
that mechanism of coagulation by OFI is inter-particle bridging (as shown in Figure 2 below).
Measurement of total organic carbon (TOC) was done and slight increment in TOC
was observed after treatment of OSPW. A comparative study between natural
coagulant and alum was also done and it was found that less quantity of compact
sludge was produced by natural coagulant compared to alum. Once optimized,
application of this readily available plant may offer a practical, inexpensive,
and appropriate solution for pre-treatment of OSPW.

Keywords:
OSPW; Natural coagulant; Cactus.

Figure 1.
 Effect of natural
coagulant dosages and pH on turbidity removal from OSPW.

Figure 2. (a) Flocs produced while using alum (b) Flocs
produced while using bio coagulant

References

[1] Lari, E.,
et al. "Determining the effect of oil sands process-affected water on
grazing behaviour of Daphnia magna, long-term consequences, and
mechanism." Chemosphere 146 (2016): 362-370.

[2] Renault, S., et al. "Effect of
high salinity tailings waters produced from gypsum treatment of oil sands
tailings on plants of the boreal forest." Environmental Pollution 102.2
(1998): 177-184.

[3] Martyn, C.
N., et al. "Geographical relation between Alzheimer's disease and
aluminium in drinking water." The Lancet 333.8629 (1989):
61-62.