Assessment of Coagulation–Flocculation Process Efficiency for the Natural Organic Matter Removal in Drinking Water Treatment

Abstract

Natural organic matter (NOM) represents a range of heterogeneous hydrophobic and hydrophilic components naturally occurring in the water source and, due to the fact that they can act as precursors for the disinfection, by-products may have a considerable impact on drinking water quality. Coagulation–flocculation (C/F) is among the most applied processes for NOM removal from water sources (especially rivers). In this study, C/F efficiency for a river water supply was investigated in cold and warm conditions, by varying the coagulant dose and mixing conditions. In this study, polyhydroxy aluminum chloride PAX XL 60, and polyacrylamide FloPam AN 910 SEP were used as coagulant and flocculant, respectively. Multiple water quality indicators were determined, such as turbidity, chemical oxygen demand (COD), dissolved organic carbon (DOC), and residual aluminum concentration. Some unconventional parameters relevant for NOM removal were also considered, like absorbance at 254 nm (A254), at 280 nm (A280), and at 365 nm (A365), as well as the ratios A254/DOC, A254/280, and A254/A365. After coagulation–flocculation, turbidity was completely removed in all the studied conditions. The DOC content was reduced by up to 22.65% at a low temperature and by up to 31.81% at a high temperature. After the addition of polyelectrolyte in cold conditions, the efficiency in terms of A254 increased by up to 37.4%, while the specific absorbance decreased. The high molecular weight NOM increased after C/F, based on the A254/A365 ratio. Chemometric analysis was employed in order to determine the effect of the coagulant dose on the process efficiency. The optimum coagulation–flocculation conditions were corroborated by means of the principal component analysis.

Competitive Removal of Antimony and Humic Acid by Ferric Chloride: Optimization of Coagulation Process Using Response Surface Methodology

“…The sodium hydroxide (NaOH) solution was used to adjust pH of HA stock solution to 11 and was stirred at 100 rpm for 24 h [29]. This model organic matter is widely used to simulate natural water conditions [18,24]. The 1000 mg/L coagulant stock solution was prepared by adding ferric chloride hexahydrate (FeCl 3 •6H 2 O) in pure water.…”

“…The predetermined quantity of FC dosage was first supplied to test samples in all trials during a rapid coagulation phase followed by a pH adjustment to 7, which is close to real groundwater conditions. The experimental procedure was then executed using a jar tester apparatus (Model: SJ-10, Young Hana Tech Co., Ltd., Gyeongsangbuk-Do, Korea) in various phases: Flash mixing phase (coagulation at 140 rpm for 3 min); slow mixing phase (flocculation at 40 rpm for 20 min); and sedimentation phase (settling of particles for 30 min) [24,25,29,31]. The aliquots were collected after experimental procedure and analyzed for quantifying TOC content using an unfiltered sample using a TOC analyzer (TOC-5000A, Shimadzu Corp, Kyoto, Japan).…”

“…By contrast, the coagulation behavior of Sb ions was remarkably affected due to coexistence of other organic substances, including humic acid (HA) in aqueous solutions [21,23]. Various categories of organic molecules are all over present in the water bodies, with concentrations values up to 10 mg C/L [18,24]. These organic species tend to bind with Sb ions, which may account for mobility of metal ions in the natural environment by several means, which makes interaction between organic matter and Sb an attractive topic for research [18,24,25].…”

“…Various categories of organic molecules are all over present in the water bodies, with concentrations values up to 10 mg C/L [18,24]. These organic species tend to bind with Sb ions, which may account for mobility of metal ions in the natural environment by several means, which makes interaction between organic matter and Sb an attractive topic for research [18,24,25]. Among various organic species, HA molecules are high molecular weight hydrophobic compounds having phenol, carboxyl, amine, and hydroxyl groups, with strong interactive capacity with metals [26].…”

“…The existence of organic ligands, i.e., HA in Sb-contaminated water, may offer a probable route for humans, particularly if it is used for drinking purposes. This necessitates the removal of both Sb and HA from drinking water, whereby conventional water treatment processes are commonly applied [18,24,25]. Therefore, it is essential to obtain optimal operating conditions for both Sb and HA removal by coagulation.…”