Volatile compounds, biological treatment

Biological Treatment of Gases Polluted by Volatile Sulfur Compounds (V. Herrygers, H. Van Langenhove, E. Smet)... 

Herrygers, V., H. van Langenhove, and E. Smet (2000), Biological treatment of gases polluted by volatile sulfur compounds. In P.N. L. Lens and L. H. Pol (eds.), Environmental Technologies to Treat Sulfur Pollution — Principles and Engineering, IWA Publishing, pp. 281—304. 

There are six primary in-plant control methods for removal of priority pollutants and pesticides in pesticide manufacturing plants. These methods include steam-stripping, activated carbon adsorption, chemical oxidation, resin adsorption, hydrolysis, and heavy metals separation. Steam-stripping can remove volatile organic compounds (VOCs) activated carbon can remove semi volatile organic compounds and many pesticides and resin adsorption, chemical oxidation, and hydrolysis can treat selected pesticides [7]. Heavy metals separation can reduce toxicity to downstream biological treatment systems. Discussion of each of these methods follows. 

The technology is a slurry-phase biological treatment that, according to the vendor, has successfully treated soil, sludge, groundwater, and process water contaminated with volatile and semivolatile organic compounds (VOCs and SVOCs) such as toluene, naphthalene, fluoranthene, pentachlorophenol, and creosote. 

OMD offers major advantages in comparison with the conventional thermal concentration techniques. The low temperature employed can help avoid chemical or enzymatic reactions associated with heat treatment [85] and prevent degradation of flavor, color, and loss of volatile aroma [38]. The low-operating pressure (atmospheric pressure) results in low investment costs, low risks of fouling, and low limits on compactive strength of the membrane. Since the separation is based on vapor-liquid equilibrium, only volatile compounds which can permeate the membrane and the nonvolatile solutes such as ions, sugars, macromolecules, cells, and colloids are totally retained in the feed. These factors make OMD an attractive alternative to traditional thermal routes currently used for concentration of liquid foods or aqueous solutions of thermally labile pharmaceutical products and biologicals [86]. 

Although the two terms occasionally are interchanged, biodegradation is not synonymous with mineralization. Mineralization, which is the process by which compounds are transformed into carbon dioxide and water, is only one of several fates of contaminants in biological treatment systems. Contaminants also may be volatilized, bind to organic materials, be assimilated into an active biomass, or be transformed into compounds... 

Recently, Mazzoleni et al. (1994) used gas-phase chromatography coupled with mass spectrometry (GCMS) to identify 107 volatile compounds in powdered new and used corks. These findings are not qualitative, but they certainly confirm the complexity of the cork taint issue. Cork is a biological medium, and therefore necessarily complex. Even after boiling and chloride treatment, it retains a nutritional value that mold, bacteria and even yeasts are capable of... 

The type of decomposition of the sample (reactive to use) depends on the nature of the matrix in reactors. Many matrices require HF to break the Si-O bonds of the silicates and HNO3 to oxidize the C. Organic samples (biological, botanical, polymeric pharmaceutical, etc.) and geological samples (soils, sediments, rocks, clays, etc.) are of interest for this type of treatment, since the C and the Si are transformed, by the acids mentioned, to volatile compounds (CO2 and SiF4, respectively) and the... 

All the compounds under discussion occur at low concentrations in sewage, and in many industrial effluents. During the course of normal biological treatment, the volatile compounds (mono- and dichlorobenzenes) are lost by volatilization, while the rest are reduced, by 50%-70%, mainly by adsorption on sludge, with little evidence of biodegradation [40, 60, 119]. 

The Biocube aerobic biofilter is an ex situ off-gas filtration system that is commercially available. The technology utilizes microbes to biologically oxidize volatile organic compounds (VOCs) and complex odors. It can be used in conjunction with vapor-vacuum-extraction (VVE), a process that draws gases from subsurface soil. These gases often require further treatment before being released into the atmosphere. Biocube has been field tested and has been implemented at over 100 sites for the treatment of hydrocarbon vapors. The technology has also been successfully used for odor control at a variety of sites. In addition, the Biocube system can treat odor and VOC emissions simultaneously. The units are modular, so additional stacks can be added as needed for increased flow and/or removal rates. 

Despite the fact that the destruction of toxic organic chemicals as fuels can be as high as 99.9%, with adequate residence time, many materials are more resistant (e.g., cholorobenzenes). Total COD reduction is usually only 75-95% or lower, indicating that while the toxic compounds may satisfactorily undergo destruction, certain intermediate products remain unoxidized. Because the wet-air oxidation is not complete, the effluent from the process can contain appreciable concentrations of volatile organics and may require additional treatment such as biological oxidation or adsorption on activated carbon [31]. 

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