Concept (need and benefits)
Smells are the sensation that results after receiving a stimulus caused by a combination of gases, vapors and microparticles in the olfactory sensory system. Depending on the composition of the mixture, the smell can be perceived as pleasant or unpleasant, according to very subjective factors, such as the sensitivity of the person or the environment in which it is perceived. Moreover, the quantification of their intensity is complex, precisely because of this subjective nature.
The closer the person is to the emission source (e.g. from industry, a waste dump or wastewater treatment plant), the more intense the smell is perceived. When the odor causes excessive discomfort to the population, there is talk of odoriferous contamination and air treatment processes should be considered for its elimination.
Technology and the Condorchem Envitech Offer
Condorchem Envitech has an interdisciplinary team with a long history of designing and building turnkey emission treatment plants. Depending on the flow and composition of the emission to be treated, the most appropriate operations, individually or in combination, are the following:
- Absorption (scrubbers)
This is a non-destructive technique whereby the odoriferous components are removed from the air by an absorbent solution. This is efficient for treating air contaminated with polar compounds such as NH3, H2S, amines and some water-soluble VOCs. The absorbent solutions used depend on the contaminants to be removed. In some cases, several washing steps are necessary to achieve high efficiencies. This technique consumes chemical reagents and produces liquid waste that has to be properly treated before discharge. It is a technique applicable for all types of flows.
Adsorption does not destroy the contaminants, but transfers them from the gas phase to the solid phase. The universal adsorbent is activated carbon, although zeolites and alumina can also be used. Adsorbents have a finite capacity and have to be either regenerated or replaced when the adsorbent is saturated. If the adsorbent cannot be regenerated in situ, it is not advisable to treat air flow rates which are high or have a high load. When pollutants are nonpolar, the adsorption efficiency is high.
In this operation the air flow is treated by passing the current through a porous bed filled with plant-based material (e.g. wood chips, bark or coconut fiber), whose surface acts as a support to colonize the microorganisms that consume the contaminants. The emission must be pretreated by incorporating moisture and nutrients that the microorganisms will subsequently need.
This is a technique applicable when the pollutant load is low and biodegradable and the gas flow treated is constant. The use of chemical reagents is not required and no waste is generated. The microorganisms grow attached to the biofilter support and convert the contaminants into harmless products. The investment and operating costs of these processes are low; however, their application is restricted to biodegradable VOCs, moderate loads of hydrogen sulfide or ammoniacal compounds and the emission must not contain toxic or inhibitory substances.
- Percolator biofilter system
This consists of circulating the flow through a bed filled with a support where attached microorganisms grow and an aqueous current is recirculated in countercurrent. The contaminants are transferred from the gas phase to the liquid phase and from this to the biofilm where they are consumed by microorganisms. These systems do not consume chemical reagents or produce waste.
They are applicable for all types of air flows and hydrogen sulfide or ammoniacal compound pollutant loads. The removal efficiency is very high, even with low air residence times inside the percolator. Investment costs are of the same order as chemical absorption towers (scrubbers), but with much lower operating costs. Like any biological process, this technique is not applicable when the air contains toxic and/or inhibitory substances.
- Regenerative thermal oxidation
This operation oxidizes the VOCs to CO2 and water at high temperatures (760-850ºC). The emission containing the pollutants is heated by a ceramic heat exchanger up to the combustion temperature. The VOCs oxidize to CO2 and water In the combustion chamber. The hot gases then pass over a second ceramic bed to recover the heat. This technique is used to treat high air flows with a moderate/high concentration of VOCs. The efficiency obtained depends on the air residence time and temperature, but can be more than 99%.
- Catalytic oxidation
This consists of oxidizing VOCs to CO2 and water using a catalyst, at temperatures lower (250-400°C) than for thermal oxidation. Destruction efficiency is over 95% and depends on the temperature and the catalyst. Although the operating costs are higher than for thermal oxidation, due to the catalyst becoming deactivated and having to be replaced, this is offset by the energy savings of working at lower temperatures. In addition, the risk of oxidation of by-products, such as CO, NOX and dioxins, is reduced by working at lower temperatures.
In general, the problems associated with odor pollution are not easily resolved, as factors such as the subjectivity of perception, the dispersion of odoriferous substances in the air and their transport are subject to the meteorological conditions in the area and the complexity of quantifying the complex smell intensity. Thus, it is very important to have extensive experience in resolving these cases, which the work team at Condorchem Envitech has.