Comparison of disinfection performance of UVC-LED and conventional upper-room UVGI systems

We developed a novel, compact upper-room ultraviolet germicidal irradiation system with light-emitting diode sources (UR-UVGI-LED) to enhance the disinfection of bioaerosols in an enclosed room space. Its effectiveness was evaluated and compared with the conventional upper-room ultraviolet germicidal irradiation system with mercury vapor sources (UR-UVGI-MV). Escherichia coli, Serratia marcescens, and Staphylococcus epidermidis were atomized under the well-mixed condition and exposed to UR-UVGI-LED (or UR-UVGI-MV) device. The intensity output of the UR-UVGI-LED was also varied from 0% (no LED), 25%, 50% to 100% to further evaluate the UR-UVGI-LED disinfection effectiveness under different power levels. The decay rates for UR-UVGI-LED ranged from −0.1420 ± 0.04 min⁻¹ to −0.3331 ± 0.07 min⁻¹ for Escherichia coli, −0.1288 ± 0.01 min⁻¹ to −0.3583 ± 0.02 min⁻¹ for Serratia marcescens, and −0.0330 ± 0.01 min⁻¹ to −0.0487 ± 0.01 min⁻¹ for Staphylococcus epidermidis. It was noticed that the intensity level had a non-linear influence on the UR-UVGI-LED’s performance. The decay rates achieved by the UR-UVGI-MV system were −0.3867 ± 0.08 min⁻¹, −0.4745 ± 0.002 min⁻¹, and −0.1624 ± 0.02 min⁻¹ for Escherichia coli, Serratia marcescens, and Staphylococcus epidermidis, respectively. Hence, the disinfection performance of both UR-UVGI-LED and UR-UVGI-MV systems was comparable for Escherichia coli and Serratia marcescens. These results demonstrate that the UR-UVGI-LED system has a high potential to be used as a safe and effective irradiated light source to disinfect indoor airborne pathogens.     

Emission strength of airborne pathogens during toilet flushing

The flushing of toilets generates contaminated aerosols, the transmission of which may cause the spread of disease, particularly in the immunocompromised or the elderly. This study investigated the emission strength of three types of airborne bacteria, namely Staphylococcus epidermidis, Escherichia coli, and Pseudomonas alcaligenes, during toilet flushing in a custom‐built toilet under a controlled environment. Flushing was activated by a flushometer operated at two pressure levels, 400 kPa (high pressure [HP]) and 200 kPa (low pressure [LP]), and by a water cistern tank placed 95 cm (high tank [HT]) and 46 cm (low tank [LT]) above the toilet seat. The pathogens emitted by the first flush were calculated, with the correlations between airborne pathogen emissions and droplet concentration (HP, r=0.944, P<.001; LP, r=0.803, P<.001, HT, r=0.885, P<.05) and bacterial size (HP, r=?0.919, P<.001; LP, r=?0.936, P<.001; HT, r=?0.967, P<.05) in the different conditions then tested. The emission strength in the HP condition was statistically greater than that in the LP condition, whereas the cistern tank system produced less emissions than the flushometer system, and tank height was not found to be a sensitive parameter.     

坐便器冲洗功能试验介质的比较分析

介绍了国内外坐便器冲洗功能试验相关的冲洗介质,通过比较国内外标准中冲洗介质的区别,分析不同国家之间的差异及关键影响因素。     

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.     

A dimensionless approach for the urban-scale evaluation of domestic rainwater harvesting systems for toilet flushing and garden irrigation

A dimensionless methodology to evaluate the water saving obtainable from large-scale implementation of domestic rain water harvesting (RWH) systems in urban areas is presented. The methodology combines the use of regressive relationships for water saving evaluation based on the results of the dimensionless rainwater tank water balance and of catchment-wide information obtained from geospatial databases. The adopted RWH scheme included internal use of rainwater for toilet flushing and external use for garden irrigation. An application to a portion of the city of Rome, Italy showed the methodology to allow systematic and accurate evaluation of RWH system performance at the selected urban scale. Results pointed out high water saving potential for toilet flushing ranging between 38–65% for tank sizes within 1–50 m³. Furthermore, more than one third of the systems provided water saving benefit for irrigation larger than 20% by using a 50 m³ tank.     

Eggcrate UV: a whole ceiling upper‐room ultraviolet germicidal irradiation system for air disinfection in occupied rooms

A novel whole ceiling upper‐room ultraviolet germicidal irradiation (UVGI) system [eggcrate ultraviolet (UV)] has been developed that incorporates open‐cell ‘eggcrate’‐suspended ceiling panels and bare UV lamps with a ceiling fan. Upper‐room UVGI is more effective for air disinfection than mechanical ventilation at much lower installation and operating costs. Conventional upper‐room UVGI fixtures employ multiple tightly spaced horizontal louvers to confine UV to the upper‐room. These louvered fixtures protect occupants in the lower‐room from UV‐induced eye and skin irritation, but at a major cost to fixture efficiency. Using a lamp and ballast from a conventional upper‐room UVGI fixture in the eggcrate UV system, the germicidal efficacy was markedly improved even though the UV radiation emitted by the lamp was unchanged. This fundamental change in the application of upper‐room UVGI air disinfection should permit wider, more effective application of UVGI globally to reduce the spread of airborne infection.     

Comparison of engineering costs of raw freshwater, reclaimed water and seawater for toilet flushing in Hong Kong

Hong Kong is one of the very few coastal cities in the world that use ‘dual water supply systems’. Dual water supply involves two distribution systems: a freshwater system for potable use and a seawater system for toilet flushing. This study looks into the feasibility, from an engineering cost point of view, of extending seawater supply into districts where potable water is still being used for toilet flushing, including South District of Hong Kong Island, Sai Kung, Northern New Territories and Northwest New Territories. Besides seawater, raw (untreated) freshwater and reclaimed water (treated effluent from local sewage treatment works) are also considered to be used for toilet flushing for these districts. Six cases are developed for comparison by using the lowest net present value of cost criterion. The result shows that using seawater for toilet flushing in these districts has the best engineering economy.     

Electrochemical disinfection of biologically treated wastewater from small treatment systems by using boron-doped diamond (BDD) electrodes – Contribution for direct reuse of domestic wastewater

The aim of the study was to demonstrate the application potential of boron-doped diamond electrodes (BDD) in electrochemical disinfection of biologically treated sewage for direct recycling of domestic wastewater. Discontinuous bulk disinfection experiments with secondary effluents and model solutions were performed to investigate the influence of operating conditions and wastewater parameters on disinfection efficiency and formation of disinfection by-products (adsorbable organically bound halogens, AOX). The inactivation rate accelerates with increasing current density caused by a faster generation of electrochemical oxidants (ECO). It could be shown that the effect of OH radicals in case of the direct electrochemical disinfection of chloride-containing secondary effluents with BDD is negligible because of their fast reaction with typical radical scavengers. The dominating role of electrochemically generated free chlorine in the disinfection process could be explicitly verified. It could be also shown that the disinfection efficiency is strongly affected by the specific wastewater parameters temperature and pH. These effects can be explained by the behaviour of the reactive species. The migration-controlled generation of ECO can be accelerated under turbulent hydrodynamic conditions. The formation of disinfection by-products (AOX) correlates with the introduced electric charge Q applied per volume and is independent of the applied current density.     

A new system for the construction of large shallow tunnels by microtunnelling technology

The article describes the results of a numerical analysis intended to simulate the behaviour of an elliptical tunnel lining which has been installed using a new methodology able to reduce drastically the phenomenon of subsidence. The innovation of this method, called the “pre-assembled shell”, is the construction method of the lining, consisting of high-resistance reinforced concrete tubing inserted into the ground by microtunnelling technology. The tubing elements are suitably connected to each other both longitudinally and transversally, to create a highly rigid and stable lining, before the excavation of the ground from within the cavity. The results of the analysis have highlighted a rigid behaviour of the lining with small ground subsidence, which could make this technique particularly suitable for large tunnels with small degrees of cover.     

Protection against UV disinfection of E. coli bacteria and B. subtilis spores ingested by C. elegans nematodes

Nematodes, which occur abundantly in granular media filters of drinking water treatment plants and in distribution systems, can ingest and transport pathogenic bacteria and provide them protection against chemical disinfectants. However, protection against UV disinfection had not been investigated to date.In this study, Caenorhabditis elegans nematodes (wild-type strain N2) were allowed to feed on Escherichia coli OP50 and Bacillus subtilis spores before being exposed to 5 and 40 mJ/cm² UV fluences, using a collimated beam apparatus (LP, 254 nm). Sonication (15 W, 60 s) was used to extract bacteria from nematode guts following UV exposure in order to assess the amount of ingested bacteria that resisted the UV treatment using a standard culture method. Bacteria located inside the gut of C. elegans were shown to benefit from a significant protection against UV. Approximately 15% of the applied UV fluence of 40 mJ/cm² (as typically used in WTP) was found to reach the bacteria located inside nematode guts based on the inactivation of recovered bacteria (2.7 log reduction of E. coli bacteria and 0.7 log reduction of B. subtilis spores at 40 mJ/cm²). To our knowledge, this study is the first demonstration of the protection effect of bacterial internalization by higher organisms against UV treatment, using the specific case of E. coli and B. subtilis spores ingested by C. elegans.     

A new operating strategy for economizer dampers of VAV system

The paper proposes a new operating strategy for the outdoor, discharge, and recirculation air dampers of the economizer in VAV system, called split-signal damper control strategy. The strategy controls the outdoor air by only one damper while keeping the remaining dampers full open. The discharge or recirculation air damper is modulated to control the amount of outdoor air introduced into the system while keeping the two remaining dampers full open. Since at least two dampers are always kept fully open during the occupied times, the strategy can provide a minimum static pressure drop in economizer dampers and results in minimum energy use in return and supply fans. An additional advantage is that the proposed strategy prevents reverse airflow through the discharge air damper of a VAV system that uses a volume matching control strategy. The proposed strategy along with the existing strategies such as the three-coupled dampers used in most existing system and the two-coupled dampers are evaluated on an existing system using 1-year long measured data set, along with an economizer damper model developed and validated in this paper. The simulation results show that the annual energy savings in supply and return fans of an existing system, compared to the traditional strategy of three-coupled dampers, are 12% and 5%, respectively.     

Experimental analysis of energy recovery for humidity control in split A/C system

This study presents a proposed idea about making use of the thermal energy rejected by the condenser in a water-cooled split-air-conditioning systems to decrease the relative humidity of the cold air supplied by such air conditioners. Most of split air-conditioner systems cool air without controlling its humidity. An amount of heat is rejected from the air conditioner, through the condenser, into the surrounding in order to allow the refrigerant to cool down and condense, thus, part of the lost energy can be exploited to decrease the relative humidity of the sub-cooled air that leaves the evaporator as saturated humid air. Four variables, viz. the coil type (single or double), the amount of flowing water, water, temperature, and the cooled air velocity were studied to find out the optimum conditions required for this purpose. The requisite amount of heat that may adjust the relative humidity of the conditioned air was also determined. The experimental results suggest an optimum design of a heat exchanger for performing the use of the heat rejected from the condenser to achieve the aim. As a result, the proposed heat recovery concept can be worthily adopted to achieve economic results in large-scale systems.     

新损伤模型研究硫酸盐侵蚀后砂浆的性能

假设损伤变量D服从二参数的Weibull分布,建立一种新的损伤模型,推导出本构方程,并将其运用到硫酸盐侵蚀后砂浆的性能研究.大量的试验证实了假设的合理性.     

城市独立坐标系转换为CGCS2000椭球时投影参数的选取方法

本文提出一种将原城市坐标系转换为CGCS2000椭球时投影参数的最佳选取方法,该方法采用坐标转换、高斯投影等模型,通过修正投影面高程和子午线收敛角来保证新老城市坐标投影变形尺度比一致,实现了老城市坐标系到基于CGCS2000的新城市坐标系的转换,使得新老城市坐标差异极小,老城市坐标无须转换就可以直接在新坐标系下使用,极...     

A new early-warning prediction system for monitoring shear force of fault plane in the active fault

The most common method used to describe earthquake activity is based on the changes in physical parameters of the earth＇s surface such as displacement of active fault and seismic wave.However,such approach is not successful in forecasting the movement behaviors of faults.In the present study,a new mechanical model of fault activity,considering the shear strength on the fault plane and the influence of the resistance force,is established based on the occurrence condition of earthquake.A remote real-time monitoring system is correspondingly developed to obtain the changes in mechanical components within fault.Taking into consideration the local geological conditions and the history of fault activity in Zhangjiakou of China,an active fault exposed in the region of Zhangjiakou is selected to be directly monitored by the real-time monitoring technique.A thorough investigation on local fault structures results in the selection of two suitable sites for monitoring potential active tectonic movements of Zhangjiakou fault.Two monitoring curves of shear strength,recorded during a monitoring period of 6 months,turn out to be steady,which indicates that the potential seismic activities hardly occur in the adjacent region in the near future.This monitoring technique can be used for early-warning prediction of the movement of active fault,and can help to further gain an insight into the interaction between fault activity and relevant mechanisms.     

瓷砖生产线中一种新设备——辊道窑入窑和旁路贮坯系统

辊道窑入窑及旁路贮坯系统是瓷砖生产线上贮坯的一种新型系统,具有投资小,占地少,坯损低,节省电耗等优点.适应于瓷砖生产线贮坯系统的技术改造,本文介绍此项专利技术的基本构成和系统特点.     

A new approach for simulating aerodynamic vibrations of structures in a wind tunnel—development of an experimental system by means of hybrid vibration technique

The present paper describes a newly proposed technique for simulating aerodynamic vibration of structures, which is referred to as the hybrid vibration technique or HVT. This technique is a combination of step-by-step computer calculation and measurement of the aerodynamic force acting on a model structure in a wind tunnel test. Even though the HVT can be applied effectively, problems still exist with respect to obtaining accurate simulations. These problems include response delay in controlling the model behavior and the inertia force component present in the measured aerodynamic force. Techniques for compensating for response delay and for eliminating inertia force from measured aerodynamic force are applied to a developed system based on HVT simulations of aerodynamic vibration of elastic structures and structures exhibiting elasto-plastic behavior are performed by means of the newly developed system. The effectiveness of the techniques for compensating for the response delay and eliminating the inertia force can be confirmed from the results of the simulations. In addition, the possibility and applicability of HVT is indicated.     

A new device for measurement and control of gas production by bench scale anaerobic digesters

On the basis of an analysis, in terms of desirable characteristics and main sources of error, of existing apparatus for measuring biogas production by laboratory anaerobic digesters, we have developed a new device that is precise, inexpensive, easily constructed and capable of functioning autonomously for long periods. A slightly costlier version suitable for use in automatic control systems is also described.     

A new method for characterizing denitrifying phosphorus removal bacteria by using three different types of electron acceptors

This study investigated the characteristics of denitrifying phosphorus removal bacteria by using three different types of electron acceptors as well as the positive role of nitrite in phosphorus removal process. Denitrifying phosphorous removal bacteria was enriched under anaerobic-anoxic (A/A) condition. To understand A/A sludge better, sludge from two other sources were also studied. These include sludges obtained from a lab-scale anaerobic-anoxic-aerobic (A/A/O) system and a local sewage treatment plant. Three types of possible electron acceptors (oxygen, nitrate and nitrite) were examined for their roles in phosphorus uptake. The results obtained indicated that oxygen, nitrate and nitrite were able to act as electron acceptors successfully. This observation suggested that in addition to the two well-accepted groups of phosphorus removal bacteria (one can only utilize oxygen to take up phosphorus, P(O), while the other can use both oxygen and nitrate, P(ON)), a new group of phosphorus removal bacteria, P(ON(n)), which could use oxygen, nitrate or nitrite to take up phosphorus was identified. The relative population of these three types of bacteria could be calculated from results obtainable from phosphorus uptake batch experiments with either oxygen or nitrate or nitrite as electron acceptor. The results obtained in this study showed that A/A sludge had similar phosphorus removal performance as the A/A/O sludge. However, it has better denitrifying phosphorus removal capability, which was demonstrated by the relative population of the three groups of bacteria. The results also suggested that nitrite was not an inhibitor to phosphorus removal process. Instead, it is an alternative electron acceptor to oxygen or nitrate.