Impact of Temperature and Coagulants on Sludge Dewaterability
Corresponding email: dewifit_ria@yahoo.com
Published at : 01 Jul 2022
Volume : IJtech
Vol 13, No 3 (2022)
DOI : https://doi.org/10.14716/ijtech.v13i3.4886
Fitria, D., Scholz, M., Swift, G. M., Al-Faraj, F., 2022. Impact of Temperature and Coagulants on Sludge Dewaterability. International Journal of Technology. Volume 13(3), pp. 596-605
| Dewi Fitria | Environmental Engineering Study Program, Faculty of Engineering, Universitas Riau, Kampus Bina Widya Km 12,5, SimpangBaru, Kec. SimpangBaru, Kota Pekanbaru, Riau, Indonesia 28293 |
| Miklas Scholz | 1. Division of Water Resources Engineering, Faculty of Engineering, Lund University, P.O. Box 118, 221 00 Lund, Sweden 2. Institute of Environmental Engineering, Wroclaw University of Environmental a |
| Gareth M Swift | Geotechnical Engineering, University of Portsmouth, University House, Winston Churchill Ave, Portsmouth PO1 2UP, United Kingdom |
| Furat Al-Faraj | Civil Engineering, University of Bolton, A676 Deane Rd, Bolton BL3 5AB, United Kingdom |
Temperature
and coagulant types have an important impact on the quantity and quality of the
residue (sludge) in water and wastewater treatment processes. Temperature
influences water viscosity and the distribution of the coagulant in water. Coagulants
can promote the agglomeration of fine particles into larger flocs so that they
can be more easily separated from the water. Experiments have been conducted to
explore the relationship between temperature (16-26°C), the type of coagulant, and
sludge dewaterability (estimated using the capillary suction time (CST)). Alum,
Ferric, and Moringa oleifera Lam were
used as coagulants. The influences of different mixer shapes, turbidity values,
and flocs sizes on sludge dewaterability have been assessed. The results show
that ferric chloride was unaffected by temperature, whereas alum and M.
oleifera performances were influenced by temperature. CST results using the
coagulant ferric chloride, regardless of mixer shape, turbidity, and floc size,
were insensitive to temperature differences.
Capillary suction time; Coagulants; Floc sizes; Sludge dewaterability; Temperatures.
A large volume of
sludge is produced by water and wastewater treatment plants every day, and;
unfortunately, this is unavoidable in water and wastewater treatment processes.
Hernando et al. (2010) estimated that around 40% of the treatment costs of a
typical treatment plant are linked to dewatering and the disposal of sludge. In
modern societies where populations are globally increasing, and access to
sewage and water treatment has become easier, the amount of sludge increases
steadily. The type of treatment process in the wastewater plant defines the
quality and quantity of sludge (Sanin et al., 2011). Considered one of the mostimportant issues related to sludge management,
dewatering sludge is also the most expensive process in water and wastewater
treatment plants (Jin
Temperature and type of coagulant are equally
effective on the coagulation efficiency (Duan &
Gregory, 2003; Rodrigues et al., 2008). Temperature can affect the metal
ion hydrolysis reaction rate (Inam
et al., 2021). A higher temperature causes an enhanced reaction rate and
vice versa. Furthermore, Duan and Gregory (2003)
emphasize that temperature is a significant parameter in determining the
distribution of the coagulant and the formation of the hydrolysis products. In
turn, it will also affect the coagulation and flocculation efficiency (Gao et al., 2005).
Low reaction rates produce an inhomogeneous
distribution of coagulation species caused by ineffective coagulation that
results from low water temperature. In fact, water temperature not only affects
the performance of coagulation in general, but also differentiates the
efficiency of different types of coagulants (Duan &
Gregory, 2003), and the removal of turbidity (Xiao
et al., 2009).
Literature highlights research work conducted
on the effect of temperature on coagulant efficiency (Xiao
et al., 2008; Xiao et al., 2009). However, contradictory results have
been reported. Some of the findings indicated that temperature does have an
impact on coagulation efficiency (Xiao et al.,
2008; Xiao et al., 2009). Comparing alum with ferric performances, Duan and Gregory (2003) found that ferric has a
better performance than alum under low-temperature conditions.
Many coagulants have been commonly used in
conventional water resources recovery facilities (Duan
& Gregory, 2003). Coagulants can be inorganics (e.g., aluminium
sulphate and ferric sulphate), synthetic organics (e.g., polyacrylamic derivatives),
or natural flocculants (microbial flocculants). These have different impacts on
the coagulation process (Karamany, 2010).
Alum and ferric chloride-based salts such as alum, aluminium chloride, ferric
chloride, and ferric sulphate are frequently used as traditional coagulants (Bektas, 2004). Alum and ferric can have good
coagulant properties (Lubis et al, 2019).
Natural coagulants like M. oleifera can also be used as a substitute for metal-based
coagulant in selected water and wastewater treatment processes such as
coagulation and flocculation (Tat et al., 2010).
Moringa oleifera is a pan-tropical, multi-purpose tree, the seed from which
contains high-quality edible oil (up to 40% by weight) and water-soluble
proteins that act as an active agent for water and wastewater treatment. The further
advantage of using M. oleifera include safe, natural, and
environmentally friendly coagulant handling processes (Bhatia
et al., 2007).
Capillary suction time
(CST) is a measurement of sludge dewaterability properties. It can be used for
the rapid determination of filterability after the addition of coagulant aids (Scholz, 2005). Sawalha
and Scholz (2012) observed that the results of CST tests were sensitive
to variations in temperature. The results tend to reduce with higher
temperatures, probably due to the increase in filtrate viscosity with
increasing temperature.
Despite differences in coagulant performance
responding to temperature variation, further research is needed to investigate
the correlation between temperature and coagulants on sludge dewaterability.
This paper aims to assess the impact of (a) different temperatures on sludge
dewaterability indicated by CST values using alum, ferric chloride, and M. oleifera as coagulants, and (b)
different temperatures on sludge dewaterability indicated by turbidity and
median floc size using ferric chloride or alum as a coagulant.
Findings illustrate that CST values are altered by differences in temperature
(between 16 and 26°C) for the coagulants alum and M. oleifera. An increase in temperature lowers the CST value, which
can be explained by the change in synthetic sludge viscosity. In comparison,
ferric chloride is virtually unaffected by temperature, which has been
confirmed by turbidity and floc size results. If temperature fluctuations are
between 20°C and 26°C, an axial mixer and ferric chloride should be used to obtain stable
results. M.oleifera performed better
at higher temperatures. Further investigations should explore more the
relationship between other variable combinations, such as temperature and M. oleifera, using wider numerical
ranges. A study on the deterioration of M.
oleifera solutions is also recommended. Synthetic sludge has been used for
reference purposes and to keep the number of variables low. Further research
should also look at the assessment of dewaterability tests as a function of
more specific sludge types obtained directly from the industry. The
relationship between CST, specific resistance to filtration and other sludge
dewaterability tests should be assessed for real sludges under dynamic
environmental boundary conditions. Finally, the authors recommend to develop
the CST test further to create a new sludge dewaterability test that addresses
identified shortcomings with the CST such as temperature dependency.
This work was financially supported by Beasiswa
DIKTI and Rain Solutions (Water JPI 2018 Joint Call project) and WATERAGRI
(European Union Horizon 2020 research and innovation programme under Grant
Agreement Number 858375) in support of the development of a new sludge
dewaterability estimation test.
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