Methanol denitrification

Denitrification of wastewater in treatment plants offers another potential use for methanol. There are a few such plants in the world however, this use is not expected to grow appreciably, as there are more proven methods for nitrogen removal commercially available. 

The study reported some problems regarding the data for the biofilm from the media after 3 weeks of operation, and also sludge accumulation at the bottom of the bioreactor. It was also found that an external carbon source, such as methanol, was necessary for controlling the denitrification stage. 

Anoxic (deoxygenated) water from the deaeration tank flows into a 1 500-L denitrification reactor containing colonies of Pseudomonas bacteria in a porous medium. Methanol is injected continuously and nitrate is converted into nitrite and then into nitrogen ... 

Conventional uses of methanol account for 90% of present consumption and include formaldehyde, dimethyl terephthalate, methyl methacrylate, methyl halides, methylamines and various solvent and other applications. Newer uses for methanol that have revitalized its growth and outlook include a new technology for acetic acid, single cell protein, methyl tertiary butyl ether-(MTBE), and water denitrification. Potential uses for methanol include its use as a carrier for coal in pipelines, as a source of hydrogen or synthesis gas used in direct reduction of iron ore, as a direct additive to or a feedstock for gasoline, peak power shaving and other fuel related possibilities. Table II lists the world methanol demand by end use in 1979. 

Very small quantities of methanol are now consumed in the denitrification of waste water. Methanol is used as a carbon source by bacteria which convert nitrates and nitrites to nitrogen. Methanol is an efficient carbon source and decreases the production of byproducts. The potential requirement for a carbon source for water denitrification is large but the use of methanol is threatened by cheaper feedstocks. One large denitrification plant in the U.S., for example, uses brewery waste as a carbon source. In the future, water treatment plants designed for water denitrification may utilize a less expensive alternate carbon source than methanol. 

Another alternative for removal of combined nitrogen is by denitrification of nitrate and nitrite using appropriate bacteria in the presence of a carbon source such as methanol (Eq. 5.27). 

The ability to carry out denitrification is known among.a broad range of facultative anaerobic and anaerobic bacteria such as Pseudomonas. Denitrification requires a source of carbon, and methanol is often used for this... 

In MWW, denitrification consumes from 4 to 6 mg of BOD5 per mg of N.NO3 removed. In refinery WW, the naturally existing BOD5 may not be sufficient and so the organic substrate must be supplemented by an outside source (ethanol, methanol, molasses, etc.). Phenol input is not advisable since at certain concentrations phenols have an inhibiting effect on the nitrifying bacteria themselves. 

Typically, denitrification is carried out in an anoxic column with added methanol as a food source (microbial reducing agent). Methanol is a synthetic chemical that poses some toxicity and flammability hazards. A greener option is the use of biomass, such as carbohydrates from plants as the microbial reducing agent. One of the best organic reductants for this purpose is high-fructose com syrup. 

How many liters of methanol would be required daily to remove the nitrogen from a 200,000-L/day sewage treatment plant producing an effluent containing 50 mg/L of nitrogen Assume that the nitrogen has been converted to NOJ in the plant and that the methanol is consumed in a denitrification reaction. 

A methanol to nitrate-nitrogen mass ratio of 3.0, which results in about 90% denitrification yield, has been su sted as a design guideline... 

High ammonia and calcium concentrations as well as a 0.5 g/m3 nickel concentration are reported to be inhibitory for denitrification [35]. Methanol does not inhibit the reaction up to a concentration of 15 kg/m3 of carbon content. 

The denitrification process shown in Reaction 13.9.6 can be carried out either in a tank or on a carbon column. In pilot plant operation, eonversions of 95% of the ammonia to nitrate and 86% of the nitrate to nitrogen have been achieved. Although methanol is shown in the reaction as a source of reducing agent for the mierobial reduction of nitrate, other organic substances can be used as well. Ethanol from the fermentation of otherwise waste carbohydrates would serve as a reducing substance. 

Koch, G. and H. Siegrist, Denitrification with Methanol in Tertiary Filtration,... 

Because the microflora that most optimally performed these two distinct operations was different, most felt that there had to be intermediate clarification. Also, because denitrification requires energy to derive the reaction, methanol or some other biologically oxidizeable carbonaceous material was added to the second section. 

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