The coagulation/flocculation process is an important part of surface water treatment. It has direct impact on the reliability of plant operations and final water qualities together with cost control. Low water temperature has a significant impact on the operation of drinking water treatment plants, especially on coagulation/flocculation processes.<p> A microscopic image technique has been used to study the coagulation and flocculation process in recent years, but it requires sample handling that disturbs the floc characteristics during measurement. A high resolution photographic technique was applied to evaluate flocculation processes in the present work. With this technique, the images of the flocs were obtained directly while the flocculation process was taking place. In combination with camera control software and particle size analysis software, this procedure provided a convenient means of gathering data to calculate size distribution. Once the size distribution was calculated, the floc growth and floc size change in the aggregation process could be analyzed. Results show that low water temperature had a detrimental impact on aggregation processes. A water temperature of 0 °C resulted in a slow floc growth and small floc size. Although the floc growth rates at 4 °C and 1 °C were less than those at 22 °C, they were higher than at 0 °C. To improve aggregation processes at low water temperature, adding the coagulant aid of anionic copolymer of acrylamide into the water was found to be effective when the temperature was not less than 1 °C. However, it made only a slight impact on aggregation when the temperature approached 0 °C. At water temperatures of 22 °C, 4 °C and 1 °C, the polymer caused the formation of large floc (larger than 0.5 mm2 in projected area). The polymer significantly shortened the required time of flocculation and sedimentation. Three minutes of flocculation and 20 minutes of sedimentation were sufficient for the polymer to achieve good treatment performance, while the flocculation time and sedimentation time had to be 20 and 60 minutes, respectively, without using the polymer. On the other hand, when the temperature was close to 0 °C, the polymer did not cause the formation of the large floc, nor did it shorten the time of flocculation and sedimentation.<p> The experimental results in this research agree with the model for flocculation kinetics given by Argaman and Kaufman (1970). With decreasing water temperature, the aggregation constant (KA) decreased and breakup constant (KB) increased. KA and KB with aluminum sulfate was close to those with ferric sulfate, respectively. <p> In treating the South Saskatchewan River water, an aluminum sulfate or ferric sulfate dosage greater than 50 mg/L resulted in marginal gains in treatment efficiency. Decreasing dosages of aluminum sulfate or ferric sulfate caused lower floc growth rates and smaller floc sizes. Extremely low dosages (5 mg/L or less) resulted in poor floc formation and extremely small sizes.

The coagulation/flocculation process is an important part of surface water treatment. It has direct impact on the reliability of plant operations and final water qualities together with cost control. Low water temperature has a significant impact on the operation of drinking water treatment plants, especially on coagulation/flocculation processes.<p> A microscopic image technique has been used to study the coagulation and flocculation process in recent years, but it requires sample handling that disturbs the floc characteristics during measurement. A high resolution photographic technique was applied to evaluate flocculation processes in the present work. With this technique, the images of the flocs were obtained directly while the flocculation process was taking place. In combination with camera control software and particle size analysis software, this procedure provided a convenient means of gathering data to calculate size distribution. Once the size distribution was calculated, the floc growth and floc size change in the aggregation process could be analyzed. Results show that low water temperature had a detrimental impact on aggregation processes. A water temperature of 0 °C resulted in a slow floc growth and small floc size. Although the floc growth rates at 4 °C and 1 °C were less than those at 22 °C, they were higher than at 0 °C. To improve aggregation processes at low water temperature, adding the coagulant aid of anionic copolymer of acrylamide into the water was found to be effective when the temperature was not less than 1 °C. However, it made only a slight impact on aggregation when the temperature approached 0 °C. At water temperatures of 22 °C, 4 °C and 1 °C, the polymer caused the formation of large floc (larger than 0.5 mm2 in projected area). The polymer significantly shortened the required time of flocculation and sedimentation. Three minutes of flocculation and 20 minutes of sedimentation were sufficient for the polymer to achieve good treatment performance, while the flocculation time and sedimentation time had to be 20 and 60 minutes, respectively, without using the polymer. On the other hand, when the temperature was close to 0 °C, the polymer did not cause the formation of the large floc, nor did it shorten the time of flocculation and sedimentation.<p> The experimental results in this research agree with the model for flocculation kinetics given by Argaman and Kaufman (1970). With decreasing water temperature, the aggregation constant (KA) decreased and breakup constant (KB) increased. KA and KB with aluminum sulfate was close to those with ferric sulfate, respectively. <p> In treating the South Saskatchewan River water, an aluminum sulfate or ferric sulfate dosage greater than 50 mg/L resulted in marginal gains in treatment efficiency. Decreasing dosages of aluminum sulfate or ferric sulfate caused lower floc growth rates and smaller floc sizes. Extremely low dosages (5 mg/L or less) resulted in poor floc formation and extremely small sizes.

Poor settling of solids increases land requirement for tailings containment and imposes severe constraints on the water balance. Consequent to these considerations, the alternating current electrocoagulation (AC/EC) technique emerged as a candidate for enhancing the settling behaviour of suspensions in the mineral, coal and oil sands industries. Hence, a fundamental study of AC/EC was undertaken with aluminum electrodes. Ground silica (d50 = 20 m), which formed a stable suspension, served as the model tailings solid at 5.0 wt % in water. The AC/EC process consisted of two developmental stages: coagulation, marked by pH decrease in the silica suspension; and floc growth, characterized by pH increase from the minimum (i.e., the end of coagulation). AC/EC enhanced the initial settling rate of silica by over three orders of magnitude, and exhibited remarkable flexibility by virtue of the wide range of process parameters that could be optimized. For example, AC/EC can be operated in either the indirect or direct mode. The settling behaviour of bentonite (estimated d50 < 1 m) was more enhanced by indirect AC/EC, while that of silica benefited more from direct AC/EC. Any condition that increased aluminum dosage (e.g., current, retention time), increased the initial settling rate of silica. Over the feed water pH range of 3.0 to 9.1, AC/EC was effective in enhancing the settling behaviour of silica. AC/EC was also effective over a wide range of temperatures (23 to 85C). High electrical energy demand by AC/EC was observed throughout this study. Its optimization was beyond the scope of this work. Dilution of a sample of Syncrude mature fine tailings (MFT) to 4.6 wt % solids sustained a stable suspension. Settling occurred after AC/EC treatment, a crystal-clear supernatant resulted and bitumen was recovered as froth. Entrained solids were easily spray-washed from the froth with water. The settling behaviour of a Luscar Sterco fine coal tailings sample was not augmented by AC/EC, possibly due to contamination by the companys own electrocoagulation operation. After having been stored dry for more than a year, electrocoagulated silica was an effective coagulant for as-received silica and Syncrude MFT. / Chemical Engineering

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