Wastewater collected in treatment facilities contains high levels of ammonia, which is converted into nitrate through bacterial degradation. If discharged into the environment, the nutrient-rich nitrate in effluent can have a devastating effect on water ecosystems. Denitrification is the practice of using chemical additives to convert nitrate into inert nitrogen gas, which is safely released into the atmosphere.
Although nitrogen is omnipresent, when it enters waterways in large quantities as a solid, it causes an abundant growth of algae. The resulting algae “blooms” can cover hundreds of square miles and absorb a disproportionate amount of oxygen from the water, suffocating all but the most hearty forms of aquatic life.
The activated-sludge wastewater treatment process requires that a readily available organic compound be added to enable bacteria to eliminate the excess nitrate. The carbon source most often chosen is methanol.
The advantages of methanol in the denitrification process are copious. It contains no solids or additional nutrients, has a neutral pH, is inexpensive, and contains 100% readily degradable substrate. Methanol offers the ideal solution to nitrogen reduction, both in its ease of use and in its positive effects.
While most methanol is produced from the steam reformation of natural gas — which the U.S. now has in abundance — methanol also can be made from biomass, forest thinnings, agricultural waste, landfill gas, and even carbon dioxide captured from the atmosphere. This “polygeneration” means that methanol ultimately can be produced from a number of renewable feedstocks and wastestreams, especially those that are local to the wastewater plant, adding to its overall sustainable impact.
A good example
Today, nearly 200 water resource recovery facilities (WRRFs) use methanol to denitrify in the U.S. alone. One of the largest facilities in the country, the Blue Plains Advanced Wastewater Treatment Facility in Washington, D.C., has had one of the best success stories related to methanol denitrification.
Blue Plains releases nearly 1.4 billion L (370 million gal) of effluent to the Potomac River each day, but the facility now releases only 9 Mg/d (10 ton/d) of nitrogen, half its premethanol output.
With methanol denitrification, Blue Plains has continually met its limit of 2.1 million kg (4.7 million lb) of nitrogen released per year and has come in well below that standard on many occasions.
In another example, nitrogen removal projects in Connecticut have drastically reduced the nitrogen pollution to Long Island Sound. There also are global examples. The Rosedale Wastewater Treatment Plant in New Zealand, the De Groote Lucht Wastewater Treatment Plant in the Netherlands, the Seine-Center Wastewater Treatment Plant in France, and the Jiashan City Wastewater Treatment Plant in China all use methanol denitrification to produce water suited to augment wetlands and recharge aquifers.
Although methanol use has many benefits, it also is a toxic substance that must be handled responsibly. The key to working with methanol is to understand its physical properties and risks, and simple risk-mitigation strategies to ensure its safe use. Four protection measures are needed to minimize the routes by which methanol can get into the human body.
The key to personal protection is wearing the right clothes and equipment to prevent any exposure. This may include the use of fire-retardant clothing, nitrile gloves, and rubber boots. Although skin absorption time is very slow and therefore poses only a slight risk of toxicity, methanol should be washed from the skin immediately with soap and water on contact.
Safety glasses with side shields or full-face shields should be worn when working around methanol. When methanol vapors contact the eye, irritation may occur after short-term exposure. This includes a burning sensation, tearing, redness, or swelling. Upon direct contact, conjunctivitis and corneal burns may occur and progress into permanent blindness if not treated immediately, as the primary effect of methanol is exerted on the optic nerve and the retina. If methanol is splashed into the eyes, immediately flush with copious amounts of water for at least 15 minutes, then visit a health-care facility, and consider seeing an ophthalmologist.
A full-face shield or a mouth mask should be worn when working around methanol. Although methanol has a faintly sweet alcohol odor to the nostrils, breathing in methanol is the most common type of exposure and can lead to serious respiratory conditions if proper ventilation is not used. Fixed and hand-held methanol sensors are used to detect methanol in the air. In more extreme cases, such as responding to a methanol spill, the use of a self-contained breathing apparatus is recommended.
Drinking as little as 50 mL of methanol — less than one-quarter cup — can be fatal. Symptoms of methanol consumption include weakness, dizziness, nausea, and vomiting. If methanol is swallowed, call 911 immediately — outcomes are excellent when asymptomatic methanol-poisoned patients are treated promptly.
At room temperature, methanol is a clear and colorless liquid. However, it is flammable both as a liquid and a vapor. A storage tank that appears to be empty of liquid methanol may still contain methanol vapors that can ignite easily.
Methanol burns with a clear, blue low-heat flame that may be difficult to see in bright sunlight, and the only indication of a methanol fire may be a shimmering “heat haze” or something nearby burning. By comparison, methanol is harder to ignite than gasoline and burns with only one-eighth the heat. Depending on the size of a methanol fire and its location, firefighting equipment, such as carbon dioxide extinguishers, dry-chemical extinguishers, and alcohol-resistant foam, can be used. Water also can be used to put out methanol fires, but any methanol–water mixtures should be contained for proper cleanup.
The basics of fire prevention apply to methanol, with all three elements of the fire triangle — fuel (methanol), an ignition source, and oxygen — required to be present to start a fire. To prevent fires, the aim is the break the fire triangle. The best precaution is to eliminate any ignition sources near the methanol fuel. Another way to prevent methanol fires is to remove oxygen from the equation. This may involve the use of nitrogen blanketing in larger storage tanks.
The methanol industry is committed to proper safety and regulation to ensure that appropriate care and measures are taken when using methanol. The Methanol Institute (Alexandria, Va.), working with industry leaders, technology partners, and customers created the Methanol Safe Handling Manual to address both common and technical questions related to methanol handling, storage, and transport.
Methanol for denitrification
In July 2012, the Methanol Institute worked with the consulting firm, Exponent Inc. (Menlo Park, Ca.) to compile a manual on the use of methanol as a real and effective mechanism for wastewater denitrification at municipal WRRFs. The manual presents substantive background data on nitrogen in the environment, the regulatory climate for nitrogen in wastewater, the biochemistry of biological nitrogen removal, denitrification systems design, a life-cycle analysis of organic carbon sources, methanol properties, and health and safety information. It also provides global case studies describing the use of methanol at WRRFs in the U.S., Europe, and Asia.
The report analyzes the technical use of methanol and its practical application in the industry. It also looks at the economics of methanol use. Methanol denitrification continues to grow as an effective solution for wastewater treatment. Both the Methanol Safe Handling Manual and the Methanol Use in Wastewater Denitrification Manual can be downloaded from the Methanol Institute website at