Reduction of dissolved organic matter in secondary municipal effluents by enhanced coagulation

Abstract

Jar test experiments were performed to investigate the reductions of dissolved organic matter (DOM) in secondary municipal effluents by coagulation, as well as the effect of coagulation on the structural and functional properties of DOM fractions. The reductions of 9-58% and 17-71% in dissolved organic carbon (DOC) and the removals of 30-75% and 30-83% in absorbance of ultraviolet light at 254 nm (UV-254) were obtained by coagulation of two secondary municipal effluents, respectively. Moreover, the order of DOC and UV-254 removals by coagulation was pH 5 > pH 6 > unadjusted pH at all coagulant dosages. The reductions of the bulk fluorescent materials by coagulation were lower than those of UV-254 absorbing compounds. Among four types of fluorophores, aromatic protein-like fluorophores were preferentially removed by coagulation. The coagulation treatability of hydrophobic acid (HPO-A) was the highest and that of hydrophilic fraction (HPI) was the lowest, among five DOM fractions. In addition, the value of specific ultraviolet light absorbance for each DOM fraction decreased significantly after coagulation. The Fourier-transform infrared spectra revealed that aromatics were effectively removed by coagulation while coagulation seemed to be inefficient in removing amide-2 functional groups and those hydrocarbons exhibiting absorbance characters at 2950-2850 cm 21 .

Application progress of enhanced coagulation in water treatment

“…Optimized coagulation is proposed based on enhanced coagulation, which is a coagulation process with multiple goals: maximizing particulate matter and turbidity removal, maximizing TOC and DBP precursor removal, reducing residual coagulant content, reducing sludge production, and minimizing production costs. 4,5 In recent years, the intensity of research on enhanced coagulation has been unprecedentedly increased, with many scholars conducting more in-depth research on enhanced coagulation. For example, studies have attempted to gain an indepth understanding of the characteristics of organic matter in water bodies, identify organic matter removal rules to establish an organic matter removal mode, and summarize the mechanisms of enhanced coagulation removal of organic matter.…”

Molecular Characterization of Organics Removed by a Covalently Bound Inorganic–Organic Hybrid Coagulant for Advanced Treatment of Municipal Sewage

“…Coagulation can efficiently remove organics in wastewater, and the removal efficiency depends on organics properties (e.g., chemical composition and structure), coagulant’s type and dosage, and water quality conditions such as pH and temperature . Conventional coagulants (e.g., iron salt, aluminum salt, and polydiallyldimethylammonium chloride (polyDADMAC)) can effectively remove high molecular weight (HMW) organics, hydrophobic neutral compounds, and hydrophobic acid compounds in natural organic matter and EfOM, , but they are less efficient in removing low molecular weight (LMW) organics and hydrophilic compounds. , Fortunately, a new class of hybrid coagulants, covalently bound inorganic–organic hybrid coagulant (CBHyC), can remove the HMW and hydrophobic organics and also the LMW and hydrophilic organics . Most previous studies focus on changes in bulk physical and chemical characteristics (e.g., molecular weight, hydrophilicity) of organics during coagulation.…”