• International Journal of Technology (IJTech)
  • Vol 13, No 3 (2022)

Impact of Temperature and Coagulants on Sludge Dewaterability

Impact of Temperature and Coagulants on Sludge Dewaterability

Title: Impact of Temperature and Coagulants on Sludge Dewaterability
Dewi Fitria, Miklas Scholz, Gareth M Swift, Furat Al-Faraj

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Cite this article as:
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
Email to Corresponding Author

Impact of Temperature and Coagulants on Sludge Dewaterability

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 et al., 2004). Basically, the chemical composition and physical configuration of the flocs or solid particles that form the sludge determine the dewaterability characteristics of sludge (Verrelli et al., 2009). When treating water in water and wastewater treatment plants, a number of process phases are performed to remove contaminants. According to Zhan et al. (2011), coagulation is identified as one of the significant elements within the treatment process, whilst Diaz et al. (2011) and Verrelli et al. (2009) stressed the importance of the coagulation’s influence on both production and the dewaterability of sludge.

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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