Wencui Ling

Development of systems for detection, early warning, and control of pipeline leakage in drinking water distribution: A case study

Water leakage in drinking water distribution systems is a serious problem for many cities and a huge challenge for water utilities. An integrated system for the detection, early warning, and control of pipeline leakage has been developed and successfully used to manage the pipeline networks in selected areas of Beijing. A method based on the geographic information system has been proposed to quickly and automatically optimize the layout of the instruments which detect leaks. Methods are also proposed to estimate the probability of each pipe segment leaking (on the basis of historic leakage data), and to assist in locating the leakage points (based on leakage signals). The district metering area (DMA) strategy is used. Guidelines and a flowchart for establishing a DMA to manage the large-scale looped networks in Beijing are proposed. These different functions have been implemented into a central software system to simplify the day-to-day use of the system. In 2007 the system detected 102 non-obvious leakages (i.e., 14.2% of the total detected in Beijing) in the selected areas, which was estimated to save a total volume of 2,385,000 m3 of water. These results indicate the feasibility, efficiency and wider applicability of this system.

Kinetics and mechanism for omethoate degradation by catalytic ozonation with Fe(III)-loaded activated carbon in water.

The kinetics and mechanism for degradation of omethoate (OMT) by catalytic ozonation with Fe(III)-loaded activated carbon (Fe@AC) were investigated in this study with focus on identification of degradation byproducts. The rate constants of OMT reacting with ozone and hydroxyl radical ((·)OH) were determined to be 0.04 and 5.3×10(8) M(-1) s(-1) at pH 7.5 and 20 °C, respectively. OMT was predominantly degraded by ()OH in the catalytic ozonation with Fe@AC. The high-molecular-weight degradation byproducts identified were O,O,O-trimethyl phosphoric ester (TMP), pyrrolidin-2-one, N-methyl-2-sulfanylacetamide, 2-(methylthio)acetamide, O,O,S-trimethylthiophosphate (STMP), and N-methyl-2-(methylthio)acetamide. Besides, low-molecular-weight organic acids and inorganic anions were also detected and quantified, including formic, acetic and oxalic acids as well as nitrate, sulfate and phosphate ions. In the catalytic ozonation, TMP and phosphate were two major P-containing byproducts resulting from OMT degradation. The toxicity of OMT solution gradually decreased during the catalytic ozonation, indicating that Fe@AC is a safe catalyst for OMT removal by ozone in water.

A comparison of disinfection by-products formation during sequential or simultaneous disinfection of surface waters with chlorine dioxide and chlor(am)ine

The effect of chlorine dioxide (ClO2) oxidation on the formation of disinfection by-products (DBPs) during sequential (ClO2 pre-oxidation for 30 min) and simultaneous disinfection processes with free chlorine (FC) or monochloramine (MCA) was investigated. The formation of DBPs from synthetic humic acid (HA) water and three natural surface waters containing low bromide levels (11–27 μg/L) was comparatively examined in the FC-based (single FC, sequential ClO2-FC, and simultaneous ClO2/FC) and MCA-based (single MCA, ClO2-MCA, and ClO2/MCA) disinfection processes. The results showed that much more DBPs were formed from the synthetic HA water than from the three natural surface waters with comparative levels of dissolved organic carbon. In the FC-based processes, ClO2 oxidation could reduce trihalomethanes (THMs) by 27–35% and haloacetic acids (HAAs) by 14–22% in the three natural surface waters, but increased THMs by 19% and HAAs by 31% in the synthetic HA water after an FC contact time of 48 h. In the MCA-based processes, similar trends were observed although DBPs were produced at a much lower level. There was an insignificant difference in DBPs formation between the sequential and simultaneous processes. The presence of a high level of bromide (320 μg/L) remarkably promoted the DBPs formation in the FC-based processes. Therefore, the simultaneous disinfection process of ClO2/MCA is recommended particularly for waters with a high bromide level.

Effective Inhibition of Bromate Formation with a Granular Molecular Sieve Catalyst Ce-MCM-48 during Ozonation: Pilot-Scale Study

The inhibition of bromate (BrO − ) formation during ozonation with a novel granular molecular sieve catalyst, Ce-MCM-48, was investigated in pilot-scale under simulated practical conditions by varying the initial bromide (Br − ) concentration, total organic carbon (TOC) content, aqueous ozone concentration, water pH, and hydraulic retention time (HRT). The results indicate that the inhibition efficiency of Ce-MCM-48 for BrO − formation could reach 82-90% as the initial Br − concentration varied from 200-800 μg=L under typical water treat- ment conditions: aqueous ozone concentration ¼ 2.0 � 0.1 mg=L, HRT ¼ 10 min, initial pH ¼ 7.7-7.9, and T ¼ 18 � 2°C. The extension of HRT from 10 to 20 min and pH variation in the range of 6.0-9.0 had insignificant impact on the inhibition efficiency of BrO − formation. Compared with ozonation alone, the catalytic ozonation could achieve almost the same efficiencies for TOC removal and Escherichia coli inactivation. A long-term continuous operation experiment for 33 days demonstrated that the granular catalyst Ce-MCM-48 possesses not only a high efficiency, but also a large treatment capacity for minimizing BrO − formation during the ozonation process, and thus has potential applications to water treatment. DOI: 10.1061/(ASCE)EE.1943-7870.0000585.

Ozonation of norfloxacin and levofloxacin in water: Specific reaction rate constants and defluorination reaction

The degradation kinetics and mechanism of two typical fluoroquinolones (FQs), norfloxacin (NF) and levofloxacin (LOF), by ozone in water were investigated. Semi-continuous mode and competition kinetics mode experiments were conducted to determine the reaction rate constants of target FQs with ozone and OH, separately. Results indicate that both NF and LOF were highly reactive toward ozone, and the reactivity was strongly impacted by the solution pH. The specific reaction rate constants of the diprotonated, monoprotonated and deprotonated species were determined to be 7.20 × 102, 8.59 × 103, 4.54 × 105 M-1 s-1 respectively for NF and 1.30 × 103, 1.40 × 104, 1.33 × 106 M-1 s-1 respectively for LOF. The reaction rate constants of target FQs toward OH were measured to be (4.81-7.41) × 109 M-1 s-1 in the pH range of 6.3-8.3. Furthermore, NF was selected as a model compound to clarify the degradation pathways, with a particular focus on the defluorination reaction. The significant release of F- ions and the formation of three F-free organic byproducts indicated that defluorination was a prevalent pathway in ozonation of FQs, while six F-containing organic byproducts indicated that ozone also attacked the piperazinyl and quinolone moieties. Escherichia coli growth inhibition tests revealed that ozonation could effectively eliminate the antibacterial activity of target FQ solutions, and the residual antibacterial activity had a negative linear correlation with the released F- concentration.