Effects of Low Temperature on the Removal of Trihalomethane Precursors by Coagulation

Abstract

This study showed that the trihalomethane (THM) concentration in finished water that had ken treated at 35.6" F (2°C) was significantly lower than in water treated at 71.6" F (22°C). Water temperature did not appear to affect the removal of total organic carbon (TOC) during coagulation with metal ion salts, but color removal was slightly reduced at low temperatures. The efficiency of coagulation for removing TOC, color, and THM formation potential improved when the water was treated at pH 5 rather than pH 7, regardless of temperature. Removal of low-molecular-weight organic substances was found to be more difficult at 35.6" F (2°C) than at 71.6" F (22°C). The data obtained suggest that reduced THM concentrations in finished water during winter are strictly a function of the reduced rate of THM formation.Campet alaconcluded that although low temperature did not affect the flocculation step of treatment, settling efficiency was impaired. Morris and Knocke6 presented quantitative results showing that low temperatures reduced the efficiency of metal ion coagulants for removal of turbidity from surface waters. They concluded that low temoeratures at times During the past ten years, considerable research has been conducted to determine how the disinfection of drinking water with chlorine can lead to the formation of potentially carcinogenic compounds, particularly trihalomethanes (THMs). Studies have also been conducted to evaluate methods of removing THMs from water with treatment methods such as air stripping' :' and adsorption by activated carbon columns." -" In addition, significant research has focused on methods of removing the organic precursors of THMsmethods such as the optimization of coagulation-flocculation systems.promoted the formation of extremely ciency and poor coagulation. Earlier work small particles, which did not settle mentioned possible problems with tur-well. Thus, their results showed that bidity removal when alum coagulation temperature affected both the flocculawas used at low temperatures, although tion and settling phases of treatment. little quantitative data were presented.7With the current need to control the One major operational difficulty that water treatment plants face in attempting to meet the THM standards is related toseasonal fluctuations in water quality. For example, changes in water temperature appear to affect the kinetics and equilibrium of metal hydroxide precipitation, resulting in a potentially adverse effect on coagulation systems.6 The flocculation and sedimentation stages of water treatment can also be affected by water temperature as a result of changes in solution viscosity and density. Until recently, temperature variations were not recognized as one of the potential causes of water treatment plant ineffi-APRIL 1986 Figure 1. Effect of incubation temperature on the rate of THM formation in Harwood' s Mill Reservoir water treated with 60 mg alum/L at pH 7 Figure 2. Effect of alum dose and temperature on turbidity removal from Chickahominy River water by coagulation ...

Monitoring and modeling of trihalomethanes (THMs) for a water treatment plant in Istanbul

“…In our study the temperature value of the drinking water ranged from 7.20°C to 22.70°C, which was associated with the formation of THM values in a wide range of 48.0/.tg/L to 102.0/.tg/L. A study by Knocke et al [30] indicated that the rate of THM formation at 2°C was normally 60-70% less than observed at 22°C.…”

Review on Chemical treatment of Industrial Waste Water

“…Temperature also significantly affects turbidity and particle counts during coagulation (Braul et al, 2001). However, dissolved organic carbon (DOC) and colour removal are not sensitive to temperature (Knocke et al, 1986;Hanson and Cleasby, 1990;Randtke, 1998).The The negative effect of temperature tends to be greatest with dilute suspensions. Direct filtration and DAF processes are much less affected by cold-water temperatures than sedimentation .…”

Mn(VII)–Fe(II) pre-treatment for Microcystis aeruginosa removal by Al coagulation: Simultaneous enhanced cyanobacterium removal and residual coagulant control

“…This differed from the hydrolysis behavior of Al when applied alone (Safarikova et al, 2013). This is attributed to the higher affinity of released proteins to Al species than to iron compounds (Pivokonsky et al, 2006), which might also explain the greater efficiency of iron salts in terms of DOC removal (Knocke et al, 1986). Similarly, introducing Fe(II) into the pre-treatment improved the precipitation of Al salts (Fig.…”

“…The combined use of different coagulants might be especially desirable in algae coagulation. Aluminum exhibited higher efficiencies in terms of the removal of turbidity, bacteria, and color than iron salts did (Cheng et al, 2003), whereas iron salts were better than aluminum towards the removal dissolved organic carbon (DOC) (Cheng et al, 2003;Knocke et al, 1986). The treatment of algae-burdened water not only involves the removal of suspended algae cells but also that of soluble DOM, the dualcoagulant approach can be advantageous in this case.…”