Contaminant Removal Effectiveness Research Articles

Comparison between vortex flow and bottom-supply flow on contaminant removal in a ventilated cavity

To maintain the indoor air quality, it is critical to remove indoor contaminant by ventilation system with effective air distribution. This paper presents a new air distribution model termed as vortex flow model by using the principle of column vortex. The flow field characteristics and transient contaminant movement in vortex flow model are numerically investigated in a ventilated cavity under an isothermal condition, and comparisons are made with traditional bottom-supply flow model. The results show that the contaminant diffusion in vortex flow model are greatly restricted by the column vortex, which leads to smaller diffusion range in occupied zone than that of bottom-supply flow model. Meanwhile, it needs less response time for the vortex flow model to remove the contaminant in occupied zone. Furthermore, the vortex flow model exhibits higher ventilation effectiveness of contaminant removal than that of bottom-supply flow model for different ventilation flow rates. The studies in the paper are beneficial to the future research and design of this air distribution system.

Life cycle assessment comparison of industrial effluent management strategies

Abstract A process model was analysed with life cycle assessment (LCA) to evaluate the environmental tradeoffs of fourteen process alternatives treating a pulp and paper effluent with high levels of chemical oxygen demand (COD) and adsorbable organic halides (AOX). The process alternatives were constructed from six unit processes: dissolved air flotation, clarification, activated sludge, upflow anaerobic sludge blanket reactor, ultrafiltration and reverse osmosis (RO) treatment. The tradeoffs between environmental impact categories were investigated, focussing on eutrophication, freshwater aquatic ecotoxicity (FWAE), greenhouse gas (GHG) emissions and water extraction. For each configuration, the water recovery and contaminant removal effectiveness were compared against GHG emissions. While the most intense treatment option was able to reduce AOX by 99.6% and COD by 99.9%, the FWAE and eutrophication categories had a reduction of only 98.6% and 94.2%, respectively. The GHG emissions were heavily influenced by sludge landfilling contributing between 39% and 71% of overall emissions, with electricity production becoming significant as treatment intensity increased. The alternatives considered were able to produce a recycled water stream composed of 3%–100% of treated effluent. Configurations using RO produced effluent with sufficient quality to be used in recycled water applications without dilution. Configurations with ultrafiltration as the highest level of treatment could produce a recycled water stream composed of 35%–81% treated effluent. Contaminant discharge impacts, water recovery and GHG emissions did not have a single optimal configuration. The study demonstrates the ability of this model to identify marginal tradeoffs between environmental impacts.

On the Trade-Off between Industrially Feasible Silicon Surface Preconditioning Prior to Interface Passivation and Iron Contaminant Removal Effectiveness

We are investigating the effect of different wet chemical surface preconditioning sequences for silicon wafers prior to the deposition of aluminum oxide based passivation layers coated by plasma enhanced chemical vapor deposition. We are focusing on the development of a simple and industrially feasible preconditioning process to achieve a high level of interface passivation after the firing process applied to industrial solar cells. Our process optimization is monitored by characterizing the passivation quality before and after a firing process. We are also investigating the effectiveness of the removal of residual surface iron concentrations by the wet chemical process.

Comparison of air change efficiency, contaminant removal effectiveness and infection risk as IAQ indices in isolation rooms

An effective design of the ventilation system of the isolation rooms for infectious patients can reduce the risk of spreading infections. However, no consensus exists regarding the placement of the air inlets and outlets which minimises the risk of spreading infection. In this work, we use computational fluid dynamics (CFD) to evaluate the ability of the ventilation system to minimise the risk of infection in the rooms of isolated infectious patients. We analyse the influence of the position of the air inlets and outlets. We take into account the deposition and viability of the infectious particles. To compare the different configurations quantitatively, three types of indices are employed: those which quantify the capacity to renew the air; those which quantify the capacity to remove a contaminant and those which quantify the risk of airborne infection. These three types of indices are applied to the entire isolation room and in specific zones of the room in order to evaluate the quality of the ventilation globally and locally respectively. Likewise, using different air diffusers we demonstrate the importance of the diffuser on the air flow pattern and, therefore, on the quality of the ventilation.

Air distribution and ventilation effectiveness in an occupied room heated by warm air

Air distribution, ventilation effectiveness and thermal environment were experimentally studied in a simulated room in a low-energy building heated and ventilated by warm air supplied by a mixing ventilation system. Measurements were performed for various positions of the air terminal devices and at different simulated outside conditions, internal heat gains and air change rates. Floor heating was also simulated and compared with the warm air heating system. Vertical air temperature profiles, air velocity profiles and equivalent temperatures were derived in order to describe the thermal environment. Contaminant removal effectiveness and air change efficiency were used to evaluate ventilation effectiveness. No significant risk of thermal discomfort due to vertical air temperature differences or draught was found. When the room was heated by warm air, buoyancy forces were important for ventilation effectiveness at low air change rates. The effect of increasing air change on the ventilation effectiveness depended on the position of air terminal devices. Depending on the position of air terminal devices, the ventilation effectiveness varied between 0.4 and 1.2, where 1 is complete mixing. When a radiant floor heating system was simulated, the cooler ventilation air introduced to the room mixed well and created uniform conditions with a ventilation effectiveness of about 1.

Impact of Room Supply Register Location on Predicted Thermal Comfort and IAQ

For residential forced air heating and cooling systems conventional thinking is that air supply registers should be located under exterior windows. There were good reasons for this in the past (primarily to counteract the cold downdraught from the window) but new construction standards (well-insulated walls, better glazing and air tight wall/window interface) mean that there is now less downdraught. Positioning the supply air register away from a window could have a large impact for new construction as duct lengths could be shortened (saving materials and construction time). This could also allow greater architectural freedom as the forced air system would not need to be ducted to the building perimeter. This paper presents results from experiments conducted in a new, well-constructed building to evaluate whether the supply registers can be moved away from the traditional location without impacting indoor air quality or predicted thermal comfort. The physical experiments showed that in both traditional and non-traditional placement: (1) there are minimal changes in predicted thermal comfort (a measure of thermal discomfort - vertical air temperature difference much lower than 3K), and (2) contaminant-removal effectiveness (a measure of indoor air quality) values were in the same range.

Mitigation of cross-contamination in an aircraft cabin via localized exhaust

Most aircraft cabin ventilation designs currently use a 50% mix of fresh and recirculated, filtered air and supply approximately 8–10 l/s per person. In order to make the most efficient use of the air supply at hand, the 50% of cabin air that is exhausted from the aircraft should remove with it as much contaminant from within the cabin as possible. This will thereby reduce cross-contamination among passengers and improve overall air quality. This study examines the use of localized suction orifices near and around the source occupant to unobtrusively ingest the individual’s thermal plume and exhaust it from the aircraft cabin before contaminants entrained in the plume can significantly mix with the bulk airflow. Through the use of Computational Fluid Dynamics (CFD), various suction seat designs have been tested for their contaminant removal effectiveness and subsequent cross-contamination reduction. CFD results indicate significant improvements over conventional mixing air ventilation systems with a 40–50% decrease in passenger exposure predicted in a conventional coach-class seating arrangement.

Laboratory Batch Test Evaluation of Five Filter Materials for Removal of Nutrients and Pesticides from Drainage Waters

Where subsurface drainage practices are employed, fertilizer nutrients and pesticides applied on farm fields and municipal locations are commonly intercepted by the buried drainage pipes and then discharged into local streams and lakes, oftentimes producing adverse environmental impacts on these surface water bodies. Various filter materials have the potential to remove nutrient and pesticide contaminants from subsurface drainage waters before these waters are released offsite. For this study, laboratory batch tests were conducted to evaluate the contaminant removal effectiveness and efficiency of five potential filter materials. The five materials, isolated from previous screening tests, were steam activated carbon, high calcium oxide - high carbon fly ash, iron sulfide, sulfur-modified iron, and surfactant-modified zeolite. Filter material effectiveness was tested against initial contaminant solution concentrations that varied between 10 and 200 mg L-1 for nitrate-N, 0.1 and 1.0 mg L-1 for phosphate-P, and 0.1 and 0.5 mg L-1 for atrazine, while filter material efficiency was evaluated with respect to exposure time by varying test durations from 1 to 24 h. Sulfur-modified iron proved best for treating nitrate, based on reductions greater than 95% across the range of initial concentration levels and exposure times. Surfactant-modified zeolite and high calcium oxide - high carbon fly ash affected the greatest removal of phosphate, 50% or more in all cases. For atrazine, the most promising results were obtained with steam activated carbon and high calcium oxide - high carbon fly ash, which removed almost 100% of this particular pesticide regardless of initial concentration level and exposure time. Consequently, there are several filter materials, when used either alone or in combination, that show promise for removing mixed contaminants from subsurface drainage water; however, more laboratory testing followed by field experiments are needed to completely evaluate their feasibility for widespread use.

Removal of inorganic trace contaminants by electrodialysis in a remote Australian community

Water provision for developing countries is a critical issue as a vast number of lives are lost annually due to lack of access to safe drinking water. The presence and fate of inorganic trace contaminants is of particular concern. Trace inorganic contaminants have been found in elevated concentrations in drinking waters supplied directly from brackish groundwaters in developing countries. Desalination and the removal of trace inorganic contaminants from bore water sources from a remote community in Australia using electrodialysis (ED) were investigated. The influence of applied voltage on the removal of the trace contaminants was evaluated. While the results from this study demonstrated that ED is an effectual method for the removal of total dissolved solids and a number of trace inorganic contaminants from brackish groundwaters to below drinking water guideline levels, the deposition of trace contaminants on the membranes (fouling) influenced the ED process in relation to ionic flux and the effectiveness of trace contaminant removal.

Three-dimensional analysis for hospital operating room thermal comfort and contaminant removal

This paper presents a three-dimensional analysis for thermal comfort and contaminant removal in a hospital operating room. The room model includes a patient lying on an operating table, four surgical staff members standing around, and surgical lights above the patient. Cold clean air is supplied to the room through high sidewall grilles and exhausted through low sidewall grilles on the opposite wall. Steady-state heat and mass transfer in the room are simulated by employing computational fluid dynamics modeling approach. Solutions of the distribution of airflow velocity, temperature, relative humidity, and contaminant concentration are presented and discussed. The simulation results show a good agreement with experimental data from the literature. The predicted mean vote (PMV) is calculated for assessing thermal comfort of the occupants. The contaminant removal effectiveness (CRE) and the mean contaminant concentration in the breathing zone are used to assess the ventilation performance of the room. Effects of horizontal locations of supply and exhaust grilles on thermal comfort and contaminant removal are explored. Regression models for thermal comfort and contaminant removal as functions of these locations are built for design optimization. It is found that an overall better performance can be achieved by placing the supply grilles closer to the vertical centerline of the wall while the location of the exhaust grilles is somewhat insignificant.

Field synergy analysis and optimization of the convective mass transfer in photocatalytic oxidation reactors

A convective mass transfer field synergy equation with a specific boundary condition for photocatalytic oxidation reactors developed based on the extremum principle of mass transfer potential capacity dissipation can be used to increase the field synergy between the velocity and contaminant concentration gradient fields over the entire fluid flow domain to enhance the convective mass transfer and increase the contaminant removal effectiveness of photocatalytic oxidation reactors. The solution of the field synergy equation gives the optimal flow field, having the best field synergy for a given viscous dissipation, which maximize the contaminant removal effectiveness. As an illustrative example, the field synergy analysis for laminar mass transfer in plate type reactors is presented. The analysis shows that generating multiple longitudinal vortex flow in the plate type reactor effectively enhances the laminar mass transfer. With the guide of the optimal velocity pattern, the discrete double-inclined ribs can be introduced in actual applications to generate the desired multi-longitudinal vortex flow, so as to enhance the laminar mass transfer, and consequently, improve the contaminant removal performance. The experimental result shows that the contaminant removal effectiveness for the discrete double-inclined ribs plate reactor is increased by 22% compared to the smooth plate reactor.

The effect of perceived indoor air quality on productivity loss

This theoretical study reports on the impact of perceived indoor air quality for productivity loss in air-conditioned office buildings. A new derivation of productivity calculation model based on pollution loads and contaminant removal effectiveness is applied and the effect of the improved ventilation efficiency on productivity is estimated. The findings show that the proportion dissatisfied is a good predictor of productivity loss due to indoor air quality in different kinds of office work. It is possible to calculate the proportion dissatisfied from olf and decipol units. Productivity is possible to improve by increasing outdoor airflow rate, decreasing emissions and improving ventilation efficiency e.g. with displacement ventilation. In a case of one person per 10 m 2 (0.1 olf/m 2) and low-emitted material (0.1 olf/m 2), the total sensory pollution load is 0.2 olf/m 2. Normally, the minimum admissible outdoor airflow rate is 0.5–1.5 l/s per m 2 in office spaces. This means that 5–9% productivity loss should be accepted using the minimum airflow rate design method. With displacement ventilation, it is possible to improve indoor air quality in a manner that significantly increases productivity compared with traditional mixing system. The effect of the contaminant removal effectiveness on the productivity loss is about 0.5–2% between these systems using the same airflow rate.

Numerical investigation on the efficiency of transient contaminant removal from a food processing clean room using ventilation effectiveness concepts

Clean rooms are widely used in food-processing industries to guarantee the quality of food products. To maintain the desired cleanliness class in these large and complex enclosures, high ventilation rates are usually used. The recommended air change rates, based on empirical formulas, generate large energy consumptions and do not always guarantee the desired cleanliness class. The objective of this work is to provide a new methodology to properly design the air distribution in clean rooms and to optimise the process arrangement. A complete numerical study is made on the efficiency of transient contaminant removal from a full scale clean room intended for food manufacturing. We combine CFD simulations with the calculation of selected ventilation criteria. The contaminant removal effectiveness and the mean age of air permit to optimise the contaminant source position and to determine decontamination time respectively. These numerical results corroborate previous experimental observations and can lead to new recommendations.

Ventilation Effectiveness Parameters Resulting from Mechanical Ventilation with Recirculation

The effectiveness of a ventilation system in terms of the age of air and its ability to remove contaminants will be significantly affected if part of the exhaust air is recirculated. In this paper the consequences of recirculation of air in mechanical ventilation systems on ventilation effectiveness parameters is examined. Two alternative methods of establishing ventilation effectiveness parameters relating to air change efficiency and contaminant removal effectiveness when recirculation of air is present are presented. The procedures are compared by way of a four-zone example, which demonstrates equivalence between the two methods. The effect of recirculation on quality of air in terms of local mean age and local air quality index are investigated as is the sensitivity of internal air quality to the fraction of the supply air which is recirculated.

CONTAMINANT AND HEAT REMOVAL EFFECTIVENESS OF THREE VENTILATION SYSTEMS IN NURSERY ROOMS FOR PIGS

In this research, three ventilation systems (ground channel, porous ceiling, and door ventilation) were tested on their performance in supplying fresh air to the animal occupied zone (AOZ), each in a room for 70 weaned piglets. Measurements of the CO2 concentration and temperature of the inlet air, at one point in the AOZ, and in the outlet air were recorded every 36 minutes for three successive batches. Less frequent measurements were done on the CO2 concentration in two other points in the AOZ. System effectiveness was expressed as the contaminant removal effectiveness (CRE) for CO2 and the heat removal effectiveness (HRE): CRE or HRE equals 1 when the CO2 concentration or temperature in the AOZ equals that of the outlet air. Values lower than 1 reflect higher CO2 concentrations or temperatures within the AOZ; values higher than 1 the reverse. In all rooms, the value of CRE or HRE varied in time by varying the ventilation rate. CRE was highest in the room with ground channel ventilation, varying with measurement location. CRE was 1.39 on average and HRE was 1.13 on average in the middle of the pen. CRE was higher closer to the air inlet and lower further to the back of the pen, closer to the outlet, because air renewal was based on displacement of old air by fresh air. In the room with door ventilation, CRE was 1.20 and HRE was 0.95 at a point in the second half of the room in the back of a pen. Air passed over the operator walkway to the back of the room, and back over the pens, resulting in a decreased CRE in the pens closer to the door that acted as an air inlet. In the room with a porous ceiling, CRE values were lower. At one sampling point, CRE was 1.01 and HRE was 0.94. In the lying area of the animals in the back of the room, CRE values were lower than at a sampling point in the front of the room. In the lying area, the heat production of the animals resulted in an upward airflow, which lowered the CRE.

Influence of the floor-based obstructions on contaminant removal efficiency and effectiveness

Dimensioning of dilution ventilation is often made using the perfect mixing approximation, assuming uniform contaminant concentration throughout the room space. However, the contaminant removal efficiency and effectiveness of air conditioning system should be accounted for during design. The effectiveness is in this context used as a measure of the contaminant distribution uniformity within the occupied zone. Influence of an occupied zone obstruction level, air distribution method, air change rate, cooling load and contaminant source non-uniformity on the contaminant removal efficiency and occupied zone contaminant concentration uniformity were studied in scale model. The room air distribution method results in contaminant concentration non-uniformity inside the occupied zone. A method was developed to take this into account during the design of air distribution system. Contaminant supply non-uniformity was found to have great influence on the concentration non-uniformity with two tested air distribution methods.

Non-buoyant pollutant sources and particles in displacement ventilation

Particle transportation and ventilation efficiency, with non-buoyant pollutant sources, in a displacement-ventilated room were evaluated. A resuspension of floor deposited particles caused by the influence of the supply air or people moving around may increase the number of particles in the convection flows. Particle concentrations at different positions under steady state and transient conditions were measured. The results indicate that there seem to be little risk of resuspension of particles, in the measured size interval, by the influence of the supply air. With a forced resuspension the particle concentrations in the convection flows differ from the concentration outside the convection flow. The contaminant removal effectiveness was much dependent on the position of the pollutant sources.

Airborne Contaminant Exposure Control in a Partitioned Work Environment by Exhaust Ventilation Systems

The evaluation of contaminant removal effectiveness can play a key role in a working environment quality investigation and in remediation efforts. In this study a computer simulation technique was developed for assessing the efficiency of contaminant removal within a partitioned working environment. To determine the effect of the physical parameters of each partitioned space on contaminant removal effectiveness, a relative contaminant concentration unit was used to show the simulation results. In addition, tracer gas techniques were adopted to validate the accuracy of the prediction model. A comparison of measured CO2 concentrations in a controlled environment chamber with the results of a simulation model is presented. This study investigated the partition configuration of work environment and environment parameters including openings operation, constant concentration, and exhaust air volume mode. Results indicated that variations of the above three parameters can produce great differences in overall ventilation performance. Through this type of study, the interaction of airflow and contaminant concentration between partitioned spaces can be understood in advance and adequate knowledge can be provided to maintain a high-quality and healthy environment for workers.

NUMERICAL PREDICTION OF CONTAMINANT TRANSPORT AND INDOOR AIR QUALITY IN A VENTILATED OFFICE SPACE

ABSTRACT A numerical study of air movement and contaminant transport is made to predict air flow patterns, ventilation performance and indoor air quality in a typical office space. Both conventional cooling and cold air jet cooling methods are investigated. The space heat load is from a hot wall that creates a plume. This plume either opposes or aids the flow of the jet depending on its location. The transient variation of room occupied zone average concentration is exponential after a change of the source strength equivalent to a change in the number of people in the room. The ventilation efficiency as well as the contaminant removal effectiveness of cold jet cooling is nearly the same as conventional cooling. Turnover time for cold air jet cooling is about 53% higher than conventional cooling when the hot plume aids the jet and 43% higher when it opposes the jet. The highest ventilation efficiency was ηv = 1.3 when the room is cooled with conventional temperature supply air, the plume opposed the jet and the contaminant source was located near the hot wall. The worst condition, ηv = 0.8, occurs when the air close to the pollutant source is stagnant. This happens for the room with an opposing plume, cold air jet cooling and a contamination source near the wall opposite the heated wall.

Assessment of horizontal displacement flow with tracer gas pulse technique in reinforced plastic plants

Displacement ventilation systems are usually based on thermal stratification due to buoyancy forces generated by warm processes in industrial buildings. However, there are many processes in which contaminant emission and heat generation are not coupled together, e.g. lamination of glass-fibre reinforced polyester products. In order to control air contaminants in processes like this, a displacement flow created horizontally across a room may be useful. This study evaluates the performance of a horizontal displacement ventilation system in two lamination rooms where reinforced plastic boats up to 17 m in length are manufactured. The tracer gas pulse technique was used to measure air change efficiency, local air change index and contaminant removal effectiveness.