Process and actions
Biofiltration is realizing in devices called biofilters. They were first designed for composting waste and to odors control.
In the present are the most often used to treat gaseous flows loaded with VOCS and toxic organic pollutants.
Biofilters have a technology which uses micro-organisms, bacteria in generally, for treating gas emissions, in a safe and economic manner for environment.
Biofilters is used to treat emissions contaminated with hazardous organic pollutants and/or VOCS, which requires an enclosed space reactor containing a porous medium that is designed to encourage the development of different species of microorganisms.
Biofilters consist of porous filters, through which the current is distributed to a residual gas. Microorganisms that feed on waste gas are attached to this porous substrate.
Biofilters process akin to the process of treating the precipitate obtained, in both cases, microorganisms are used to completely oxidize organic compounds in CO2 şi H2O.
Previous investigations have reported that the effectiveness of bio-filters used in the removal of toxic organic compounds and/or VOCS is limited by solubility in water of contaminants.
Therefore, to sustain an effective treatment, it is essential that bio-filters environment to be monitored to maintain conditions conducive to the transfer of contaminants from the air in the liquid phase of the bio-filters environment and for growth and biological activity. Oxygen content, moisture level, temperature and nutrient availability in the bio-filters should also be monitored during treatment of toxic pollutants and VOCS why contaminated air streams, to ensure that the process operates in optimum conditions of distance of the contaminant
Bio-filters (used to control gaseous emissions) are of the fixed-film bioreactors, using micro-organisms attached to the substrate material, to convert organic waste products/VOC in CO2 and water.
The colony of microbes needed for good acting on the surface of the bio-filter a suitable natural support through which air is blown to be treated.
Support, which is the “bed” bio-filter can be formed by mold, peat, wood pieces, green compost, or mixtures of these materials or of others, including plastics.
The substrate provides structural support and basic nutrients for microorganisms.The porous structure provides a proper area, at a reasonable pressure loss of gas. As the waste gases are passed through the reactor, pollutants must be promulgated in intra-abdominal. Pollutants are then broken down by aerobic process through a natural biodegradation. Bio-filterare economic when applied gas flows with low concentration (< 1000ppm), rich in oxygen.
The flow of air laden with pollutants is captured and transported through a pipeline to the system of gas where the particles are removed with air penetration and gross potential fat particles that could affect the bio-filter. The next step is raising the pressure in a fan to compensate for losses through subsequent elements of the process. Further air flow passing through a humidifier where is uploaded with water because when you pass through the porous layer it tends to dry up, thereby decreasing the effectiveness of bio-filter process. The final residual gas treatment takes place for the removal of pollutants and temperature adjustment and umiditătii up to saturation.
Soda odorous substance is absorbed by the filter material and degraded by microbial flora in particular bacteria and fungi, which uses it as a nutrient, together with part of the filter material itself. Biological activity requires oxygen that is provided by the same current gas entering the bio-filter.
The surface of the material emits carbon dioxide (CO2), water, inorganic compounds and biomass. The bio-filter will be very small amounts of polluted falling.
Bio-filter environment does not retain any residue from organic pollutants contained of air flow due to extremely good efficiency of the system of microorganisms that degrade these compounds. Contaminant molecules floating inside the bio-filter until it sits and are consumed by micro-organisms. During the bio-transformation of the source of nourishment is what forms the final products include carbon dioxide, water, mineral salts and energy to produce more microorganisms.
A bio-filter can be open or closed, can be built directly into the ground or in the form of a reactor, can have only one filter layer or even more, and besides basic components may include a heat exchange is using it to cool or warm air flow at optimal environmental temperature bio-filter.
For the smooth operation of procedures of bio-filter should be meet the following conditions:
- the surface of the transfer must be to encourage maximum uptake VOCS contained in air;
- the temperature should be maintained so that it doesn’t freeze;
- gas must contain enough oxygen to maintain aerobic processes.
Bio-filter works effectively and economically for streams with low concentrations (up to 1500 < 1000 ppm) for VOCS and toxic organic pollutants.
Bio-filter efficiency for VOCS shall be 65-99 %.
Main features of bio-filter are as follows:
- bio-filter :environment can have a depth between 0.5 to 2 metres, but most have a depth of bio-filters 1 meter; It can be formed from the soil, compost, sand, volcanic ash or a mixture of these components;
The most widely used are the soil and compost, and the typical parameters include a neutral PH, pore volume to be greater than 80%, and total organic content of over 55%.
- The soil is a stable environment for bio-filter because it doesn’t degrade. Instead it is poorer in the complex of microorganisms is the compost.
- Compost has a greater permeability to air and water, but over this time it breaks down and the rate of particle size bio-filter environment decreases considerably. Media for the bio-filter environment is around 5 years.
- Environmental bio-filter content :generally use 3 types of microorganisms in a bio-filter: fungi, bacteria and actinomycetes. Because they exist in an environment and to meet their role must have oxygen, absence of toxic materials, optimal conditions such as suitable temperature and PH neutral.
For putting in service of a bio-filter, micro-organisms, requires a period of adaptation, usually 10 days, and then grow and fulfill its role in treating gaseous streams loaded with pollutants. Typically, bio-filter does not work continuously. They can be used intermittently or seasonally, depending on the treatment process. It has been shown that biomass is viable for about 2 weeks after you close a bio-filter, and if it is fed constantly with inorganic nutrients and oxygen can be maintained for a period of 2 months.
- The contents of the water from bio-filter: this parameter is the most important because of its existencedepends effectiveness of bio-filtration, because during the process, the flow of air does tend to dry out the bio-filter environment. A too low amount of water leads to a decrease in the ability of microorganisms to degrade pollutants, and the resulting gas remains to some extent with what pollutants are subsequently eliminated. Too much water can also affect the appearance of anaerobic zones, with a potential production of odors. Water may be added to the system by two ways: by humidify the air flow or through direct application of water on the surface of bio-filter.
- Temperature: microbial activity takes place between the temperature limits 10-400 a higher temperature will destroy the algal biomass, and a temperature below will result in a low activity of microorganisms.
- pH-ul : should be maintained within the limits of 7-8 time
- Time to the minimum of :: time of stationary gas is between 30 s for compost, environment and minimum 1 minute for the environment made up of soil.