Evaluating effectiveness of dust by-product treatment with scrubbers to mitigate explosion risk in ZrO2 atomic layer deposition process.

In processes of manufacturing semiconductors, reactive by-products (as a form of fine powder, i.e., dust) are deposited in pipes installed on post processing and exhaust systems, potentially involving a considerable explosion risk. In this study, the effectiveness of scrubber methods (e.g., dry scrubber and burn-wet scrubber) to mitigate the risk was evaluated. To this end, three by-products generated from a ZrO2 atomic layer deposition (ALD) process were collected from semiconductor manufacturers, which were treated with different methods (i.e., no treatment, treatment using dry scrubber, and treatment using burn-wet scrubber), and their characteristics were analyzed and compared. Particle size measurements of the by-products proved that the burn-wet scrubber treatment less decreased their particle size than the dry scrubber treatment. The burn-wet scrubber treatment made the by-product thermally stable, confirmed by thermogravimetric analysis. Fourier-transform infrared spectroscopy of the by-products before and after the scrubber treatments showed that burn-wet scrubbing of the by-product decreases surface functionalities that play a role in explosion. Dust explosion testing proved that robustness of explosion of the untreated by-product is about 7 times higher than the by-product treated with the burn-wet scrubber. Based on the results of this study, it would be suggested that burn-wet scrubber is a useful treatment method to decrease the explosion risks caused by dust by-products generated from ALD in semiconductor manufacturing processes.

Reactivation of Giardia lamblia cysts after exposure to low-pressure UV irradiation.

In this study, we determined the repair capabilities of Giardia lamblia cysts when they were exposed to low-pressure (LP) UV and then 4 different repair conditions. A UV collimated beam apparatus was used to expose shallow suspensions of G. lamblia cysts in buffered reagent water (PBS, pH 7.2) to various doses of LP UV irradiation. After UV irradiation, samples were exposed to 4 repair conditions (light and dark repair conditions with 2 temperatures (25 °C and 37 °C) for each condition). The inactivation of G. lamblia cysts by LP UV was very extensive (∼ 5 log10) even with a low dose of LP UV (1 mJ/cm(2)). More importantly, there was significant restoration of infectivity in G. lamblia cysts when they were exposed to a low dose of LP UV and then to all the repair conditions tested. Overall, the results of this study indicate that G. lamblia cysts do have the ability to repair their UV-damaged DNA when they are exposed to low doses of LP UV irradiation. This is the first study to report the presence of repair in UV-irradiated G. lamblia cysts.

Inactivation of human adenovirus by sequential disinfection with an alternative UV technology and free chlorine.

There has been growing concern over human exposure to adenoviruses through drinking water due to the extreme resistance of human adenoviruses to the traditional UV technology (low-pressure (LP) UV). As an effort to develop an effective treatment strategy against human adenoviruses in drinking water, we determined the effectiveness of sequential disinfection with an alternative UV technology (medium-pressure (MP) UV) and free chlorine. Human adenovirus 2 (Ad2) was irradiated with a low dose of MP UV irradiation (10 mJ/cm(2)) through UV collimated apparatus and then exposed to a low dose of free chlorine (0.17 mg/L) at pH 8 and 5°C using a bench-scale chemical disinfection system. A significant inactivation (e.g. 4 log(10)) of Ad2 was achieved with the low doses of MP UV and free chlorine within a very short contact time (∼1.5 min) although there was no apparent synergistic effect on Ad2 between MP UV and free chlorine. Overall, it is likely that the sequential disinfection with UV irradiation and free chlorine should control the contamination of drinking water by human adenoviruses within practical doses of UV and free chlorine typically used in drinking water treatment processes.

Inactivation of human adenovirus by sequential disinfection with an alternative ultraviolet technology and monochloramine.

In an effort to reduce human exposure to adenoviruses through drinking water, we determined the effectiveness of sequential disinfection with an alternative ultraviolet (UV) technology (medium-pressure (MP) UV) and monochloramine. The results of this study showed that MP UV was much more effective than traditional UV technology (low-pressure (LP) UV) against human adenovirus 2 (Ad2). Specifically, an inactivation of approximately 3 log10 was achieved by a dose of 40 mJ/cm2 of MP UV compared to ~1 log10 by the same dose of LP UV. However, because of the ineffective inactivation of Ad2 by monochloramine, a very high dose (40 mJ/cm2) of MP UV and a very large Ct99 value (approximately 1200 mg/L.min) was still needed to achieve a significant inactivation (e.g., 4 log10) of Ad2. Also, it appears that the inactivation of Ad2 by monochloramine is not enhanced by prior exposure to MP UV. Overall, the results of this study indicated that, in spite of the enhanced effectiveness of alternative UV technologies on human adenoviruses, sequential disinfection with an alternative UV technology (MP UV) and monochloramine still may not provide adequate inactivation of human adenoviruses - especially at high pH and low temperature - in drinking water treatment processes.

Enhanced effectiveness of medium-pressure ultraviolet lamps on human adenovirus 2 and its possible mechanism.

There has been growing concern over human exposure to adenoviruses through drinking water due to their apparent high resistance to UV irradiation and the anticipated widespread use of ultraviolet (UV) disinfection in drinking water treatment processes. However, most inactivation studies on adenoviruses were performed using only one type of UV technology--low-pressure (LP) UV, and little is known about the effectiveness of different UV technologies such as medium- pressure (MP) UV or other polychromatic UV technologies. In this work, the kinetics and extent of inactivation of a human adenovirus (adenovirus 2 (Ad2)) by both monochromatic LP and polychromatic MP UV were evaluated to determine the effectiveness of these UV technologies on human adenoviruses. Inactivation of Ad2 by LP UV was very slow and only 0.87 and 2.17 log(10) inactivation was achieved with UV doses of 30 and 90 mJ/cm(2), respectively. However, inactivation of Ad2 by MP UV was much faster and 2.19 and 5.36 log(10) inactivation was observed with the same UV doses (30 and 90 mJ/cm(2), respectively). It appears that MP UV is more effective against Ad2 than LP UV and the enhanced effectiveness of MP UV on Ad2 is likely due to its ability to inhibit the repair process in UV-irradiated Ad2.

An observational study on the effectiveness of point-of-use chlorination.

Although the efficacy of chlorine disinfection under controlled laboratory conditions is well known, the effectiveness of chlorine under field point-of-use (POU) conditions is still not clearly understood and may be impacted by a variety of factors. This study evaluated the effectiveness of POU chlorine disinfection in rural Ecuador under typical use conditions and compared this effectiveness with the efficacy in controlled laboratory conditions. While reductions of indicator organisms were slightly higher in households that used chlorination, no significant differences were seen between households employing POU chlorination and the households with no chlorination (1-1.5 log10 median reductions for chlorinating households and 0.31-0.55 log10 for nonchlorinating households, depending on the indicator organism). In contrast, significant reduction of all test organisms was found when simulating POU conditions in the laboratory. This study demonstrates that POU chlorination can be considerably less effective under actual field conditions than would be predicted based on its laboratory efficacy (3-5 log10 median reductions for chlorinated and 0-0.3 log10 for nonchlorinated samples). Human factors (including improper storage and chlorine dosing) and uncontrolled water quality effects are hypothesized to impact significantly the effectiveness of chlorine disinfection.

Inactivation of norovirus by chlorine disinfection of water.

In an effort to validate previous research suggesting remarkable resistance of norovirus to free chlorine disinfection, we characterized the disinfection response of purified and dispersed Norwalk virus (NV) by bench-scale free chlorine disinfection using RT-PCR for virus assays. The inactivation of NV by two doses of free chlorine (1 and 5mg/L) at pH 6 and 5 degrees C based on two RT-PCR assays was similar to that of coliphage MS2, but much faster than that of poliovirus 1. Despite the underestimation of virus inactivation by RT-PCR assays, the predicted CT values for NV based on RT-PCR assays are lower than the ones for most other important waterborne viruses and the CT guidelines for chlorine disinfection of viruses under the Surface Water Treatment Rule by the United States Environmental Protection Agency. Overall, the results of this study indicate that NV is not highly resistant to free chlorine disinfection as suggested by previous research and it is likely that NV contamination of drinking water can be controlled by adequate free chlorine disinfection practices with provision of proper pre-treatment processes before chlorination.

Inactivation of Mycobacterium avium complex by UV irradiation.

The effectiveness of two major UV technologies against a highly prevalent species of Mycobacterium avium complex was investigated. Our study indicates that M. avium is much more resistant to UV irradiation than most waterborne pathogens and that it is one of the rare microorganisms that are highly resistant to both chemical and UV disinfection in water.

Reduction of Norwalk virus, poliovirus 1, and bacteriophage MS2 by ozone disinfection of water.

Norwalk virus and other human caliciviruses (noroviruses) are major agents of gastroenteritis, and water is a major route of their transmission. In an effort to control Norwalk virus in drinking water, Norwalk virus reduction by bench-scale ozone disinfection was determined using quantitative reverse transcription (RT)-PCR for virus assays. Two other enteric viruses, poliovirus 1 and coliphage MS2, were included for comparison, and their reductions were assayed by infectivity assays as well as by RT-PCR. Virus reductions by ozone were determined using a dose of 0.37 mg of ozone/liter at pH 7 and 5 degrees C for up to 5 min. Based on two RT-PCR assays, the reductions of Norwalk virus were >3 log(10) within a contact time of 10 s, and these were similar to the reductions of the other two viruses determined by the same assay methods. Also, the virus reductions detected by RT-PCR assays were similar to those detected by infectivity assays, indicating that the RT-PCR assay is a reliable surrogate assay for both culturable and nonculturable viruses disinfected with ozone. Overall, the results of this study indicate that Norwalk virus as well as other enteric viruses can be reduced rapidly and extensively by ozone disinfection and that RT-PCR is a useful surrogate assay for both culturable and nonculturable viruses disinfected with ozone.

UV disinfection of Giardia lamblia cysts in water.

The human and animal pathogen Giardia lamblia is a waterborne risk to public health because the cysts are ubiquitous and persistent in water and wastewater, not completely removed by physical-chemical treatment processes, and relatively resistant to chemical disinfection. Given the recently recognized efficacy of UV irradiation against Cryptosporidium parvum oocysts, the inactivation of G. lamblia cysts in buffered saline water at pH 7.3 and room temperature by near monochromatic (254 nm) UV irradiation from low-pressure mercury vapor lamps was determined using a "collimated beam" exposure system. Reduction of G. lamblia infectivity for gerbils was very rapid and extensive, reaching a detection limit of >4 log within a dose of 10 JM-2. The ability of UV-irradiated G. lamblia cysts to repair UV-induced damage following typical drinking water and wastewater doses of 160 and 400 JM(-2) was also investigated using experimental protocols typical for bacterial and eucaryotic DNA repair under both light and dark conditions. The infectivity reduction of G. lamblia cysts at these UV doses remained unchanged after exposure to repair conditions. Therefore, no phenotypic evidence of either light or dark repair of DNA damage caused by LP UV irradiation of cysts was observed at the UV doses tested. We conclude that UV disinfection at practical doses achieves appreciable (much greater than 4 log) inactivation of G. lamblia cysts in water with no evidence of DNA repair leading to infectivity reactivation.