Disinfection Unit Research Articles

Effects of the interaction between Microcystis aeruginosa and nitrobenzene on coagulation-sedimentation performance

It is rarely reported that the interaction between xenobiotics and algae may cause potential water quality risks and affect the drinking water treatment process. In the present study, a bench-scale jar test was performed to investigate the effects of the interaction between nitrobenzene (NB) and Microcystis aeruginosa on the performance of coagulation-sedimentation by comparing differences in turbidity, optical density at 680 nm (OD680), trihalomethane formation potential (THMFP) and microcystin-LR (MC-LR) in an M. aeruginosa solution with or without NB. The results indicated that the quality of M. aeruginosa -containing water can be improved significantly by coagulation-sedimentation, and all of the removal rates were more than 80%. The presence of NB did not affect the performance of coagulation-sedimentation directly. However, the interaction between NB and M. aeruginosa did change the characteristics of the raw water and affect the performance of coagulation-sedimentation. At a non-lethal concentration, NB did not inhibit the growth of M. aeruginosa but weakened the zeta potential of M. aeruginosa , which enhanced the removal of turbidity. The products of NB degradation by M. aeruginosa cause an increased THMFP in extracellular organic matters, which cannot be removed by coagulation-sedimentation efficiently, increasing the risk of disinfection by-products formation in the following disinfection unit.

VOC Contamination in Hospital, from Stationary Sampling of a Large Panel of Compounds, in View of Healthcare Workers and Patients Exposure Assessment

BackgroundWe aimed to assess, for the first time, the nature of the indoor air contamination of hospitals.Methods and FindingsMore than 40 volatile organic compounds (VOCs) including aliphatic, aromatic and halogenated hydrocarbons, aldehydes, alcohols, ketones, ethers and terpenes were measured in a teaching hospital in France, from sampling in six sampling sites – reception hall, patient room, nursing care, post-anesthesia care unit, parasitology-mycology laboratory and flexible endoscope disinfection unit – in the morning and in the afternoon, during three consecutive days. Our results showed that the main compounds found in indoor air were alcohols (arithmetic means ± SD: 928±958 µg/m3 and 47.9±52.2 µg/m3 for ethanol and isopropanol, respectively), ethers (75.6±157 µg/m3 for ether) and ketones (22.6±20.6 µg/m3 for acetone). Concentrations levels of aromatic and halogenated hydrocarbons, ketones, aldehydes and limonene were widely variable between sampling sites, due to building age and type of products used according to health activities conducted in each site. A high temporal variability was observed in concentrations of alcohols, probably due to the intensive use of alcohol-based hand rubs in all sites. Qualitative analysis of air samples led to the identification of other compounds, including siloxanes (hexamethyldisiloxane, octamethyltrisiloxane, decamethylcyclopentasiloxane), anesthetic gases (sevoflurane, desflurane), aliphatic hydrocarbons (butane), esters (ethylacetate), terpenes (camphor, α-bisabolol), aldehydes (benzaldehyde) and organic acids (benzoic acid) depending on sites.ConclusionFor all compounds, concentrations measured were lower than concentrations known to be harmful in humans. However, results showed that indoor air of sampling locations contains a complex mixture of VOCs. Further multicenter studies are required to compare these results. A full understanding of the exposure of healthcare workers and patients to complex mixtures of chemical compounds can then be related to potential health outcomes.

Treatment of ametryn in wastewater by a hybrid MBR system: a lab-scale study

Agricultural discharge of herbicides to the Great Barrier Reef (GBR) poses significant threat to the marine ecosystem. This study evaluates the performance of a hybrid treatment system consists of a membrane bioreactor (MBR), UV disinfection unit and a granular activated carbon (GAC) column in treating ametryn which is one of the major herbicides in agricultural discharges. While the MBR alone removes only 40% of ametryn at a hydraulic retention time of 7.8 h, the hybrid system removed ametryn to below detection levels.

Low Cost Water Disinfectant System Using Solar Energy

Solar disinfection unit is unsophisticated, efficient and reasonably priced water treatment process appropriate for use in developing countries. Water was filtered through cloth, net and coconut husk to remove any suspended particles in water which would directly increase the efficiency of solar disinfection. The filtered water is then transferred in solar disinfection unit. Water with Escherichia coli as indicator organism was filled in the solar disinfection unit comprising of four polyethylene terepthalate (PET) plastic bottles joined together with PVC pipes. These bottles were kept in direct sunlight for 12-48 hours. Weather conditions and solar radiation were obtained using different programs. Solar radiations and elevated temperature destroyed the indicator organism efficiently. Health peril of chemical released in water was well thought-out and was determined to be safe with respect to human consumption. The efficiency of solar disinfection was augmented by use of semi-conductor titanium dioxide (TiO2) which reduced the time for exposure up to 90%. The temperature increase and dissolved oxygen decrease in the disinfection process which was overcome by retaining this water in traditional earthenware water storage vessels (mutka). Allowing accessibility to better life through improved quality of water.

Synthesis and Bactericidal Ability of TiO2and Ag-TiO2Prepared by Coprecipitation Method

Preparation of photocatalysts of TiO<sub >2</sub> and Ag-TiO<sub >2</sub> was carried out by coprecipitation method. The prepared photocatalysts were characterized by X-ray diffraction (XRD), SEM, EDX, and XRF analysis. The disinfection of <i >E. coli</i>, a model indicator organism for the safe water supply, was investigated by using TiO<sub >2</sub> and Ag-TiO<sub >2</sub> under different light sources. The treatment efficacy for the inactivation of <i >E. coli</i> would be UV/Ag-TiO<sub >2</sub>; visible/Ag-TiO<sub >2</sub>; dark/Ag-TiO<sub >2</sub>; UV (all 100&#x25;) &#x3e; UV/TiO<sub >2</sub> (99&#x25;) &#x3e; visible/TiO<sub >2</sub> (96&#x25;) &#x3e; dark/TiO<sub >2</sub> (87&#x25;) &#x3e; visible (23&#x25;) &#x3e; dark (19&#x25;). The order of disinfection efficiency by their corresponding kinetic initial apparent rate constants, <svg style="vertical-align:-5.03984pt;width:25.012501px;" id="M1" height="16.85" version="1.1" viewBox="0 0 25.012501 16.85" width="25.012501" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(1.25,0,0,-1.25,0,16.85)"> <g transform="translate(72,-58.52)"> <text transform="matrix(1,0,0,-1,-71.95,63.6)"> <tspan style="font-size: 12.50px; " x="0" y="0">𝑘</tspan> </text> <text transform="matrix(1,0,0,-1,-65.17,60.47)"> <tspan style="font-size: 8.75px; " x="0" y="0">a</tspan> <tspan style="font-size: 8.75px; " x="3.8858881" y="0">p</tspan> <tspan style="font-size: 8.75px; " x="8.2618876" y="0">p</tspan> </text> </g> </g> </svg>, (min<sup >&#x2212;1</sup>) would be UV/Ag-TiO<sub >2</sub>; visible/Ag-TiO<sub >2</sub> (both 6.67) &#x3e; UV (6.6) &#x3e; dark/Ag-TiO<sub >2</sub> (6.56) &#x3e; UV/TiO<sub >2</sub> (1.62) &#x3e; visible/TiO<sub >2</sub> (1.08) &#x3e; dark/TiO<sub >2</sub> (0.7) &#x3e; visible (0.28) &#x3e; dark (0.03). The application of TiO<sub >2</sub> doped with silver strongly improved the ability of disinfection treatment. The study of mineralization of <i >E. coli</i> by measurement of TOC (total organic carbon) removal percentage showed that the visible light may effectively be applied for the disinfection unit of water and wastewater treatment system by using photocatalysts of Ag-TiO<sub >2</sub>.

Environmental contamination and airborne microbial counts: a role for hydroxyl radical disinfection units?

Environmental contamination is thought to play a role in the spread of infection in hospitals and there has been increased interest in novel air disinfection systems in preventing infection. In this study the efficacy of a hydroxyl radical air disinfection system (Inov8 unit) in reducing the number of airborne bacteria was assessed in a clinical setting. Environmental contamination was assessed using settle plates and air samples in three settings: (1) non-clinical room; (2) non-clinical room with defined activity; and (3) single intensive care unit cubicle. A comparison of air counts and environmental contamination rates was made with the Inov8 units on and off. The Inov8 unit produced an overall reduction in both air sample and settle plate counts in each setting (P<0.001, Wilcoxon signed-rank test). There was a mean reduction in air sample counts of 26%, 39% and 55% for settings 1, 2 and 3 respectively. The corresponding reductions in settle plate counts were 35%, 62% and 54%. These results suggest that this type of novel air disinfection may have a role in improving air quality and reducing environmental contamination within clinical isolation rooms. Further work is required to assess the effect on specific pathogens, and to establish whether this will reduce the risks of patients and/or healthcare workers acquiring such pathogens from the environment.

Development of a Mobile Water Disinfection Unit Powered by Renewable Energy

Following such natural disasters as Hurricanes Katrina and Ike and the 2010 Haiti earthquake, supplying a reliable source of clean drinking water has apparently become essential. Providing a water supply and the associated transportation of potable water is a considerable burden on recovery efforts following a natural disaster. To reduce this burden and meet the water requirements of a community, a low-maintenance, low-cost trailer-mounted water disinfection system has been developed that has the capability to provide potable water from local surface water bodies until the infrastructure is repaired. To achieve disinfection of contaminated surface water, the system uses a series of prefilters and an ultraviolet (UV) disinfection unit. The system is powered using a hybrid photovoltaic array and wind turbine system. To increase the storage capability and decrease the maintenance required by the system, traditional, relatively high-maintenance batteries have been replaced with an ultracapacitor to store the ...

Examination of the operator and compensator tank role in urban wastewater treatment using activated sludge method

No doubt, operator is one of the main fundaments in wastewater treatment plants. By identifying the inadequacies, the operator could be considered as an important key in treatment plant. Several methods are used for wastewater treatment that requires spending a lot of cost. However, all investments of treatment facilities are usable when the expected efficiency of the treatment plant was obtained. Using experienced operator, this goal is more easily accessible. In this research, the wastewater of an urban community contaminated with moderated, diluted and highly concentrated pollution has been treated using surface and deep aeration treatment method. Sampling of these pilots was performed during winter 2008 to summer 2009. The results indicate that all analyzed parameters were eliminated using activated sludge and surface aeration methods. However, in activated sludge and deep aeration methods in combination with suitable function of operator, more pollutants could be eliminated. Hence, existence of operator in wastewater treatment plants is the basic principle to achieve considered efficiency. Wastewater treatment system is not intelligent itself and that is the operator who can organize even an inefficient system by its continuous presence. The converse of this fact is also real. Despite the various units and appropriate design of wastewater treatment plant, without an operator, the studied process cannot be expected highly efficient. In places frequently affected by the shock of organic and hydraulic loads, the compensator tank is important to offset the wastewater treatment process. Finally, in regard to microbial parameters, existence of disinfection unit is very useful.

Performance of UV disinfection and the microbial quality of greywater effluent along a reuse system for toilet flushing

This paper examines the microbial quality of treated RBC (Rotating Biological Contactor) and MBR (Membrane Bioreactor) light greywater along a continuous pilot-scale reuse system for toilet flushing, quantifies the efficiency of UV disinfection unit, and evaluates the regrowth potential of selected microorganisms along the system. The UV disinfection unit was found to be very efficient in reducing faecal coliforms and Staphylococcus aureus. On the other hand, its efficiency of inactivation of HPC (Heterotrophic Plate Count) and Pseudomonas aeruginosa was lower. Some regrowth occurred in the reuse system as a result of HPC regrowth which included opportunistic pathogens such as P. aeruginosa. Although the membrane (UF) of the MBR system removed all bacteria from the greywater, bacteria were observed in the reuse system due to “hopping phenomenon.” The microbial quality of the disinfected greywater was found to be equal or even better than the microbial quality of “clean” water in toilet bowls flushed with potable water (and used for excretion). Thus, the added health risk associated with reusing the UV-disinfected greywater for toilet flushing (regarding P. aeruginosa and S. aureus), was found to be insignificant. The UV disinfection unit totally removed (100%) the viral indicator (F-RNA phage, host: E. coli F amp +) injected to the treatment systems simulating transient viral contamination. To conclude, this work contributes to better design of UV disinfection reactors and provides an insight into the long-term behavior of selected microorganisms along on-site greywater reuse systems for toilet flushing.

ULTRAVIOLET‐C LIGHT PROCESSING OF GRAPE, CRANBERRY AND GRAPEFRUIT JUICES TO INACTIVATE SACCHAROMYCES CEREVISIAE

ABSTRACT Two “Infinity” liquid disinfection systems were coupled in a serial arrangement to assemble one Ultraviolet‐C disinfection unit. Two inner mercury lamps (intensity, 25 mW/cm2) were used as germicidal sources. Pasteurized grape, cranberry and grapefruit juices, inoculate with Saccharomyces cerevisiae, were processed by Ultraviolet (UV) light at six flow rates (0.073–1.02 L/min) and six UV light doses (75–450 kJ/m2). The first order kinetics modeling for S. cerevisiae inactivation proved that Duvvalues (i.e., ultraviolet decimal reduction time) ranged from 61.7 to 113.7 (R2 &gt; 0.900), 12.2 to 40.7 (R2 &gt; 0.930) and 12.5 to 20.7 (R2 &gt; 0.860) min for grape, cranberry and grapefruit juices, respectively. The maximum log reduction (cfu/mL) was 0.53, 2.51 and 2.42 for yeast count in grape, cranberry and grapefruit juices, respectively, after 30 min of UV light treatment at the maximum flow rate (1.02 L/min). The total color difference (ΔE*) in the three fruit juices tested increased as UV light treatment time increased.PRACTICAL APPLICATIONSUltraviolet (UV) light processing of liquid food products is an emerging nonthermal technology that can be used to treat liquid food products. Fruit juices and nectars used to be thermally treated to deliver microbiologically safe fruit products. However, thermal treatment can produce some sensory changes in fruit products. Changes such as caramelization of sugar may darken the food and consequently give a light bitter flavor to the product. Liquid fruit products can be UV light treated to obtain a commercially sterile product that is ready to drink. UV light processing equipment can be built in a serial arrangement to apply the dosage needed to obtain a microbiologically safe liquid fruit product with adequate sensory characteristics. An added advantage to UV processing is that compared to thermal treatment, less energy is required to obtain liquid food products similar to fresh products.

Photo-degradation of clofibric acid by ultraviolet light irradiation at 185 nm

As a metabolite of lipid regulators, clofibric acid (CA) was investigated in this study for its ultraviolet (UV) degradation at monochromatic wavelength of 185 nm using Milli-Q water and sewage treatment plant (STP) effluent. The effects of CA initial concentration, solution pH, humic acid (HA), nitrate and bicarbonate anions on CA degradation performances were evaluated. All CA degradation patterns well fitted the pseudo-first-order kinetic model. The results showed that OH generated from water photolysis by UV185 irradiation was involved, resulting in indirect CA photolysis but contributed less to the whole CA removal when compared to the main direct photolysis process. Acid condition favored slightly to CA degradation and other constituents in solution, such as HA (5.0-100.0 mg L(-1)), nitrate and bicarbonate anions (1.0x10(-3) mol L(-1) and 0.1 mol L(-1)), had negative effects on CA degradation. When using real STP effluent CA degradation could reach 97.4% (without filtration) and 99.3% (with filtration) after 1 hr irradiation, showing its potential mean in pharmaceuticals removal in UV disinfection unit. Mineralization tests showed that rapid chloride ion release happened, resulting in no chlorinated intermediates accumulation, and those non-chlorinated intermediate products could further be nearly completely degraded to CO2 and H2O after 6 hrs.

Virological evaluation of domestic water purification devices commonly used in India emphasizes inadequate quality and need for virological standards

To evaluate the performance of domestic water purification units with respect to contaminating enteric viruses. Eight domestic water purification systems widely used in India were evaluated using hepatitis E virus (HEV) as a model virus. For HEV concentration and detection, membrane filtration and real-time PCR were used respectively. Viral log reduction value (LRV) was calculated for each unit. Viral log reduction value was 0.21 for unit 6 (polyester + carbon), 1.45 for unit 4 (filter + UV), 1.52 for unit 3 (filter + chlorine), 1.70 for a carbon + exhaust indication contact disinfection unit, 2.20 for an iodine resin unit, 2.51 for a dual filter unit and 6.53 for a hollow fibre membrane unit and a gravity-fed filter unit. Thus, only the technologies employed by the latter two were efficient in complete removal of HEV. The majority of the water purifiers under use are inadequate. Virological standards in evaluating such devices need to be established urgently, in order to help manufacturers to improve the performance of such products and most importantly, to help consumers.

Waste management in primary healthcare centres of Iran

The waste management practices in primary healthcare centres of Iran were investigated in the present study. A total of 120 primary healthcare centres located across the country were selected using the cluster sampling method and the current situation of healthcare waste management was determined through field investigation. The quantities of solid waste and wastewater generation per outpatient were found to be 60 g outpatient(-1) day(-1) and 26 L outpatient(-1) day(-1), respectively. In all of the facilities, sharp objects were separated almost completely, but separation of other types of hazardous healthcare solid waste was only done in 25% of the centres. The separated hazardous solid waste materials were treated by incineration, temporary incineration and open burning methods in 32.5, 8.3 and 42.5% of the healthcare centres, respectively. In 16.7% of the centres the hazardous solid wastes were disposed of without any treatment. These results indicate that the management of waste materials in primary healthcare centres in Iran faced some problems. Staff training and awareness, separation of healthcare solid waste, establishment of the autoclave method for healthcare solid waste treatment and construction of septic tanks and disinfection units in the centres that were without access to a sewer system are the major measures that are suggested for improvement of the waste management practices.

Pilot-scale assessment of the impacts of transient particulate water quality events on the UV disinfection of indigenous total coliform bacteria in drinking water treatment

On-line particle count and turbidity data was used to monitor the impacts of transient particulate water quality events on the inactivation of indigenous total coliform bacteria by a pilot-scale ultraviolet (UV) disinfection unit at two drinking water treatment plants (referred to as WTPs ‘A’ and ‘B’). The intent of the study was to assess the performance of UV disinfection when exposed to temporary ‘worst case’ particulate water quality conditions in a drinking water treatment context. The pilot unit was installed downstream of a poorly operating filter at WTP ‘A’ and downstream of an intentionally destabilized Actiflo® system at WTP ‘B’. In each case, elevated particle content (turbidity up to 2.9 NTU) did not cause observable adverse effects on the UV disinfection of total coliform bacteria over the test periods, even when a particle extraction technique was applied to count particle-associated bacteria in the water samples.

Restaurant Wastewater Treatment by Constructed Wetlands

AbstractA low‐cost method for domestic wastewater treatment has been developed for scattered settlements in rural areas with no sewer facilities. The system was operated with only restaurant wastewaters having pollutant strengths 2 to 4 times higher than typical domestic wastewater. The system dimensions were 1 m×4 m×0.4 m (W×L×H). The three layers inside were separated by plastic sheets and filled with 10 cm thick peat layers. The system could treat up to 400 L of restaurant wastewater daily with removal rates of COD, TKN, PO4‐P, N‐Total, and SS of 94.4, 2.7, 0.23, 2.95, and 87.2 g/m2, respectively. The system was equipped with a disinfection unit having two 8 W UV lamps. The efficiency of disinfection was tested based on the pathogen count in the effluent. No Escherichia coli or fecal coliforms were detected in the effluent.

Reuse potential of urban wastewater treatment plant effluents in Turkey: a case study on selected plants

The paper summarizes the current situation of urban wastewater treatment plants (UWWTP) in Turkey. Results of a detailed survey on the performance of four selected plants were given both in terms of influent and effluent quality and in comparison with the current legislation on discharge limits to receiving waters. All the selected plants were operating efficiently especially according to conventional control parameters and heavy metal content. The suitability of the effluents for irrigation purposes is then evaluated according to the existing national irrigation water quality standards. From the data inventory, it was evident that the current situation is not promising especially regarding the bacteriological parameter, i.e. fecal coliform. The main cause of this problem is either the lack of disinfection units and/or improper operation of the existing ones. Turkey, which has already established its irrigation water quality standards, however, needs to accelerate the reuse of effluents in irrigation in the most proper manner.

Evaluation for the Reclamation Potential of High-Tech Industrial Wastewater Effluent Treated with Different Membrane Processes

Due to the shortage of water supplies, the reclamation and reuse of the effluents from wastewater treatment plants has become an important issue in Taiwan, especially for industrial parks. By constructing a reclaimed water distribution system, the reclaimed water could be used as nonpotable and industrial water. This research used three advanced integrated treatment processes, including sand filtration (SF), microfiltration (MF), granular activated carbon (GAC), ion exchange (IE), reverse osmosis (RO), and an ultraviolet disinfection (UV) unit, to treat the effluent from the wastewater treatment plant of Hsin-Chu Science-Based Industrial Park. The reclamation potential of treated water was examined compared with different water reuse criteria. The results of the experiments showed that different process could achieve different levels of water purification. This was dependent on the complexity and sequence of the units. The effluent from the simplest process, called process A, which combined the SF, MF, GAC, and UV units in that order, could meet the criteria of nonindustrial water. The effluent of process B and C, which additionally installed IE–MF–RO and MF–RO–IE units in sequence, respectively, between the GAC and UV units of process A, could be reused as sprinkling, landscaping and recreational water; cooling-system makeup water; low-pressure boiler feed water; as well as potable water or Newater with suitable advanced treatment.

The impact of electrochemical disinfection on Escherichia coli and Legionella pneumophila in tap water

In order to reduce the risks of Legionnaires' disease, caused by the bacterium Legionella pneumophila, disinfection of tap water systems contaminated with this bacterium is a necessity. This study investigates if electrochemical disinfection is able to eliminate such contamination. Hereto, water spiked with bacteria (10(4)CFU Escherichia coli or L. pneumophila/ml) was passed through an electrolysis cell (direct effect) or bacteria were added to tap water after passage through such disinfection unit (residual effect). The spiked tap water was completely disinfected, during passage through the electrolysis cell, even when only a residual free oxidant concentration of 0.07 mg/l is left (L. pneumophila). The residual effect leads to a complete eradication of cultivable E. coli, if after reaction time at least a free oxidant concentration of 0.08 mg/l is still present. Similar conditions reduce substantially L. pneumophila, but a complete killing is not realised.

크립토스포리디움의 활성/감염성 판별법을 이용한 오존 및 자외선 소독능 평가

크립토스포리디움은 염소내성이 매우 강해 일반적인 표준정수처리공정의 소독으로는 제거가 불가능하다. 따라서 본 연구에서는 오존 및 UV를 이용한 단위소독공정에서 DAPI/PI 및 in vitro excystation을 이용하여 크립토스포리디움 불활성화를 평가하였으며, 또한 오존을 이용한 고도산화처리 파일럿에서는 세포배양법을 이용하여 크립토스포리디움 불활성화를 평가하였다. 오존 소독연구는 50 mL 용량의 piston type batch reactor에서 용존오존을 자동적으로 측정해주는 flow injection analysis (FIA) 시스템을 이용하여 실험한 결과, 1 log 제거에 필요한 CT값은 <TEX>$25^{\circ}C$</TEX>에서 DAPI/PI 및 in vitro excystation에 의해 각각 약 1.8, 2.2 <TEX>$mg/L{\cdot}min$</TEX>으로 나타났으며, 2 log 제거에 필요한 CT값은 각각 약 3.2, 3.8 <TEX>$mg/L{\cdot}min$</TEX>으로 나타났다. 또한 <TEX>$5^{\circ}C$</TEX>에서 크립토스포리디움 1 log 제거에 필요한 CT값은 DAPI/PI 방법에 의해 약 9.1 <TEX>$mg/L{\cdot}min$</TEX>으로 나타났으며, 2 log제거에 필요한 CT값은 14.8 <TEX>$mg/L{\cdot}min$</TEX>로 나타나, 같은 소독효과를 나타내기 위해서 저온에서는 상온에서보다 요존 요구량이 약 <TEX>$4{\sim}5$</TEX>배 정도 증가하여야 함을 확인하였다. 40 L규모의 오존 반응조를 이용한 파일럿 실험에서는 정수처리공정상 모래여과를 거친 물에 살아있는 크립토스포리디움을 접종한 것을 시료로 하여 연속적으로 흐르게 한 다음, 오존량을 변화시키고 체류시간은 5분으로 고정하여 불활성화를 평가하였다. 실험결과, 8 <TEX>$mg/L{\cdot}min$</TEX>의 CT값에서 DAPI/PI 및 excystation과 같은 생사판별법을 이용하였을 경우에는 약 0.2 log정도의 불활성화를 나타내었으며, 세포감염시험법을 이용하였을 경우에는 약 1.2 log정도의 불활성화를 나타냈다. 오존에 의한 크립토스포리디움의 소독능 평가에 단위공정 및 파일럿 실험 모두 2가지 생사판별법(DAPI/PI와 excystation) 사이에는 큰 차이를 나타내지 않았으나, 생사판별법과 세포감염시험법 사이에는 현저한 차이를 나타내었는데, 이는 세포감염시험법으로 측정하는 sporozoite 및 merozoite로의 분화과정이 생사판별법이 근거한 세포벽의 구조와 기능 유지 보다 더 오존 소독에 더 민감함을 알 수 있었다. 파일럿 실험에서의 CT값이 piston batch reactor에서의 CT값 보다 낮게 나타난 것은 파일럿 실험에서 수작업으로 인한 용존 오존 측정이 정밀하지 못하여 IOD가 농도에 반영되지 않았고, 반응조 규모(50 mL vs 40 L) 및 형태(회분식 vs 연속식)의 차이에 기인하는 것으로 여겨진다. 한편, UV를 이용한 단위공정에서는 크립토스포리디움 1, 2 log 제거에 필요한 IT값은 <TEX>$25^{\circ}C$</TEX>에서 각각 DAPI/PI 방법에 의해 약 25, 50 <TEX>$mWs/cm^2$</TEX>로 나타났으며, <TEX>$5^{\circ}C$</TEX>에서의 크립토스포리디움 1, 2 log제거에 필요한 IT값은 약 40, 80 <TEX>$mWs/cm^2$</TEX>로 나타났다. 온도 <TEX>$20^{\circ}C$</TEX> 감소 시 약 60% 정도의 IT값이 더 필요한데, 이것은 저온에서는 약한 자외선을 발산하는 저압저출력 UV 램프의 특성 때문인 것으로 사료되었다. In the ozone disinfection unit process of a piston type batch reactor with continuous ozone analysis using a flow injection analysis (FIA) system, the CT values for 1 log inactivation of Cryptosporidium parvum by viability assays of DAPI/PI and excystation were <TEX>$1.8{\sim}2.2\;mg/L{\cdot}min$</TEX> at <TEX>$25^{\circ}C$</TEX> and <TEX>$9.1mg/L{\cdot}min$</TEX> at <TEX>$5^{\circ}C$</TEX>, respectively. At the low temperature, ozone requirement rises <TEX>$4{\sim}5$</TEX> times higher in order to achieve the same level of disinfection at room temperature. In a 40 L scale pilot plant with continuous flow and constant 5 minutes retention time, disinfection effects were evaluated using excystation, DAPI/PI, and cell infection method at the same time. About 0.2 log inactivation of Cryptosporidium by DAPI/PI and excystation assay, and 1.2 log inactivation by cell infectivity assay were estimated, respectively, at the CT value of about <TEX>$8mg/L{\cdot}min$</TEX>. The difference between DAPI/PI and excystation assay was not significant in evaluating CT values of Cryptosporidium by ozone in both experiment of the piston and the pilot reactors. However, there was significant difference between viability assay based on the intact cell wall structure and function and infectivity assay based on the developing oocysts to sporozoites and merozoites in the pilot study. The stage of development should be more sensitive to ozone oxidation than cell wall intactness of oocysts. The difference of CT values estimated by viability assay between two studies may partly come from underestimation of the residual ozone concentration due to the manual monitoring in the pilot study, or the difference of the reactor scale (50 mL vs 40 L) and types (batch vs continuous). Adequate If value to disinfect 1 and 2 log scale of Cryptosporidium in UV irradiation process was 25 <TEX>$mWs/cm^2$</TEX> and 50 <TEX>$mWs/cm^2$</TEX>, respectively, at <TEX>$25^{\circ}C$</TEX> by DAPI/PI. At <TEX>$5^{\circ}C$</TEX>, 40 <TEX>$mWs/cm^2$</TEX> was required for disinfecting 1 log Cryptosporidium, and 80 <TEX>$mWs/cm^2$</TEX> for disinfecting 2 log Cryptosporidium. It was thought that about 60% increase of If value requirement to compensate for the <TEX>$20^{\circ}C$</TEX> decrease in temperature was due to the low voltage low output lamp letting weaker UV rays occur at lower temperatures.

Bacteriophage MS-2 removal by submerged membrane bioreactor

A membrane bioreactor (MBR) may serve as a pre-disinfection or disinfection unit, in addition to its solid/liquid separation and biological conversion functions, to produce sewage effluent of high quality. This bench-scale pilot study focuses on investigating the performance of a submerged MBR in pathogen removal and the factors affecting the removal, using a 0.4-μm hollow-fiber membrane module submerged in an aeration tank and bacteriophage MS-2 as the indicator organism. Removal of the MS-2 phage was found to be contributed by physical filtration by the membrane itself, biomass activity in the aeration tank and bio-filtration achieved by the biofilm developed on the membrane surface. The membrane alone gave poor virus removal (0.4±0.1 log) but the overall removal increased substantially with the presence of biomass and the membrane-surface-attached biofilm. The contributions of the suspended biomass and attached biofilm to the phage removal are dependent on the inter-related parameters including the concentration of mixed liquor suspended solids (MLSS), the sludge retention time (SRT) and the food to mass (F/M) ratio. The correlations between effluent flux/trans-membrane pressure and virus removal give evidence that phage removal in the MBR is most likely susceptible to both biological and physical factors including the quantity and property of the biomass and the biofilm and the membrane pore size reduction.