Coagulation: its effect on organic matter

Abstract

Mass spectra obtained using fast atom bombardment provided qualitative information about coagulation's effectiveness under various treatment conditions. Removal of natural aquatic dissolved organic matter (DOM) by conventional coagulation using ferric chloride was investigated. Reverse osmosis was used to isolate DOM from the Suwannee River in southern Georgia and from Lake Allatoona in northwestern Georgia. The two most significant differences between the source waters are pH and organic carbon concentration. Extensive jar‐testing identified regions of removal based on initial concentration of DOM, coagulant dosage, and pH conditions. Fast atom bombardment mass spectrometry was used to characterize the molecular‐weight distributions of DOM before and after coagulation. Trends in the shape of the mass spectra correlated well with data for DOM removal and suggested that the mechanism for DOM removal varies with the pH and coagulant dosage. At higher pH conditions and lower coagulant dosages, masses up to 1,000 daltons (D) were detected in the mass spectra after coagulation. At lower pH conditions and higher coagulant dosages, no masses above 750 D appeared in the mass spectra.

Structural stability of coprecipitated natural organic matter and ferric iron under reducing conditions

“…The apparent exclusion of the amide and aromatic rich OM is surprising given that, according to SUVA measurements in this and previous studies, aromatic OM is preferentially removed from solution through flocculation (Dennett et al, 1996). However, it is possible that the more hydrophobic aromatic OM is prone to partition out of solution phase to form micellar associations within the floc or requires only a very small amount of associated Fe for the purposes of charge balance in order to induce precipitation.…”

Transformations of particles, metal elements and natural organic matter in different water treatment processes

“…Meanwhile, some common observations exist, including: coagulation removes higher molecular weight and hydrophobic NOM (Dennett et al, 1996;Amy et al, 1992;Jacangelo et al, 1994;Owen et al 1995); ozonation can convert NOM from humic substances to non-humic fractions and from higher-to lower-MW fractions (Chiang et al, 2002;Owen et al, 1995); granular activated carbon (GAC) can remove intermediate or small humic molecules more efficiently (Johannsen et al, 1993), and therefore ozonation after filtration can result in enhanced adsorption capacity of GAC (Amy et al, 1992).…”

Assessment of Trace Estrogenic Contaminants Removal by Coagulant Addition, Powdered Activated Carbon Adsorption and Powdered Activated Carbon/Microfiltration Processes

“…The widely used physicochemical processes in water treatment include activated carbon adsorption and coagulation. Adsorption to hydrolysable coagulants is often very effective in removing acidic and basic components of the dissolved organic matter in natural waters provided pH conditions and dosage are properly controlled (Dennett et al 1996). Randtke and McCarty (1979) assessed the potential of various physicochemical processes for the removal of soluble secondary-effluent organics and demonstrated that activated carbon adsorption is generally the most proficient in removal of soluble organic matter.…”