This study was aimed to evaluate the performance of water treatment processes and to find the critical control points in treating protozoan oocysts, which is known as the most resistant microorganisms against chlorine disinfection, to assure the safe water supply. The study consists of i) evaluation...
This study was aimed to evaluate the performance of water treatment processes and to find the critical control points in treating protozoan oocysts, which is known as the most resistant microorganisms against chlorine disinfection, to assure the safe water supply. The study consists of i) evaluation of protozoan detection methodology for both removal and inactivation processes, ii) bench-scale study of the separate unit process for protozoan control by column and jar-test, and iii) pilot-scale study for the protozoan removal with conventional and/or advanced water treatment systems. For the third year study, small scale pilot column test for rapid filtration, and large scale pilot test for conventional water treatment and advanced post-ozone treatment were performed under the various conditions to estimate the separate and combined sequential unit processes. The environmental and operational parameters were monitored and evaluated with the Cryptosporidium oocysts and its surrogates. The followings are the summary of this study. 1) The rapid filtration tests were performed with small scale pilot with 40 mm x 3,600 mm column. The removals of Cryptosporidium were studied under the additional 6 different operating conditions, which were various in types of media (anthracite/sand dual media with two different packing conditions of 50:25, and 45:30), water flow (170 m/day and 360 m/day), and intake water turbidity. The log removals of Cryptosporidium were >4 log at the suitable operating conditions. Under the conditions with high water flow and high intake water turbidity, the removal decreased. After the backwash, the log removals were reduced to 1.12~3.15 at the filter ripening stages, which were similar to the previous studies. 2) For the dual media, the removal of the Cryptosporidium were significantly affected by the intake water turbidity, water flow and the composition of the media in order, in contrast to the sand media, which were not affected significantly by the water quality, although the highly turbid water increased the load on the filter media, indicated by the increment of the pressure drop. The dual media seems to affect the filtration breakthrough. The filtrate of dual media showed the consistent increment of the turbidity and total particle counts(TPC) during the whole operation period as well as after the effective filtration stage whose filtered water turbidity were under the 0.3 NTU. Therefore, the monitoring the filtered water turbidity and its breakthrough were critical for rapid filtration, especially with the dual media. The TPC and 4~7 μm particles fit well with the turbidity especially when the column operated optimally. 4~7 μm particles fit better when the operation conditions were not favorable for removal. 3) The relation between the removal of Cryptosporidium oocyst and fluorescence bead called cryptracer were tested in the small scale pilot of rapid filtration, to evaluate usage of the cryptracer as the surrogate of Cryptosporidium. The results showed that cryptracer tended to be removed less effectively than Cryptosporidium, and that the removal of the cryptrace were highly related with the removal of Cryptosporidium with regression analysis (r2=0.83). Therefore, cryptracer were used as a conservative surrogate. 4) The large scale pilot with sand filtration practiced PAC as a coagulant. The spike tests with cryptracer(107/L, final conc.) were performed 4 times with the intake waters whose turbidity ranged from 1.2 to 51.8 NTU. The removal of the Cryptosporidium at the whole procedures were higher than 4 log except one condition (experiment 1). The turbidity of the filtered water at the experiment 2,3 and 4 were maintained under 0.2 NTU. In the experiment 1, the intake water turbidity were unusually high due to the rainfall, and the log removal was 2.66. The turbidity of the filtered water of the experiment 1 reduced from 10 NTU to 0.5 NTU. Therefore, keeping the turbidity of the filtered water under the 0.3 NTU was critical. The log removal at the coagulation-flocculation-sedimentation process were 0.53 for experiment 1 and about 1 for rest of the experiments. The particle distribution of the intake water and filtered water has not changed significantly. 5) The disinfection ability of ozone on Cryptosporidium were studied with the 40 L scale ozone reactors. The experiment was performed at 9 ℃ using filtered water. Due to the limitation of the reactor, CT were controled with constant contact time (5 minute) and various ozone concentrations from zero to 1.7 mg/L. At the 8 mg/L·min, the highest CT values of this experiment, the live Cryptosporidium inactivated 0.2 log by DAPI/PI and excystation method, and inactivated 1.0 log by cell culture method. Therefore, DAPI/PI and excystation tended to underestimate the disinfection ability of ozone in comparison to the cell culture method.
This study was aimed to evaluate the performance of water treatment processes and to find the critical control points in treating protozoan oocysts, which is known as the most resistant microorganisms against chlorine disinfection, to assure the safe water supply. The study consists of i) evaluation of protozoan detection methodology for both removal and inactivation processes, ii) bench-scale study of the separate unit process for protozoan control by column and jar-test, and iii) pilot-scale study for the protozoan removal with conventional and/or advanced water treatment systems. For the third year study, small scale pilot column test for rapid filtration, and large scale pilot test for conventional water treatment and advanced post-ozone treatment were performed under the various conditions to estimate the separate and combined sequential unit processes. The environmental and operational parameters were monitored and evaluated with the Cryptosporidium oocysts and its surrogates. The followings are the summary of this study. 1) The rapid filtration tests were performed with small scale pilot with 40 mm x 3,600 mm column. The removals of Cryptosporidium were studied under the additional 6 different operating conditions, which were various in types of media (anthracite/sand dual media with two different packing conditions of 50:25, and 45:30), water flow (170 m/day and 360 m/day), and intake water turbidity. The log removals of Cryptosporidium were >4 log at the suitable operating conditions. Under the conditions with high water flow and high intake water turbidity, the removal decreased. After the backwash, the log removals were reduced to 1.12~3.15 at the filter ripening stages, which were similar to the previous studies. 2) For the dual media, the removal of the Cryptosporidium were significantly affected by the intake water turbidity, water flow and the composition of the media in order, in contrast to the sand media, which were not affected significantly by the water quality, although the highly turbid water increased the load on the filter media, indicated by the increment of the pressure drop. The dual media seems to affect the filtration breakthrough. The filtrate of dual media showed the consistent increment of the turbidity and total particle counts(TPC) during the whole operation period as well as after the effective filtration stage whose filtered water turbidity were under the 0.3 NTU. Therefore, the monitoring the filtered water turbidity and its breakthrough were critical for rapid filtration, especially with the dual media. The TPC and 4~7 μm particles fit well with the turbidity especially when the column operated optimally. 4~7 μm particles fit better when the operation conditions were not favorable for removal. 3) The relation between the removal of Cryptosporidium oocyst and fluorescence bead called cryptracer were tested in the small scale pilot of rapid filtration, to evaluate usage of the cryptracer as the surrogate of Cryptosporidium. The results showed that cryptracer tended to be removed less effectively than Cryptosporidium, and that the removal of the cryptrace were highly related with the removal of Cryptosporidium with regression analysis (r2=0.83). Therefore, cryptracer were used as a conservative surrogate. 4) The large scale pilot with sand filtration practiced PAC as a coagulant. The spike tests with cryptracer(107/L, final conc.) were performed 4 times with the intake waters whose turbidity ranged from 1.2 to 51.8 NTU. The removal of the Cryptosporidium at the whole procedures were higher than 4 log except one condition (experiment 1). The turbidity of the filtered water at the experiment 2,3 and 4 were maintained under 0.2 NTU. In the experiment 1, the intake water turbidity were unusually high due to the rainfall, and the log removal was 2.66. The turbidity of the filtered water of the experiment 1 reduced from 10 NTU to 0.5 NTU. Therefore, keeping the turbidity of the filtered water under the 0.3 NTU was critical. The log removal at the coagulation-flocculation-sedimentation process were 0.53 for experiment 1 and about 1 for rest of the experiments. The particle distribution of the intake water and filtered water has not changed significantly. 5) The disinfection ability of ozone on Cryptosporidium were studied with the 40 L scale ozone reactors. The experiment was performed at 9 ℃ using filtered water. Due to the limitation of the reactor, CT were controled with constant contact time (5 minute) and various ozone concentrations from zero to 1.7 mg/L. At the 8 mg/L·min, the highest CT values of this experiment, the live Cryptosporidium inactivated 0.2 log by DAPI/PI and excystation method, and inactivated 1.0 log by cell culture method. Therefore, DAPI/PI and excystation tended to underestimate the disinfection ability of ozone in comparison to the cell culture method.
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