Natural Organic Matter Removal in Surface Water Treatment via Coagulation—Current Issues, Potential Solutions, and New Findings

Abstract

Considerable changes have been observed in surface waters’ quality in recent years. They include an increase in dissolved organic carbon (DOC) concentrations, as well as a shift of natural organic matter (NOM) composition in favor of low molecular weight (LMW), and they are expected to occur on a wider scale in the future. Those predictions are particularly worrying given the importance of surface water as the main potable water source for numerous communities across the globe. Conventional methods of surface water treatment for drinking purposes mostly focus on the process of coagulation. The progressing changes in the quality of surface waters, however, render the conventional treatment via coagulation inefficient. The issue of the presence of natural organic matter in drinking water sources, its anticipated changes, and the related treatment problems are all complex and pressing matters that need addressing. This paper aims to provide a critical review of recent findings regarding NOM removal via coagulation in reference to the current NOM-related issues and their potential solutions. The paper discusses the application of different types of coagulants, and their respective advantages and disadvantages. Coagulation-integrated processes including adsorption, membrane filtration, biological processes, and oxidation are also addressed. Lastly, insights on the future approach to the discussed issues and conclusions are presented.

A Novel Process for the On-Site Preparation and Application of Polyferric Chloride (PFC) for Surface Water Treatment

“…For this reason, various treatment technologies have been applied to remove effectively suspended solids and organic compounds (mainly NOM) from surface waters. Conventional water treatment technologies include coagulation/flocculation, sedimentation, filtration (with simple filter media, e.g., sand filters), and disinfection processes, while advanced treatment technologies usually refer to the application of membrane separation processes, such as microfiltration or ultrafiltration [3,4]. The latter presents the advantages of superior effluent quality and easy operation; however, their widespread application is still limited due to membrane fouling and high membrane costs.…”

“…However, these coagulants have been replaced during recent decades mainly by pre-polymerised aluminium chloride (PAC), which presents a superior performance mainly in terms of NOM removal. When simple aluminium or iron salts, such as Al 2 (SO 4 ) 3 or Fe 2 (SO 4 ) 3 , are employed, rapid precipitation can occur, and the formation of corresponding metal hydroxides, namely Al(OH) 3 and Fe(OH) 3 , results in a reduction in positive surface charges and, consequently, decreases the adsorption of negatively charged organic colloids which initially occurs. On the contrary, during the application of pre-polymerised coagulants, such as PAC, the respective precipitation process is delayed; therefore, a better adsorption and removal of NOM can be achieved [8][9][10].…”