Comparisons of coagulation efficiency of conventional aluminium sulfate and enhanced composite aluminium sulfate/polydimethyldiallylammonium chloride coagulants coupled with rapid sand filtration

Coagulation efficiency and removal mechanism for composite coagulant polyaluminium chloride/polydimethyldiallylammonium chloride in treating lightly micro-polluted raw water of Yangtze River in autumn

“…As a result, excess inorganic coagulant dosage has introduced the problem of not only increased treatment cost, but also residual aluminium and iron content that has exceeded maximum allowable limits set by the World Health Organization for drinking water (WHO, 2008;Yang et al, 2013;Alzahrani et al, 2020). Treatment methods for lightly micropolluted raw water may also involve pre-oxidation and technologies such as enhanced coagulation, and advanced treatment technology or using membrane and advanced oxidation processes in combination with conventional treatment methods such as coagulation, sedimentation, filtration and disinfection (Yu and Graham, 2015;Brandt et al, 2017;Nascimento et al, 2019;Adebayo et al, 2021). Among these treatment technologies, enhanced coagulation using new coagulants, controlling the pH, or improvement of treatment facilities are the most commonly used, but the most feasible, efficient, and low-cost method is to enhance coagulation by using effective coagulants that have application advantages such as simple operation, and easy implementation which does not necessarily require changing the existing facilities (Moussas and Zouboulis, 2009;Yang et al, 2012 (Tolkou andZouboulis, 2020;Wang et al, 2020).…”

“…Usually, various inorganic aluminium and iron salt coagulants are the main coagulants used by drinking water production plants worldwide, and have performed well for many years for many countries (Nowacka et al, 2014;Bratby, 2016;Cui et al, 2020;Adebayo et al, 2021). However, because of the challenge of meeting stringent water regulations and the demand for continuous improvement of water quality, the role those inorganic coagulants or their complexes can play is becoming increasingly limited, given the practical constraints of effectiveness and cost.…”

“…Furthermore, it greatly improved the removal rate of water quality parameters at lower and optimum dosage ranges, and can replace the pre-chlorination oxidation process, helping to reduce the cost of treating surface raw water. Therefore, research on PDMDAAC is developing rapidly, and significant progress has been made (Zhang et al, 2010;Shen et al, 2017;Adebayo et al, 2021).…”

“…In recent decades, researchers have focused on improving the performance and removal efficiency by composite coagulants composed of inorganic salt/PDMDAAC, reporting the effect of dosing method (single or dual dosing), coagulation/application mode, intrinsic viscosity of PDMDAAC and mass ratio (Bolto et al, 2001;Sillanpää et al, 2018;Liu et al, 2019). For instance, some researchers have reported the use of composite coagulants composed of inorganic salt/PDMDAAC to enhance coagulation in the treatment of lightly micro-polluted and highly polluted surface raw waters, focusing on two major coagulation/application modes for the composite coagulants and corresponding inorganic coagulants (Moussas and Zouboulis, 2009;Li et al, 2015;Adebayo et al, 2021), namely: (i) same supernatant turbidity (SST) using different dosages for the composite coagulants and corresponding inorganic coagulant, calculated as Al 3 O 2 and Fe +n . In this application mode, the dosage of aluminium or iron salts can be significantly reduced, which can reduce the cost of water treatment and help to reduce the residual aluminium content in the resulting supernatant (Zhang et al, 2010;Adebayo et al, 2021); (ii) same dosage mode (SD) for all coagulants -when this is applied, it can significantly improve the water quality of the resulting supernatants after coagulation treatment, withstand the impact of a sudden increase in the quantity of surface raw water while ensuring the quality of the supernatant, and replace the pre-oxidation step for high-temperature algae-containing water, leading to a reduction in generated disinfection byproducts, etc.…”

“…In this application mode, the dosage of aluminium or iron salts can be significantly reduced, which can reduce the cost of water treatment and help to reduce the residual aluminium content in the resulting supernatant (Zhang et al, 2010;Adebayo et al, 2021); (ii) same dosage mode (SD) for all coagulants -when this is applied, it can significantly improve the water quality of the resulting supernatants after coagulation treatment, withstand the impact of a sudden increase in the quantity of surface raw water while ensuring the quality of the supernatant, and replace the pre-oxidation step for high-temperature algae-containing water, leading to a reduction in generated disinfection byproducts, etc. However, these studies were carried out under the requirement of limiting the residual turbidity of the supernatant water to between 2.0 and 4.0 NTU (Yang et al, 2012;Adebayo et al, 2021). Furthermore, some literature reviews have found that the composite inorganic salt/PDMDAAC coagulant can enhance the charge neutralization, polymer-bridging, and net capturing of suspended colloidal particles in the treatment of lightly micropolluted surface raw water, which strengthens the flocculation/ precipitation and adsorption processes resulting in improved water quality parameters (Wei et al, 2009;Bolto et al, 1999;Shen et al, 2017;Olukowi et al, 2022).…”