Type: Process Essays
Sample donated: Colleen Baldwin
Last updated: October 1, 2019
Thereare many physical and chemical methods to treat air pollution.
Bioprocesseshave been very efficient for the treatment of air pollution. The most popularbioreactor configuration is the conventional biofilter. Biofilters wereinitially designed for odour control at wastewater treatment plants, but nowthey are becoming renowned for the treatment of volatile organic compounds(VOCs) and other organic compounds. These gases have bad odour and aredangerous for humans and animals. Biofiltrationprocess is preferred over other air pollution control techniques and has gainedpopularity because it has economic advantages,as the energy requirement is significantly low and avoids cross media transferof pollutants. This technology can be mainly applied to waste gases to controlair pollution, which have low concentration and readily biodegradablepollutants. Biofilters utilizes microorganisms to reduce air pollution.
Airpollutants come in contact with microorganisms inside the biofilter, wheremicroorganisms demean pollutants to produce energy and by-products (C02 andH20). Biofilter includes a filter material, where microorganisms breed. Biofilmis a very important part of the biofilter. Biofilm is a thin layer of moisturewhere the microorganisms reside. In the process of biofiltration polluted airis pushed inside the biofilter slowly thereby, the pollutants in the air getabsorbed in the filter media, then as a result the polluted gas is dispersed inthe biofilter and absorbed onto the biofilm. Afterthe escalation of the conventional biofilter, new configurations were developedfor air pollution control which is known as biotrickling filters and bioscrubbers.A new set of technologies were also introduced for air pollution control suchas membrane bioreactor and rotating biological contractor.
A lot of industriesuse this biofilter technology for example the food industry, pharmaceuticals,wood products manufacturing, paint and coatings application, petroleumindustry, sewage treatment etc. Polluted air stream comprises VOCs and manysulfur compounds. Biofilters require a large area while treating largeairflows, which can be as big as a basketball court.
Recent research shows thatbiofilters can be used to remove a variety of airborne contaminants whichincludes aliphatic and aromatic hydrocarbons, alcohols, aldehydes, organicacids, acrylate, carbolic acids, amines and ammonia. The main three bio reactor configurations used forair pollution control are biofilters, biotrickling filters and bioscrubbers. Thecore mechanism is same for all but they make use of microbes in differentphases which may be suspended, fixed or in a liquid state. Biofilters are notexactly filtration units but a combination of different unit operations such asabsorption, adsorption, degradation and desorption of gas phase contaminants.Water is added into the biofilter system to controlthe moisture content and add essential nutrients. Humidification of gas streamsis generally carried out before feeding it into the system.
BIOFILTER CONFIGURATION AND ELEMENTS CONVENTIONAL BIOFILTERS Biofilters can be either open orclosed beds. Open-bed biofilters are the most common, typically 10 to 18 inchesdeep, and larger than closed-bed biofilters. Open-bed biofilters are typicallybuilt outdoors on the ground and are exposed to the weather.
Closedbed biofiltersare mostly enclosed, with a small exhaust port for venting the cleaned air.Closed-bed biofilters usually treat smaller airflows and typically have deepermedia (2-3 feet), reducing the space needed to achieve odor control, and aremore expensive In a nutshell, the conventionalbiofilter is a fixed-film or packed bed bioreactor in which a natural filterbed is most often used (Fig. 3(a)), although recently inert packing materialshave proven successful as well (Fig. 3(b)). Polluted air is fed in either adownflow or an upflow mode through the reactor and the pollutants of the wasteair are biodegraded by the biocatalyst present in the packed bed.. Therefore,this reactor will be especially suitable for the treatment of hydrophobic andpoorly water soluble compounds.
Also, because of the absence of a mobile liquidphase, conventional biofilters are not the best choice for treating pollutants,such as, for example, chlorinated compounds, leading to medium acidification..Key elements of a biofilter are described hereafter. .
Figure 1 illustrates elements ofan open-bed biofilter. They are: • a mechanically ventilated space withbiodegradable gaseous emissions; • an air handling system to move the odorousexhaust air from the building or manure storage through the biofilter; • an airplenum to distribute the exhaust air evenly beneath the biofilter media; • astructure to support the media above the air plenum; • porous biofilter mediato act as a surface for microorganisms to live on, a source of some nutrients,and as a structure where moisture can be applied, retained, and available tothe microorganisms