Variation of assimilable organic carbon during coagulation by aluminum and iron in drinking water treatment

Abstract

The variation of Assimilable Organic carbon {AOC) during the coaguiation of raw surface water and synthetic water was investigated. It was found that the removal rate of AOC concentration during alum coagulation of raw surface water was only about 24.5% at high coagulant dosages, A higher removal rate of AOC in the case of FeCl3 coagulation {about 65,9%) was observed under the same dosages, but AOC-NOX increased from 143 (igL "• to 473^gL"'' during FeCb coagulation. The results showed a relationship between the solution pH in the coagulated water and the reduction of AOC. The AOC of water decreased efficiently during coagulation in the case of synthetic water at lower coagulant dosages, and the case of coagulation with FeCb also resuited in a better removal of AOC, The lowest value of AOC achieved in the case of synthetic water (54(xgL ''), was close to the biostability criteria of drinking water (50(j.gL"^), it can be concluded that not only large molecules but also low-molecular weight fractions of organics can be removed during coagulation. The performance of coagulation effect was evaluated based on the following parameters: pH, turbidity, UV absorbance at 254 nm (UVssa) and Total Organic Carbon (TOC), The resuits showed that the coagulation effectiveness has a substantial impact on AOC reduction.

Variation in assimilable organic carbon formation during chlorination of Microcystis aeruginosa extracellular organic matter solutions

“…When the dosage of chlorine increased to 20 mg/L, the AOC concentrations decreased to 594.16 μg/mg DOC, 415.6 μg/mg DOC and 252.74 μg/mg DOC with chlorine residual values of 8.76 mg/L, 10.04 mg/L and 11.74 mg/L, respectively. The initially decreasing tendency supports the observation that there are more low MW and fewer high MW compounds in the EOM (Wei, 2013;Liang, 2009). The reduction in AOC levels depends on the concentration of small organic molecules that can be hydrolyzed and oxidized to H 2 O and CO 2 by chlorine at a chlorine dosage below 4 mg/L.…”

“…AOC monotonically increased with increasing chlorine dosages, to 10 mg/L. This can be explained by the presence of a small amount of organic matter which is not easily oxidized, but is gradually decomposed into small molecules with increasing chlorine dosage, thus producing AOC (Liang, 2009). The yields of AOC depend on macromolecular oxidation products being decomposed faster by oxidation or hydrolyzation than their rate of formation at chlorine dosages higher than 20 mg/L.…”

“…1 (Wei, 2013;Liang, 2009). The chlorine disinfectant oxidized many of the lower MW compounds within 2 hr.…”

Using coagulation to restrict microbial re-growth in tap water by phosphate limitation in water treatment

“…Sathasivan and coworkers also have investigated microbial re-growth potential (MRP) in Tokyo metropolitan drinking water distribution system [14] and clearly demonstrated that inorganic P was the MRP limiting factor. In the case described above, microbial re-growth in the raw water used was generally C-limited [9], whereas, as shown here, the produced water was P-limited. This shift in the limitation regime indicates that drinking water treatment processes may play a crucial role.…”

“…In most regions, organic carbon is the principal limiting factor for microbial re-growth during distribution [2,[6][7][8][9]. However, in some regions of the world (particularly in Northern European countries), phosphate (P) was also reported to be the limiting factor for microbial re-growth in drinking water distribution system with carbon being in excess [10,11].…”