A Glass-Fiber-Optic Turbidity Sensor for Real-Time In Situ Water Quality Monitoring

Turbidity is an important water quality parameter, especially for drinking water. The ability to actively monitor the turbidity level of drinking water distribution systems is of critical importance to the safety and wellbeing of the public. Traditional turbidity monitoring methods involve the manual collection of water samples at set locations and times followed by laboratory analysis, which are labor intensive and time consuming. Fiber-optic measurement permits real-time, in situ turbidity monitoring. But the current technology is based on plastic fibers, which suffer from high optical attenuation and hence are unsuitable for large-scale remote monitoring. In this paper, we report the demonstration of a fiber-optic turbidity sensor based on multi-mode glass fibers. The system uses a single fiber to both deliver laser light into the water sample and collect the back-scattered light for detection. A balanced detection scheme is utilized to remove the common-mode noise to enhance the turbidity sensitivity. Highly linear turbidity responses are obtained and a turbidity resolution as low as 0.1 NTU is achieved. The test unit is also shown to have excellent reproducibility against repeated measurements and good stability against temperature changes. Turbidity measurement in real environmental matrices such as tap water and pond water is also reported with an assessment of the impact of flow rate. This work demonstrates the feasibility of future large-scale distributed fiber-optic turbidity monitoring networks.

Inhibition of bromate formation in plasmon-enhanced catalytic ozonation over silver-doped spinel ferrite

High energy consumption and formation of harmful byproducts are two challenges faced by advanced oxidation processes (AOPs). While much research efforts have been devoted to improving the treatment efficiency, byproduct formation and control calls for more attention. In this study, the underlying mechanism of bromate formation inhibition during a novel plasmon-enhanced catalytic ozonation process with silver-doped spinel ferrite (0.5wt%Ag/MnFe2O4) as the catalysts was investigated. By scrutinizing the effects of each factor (i.e. irradiation, catalyst, ozone) as well as the combinations of different factors on major Br species involved in bromate formation, examining the distribution of Br species, and probing the reactive oxygen species partaking in the reactions, it was found that accelerated ozone decomposition which inhibited two main bromate formation pathways and surface reduction of Br species (e.g. HOBr/OBr- and BrO3-) contributed to the inhibition of bromate formation, both of which can be enhanced by the plasmonic effects of Ag and the good affinity between Ag and Br. A kinetic model was developed by simultaneously solving 95 reactions to predict the aqueous concentrations of Br species during different ozonation processes. The good agreement between the model prediction and experimental data further corroborated the hypothesized reaction mechanism.

Improving Fe-based heterogeneous Electro-Fenton nano catalyst using transition metals in a novel orbiting electrodes reactor

In recent decades the electro-Fenton process has widely been utilized for removing recalcitrant compounds. However, this process is accompanied by several problems such as limited working pH range, production of significant amount of iron sludge, and incapability in reusing used iron ions. Hence, the heterogeneous electro-Fenton process is a convenient way to address these problems. One of the shortcomings of this method, in comparison with the homogeneous electro-Fenton process, is its lower reaction rate. In the first phase of this study, a heterogeneous Fe-based nanocatalyst was prepared. After optimizing the affecting parameters, three transition metals (M: Cu, Co and, Cr) were used in the second phase of the study to improve the performance of this nanocatalyst in removing the indicator pollutant (acid blue 25). The characteristics of nanocatalysts were determined via FESEM, XRD, FTIR, and N₂ adsorption-desorption techniques. The results indicated an enhancement in dye removal efficiency (nearly 8 percent), and the reaction rate (nearly 64 percent) due to the nanocatalysts improved by the presence of transition metals. The reactions with Fe-based nanocatalyst containing copper ions in pH = 3, initial dye concentration = 200 mg L^-1, I = 3.57 mA cm^-2, nanocatalyst concentration = 100 mg L^-1, electrodes angular velocity = 50 rpm, Na₂SO₄ concentration = 0.01 M were capable of removing 97% of dye, 79% of COD and, 65% of TOC. The nanocatalysts were used in 5 cycles, and the dye removal efficiency did not drop considerably, a feature that adds to their importance from an economic point of view. The concentration of leached transition metals into the solution was measured using the ICP-AES technique, which was less than the allowable Iranian standard concentration of discharge into the surface water bodies, thus no need for secondary treatment of wastewater.

Impacted cuspids in a Saudi population: prevalence, etiology and complications

The prevalence, etiology and related complications of impacted maxillary and mandibular cuspids were studied among a convenient sample of 4,898 Saudi patients aged 13 years and older. Results indicate that 175 patients (3.6%) out of a sample had at least one impacted cuspid. Most (22.9%) possessed multiple involvement. Female patients were found to be more concerned about the problem (p < .001). The maxillary arches were usually affected more frequently. The most common location of maxillary cuspid impactions was palatal and the lingually located impaction in the mandible was found to be very rare. In most of the subjects the lack of arch space was the main etiological factor. Cuspid impactions were found to be occasionally associated with various unfavorable sequelae.