Efficiency contaminant removal

Application of contaminant removal effectiveness indices is relatively simple for scenarios with one or a few dominant contaminants being released. That is often the case in industrial mails. Where there are many polluting substances to consider the contaminant removal efficiency should ideally be evaluated for each one. Consequently, applications for regular indoor climate— for example, in a restaurant—are limited, except when addressing specific pollutants like smoking and ctxrking hunes. 

The contaminant removal efficiency can be derived from the coniaminaiu removal effectiveness as follows  

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Ventilation efficiency has traditionally been defined as the ratio between contaminant concentration in the occupied spaces and the concentration in the exhaust air. Sandberg and Skaret differentiate between the terms air change efficiency and contaminant removal effectiveness. Air change efficiency is a measure of how effectively the air present in a room is replaced by fresh air from the ventilation system, whereas contaminant removal effectiveness is a measure of how quickly an air-borne contaminant is removed from the room. A third similar criterion that is used is contaminant removal efficiency. ... 

Where small and/or single contaminant effluents are encountered, packaged treatment plants may be acceptable. Consideration should, however, be given to capital cost, payback period, reliability of equipment, maintenance, plant-life expectancy and contaminant-removal efficiencies. 

A schematic block-flow diagram is presented as Figure 1. Contaminated soil is passed continuously through an indirectly heated desorber which can be one of many types of conventional equipment applicable for thermal processing of solids. The treatment performance of the desorber is controlled by the residence time and temperature of the soil. Treatment requirements (i.e., operating conditions) are determined by the volatility of the soil contaminants and the required contaminant removal efficiency (final versus initial concentration). 

MF may be used to remove these heavy metals provided pretreatment chemicals are added to precipitate the metals to particles of filterable size. The chemical pretreatment step is crucial since it will affect the performance of the membrane and the resultant sludge volume as well as the contaminant removal efficiency. Reduction/oxidation, absorption/oxidation, and/or catalytic reactions are utilized along with pH adjustment to provide the optimum precipitation. Although conventional methods of waste water treatment may use a similar pretreatment chemistry, the final solid/liquid separation by gravity settling is usually not as effective as membrane filtration. 

Below, laboratory studies on the electrokinetic removal of PAHs are discussed according to the types of solubility-enhancing agents used and the effects of electrokinetic variables on contaminant removal efficiency. 

The application of an electric flied to moisten a porous matrix also induces chemical reactions in the soil and upon the electrodes. Chemical reactions include acid-alkaline reactions, redox reactions, adsorption-desorption reactions, and dissolution-precipitation reactions. Such reactions dramatically affect the speciation of the contaminants and therefore affect the transportation and contaminant removal efficiency [4]. 

Table 13.1 summarizes the contaminant removal efficiencies of some of the technologies listed above. 

Some manufacturers do not base their nominal rating on 98% contaminant removal by weight, hut instead a contamination removal efficiency of 95%, 90%, or even lower. Thus, it often happens that a filter with an absolute rating of 10 tm is actually finer than another filter with a nominal rating of 5 pm. Therefore, it is always advisable to check the criteria upon which a nominal rated filter is based. 

Process condensate from reforming operations is commonly treated by steam stripping. The stripper is operated at a sufficiently high pressure to allow the overhead stripping steam to be used as part of the reformer steam requirement (71). Contaminants removed from the process condensate are reformed to extinction, so disposal to the environment is thereby avoided. This system not only reduces atmospheric emissions, but contributes to the overall efficiency of the process by recovering condensate suitable for boiler feedwater make-up because the process is a net water consumer. 

Mechanical Gleaning. A cleaner is a hydrocyclone device utilizing fluid pressure to create rotational fluid motion (20). Pulp is introduced tangentially near the top of the cleaner. Contaminants denser than water such as chemically treated toner inks and sand migrate toward the outer wall of the cleaner and exit in a separate (reject) stream. For most forward cleaners, optimal ink removal efficiency is obtained at a pulp consistency of 0.2—0.3%. Most forward cleaners deinking efficiency declines at pulp feed consistencies greater than 0.4%. However, a cleaner said to be efficient at 1.2% pulp consistency has been reported (39). 

Tank settling as a means of contaminant removal is not very efficient with fuels having the viscosity of kerosene. It is common practice to design tanks with cone-down drains and floating suctions to facilitate water and solids removal. 

Relatively low removal efficiency for gaseous contaminants (at concentrations typical of pollution-control applications)... 

Chemical pretreatment is often used to improve the performance of contaminant removal. The use of chemical flocculants is based on system efficiency, the specific DAF application and cost. Commonly used chemicals include trivalent metallic salts of iron, such as FeClj or FeSO or aluminum, such as AISO. Organic and inorganic polymers (cationic or anionic) are generally used to enhance the DAF process. 

As mentioned above, the traditional definition of ventilation efficiency or, in approved terms, contaminant removal effectiveness, is the ratio between contaminant concentration in the exhaust air and the concentration at a point in the occupied space, i.e.,... 

The contaminant removal and temperature effectiveness in the mixing strategy are equal to 1. In practical installations incomplete mixing in the room and unfavorable temperature gradient and location of the exhaust openings in relation to air supply may, however, cause short-circuiting of the supply air into the exhaust openings and the efficiency may remain below 1. 

In catalytic incineration, organic contaminants are oxidized to carbon dioxide and water. A catalyst is used to initiate the combustion reaction, which occurs at a lower temperature than in thermal incineration. Catalytic incineration uses less fuel than the thermal method. Many commercial systems have removal efficiencies eater than 98%. 

Dust and fume masks consist of one or two cartridges containing a suitable filter (e.g. paper or resin-impregnated wool) to remove particulate contaminant. The efficiency of the filters against particles of various sizes is quoted in manufacturers literature and national standards. Such masks do not remove vapour from the air. 

We recently demonstrated that photocatalyzed destruction rates of low quantum efficiency contaminant compoimds in air can be promoted substantially by addition of a high quantum efficiency contaminant, trichloroethylene (TCE), in a single pass fixed bed illuminated catalyst, using a residence time of several milliseconds [1-3]. Perchloroethylene (PCE) and trichloropropene (TCP) were also shown to promote contaminant conversion [2]. These results establish a novel potential process approach to cost-effective photocatalytic air treatment for contaminant removal. 

The fourth factor is the current density. At an inert anode and for 100% Faradaic efficiency for water oxidation, the density of the current controls the flux of H+ ions. The cathodic current density and the species available in its vicinity establish the efficiency of the reduction processes (Pb2+ —> Pb). These vary to a greater extent than the anode process, because the pH and the species reaching the cathode vary with processing time. Thus, control of the current density is critical to ensure optimal EO efficiency and contaminant removal. 

GIL in Equation 18.17a is the theoretical air/water ratio required for the removal efficiency/for a specific contaminant following Henry s law. In this context, the GIL is denoted (GIL)theory, indicating the theoretical air/water ratio. This also means that a minimum amount of air must be brought into contact with the water for a certain length of detention time, the sparging size of the water droplets also affects the mass transfer, as does the air pressure. 

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