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Methanol in Wastewater Systems

Methanol usage in Wastewater SystemsMethanol is a chemical common to industrial settings. It is found as a constituent of gasoline, and is used as a feed-stock for a variety of chemicals such as acetic acid and chloromethane. Methanol is also a common household chemical used as a solvent in windshield washer solutions and paint strippers. Methanol can be degraded at all oxidation states including aerobic, facultative, and anaerobic states. The carbon products of methanol degradation are carbon dioxide and, if methanogenesis is occurring, methane. Feeding methanol in wastewater systems is a common practice that often offers benefits such as increasing production of methane gas in anaerobic digestors. The methane produced is used as a fuel source to offset the energy needs of running the wastewater system. Methanol has also been used as a carbon source for anaerobic bacteria in the process of denitrification in order to reduce nitrate concentrations. However, methanol can also fuel non-selected bacteria such as sulfur reducers that produce hydrogen sulfide during metabolism. The layout and method of feeding methanol is an important consideration to avoid creating highly septic systems.   Under natural environments methanol is rapidly degraded. Due to this rapid breakdown, methanol has an expected half-life of only a few days in surface water, which has low amounts of bacteria relative to wastewater systems.   Toxicity of methanol is generally considered to be above 10,000 mg/L, similar to most alcohols. In experiments with natural environments, concentrations up to 1,000mg/L methanol were degraded with no signs of toxicity (Novak et al., 1985).   The exact concentration of methanol that will cause toxicity can vary among different bacterial species from 5000mg/L to over 10,000mg/L. Higher life forms will often begin to disappear as toxic levels of any particular compound are reached allowing these organisms to be used as indicators for toxicity. However, Verschueren (1983) showed even some protozoa have a toxicity threshold for methanol above 10,000 mg/L. In this instance, the higher life forms appear to be slightly less sensitive than bacteria, which is an unusual circumstance. Bacterial toxicity of methanol is generally not a concern because concentrations of methanol at these high levels are only possible at the source of highly concentrated streams. The concentration will rapidly decrease with distance from the source due to methanol’s high solubility in water.

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Novak, J.T., Goldsmith, C.D., Benoit, R. E. and O’Brien, J. H. 1985. Biodegradation of methanol and teriary butyl alcohol in subsurface systems. Water Sci. Technol. 17: 71-85.

Verschueren, K. 1983. Handbook of environmental data on organic chemicals. Van Nostrand Reinhold Company. New York, NY.