Degradation of cyanotoxin cylindrospermopsin by TiO2-assisted ozonation in water.

The stable tricyclic structure of the cylindrospermopsin (CYN), a cynotoxin, has presented several challenges to water treatment facilities, as conventional treatment methods have a limited ability to remove it from water. This study examines the effectiveness of titanium dioxide (TiO2) in catalytic ozonation for degrading CYN. The chemical kinetics of the reactions of ozone (O3) and hydroxyl radicals (OH(•)) with CYN were determined. The results reveal that TiO2 significantly increases the rate of degradation of CYN by increasing the rate of production of hydroxyl radicals (OH(•)) by initiating the decomposition of O3 on the surface of the catalyst. At a pH of 7 with 1.0 mg L(-1) O3 and 500 mg L(-1) TiO2; the pseudo-first-order ozone decomposition rate constant (k(D)) increased from 3.04 × 10(-3) to 16.53 × 10(-3) s(-1) and the ratio of OH(•) to O3 concentrations (R(ct)) increased from 1.87 × 10(-8) to 126.4 × 10(-8). The calculated second-order rate constant (k(overall)) of the reaction of CYN with O3 and OH(•) was 3.22 M(-1)s(-1) without TiO2. However, the greatest improvement in k(overall) in this study was observed using 500 mg TiO2 L(-1), which increased koverall by a factor of five. TiO2-catalyzed ozonation is an efficient method of oxidation that reduces the toxic activity of CYN. The results of a Microtox test concerning the toxic activity of CYN during oxidation reveal that catalytic ozonation may either increase or reduce the toxicity of CYN toward test samples. The toxic effects of CYN on the samples are greatly influenced by the TiO2 dosage and reaction time, possibly yielding by-products that may change the mutagenic properties of CYN. Three water samples from a eutrophic lake in Taiwan were examined to evaluate the effect of dissolved organic carbon (DOC) and alkalinity on the oxidation of CYN. DOC had the greatest effect on the oxidation of CYN in the ozonation of eutrophic water. Overall, the degree of CYN oxidation depended on the rate constant of the reaction with ozone and the consumption of ozone by the natural water matrix.

Bioaccumulation and toxicity of arsenic in cyanobacteria cultures separated from a eutrophic reservoir.

The bioaccumulation and toxicity of arsenate (arsenic (As)(V)) was studied using three cultures of cyanobacterial species-Oscillatoria tenuisa, Anabaena affinis, and Microcystis aeruginosa-that were isolated from a eutrophic reservoir. The As(V) uptake depended on the cyanobacterial species, the growth phase of the cyanobacteria, the duration of exposure, and the initial concentration of As(V). The specific growth rates of the three cultures immediately following the logarithmic phase were 0.033-0.041 L/day when the initial concentration of As(V) was 50 mg/L. These rates were 2.3-3.6 times less than those in the original culture medium without As(V). The rate of intake of As(V) in the logarithmic phase cultures greatly exceeded that in the stationary cultures. The accumulation of As(V) by the three cultures increased rapidly within 1 week from the initial value of 3.23 × 10(-2)-5.40 × 10(-2) to 5.06 × 10(-1)-6.73 × 10(-1) ng/cell in the logarithmic phase. The effective concentrations (EC50) of As(V) for inhibiting the growth of the three cyanobacterial species growth of at 72 h followed the order Oscillatoria tenuisa (3.8 mg/L) > A. affinis (2.6 mg/L) > M. aeruginosa (1.2 mg/L). The cyanobacterial species that was most sensitive to As(V) was M. aeruginosa. Preliminary results from SEM-map studies suggest most of the As(V) in Microcystis aeruginosa accumulated in the cytoplasm (intercellular), while in O. tenuisa and A. affinis, a large proportion of As(V) bound to the cell wall (extracellular). These differences were understood with reference to the variation among the metabolic properties and morphological characteristics of the cyanobacterial species.

Effects of Al-coagulant sludge characteristics on the efficiency of coagulants recovery by acidification.

This study evaluated the effects of Al-coagulant sludge characteristics on the efficiency ofcoagulant recovery by acidification with H2SO4. Two sludge characteristics were studied: types of coagulant and textures of the suspended solid in raw water. The coagulant types are aluminium sulphate and polyaluminium chloride (PACl); the textures of the suspended solid are sand-based and clay-based. Efficiency of aluminium recovery at a pH of 2 was compared for different sludges obtained from water treatment plants in Taiwan. The results showed that efficiency of aluminium recovery from sludge containing clayey particles was higher than that from sludge containing sandy particles. As for the effect of coagulant types, the aluminium recovery efficiency for sludge using PACl ranged between 77% and 100%, whereas it ranged between 65% and 72% for sludge using aluminium sulphate as the coagulant. This means using PACl as the coagulant could result in higher recovery efficiency of coagulant and be beneficial for water treatment plants where renewable materials and waste reduction as the factors for making decisions regarding plant operations. However, other metals, such as manganese, could be released with aluminium during the acidification process and limit the use of the recovered coagulants. It is suggested that the recovered coagulants be used in wastewater treatment processes.

The influence of neonatal intensive care unit design on sound level.

BACKGROUND: Excessive noise in nurseries has been found to cause adverse effects in infants, especially preterm infants in neonatal intensive care units (NICUs). The NICU design may influence the background sound level. We compared the sound level in two differently designed spaces in one NICU. We hypothesized that the sound level in an enclosed space would be quieter than in an open space. METHODS: Sound levels were measured continuously 24 hours a day in two separate spaces at the same time, one enclosed and one open. Sound-level meters were placed near beds in each room. Sound levels were expressed as decibels, A-weighted (dBA) and presented as hourly L(eq), L(max), L(10), and L(90). RESULTS: The hourly L(eq) in the open space (50.8-57.2dB) was greater than that of the enclosed space (45.9-51.7dB), with a difference of 0.4-10.4dB, and a mean difference of 4.5dB (p<0.0001). The hourly L(10), L(90), and L(max) in the open space also exceeded that in the enclosed space (p<0.0001). CONCLUSION: The sound level measured in the enclosed space was quieter than in the open space. The design of bed space should be taken into consideration when building a new NICU. Besides the design of NICU architecture, continuous monitoring of sound level in the NICU is important to maintain a quiet environment.

Control of disinfection byproduct formation in Feng-Shan reservoir by the traditional treatment processes plus O3-pilot-plant test.

Two processes in the pilot plant were studied and compared to reduce the disinfection byproduct risk of the potable finished water of Feng-shan treatment utility in Taiwan. For 5 months study, two processes have both demonstrated to achieve a significant removal on the organic precursors of DBPs, including NPDOC and A-254. With the analysis of molecular weight distribution of organics in raw water, the study found the post ozonation plus BAC can provide additional enhancement in degrading organic contents. A process of coagulation/sedimentation/rapid sand filtration/post ozonation/BAC would be suggested as the advanced treatment process improving the supply quality of Feng-shan utility.

Treatment of landfill leachate by ozone-based advanced oxidation processes.

In this study, laboratory experiments are conducted to compare the efficacy using several ozone-based advanced oxidation processes (AOPs), such as O3, O3/H2O2, and O3/UV, to treat landfill leachate. Raw leachate was initially coagulated by ferric chloride (FeCl3) at the experimental-determined optimal dosage of 900 mgl(-1), and the ozone-based AOPs were subsequently applied. Results indicate that all AOPs would result in a significant increase on the ratio of BOD5/COD from 0.06 to 0.5 at the applied ozone dosage of 1.2 gl(-1). The increase on biodegradability for ozonated leachate indicates that these AOPs would be beneficial to the subsequent biological treatment process. To better explain the alteration of high organic molecules after oxidation, ultrafiltration was used to separate the leachate by several molecular weight cutoffs (MWCO). The COD distribution for coagulated leachate is 34% for MWCO>10 kDa, 7% for MWCO between 5 and 10 kDa, 22% for MWCO between 1 and 5 kDa, and 37% for MWCO<1 kDa. Following ozonation or AOPs, the predominant distribution of COD would be obviously shifted to the MWCO less than 1000 gmol(-1) (72-85%) over the other MWCO ranges. In addition, Gel Permeation Chromatograph (GPC) analysis has showed a substantial agreement on the cleavage of larger organic compounds into smaller ones. O3/UV was found to be the most effective approach among these ozone-based AOPs to enhancing the biodegradability and eliminating the color of leachate.