In this study, the effects of operating conditions on the formation of reversible and irreversible fouling were investigated in the filtration using ceramic membrane for water treatment process. The effect of coagulation pretreatment on fouling formation was also evaluated by comparing the performance of membrane filtration both with and without addition of coagulant. A resistance-in-series-model was applied for the analysis of membrane fouling. Total resistance (RT) and internal fouling resistance (Rf) increased in the membrane filtration process without coagulation as membrane flux and feed water concentrations increased. Internal fouling resistance, which was not recovered by physical cleaning, was more than 70% of the total resistance at the range of the membrane flux more than 5 m3/m2･day. In the combined process with coagulation, the cake layer resistance (Rc) increased to about 30-80% of total resistance. As the cake layer formed by coagulation floc was easily removed by physical cleaning, the recovery rate by physical cleaning was 54~90%. It was confirmed from the results that the combined process was more efficient to recover the filtration performance by physical cleaning due to higher formation ratio of reversible fouling, resulted in the mitigation of the frequency of chemical cleaning.
This study aimed to investigate the feasibility of improving dewaterability and settleability of sewage sludge using coagulation sludge. When mixed with sewage sludge and coagulation sludge at 1:1 ratio, capillary suction time(CST) and specific resistance to filtration(SRF) decreased by about 56% and 68%, respectively. It is found that total solids(TS) and volatile solids(VS) of mixing sludge are increased by about 59% and 53%, respectively. Also, the turbidity of the mixing sludge supernatant was reduced from 99 to 16 NTU. It is observed that the mixing of sewage sludge and coagulation sludge at 1:1 showed better effect than using poly-aluminum chloride(PAC) coagulant at 25 mg/L.
In this study, the effect of chemically enhanced backwash(CEB) coping with algal(Heterosigma Akashiwo) inflow was evaluated in the seawater desalination pretreatment process using ceramic membrane. In order to confirm the possibility of long-term filtration operation, the recovery rate of transmembrane pressure(TMP) due to the CEB using NaOCl was examined. When the membrane flow rate was 83.3 LMH, the TMP was maintained within 200 kPa for 84 hours in seawater influent. As the algal counts of 30,000 cell/mL were injected into the influent of seawater, however, the TMP rapidly increased and exceed maximum value. Membrane fouling caused by the algae was very poorly recovered by usual physical backwash. The CEB was performed for 30 min(3 min circulation / 27 min immersion) with 300 mg/L of NaOCl. As a result of the CEB application, it was possible to maintain a stable operating of filtration during 10 days and the average recovery rate of TMP by the CEB was 98.1%. It has been confirmed that the CEB using NaOCl is very effective in removal of membrane fouling by algae, resulted in stable membrane filtration for the long-term operation.
Maintaining adequate residual chlorine concentration is an important criteria to provide secure drinking water. The chlorine decay can be influenced by unstable flow due to the transient event caused by operation of hydraulic devices in the pipeline system. In order to understand the relationship between the transient event and the chlorine decay, the probability density function based on the water demand curve of a hypothetical water distribution system was used. The irregular transient events and the same number of events with regular interval were assumed and the fate of chlorine decay was compared. The chlorine decay was modeled using a generic chlorine decay model with optimized parameters to minimize the root mean square error between the experimental chlorine concentration and the simulated chlorine concentration using genetic algorithm. As a result, the chlorine decay can be determined through the number of transients regardless of the occurrence intervals.
Direct spring loaded pressure relief valve(DSLPRV) is a safety valve to relax surge pressure of the pipeline system. DSLPRV is one of widely used safety valves for its simplicity and efficiency. However, instability of the DSLPRV can caused by various reasons such as insufficient valve volume, natural vibration of the spring, etc. In order to improve reliability of DSLPRV, proper selection of design factors of DSLPRV is important. In this study, methodology for selecting design factors for DSLPRV was proposed. Dynamics of the DSLPRV disk was integrated into conventional 1D surge pressure analysis. Multi-objective genetic algorithm was also used to search optimum design factors for DSLPRV.
This paper provided the information related to the removal of 2,4,6-tribromophenol using in-situ and stable liquid ferrates(VI). This research’s goal was to observe the differences of oxidation power between in-situ liquid ferrate(VI) and stable liquid ferrate(VI). The in-situ liquid ferrate(VI) (FeO4 2-) has been successfully produced with the concentration 42,000 ppm (Fe) after 11 minutes of reaction time. The stable liquid ferrate(VI) was also successfully produced following the modification method by Sharma with the produced concentrations 7,000 ppm. The stable liquid ferrate(VI) was stable for 44 days and slightly decreased afterwards. This research has been carried out using 2,4,6-tribromophenol as the representative compound. Both of ferrates(VI) have the highest oxidation capability at the neutral condition. Furthermore, the stable liquid ferrate(VI) has higher oxidation power than the in-situ liquid ferrate(VI).
Phosphorus (P) is a limited, essential, and irreplaceable nutrient for the biological activity of all the living organisms. Sewage sludge ash (SSA) is one of the most important secondary P resources due to its high P content. The SSA has been intensively investigated to recover P by wet chemicals (acid or alkali). Even though H2SO4 was mainly used to extract P because of its low cost and accessibility, the formation of CaSO4 (gypsum) hinders its use. Heavy metals in the SSA also cause a significant problem in P recovery since fertilizer needs to meet government standards for human health. Therefore, P recovery process with selective heavy metal removal needs to be developed. In this paper some of the most advanced P recovery processes have been introduced and discussed their technical characteristics. The results showed that further research is needed to identify the chemical mechanisms of P transformation in the recovery process and to increase P recovery efficiency and the yields.
This study is focused on manganese (Mn(II)) removal by ozonation in surface water. Instant ozone demand for the water was 0.5 mg/L in the study. When 0.5 mg/L of Mn(II) is existed in water, the optimum ozone concentration was 1.25 mg/L with reaction time 10 minutes to meet the drinking water regulation. The ozone concentration to meet the drinking water regulation was much higher than the stoichiometric concentration. The reaction of soluble manganese removal was so fast that the reaction time does not affect the removal dramatically. When Mn(II) is existed with Fe, the removal of Mn(II) was not affected by Fe ion. However As(V) is existed as co-ion the removal of Mn(II) was decreased by 10%. Adding ozone to surface water has limited effect to remove dissolved organic matter. When ozone is used as oxidant to remove Mn(II) in the water, the existing co-ion should be evaluated to determine optimum concentration.
In this study, effects of nutrient and inorganic carbon on single cell emergence during the cultivation of microalgae were observed using colonial green algae, Pediastrum duplex. The concentration of inorganic carbon had significant effect on single cell emergence and its growth, but nitrogen and phosphorus concentration showed minor effects. According to P. duplex cultivation experiment, single cell started to be emerged around 500~750 mg-C/L of inorganic carbon concentration and it was bloomed dramatically at the higher values. And growth of P. duplex was started to be surpressed at the single cell formation concentration. From the results, it could be said that when we operate the microalgae systems for cultivation/harvesting or wastewater treatment, in order to avoid single cell formation, inorganic carbon should be maintained to the proper level
Climate change is believed to increase the amount of dissolved organic matter in surface water, as a result of the release of bulk organic matter, which make difficult to achieve a high quality of drinking water via conventional water treatment techniques. Therefore, the natural water treatment techniques, such as managed aquifer recharge (MAR), can be proposed as a alternative method to improve water quality greatly. Removal of bulk organic matter using managed aquifer recharge system is mainly achieved by biodegradation. Biodegradable dissolved organic carbon (BDOC) and assimilable organic carbon (AOC) can be used as water quality indicators for biological stability of drinking water. In this study, we compared the change of BDOC and AOC with respect to pretreatment methods (i.e., ozone or peroxone). The oxidative pretreatment can transform the recalcitrant organic matter into readily biodegradable one (i.e., BDOC and AOC). We also investigated the differences of organic matter characteristics between BDOC and AOC. We observed the decreases in dissolved organic carbon (DOC) and the tryptophan-like fluorescence intensities. Liquid chromatographic - organic carbon detection (LC-OCD) analysis also showed the reduction of the low molecular weight (LMW) fraction (15% removed, less than 500 Da), which is known to be easily biodegradable, and the biopolymers, high molecular weight fractions (66%). Therefore, BDOC consists of a broad range of organic matter characteristics with respect to molecular weight. In AOC, low molecular weight organic matter and biopolymers fraction was reduced by 11 and 6%, respectively. It confirmed that biodegradation by microorganisms as the main removal mechanism in AOC, while BDOC has biodegradation by microorganism as well as the sorption effects from the sand. O3 and O3 + H2O2 were compared with respect to biological stability and dissolved organic matter characteristics. BDOC and AOC were determined to be about 1.9 times for O3 and about 1.4 times for O3 + H2O2. It was confirmed that O3 enhanced the biodegradability by increasing LMW dissolved organic matter.
For performance analysis of flood prevention projects, this study performed simulation (SWMM) for the five sites where the projects have been completed. The models were constructed using watershed and sewer information of the project sites and were verified using flood records in the past to improve accuracy. In this simulation, the design rainfall data (probability 30~50 years) and the rainfall data in the summer of 2017 were applied. When the design rainfall data was applied to the models, simulation results presented that all the sites were flooded before the projects, but after the projects all the sites were not flooded due to improve discharge capacity. And when the rainfall data in the summer of 2017 was applied to the models, simulation results presented that all the sites were flooded before the projects, but after the projects any sites did not occur flooding in this summer. So if the projects had not been completed, all the sites might be flooded in the summer of 2017. These effects were analyzed as the improvement of discharge capacity due to rehabilitation of sewer, construction of underground tunnel and pumping station, etc. As the results, ratio of sewer that water depth exceed diameter reduced from 52.3~75.8% to 17.1~39.8%.
Applicability of corrosion inhibitor was evaluated using pilot scale water distribution pipe simulator. Calcium hydroxide was used as corrosion inhibitor and the corrosion indices of the water were investigated. Corrosion indices, Langelier saturation index (LI) increased by 0.8 and calcium carbonate precipitation potential (CCPP) increased by 9.8 mg/L. This indicated that corrosivity of water decreased by corrosion inhibitor and the effects lasted for 18 days. Optimum calcium hydroxide dose was found to be 3~5 mg/L for corrosion inhibition. We suggest that monitoring of CCPP as well as LI need to be conducted to control corrosivity of water.
Owing to the development in information and communications technologies have improved the technology for high-speed transmission of massive data, which has changed closed-circuit television (CCTV) video transmission technology. In particular, digitization of the CCTV video format and streaming technology has made it possible to minimize transmission loss and integrate video transmission and camera control(pan/tilt). It has also become possible to provide additional services like remote emergency warning broadcasting with just Internet Protocol (IP). However, because of the structural problems of IP, these changes have also brought about the threat of hacking of CCTV monitoring systems. In this study, we propose a methode to optimize network management by examining cases of enhancement of operational efficiency and security by improving the structure of CCTV monitoring network.